Correlating Strength and Stiffness Data of the PENCEL Pressuremeter and Triaxial

Compression Tests in Florida Sands

by

Jacob William Jansen

Bachelor of Science

Civil Engineering

Florida Institute of Technology

2015

A thesis submitted to the College of Engineering at

Florida Institute of Technology

in partial fulfillment of the requirements

for the degree of

Master of Science

in

Civil Engineering

Melbourne, Florida

April, 2017

©Copyright 2017 Jacob W. Jansen

All Rights Reserved

The author grants permission to make single copies _________________________

We the undersigned committee, having examined the attached thesis;

“Correlating Strength and Stiffness Data of the PENCEL Pressuremeter and

Triaxial Compression Tests in Florida Sands”

By

Jacob William Jansen

Hereby indicate its unanimous approval.

_________________________________________________

Paul J. Cosentino, Ph.D., P.E

Professor, Civil Engineering

Thesis Advisor

_________________________________________________

Rodrigo Mesa Arango, Ph.D.

Professor, Civil Engineering

_________________________________________________

Matthew Jensen, Ph.D.

Professor, Mechanical and Aerospace Engineering

_________________________________________________

Ashok Pandit, Ph.D., P.E

Professor, Civil Engineering

Department Head

iii

Abstract

Correlating Strength and Stiffness Data of the PENCEL Pressuremeter and Triaxial

Compression Tests in Florida Sands

By: Jacob William Jansen

Major Advisor: Paul J. Cosentino, Ph.D., P.E

The poorly graded sands found throughout Florida provide geotechnical engineers

with a difficult challenge when performing testing samples in laboratory tests.

These challenges have caused lab tests such as the triaxial compression test to be

overlooked. Since geotechnical engineers estimate strength and stiffness parameters

from basic field tests, they often produce overly conservative designs.

Understanding how the automated in-situ PENCEL Pressuremeter (PPMT) test

correlates with the triaxial compression test can reduce the time and costs

associated with laboratory triaxial testing. Results from triaxial tests yield a

Young’s Elastic Modulus, shear strength, and internal friction angle. Results from a

PPMT test yield a pressuremeter modulus, lift off pressure, and a limit pressure.

The different types of outputted data do not allow for direct comparisons to be

made between the triaxial compression test and the PPMT test. This research seeks

to correlate the outputted data.

This research involved twenty PPMT tests performed in poorly graded sands, with

loose to medium dense texture. PPMT results were compared with results from

twenty-one triaxial compression tests performed using soil removed from the test

iv

sites. The triaxial test density ranged from 20% to 65% of the soils relative density.

An equation from Baguelin (1978) was proven to correlate triaxial shear strength

with PPMT limit pressure.

Correlations indicate that triaxial elastic modulus and triaxial shear strength

correlate moderately well. The triaxial modulus is 93 times greater than the shear

strength. The PPMT modulus correlates well with the limit pressure, the PPMT

modulus is 8.3 times greater than the limit pressure in loose to medium dense sands

(R2=0.89). The triaxial elastic modulus and PPMT elastic modulus correlation

show PPMT moduli being on average 60% greater than triaxial moduli in similar

density and confining conditions. The correlations from this study indicate that data

from the triaxial compression test and the PPMT test can be correlated.

v

Table of Contents Abstract ................................................................................................................................. iii

Table of Figures .................................................................................................................... vii

List of Tables ......................................................................................................................... ix

List of Symbols ....................................................................................................................... x

1 Introduction ................................................................................................................... 1

1.1 Background ............................................................................................................ 1

1.2 Objective ................................................................................................................ 2

1.3 Approach................................................................................................................ 2

1.3.1 Literature Review ........................................................................................... 3

1.3.2 Site Selections ................................................................................................ 3

1.3.3 Laboratory Testing ......................................................................................... 3

1.3.4 Field Testing ................................................................................................... 4

1.3.5 Results ............................................................................................................ 4

1.3.6 Analysis .......................................................................................................... 4

1.3.7 Conclusions and Recommendations .............................................................. 4

2 Literature Review ........................................................................................................... 5

2.1 The Pressuremeter ................................................................................................ 5

2.1.1 Pressuremeter Development......................................................................... 5

2.1.2 Pressuremeter Insertion ................................................................................ 7

2.1.3 Pressuremeter data interpretation ............................................................... 9

2.1.4 Variations of strain-controlled PMT Tests ................................................... 15

2.1.5 Pressuremeter Theories............................................................................... 17

2.2 Triaxial Testing ..................................................................................................... 18

2.2.1 Apparatus ..................................................................................................... 18

2.2.2 Test Description ........................................................................................... 22

2.2.3 Test Data ...................................................................................................... 26

2.3 Methods of determining the at rest earth pressure ........................................... 30

2.3.1 Jaky Determination, 1944 ............................................................................ 30

2.3.2 Laboratory Methods .................................................................................... 31

vi

2.3.3 In-Situ tests .................................................................................................. 33

3 Description of Test Sites .............................................................................................. 38

3.1 Test Site Locations ............................................................................................... 38

3.1.1 Florida Tech Overflow lot ............................................................................ 39

3.1.2 Southgate Field ............................................................................................ 40

4 Test Methods ............................................................................................................... 42

4.1 In-Situ tests .......................................................................................................... 42

4.1.1 PPMT ............................................................................................................ 42

4.2 Laboratory Tests .................................................................................................. 49

5 Results and Correlations .............................................................................................. 51

5.1 Soil Properties Results ......................................................................................... 51

5.1.1 Grain Size ..................................................................................................... 51

5.1.2 Optimum Moisture ...................................................................................... 52

5.1.3 Relative Density ........................................................................................... 53

5.2 Triaxial Results ..................................................................................................... 55

5.3 Pressuremeter Results ......................................................................................... 57

5.4 Correlations ......................................................................................................... 59

5.4.1 Triaxial correlations between strength and stiffness .................................. 59

5.4.2 Pressuremeter moduli and strength correlation ......................................... 60

5.4.3 Triaxial and pressuremeter stiffness correlation ......................................... 64

6 Conclusions and Recommendations ............................................................................ 68

6.1 Conclusions .......................................................................................................... 68

6.2 Recommendations ............................................................................................... 69

References ........................................................................................................................... 71

Appendix A ........................................................................................................................... 74

Appendix B ........................................................................................................................... 85

vii

Table of Figures

Figure 2-1: From right to left; Pencel, Ménard, and Texam Pressuremeter types (From

RocTest) ................................................................................................................................. 6

Figure 2-2: Typical Pressuremeter results curve (from Shaban 2016) .................................. 9

Figure 2-3: Determination of lift off pressure for a self-boring and pre-bored

pressuremeter (Mair and Wood 1987). ............................................................................... 10

Figure 2-4: PMT unload-reload cycle (From Shaban 2016) ................................................. 12

Figure 2-5 Typical Load/Unload PMT test data ................................................................... 16

Figure 2-6 Inflated probe shapes in an unconfined environment vs in a confined

environment (from Murat and Lemoigne 1988) ................................................................. 17

Figure 2-7 Durham Geo Load frame .................................................................................... 19

Figure 2-8 Durham Geo triaxial cell ..................................................................................... 20

Figure 2-9 Humboldt data aquisition unit ........................................................................... 21

Figure 2-10 Triaxial control panel ........................................................................................ 22

Figure 2-11 Idealized relation for dilation angle, Ψ, from triaxial results ........................... 24

Figure 2-13a: Typical Mohr's Circle for CD triaxial data (From Holtz and Kovacs 1981) ..... 28

Figure 2-13b: Typical Mohr's Circle for CU triaxial data (From Holtz and Kovacs 1981) ..... 28

Figure 2-14: Soft Oedometer Ring (Kolymbas, 1993) .......................................................... 32

Figure 2-15: Correlation between the SPT N values, normalized effective overburden, and

the triaxial compression phi value (DeMello, 1971) ............................................................ 33

Figure 2-16: Correlation between CPT data and the effective phi angle in sand soils

(Robertson and Campanella, 1983) ..................................................................................... 35

Figure 2-17: Chart developed by Mair and Wood (1987) to determine the phi value using

stress strain slope. ............................................................................................................... 37

Figure 3-1: General location of testing sites on the FIT campus shown by stars. ............... 39

Figure 3-2: Arial overview of the overflow test site. The transect on which tests were

performed is shown by the yellow line. .............................................................................. 40

Figure 3-3: Southgate field test site. The transect tested is shown by the yellow line. ...... 41

Figure 4-1 Pressuremeter control unit with added digital instrumentation (From Shaban,

2016) .................................................................................................................................... 43

Figure 4-2 Screenshot of the APMT user interface and data reduction .............................. 44

Figure 4-3 Typical membrane calibration curve for PPMT tests ......................................... 46

Figure 4-4 Typical volume calibration curve from a PPMT test ........................................... 47

Figure 4-5 Borehole driving guide, with thin wall driving tube (From Shaban 2016).......... 49

Figure 5-1 Grain size distributions for test sites in FIT campus ........................................... 52

Figure 5-2 Standard Proctor moisture density data from a mixed sample, optimum

moisture content was determined to be 12% ..................................................................... 53

viii

Figure 5-3 Typical Triaxial stress-strain plot ........................................................................ 56

Figure 5-4 Correlation between the triaxial initial moduli and the shear strength of the soil

at 5% strain .......................................................................................................................... 59

Figure 5-5 Comparison between the calculated limit pressure, measured initial modulus

and shear strength ............................................................................................................... 61

Figure 5-6 Correlation between PMT initial modulus and PMT limit pressure using all data

points ................................................................................................................................... 62

Figure 5-7 Limit pressure vs pressuremeter modulus for loose to compact sands ............ 63

Figure 5-8 Relationship between strength and stiffness data for both triaxial and PPMT

tests ..................................................................................................................................... 64

Figure 5-9 Predicted PMT modulus from measured Triaxial data ....................................... 65

Figure 5-10 Prediction of triaxial moduli using field measured PMT moduli ...................... 66

ix

List of Tables Table 2-1 Pressuremeter insertion recommendation table (Winter 1986) .......................... 8

Table 5-1 Summary of moisture density results from mixed samples ................................ 53

Table 5-2 Summary of maximum density tests ................................................................... 54

Table 5-3 Summary of minimum density tests .................................................................... 55

Table 5-4 Summary of triaxial test results ........................................................................... 56

Table 5-5 Averages of triaxial data, based off of density .................................................... 57

Table 5-6 Summary of PPMT test results ............................................................................ 58

Table 5-7 Averages of PPMT data based off of site ............................................................. 58

Table 5-8 Relationships and correlations between the strength and stiffness for PPMT,

triaxial, and combined data ................................................................................................. 64

Table 5-9 Correlation summary ........................................................................................... 67

x

List of Symbols Symbol Description

DPMT Pressuremeter Diameter Po Lift off pressure

G Elastic shear modulus

Vm Mean volume of the cylindrical cavity

∆V Change in volume over the corresponding change in pressure, ∆P

𝜈 Possion’s ratio Pl Limit Pressure Ei Initial elastic modulus

Er Reload elasticmodulus

σ’ Effective stress

σtotal Total stress

σ1 Maximum principle stress

σ3 Confining stress/minimum principle stress

Ψ Angle of dilation

𝜀 Measured Strain

𝛼 Failure angle

𝛷 Angle of internal friction

𝜏 Shear stress

𝐾𝑜 At rest earth pressure coefficient

𝑆𝑢𝑝 Pressuremeter shear strength

𝑆𝑢𝑡 Triaxial shear strength

xi

Acknowledgements

I would firstly like to acknowledge the faculty and staff of the Civil Engineering

Department at Florida Tech for their support in my graduate studies. I would like to thank

my committee chair, Dr. Paul Cosentino for his guidance and helping my academic

growth. Additionally I would like to Thank Dr. Alaa Shaban for his help performing the

Pressuremeter tests and helping guide my research process. Finally, I would like to thank

my parents and family for the support they provided through my time here at Florida

Tech.

1

1 Introduction

1.1 Background In the state of Florida, the most commonly found soil is a poorly graded sand,

referred to here as Florida sands. Geotechnical investigations used to determine the soil

properties of these sands can range from simple observational tests with no sampling, to

more involved field testing and/or sampling. These more involved tests can provide the

strength and stiffness characteristics of the soil at the site can either be performed in a

geotechnical laboratory or in-situ.

A commonly used laboratory test to determine the soil strength and stiffness is the

triaxial compression test. This test uses samples transported from the site to a laboratory,

where the sample is prepared, and then tested in compression with confinement to

obtain the axial strength data. This process of sampling, drying, remolding, and testing

take between a hour and a day per test. This test has been used by engineers since the

late 1930’s, and provides a wide range of engineering data, under various soil drainage

conditions. The data from a triaxial compression test can be used to determine the

Young’s elastic modulus (E), soil shear stress (τ), and angle of internal friction (φ) as a

function of unit weight. These engineering parameters are integral parts of many design

equations used in geotechnical applications. However, instead of attempting to mimic the

conditions of an in-situ soil in a laboratory engineers have designed a device to directly

measure the soil’s strength and stiffness characteristics in-situ.

2

The pressuremeter (PMT), first successfully developed in 1956 (Ménard, 1956),

has allowed geotechnical engineers to examine soil strength and stiffness in-situ. This

device allows the radial strength data of the soil to be measured, without having to

transport soil samples and attempt to replicate site conditions in a laboratory. Cosentino

et al. (2006) automated the PENCEL pressuremeter unit, leading to a significant increase

in its use. The data from the automated PMT can be used to determine the PMT modulus

(E), rebound modulus (Er), lift off pressure (Po), and limit pressure (Pl). These data

parameters can take between 30 minutes and an hour per test. These engineering

parameters are used in some geotechnical design equations; however they are not as

commonly used. The time and cost savings to perform an automated PPMT could lead to

large savings in engineering design and construction if the relationship between PPMT

data and other more common tests can be determined.

1.2 Objective The objective of this research is to correlate in-situ soil strength and stiffness parameters

obtained from PMT tests in Florida sands with the engineering properties obtained from

the triaxial compression test.

1.3 Approach This research will use the PENCEL Pressuremeter (PPMT) in pre-bored holes to determine

the strength and stiffness characteristics of the soil. Previously determined relationships

found in literature will be used to relate the PMT data with the soil shear strength. Finally

triaxial tests of samples will be performed to determine the soils’ laboratory shear

strength and stiffness. Correlations between the PPMT and the triaxial engineering

3

parameters of the Florida sands will be determined. The steps required in this process

are outlined below.

1.3.1 Literature Review

A full review of the pressuremeter history and test procedure was performed; this

provided the background on the aspects of the pressuremeter being used, as well as prior

methods used for testing of different soil parameters. Additionally, a review of triaxial

testing and the behavior of granular material in shear was conducted to gain an

understanding of the mechanical behaviors exhibited by the soil during testing. Finally a

review of the development of methods for determining soil properties from both the

PPMT and triaxial shear test was presented.

1.3.2 Site Selections

The sites selected for field testing were selected based upon their location, uniformity,

and soil type. The two main sites that were selected contain a loose to medium dense,

poorly graded fine sandy soils (SP).

1.3.3 Laboratory Testing

Laboratory testing was used to measure data in a controlled and reproducible

environment. The soil properties and strengths were determined using the Consolidated

Drained Triaxial test (ASTM D7181). The soil gradation and USCS (Unified Soil

Classification System) classification were determined from ASTM D6913 (soil gradation)

and ASTM D2487 (USCS soil classification). In order to determine relative density a

minimum and maximum density test was performed (ASTM D4253, ASTM D4254). The

optimum moisture content was determined from the standard Proctor test (ASTM D698).

4

1.3.4 Field Testing

The sites selected in task 1.3.2 were used for field testing. A transect was set up at both

sites, with test points every 25ft along the transect. PPMT tests were performed at each

point to gather data over a very contained and uniform sample. A total of 20 test points

were accumulated in the field testing procedures.

1.3.5 Results

Results from the PPMT tests and triaxial tests were compiled into tables to compare the

data from each test. These tables included the site, modulus of elasticity, moisture

content, densities, as well as parameters specific to each type of test.

1.3.6 Analysis

Test data from both laboratory and field tests were reduced to standard and usable

engineering parameters. The data were analyzed using a Excel and R-studio, and multiple

linear regression analyses were performed with the data. Additionally, correlations to

previous methods discussed in literature were examined.

1.3.7 Conclusions and Recommendations

Using the correlations and their corresponding statistical significance, as well as the

theoretical results conclusions were made. Recommendations for further studies were

developed based on the process and findings from this study.

5

2 Literature Review This section seeks to discuss the background, development, uses and interpretation of the

pressuremeter tests and the triaxial tests. Additionally, uses and implications of previous

studies will be examined in this section.

2.1 The Pressuremeter

2.1.1 Pressuremeter Development

Geotechnical engineers have used laboratory test methods to determine the stress-strain

relationships of soils for decades. However, many problems arose from trying to extract,

transport, and test undisturbed samples in the lab. The problems associated with

transporting and testing caused geotechnical researchers to develop in-situ devices in

order to determine the stress-stain relationships of soils. By testing these relationships at

the site, researches figured the least amount of disturbance would be applied to the soil,

with the main disturbance being due to the testing process itself.

The Pressuremeter was initially developed by Kögler in 1933; however, was not

successfully deployed until Louis Ménard in 1956. This device is defined as a “cylindrical

device designed to apply uniform pressure to the walls of a borehole by means of a

flexible membrane” (Mair and Wood, 1987). Ménard’s Pressuremeter used a three cell

system, with all cells being inflated to the same pressure. The cells are rubber membranes

fixed around a metal core, and bound by two metal endplates (Mair and Wood, 1987).

The middle cell was used to take measurements, while the two cells on each side, known

6

as guard cells, were used to reduce end effects. The guard cells make the probe function

as an infinite cylinder, allowing for the assumption of plane strain to be used for analysis

(Baguelin et al, 1978).

Many different types of pressuremeter’s have been developed since Ménard’s initial

Pressuremeter. The tri-celled Pressuremeter was adapted into a mono-cell version. The

two main type of mono-celled Pressuremeter’s are the TEXAM Pressuremeter and the

PENCEL Pressuremeter. The TEXAM is approximately 2.75 inches in diameter by 18 inches

long, while the PENCEL is approximately 1.3 inches in diameter by 9 inches long. Both

Pressuremeters are shown in Figure 2-1.

Figure 2-1: From right to left; Pencel, Ménard, and Texam Pressuremeter types (From RocTest)

7

2.1.2 Pressuremeter Insertion

Results from the Pressuremeter test will vary depending on how the probe is inserted into

the soil. This insertion process will affect the stress-strain characteristics of the soil at the

site. The soil type and relative density should be considered when selecting an insertion

method.

2.1.2.1 Insertion of Pre-bored Pressuremeter

Insertion of a pre-bored Pressuremeter (PBPM) entails lowering the Pressuremeter into a

hole slightly larger than the diameter of the probe (between 1.03DPMT and 1.2DPMT). This

method is the most common for probe insertion. PBPM works best for shallow depth

testing, due to the higher probability of borehole collapse in deeper boreholes. The two

main methods of borehole preparation for the PBPM are either, drilled or pushed thin

wall sampler. Drilled methods include rotary drilling, continuous flight auger, and hand

auguring. These methods are not recommended in granular strata due to the large soil

disturbance associated with drilling. A pushed or driven thin wall sampler is best used in

granular soils. In cohesive soils, the interaction between the soil and the thin walled

sampler may cause large disturbance in the layer. In deep test sites a prepared drillers

mud is recommended to support the borehole wall (Winter 1986).

2.1.2.2 Insertion of the Self-Boring Pressuremeter

The self-boring Pressuremeter (SBPM) has an internal rotary bit leading the

Pressuremeter during insertion. The shavings are flushed with drilling mud up an internal

flushing tube, where they are collected in a settling tank. This method of insertion

requires the most effort and materials and is primarily used when inserting the probe

through cemented layers, or weathered rock (Winter 1986).

8

2.1.2.3 Insertion recommendation chart

The method of insertion of the pressuremeter should be carefully considered, as the

insertion method can alter the overall test results. The following table from (Winter,

1986) can be used as a guide for deciding the insertion method. However, additional

factors, such as the cohesiveness, depth, grain size, aggregate size for road base course,

water table, and permeability are important factors to consider.

Table 2-1 Pressuremeter insertion recommendation table (Winter 1986)

9

2.1.3 Pressuremeter data interpretation

The Pressuremeter test method produces a stress-strain graph, similar to that of many

materials tests. There are three distinctive sections that make up this graph, these are

listed and explained below.

Initial phase: is a re-establishing curve portion at which the membrane becomes into a

full contact with the walls of a borehole (from point A to point B),

Elastic phase: is a straight-line portion during which the change in volumetric-strains of

the membrane are assumed to be constant (from point B to point C),

Plastic phase: is a nonlinear curve portion at which the stressed soil cavity increases

significantly with a little increase in applied pressure (from point C to Point D).

Figure 2-2: Typical Pressuremeter results curve (from Shaban 2016)

10

2.1.3.1 Lift off pressure

To estimate the lift off pressure (Po) is estimated from the curve where the tangent line

from the initial phase intersects the tangent line from the elastic phase on a pre-bored

PMT test, while it is the displacement of the graph above the strain axis on a self-boring

PMT test. The data reduction process is typically done by hand, drawing the two tangent

lines on a scale graph and visually determining this stress point. A hand analysis method is

highly variable, and may be best represented as a range instead of a single point. The lift

off pressure can be approximately related to the in-situ horizontal at rest earth pressure

for pre-bored tests. It is however not practical to predict the horizontal earth pressures

due to the relaxation and disturbance of the surrounding soil during the boring process.

The following figures show the methods of determining the lift off pressure (Mair and

Wood, 1987).

(a): SBPMT Curve (b): PBPMT

Curve Figure 2-3: Determination of lift off pressure for a self-boring and pre-bored pressuremeter (Mair and Wood 1987).

11

2.1.3.2 Initial Elastic Modulus

The straight portion of the curve between the lift off pressure and the plastic zone (figure

2-2 section BC) is the soils elastic response region of the sample. Soil is considered elastic

in this region due to the straight line nature of this curve. Lamè (1852) proposed that the

radial expansion of a cylindrical cavity in an infinite elastic medium is shown with the

following equation:

G = Vm (∆P

∆V) (2-1)

where:

G : Elastic shear modulus Vm : Mean volume of the cylindrical cavity ∆V : Change in volume over the corresponding change in pressure, ∆P

The shear modulus is found in the initial elastic portion of the pressuremeter curve, which

makes it prone to influence from soil disturbance (Baguelin, 1978). To account for the

influence of soil disturbance, an unload reload cycle is preformed to determine the reload

modulus; these cycles are shown in Figure 2-4. The entire portion of the unload-reload

cycle could be used to determine the shear modulus; however a single section over the

anticipated strain region can be used to get a more precise modulus.

12

The initial elastic modulus can be related to the shear modulus by using Possion’s ratio

(𝜈). This relationship is as follows:

G =E

2(1 + 𝜈) (2-2)

Therefore, Young’s elastic modulus can be directly measured by substituting Equation (2-

2) in Equation (2-3) as given below:

E = 2(1 + 𝜈)Vm (∆P

∆V) (2-3)

Possion’s ratio is often assumed to be 0.3 in non-saturated soil, 0.4 in mostly saturated

soil, and 0.5 in fully saturated soil.

Figure 2-4: PMT unload-reload cycle (From Shaban 2016)

13

In many cases, however, it is not practical to plot PMT data using volumetric expansion

(∆V), instead radial strain should be used. Radial strain is used instead, because of the

differences in probe volumes can cause inconsistent results between different

apparatuses. Instead, Briaud (1986) suggests that the strain be represented in radial

strain units (εr). The conversion between volumetric strain and radial strain can be easily

made, when using the assumption that the fluid being used in the pressuremeter is

homogenous and incompressible. A change in volume, converted to a change in radius

(∆R) can then be inserted into the following equation to determine the radial strain.

εr = 2πRf − 2πRo

2πRo=

Rf − Ro

Ro=

∆R

Ro (2-4)

where:

Ro : Initial cavity radius

R𝑓: Final cavity radius

ΔR: Change in radius

Using this radial strain, the equation for the area of a circle, and the assumption the

probe expands with a uniform circular cross section, Equation 2-4 can be combined with

Equation 2-3 to determine the incremental Young’s modulus of elasticity in terms of the

radial strain. This is shown in Equation 2-5 below.

14

E = (1 + 𝜈)(𝑃2 − 𝑃1)[(1 +

ΔR2

𝑅𝑜)

2

+ (1 +Δ𝑅1

𝑅𝑜)

2

]

[(1 +ΔR2

𝑅𝑜)

2

− (1 +Δ𝑅1

𝑅𝑜)

2

]

(2-5)

where:

Ro : Initial cavity radius

υ : Poisson’s ratio

P1 : Cavity radial stress at the beginning of the pressure increment

P2 : Cavity radial stress at the end of the pressure increment

ΔR1: Increase in probe radius at the beginning of the pressure increment

ΔR2: Increase in probe radius at the end of the pressure increment

This initial modulus is ideally uniform through the initial elastic phase of the stress vs

strain plot. However, there is typically variation between adjacent data points, therefore a

large segment of the elastic portion of the curve is usually used in order to decrease any

noise in the data.

2.1.3.3 Limit Pressure

The limit is defined as the pressure reached for the infinite expansion of the cylinder

(Briaud, 1986). This is the point where no additional pressure is needed to be applied to

continue to apply strain to the soil. The limit pressure (Pl) typically cannot be reached in

the normal testing procedure, due to the large strain that is applied. Baguelin (1978)

defined the limit pressure as the point where the cavity is twice the initial size (Vf=2Vo).

There are many different ways to extrapolate the data to reach the limit pressure, many

of these methods were developed by Baguelin (1978), however the most reliable is to

15

extrapolate the data by hand (Briaud 1986). The limit pressure is shown in Figure 2-2 at

point D.

Although disturbance caused by the borehole can have a large effect, up to 20%, on Po

and E, the limit pressure is typically not influenced from borehole disturbance, due to the

large applied strains in the determination of the limit pressure (Briaud 1986). Soil at radial

distances up to 1.6Ro can be remolded into a disturbed annulus without affecting the limit

pressure (Baguelin, 1978). It should however be noted, that the disturbance should be

minimized in order to provide accurate data.

2.1.4 Variations of strain-controlled PMT Tests

The Pressuremeter is a device that lends itself to testing sites in multiple ways, ranging

from a single load/unload test to an in depth cyclical and creep test. These will be

discussed with their uses and interpretations. The tri-celled probes use stress controlled

procedures, while mono-cell probes use strain controlled procedures. This study will focus

on the mono-cell, strain controlled tests.

2.1.4.1 Load/unload test

The load-unload strain controlled sequence test is the quickest strain controlled test in

pressuremeter testing. Once the borehole is created, and pressuremeter inserted, the

volume is increased using equal incremental volumes until the probe’s maximum volume

is reached. Each incremental reading is recorded after the pressure in the probe stabilizes.

Once the maximum volume is reached, the volume is reduced using equal volume

increments.

16

The load/unload test will provide a lift off pressure (Po), initial elastic modulus (Ei), limit

pressure (Pl), as well as a rough value of a reload modulus (Er). A typical data graph of this

test is shown in Figure 2-5.

Figure 2-5 Typical Load/Unload PMT test data

2.1.4.2 Unload-reload loop

The pressuremeter test with an intermittent unload reload loop is another type of strain

controlled PMT test. Briaud (1986) added the single unload reload cycle to improve the

PMT test for pavement testing. The probe is inflated to a pressure “P” then incrementally

deflated to “0.5P”. The probe is then gradually re-inflated and the test continues to its

limit pressure, or max volume, whichever occurs first. By initiating the unload/reload

loop, the entire curve was able to be graphed, as well as provided more reliable data. This

test was shown in Figure 2-4.

17

2.1.5 Pressuremeter Theories

2.1.5.1 Plane Strain Assumption

All pressuremeter theories base many of the assumption that the pressuremeter expands

in the bounds of plane strain conditions. Holtz and Kovacs( 1981), say that plane strain

conditions occur when one dimension is significantly longer than the other relative

dimensions. By having one dimension significantly longer, it allows this axis to be called

infinite, and analysis can be done in only one direction. The plane strain assumption with

the pressuremeter relies on an infinitely long cylinder expanding in only the radial

direction. End effects can play a large role in changing the assumption of an infinite

cylinder. Figure 2-9 below shows a PPMT probe as slightly egg shaped when inflated in

the air. However, Murat and Lemoigne (1988)show that the PPMT probe becomes much

more cylindrical when it is inflated in a confined environment.

Figure 2-6 Inflated probe shapes in an unconfined environment vs in a confined environment (from Murat and

Lemoigne 1988)

18

2.1.5.2 Shape Effects of PMT Probe

The shape of the pressuremeter probe plays a large role in determining the quality and

reliability of data. The ratio of length to diameter is known as the slenderness ratio or the

L/D ratio. This ratio is important in monocell probes to be able to use the assumption of

an infinite cylinder. This dimension is not as important with tri-cell probes, because the

guard cells reduce the end effects that are present on monocell devices.

Hartman (1974) shows that the maximum error in soil modulus will occur when the L/D

ratio is equal to 1, or the probe is spherical. This error is shown to be 33% larger than the

actual soil modulus. Current probes have an L/D ratio much greater than 1, meaning the

error in soil modulus is much less than the 33% found in spherical probes. An L/D ratio of

greater than 6.5 will yield an error of less than 5% for soil modulus, and in many cases can

be neglected (Briaud, 1986). Even though the modulus has little change with the L/D

ratio, the limit pressure is more greatly influenced by a change in slenderness. Laier

(1973) found that a decrease in the L/D ratio by a factor of two increased the Pl by a factor

of 1.28. This can lead to errors in the Pl of 10% to 15% between different types of probes,

under the same test conditions.

2.2 Triaxial Testing Triaxial testing is to be performed to determine the laboratory properties of the soils

being examined in this study.

2.2.1 Apparatus

The triaxial apparatus consists of four main components, a motor controlled load frame, a

triaxial cell, triaxial panel, and a data acquisition unit. A thorough understanding of each is

critical for the operator.

19

2.2.1.1 Load frame

A variable speed motor is attached to the load frame so a variable load rate from 0.0001

inches per minute to 0.2 inch per minute can be used during testing. This range allowed

for a large range in the strain rate to be applied to the samples.

Figure 2-7 Durham Geo Load frame

20

2.2.1.2 Triaxial Cell

The triaxial cell, from Durham Geo Slope Indicator Inc., can be used to test samples from

1.3” in diameter to 4.2” in diameter; as well as samples up to 9” in height.

2.2.1.3 Data Acquisition Unit

The Humboldt Data acquisition unit ® is calibrated with 1000 lbs, 5000 lbs, and 10,000 lbs

load cells. This system allows for tests to be performed with greater accuracy, depending

on the total load applied to the sample. In addition, the data acquisition unit includes a

displacement transducer with an accuracy of 0.0001 inches.

Figure 2-8 Durham Geo triaxial cell

21

2.2.1.4 Triaxial Panel

The triaxial panel is used to measure the cell pressure and volume changes in the sample.

Pressure regulators in the panel allow for pressure control to 0.1 psi, and volume

increments of 0.1 ml.

Figure 2-9 Humboldt data aquisition unit

22

Figure 2-10 Triaxial control panel

2.2.2 Test Description

The triaxial test can be performed under a variety of load, sample, and drainage

conditions. These features allow for a variety of types of tests to be conducted, allowing

for a broad spectrum of data to be collected. Tests of undisturbed samples can be

performed by extruding the sample from a Shelby tube directly into the sample

membrane. However, many times samples are remolded into the sample membrane.

Remolding of samples allows for tests to be performed at a wide variety of densities. The

three main types of triaxial tests are; Consolidated Drained (CD), Consolidated Undrained

23

(CU), and Unconsolidated Undrained (UU). These tests are discussed in the following

sections.

2.2.2.1 Consolidated Drained (CD)

During Consolidated Drained (CD) test, or ‘S’ test, the soil is consolidated prior to shearing

by opening the drainage valve to the specimen (figure 2-11), and applying a hydrostatic

confining pressure to the soil. This hydrostatic pressure is equal in all directions,

producing isotropic consolidation (Holts and Kovacs, 1981). Consolidation occurs until

volume change in the sample has stopped. The drainage lines remain open during shear

testing to allow for volume change to occur. The load which applies the normal stress

during shear must be applied slowly and the loading rate is based on the permeability of

the sample, in order to prevent pore pressures from building.

Since drainage is permitted during shearing the effective stress (σ’) is equal to the total

stress (σtotal). When effective stress equals total stress the Mohr’s circle analysis is

simplified. If these two stress’ are not equal, then the total stress circle is shifted by the

value of pore water pressure shown in Figure 2-13b.

2.2.2.1.1 Behavior of Sands during CD tests

The CD test allows for volume change to occur during shear, making the initial void ratio

of the sample important (Holtz and Kovacs, 1981). A sample with a high void ratio is

‘loose’ while a sample with a lower void ratio is ‘dense’. Additionally, the sample must be

fully saturated to observe volume change during shear. The volume change is measured

using a burette attached to the sample. When a loose sand is sheared, the void ratio will

decrease from the initial loose void ratio, down to a constant, characteristic, void ratio

24

(Holtz and Kovacs,1981). This characteristic void ratio is known as the critical void ratio, it

is the “ultimate void ratio at which continuous deformation occurs with no change in the

principle stress difference (σ1-σ3)” (Casagrande, 1936). Dense sands display the opposite

affect. The volume of dense sands will decrease slightly during shear, then the volume will

increase as the sample dilates until its critical void ratio is reached (Holtz and Kovacs,

1981). The ultimate values of the deviatoric stresses (σ1-σ3) should be the same for both

loose and dense sands (Hirschfeld, 1963). Volume change vs. strain graphs can be used to

determine the angle of dilation (Ψ). This angle can be used to determine the liquefaction

potential of sands, as well as losses of strength in sands (Holtz and Kovacs, 1981). These

trends are shown in figure 2-14.

Figure 2-11 Idealized relation for dilation angle, Ψ, from triaxial results

25

2.2.2.2 Consolidated Undrained

The Consolidated Undrained (CU) test, also known as the ‘R’ test, requires the same initial

set up as the CD test. Once the sample is prepared and saturated, the drainage valve is

opened, and a hydrostatic confining pressure is applied to the sample to consolidate it.

Once volume change stops, the drainage valve is closed. When drainage is not allowed, no

volume change can occur during shear. In the CU test the pore water pressure is typically

measured, allowing the effective stress to be calculated. This test may be either a total or

effective stress test (Holtz and Kovacs, 1981). Because both total and effective stresses

are determined, this is the most common triaxial test performed. Testing labs also prefer

this test because the load can be applied at a more rapid rate, since drainage is not

allowed during shearing.

2.2.2.2.1 Behavior of Sands in CU tests

By preventing volume change and the tendency of soil in shearing to change volume,

other than when initially set to critical conditions, will cause either a positive or negative

pore water pressure to develop (Holtz and Kovacs, 1981). In a Mohr’s circle analysis of a

CU test, the pore pressure will shift the total stress circle along the sigma axis. The pore

pressure shift is shown in Figure 2-13b below. Both circles have the same diameter,

because total deviator stress is equal to effective deviator stress. Even though the

deviator stress remains constant, the shift along the sigma access significantly changes

the friction angle (Holtz and Kovacs, 1981).

26

2.2.3 Test Data

The triaxial shear test will produce multiple types of data for analysis. These are all

determined from data reduction methods. The modulus of elasticity (E), Mohr’s circle and

failure envelope, friction and failure angle, and the angle of dilation can be determined

from the triaxial test.

2.2.3.1 Modulus of Elasticity

The Modulus of Elasticity can be determined as either strain based or volume based.

Strain based moduli, known as deformation modulus, is calculated from load and

displacement. This is shown in Equation 2-6.

𝐸 =𝜎

𝜖 (2-6)

where:

E : Deformation elastic modulus σ: Applied deviatoric stress 𝜀 : Measured Strain

Additionally, in triaxial tests where the change in volume is measured, the shear modulus

(G) can be determined. The shear modulus relates the applied stress to the volumetric

strain of the sample. This is shown in Equation 2-7.

27

G = ∆P

(∆V𝑉0

) (2-7)

where:

G : Elastic shear modulus V0 : Initial Volume of sample in test ∆V : Change in volume over the corresponding change in pressure, ∆P

2.2.3.2 Mohr’s Circle

The data from the triaxial tests can be used to construct Mohr’s circles. The Mohr’s circle

analysis can be used to determine the shear and normal forces at any plane in a sample.

In addition, the friction angle, and failure angle can be determined graphically from this

analysis. The circle is constructed using two points. The first point is the confining stress

applied to the sample, while the second point is the sum of the confining stress and the

deviator stress. These two points are the principle stresses, and represent the points of

zero shear in the sample. Examples of Mohr Circle’s for CD, and CU tests are shown in the

figures below.

28

Figure 2-13a: Typical Mohr's Circle for CD triaxial data (From Holtz and Kovacs 1981)

Figure 2-13b: Typical Mohr's Circle for CU triaxial data (From Holtz and Kovacs 1981)

29

2.2.3.3 Angle of Internal Friction

The angle of internal friction can be found from the Mohr’s circle analysis above. It can be

determined by drawing a line from the origin to a tangent point on the Mohr’s circle. All

granular soils will have a cohesion of nearly zero, as well as normally consolidated clays

(Holtz and Kovacs, 1981). However, over consolidated clays will have a cohesion value due

the preconsolidation hump. This angle can be measured directly from the plot, or can be

calculated through trigonometric relations. It is however, easiest to measure directly from

the plot. The angle of internal friction will intersect with the failure angle at the same

tangent point on the circle. The failure angle (α) can be calculated as:

𝛼 = 45° +𝛷

2

(2-8)

The failure relationship can be derived from the obliquity relationships, where the

inclination of the Mohr failure envelope is at its maximum (Holtz and Kovacs, 1981).

In addition to using the Mohr’s circle approach from triaxial testing, the friction angle can

be determined from a direct shear test. The direct shear test will yield a shear and normal

force at failure. These two values can be used to determine the friction angle

geometrically.

𝛷 = 𝑡𝑎𝑛−1(𝜏

𝜎) (2-9)

where:

Φ : Friction angle τ: Shear stress at failure σ : Applied stress at failure

The relationship is only applicable to granular soil, where the cohesion of the soil can be

assumed to be zero. If there is cohesive material, multiple trials must be conducted, and

30

the cohesion can be determined from the intercept with the shear axis. Additionally, the

friction angle can be determined from each test using a trigonometric relationship, using

the confining stress and the maximum applied stress of the test. This relationship is

shown in Equation 2-10:

𝛷 = 𝑠𝑖𝑛−1(𝜎1 − 𝜎3

𝜎1 + 𝜎3) (2-10)

where:

Φ : Friction angle σ1: Applied stress at failure σ3 : Applied confining stress at failure

The benefit of this form of the equation is a direct calculation from triaxial data. This

allows for more data points be found for each set of tests, one phi value per confining

stress. The use of the Mohr’s Circle and the listed geometric relationships can provide the

majority of engineering data for a given soil.

2.3 Methods of determining the at rest earth pressure

2.3.1 Jaky Determination, 1944

In 1944 Dr. Josef Jaky derived a theoretical equation for determining the coefficient of

earth pressure at rest. His method used an infinatly long prismatic soil section with side

slopes at the natural angle of repose, which Jaky assumed to be equal to the angle of

internal friction (phi). Jaky then used a series of differential equations to determine a

mathematical relationship between the angle of internal friction and the at rest earth

pressures.

31

Jaky’s initial solution to the differential equation’s simplified into what is shown in

Equation 2-11. However for Φ values between 20 and 45 degrees, the second portion of

Equation 2-11 simplifies to 0.9. Since most soils have Φ values withing 20 to 45 degrees,

Jaky simplified the equation to what is shown in Equation 2-12.

𝐾𝑜 = (1 − 𝑠𝑖𝑛𝛷) (1 +

23

𝑠𝑖𝑛𝛷

1 + 𝑠𝑖𝑛𝛷) (2-11)

where:

Φ : Friction angle Ko: At rest earth pressure coefficient

The final equation was then simplified to:

𝐾𝑜 = 0.9(1 − 𝑠𝑖𝑛𝛷) (2-12)

In a follow up paper in 1948, Jaky drops the 0.9 from the equation leaving the equation

that is currently used by many engineering texts.

2.3.2 Laboratory Methods

2.3.2.1 Triaxial

The Ko value can be determined multiple ways with the triaxial test data. The simplest and

quickest way to determine the at rest pressure coefficient is to use a Mohr’s circle

analysis to determine the phi angle, and then the angle can be plugged into one of the

equations derived by Jaky.

A more complex approach to find Ko is to determine the horizontal and vertical pressures

during shear with no volume change. By not allowing volume change in the sample the

stresses are characteristic of the at rest condition. The confining stress must be adjusted

32

during axial loading so no compression or dilation occurs. When the horizontal pressure is

adjusted with the vertical pressure, Terzaghi’s assumptions of σh/σv can be directly

measured.

2.3.2.2 Soft Oedometer Ring

The Soft Oedometer Ring (SOR) is a laboratory test apparatus used to obtain the

engineering parameters of soils (Kolymbas, 1993). The SOR consists of a load frame, strain

and load gauges, and an extensible metal ring. By using the SOR, the problems with non-

homogeneous deformations found within triaxial testing are greatly reduced, due to the

shallow depth of the ring (0.75”-1.5”). By keeping the depth of the ring small, load is

transferred equally throughout the soil structure, as well as the skin friction between the

ring and soil sample is reduced. The SOR is shown in Figure 2-14 below. The SOR test

method can work efficiently to determine the Ko value of a soil, because it measures

horizontal and axial strain directly. There is no need to use correlations and equations to

determine the at rest condition. However, to avoid failing the soil into an active condition

the test must occur far below the stress limits (Kolymbas, 1993).

Figure 2-14: Soft Oedometer Ring (Kolymbas, 1993)

33

2.3.3 In-Situ tests

2.3.3.1 Standard Penetration Test

The Standard Penetration Test (SPT) is an in-situ test which requires a 140 lbs hammer to

be dropped from a height of 30 inches to drive a sampler tube through a soil stratum. The

number of blows required to drive the sampler head 12 inches into a soil layer is reported

as the ‘N’ value as blows per foot. There is no strong method for determining the Ko value

from the SPT. However, DeMello (1971) produced an empirical correlation between the

Φ’ value of an uncemented sand in triaxial compression and the N value from SPT tests.

This Φ’ can then be used in the Jaky (1941) equation to determine a reasonable Ko value.

The chart from DeMello (1971) is shown in Figure 2-15 below.

Figure 2-15: Correlation between the SPT N values, normalized effective overburden, and the triaxial compression phi value (DeMello, 1971)

34

2.3.3.2 Cone Penetration Testing

The Cone Penetration Test (CPT) was developed in the 1950’s and is under constant

improvement, from a mechanically driven analogue device to the current hydraulically

pushed digital version (Schmertmann, 1978). The latest CPT cone is an electric device that

is instrumented to record the cone resistance (qc) and the side friction (fsc) as it is

hydraulically pushed through the soil. An empirical correlation similar to the SPT

correlation was determined by Robertson and Campanella (1983). Their correlation uses

the value of qc, as well as the effective stress in order to make a correlation to a Φ’ value

from a triaxial compression test. This chart is shown in the figure below. Once the Φ’

value is determined from the Robertson correlation, this value may be used in the Jaky

(1944) equation to determine the Ko value.

35

Figure 2-16: Correlation between CPT data and the effective phi angle in sand soils (Robertson and Campanella, 1983)

2.3.3.3 Pressuremeter

Lift off pressure is the existing or in-situ horizontal pressures. The most common

pressuremeter method of determining the at rest earth pressure is to use the lift off

pressure. This method however is highly variable to the quality and type of the borehole.

Different boring methods produce different amount of borehole disturbance, causing

variability in the lift-off pressure. To reduce the amount of disturbance, a self-boring

pressuremeter can be used to determine more accurate lift-off pressures.

36

Another method, called the strain slope method, uses the slope of the log-log stress strain

diagram to correlate an angle of internal friction. By using the slopes of the elastic portion

of the stress strain diagram, and assuming a critical value phi angle (between 30 and 35

degree’s for sands), the chart shown in Figure 2-17 can be used to determine an angle of

internal friction. By using the angle determined from the chart, the at-rest earth pressure

coefficient can be determined from the Jaky (1944) method. The strain slope method was

developed by (Mair and Wood, 1987); however this method is most reliable with a self-

boring pressuremeter. This method can be used with pre-bored and pre-driven

pressuremeters, however the larger the disturbance of the soil, the less reliable the

results will be. This method still assumes a value needed to determine the angle of

internal friction, making this method subject to borehole disturbance as well as

assumptions based on the soil type.

37

Figure 2-17: Chart developed by Mair and Wood (1987) to determine the phi value using stress strain slope.

38

3 Description of Test Sites

3.1 Test Site Locations Two test sites were used on the campus of the Florida Institute of Technology (FIT) in

Brevard County, FL. The first site was located east of Country Club Rd in the remaining

undeveloped lot, and the second site North of East University Blvd and East of SR 507

(Babcock St.) in the current Southgate intramural fields. The site locations are shown in

Figure 3-1 below. These two sites contained a stratum, greater than 5 feet, of a poorly

graded sand material, with similar densities throughout the sites, and varied densities.

These two sites were chosen due to their accessibility for testing, the range of densities

found at the site, and thin layer of vegetation.

39

Figure 3-1: General location of testing sites on the FIT campus shown by stars.

3.1.1 Florida Tech Overflow lot

The first site tested was at the grass overflow lot on the southwest corner of the Olin

Complex on the FIT campus (Figure 3-2). A 250 ft transect was measured to allow for

reproducible tests (Figure 3-2). An overflow lot was selected due to previous compaction

from vehicular traffic; slightly increasing densities of the top strata at this site. There is

very little variation in the soil gradation across the site, which will cause the moisture

40

density, and minimum and maximum densities to be similar across the soil (Holtz and

Kovacs, 1981). The moisture contents of the soil at this location varied from 11% to 21%,

this variation was due to water table flow direction, and grass cover holding moisture in

some area’s while exposed sand in other areas.

Figure 3-2: Arial overview of the overflow test site. The transect on which tests were performed is shown by the yellow line.

3.1.2 Southgate Field

The second site test was the southgate field, located at the corner of Babcock st. and

University Blvd. Similar to the first testing location, this is a grass covered field located on

the FIT campus (Figure 3-3). The major difference is that the southgate field does not

41

experience vehicle traffic on its surface, making the density at this site lower than at the

overflow lot site. The soil present at this site is a poorly graded sand soil (SP) with a

gradation similar across the length of the test site. The moisture content in this location

ranged from 10% to 30%. This large variation was due to rainstorms between testing

days.

Figure 3-3: Southgate field test site. The transect tested is shown by the yellow line.

42

4 Test Methods The tests methods were separated between in-situ and laboratory tests. The testing

procedures for each method are described here.

4.1 In-Situ tests

4.1.1 PPMT

The PPMT test is comprised of three different parts: saturation, calibration, and testing.

The basic procedure involves calibrating the pressuremeter unit, preparing the test site

and borehole, and conducting the test. The test involves water being forced through

tubing into a probe using a crank handle and piston housed in box called the control unit.

4.1.1.1 Control Unit

The PPMT control unit used to perform the tests, has been instrumented with digital

sensors that are an upgrade, developed by Cosentino et al (2006) to improve the accuracy

of the results. These digital instruments are used to measure and record the pressure and

volume during testing, as shown in Figure 4-1. These items, as well as the standard

measurement items, are housed in a plastic case.

43

The linear string potentiometer and pressure transducer, which yield volume change and

pressure respectively, were added to digitally and accurately record the applied volume

and corresponding pressure. These instruments are connected to a data port, where the

outputs can be viewed with a computer. The instrumentation process can be found in

Cosentino et al (2006) (PP. 54-57). In addition to the digital instruments, the following

components are contained in the pressuremeter control unit.

A 138 cm3 screw piston

A 2500 kPa dial pressure gauge

A volume indicator

Several valves and tubing

4.1.1.2 Automated Pressuremeter Software

The digital instrumentation added to the pressuremeter needed to be read by a software

package. The calibrated digital outputs from the pressure transducer and the

Figure 4-1 Pressuremeter control unit with added digital instrumentation (From Shaban, 2016)

44

potentiometer were inputted into a Labview ® based software package called The

Automated Pressuremeter Software (APMT) (Cosentino et al, 2006). By using a Labview ®

based software, an easy to use graphical user interface (GUI), shown in Figure 4-2, was

developed.

The APMT software records the data from the calibration processes, test and site

parameters, and field test data. These inputs are then reduced in the program to produce

a final data curve. The raw data is shown in Figure 4-2 as the red line, the reduced data is

shown in blue. Data is then outputted in a comma separated value (CSV), for use in other

data management programs.

Figure 4-2 Screenshot of the APMT user interface and data reduction

45

4.1.1.3 PPMT Calibration

The PPMT calibration process consists of three main steps: saturation, membrane

calibration, and volume calibration. These steps are necessary to ensure the PMT is

properly operating and for proper data reduction.

4.1.1.3.1 Saturation

The entire PPMT system must contain no air voids, the saturation process is intended to

ensure no air voids are present during testing. The cylinder is filled and emptied multiple

times with de-aired water. While the cylinder is still connected to the de-aired water

source, the tubing and probe are inflated using the de-aired water. The tubing and probe

are lightly agitated to pass any air bubbles to the valve at the end of the probe. De-aired

water is pushed through this valve to remove the air bubbles. This inflation and agitation

process is repeated until no air bubbles can be detected in the system. The probe is then

deflated and the PMT control unit is disconnected from the de-aired water source. A full

description of the saturation process is given in ASTM 4719-07.

4.1.1.3.2 Membrane Calibration The membrane calibration is used to measure the pressure exerted by the flexible

membrane at any given volume. The membrane calibration is performed using the APMT

program. With the probe placed at the same elevation as the control unit, and the

membrane able to expand unobstructed, the probe is expanded in 5 cm3 increments.

Pressure readings are recorded from the APMT software at every volume increment.

Readings should be taken for the entire range of the predicted test volume, 95 cm3 is

typically a sufficient volume for this calibration. A typical membrane resistance curve is

shown in Figure 4-3

46

Figure 4-3 Typical membrane calibration curve for PPMT tests

4.1.1.3.3 Volume Calibration The last step in the calibration process is a volume calibration. The volume calibration

yields the change in the system volume during testing. As pressure increases during

testing the tubing, piston, and other components of the system can expand; this

expansion is accounted for with the volume calibration. The probe is fitted into a rigid

metal sleeve, and the volume is incrementally increased at a rate of 5 cm3 until full

contact is made with the metal sleeve. Once full contact has been made (see Figure 4-4),

pressure is incrementally increased at a rate of 500 kPa until 2500 kPa is reached. For data

reduction, the point where full contact is made (usually a sharp increase in pressure), is

set to the origin and then represents the volume change in the system.

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

Pre

ssu

re (

kPa)

Volume (cm3)

47

Figure 4-4 Typical volume calibration curve from a PPMT test

4.1.1.4 PPMT Field Test

The PPMT field test procedure follows, in general, the procedures presented in the ASTM

D4719-07 using the equal volume method. Slight variations were made between the

ASTM method, in particular in the borehole creation, and the volume increments used.

1) Place control unit at desired test location, and attach probe and computer to the

control unit.

2) Secure the borehole driving guide (Figure 4-5) to the location using soil nails, or

equivalent method to prevent shifting of the guide during the boring process.

3) Drive thin walled boring tube (outside diameter 1.3”) through the guide sleeve

using a 5 pound sledge hammer, taking care to remove and empty the sampler

periodically throughout the boring process. By emptying the sampler, the chances

of soil plugging the tube reduces.

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30 35 40 45

Pre

ssu

re (

kPa)

Volume (cm3)

Full contact made

with calibration

sleeve

48

4) Collect a moisture content sample from the base of the bore hole.

5) Slide the PPMT probe into the hole immediately after the boring is complete to

reduce the chances of the borehole caving in.

6) Using the APMT software, select the appropriate calibration data files to associate

with the test. Input the general test data required (date, location, borehole

number, control unit height, and test depth).

7) Select ‘run Automated PMT test’ from APMT software menu. Then increase the

volume in the probe by 5 cm3, selecting ‘take reading’ on APMT screen after each

increase in volume. Repeat this step until the limit equilibrium (Pl) is reached or

the unit hits its maximum volume.

8) Reduce the volume 2 cm3 per increment, selecting ‘take measurement’ after each

increment until a volume of 0.75 x Vmax is reached for the rebound slope.

9) Select ‘Save test’ from APMT test screen to complete the test.

49

Figure 4-5 Borehole driving guide, with thin wall driving tube (From Shaban 2016)

4.2 Laboratory Tests

Laboratory tests were used to classify and determine soil properties, including USCS soil

classification methods, grain size analyses , moisture density relationships, minimum and

maximum densities, and consolidated drained triaxial tests. Each test procedure will be

briefly discussed, along with deviations from the corresponding ASTM methodology.

4.2.1.1 Unified Soil Classification (ASTM D2487)

Soil at each site was classified using the Unified Soil Classification System (USCS). The

procedure for the USCS classification follows the flow chart in the ASTM D2487

procedure.

50

4.2.1.2 Grain Size Analysis (ASTM D6913)

The grain size analysis was performed to compare the soil gradation at each test site.

Samples were taken from each site, dried, and organic material removed for each. The

grain size analysis was performed according to ASTM D6913.

4.2.1.3 Standard Proctor (ASTM D698)

A standard proctor test was performed on the soil samples received from the field. This

test allowed the optimum compaction moisture to be determined for the relative density

testing.

4.2.1.4 Relative Density (ASTM D4253, D4254) The minimum and maximum density was determined to compare data on a percentile

scale. Using both dry and optimum moisture conditions, the maximum and minimum

density was determined.

4.2.1.5 Consolidated Drained Triaxial (ASTM D7181) Mechanical properties of the soil were determined by using a consolidated drained (CD)

triaxial test. The test was run in accordance with ASTM D7181, the method of sample

compaction is not specified in ASTM D7181; the method used for compaction is given

below.

1) Calculate the total mass of soil needed for a set value of dimensions (1.4” x 2.8”)

2) Define three equal lift heights and separate the total mass of soil into three equal

parts.

3) Using gentle tamping and vibration, compact each lift in the mold until the final

height for each lift is met.

4) After seating the top cap onto the sample, verify the final height and diameter.

51

5 Results and Correlations

5.1 Soil Properties Results Laboratory classification, moisture density, and relative density of the soil were

performed to properly classify the soil, and allow for the soil to be grouped into

appropriate categories for correlations. Results of these tests are given in the following

sections.

5.1.1 Grain Size

All soils in this study were found to be poorly graded sand (SP) according to the Unified

Soils Classification System (USCS). The grain size analyses are shown in Figure 5-1. The

research and testing were performed on SP type soils, results and correlations were made

only on data from SP soils. The average coefficient of uniformity (Cu) is 2.5 and the

average coefficient of curvature (Cc) is 1.3. The low Cu value (Cu< 6) show a uniformly

graded soil, and a Cc value between 1 and 3 shows the soil is not gap graded. These shape

parameters show that uniformity is the reason the sand is poorly graded, not gap graded.

52

Figure 5-1 Grain size distributions for test sites in FIT campus

5.1.2 Optimum Moisture

Standard proctor tests (ASTM D698) were performed on soil from the overflow lot test

site to determine the optimum compaction moisture of the soil. This moisture content

would then be used to determine the compaction water content for the maximum

relative density test. The results of the standard proctor tests are shown in Figure 5-2. The

maximum wet proctor density is 126 pcf when compacted at 12% moisture content,

producing to a 113 pcf dry density. The shape of the moisture density curve shows a steep

drop off in density when the soil is compacted dry of optimum, while a smaller loss of

density is experienced when the soil is compacted wet of optimum. Therefore the relative

density test should be performed at optimum moisture density, however deviations

should err to wet of optimum.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.010.1110

Pe

rce

nt

fin

er

Sieve Size (mm)

Grain size distribution FIT campus

Overflow lot North

Overflow lot Center

Overflow lot South

Southgate Field

# 4 #40 #100

53

Table 5-1 Summary of moisture density results from mixed samples

Trial MC Wet

Density Dry

density

% pcf pcf

1 7% 117 109

2 8% 122 112

3 12% 126 113

4 16% 125 108

5 21% 122 101

Figure 5-2 Standard Proctor moisture density data from a mixed sample, optimum moisture content was determined to be 12%

5.1.3 Relative Density

The minimum and maximum relative densities were determined in order to determine

the consistency of the soil tested. The soil from the test site, as well as in the triaxial tests

ranged from loose to medium dense (20% to 65% relative density). The relative density is

important to consider, because the behavior of sands change as the relative density

increases. Additionally, the PPMT soil strengths corresponded with loose to medium

dense, as defined by Briaud (1986).

110

112

114

116

118

120

122

124

126

128

0.0% 5.0% 10.0% 15.0% 20.0% 25.0%

We

t D

en

sity

(p

cf)

Moisture Content

Standard Proctor Results

54

5.1.3.1 Maximum Density

To determine the range of densities to perform triaxial tests, minimum and maximum

relative density tests (ASTM D4253/4253) were performed. The test was performed at

both oven dry conditions and near optimum moisture content. A maximum density of 137

pcf was determined with a moisture content of 14%. The water content is very close to

the 12% determined from the standard proctor test. Additional compaction effort will

result in greater density at a greater moisture content (Holtz and Kovacs, 1981). A

summary of the maximum density tests are shown in table 5-2 below.

Table 5-2 Summary of maximum density tests

Sample W.C Wet Density Dry Density

% pcf pcf

1 0% -- 102

2 0% -- 103

3 0% -- 104

4 11% 122 110

5 14% 137 120

6 13% 135 119

7 13% 136 120

5.1.3.2 Minimum Density

In order to determine the relative density of the samples the minimum relative density

was determined. Minimum relative density tests are performed at oven dry conditions, as

per ASTM D4254. A summary of the minimum density tests are shown in Table 5-3 below.

55

Table 5-3 Summary of minimum density tests

Mold Weight

Mold Volume

Total Weight

Soil Weight

Density

lbs ft3 lbs lbs lbs/ft3

9.63 0.033 12.47 2.84 85.2

9.63 0.033 12.48 2.85 85.5

5.2 Triaxial Results Consolidated drained (CD) triaxial tests were performed on the SP samples from the FIT

test sites. Confining stresses of 5 psi, 10 psi, and 15 psi were chosen for testing to allow

for better quality data to be collected. Tests at low confining stress (less than 3 psi) often

have too much noise in the data to allow for accurate data analysis. The raw data was

recorded using the Humbolt Data Acquisition software and reduced using Microsoft Excel.

The initial modulus (from Equation 2-6), and the normal stress at 5% strain were

determined. The normal stress at 5% strain was chosen as the deviator stress because this

value corresponded best to the maximum applied normal stress. While in a few cases

larger applied stress’ at different strains were found, the stress at 5% was always within

one psi of maximum normal stress. A typical triaxial stress strain plot is shown Figure 5-3.

To develop the Mohr-Coulomb failure envelope the normal stress at 5% strain was set as

the deviator stress (σ1- σ3); confining stress was set as the minor principle stress (σ3). The

shear stress was determined by using half the deviator stress at 5% strain. The major

principle stress (σ1) was determined by adding the deviator stress to the confining stress.

A typical Mohr’s circle and failure envelope is shown in Figure 2-13. The angle of internal

friction was determined by using Equation 2-10. The results of the 21 triaxial tests are

summarized in Table 5-4 below.

56

Figure 5-3 Typical Triaxial stress-strain plot

Table 5-4 Summary of triaxial test results

Sample Density Confining Pressure

Initial Moduli

Deviator Stress (5% ε)

Friction Angle

Shear Stress (5% ε)

pcf psi psi psi deg psi

1 100 5 1306 18.3 40.3 9.2

2 100 10 1760 35.3 39.7 17.7

3 100 15 2674 45.4 37.0 22.7

4 100 5 1257 15.5 37.4 7.8

5 100 10 2455 32.4 38.2 16.2

6 100 15 2625 50.8 39.0 25.4

7 100 5 1040 16.8 38.8 8.4

8 100 10 1594 31.7 37.8 15.9

9 100 15 2607 40.7 35.1 20.4

10 90 5 1029 19.6 41.5 9.8

11 90 10 2448 37.8 40.8 18.9

12 90 15 2812 55.5 40.5 27.8

13 90 5 691 18.2 40.2 9.1

14 90 10 1253 36.0 40.0 18.0

15 90 15 1746 47.5 37.8 23.8

16 90 5 880 13.7 35.3 6.9

17 90 10 1513 24.1 33.1 12.1

18 90 15 1877 33.7 31.9 16.9

19 105 3 870 15.2 45.8 7.6

20 105 5 990 25.3 45.8 12.7

21 105 7 1340 29.5 42.7 14.8

0

5

10

15

20

25

30

35

40

0% 5% 10% 15% 20%

Stre

ss (

psi

)

Strain

5% Strain

Deviator Stress at 5% strain

Ei

57

Table 5-5 Averages of triaxial data, based off of density

Density Confining Pressure

Average Initial

Modulus

Average Normal Stress

Average Shear Stress

Average Phi Angle

pcf psi psi psi psi degrees

100

5 1201.0 16.9 8.4 38.8

10 1936.3 33.1 16.6 38.6

15 2635.3 45.6 22.8 37.0

90

5 866.7 17.2 8.6 39.0

10 1738.0 32.6 16.3 38.0

15 2145.0 45.6 22.8 36.7

5.3 Pressuremeter Results Twenty pressuremeter tests were performed using the PENCEL Pressuremeter. Ten PPMT

test were performed in the overflow lot (OF) and ten were performed in the Southgate

field (SG). These ten tests were performed along the transects shown in Figure 3-2 and

Figure 3-3, spaced twenty-five feet apart. The APMT software was used to determine the

three soil parameters, initial modulus, limit pressure, and lift off pressure. The results of

the twenty PPMT performed are summarized in Table 5-6.

58

Table 5-6 Summary of PPMT test results

Site Number Depth Initial

Modulus Limit

Pressure Lift off

Pressure Briaud’s

Classification1

-- -- ft psi psi psi

OF 101 2.48 1695 260 7.98 Dense

OF 102 2.44 1779 206 7.25 Compact

OF 103 2.48 1913 165 5.80 Compact

OF 104 2.48 1612 166 5.51 Compact

OF 105 2.41 1651 173 8.70 Compact

OF 106 2.41 1534 151 4.06 Compact

OF 107 2.54 1280 146 5.80 Compact

OF 108 2.34 1299 179 5.08 Compact

OF 119 2.48 2910 212 7.25 Compact

OF 120 2.48 2425 184 6.53 Compact

SG 201 2.48 650 78 5.80 Compact

SG 202 2.48 790 73 2.90 Compact

SG 203 2.51 841 70 3.63 Loose

SG 204 2.48 585 57 5.08 Loose

SG 205 2.51 719 63 6.96 Loose

SG 206 2.48 543 54 2.61 Loose

SG 207 2.54 710 59 3.63 Loose

SG 208 2.54 721 60 3.63 Loose

SG 209 2.54 727 56 2.90 Loose

SG 210 2.54 665 56 3.05 Loose 1 Soil texture classifications from Briaud 1986

Table 5-7 Averages of PPMT data based off of site

Site Average

Initial Modulus

Average Limit

Pressure

Average Lift off

pressure

-- psi psi psi

OF 1810 184 6.40

SG 695 63 4.02

59

5.4 Correlations

5.4.1 Triaxial correlations between strength and stiffness

The correlation process began by examining the relationship between the initial triaxial

modulus (Ei) and the triaxial shear (Su) strength of the soil. The results are plotted in

Figure 5-4. The most promising relationship was produced by power regression was

produced as shown in Equation 5-1. The triaxial initial modulus is about 100 times greater

than the shear strength. This correlation was developed from 21 tests in SP sands ranging

from 20% to 65% of relative density.

𝐸𝑖 = 167𝑆𝑢0.84 (5-1)

𝑅2 = 0.72

Figure 5-4 Correlation between the triaxial initial moduli and the shear strength of the soil at 5% strain

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30

Tria

xial

In

itia

l Mo

du

lus

(psi

)

Shear Strength (psi)

60

5.4.2 Pressuremeter moduli and strength correlation

An equation developed by Baguelin (1978) (Eq 5-2), was used to relate the PPMT limit

pressure to the shear strength. This relationship was used to calculate shear strengths

from the field measured PPMT limit pressures.

Baguelin’s equation was used, instead of developing a site specific equation due to

limitations in testing capabilities. A separate, in-situ, shear testing apparatus, such as a

vane shear test probe, would be needed to develop a site specific shear versus limit

pressure equation.

The calculated shear strengths (Eq 5-2), with confidence intervals, were then added to the

triaxial modulus versus shear strength plot (Figure 5-4). The confidence intervals of 95%,

99%, and 99.9% were then compared for both limit pressure versus shear and initial

modulus versus shear. In Figure 5-5 the 99.9% confidence interval (α=0.001), which

includes the 85% of measured data, shows the confidence intervals of the two data sets

overlapping at a limit pressure of 200 psi. A confidence interval of 99.9% was used

because it considers more data in the analysis than a 95% confidence interval, which only

uses 60% of measured data. Since a limited number of data points were measured,

reducing the total number of points used by 40% may significantly bias the results.

Measured and predicted values begin to differ significantly for dense and very dense

sands (> 50% for Dense sand, >85% for Very Dense sand).

𝑆𝑢 = 0.21 × 𝑃𝑙0.75 (5-2)

61

Figure 5-5 Comparison between the calculated limit pressure, measured initial modulus and shear strength

The relationship between the pressuremeter initial modulus was then compared to the

limit pressures, allowing for a correlation to be made between the PMT limit pressure and

the PMT initial modulus. This relationship is shown in Figure 5-6, and the regression

equation is.

𝐸𝑝𝑚𝑡 = 8.6 × 𝑃𝑙 + 180 (5-3)

𝑅2 = 0.75

0

50

100

150

200

250

300

0

500

1000

1500

2000

2500

3000

1 10 100

Lim

it p

ress

ure

(p

si)

Init

ial m

od

ulu

s (p

si)

Shear strength (psi)

Triaxial Data

Confidenceinterval

Power ( LimitPressure)

62

Figure 5-6 Correlation between PMT initial modulus and PMT limit pressure using all data points

When the data for only loose to compact sands (limit pressure <200 psi and Initial

modulus < 2000 psi) the regression correlation increases, as well as the relationship

between these values reduces from 8.6 times greater to 8.3. The data for the loose to

compact sands are shown in Figure 5-7 and the regression equation is shown in Equation

5-4.

𝐸𝑖 = 8.3 × 𝑃𝑙 + 180 (5-4)

𝑅2 = 0.89

0

500

1000

1500

2000

2500

3000

3500

0 50 100 150 200 250 300

Pre

ssu

rem

ete

r M

od

ulu

s (p

si)

Limit Pressure (psi)

63

Figure 5-7 Limit pressure vs pressuremeter modulus for loose to compact sands

The correlation between the PMT limit pressure and the triaxial initial modulus was

compared to the limit pressure vs PMT initial modulus correlations from Cosentino et al.

(2007). Cosentino et al. found the PMT initial modulus was 8 to 16 times greater than the

PMT limit pressure, with lower density soils ranging toward 8 times greater, and very

dense soils ranging toward 16 times greater. Figure 5-6 shows the triaxial initial modulus

is 8.6 times greater than the PMT limit pressure, while Figure 5-7 shows the modulus is

only 8.3 times greater. The ratio determined in testing is within the range Cosentino

presented for loose soils, verifying the relationship in Equation 5-4. Since the densities

from the two field test sites do not overlap, there is a void in the data, most prominent on

the limit pressure axis.

The shear strength and the initial modulus for both the PPMT and triaxial tests were

plotted together to show that the strength parameters have similar influence on both the

triaxial and PPMT initial modulus. The relationship between the strength and stiffness for

0

500

1000

1500

2000

2500

0 50 100 150 200

Pre

ssu

rem

ete

r M

od

ulu

s (p

si)

Limit Pressure (psi)

64

both PPMT and triaxial data is a power relationship, with stiffness increasing as strength

increases as shown in Figure 5-8.

Figure 5-8 Relationship between strength and stiffness data for both triaxial and PPMT tests

Table 5-8 Relationships and correlations between the strength and stiffness for PPMT, triaxial, and combined data

Data Power equation R2 Linear equation R2

PPMT 𝐸𝑖 = 121 × 𝑆𝑢1.14 0.88 𝐸𝑖 = 185 × 𝑆𝑢 − 152 0.76

Triaxial 𝐸𝑖 = 167 × 𝑆𝑢0.84 0.72 𝐸𝑖 = 93 × 𝑆𝑢 + 232 0.73

Combined 𝐸𝑖 = 223 × 𝑆𝑢0.77 0.74 𝐸𝑖 = 88 × 𝑆𝑢 + 440 0.63

5.4.3 Triaxial and pressuremeter stiffness correlation

Equations 5-2 and 5-4 were then used to develop a predicted PMT modulus from each

measured triaxial shear strength. Equation 5-2 was used to predict the limit pressure

0

500

1000

1500

2000

2500

3000

3500

1 10 100

Init

ial M

od

ulu

s (p

si)

Shear strength (psi)

Triaxial Data

PMT Modulus

65

from the measured triaxial shear strength. Using these limit pressures the PMT modulus

was then predicted using Equation 5-4. These predicted PMT moduli and corresponding

triaxial moduli are shown in Figure 5-9. The resulting predicted PMT modulus is on

average 68% larger than the measured triaxial modulus, indicating a triaxial modulus

could give a more conservative design value. The results of predicting the PMT modulus

from the triaxial modulus are shown in Figure 5-9.

𝐸𝑃𝑀𝑇 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑒𝑑 = 1.68 × 𝐸𝑡𝑟𝑖 − 250 (5-5)

𝑅2 = 0.72

Figure 5-9 Predicted PMT modulus from measured Triaxial data

Assuming Equation 5-5 can be used to predict moduli from PMT limit pressures, the

correlation was worked the opposite direction. The triaxial initial modulus was predicted

using the measured field PMT moduli. Using Equation 5-4, the limit pressure was

determined from PMT moduli, Baguelin’s Equation (5-2) was then used with the predicted

limit pressure to determine the shear strength, and then finally the corresponding triaxial

0

1000

2000

3000

4000

5000

6000

7000

0 500 1000 1500 2000 2500 3000

Pre

dic

ted

PM

T m

od

ulu

s

Measured Triaxial Modulus (psi)

Predicted PMT modulus using Triaxial data

66

modulus was determined from the shear strength Equation 5-1. Figure 5-10 is a plot of

these data, producing a linear relationship between the triaxial and PMT moduli. The

regression equation (Eq 5-6) has a very strong correlation and indicates the triaxial moduli

on average 50% less than the corresponding PMT moduli.

𝐸𝑡 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑒𝑑 = 0.5 × 𝐸𝑝𝑚𝑡 + 330 (5-6)

𝑅2 = 0.91

Figure 5-10 Prediction of triaxial moduli using field measured PMT moduli

0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000 2500

Pre

dic

ted

Tri

axia

l Mo

du

lus

(psi

)

Measured PMT Modulus (psi)

67

Table 5-9 Correlation summary

Description Equation R2 Equation

number Triaxial modulus vs triaxial shear 𝐸𝑖 = 93 × 𝑆𝑢 + 230 0.73 5-1

Limit pressure vs PMT modulus in loose to compact sands

𝐸𝑖 = 8.3 × 𝑃𝑙 + 180 0.89 5-3

PMT modulus conversion from triaxial data 𝐸𝑃𝑀𝑇 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑒𝑑 = 1.68 × 𝐸𝑡𝑟𝑖 − 250 0.72 5-4

Triaxial modulus conversion from PMT data 𝐸𝑡 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑒𝑑 = 0.5 × 𝐸𝑝𝑚𝑡 + 330 0.91 5-5

68

6 Conclusions and Recommendations

The research objectives in this study were to correlate the data from PPMT tests to the

data produced from laboratory triaxial testing. The parameters used from the PPMT tests

were the limit pressure and the initial elastic modulus, because these parameters were

least influenced by the insertion process. The parameters used from the triaxial tests

were the shear strength, angle of internal friction, and the initial elastic modulus. These

parameters were used because of their common use in many geotechnical design

calculations. The following conclusions and recommendations were made based on the

test results.

6.1 Conclusions

All conclusions made would be applicable only to loose to medium dense, poorly graded

sand soils.

1) From the triaxial testing, the shear strength can be predicted with moderate

accuracy (R2 of 0.73). This relationship is needed to relate shear strength from

PPMT data to initial triaxial modulus.

2) Using both previously developed correlations and correlations developed from

testing, the triaxial initial modulus is on average 60% less than the PPMT initial

modulus, when using PPMT data corresponding to limit pressures less than 200

psi. The triaxial initial modulus can be predicted with more certainty using field

69

PPMT data (R2 of 0.91) than the PPMT initial modulus being predicted by using

triaxial data (R2 of 0.72).

3) The shear strength and limit pressure equation developed by Baguelin (1978) falls

within one standard deviation of the triaxial and shear strength correlation

developed in this study (α=0.001) in the range of 200 psi limit pressure or less.

6.2 Recommendations Although strong correlations were developed from the testing, recommendations are

made to ensure accurate use of the correlations and recommendations for further studies

of this topic.

1) Due to large deviations, greater than one standard deviation, in the correlations

when the soil initial moduli is greater than 2000 psi or the PPMT limit pressure is

greater than 200 psi, as shown in Figure 5-5, it is recommended that these

correlations only be used when soil limit pressure is below 200 psi and the initial

modulus is less 2000 psi. These values correspond with Briaud’s loose to compact

soil, or the USCS loose to medium dense soils.

2) In order to insure accuracy when using these correlations, it is recommended that

the correlations be used with testing in poorly graded sand soil. The consistency

of the soil tested should be classified as loose to medium dense.

70

3) It is recommended for further studies that densities between 65% and 100% of

relative density be used in order to verify that these correlations are accurate

irrespective of the soil density.

71

References

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74

Appendix A

Pressuremeter Data

75

A 1- Overflow lot 101

A 2- Overflow lot 102

0

100

200

300

400

500

600

700

800

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 101

0

100

200

300

400

500

600

700

800

900

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 102

76

A 3- Overflow lot 103

A 4- Overflow lot 104

0

200

400

600

800

1000

1200

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 103

0

100

200

300

400

500

600

700

800

900

1000

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 104

77

A 5- Overflow lot 105

A 6- Overflow lot 106

0

100

200

300

400

500

600

700

800

900

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 105

0

100

200

300

400

500

600

700

800

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 106

78

A 7- Overflow lot 107

A 8- Overflow lot 108

0

100

200

300

400

500

600

700

800

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 107

0

100

200

300

400

500

600

700

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 108

79

A 9- Overflow lot 119

A 10- Overflow lot 120

0

200

400

600

800

1000

1200

1400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 119

0

200

400

600

800

1000

1200

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Overflow lot site 120

80

A 11- Southgate 201

A 12- Southgate 202

0

50

100

150

200

250

300

350

400

450

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 201

0

50

100

150

200

250

300

350

400

450

500

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 202

81

A 13- Southgate 203

A 14- Southgate 204

0

50

100

150

200

250

300

350

400

450

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 203

0

50

100

150

200

250

300

350

400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 204

82

A 15- Southgate 205

A 16- Southgate 206

0

50

100

150

200

250

300

350

400

450

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 205

0

50

100

150

200

250

300

350

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 206

83

A 17- Southgate 207

A 18- Southgate 208

0

50

100

150

200

250

300

350

400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 207

0

50

100

150

200

250

300

350

400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 208

84

A 19- Southgate 209

A 20- Southgate 210

0

50

100

150

200

250

300

350

400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 209

0

50

100

150

200

250

300

350

400

0% 5% 10% 15% 20% 25%

Stre

ss (

kPa)

Strain

Southgate site 210

85

Appendix B

Triaxial Data

86

B 1- Overflow lot center (90 pcf 5psi)

B 2- Overflow lot center (90pcf/10psi)

0

2

4

6

8

10

12

14

16

18

0% 2% 4% 6% 8% 10% 12% 14%

Stre

ss (

psi

)

Strain (in/in)

Overflow lot center (90 pcf/5 psi)

0

5

10

15

20

25

30

0% 2% 4% 6% 8% 10% 12% 14% 16%

Stre

ss (

psi

)

Strain

Overflow lot center (90 pcf/10 psi)

87

B 3- Overflow lot center (90pcf/15psi)

B 4- Overflow lot north (90pcf/5psi)

0

5

10

15

20

25

30

35

40

45

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot center (90 pcf/15 psi)

0

2

4

6

8

10

12

14

16

18

0% 2% 4% 6% 8% 10% 12% 14%

Stre

ss (

psi

)

Strain

Overflow lot north (90pcf/5psi)

88

B 5- Overflow lot north (90pcf/10psi)

B 6- Overflow lot north (90pcf/15psi)

0

5

10

15

20

25

30

35

0% 2% 4% 6% 8% 10% 12% 14%

Stre

ss (

psi

)

Strain

Overflow lot north (90pcf/10psi)

0

5

10

15

20

25

30

35

40

45

0% 2% 4% 6% 8% 10% 12% 14% 16%

Stre

ss (

psi

)

Strain

Overflow lot north (90pcf/15psi)

89

B 7- Overflow lot south (90pcf/5psi)

B 8- Overflow lot south (90pcf/10psi)

0

2

4

6

8

10

12

14

16

18

20

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot south (90pcf/5psi)

0

5

10

15

20

25

30

35

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot south (90pcf/10psi)

90

B 9- Overflow lot south (90pcf/15psi)

B 10- Overflow lot center (100pcf/5psi)

0

10

20

30

40

50

60

70

0% 2% 4% 6% 8% 10% 12% 14% 16%

Stre

ss (

psi

)

Strain

Overflow lot south (90pcf/15psi)

0

2

4

6

8

10

12

14

16

18

20

0% 2% 4% 6% 8% 10% 12% 14% 16%

Stre

ss (

psi

)

Strain

Overflow lot center (100pcf/5psi)

91

B 11- Overflow lot center (100pcf/10psi)

B 12- Overflow lot center (100pcf/15psi)

0

5

10

15

20

25

30

35

40

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot center (100pcf/10psi)

0

5

10

15

20

25

30

35

40

45

50

0% 5% 10% 15% 20% 25%

Stre

ss (

psi

)

Strain

Overflow lot center (100pcf/15psi)

92

B 13- Overflow lot north (100pcf/5psi)

B 14- Overflow lot north (100pcf/10psi)

0

5

10

15

20

25

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot north (100pcf/5psi)

0

5

10

15

20

25

30

35

40

0% 5% 10% 15% 20%

Stre

ss (

psi

)

Strain

Overflow lot north (100pcf/10psi)

93

B 15- Overflow lot north (100pcf/15psi)

B 16- Overflow lot south (100pcf/5psi)

0

5

10

15

20

25

30

35

40

45

50

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot north (100pcf/15psi)

0

2

4

6

8

10

12

14

16

18

20

0% 2% 4% 6% 8% 10% 12% 14% 16% 18%

Stre

ss (

psi

)

Strain

Overflow lot south (100pcf/5psi)

94

B 17- Overflow lot south (100pcf/10psi)

B 18- Overflow lot south (100pcf/15psi)

0

5

10

15

20

25

30

35

0% 5% 10% 15% 20%

Stre

ss (

psi

)

Strain

Overflow lot south (100pcf/10psi)

0

10

20

30

40

50

60

0% 5% 10% 15% 20%

Stre

ss (

psi

)

Strain

Overflow lot south (100pcf/15psi)

95

B 19- Mixed sample (105pcf/3psi)

B 20- Mixed sample (105pcf/3psi)

0

2

4

6

8

10

12

14

16

18

0% 2% 4% 6% 8% 10% 12% 14%

Stre

ss (

psi

)

Strain

Mixed sample (105pcf/3psi)

0

2

4

6

8

10

12

14

16

18

0% 2% 4% 6% 8% 10% 12% 14%

Stre

ss (

psi

)

Strain

Mixed sample (105pcf/3psi)

96

B 21- Mixed sample (105pcf/7psi)

0

5

10

15

20

25

30

35

0% 2% 4% 6% 8% 10% 12% 14% 16%

Stre

ss (

psi

)

Strain

Mixed sample (105pcf/7psi)