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DEMONSTRATION OF DILATOMETER AND PRESSUREMETER TEST EQUIPMENTS

Write a report comprising of: -

1) Types of penetrometers (SPT, DMT, PMT & CPT)2) Basic Working Principle of each of the above devices

a) Data Analysisb) Data Interpretation

3) Applications4) Advantages & Disadvantages

STANDARD PENETROMETER

It is an in-situ dynamic penetrometer designed to provide information on the engineering properties of soil. Standard Penetration Test (SPT) was developed in 1927 & standardized in 1958, the standard used is ASTM D-1586 (www.astm.org/ Standards /D1586.htm ), parameters obtained in the test are SPT ‘N’ Value (No. of blows/ft of penetration)

BASIC WORKING PRINCIPLE, DATA ANALYSIS & DATA INTERPRETATION

In this test there is a sampler tube, with an outside diameter of 50 mm and an inside diameter of 35 mm, and a length of around 650 mm which is driven into the ground at the bottom of a borehole by blows from a slide hammer with a weight of 63.5 kg (140 lb) freely falling through a distance of 760 mm (30 in). The sampler tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is termed the standard penetration resistance or the N-value.

Sometimes when 50 blows are insufficient to advance through a 150 mm (6 in) interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the ground.

APPLICATIONS

This test can be applied to various soil types with fine-grained sands giving the most useful results, with coarser sands and silty sands giving reasonably useful results, and clays and gravelly soils yielding results which may be very poorly representative of the true soil conditions.

Muhammad Arslan (2007 – CIVIL – 123)

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ADVANTAGES & DISADVANTAGES

Advantages:

Quick & simple to perform Equipment & Expertise easily available Can penetrate into dense layers, gravel & fill Provides a representative sample

Disadvantages:

Does not provide continuous data (5ft interval). Limited applicability to cohesive soils, gravels, boulders, cobbles A No. of corrections is to be applied in order to get a standard value.

AKBAR NEWCASTLE DILATOMETER (ANDMT) OR NEWCASTLE DILATOMETER (NDMT)

It is a new dilatometer which uses a rigid piston to load the soil and is used for in-situ soil testing. It has been developed by Dr. Aziz Akbar at New Castle, through modification of Dilatometer Test (MDMT) Developed by Marchietti in 1980 A "Standard Test Method for Performing the Flat Plate Dilatometer" is currently being prepared by ASTM (approved Draft 2001), parameters obtained in the test are ED = Dilatometer Modulus, KD = Lateral Stress Index and ID = Material Index.

BASIC WORKING PRINCIPLE

The NDMT uses displacement and pressure transducers which can record the data throughout the penetration of its piston into the soil. The two transducers together can produce applied pressure-displacement curves for obtaining soil parameters which can be more reliable than those obtained based on just one or two contact pressures values as in the Marchetti dilatometer.

The Newcastle Dilatometer (NDMT) uses a Hall effect transducer and a magnet system to measure the penetration of the piston during loading of the soil. The membrane of the MDMT is replaced with the piston assembly. The use of the wave spring washer between the piston flange and the retaining ring keeps the piston flush with the blade until the piston is pressurized using dry N2 gas and brings the

piston back when depressurized. Two O-rings are incorporated in the NDMT to keep the assembly air and water tight. The applied gas pressure is recorded using a pressure transducer.A magnet has been glued inside a hole at the centre of the piston. An HET has been glued to the blade facing this magnet. This system of a Hall effect transducer (HET) and a magnet is used for measuring the displacement of the piston. When the piston moves by internally pressurizing the blade, the HET produces a change in its output according to the flux intensity. This output is non-linear but non-hysteretic and a second-degree curve fits the data. Access to the connections between the HET and the cable is via steel cover.

Muhammad Arslan (2007 – CIVIL – 123)

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DATA ANALYSIS & DATA INTERPRETATION

The final parameters obtained in this test are ED = Dilatometer Modulus, KD = Lateral Stress Index and ID = Material Index. The yield pressure pE is determined by tracing back the trend of (or tangent to) the initial part of the plastic loading curve to intercept the pressure axis at point E. This pressure corresponds to zero displacement of the piston. Note that pushing the blade into the soil causes the soil to yield, which implies the initial pressure on the piston should be pE. The fact that the initial pressure is less than pE is a result of unloading that occurs as the soil is unloaded as it moves past the shoulder of the blade. The piston is forced to move by at least 1.1 mm to D. The pressure corresponding to point D is p1.1.

The equations used for the calculation of these parameters are: -

ED = 42.8 (p1.1 – pE)

ID = pE– u0σ′v

KD = pE– u0σ′v

Where u0 = in-situ pore water pressure.

KD is a very useful parameter in understanding the stress history (OCR profile) of a deposit. ID is related to the prevailing grain size. ED is a function of the soil stiffness and is based on the loading of a rigid, circular plate on elastic soil.

ADVANTAGES & DISADVATAGES

Advantages:

Settlement prediction has been considered more reliable than any other test DMT can evaluate the OCR & KD of any type of soil.

Horizontal coefficient of consolidation & horizontal permeability can be determined. Can identify active or old slip surfaces in clay slopes using KD profiles of DMT.

Disadvantages:

No Sample is recovered. Blade penetration affects the strength and stiffness. Results of DMT are affected if the blade drifts out from vertical during penetration.

CONE PENETROMETER

Cone Penetration Test (CPT) was developed in Netherlands so also called as Dutch Cone Test (DCT) Standard followed are ASTM D-3441 & ASTM D-5778. Types of cone penetration tests are mechanical CPT, electric CPT, piezo cone, electric piezo/friction seismic cone. It is a field test used to collect data about bearing capacity and resistance of soil. Parameters Obtained Cone End Resistance ‘qc’ Sleeve Resistance ‘qf’ Friction Ratio ‘FR’

Muhammad Arslan (2007 – CIVIL – 123)

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BASIC WORKING PRINCIPLE

It consists of a cone which has an apex angle of 60° and base diameter of 35.7mm equivalent to area of 10 cm2.The cone is connected with sounding rods which are protected by mantle tubes. The assembly of sounding rod and mantle tube is pushed into the soil, by means of a mechanical rack jack or by an engine driven hydraulic pump. The readings are taken for every 20cm of penetration, and thus continuous data of end bearing and frictional resistance of soil is recorded and correlated with bearing capacity of soil. These data can be related to the N-value obtained in SPT and due to this reason the test is used most commonly worldwide.

APPLICATION

The test can be performed on a wide range of soil types.

ADVANDAGES & DISADVANTAGES

Advantages:

The test can be performed on a wide range of soil types. It provides a continuous or near continuous data.

Disadvantages:

The test does not provide any soil samples. It cannot penetrate into very dense soils or soils containing boulders and cobbles.

PRESSURE METER

Pressure Meter Test (PMT) was developed by Maynard in 1956. The standard followed for this test is ASTM D 4719. Types of pressure meters are Maynard Pressure Meter, Self Boring Pressure meter, Screw Plate Pressure meter. The parameters obtained in the test are Po = Lift off pressure, Pf = Yield pressure and PL = Limit pressure.

BASIC WORKING PRINCIPLE

In this test a carefully prepared borehole that is sufficiently – but not over about 10% -- oversized is used. The pressure meter probe consisting of three parts top, cell and bottom is then inserted and expanded to and then into the soil. The top and bottom guard cells are expanded to reduce end-condition effects in the middle (cell) part which is used to obtain the volume versus cell pressure relationship used in data reduction.

ADVANTAGES & DISADVATAGES

Advantages:

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Allows assessment of in-situ horizontal stress. Allows direct measurement of shear stiffness and undrained strength. Well conditioned boundary conditions.

Disadvantages:

Not very cheap. Can only be performed in soils where borehole can be shaped and will stand open until the

probe is inserted. Operators need to be skilled. An appreciable amount of data processing is required.

REFERENCES

Foundation Analysis & Design by Joseph E. Bowles, Fifth edition. Principles of Geotechnical Engineering by Braja M. Das (Google Books) Others.

Muhammad Arslan (2007 – CIVIL – 123)