Geotechnical investigation

Group Members:Names:GROUP LEADERABDUL MUTAKABER Umair Shams Muhammad Umar Ramzan Judge Muhammad Irfan Asadullah Shahid Ali Farooq Akram Mohsin Ali Zeeshan Zain ul Hassan Rana Shah Zaman Hafiz Mateen Arif Muhammad Noman Muhammad Junaid Muhammad Tariq Waqas Ali

Registration Nos:

BSCT01133006 BSCT01133002 BSCT01133009 BSCT01133015 BSCT01133018 BSCT01133028 BSCT01133033 BSCT01133034 BSCT01133039 BSCT01133079 BSCT01133158 BSCT01133200 BSCT01133235 BSCT01133220 BSCT01133222 BSCT01133116 BSCT01133074

PRESENTATION

TOPIC:

GEOTECHNICAL INVESTIGATION

(SOIL EXPLORATION)

CONTENT OF PRESENTATION1. Introduction

2. Purpose and objectives of soil exploration

3. Investigation phases

I. Phase I.

II. Phase II.

III. Phase III.

IV. Phase IV.

4. Exploration methods

I. Direct Methods.

II. Indirect Methods.

Geotechnical investigation

CONTENT OF PRESENTATION(Cont………)5. Soil sampling

I. Disturbed Soil Sample.

II. Undisturbed Soil Sample.

6. Amount of exploration

7. In-situ Tests

8. Planning an investigation

9. Records and Reports

I. Bore Hole/Test Pit Logs

II. Data Sheets Of In-situ Tests

10. Conclusion Geotechnical investigation

1. INTRODUCTION Two very essential requirements for design and

construction of any civil engineering facility:

I. SOIL INVESTIGATION

• Also called site investigation.

• Provides data regarding subsoil conditions(i.e.

underground conditions), ground water position and

its fluctuations.

II. TOPOGRAPHIC SURVEY

• Furnishes information regarding ground surface

features of the site (i.e. surface conditions of the site).Geotechnical investigation

1. INTRODUCTION(Cont…….)

i. Soil Exploration Is Needed For:

• Planning, designing and constructing new facilities,

• Investigating the causes of distress or failure and

developing remedial measures,

• Assessing quality and quantity of construction

materials.(i.e. aggregates for concrete/asphalt mix

etc)


2. PURPOSE AND OBJECTIVES

• To determine the stratigraphy of the site

Primary Objectives:

• To assess sequence and thickness of strata.

• To assess quality of bedrock and depth of overburden

soil.

• To determine position of GWT.

• To evaluate the characteristics of subsoil, rock, and

GWT(ground water table).Geotechnical investigation

3. INVESTIGATION PHASES

In general can have Four Phases, as given below:

I. Feasibility or reconnaissance

II. Preliminary exploration pre-

construction

III. Detailed exploration phases

IV. Construction/post construction stage exploration

• For small projects, all pre-construction phases are

combined into a single exploration operation and phase-4

may not be operated at all.Geotechnical investigation

3. INVESTIGATION PHASES(Cont…..)

phase-II. Feasibility or Reconnaissance:

Generally following information is collected in this

phase:

• Project details(type of structure to be constructed,

structural loads, intended use of the structure )

• Surface and sub-surface conditions of the site

(obtained through study of geological maps, aerial

photographs, etc)

• Study of existing structures in the area.(behavior of

existing structure adjacent to the site)Geotechnical investigation

3. INVESTIGATION PHASES(Cont…..)

phase II

II. Preliminary exploration:

During this phase

• Bedrock or hardpan is established

• Disturbed soil samples are recovered

• Position of GWT may also be established


3. INVESTIGATION PHASES(Cont……..)

phase III

III. Detailed exploration:

This phase may include:

• Test pits excavation, boreholes, in-situ testing

• Collection of both disturbed and undisturbed

samples for detailed laboratory testing

• GWT may also be monitored by installing

piezometers.


3. INVESTIGATION PHASES(Cont………)

phase IV

IV. Construction/post construction stage

exploration:

• Additional exploration may be required during

construction stage to cope with the unexpected

subsoil conditions.

• Monitoring of the movement of structure,

• Monitoring of groundwater fluctuations, both

during and after construction, may be required.Geotechnical investigation

4. EXPLORATION METHODS

I. Indirect methods• Establish boundaries

between strata of different composition,

• Determine the quality by detecting changes in the electrical resistivity or wave velocity in the soil.

II. Direct methods• Soil samples are taken

from the soil/rock strata by making actual excavations through probing, borings, test pits etc.

• Subsoil/GWT characteristics are determined by field /laboratory test performed on sample recovered. The indirect methods do not provide direct information

regarding the characteristics of subsoil/rock and must be used in conjunction with direct methods.


I. INDIRECT METHODS

• Also termed as GEO-PHYSICAL METHODS

• Used when soil exploration is to be carried out over

large area and where speed is of prime importance.

• These soil exploration methods are based on principle

that physical properties (like electrical conductivity,

elasticity or seismicity, magnetic susceptibility,

density etc) vary for different types of soils.


I. METHODS USED IN INDIRECT METHODS(Cont…….)

• Seismic refraction method.

• Electrical resistivity method.

• Magnetic measurements method.

• Gravitational measurements method.

• NOTE:

Here we will discuss only those methods which are

being widely used.


Widely used methods


i. Seismic refraction method.

• This soil exploration method is based on the principle

that sound waves travel faster in rock than in soil.

• shock waves (or sound waves of vibration) are created

into the soil at ground level or at a certain depth below

it, either by striking a plate on the soil with the

hammer or by exploding small charge in the soil.

• The shock waves so produced travel down in the sub-

soil strata and get refracted after striking a hard rock

surface below.Geotechnical investigation


i. Seismic refraction method.(Cont…….)

• The refracted or radiated shock waves are picked

up by the vibration detector (also known as

geophone) where the time of travel of the shock

waves gets recorded.

• Knowing the time of travel of the primary and

refracted waves at various geophones, tune and

distance graphs are drawn based on which it is

possible to evaluate the depth of various strata in

the sub-soil. Geotechnical investigation

Fig. Seismic refraction method.



ii. Electrical resistivity method• This soil exploration method is based on the

principle that each soil has different electrical resistivity, depending upon the type of soil, its water content, compaction and composition

• 4 electrodes are driven in the ground at equal distance apart and in a straight line.

• A current is passed between the two outer electrodes and the potential drop between the inner electrodes is measured by use of potentiometer.

• Thus on knowing the values of change in resistivity of sub soil strata at site, it is possible to establish the nature and distribution of different type of soils in the formation.Geotechnical investigation

Fig. Electrical resistivity method


II. Direct Methods• A more detailed description of underground

conditions at specific locations are revealed with direct investigation methods which obtain information by physically sampling or testing soil, rock and groundwater.

• The sampling or testing devices are inserted into a borehole advanced into the ground by drilling methods, and either samples are returned to the surface for evaluation and testing, or the properties of the underground profile are measured by in-place testing

i. Methods used in DIRECT METHODSa. Tests pits, trenches, shafts, tunnelsb. Probing or soundingc. Test boreholes


i. METHODS USED IN DIRECT MTHODS

a. Test pits, Trenches, Shafts, Tunnels:

• Also termed as open excavations.

• The most satisfactory method of inspecting soil

stratification through visual observations and

recovering both disturbed and undisturbed

samples.

• Excavations may be made by hand by using

manual labor or by using earth moving equipments

(i.e. backhoe, trencher or dozer)Geotechnical investigation

i. METHODS USED IN DIRECT MTHODS(Cont………)

MERITS

• Visual inspection of stratification.

• Suitable for best quality disturbed and undisturbed sampling.

• Difficulties of excavating can be assessed.

DEMERITS

• Limited to a depth of about 3 m as the cost beyond limit increase rapidly.

• Suitable for exploration only above GWT.

• Limited to shallow exploration only.


a. Test pits, Trenches, Shafts,

Tunnels(Cont……...)


b. Probing or sounding

• Probing or sounding is made by driving a steel rod

about 25 mm diameter into the ground.

• The soil type and its properties are related to the

driving resistance to the rod and from particles

adhering to the rod when it is pulled out.

• Sometime some small grooves are made along the

rod to collect some traces of soils through which it

passes during probing.Geotechnical investigation


MERITS

• Suitable to locate the thickness of loose overburden soil.

• Rapid method and relative cost is very low.

• Very cheap and rapid method of exploration.

DEMERITS

• A boulder may be mistaken for bedrock.

• Method is of limited use as soil sample for identification are not recovered.

• Suitable for depth about 10 to 20 m.


b. Probing or sounding(Cont………)


C. Test Boreholes:

Boreholes in soil/rock may be drilled using:

Auger Boring,

Percussion rig,

Wash boring rig and

Rotary drilling rig. Auger Boring:

• Hand augers are used only for boring above GWT to a

maximum depth of about 10m.

• The range of diameter of holes is from 50mm(2inch) to

about 300mm(12 inch) drilled by different augers.Geotechnical investigation


Auger Boring(Cont………)

• Fast and economical, using simple, light,

instruments for large to small holes.

• Soil removed by this is disturbed but it is better

than wash boring, percussion or rotary drilling.

• It is not suitable for very hard or cemented soils,

very soft soils.Geotechnical investigation


Fig. Augers



Percussion rig:

• In case of hard soils or soft rock, auger boring or wash

boring cannot be employed. For such strata, percussion

drilling is usually adopted.

• Here advancement of hole is done by alternatively lifting

and dropping a heavy drilling bit which is attached to

the lower end of the drilling bit which is attached to the

cable.Geotechnical investigation


Fig. Percussion Drilling


Lifting, dropping, cutting by drilling bit.


Wash boring rig:

• It is a popular method due to the use of limited

equipments.

• Here first an open hole is formed on the ground so

that the soil sampling or rock drilling operation can

be done below the hole.

• The hole is advanced by chopping and twisting

action of the light bit.

• Cutting is done by forced water and water jet under

pressure through the rods operated inside the hole.Geotechnical investigation


Fig. Wash Boring



Rotary drilling rig:

• Rotary drilling method of boring is useful in case of

highly resistant strata.

• It can conveniently be used in sands and silts also.

• Here, the bore holes are advanced in depth by

rotary percussion method which is similar to wash

boring technique.Geotechnical investigation


Fig. Rotary Drilling System


5. SOIL SAMPLING

• A sample is said to be a representative sample when it

truly represents the characteristics of the stratum

from which it is recovered.

In geotechnical engineering, generally following types

of samples are retrieved.

I. Disturbed Soil Samples (DS).

II. Undisturbed Soil Samples (UDS).


5. SOIL SAMPLING(Cont………)I. Disturbed Soil Samples:

• In disturbed soil samples the natural structures of

soils gets partly or fully modified or destroyed,

• Although with suitable precaution the natural water

content may be preserved.

• Disturbed sample can be obtained by direct

excavations by augers.

II. Undisturbed Soil Samples:

• In undisturbed soil samples the natural structure and

properties remain preserved.

• These samples are used to tests for shear,

consolidation and permeability.Geotechnical investigation

5. SOIL SAMPLING(Cont………) Causes Of Sample Disturbance:

• Volume disturbance.

• Side friction between the sampler and the soil.

• Moisture content changes.

• Loss of hydraulic pressure.

• Working environment.

• Improper shearing of the sample.

• Failure to shut-off the drilling fluid during sampling

operation.


6. AMOUNT OF EXPLORATION

• By amount of exploration is meant to decide about

the extent of investigation i.e. to determine the

number, location, and depth of open excavation and

boring soundings.

i. The extent of exploration depends upon:

• Site conditions

• Nature and extent of the project.

• Availability of time, funds, equipment for exploration Geotechnical investigation

7. IN-SITU TESTS

Following are the different tests performed in soil

exploration:

• Standard Penetration Test (SPT).

• Static Cone Penetration Test (CPT).

• Field Vane Shear Test (FVT).

• Plate Load Test (PLT).

• Pressure meter Test (PMT).

• Dilatometer (DMT).Geotechnical investigation

8. PLANING AN INVESTIGATION

The aim of planning an investigation programmed is to

gather adequate data regarding surface and

subsurface conditions of the site necessary for the

design and construction of the new facilities for

evaluating the causes of distress and developing

remedies for the existing facilities.

i. Investigation program must include;

a. Amount and extent of exploration:

Spells out number of boring and test pits


8. PLANING AN INVESTIGATION(Cont............)b. Method of exploration:

Based on the information gathered from a critical review of the background data of the site. It may be split into following phase:

• Feasibility or reconnaissance• Preliminary exploration• Detailed exploration• Construction/post construction stage exploration

c. Sampling method:Types of method should be specified in the

program. the program should also specify the labeling, packing, transporting procedures etc, of the samples from the site to the laboratory.


8. PLANING AN INVESTIGATION(Cont……..)d. Laboratory testing program:

should include the number and types of tests required for the investigation.

e. In-situ tests:

should specify the number and types of in-situ tests needed for collecting information essential for the adequate design of the works.

f. Recording of Field Data and Preparation of the Geotechnical Report

It should specify the procedure of recording field data and should include specimen boring logs or data recording sheets.

g. Time and cost of exploration

It should make estimates for the time and cost of investigation. it must include the bill of quantities of the investigation.(BOQ)


9. RECORDS AND REPORTSI. Borehole/Test Pits Logs:

• should be prepared in the field providing all necessary information about the site.

II. Data Sheets of In-situ Tests:A geotechnical report should include:

• Introduction• Brief project description• Purpose and scope• Techniques and geophysical survey record• Boring logs and in-situ and laboratory test result• Comments , Conclusion , and Recommendation


10. CONCLUSION OF PRESENTAION

• For any construction the soil that it’s built on is of

great importance.

• If the foundation is not set on solid ground it can have

disastrous impact on the building.

• Necessary for the design and construction of the new

facilities for evaluating the causes of distress and

developing remedies for the existing facilities.


Technology

Geotechnical investigation