SOIL SAMPLING IN SOIL SAMPLING IN GEOTECHNICAL GEOTECHNICAL

ENGINEERINGENGINEERING

ByBy

Sana Jehan AnsariSana Jehan Ansari

IntroductionIntroduction

Soil Sampling is performed Soil Sampling is performed by geotechnical engineers to by geotechnical engineers to obtain information on the obtain information on the physical properties of soil physical properties of soil and rock around a site to:and rock around a site to:

1) design foundation for 1) design foundation for proposed structures proposed structures

2) for repair of distress to 2) for repair of distress to earthworks and structures earthworks and structures caused by subsurface caused by subsurface conditions conditions

What is Soil Sampling?What is Soil Sampling? Soil Sampling is also known as Geotechnical Soil Sampling is also known as Geotechnical

Investigation.Investigation. A geotechnical investigation will include surface A geotechnical investigation will include surface

exploration and subsurface exploration of a site. exploration and subsurface exploration of a site. To obtain information about the soil conditions below To obtain information about the soil conditions below

the surface, some form of subsurface exploration is the surface, some form of subsurface exploration is required.required.

Methods of observing the soils below the surface, Methods of observing the soils below the surface, obtaining samples, and determining physical obtaining samples, and determining physical properties of the soils and rocks include, trenching properties of the soils and rocks include, trenching (particularly for locating faults and slide planes), (particularly for locating faults and slide planes), boring, and in situ tests. boring, and in situ tests.

Disturbed SamplesDisturbed Samples A disturbed sample is one in A disturbed sample is one in

which the structure of the which the structure of the soil has been changed soil has been changed sufficiently that tests of sufficiently that tests of structural properties of the structural properties of the soil will not be soil will not be representative of in-situ representative of in-situ conditions, and only conditions, and only properties of the soil grains properties of the soil grains (e.g., grain size distribution, (e.g., grain size distribution, Atterburg’s Limits, and Atterburg’s Limits, and possibly the water content) possibly the water content) can be accurately can be accurately determined. determined.

Undisturbed SampleUndisturbed Sample

““Undisturbed" samples are Undisturbed" samples are not truly undisturbed.not truly undisturbed.

An undisturbed sample is An undisturbed sample is one where the condition of one where the condition of the soil in the sample is the soil in the sample is close enough to the close enough to the conditions of the soil in-situ, conditions of the soil in-situ, so that tests of structural so that tests of structural properties of the soil can be properties of the soil can be approximated. approximated.

Soil BoringSoil Boring

BoringBoring

Used for subsurface exploration of site.Used for subsurface exploration of site. Come in two main varieties, large-diameter and small-Come in two main varieties, large-diameter and small-

diameter.diameter. Large-diameter borings are rarely used due to safety concerns Large-diameter borings are rarely used due to safety concerns

and expense, but are sometimes used to allow a geologist or and expense, but are sometimes used to allow a geologist or engineer to visually and manually examine the soil and rock engineer to visually and manually examine the soil and rock in-situin-situ..

Small-diameter borings are frequently used to allow a Small-diameter borings are frequently used to allow a geologist or engineer examine soil or rock cuttings or to geologist or engineer examine soil or rock cuttings or to retrieve samples at depth using retrieve samples at depth using soil samplers, and to perform , and to perform in-place soil tests in-place soil tests

Types of BoringTypes of Boring

1) 1) Hand/Machine Driven Hand/Machine Driven Auger. Auger.

This sampler typically This sampler typically consists of a short cylinder consists of a short cylinder with a cutting edge attached with a cutting edge attached to a rod and handle. The to a rod and handle. The sampler is advanced by a sampler is advanced by a combination of rotataion combination of rotataion and downward force. and downward force. Samples taken this way are Samples taken this way are disturbed samples. disturbed samples.

Types of BoringTypes of Boring

2) 2) Continuous Flight Continuous Flight AugerAuger

A method of sampling using A method of sampling using an auger as a corkscrew. an auger as a corkscrew. The auger is screwed into The auger is screwed into the ground then lifted out. the ground then lifted out. Soil is retained on the Soil is retained on the blades of the auger and kept blades of the auger and kept for testing. The soil sampled for testing. The soil sampled this way is considered this way is considered disturbed. disturbed.

In-situ TestsIn-situ Tests

Standard Penetration TestStandard Penetration Test A standard penetration test A standard penetration test

(SPT)(SPT) is an in-situ dynamic is an in-situ dynamic penetration test designed to penetration test designed to provide information on the provide information on the properties of soil, while also properties of soil, while also collecting a disturbed soil collecting a disturbed soil sample for grain-size sample for grain-size analysis and soil analysis and soil classification.classification.

In-situ TestsIn-situ Tests CCone Penetration Test A CPT is performed using A CPT is performed using

an instrumented probe with an instrumented probe with a conical tip, pushed into the a conical tip, pushed into the soil hydraulically at a soil hydraulically at a constant rate. A basic CPT constant rate. A basic CPT instrument reports tip instrument reports tip resistance and shear resistance and shear resistance along the resistance along the cylindrical barrel. CPT data cylindrical barrel. CPT data has been correlated to soil has been correlated to soil properties. properties.

Laboratory TestsLaboratory Tests

A wide variety of laboratory tests can be A wide variety of laboratory tests can be performed on soils to measure a wide variety performed on soils to measure a wide variety of soil properties.of soil properties.

Some soil tests measure direct properties of Some soil tests measure direct properties of the soil, while others measure "index the soil, while others measure "index properties" which provide useful information properties" which provide useful information about the soil without directly measuring the about the soil without directly measuring the property desired.property desired.

Laboratory TestsLaboratory Tests Some of the lab tests are as follows:Some of the lab tests are as follows:

1. Atterberg limits   The Atterberg limits define the boundaries of several The Atterberg limits define the boundaries of several

states of consistency for plastic soils. The boundaries are states of consistency for plastic soils. The boundaries are defined by the amount of water a soil needs to be at one defined by the amount of water a soil needs to be at one of those boundaries. The boundaries are called the plastic of those boundaries. The boundaries are called the plastic limit and the liquid limit, and the difference between limit and the liquid limit, and the difference between them is called the plasticity index. The shrinkage limit is them is called the plasticity index. The shrinkage limit is also a part of the Atterberg limits. The results of this test also a part of the Atterberg limits. The results of this test can be used to help predict other engineering properties.can be used to help predict other engineering properties.

Laboratory TestsLaboratory Tests

2. 2. Direct Shear TestDirect Shear Test The direct shear test determines the The direct shear test determines the

consolidated, drained strength properties of a consolidated, drained strength properties of a sample. A constant strain rate is applied to a sample. A constant strain rate is applied to a single shear plane under a normal load, and single shear plane under a normal load, and the load response is measured. If this test is the load response is measured. If this test is performed with different normal loads, the performed with different normal loads, the common shear strength parameters can be common shear strength parameters can be determined determined

Laboratory TestsLaboratory Tests

3. 3. Water ContentWater Content This test provides the This test provides the

water content of the water content of the soil, soil, normally normally expressed as a expressed as a percentage of the percentage of the weight of water to the weight of water to the dry weight of the soil.dry weight of the soil.

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