Geological And Geophysical Investigations

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are performed by geotechnical engineers or engineering geologists to obtain information on the physical properties of soil and rock around a site to design earthworks and foundation for proposed structures and for repair of distress to earthworks and structures caused by subsurface conditions

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Geotechnical Investigations

Hint 1

will include surface exploration and subsurface exploration of a site.

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is tasked with discovering the current soil status and subsurface conditions

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Site Investigations

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will be conducted during a geotechnical investigation and soil samples will be taken and studied to determine the feasibility of building on a site

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Surface-level and subsurface field tests

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Purpose of Geotechnical Investigations

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To provide information for:

Design and Construction

Environmental Assessment

Project Due Diligence

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Phases of Geotechnical Investigation

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1. Desk Study

2. Preliminary reconnaissance or a site visit

3. Detailed soils exploration

4. Laboratory Testing

5. Write a Report

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To determine the suitability of the site and the environment for the proposed work.

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Sustainability

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To enable an adequate and economic design including temporary works design which can be provided

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Design

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To plan the best construction method depending on the sources of materials/waste.

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Construction Method

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To determine the changes that will occur in the soil and surrounding circumstances, either naturally or because of work.

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Effect of Changes

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When there is a site option, to provide advice and guidance.

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Site Selection

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Components of Geotechnical Investigations

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Sustainability

Design

Construction Method

Effect of Changes

Site Selection

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Technical Objective of the Investigation

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1. Determine the sequence, thickness, lateral extent of the soil strata, and where appropriate the level of bedrock

2. Obtain representative samples of the soils for identification and classification

3. Identify the groundwater conditions

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is a term used for all in-situ based methods and techniques used to determine different properties of soils qualitatively and quantitatively

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Field Testing

Hint 13

measure the properties of the subsurface soil directly without removal

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are nondestructive techniques used to provide spatial information on soils, rocks, and hydrological and environmental conditions.

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Geophysical Explorations

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Popukar Methods of Geophysical Explorations

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1. Ground Penetrating Radar (GPR)

2. Seismic Surveys

3. Electrical Resistivity

4. Others geophysical methods such as Gamma Density,

Neutron Porosity,

Sonic-VDL,

Microgravity

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includes penetrometer test with or without geophysical methods.

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Subsurface Sounding Explorations

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

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Standard Penetration Test

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Standard Penetration Test

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ASTM D1586

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A hardened metal drive shoe with a 1.375" opening is attached to the bottom end, and a one-way valve and drill rod adapter at the sampler head.

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Split-Spoon Sampler

(or Split-Barrel Sampler)

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This sampler is typically an 18"-30" long, 2.0" outside diameter hollow tube split in half lengthwise

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Similar in concept to the SPT sampler, the sampler barrel has a larger diameter and is usually lined with metal tubes to contain samples.

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Modified California Sampler

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Samples from the said sampler are considered disturbed due to the large area ratio of the sampler (sampler wall area/sample cross sectional area).

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Used in the collection of intact and mostly undisturbed samples of fine grain soils, like clay or silts (ASTM D1587M -15)

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Shelby Tube Sampler

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This sampler consists of a thin - walled tube with a cutting edge at the the toe

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These samplers are thin -walled metal tubes which contain a piston at the tip. The samplers are pushed into the bottom of a borehole, with the piston remaining at the surface of the soil while the tube slides past it.

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Piston Samplers

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These samplers will return undisturbed samples in soft soils, but are difficult to advance in sands and stiff clays, and can be damaged (compromising the sample) if gravel is encountered.

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this test is performed using an instrumented probe with a conical tip, pushed into the soil hydraulically at a constant rate.

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Cone penetration test (CPT)

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Instruments other than basic CPTu probe

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1. CPTu - Piezocone Penetrometer

2. SCPTu - Seismic Piezocone Penetrometer

3. Full Flow Penetrometers - T-bar, Ball, and Plate

4. Flat Plate Dilatometer Test (DMT)

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A pit is dug by hand using shovels or with a machine such as a backhoe. This method can provide excellent shallow-depth soil stratigraphy.

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Open Trial Pits

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Excavating test pits for a large depth requires more labor, cost and area which is either not feasible or uneconomical. Boring is preferred if depth of investigation is more than 2 or 3 m.

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Exploration boring

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The different types of borings methods are

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auger boring,

wash boring,

rotary drilling and

percussion boring

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carried out in soil which can stay without casing support or drilling mud. This method is not suitable for sandy or silty soil below water table.

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Auger Boring

Hint 28

1. It is pushed in the soil and rotated so that soil sample fills up in annular space.

2. Withdraw the auger and clean it

3. Add extension rod if requires and repeat step 1 and 2.

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water is flushed under pressure through an inner tube which may be rotated and moved upward and downward inside a casing pipe

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Wash Boring

Hint 29

The samples collected with this method may not be useful for laboratory testing

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This method consists of breaking up of the formation by repeated blows from a bit or chisel. Water is added at the time of boring and debris baled out at intervals.

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Percussion Boring

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This is the best method for rapid drilling of bore holes in gravelly strata.

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boring is affected by the cutting action of a rotating bit which should be kept in firm contact with the bottom of the hole.

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Rotary boring

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Another common field test is checking relative density of the soil. This is done with a sand cone, nuclear densitometer, or balloon method.

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Field Density Test

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A cone penetrometer or dynamic cone penetrometer is frequently used in fine grain soils.

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This is done to visually and manually examine soil samples with respect to texture, plasticity, and color

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Visual Classification Test

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

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Water Content Determination

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This test is used to determine the total/moist and dry densities or unit weights of soil specimen.

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Unit Weight Determination

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define the boundaries of several states of consistency for plastic soils. The boundaries are defined by the amount of water a soil needs to be at one of those boundaries. The boundaries are called the plastic limit and the liquid limit, and the difference between them is called the plasticity index. The shrinkage limit is also a part of the Atterberg limits.

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Atterberg Limits Tests

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This is done to determine the soil gradation. Coarser particles are separated in the sieve analysis portion, and the finer particles are analyzed with a hydrometer. The distinction between coarse and fine particles is usually made at 75 μm..

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Particle-Size Distribution

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This test determines the specific gravity of soil solids passing the 4.75-mm sieve (No. 4) by means of a water pycnometer.

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Specific Gravity Test

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includes Standard Proctor, Modified Proctor, and California Test. These tests are used to determine the maximum unit weight and optimal water content a soil can achieve for a given compaction effort.

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Soul Compaction Test

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is a test to determine the aptitude of a soil or aggregate sample as a road subgrade. A plunger is pushed into a compacted sample, and its resistance is measured. This test was developed by Caltrans, but it is no longer used in the Caltrans pavement design method. It is still used as a cheap method to estimate the resilient modulus.

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California Bearing Radio (CBR Test)

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

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Direct Shear Test

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This can be used to determine consolidation and swelling parameters.

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Oedometer Test

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This is a type of test that is used to determine the shear strength properties of a soil. It can simulate the confining pressure a soil would see deep into the ground. It can also simulate drained and undrained conditions

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Triaxial Shear Tests

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They include the constant head, falling head, and constant flow methods. The soil samples tested can be any type include remolded, undisturbed, and compacted samples.

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Hydraulic Conductivity Tests