Geotechnical Lab

Soil & Geotechnical Investigation

Soil&Geotechnical investigations are performed by geotechnical engineers or Civil Engineers to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structures and for repair of distress to earthworks and structures caused by subsurface conditions. Additionally, Geotechnical investigations are also used to measure the thermal resistivity of soils or backfill materials required for underground transmission lines, oil and gas pipelines, radioactive waste disposal, and solar thermal storage facilities. A geotechnical investigation will include surface exploration and subsurface exploration of a site. Sometimes, geophysical methods are used to obtain data about sites. Subsurface exploration usually involves soil sampling and laboratory tests of the soil samples retrieved.

To obtain information about the soil conditions below the surface, some form of subsurface exploration is required. Methods of observing the soils below the surface, obtaining samples, and determining physical properties of the soils and rocks include test pits, trenching, boring, and in situ tests.

Soil Sampling

 Soil samples are often categorized as being either "disturbed" or "undisturbed;" however, "undisturbed" samples are not truly undisturbed. A disturbed sample is one in which the structure of the soil has been changed sufficiently that tests of structural properties of the soil will not berepresentative of in-situ conditions, and only properties of the soil grains (e.g., grain size distribution, Atterberg limits, and possibly the water content) can be accurately determined. An undisturbed sample is one where the condition of the soil in the sample is close enough to the conditions of the soil in-situ to allow tests of structural properties of the soil to be used to approximate the properties of the soil in-situ.

Soil samplers

Soil samples are taken using a variety of samplers; some provide only disturbed samples, while others can provide relatively undisturbed samples.

·                  Shovel. Samples can be obtained by digging out soil from the site. Samples taken this way are disturbed samples.

·                  Hand/Machine Driven Auger. This sampler typically consists of a short cylinder with a cutting edge attached to a rod and handle. The sampler is advanced by a combination of rotation and downward force. Samples taken this way are disturbed samples. Continuous Flight Auger. A method of sampling using an auger as a corkscrew. The auger is screwed into the ground then lifted out. Soil is retained on the blades of the auger and kept for testing. The soil sampled this way is considered disturbed.

Split-spoon / SPT Sampler. Utilized in the 'Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils'

(ASTM D 1586). In-situ tests

·                  A Standard Penetration Test (SPT) 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.

·                  A Standard Penetration Test (SPT) 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.

·                  Dynamic Cone Penetrometer (DCP) is an in situ test in which a weight is manually lifted and dropped on a cone which penetrates the ground.

·                     Dynamic Cone Penetrometer cont. The number of mm per hit are recorded and this is used to estimate certain soil properties. This is a simple test method and usually needs backing up with lab data to get a good correlation.

A Cone Penetration Test (CPT) is performed using an instrumented probe with a conical tip, pushed into the

soil hydraulically at a constant rate. A basic CPT instrument reports tip resistance and shear resistance along the cylindrical barrel. CPT data has been correlated to soil properties.

 Laboratory tests

§     Particle-size analysis 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. The sieve analysis shakes the sample through progressively smaller meshes to determine its gradation. The hydrometer analysis uses the rate of sedimentation to determine particle gradation.

 

§     Atterberg limits The Atterberg limits 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. The results of this test can be used to help predict other engineering properties.

 

 

§     California bearing ratio 

ASTM D 1883. A test to determine the aptitude of a soil or aggregate sample as a road sub-grade. A plunger is pushed into a compacted sample, and its resistance is measured.

 

§     Direct shear test 

ASTM D3080. The direct shear test 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.

§  Triaxial shear tests

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.

 

§    Water content 

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.

 

§    Expansion Index test 

This test uses a remolded soil sample to determine the Expansion Index (EI), an empirical value required by building design codes, at a water content of 50% for expansive soils, like expansive clays.

 

 

§  Soil compaction  

Standard Proctor (ASTM D698), Modified Proctor (ASTM D1557), and California Test 216. These tests are used to determine the maximum unit weight and optimal water content a soil can achieve for a given compaction effort.

 

§  Continuous ConsolidationThis test method covers the determination of the rate and magnitude of consolidation of soil when it is restrained laterally and drained axially and subjected to controlled-strain loading.

 

Consolidation Testing Equipment

 

Electromechanical sieve shake for aggregate

 

 

 

Automatic Sieve Analysis

 

Triaxial Testing Equipment

Shear Testing equipment

Coring Machine

 

Sieve Analysis (hydrometer)

General

To perform the different tests on all building materials: Aggregates, Cement, Concrete, Soil, Rock, asphalt etc., very often, a vast range of General Laboratory Apparatus is required. This range include important equipment as, for example, ovens, balances, measuring instruments, meteorological equipment, vacuum pumps, air compressors, but also laboratory glassware and hardware as graduated cylinders, porcelain, scoops, containers, plastic

ware etc. All single items have been selected to suit the requirement of Standards and laboratory technicians.

Ø  OVENS

Ø  VACUUM PUMPS

Ø  THERMOMETERS