A.  FIELD TESTS

Drilling of Soil Investigation

To get the samples of deep soil layers it has to be by using soil drilling machines, the depth of boreholes depending on project specifications or client request. Samples divides into undisturbed samples (Shelby tube samples), distributes samples and water samples. Sampling method (No. of Samples and sampling distances) depend on project specifications or known standard. The standards of drilling are ASTM D1452, D5783 and BS 5930.

CPT (Core Penetration test):

Tests performed using this test method provide a detailed record of cone resistance that is useful for evaluation of site stratigraphy, homogeneity and depth to firm layers, voids or cavities, and other discontinuities. The use of a friction sleeve can provide an estimate of soil classification, and correlations with engineering properties of soils. When properly performed at suitable sites, the test provides a rapid means for determining subsurface conditions.

This test method provides data used for estimating engineering properties of soil intended to help with the design and construction of earthworks, the foundations for structures, and the behavior of soils under static and dynamic loads.

This method tests the soil in-situ and soil samples are not obtained. The interpretation of the results from this test method provides estimates of the types of soil penetrated. Engineers may obtain soil samples from parallel borings for correlation purposes, but prior information or experience may preclude the need for borings. ASTM D5778 , BS EN ISO 22476

Standard Penetration Test (SPT)

This test method provides a disturbed soil sample for moisture content determination and laboratory identification. Sample quality is generally not suitable for advanced laboratory testing for engineering properties. The process of driving the sampler will cause disturbance of the soil and change the engineering properties. Use of the thin wall tube sampler may result in less disturbance in soft soils. Coring techniques may result in less disturbance than SPT sampling for harder soils.

This test method is used extensively in a great variety of geotechnical exploration projects. Many local correlations and widely published correlations which relate blow count, or N-value, and the engineering behavior of earthworks and foundations are available. For evaluating the liquefaction potential of sands during an earthquake event, the N-value should be normalized to a standard overburden stress level. Practice provides methods to obtain a record of normalized resistance of sands to the penetration of a standard sampler driven by a standard energy. The penetration resistance is adjusted to drill rod energy ratio of 60 % by using a hammer system with either an estimated energy delivery or directly measuring drill rod stress wave energy.

This test method describes the procedure, generally known as the Standard Penetration Test (SPT), for driving a split-barrel sampler to obtain a representative soil sample and a measure of the resistance of the soil to penetration of the sampler.

The values stated in inch-pound units are to be regarded as the standard. ASTM D1586 or BS EN ISO 22476

Electrical Resistivity

The resistivity of the surrounding soil environment is a factor in the corrosion of underground structures. High resistivity soils are generally not as corrosive as low resistivity soils. The resistivity of the soil is one of many factors that influence the service life of a buried structure. Soil resistivity may affect the material selection and the location of a structure.

Soil resistivity is of particular importance and interest in the corrosion process because it is basic in the analysis of corrosion problems and the design of corrective measures. ASTM G187

Thermal Conductivity

The thermal conductivity of both intact and reconstituted soil specimens as well as soft rock specimens is used to analyze and design systems used, for example, in underground transmission lines, oil and gas pipelines, radioactive waste disposal, geothermal applications, and solar thermal storage facilities. This test method presents a procedure for determining the thermal conductivity (λ) of soil and soft rock using a transient heat method. This test method is applicable for both intact and reconstituted soil specimens and soft rock specimens. This test method is suitable only for homogeneous materials. This test done according to ASTM D 5334 or BS 874

B.   Laboratory Tests

Moisture Content (M.C. %)

For many materials, the water content is one of the most significant index properties used in establishing a correlation between soil behavior and its index properties.

The water content of a material is used in expressing the phase relationships of air, water, and solids in a given volume of material. The test is done according to ASTM D2216 and BS 812.

Atterberg Limits (L.L, P.L & P.I)

These test methods are used as an integral part of several engineering classification systems to characterize the fine-grained fractions of soils and to specify the fine-grained fraction of construction materials (see Specification D1241). The liquid limit, plastic limit, and plasticity index of soils are also used extensively, either individually or together, with other soil properties to correlate with engineering behavior such as compressibility, hydraulic conductivity (permeability), compatibility, and shear strength.

The liquid and plastic limits of a soil and its water content can be used to express its relative consistency or liquidity index. In addition, the plasticity index and the percentage finer than 2-μm particle size can be used to determine its activity number.

These methods are sometimes used to evaluate the weathering characteristics of clay-shale materials. When subjected to repeated wetting and drying cycles, the liquid limits of these materials tend to increase. The amount of increase is considered to be a measure of shale’s susceptibility to weathering.

The liquid limit of a soil containing substantial amounts of organic matter decreases dramatically when the soil is oven-dried before testing. Comparison of the liquid limit of a sample before and after oven-drying can therefore be used as a qualitative measure of organic matter content of a soil, ASTM D4318 and BS 1377.

Specific Gravity

The specific gravity of soil solids is used in calculating the phase relationships of soils, such as void ratio and degree of saturation.

The specific gravity of soil solids is used to calculate the density of the soil solids. This is done by multiplying its specific gravity by the density of water (at proper temperature). The test is done according to ASTM D854 and BS 1377.

Grading

Gradation of Fine-Grained: Particle-size distribution (gradation) is a descriptive term referring to the proportions by dry mass of a soil distributed over specified particle-size ranges. The gradation curve generated using this method yields the amount of silt and clay size fractions present in the soil based on size definitions, not mineralogy or Atterberg limit data.

The gradation of a soil is an indicator of engineering properties. Hydraulic conductivity, compressibility, and shear strength are related to the gradation of the soil. However, engineering behavior is dependent upon many factors, such as effective stress, mineral type, structure, plasticity, and geological origin.

The size limits of the sedimentation test are from about 100 µm to about 1 µm. The length of time required to obtain a stable initial reading on the hydrometer controls the upper range of results, and the test duration controls the lower range.

The shape and density of the grains are important to the results. Stokes’ Law is assumed to be valid for spherical particles even though fine silt- and clay-sized particles are more likely to be plate-shaped and have greater mineral densities than larger particles. ASTM D7928 or BS 1377.

Triaxial Compression Test

Triaxial tests are one of the most widely performed tests in a geotechnical laboratory. The advantages of the test over other test methods used in the geotechnical laboratory used to determine shear strength (such as direct shear) is that specimen drainage can be controlled and pore pressure can be measured. The triaxial test enables parameters such as cohesion (c’), internal angle of friction (φ’) and shear strength to be determined.

The triaxial test can also be used to determine other variables such as stiffness and permeability with the correct equipment. the standards of this test are ASTM D2850, D4767 , D2166, D7181 (according to test type) or BS 1377.

Direct Shear Test of Soils

This test is performed to determine the consolidated-drained shear strength of a sandy to silty soil. The shear strength is one of the most important engineering properties of a soil, because it is required whenever a structure is dependent on the soil’s shearing resistance. The shear strength is needed for engineering situations such as determining the stability of slopes or cuts, finding the bearing capacity for foundations, and calculating the pressure exerted by a soil on a retaining wall. The standards of this test are ASTM D3080 or BS 1377.

Consolidation Test

The consolidation properties determined from the consolidation test are used to estimate the magnitude and the rate of both primary and secondary consolidation settlement of a structure or an earth fill. Estimates of this type are of key importance in the design of engineered structures and the evaluation of their performance. The standards of this test are ASTM D2435 or BS 1377.

Compaction test

Soil placed as engineering fill (embankments, foundation pads, road bases) is compacted to a dense state to obtain satisfactory engineering properties such as shear strength, compressibility, or permeability. In addition, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and molding water content needed to achieve the required engineering properties by comparing it with maximum dry density (MDD) and optimum moisture content (OMD), and for controlling construction to assure that the required compaction and water contents are achieved. ASTM D1557, D2937 or BS 1733

Sand replacement method

This test method is used to determine the density and water content of compacted soils placed during the construction of earth embankments, road fill and structural backfill. It often is used as a basis of acceptance for soils compacted to a specified density or percentage of a maximum density

Core cutter test

This test method can be used to determine the in-place density of soils which do not contain significant amounts of particles larger than 4.75 mm (³/₁₆ in.), and which can be readily retained in the drive cylinder. This test method may also be used to determine the in-place density of compacted soils used in construction of structural fill, highway embankments, or earth dams. When the in-place density is to be used as a basis for acceptance, the drive cylinder volumes must be as large as practical and not less than 850 cm³ (0.030 ft³ ).

The general principles of this test method have been successfully used to obtain samples of various field compacted fine-grained soils having a maximum particle size of 4.75 mm (³/₁₆ in.) for purposes other than density determinations.