Standard Penetration Test in Geotechnical Engineering Site Investigations

Site investigation is essential prior to all construction activities of engineering structures for determining the suitability of the site for the construction of the proposed structure. The results from the site investigation gives us the information about the soil profile and the ground water table condition at the site. Various in-situ tests are carried out like Standard Penetration Test (SPT), Electrical Resistivity Technique (ERT), Vane Shear Test (VST), Plate Load Test (PLT), Pile Load Test, Flat Plate Dilatometer Test, Packer Test, Cone Penetration Test (CPT) and many others during the site exploration. The data and results obtained from these tests are essential in identifying the soil type, analyzing and the strength and deformation properties and parameters of soil as well as the ground water condition of the site. This paper intends to summarize the processes and various corrections that are involved in Standard Penetration Test (SPT) and its importance and implication in geotechnical analysis and site exploration. The tools and equipment in this test involved are cable percussion drilling rig, soil sampler (especially split spoon sampler), spirit level, boring machine and a hammer with few other miscellaneous. The soil sampler is pushed or penetrated into the ground by hammer of 63.5kg making it fall freely from a standard height of 750mm. The collected disturbed and undisturbed soil samples, hammer blows and energy are analyzed and interpreted to determine or more specifically to estimate the shear strength of soil, relative density and bearing strength of the soil at different depths. This test also helps in determining the aspects of soil which later can be improved by soil stabilizing or by any one or combination of various ground improvement techniques. In accordance of these interpretations, analysis and estimates, suitable foundation design and further construction work for the proposed structure are recommended.