Sampling Techniques

Sampling refers to the process of collecting representative specimens of soil from a site or location for laboratory testing, analysis, or other purposes. The sampling procedure is crucial as it directly affects the accuracy and reliability of subsequent soil testing and analysis. Soil samples collected are generally disturbed and undisturbed which depends on the availability of soil type, site conditions, soil conditions and availability of method.

a. Sampling of Undisturbed Samples

Sampling undisturbed soil samples involves collecting intact specimens of soil that closely resemble their in-situ condition without significant disturbance or alteration. Undisturbed soil samples are particularly important for geotechnical investigations, as they provide valuable information about the soil’s natural state, strength, and compressibility characteristics. 

b. Sampling of Disturbed Samples

Sampling of disturbed soil samples involves collecting soil specimens that may undergo some degree of alteration or disturbance during the sampling process. Disturbed samples are often obtained for various laboratory tests and analysis where the focus is on the soil’s physical and mechanical properties rather than preserving its natural state. Disturbed soil samples may not accurately represent the natural state and behavior of the soil. However, they are still valuable for various geotechnical testing and analysis, such as particle size distribution, compaction, and shear strength tests.

c. SPT

SPT, which stands for Standard Penetration Test, is a widely used in-situ geotechnical test to determine the subsurface soil properties. It provides valuable information about the soil’s resistance to penetration and can be used to estimate soil strength, relative density, and stratification. The N-value is a measure of the soil’s resistance to penetration and is widely used to classify soil types and estimate soil properties. It is relatively simple and cost-effective test and the N-values obtained from SPT tests can be used for preliminary design calculations. However, its efficiency highly depends on operator’s skill, equipment condition and soil conditions and hence, it may involve variability.