In-situ testing methods like the Standard Penetration Test (SPT) are used when it is difficult to obtain undisturbed soil samples. The SPT involves driving a split spoon sampler into the soil using a hammer and measuring the blow count. Corrections are made to the blow count for factors like hammer efficiency, borehole diameter, and overburden pressure. Empirical correlations with soil properties like density, shear strength, and type are then used to inform foundation design.