Depending upon details or precision of sub-soil data to be obtained, site exploration may be classified as general (or preliminary) and detailed.

The cone resistance in kg/cm² is approximately equal to 10 times penetration resistance N from standard penetration test. The Dutch cone test is very useful in cohesion-less soils.

In standard penetration test, thick wall split-tube samplers are used which has an inner diameter of 35 mm or 1.5 inches. The outer diameter of sampler is 50.8 mm.

The inside clearance of sampler should lie between 1 to 3%. The outside clearance of sampler should not be much greater than inside clearance of sampler.

The sampler should never be over driven so as to compress sample. When sampler is over driven, soil sample gets compressed due to air locked between sampler and sample.

Mechanical stabilisation involves two operations: i) changing composition of soil by addition or removal of certain constituents, and ii) densification or compaction.

Terzaghi and Peck have recommended use of equivalent penetration resistance N_e instead of observed penetration values of N, When N is greater than 15.
N_e=15+\(\frac{1}{2}\)(N-15).

On going over site, a study of following features may be useful: local topography, excavations, cuttings, escarpments, flood marks and evidence of erosion.

Exploratory borings, shallow test pits, subsurface penetration, soundings and geophysical methods are used for general exploration.

The disturbed sample of soil has natural structure of soil as modified due to disturbance caused while collecting soil sample. It is usually obtained by pump and shells with trap valve.