Cone Penetration Test (CPT)

The Cone Penetration Test pushes an instrumented cone (60° apex, 10 cm² base) into the ground at a steady 20 mm/s while continuously recording cone tip resistance (qc) and sleeve friction (fs); the piezocone (CPTu) also logs pore pressure. IS 4968 Part 3 covers the static cone test. Unlike the SPT it gives a continuous, repeatable profile with no borehole, ideal for soft clays, loose sands and stratified deposits.

The friction ratio (fs/qc) is used to interpret soil type, while qc correlates with bearing capacity, pile capacity, relative density and liquefaction potential. CPT is favoured for pile design and seismic-liquefaction assessment because of its resolution; SPT remains common where samples are needed or for very stiff/gravelly strata that stop the cone.