Critical depth

For non-cohesive soils the skin friction does not increases infinitely with depth as e.g. effective stress, but from a certain so called critical depth it acquires a constant value – see the following figure, where d_c is the critical depth, S_c is the skin friction at critical depth and d is the pile diameter. Similar rule holds also for the pile base resistance in non-cohesive soils, where the same values of the critical depth d_c are considered for simplicity.

Crtitical depth

The reference value of the critical depth for soft sand is 10d (d is the pile diameter or its width), for medium compact sand and compact sand the values are 15d and 20d, respectively.

The coefficient of critical depth k_dc can be specified in the "Ver. capacity". The critical depth follows from: