K determination using improved experimental technique Available to Purchase

Lateral soil pressures under at-rest conditions are commonly estimated as K₀ times vertical normal pressure, where K₀ is obtained from generally accepted empirical formulae, related to the soil's friction angle and the stress history. Results of a programme of laterally, rigidly confined, vertical compression and unloading tests on sand and clay are presented, in which two significant experimental techniques were employed: (a) lateral pressures were measured using null pressure gauges, preventing gauge diaphragm deflection; (b) side-wall friction was measured, and minimised using special friction reduction measures. Comparative tests in which one or both of these measures were not employed indicate the significant errors induced in both the vertical and the horizontal pressures used for K₀ determination. The bank of experimental data, which formed the basis for the commonly accepted empirical formulae, did not take account of these issues, and they are shown to be inconsistent with values measured in the present study.