The cone penetration test in unsaturated sands

Abstract

Laboratory-controlled cone penetration test results for an unsaturated sand are presented, obtained using a suction-controlled calibration chamber. The cone penetration resistances are found to increase significantly, owing to the presence of suction, when compared with those for saturated or dry states, for a given relative density and net confining stress. Increases of as much as 50% for a relative density of 0·33 and net confining stress of 50 kPa are recorded. When suction is included in the effective stress, the same semi-empirical expressions used for saturated sands are found to link penetration resistance to the relative density and effective confining stress. The expressions may also be used to back-calculate the suction changes in a soil profile when cone penetration resistances for two unsaturated states are known. It is also shown that failure to account for suction influences may lead to significant and non-conservative overestimations of relative density or peak friction angle.