Laboratory investigation of unsaturated soil-cement grout interfaces

The important parameters on which the shear strength of any interface depends are overburden stress and degree of saturation. Nowadays, grouting pressure is considered as an another important issue as it provides better interface strength than gravity grouting in case of cast-in-situ soil-cement grout interface, like soil-nail and soil-pile interfaces. In the present study, a series of interface direct shear tests are performed between compacted completely decomposed granite (CDG) soil and cement grout under different overburden stresses, matric suctions and grouting pressures. The interface shear strength envelopes are approximately linear, and the apparent interface friction angle and adhesion intercept increase with matric suction for particular grouting pressures. On the contrary, the apparent interface friction angle decreases with pressure grouting for different matric suctions except saturated condition, at which it remains constant. A mathematical model is proposed for predicting the shear strength of soil-cement interface considering the influence of matric suction, overburden stress and grouting pressure as independent parameters. It is obvious that the interface shear strength predicted from the proposed model agrees well with the experimental shear strength data for different overburden stresses, matric suctions and grouting pressures.