The Method for In-situ Large Scale Shear Test of Saturated Soils and Its Application

Due to inherent uncertainties associated with laboratory testing, such as sampling disturbance and size effect, and the limitation that conventional in-situ large scale shear tests are generally carried out for soil masses of natural water content, soil mass strength parameters determined by back analysis instead of testing are, mostly, used for geotechnical stability analyses and engineering designs. In this study, based on conventional in-situ large scale shear test apparatus, two modes of apparatus, the vertical soaking mode and the lateral soaking mode, were developed to accommodate testing techniques for saturated soil. With the apparatus, seven in-situ large scale shear tests were carried out on saturated loess masses in Heifangtai, Gansu province. The results show that the loess masses could be saturated by both modes. Compared with the lateral soaking technique, vertical soaking often causes more sample disturbance, even failure, although it takes less time to saturate. Compared with parameters from in-situ large scale shear tests of the loess masses with natural water content, cohesion from in-situ large scale shear tests of the saturated loess masses decreased sharply from 44.65 to 17.35 kPa, while internal friction angle decreased marginally from 14.18° to 11.95°. Compared with parameters obtained through consolidated quick direct shear tests on the saturated loess, the increments of cohesion and the internal friction angle from in-situ large scale shear tests of the saturated loess masses were about 4 kPa and 3° respectively. To improve the method, it is necessary to carry out comparative tests in order to improve the uniformity of water distribution and degree of saturation, as well as select more pervious materials.