Shear strength of the soil-rock mixture deposits: applicability of Barton and Kjaernsli shear strength model

Soil-rock mixture (S-RM) deposits are encountered quite often in most of the landslide sites, especially in the lower Shivalik region of the Indian Himalayas. The assessment of shear strength of such deposits is difficult due to complex interaction of rock particles with sand fines matrix. Limited studies are available in the literature which deals with shear strength response of S-RM. As a result, very few approaches are available in the literature that can be applied to assess the shear strength of S-RM. The present study makes an attempt in the direction of solving this problem through an extensive laboratory study. Laboratory tests were performed on samples of soil-rock mixture derived from four origins. The tests involved usual index tests to characterize the S-RM, Point Load Strength Index tests on rock particles to get rock strength and direct shear tests (small (i.e. conventional) and large size) on S-RM samples having different gradations. The results are analysed and existing approaches are evaluated for their applicability to S-RM. The analysis indicates that in general the existing approaches do not adequately capture the shear strength response of S-RM. Conceptually Barton-Kjaernsli approach which was originally suggested for rockfill materials was found to the most promising approach. Modifications have been suggested to Barton-Kjaernsli approach to make it applicable to S-RM.