Failure of cemented soil under decreasing effective stress

In case of cut slope made in cemented soil or stiff clay, failure is to be expected due to the detachment of bonds (brittle fracture). This field scenario could be simulated by performing triaxial extension test on these types of soils under low effective stress state. This paper presents the results of a series of triaxial compression and extension tests performed on artificially prepared cemented soil and remolded clay in the low stress range. Testing revealed that the mode of failure for cemented soil is different in compression (shear failure) and extension (brittle failure). For cemented soil, shear resistance in extension is found to be less dependent on the normal stress and the resistance is mostly due to the cementation bonds. But in remolded clay, shear resistance is found to be proportional to the effective normal stress at failure. Therefore the use of shear parameters based on compression tests may not be apposite for the stability analysis of cut slopes made in cemented soil. In such cases, failure criteria may be better taken as the difference in principal stresses.