The long-term stability of a cutting slope in an overconsolidated sensitive clay

Abstract

In the design of two 7 m high road cuttings in an overconsolidated sensitive clay in the Lachute region in Quebec, a slope inclination of 2.5:1 was retained for long-term stability. The minimum anticipated factor of safety against long-term failure was equal to 1.28 and was based on the postpeak strength parameters c′ = 7 kPa and [Formula: see text], which are typical of the Champlain Sea clays. Following a series of failures in the southern slope of one of the cuttings, only 1.5 years after their construction, a postslide analysis was performed using the critical stress curve method. The results of the analysis yielded the shear strength parameters [Formula: see text]and [Formula: see text]. It is believed that the surprisingly small cohesion intercept at the time of failure found in this study is due to the fissured nature of the clay, the spreading of the discontinuities caused by stress relief following excavation, and subsequent desiccation of the exposed clay mass.