Failure of a rock slope 16.5 years after excavation in repeated strata of sandstone and mudstone

The present study focuses on failure of a rock slope excavated in the autumn of 1997 and located in the repeated strata of sandstone and mudstone in Chongqing of China. The rock slope failed suddenly on April 28, 2014. The elapsed time from excavation to failure is about 16.5 years. The failure was sudden and unexpected seemingly, but it was mainly resulted from the initial excavation and the subsequent weathering in the long term. The initial excavation in 1997 as a reason why the rock cut slope failed was undoubted, because the excavation broke original ground stress balance, resulted in inducement or expansion of cracks and induced deformation and looseness of local rock masses. The weathering process, especially physical weathering process in the long term (16.5 years after excavation), is the most important reason of the failure, because it resulted in disintegration of material on slope surface and induced reduction of strength in the interior of the slope. Water, as a key factor speeding up the weathering process, weakened mechanical properties of rocks and discontinuities and urged formation of argillation intermediate layer. Based on the analyses of failure modes and corresponding factors of safety, an integrated stabilization system on the rock slope was put in place.