Depositional regularities analysis of incompetent beds in dam foundation of Xiaonanhai reservoir using Markov chain

Abstract

Incompetent beds, which are composed of clastic rocks, are widely distributed in Upper Jurassic red strata in Sichuan Basin. These incompetent beds are prone to lead to the instability of Xiaonanhai Reservoir. The Markovian simulation results show that the semi-rhythmic structures of J3S4-1 section are mainly of two types: one is siltstone and argillaceous siltstone alternation with great rhythmic thickness, the other is thin bedded argillaceous siltstone with interbedded mudstone. The incompetent beds are divided into three types: (I) cracked rock; (II) cracked rock with mud interbedded; (III) mudstone with cracked rock interbedded, or mudstone. Type I mainly exists in the thick mudstone or at the junction of thick mudstone and siltstone. Type II generally lies in the soft rock. Type III with more than 30% of clay, frequently appears in the second semi-rhythmic structure mentioned above.