Application Of The Subsalt Critical Taper Model In Kelasu Structure Belt Of Kuqa Depression And Simulation Experiments

The model of critical taper wedge determine the relationship between the wedge slopes and the mechanical properties of the wedge and the basal detachment.According to the formula,the bigger the internal friction coefficient of the basal detachment is,the larger wedge slopes are,while the bigger the internal friction angle of the stratum,the smaller the wedge slopes are.However,due to the weight of the upper salt which cause the pressure on the top of the Coulomb wedge,the result obtained by using the traditional critical taper formula is not in conformity with the actual condition for subsalt Coulomb wedges of Kuqa Depression Kalsu Structure Belt.In this paper,considering the weight of the upper salt,the critical taper formula applicable to subsalt Coulomb wedges is derived.According to the new critical taper formula,the internal friction angle of the Kuqa depression basal detachment is 13.4°?18.1°.According to speculation,the results of the internal friction angle are consistent with mudstone or carbonaceous shale and the detachment may be the Middle Triassic or lower Triassic mudstone and carbonaceous shale.According to the new critical taper formula applicable to subsalt wedges and the seismic interpretation charts of the Kuqa depression Kelasu belt,the parts near the foreland of the fold and thrust belt wedges brace higher pressures,so their upper surface slopes are larger.In order to verify this conclusion,an experiment of discrete element numerical simulation is designed.The experimental result show that the more parts close to the wedge foreland,the larger the wedge slopes are and the more parts close to the wedge hinderland,the smaller the wedge slopes are.This phenomenon is consistent with the characteristics of the new critical taper formula applicable to subsalt structural wedges and the seismic interpretation charts of the Kuqa depression Kelasu belt.There is a backthrust at the end of compression,and the distance between each thrust is relatively remote.The reasons for these phenomena may be due to the pressure of the upper salt.The physical simulation experiment result also appear similar phenomenon.Presumably,along vertical salt stress will make downward rotation for the stratum and along horizontal,because the salt wedge flow forward along the upper surface,the nappe brace resistance when thrusting forward.