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| Study on the thickness of karst foundation pits against outburst based on sharp point catastrophe theory and blasting cumulative damage model |
| JIANG Tengfei1,JIANG Annan1,XU Mengfei1,LI Xingsheng2 |
(1. College of Transportation Engineering,Dalian Maritime University,Dalian,Liaoning 116026,China;
2. The Second Engineering Co.,Ltd. of China Railway First Group,Tangshan,Hebei 063004,China) |
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Abstract Under the action of cyclic blasting dynamic loads,it is necessary to determine a reasonable anti-outburst thickness for the hazards of water inrush on the side walls of karst foundation pits. First,according to the mechanical characteristics of water inrush from the sidewalls of the foundation pit,a mechanical model of the truncated cone is established to prevent the instability and damage of the outburst layers. Using the cusp catastrophe theory and energy discrimination method,the anti-outburst layer potential function and the bifurcation point set equation are obtained, and the expression of the anti-outburst thickness of karst foundation pits is deduced. Furthermore,in the blasting excavation,the blasting cumulative damage model is introduced from the perspective of rock fatigue damage,and the cumulative damage value of cyclic blasting is obtained. At the same time,the elastic modulus of the anti-outburst layer is revised to form a calculation method for the anti-outburst thickness of karst foundation pits considering the number of cyclic blasting. Finally,based on the Suoyuwan South Station of Dalian Metro Line 5,the outburst prevention thickness is calculated,the parameter sensitivity analysis of the main influencing factors is carried out,and the concrete outburst prevention construction measures are put forward. The research results show that the anti-outburst thickness of karst foundation pits under different blasting times can be obtained by introducing the blasting cumulative fatigue damage variable. The anti-outburst thickness increases with decreasing the rock elastic modulus E,the Poisson¢s ratio m,the pressure diffusion angle θ and the steel support axial force F1,but is positively correlated with the karst water pressure F3,the karst zone radius R2 and the number of blasting n. In the sensitivity analysis of various influencing factors,the karst zone radius R2 and the karst water pressure F3 have the most significant influence on the thickness of anti- outburst,and the sensitivity factors are 0.869 and 0.722 respectively. This method and conclusion have good reference value for the design and safe construction of rock foundation pits under blasting excavation in karst areas.
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