落石冲击下无回填土拱形明洞结构可靠度设计

Structural Reliability Design of Non-Backfilling Arch Open Tunnel Structure under Rock-fall Impaction

为完善拱形明洞结构可靠性设计方法,利用模型试验、数值模拟及理论分析等,结合现场实际,开展了落石冲击下无回填土拱形明洞破坏特征及失效模式、极限承载力、落石冲击荷载及极限状态表达式等的研究.首先,根据落石冲击下无回填土拱形明洞结构失效破坏特征,将结构局部失效范围部分简化为四边固支方形钢筋混凝土板结构,利用塑性极限原理按刚塑性板进行准静态极限荷载计算,得到结构极限承载力即抗力;其次,将离散元颗粒流数值模拟方法得到的落石冲击力最大峰值作为钢筋混凝土板顶部落石冲击力,通过回归分析,得到用落石重力势能的幂函数表示的落石冲击荷载表达式;再次,将得到的结构抗力与落石冲击荷载联立得到极限状态方程,利用MABLAB软件编程求得结构可靠指标,通过与目标可靠指标的比较,进行结构可靠度设计与优化;最后,利用所建立的结构可靠度设计方法,对某客专双线拱形明洞设计进行了可靠度检算.研究结果表明:当落石高度为5~15 m、落石重量为1~2 k N时,原设计明洞结构可靠指标可达到4.2;当将原设计的C35混凝土调整为C40,钢筋由HRB335调整为HRB500后,落石高度为5~20 m、落石重量为1~2 k N范围时的结构可靠指标可达到5.4以上.

A structural reliability design method for a non-backfilling arch open tunnel structure under rockfall impaction was investigated to improve the reliability of structural design. Firstly, in view of the characteristics of the failure modes of a non-backfilling arch open tunnel under rockfall impaction, a four-fixed square reinforced concrete slab was simplified to a rigid perfectly-plastic slab, and the assumed failure of the structure’s ultimate load or structural resistance was calculated as a statics problem using plastic limit theory. Secondly, numerical modelling was performed using a particle flow code method, and rockfall impaction load was expressed as a power function of the gravitational potential energy of rockfall through the regression analysis of modelling results. Thirdly, the limit state equation was established by combining structural resistance and the rockfall impaction load expression.Then, the structural reliability index was obtained using a M A T L A B software p r o g r a m m i n g m e t h o d , and structure reliability design and optimization were performed by comparing the calculated structural reliability index with the target reliability index. Finally, using the established method, the structural reliability indexes of the double-line arch open tunnel of a passenger transport line were analysed. The structural reliability index of the original structure design is up to 4. 2 for a height of 5 - 15 m and a rockfall weight of 1 - 2 kN. Moreover, the structural reliability index is up to 5. 4 if the concrete grade is adjusted from the original C35 to C40 and the reinforcing steel bar grade is changed from H R B 3 3 5 to HRB500, for a height of 5 -20 m and a rockfall weight of 1 -2 kN.