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针对大跨度地下工程结构受力复杂、安全风险高的工程特点,采用理论分析、经验评价、数值模拟的综合评价方法,对某地下实验大厅的支护结构稳定性进行综合评价。通过多种塑性力学计算方法,对比了卡柯(Caquot)公式、芬纳(Fenner)公式、修正的芬纳公式或卡斯特纳(Kastner)公式在具体工程中的应用,优化分析得出适合于硬岩条件下大跨度结构的理论分析方法。采用Q评价系统和工程类比方法,确定了大跨度地下工程锚杆、锚索和喷射混凝土的支护参数,通过相似工程的经验类比,认为锚索长度应不小于跨度的40%。采用三维离散元计算方法对支护结构的稳定性进行数值模拟,数值计算中的岩体采用基于HB强度准则的应变软化模型,结构面采用基于摩尔-库仑强度准则的理想弹塑性模型。通过数值分析,对边墙上部施加3排预应力锚索,边墙变形得到抑制,同时围岩潜在失稳块体数量和范围显著得到有效的控制。通过支护结构的应力分析得出60%的锚杆轴力在2.0~2.25 MN之间,表明地下工程具有良好的安全性。建立了塑性区理论分析、经验类比和数值模拟的综合评价方法,形成三位一体的评价体系,可有效地对大跨度支护结构的合理性进行评价。综合分析可知,支护方案设计合理时,能够有效应对围岩中的块体稳定风险和高应力破坏现象;在局部安全性较差的部位,锚索和锚杆应力水平相对较高,可以考虑对适当降低锚索预张拉力、增加随机锚杆数量。
Aiming at the engineering characteristics of long-span underground engineering structure with complex forces and high safety risks, the comprehensive evaluation method of theoretical analysis, empirical evaluation and numerical simulation is used to evaluate the stability of the supporting structure of an underground test hall. Through a variety of calculation methods of plasticity mechanics, the application of Caquot formula, Fenner formula, modified Fenner formula or Kastner formula in concrete engineering is compared. The optimization analysis shows that it is suitable Theoretical analysis of long-span structures under hard rock conditions. Using Q evaluation system and engineering analogy method, the support parameters of anchor, anchor cable and shotcrete for long-span underground engineering are determined. According to the empirical analogy of similar projects, the length of anchor cable should be not less than 40% of the span. Three-dimensional discrete element method was used to simulate the stability of the supporting structure. The rock mass used in the numerical calculation was strain softening model based on the HB strength criterion, and the ideal elastic-plastic model based on the Mohr-Coulomb strength criterion was used for the structural plane. Through numerical analysis, three rows of prestressed anchorage cables are applied to the upper part of the side wall, and the deformation of the side wall is restrained. At the same time, the number and range of potential unstable blocks in the surrounding rock are obviously effectively controlled. The stress analysis of the support structure shows that 60% of the anchor axial force is between 2.0 and 2.25 MN, indicating that underground engineering has good safety. The establishment of a plastic zone theory analysis, empirical analogy and numerical simulation of the comprehensive evaluation method to form a three-in-one evaluation system, which can effectively evaluate the rationality of long-span support structure. The comprehensive analysis shows that the design of the supporting scheme can effectively deal with the stability risk and high stress failure of the block in the surrounding rock. In the parts with poor local safety, the stress level of the anchor cable and the anchor rod is relatively high, which can be considered Properly reduce the pre-tensioning of the cable, increasing the number of random bolts.