大跨度地下工程支护结构研究

Study of large-span underground engineering supporting structure

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。

According to the characteristics of long span underground engineering's complex structure and high safety risk, the paper establishes a synthetically evaluation system by theoretical analysis, numerical simulation and experience evaluation. Through a variety of plastic mechanical calculation method, the Caquot formula, Fenner formula, modified Fenner and Kastner formulas are applied to project practice; select one method is most suitable analyze way for large span structures in hard rock. Using Q system and engineering analogy, determine the supporting parameters of anchor bolt in large-span underground engineering. The length of anchor bolt depends directly on the excavation span in Q system, at same time we can get support parameters of shotcrete. By analyzing the same level span underground works, determined that cable length should longer than 40% of the underground work's span. Through the three-dimensional discrete element to evaluate the stability of supporting structures. In numerical calculations, rock strength criterion can be defined by the strain-softening model of HB. Constitutive relations of structural surface can use ideal elastoplastic model in Mohr-Coulomb strength criterion. After applying three rows of prestressed-cables at the upper side wall, the of deformation of side wall is significantly reduced. At the same time, the number of potential instability surrounding rock mass and scope are effective significantly controlled. By stress analysis of supporting structure,it is show that the 60% of the anchor's axial force is between 2.0-2.25 MN; the underground engineering has a good safety. Through the synthetically evaluation system including plastic area analysis, numerical simulation and experience analysis, the formation of three-in-one evaluation system is reached. This system can be used for large-span support structure's rationality evaluation. Through the analysis, The supporting design scheme can effectively deal with the failure phenomenon of rock block stability risk. In local lowly safety parts, anchor and anchor-cable stress level is comparatively high, can reduce the anchor-cable's pretension force and increase the number of random anchor.