马蹄形预制初期支护力学性能及设计方案研究

Study on the Mechanical Properties and Design Scheme of Horseshoe Prefabricated Primary Support

为了解决传统喷射混凝土初期支护洞内施工环境差、施工质量难控制、混凝土回弹浪费严重、强度提升慢等问题,提出一种新型预制装配式初期支护结构,结合马蹄形预制初期支护足尺试验,对预制初期支护的力学性能、变形规律进行研究,并根据试验结果和理论计算,对该新型初期支护进行设计方案研究。主要结论如下:(1)预制初期支护的极限承载能力为设计荷载的2.8倍,最大变形达115.6 mm,在满足施工安全的同时,具有良好的变形能力;(2)马蹄形预制初期支护采用奇偶环实现错缝拼装,拱脚处曲率较大,拼装难度大,凹凸榫会导致拼装时管片易发生破损,因此管片不宜设置凹凸榫;(3)预制初期支护拱脚处为受力最不利位置,需对拱脚处进行加强;(4)预制初期支护宜采用“先管后锚”方案;(5)预制初期支护拼装完成后,即以设计强度参与围岩受力,避免了喷射混凝土在强度提升阶段就承受围岩压力的情况,极大的改善了结构受力,减小裂缝发展,具有更优的力学性能。

In order to solve the problems of poor construction environment,difficult construction quality control,serious waste of concrete rebound and slow strength improvement in the traditional shotcrete initial support tunnel,a new type of prefabricated initial support structure is proposed.Combined with the full-scale test of horseshoe prefabricated initial support,the mechanical properties and deformation law of prefabricated initial support are studied.According to the test results and theoretical calculation,the research on the design scheme of the new initial support from the aspects of assembly mode,block scheme,connection mode,bolt design and deformation capacity can provide reference for the popularization and application of the new initial support.The main conclusions are as follows:(1)The ultimate bearing capacity of prefabricated initial support is 2.8 times of the design load,and the maximum deformation is 115.6 mm.It has good deformation capacity and can give full play to the self-supporting capacity of surrounding rock while meeting the construction safety;(2) The initial support of horseshoe prefabrication adopts odd and even rings to realize staggered joint assembly.The curvature of the arch foot is large and the assembly is difficult.The concave convex tenon will lead to the damage of the segment during assembly,which requires high control accuracy,so the segment should not be set with concave convex tenon;(3) The arch foot of precast initial support is the most unfavorable position,and the arch foot needs to be strengthened;(4) The scheme of "pipe before anchor" should be adopted for the initial support of prefabrication;(5) After the assembly of the prefabricated initial support is completed,the design strength is used to participate in the stress of the surrounding rock,which avoids the situation that the shotcrete bears the pressure of the surrounding rock in the strength improvement stage,greatly improves the stress of the structure,reduces the development of cracks,and has better mechanical properties.