单跨5车道公路隧道工法优化及施工力学特性研究

Study on Construction Method Optimization and Construction Mechanical Characteristics of a Single-Span Five-Lane Highway Tunnel

为解决超大断面公路隧道传统工法工序繁杂、效率低等问题,依托厦门芦澳路—海沧疏港通道2#分岔隧道大跨段(国内在建最大断面公路隧道),利用“以索代撑”的思想,并结合围岩强度高的特点,提出主动支护的钢架岩墙组合支撑法并对其进行工法优化。通过岩石三轴压缩试验和Hoek-Brown估算方法获得围岩力学参数,并采用数值计算的方法验证该工法的合理性,确定预应力锚索长度为10 m,预应力值为1000 kN,同时对其施工力学特性进行研究。结果表明:围岩变形主要发生在岩墙(⑤分部)开挖前,且以竖向变形为主,上台阶开挖是引起隧道拱部沉降和仰拱隆起的主要原因;在预应力锚索的作用下,隧道岩墙(⑤分部)的开挖和中隔壁的拆除对围岩变形和初期支护内力影响较小;初期支护拱脚处压应力集中,拱顶和仰拱处受到较大的拉应力;隧道围岩变形及初期支护承载力均满足公路隧道施工安全要求。

The traditional construction method for a super large cross-section highway tunnel is characterized by a complex process and low efficiency.Accordingly,the active steel frame-rock wall combined support method is proposed for the large-span section of the bifurcated tunnel#2 of the Haicang Shugang channel on the Xiamen Lu′ao Road(the largest cross-section highway tunnel under construction in China)based on the idea of"replacing support by cable"and the characteristics of high strength of surrounding rocks.Next,the mechanical parameters of surrounding rocks are obtained by the rock triaxial compression test and the Hoek-Brown estimation method,and the rationality of the method is verified by numerical simulation.Meanwhile,the length of the prestressed anchor cable is determined to be 10 m and the prestress value is 1000 kN.Finally,the construction mechanical characteristics are analyzed.The results show the flowing.(1)Deformation of the surrounding rocks mainly occurs before the rock wall excavation(#5);the main deformation is the vertical deformation,and the top heading excavation is the main cause for tunnel arch settlement and invert uplift.(2)Under the action of the prestressed anchor cable,the excavation of tunnel rock wall(#5)and removal of the middle partition wall has little impact on the surrounding rock deformation and primary support internal force.(3)The compressive stress at the primary supporting arch foot is concentrated,and the crown and invert are subjected to greater tensile stress.(4)Deformation of the rocks surrounding the tunnel and the primary support bearing capacity meet the safety requirements of highway tunnel construction,indicating that the construction method has certain reliability and safety.