黄土连拱隧道支护结构力学特性现场试验

Mechanical Characteristics of a Multi-Arch Tunnel Support Structure in Loess

为研究黄土连拱隧道支护体系力学特性,文章以某黄土连拱隧道为依托,采用钢弦式传感器,对围岩压力、锚杆轴力、钢支撑内力以及二次衬砌受力等进行系统测试与分析。结果表明:(1)在中墙墙顶与拱部的结合处以及在墙底与仰拱的结合处,围岩压力的波动比较大,最大压力值分别为195 kPa、115 kPa。位于围岩级别过渡段的隧道仰拱中心处的压力值较大,最大值为267 kPa,隧底出现较大底鼓趋势。围岩压力整体呈"双马鞍形"分布;(2)深埋段竖向围岩压力实测值与《公路隧规》中按连拱隧道半跨计算的结果比较接近。浅埋段按不同围岩压力计算公式得到的压力值均大于实测值,采用太沙基公式得到的压力值与实测值相对接近;(3)该黄土连拱隧道的初期支护与二次衬砌的荷载分担比例为47.66%和52.34%,二次衬砌处于明显的承载状态;(4)锚杆轴力较小,呈"鱼肚形"分布。钢拱架承受的荷载较大,在钢拱架强支护的作用下,锚杆发挥的作用有限;(5)中墙扭矩的存在,验证了黄土隧道中纵向效应的存在,在设计与施工的过程中应该加以重视。

To understand the mechanical characteristics of a multi-arch tunnel support structure in loess, the pres- sure on the surrounding rock, the axial force of the anchor bolt, the internal force of the steel arch and the force on the secondary lining are tested using steel-wire transducers. The test results indicate that： 1） the pressure of the sur- rounding rock fluctuates a lot at the juncture between the top of the mid-wall and the arch and the joint between the bottom of the wall and the invert, with maximum pressures of 195 kPa and 115 kPa, respectively. The pressure of the tunnel invert center at a rock transition section is relatively large, with a maximum pressure of 267 kPa and shaped like a large heaving floor, with the pressure of the rock mass distributing in a ＂double-saddle＂ shape; 2） the measured vertical pressure of a rock mass at a deep buried depth is close to the result calculated based on a half span of a multiple-arch tunnel specified in the ＂Code for Road Tunnels.＂The pressures on rock masses calculated by different formulas are larger than the ones measured at the shallow-buried section, while the pressures obtained by the Terzaghi formula are relatively close to the measured ones; 3） the proportions of load sharing between the ini- tial support and the secondary lining of this loess tunnel are 47.66% and 52.34%, which shows the secondary lining is in a load-bearing state; 4） the axial force of an anchor bolt is relatively small and distributed in a ＂fish-maw＂ shape, with the load largely borne by the steel arch and the anchor bolt playing a limited function due to the strong support of the steel arch; and 5） it proves that there is a longitudinal effect on the loess tunnel because of the exis- tence of middle wall torque, and attention should be paid to this during construction and design.