浅埋黄土隧道三层支护结构力学特性现场测试

为研究浅埋黄土隧道锚喷初支+初衬+二衬构成的3层支护体系力学特性，以某黄土隧道为依托，采用钢弦式传感器对围岩压力、初衬与二衬接触压力、二衬钢筋轴力、二衬混凝土应变、钢拱架应力等进行了系统测试与分析。结果表明：(1) 作用在左拱腰处的围岩压力较大，且稳定值为240 kPa；(2) 浅埋段按不同围岩压力计算公式得到压力值均大于围岩压力实测值，其中采用太沙基公式得到的压力值与实测值相对接近；(3) 该黄土隧道二衬全部受压，其分布形态呈明显的猫耳形，初支、初衬、二衬承受的荷载比例分别为51.34%、37.29%、11.38%；(4) 钢拱架整体以受压为主，在拱顶和拱腰处受力较大，接近屈服状态；(5) 初支发挥了一定的围岩自承能力，其与初衬共同承担了大部分围岩荷载，二衬主要为结构安全储备。

Field test of mechanical characteristics of three-layer support structure of shallow loess tunnel

To understand the mechanical characteristics of the three-layer support system (primary support, first liner and secondary liner) of shallow tunnel in loess region, large scale in-situ tests are conducted based on a loess tunnel. The contacting pressure on the surrounding rock, first liner and secondary liner, the axial force of steel, the strain of secondary liner and the stress of steel arch are systematically monitored by the steel string transducers. The test results indicate that: (1) The surrounding rock pressure is larger on the tunnel left hance with a maximum value of 240 kPa. (2) Under the influence of geology and construction, the rock pressure in shallow region has a large difference between the monitored and calculated values; and the pressure calculated based on the Terzaghi''s rock load theory is relatively close to that monitored in the field. (3) The secondary liner pressure approximately takes on as “cat ears”. Moreover, the loading ratio is approximately 51.34%, 37.29% and 11.38% for the primary support, first liner and secondary liner, respectively. (4) The steel arch is at pressure in majority, the hance and vault bear larger pressure, where the steel arch is close to yield. (5) The primary support coupled with the first liner bears the majority of rock load. In summary, as an effective support system, the three-layer support system presented for this case study can serve as a benchmark for effective design and safe construction of similar projects.