岩堆体隧道洞口浅埋段开挖进尺的计算与分析——以云南麻昭高速公路赵家屋隧道为例

为了解决岩堆体隧道施工经验缺乏和开挖进尺选择随意性的问题,结合云南麻昭高速公路赵家屋岩堆体隧道工程实例,基于筒仓理论,提出了岩堆体隧道洞口浅埋段开挖进尺的计算公式,分析了核心土留设长度和不同岩堆体力学参数条件下的合理开挖进尺。结果表明:岩堆体隧道施工中,若不采取预支护或预加固措施,各开挖进尺下隧道掌子面安全系数均较小,掌子面存在失稳风险;留设核心土能明显提高隧道掌子面的稳定性;开挖进尺对围岩黏聚力敏感,这对岩堆体隧道稳定性不利。

Calculation and Analysis on Excavation Cycle Length of Shallow Portal Sections of Tunnels Located in Talus Deposits: Case Study on Zhaojiawu Tunnel on Ma-Zhao Highway in Yunnan,China

At present, there is lack of experience in the construction of tunnels located in talus deposits and it is random to choose the excavation cycle length for tunnels located in talus deposits. The entrance portal section and exit portal section of Zhaojiawu tunnel on Ma Zhao highway in Yunnan, China are located in talus deposits. In the paper, the calculation formulas for the excavation cycle length of the shallow portal section of Zhaojiawu tunnel are proposed on basis of silo theory, and the appropriate excavation cycle length of the portal section in talus deposits under the condition of different core soil lengths and different mechanical parameters of the talus deposits are analyzed. Conclusions drawn are as follows: 1) Whatever the excavation cycle length is, during the construction of tunnels located in talus deposits, the safety coefficient of the tunnel face is small and the tunnel face may lose its stability if no advance support or reinforcement measures are taken; 2) Core soil kept can improve the stability of the tunnel face significantly; 3) The excavation cycle length is sensitive to the cohesion of the surrounding rock, which is unfavorable for the stability of the tunnels located in talus deposits. 