黄土塬区浅埋大断面隧道掌子面失稳机理研究

Research on the Instability Mechanism of Tunnel Face of Shallow Buried and Large Section Tunnel in Loess Tableland

研究目的:高速铁路以隧道形式穿越黄土塬区时,受地下水位高、含水量大、围岩分级高、浅埋段距离长等特点的影响,隧道掘进施工中掌子面失稳及坍塌风险高。大断面黄土隧道掌子面稳定分析中,大都集中在浅埋短距离隧道的横向二维问题上,很少提到浅埋长距离隧道的纵向变形和掌子面超前稳定问题。研究结论:(1)针对黄土塬区大断面隧道掘进施工中掌子面失稳及坍塌风险,建立了利用Terzaghi松动土压力理论的三维修正分析模型,推导出了浅埋长距离隧道掘进施工中掌子面稳定性的计算公式;(2)研究了黄土隧道三台阶预留核心土工法施工中掌子面稳定性与黄土含水量之间的关系,提出了黄土塬隧道掌子面施工稳定含水量界限参考值为20%,针对性地提出了安全预防措施;(3)该研究成果可有效指导黄土塬区浅埋慢坡隧道掌子面安全施工,为浅埋长距离隧道的纵向变形和掌子面超前稳定分析和安全控制提供理论依据。

Research purposes: When the high-speed railway passes through loess tableland in the form of tunnel,it is influenced by the characteristics of high groundwater level and high water content and high classification of surrounding rock and long distance of shallow buried section,the instability and collapse risk of tunnel face are high in tunneling construction. In the stability analysis of tunnel face of loess tunnel with large section,there are most of them focus on the transverse two-dimensional problem of shallow buried short distance tunnel,however,the longitudinal deformation and the advance stability of the tunnel face are rarely mentioned.Research conclusions:( 1) In view of the instability and collapse risk about the large section tunnel face during tunneling construction in loess tableland,a three dimensional modified analysis model based on Terzaghi loose soil pressure theory is established,and the formula for calculating the stability of tunnel face in shallow buried long distance tunneling is deduced.( 2) This paper studied the relationship between the stability of the tunnel face and the moisture content of loess in the construction with three-step reserved core method,put forward that the reference value of stable water content of tunnel face in loess tableland is 20%,and put forward safety precaution measure pertinently.( 3) The research results can effectively guide the safe construction of the tunnel face of the shallow buried and slow-slope tunnel in the loess tableland,and provide theoretical basis for longitudinal deformation analysis and advance stability analysis and safety control of shallow buried long distance tunnel.