Recent research does not fully identify the causes of surface volume loss that occur at the tunnel level in sand, as related to the excavation of a pressurized-face tunnel boring machine (PTBM). This paper focuses on the face stability of PTBM tunneling, and the response of sandy soil to the inadequate face pressure is evaluated. Data presented are from tests of a model using reduced-scale PTBM tunneling operations in dry sand. Ground displacement and the evolution of ground stress were analyzed. The relationship between the load factor at the face and the volume loss at surface was examined. The effects of soil density and tunnel depth were considered. An empirical formulation was provided allowing determination of the expected volume loss as a function of load factor (LF), cover-to-diameter ratio (C/D) and soil density (I_d). Thus providing a valuable basis for establishing relationship between volume loss associated with tunnel face advancement and face pressures in sandy soil. The results show that instability of the face is accompanied by the triggering of secondary deformation mechanisms at the surface. The volume loss at surface is complicated by the combined effects of soil arching and the dilative/contractive behavior of the soil. The variation of volume loss is sudden prior to face collapse, especially at dense sand, which is different from the progressive variation of volume loss in clays. The size of destressed zone ahead of cutter head is less dependent on C/D in loose soil than in dense soils.

最近的研究并没有完全确定在隧道层面发生的砂土表面体积损失的原因，这与加压面隧道掘进机 (PTBM) 的开挖有关。本文重点研究了PTBM隧道掘进的工作面稳定性，评估了砂土对工作面压力不足的响应。提供的数据来自在干砂中使用缩小规模的 PTBM 隧道作业的模型测试。分析了地层位移和地应力的演变。检查了表面载荷系数与表面体积损失之间的关系。考虑了土壤密度和隧道深度的影响。提供了一个经验公式，允许确定作为负载因子 (LF)、覆盖直径比 (C/D) 和土壤密度 (我_d )。从而为建立与隧道掌子面推进相关的体积损失与砂土中的掌子面压力之间的关系提供了宝贵的基础。结果表明，工作面的不稳定性伴随着表面二次变形机制的触发。由于土壤拱起和土壤的膨胀/收缩行为的综合影响，地表的体积损失变得复杂。工作面坍塌前体积损失的变化是突然的，特别是在致密砂层，这与粘土中体积损失的渐进变化不同。与密实土壤相比，松散土壤中刀盘前方的去应力区的大小对 C/D 的依赖性较小。