硬塑-流塑浅埋黄土隧道变形特性及合理预留变形量模型试验研究

Model test study of deformation characteristics and reasonable reserved deformation of shallow-buried loess tunnel with hard-flow plastic

开展硬塑-流塑浅埋黄土隧道室内大型三维YTLH岩土联合地质模型试验,对比分析了硬塑、软塑、流塑3种状态,12 m和24 m两种埋深下的围岩内部位移、预收敛变形、掌子面挤出位移和径向围岩压力。结果表明:硬塑、软塑和流塑条件下围岩内部位移差率均呈现出'拱顶极小、两侧边墙极大'的特征,拱顶位移差率小于20%、两侧边墙位移差率大于91%;拱顶设计4.5 m长锚杆抗拉效果甚微,边墙围岩内部位移差利于锚杆抗拉效应的充分发挥;硬塑、软塑、流塑预收敛率分别接近65%、70%、80%,开挖对掌子面前方影响范围分别为0.5D、0.6D、0.8D,且呈现出直立型、鼓出型、滑塌型不同失稳破坏模式;应力释放率关系为硬塑<软塑<流塑,软流塑态拱顶应力释放率最大约70%,实际工程应避免软流塑态瞬时应力释放过渡而失稳。双线浅埋黄土隧道合理预留变形量建议取值:硬塑(拱顶55~70 mm、边墙15~20 mm),软塑(拱顶166~180 mm、边墙40~50 mm),流塑(拱顶290~300 mm、边墙125~140 mm),且拱顶和边墙之间按曲线过渡非等量留设。

A geological model test of large 3D YTLH soil-rock combination was carried out to analyze the internal displacement,convergent deformation,face extrusion displacement and radial pressure of surrounding rock under the three states(hard plastic,soft plastic,flow plastic)and two different depths(12 m,24 m).The results show that the internal displacement difference of surrounding rock presents the characteristics of’minimum on arch crown and maximum at both sides’,and the displacement difference of vault is less than 20%and the value of side wall is greater than 91%.The 4.5 m long anchor bolt on the arch has little effect on the vault,but the tensile effect of anchor bolt on side walls is fully exerted.The pre-convergence rates of hard plastic,soft plastic and flow plastic nearly reach 65%,70%,and 80%,and the influence ranges on excavation face are 0.5 D,0.6 D,and 0.8 D,respectively,which shows different failure modes of vertical type,drum out type,and slump type.The stress release rate of hard plastic is the smallest,followed by soft plastic and flow plastic,and the maximum stress release rate of flow plastic is over 70%.Excess stress release should be avoided to lose stability in the actual engineering.The reasonable deformation allowance of double-line shallow-buried loess tunnel is recommended as follows:hard plastic formation(55-70 mm of vault,15-20 mm of side wall),soft plastic formation(166-180 mm of vault,40-50 mm of side wall),and flow plastic formation(290-300 mm of vault,125-140 mm of side wall).The reserved deformation between vault and side wall can be set by curve transition with non-equal quantity.