软弱围岩隧道预衬砌法实施效果模型试验研究

Model test research on implementation effect of pre-lining method of tunnel in weak surrounding rock

开展软弱围岩隧道预衬砌法大型三维地质力学室外坑内模型试验,对比分析常载和超载条件下设置预衬砌、不设置预衬砌预收敛变形、收敛变形、掌子面挤出位移、径向围岩压力及失稳破坏过程。结果表明:全风化V级花岗岩地质条件下铁路双线隧道采用预衬砌法,预收敛率减小20%～30%、拱顶沉降和水平收敛分别降低25%和80%、洞周径向围岩压力增大1.1倍;不设置预衬砌段开挖过程对超前核心土纵向影响范围约为0.7D(D为隧道跨度),设置预衬砌段影响范围缩小至0.3D、降幅近60%;超载条件下隧洞失稳过程为:边墙、拱顶、掌子面岩体"剥离–滑移–垮塌",最终形成深度分别为2,1.4,1.2m的塌穴;隧道稳定性判定参考极限位移值可取拱顶沉降157mm、水平收敛93mm、掌子面挤出位移225mm。研究成果为新意法理念下预衬砌全断面大型机械开挖提供一定的理论依据。

Preconvergent deformation,convergent deformation,face extrusion displacement,radial pressure of surrounding rock and failure process of instability are analyzed under the normal load and overload,a model test of large three-dimensional geomechanics outside the pit is carried out for the pre-lining method of tunnel in soft surrounding rock.The rate of preconvergence is reduced by 20%–30%,the settlement of the vault and the horizontal convergence can be reduced by 25%and 80%,the pressure of surrounding rock in the circumference of the hole is increased by 1.1 times while the pre-lining method is used in double line railway tunnel under the geological conditions of the fully weathered granite with grade V.The longitudinal influence range of the advanced core soil is about 0.3 D in condition A and 0.7 D in condition B,the decline is nearly 60%.The instability process of tunnel is peeling-slip-collapse of rock mass,and the collapse is finally formed with 2 m depth of side wall,1.4 m depth of vault,1.2 m depth of excavating face.Limit displacement value of stability criterion of tunnel is recommended 157 mm of vault settlement,93 mm of horizontal convergence and 225 mm of face extrusion displacement.The research results provide a certain theoretical basis for the full-face excavation of large machinery with pre-lining according to the basic theory of ADECO-RS.