高地应力深切河谷形变应力场及线路问题初探

为研究高地应力作用下河谷深切卸荷、岩体强风化的地质环境对拟建川藏铁路的影响,利用ABAQUS对高地应力背景场由河流深切卸荷下的河谷形变—应力场特征进行数值模拟研究;考虑到岩体的宏观力学性能受到卸荷回弹变形的影响而急剧减小,利用场变量实现力学参数随卸荷动态变化,对比分析河谷形变—应力场特征;针对印度板块挤压欧亚大陆板块使河谷两岸地应力值存在差异的情况,模拟主、被动盘的差异卸荷。结果表明:自重应力与40 MPa构造应力同时作用下的卸荷回弹值可达仅计自重应力场的3～6倍,出现由陡、缓倾面构成的"X"状共轭结构面,工程开挖下边坡岩体容易沿陡倾面崩塌,沿缓倾面滑移。将卸荷前后岩体偏应力比值k作为评价岩体受到卸荷影响程度的标准,高地应力作用下谷坡水平深度方向的k值介于1.5～2.5,地应力的量值对岩体卸荷程度有很大影响;较之不考虑岩体力学性质劣化情况,岩体塑性区范围将扩展,裂隙向谷坡上部延伸,坡体稳定性进一步下降;高地应力作用的河谷主动岸,坡面塑性区明显存在"X"状潜在滑移面,而被动岸仅有单向缓倾滑移面,主动岸对开挖扰动的抵抗力更低。据此提出相应的灾害预防措施的建议,为拟建进藏道路的区域工程地质选线提供参考。

Preliminary study on deformation and stress field and routes of deep-incised valley under high geostress

In order to investigate the influence of unloading of the surface due to a river’s cutting down and weathering of rock mass under high geostress on the planned Sichuan-Tibet railway,numerical simulations of deformation and stress field of deep-incised valley under high geostress were implemented with ABAQUS.Field variables were used to realize the dynamic change of mechanical parameters of rock mass under the influence of unloading deformation,the deformation and stress field of valley were also analyzed.A numerical model that boundary conditions on both sides are different was built according to the fact that Indian plate is extruding to Eurasian plate.The results show that the unloading displacement of rock mass under 40 MPa tectonic stress combined with self-weight stress was 3 to 6 times larger than that due to self-weight stress,and conjugated structural planes appeared in valley side-slope,which are composed of steep inclined and gently inclined planes,and imply an instable mode of collapse and slip in excavation.As an index to evaluate the unloading effect of rock mass,deviatoric stress ratio k was taken to describe the difference of initial and post unloading.The k in horizontal direction of valley under high geostress is 1.5 to 2.5,which means that the geostress plays an important role in valley unloading.Compared with the condition that do not consider the weakness of mechanical properties,the stability of the slope further decreased,the plastic area increased and the fracture extended to the top of the slope.The conjugated structural planes appeared on the bank under high geostress,while the other bank only has gently inclined slip planes.The bank under high geostress appears lower resistance to the excavation disturbance.Some disaster prevention suggestions and some references for route selection in deep-incised valley under high geostress are put forward.