以沪蓉高速公路某软硬互层边坡为例,基于开挖卸荷理论,采用FLAC3D软件进行数值模拟,研究分步开挖卸荷作用对软硬互层边坡稳定性的影响规律.结果表明:最大不平衡力、最大水平位移值、剪应变最大值随开挖步数的增加累积增大,最大值出现在开挖卸荷面软弱夹层剪出口位置,与开挖量呈正相关关系;每步开挖后瞬间会产生最大不平衡力"尖点",然后逐渐减小接近于零,边坡平衡;塑性区主要分布在软弱夹层位置,拉应力区分布于开挖卸荷面附近以及整体边坡的坡顶面附近20 m以内,且总体拉应力不大,低于灰岩卸荷后的抗拉强度;基于卸荷理论计算得到每步开挖后边坡的稳定性系数比不考虑卸荷对边坡岩体劣化作用的稳定性系数分别降低了0.07、0.08、0.102、0.106.综合分析得出软硬岩互层边坡稳定性的关键问题是开挖卸荷对软弱夹层力学性能的影响以及边坡面附近的拉应力区,开挖卸荷作用对岩体物理力学性能的劣化程度直接决定着边坡的稳定性.%Taking a slope with interbedding of soft and hard rocks in Shanghai-Chengdu expressway has been taken as an example, the influence of multistage excavation unloading on the slope stability is studied based on the theory of excavation unloading and the finite difference software FLAC3D.Results show that the maximum unbalanced force, the maximum horizontal displacement and the maximum shear strain increase with the increase of the number of excavation steps.The maximum values appear in the cut out position of the weak interlayer in the excavation unloading surface, and the values are positively correlated with the amount of excavation.There is a maximum unbalanced force called "sharp point" at the moment of each step of excavation, and then gradually reduced to close to zero, when the slope reaches the equilibrium state.Plastic zone is mainly distributed in the position of weak interlayer, tensile stress zone is distributed near the excavation unloading surface and in the region near the whole slope surface about 20 m.The tensile stress is basically not large, and is lower than that the tensile strength of the limestone after unloading.The stability coefficient of slope after each step of excavation considering excavation unloading were decreased by 0.07, 0.08, 0.102 and 0.106 than that does not considering excavation unloading.It can be concluded that the key issue of the stability of slopes with interbedding of soft and hard rocks is the effect of the excavation unloading on the mechanical characteristics of weak interlayer and the tensile stress zone near the slope surface.The degree of deterioration of physical and mechanical properties of rock after excavation unloading directly determines the stability of the slopes.
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