摘要
重庆市万州区某广场不稳定斜坡位于重庆市万州区和平广场冯家院片区,该不稳定斜坡纵向长度约200m,前缘宽约96m,后缘宽约100m,平面面积为21000m2,中前缘不稳定斜坡平均厚度约20m,中后缘不稳定斜坡平均厚度约8m,不稳定斜坡的体积为2.8×105m3,中前部主滑方向为43°,后部主滑方向为60°,后缘较陡峭,前缘较平坦,北侧边界位于鸡公岭,南侧以和家沟为界。不稳定斜坡的变形破坏特征明显,后部出现多处裂缝和房屋变形,如何认识不稳定斜坡的变形机制,并正确评价其稳定性,显得尤为关键。
本文以不稳定斜坡为研究对象。在前人研究的基础上,结合现场调查,总结并归纳研究区地质环境条件,通过对已有监测资料分析,研究实测监测点位移特征,在此基础上开展FLAC3D三维数值模拟,对不稳定斜坡原始条件和基坑开挖后稳定性及应力形变场特征进行了较全面的分析。具体内容如下:
(1)通过地质勘探资料,查明了不稳定斜坡区环境地质背景、不稳定斜坡规模及形状特征、物质组成、结构特征、地下水特征及变形破坏特征等。
(2)根据不稳定斜坡基本特征,建立FLAC3D模型,对比监测点的FLAC数值模拟结果与不稳定斜坡基坑开挖后的监测实测数据,如果其值相吻合,则证明不稳定斜坡的计算模型和参数取值合理。
(3)采用极限平衡法,对不稳定斜坡原始条件下和基坑开挖后不同工况下的稳定性进行分析,得出无论是原始条件还是基坑开挖后,不稳定斜坡在各种工况下整体都处于稳定状态。这与现场情况相吻合。
(4)采用FLAC3D三维数值模拟对原始条件和基坑开挖后的不稳定斜坡在天然和降雨工况下应力及形变场特征进行分析,结果表明:①原始条件下,不稳定斜坡的后缘局部已经发生了蠕动变形,但剪应变增量并未完全贯通,不稳定斜坡整体仍然处于稳定状态。②基坑开挖后,应力场分析发现,不稳定斜坡前缘及后缘最小主应力表现出明显的拉应力特征;形变场分析发现,不稳定斜坡剪应变增量并未全部贯通,不稳定斜坡整体也处于稳定状态。这也与现场情况和极限平衡法稳定性计算相吻合。③在不稳定斜坡前、中、后坡表各取一监测点,通过数值模拟其位移变化曲线,对比分析不稳定斜坡变形规律,进一步认清不稳定斜坡的变形机制。
The unstable slope is located in the fengjiayuan region Peace Plaza Wanzhou District Chongqing city, it’s longitudinal length is about 200m, front width of 96m, back width of 100m, flat area of 21000m2. The average thickness of the unstable slope is about 20m in the middlefront,and 8m in the middleback,volume of 2.8×105m3. the active slide direction is 43°in the middle-front and 60°in the back .with steep back and smooth front .the north boundary is in JiGongLing,and the south boundary is located in HeJiaGou. The deformation characteristics of the unstable slope is obvious, it appears many cracks and housing deformation in the back.It is particularly critical to know the formation mechanism and failure modes of the landslides, and correct evaluation of its stability.
In this paper, the unstable slope of some square is taken as the research object. On the basis of previous studies, combined with field investigation, the geological environment of this study area is summarized.By analysising the measured monitoring data, the displacement characteristics of the monitoring point is studied. FLAC3D numerical simulation is adopted to analyze the original slope stability conditions and the stability and the stress characteristics of deformation field after the excavation on the basis of displacement characteristics, Details are as follows:
(1) Based on the geological exploration data,find out the unstable slope area environment geology background ,volume of the unstable slope , rock structure, geo- logical structure, Characteristics of Groundwater , the characteristics of deformation and damage and so on.
(2) FLAC 3D model is established based on the basic features of unstable slope. The numerical numbers of FLAC 3D and the experimental dates of some Square after the excavation of unstable slope are compared. If the result is matched, the model and parameter are reasonable.
(3) The unstable slope under various working conditions is stable by the limit equilibrium method, in the based of the analysis of original conditions and the dates after the excavation of unstable slope of some Square. This is match with the actual situation.
(4)Using FLAC3D numerical simulation to analyse field characteristics of stress and deformation in the conditions of natural and rainfall of unstable slopes in the original conditions and after excavation,find that:①In the original conditions, the back edge of unstable slopes has occurred creep deformation locally, but the shear strain increment is not completely through, unstable slopes as a whole is still in steady state.②After excavation,analyse under stress field and find that the minimum principal stress in leading edge and trailing edge of the unstable slopes showed obvious features of tensile stress; analyse under deformation field and find that the shear strain increment of unstable slopes is not completely through, unstable slopes as a whole is also in steady state,which is also consistent with field conditions and the stability analysis results in limit equilibrium.③Take monitoring points before, during and after the unstable slopes’surface, according simulating numerically Its displacement curve and analysing comparatively the deformation of unstable slopes,and further understand the deformation mechanism of unstable slopes.
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