复合支护下深基坑的变形破坏和支护结构
Analysis of Deformation Failure and Supporting Structure Force ？？Evolution of Deep Foundation Pit Under Compound Supporting

以某深基坑工程为研究对象，利用岩土数值分析FLAC 3D软件，建立三维数值分析模型，模拟开挖和支护实际工况，分析了双排微型桩复合土钉支护下基坑开挖过程中的变形破坏和支护结构受力演化特征。结果表明：坑壁水平位移总体上呈现基坑顶部小、基坑中下部大的形式，位移等值线呈鼓肚状；基坑基底隆起量较大，随着距基坑壁距离的减小而减小；基坑边坡竖向沉降较小，最大沉降量出现在支护结构之后；土钉轴力分布呈中间大、两端小的形式，离基坑底部越近，土钉的最大轴力点越靠近基坑开挖面，且随着开挖深度增加，土钉轴力初始增长迅速而后发展较为缓慢；前排微型桩弯矩大于后排，微型桩最大弯矩随着开挖深度的增加不断增大且不断下移，开挖完成后弯矩最大值位于基坑底部以下2 m深度处；基坑开挖及支护过程中监测点的位移时程曲线和塑性区分布区域说明基坑整体稳定性较好，但在坡顶后缘出现拉张塑性区，基坑壁浅表层和基坑底角部位出现剪切破坏区，在施工中应对其采取针对性措施进行保护；该研究成果对深基坑开挖过程中动态演化过程认识和变形破坏防治具有一定参考意义。
In order to simulate the actual working conditions of excavation and supporting in a deep foundation pit project, a three？？dimensional numerical model was built using geotechnical numerical analysis software FLAC 3D, and the deformation failure and supporting structure force evolution characteristics of the deep foundation pit under double micropiles and composite soil nailing were analyzed. The results show that horizontal displacement contours of the foundation pit wall is bulging, indicating a small displacement in the upper but a big displacement in the lower. A larger uplift appears at the bottom of the foundation pit, but the uplift amount decreases with the decreasing of distance from foundation pit wall. Besides, vertical settlement of the foundation slope is small, and the maximum settlement appears after the supporting structure. The axial force of soil nail is strong in the middle and weak at the end, and the maximum axial force point is getting closer to the excavation face when approaching to the bottom of the foundation pit. With the increase of the excavation depth, the axial forces of soil nail grow quickly at the beginning and then become slow. The bending moment of the front micropiles is greater than the back row, and the maximum bending moment appears at 2 meters depth of the bottom of the foundation pit after the excavation completed. Moreover, the stability of foundation pit is obtained by the support of measuring points？？ displacement？？time curve and the plastic zone distribution characteristic. However, tension？？tensile plastic zone appears in the top of the hill edge, and the shear failure zone appears in the shallow of foundation pit wall and bottom of foundation pit, respectively, indicating the proper protecting measures should be taken. The obtained results can provide significant reference for the dynamic evolution and prevention of deformation failure in deep foundation pit excavation