某紧邻既有高速公路偏压深基坑开挖效应分析

Study on excavation effect of an unsymmetrical loaded deep foundation pit adjacent to existed expressway

以合肥城市轨道交通工程建设过程中某紧邻既有高速公路高填方路基偏压深基坑为背景,通过现场监测资料,分析该深基坑在偏压作用下围护桩的桩体深层水平位移和桩顶水平位移、支撑轴力、基坑周围地表沉降以及基坑开挖对邻近高速公路的影响。结果表明:偏压作用下,基坑两侧围护结构变形特性以及基坑开挖对周围环境的影响与对称荷载条件下存在很大差异,基坑同一断面内高荷载一侧的各项变形均大于低荷载一侧;高荷载一侧基坑长边方向中部位置的各项变形大于其两边变形,是整个基坑最薄弱区域;基坑开挖过程中,钢支撑轴力与其架设以后所在平面的围护结构水平位移增量有关,围护结构水平位移增量越大,钢支撑轴力越大;基坑开挖所引起的邻近高速公路路基不均匀沉降主要位于靠近基坑一侧;受端部效应影响,基坑短边方向左右两端的各项变形明显小于其长边方向上下两侧变形。最后,结合上述规律给出了一些工程建议。

The studied deep foundation pit under the eccentric compression is in Hefei Metro project and adjacent to the existed expressway high fill subgrade. The deep horizontal displacements of retaining piles. the horizontal displacements of pile tops, the axial forces of supports, the ground surface settlement around the foundation pit and the influence of the excavation of foundation pit on adjacent expressway were analyzed through field monitoring data. The results indicate that under the eccentric compression, the deformation characteristics of retaining structures and the influence on the surrounding environment induced by excavation are quite different from that under the symmetrical load condition. The deformations on the side under higher loading are larger than corresponding values under the lower loading side. The deformations of central position along the long side of deep foundation pit is larger than those of two sides, central position along the long side of deep foundation pit is the weakest area in the whole foundation pit. The axial force of steel support is related to the horizontal displacement increment of retaining structure in the same plane, and the bigger the horizontal displacement increment, the bigger the axial force. Differential settlement of expressway subgrade induced by excavation mainly lies on the side close to deep foundation pit. Influenced by end effect, the deformations of two sides along the short size are smaller than those of two sides along the long size of deep foundation pit obviously. Lastly, some engineering suggestions were provided for similar projects based on studies.