冠梁标高对基坑周边环境的影响分析

降低冠梁顶标高以减少基坑工程造价是目前比较盛行的一种做法,但其往往导致基坑周边环境变形过大。以某建筑深基坑工程为例,通过对比该基坑开挖期间周围道路沉降、管线沉降、建筑物沉降、桩顶变形和支撑轴力的实测数据来分析支护结构安全有效、建筑物沉降满足要求,但地表沉降过大现象的原因,认为冠梁标高降低会对基坑顶部土体变形产生较大影响。通过有限元模拟对降低冠梁顶标高对基坑坡顶土体变形的影响进行深入分析。结果表明:坑顶土体变形过大并不意味着支护结构失效;冠梁顶标高降低后,由于坡顶土体失去侧向约束,在坡顶竖向荷载作用下,会产生较大的沉降和水平变形;土体沉降与水平变形具有相关性,但冠梁顶标高对坡顶土体水平变形的影响程度远远超过其对沉降的影响。建议当基坑周围有道路或管线存在时,谨慎降低冠梁标高,如必须降低,应采取其他有效措施约束土体的变形。

Influence analysis of top beam elevation on surroundings around deep pits

Decreasing the top beam elevation to reduce the project cost, which often leads to larger displacement of the surroundings, is very popular in the design of foundation pits. Based on a deep foundation pit project, the phenomenon that the supporting structure is effective, the settlement of buildings meets the design requirements, while the ground settlement is out of control is analyzed by comparing the measured data of the strut forces, displacements of the surroundings and displacements of retaining pile tops. The decrease of top beam elevation is supposed to be a main influence factor for the larger ground settlement. Finally, the finite element simulation method is used to analyze the influence of top beam elevation on the surroundings deeply. The results show that whether the supporting structure is effective or not should not be judged by the displacement of soil at top of the foundation pit. Under the vertical load, large displacement will take place for the soil at top of the foundation pit because of the loss in the lateral restraint caused by the decreasing of top beam elevation. There exists a relationship between the settlement and the horizontal displacement of soil, but the decreasing of top beam elevation has a larger impact on the horizontal displacement than on the settlement. The top beam elevation should not be decreased when roads, pipelines and structures are near to the deep pit, and the effective measures must be taken to restrain the displacement of soil when the top beam elevation is decreased.