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.