超大沉井基础取土下沉刃脚土压力变化规律研究

Variation trend of soil pressure under cutting edges of the super large caisson during sinking stage

依托常泰长江大桥主塔沉井基础工程,采用三维有限元方法,模拟了大型沉井首次取土下沉阶段刃脚土压力的变化过程,并结合现场刃脚土压力实测数据,分析了沉井下沉工序对刃脚土压力分布的影响以及取土过程中刃脚土压力的变化规律。现场监测结果表明:刃脚实际土压力变化规律基本上佐证了数值模拟结果。井孔内取土导致取土区域沉井刃脚处土压力下降,取土区域刃脚土压力随取土厚度的增大而逐渐降低,土体压应力转移至尚未取土区域的刃脚处。在由内井孔向外井孔区域取土的过程中,刃脚土压力向外井孔刃脚区域转移,导致外井壁和外隔墙区域刃脚土压力逐渐增大,直至达到其极限承载力,外井壁区域土体进入塑性状态,沉井出现明显下沉。给出的沉井刃脚处土压力的变化规律可为同类大型沉井可控下沉提供指导。

Relying on the foundation engineering of the main tower caisson of Changtai Yangtze River Bridge, the variation of the soil pressure under the cutting edges of the caisson is modeled in the initial sinking stage by finite element method(FEM). In combination of the field measurements of the soil pressure, the variation trend of the soil pressure is analyzed along the cutting edges of the caisson during the excavation steps. The study shows that the numerical results are in agreement with the field measured soil pressures. The soil pressure will decrease in the region where the soil is excavated in caisson cells. It decreases more obviously while the excavation becomes deeper, and the soil pressure will increase in the cutting edges of the neighbouring caisson cells. In the process of excavation from internal caisson cells to outer ones, the soil pressure of the cutting edges of the outer bulkhead and skin of caisson accumulates. Finally, the soil reaches the bearing capacity and it develops into plastic state. The caisson sinks obviously. The work performed in the paper helps guide the smooth sinking of the similar caisson.