深基坑锚拉桩上外荷载及其受力变形开挖响应

在基坑的整个开挖过程中,锚拉桩上作用的外荷载是不断变化的,研究支护桩所受土压力和锚索拉力的变化规律及其内力变形开挖响应,对优化桩锚支护结构的设计、保证开挖过程中基坑的稳定性具有十分重要的意义。结合重庆市某深基坑工程,通过FLAC^3D数值模拟、现场监测的方法,分析了在基坑分步开挖过程中锚拉桩所受的土压力和锚拉力的变化规律,以及桩身变形和弯矩随基坑开挖的变化。结果表明:数值分析与现场监测所得规律较为符合;在开挖过程中,支护桩所受的土压力值逐渐由静止土压力向主动土压力转变,开挖完成后呈现“上下小,中间大”的分布特征,最终作用的土压力小于经典理论计算值;锚索预拉力在初始张拉锁定后较短时间内即发生25%~35%的损失,在开挖期间呈现波动增大的趋势,最后稳定值大致为初始预拉力的80%;桩身弯矩和变形的分布形状协调一致,均为朝向基坑开挖侧的外凸型,最大值出现位置经历“从上往下再往上”的变化轨迹。

Excavation Response of the External Loads and Characteristics of Internal Force and Deformation of Anchorage Piles in Foundation Pit

In the process of foundation pit excavation, the external loads of anchorage piles are constantly changing. Therefore, it is of great significance for optimizing the design and ensuring the stability of pit excavation to study the change law of the earth pressure and anchor tension imposed on the supporting piles and excavation response of their inner force and deformation. Combined with a deep foundation pit in Chongqing and through FLAC3D and field monitoring methods, this paper analyzes the change law of the earth pressure and anchor tension suffered by supporting piles and the change of deformation and bending moment with excavation by steps. The results show that numerical analysis results are in line with field monitoring results. The earth pressure gradually changes from static earth pressure to active soil pressure in excavation and the distribution characteristic is “small at top and bottom, big at the middle” after the excavation, and the final working earth pressure value is less than calculation value from classical theory. The anchor pretension will get reduced by 25%~35% shortly after stretch locking, then fluctuate in excavation and finally get its stable value at about 80% of initial tensile force. The bending moments of piles coordinate with the distribution form of deformation, both of which are convex towards the excavation side and keeping the track of the location at maximum from top down and upward again.