深基坑钢支撑预加力对围护墙变形影响

深基坑工程的钢支撑轴力初始实测值时常小于设计预加力。预加力的不足严重影响钢支撑的支撑效果，是造成深基坑围护墙出现较大变形的一个重要因素。以南京某地铁车站深基坑工程为例，运用Midas GTS软件建立二维数值计算模型。基于现场监测数据与数值计算结果，验证了计算模型与参数的合理性；分析不同预加力值对围护墙水平位移值、钢支撑最终轴力值的影响。研究表明：预加力是克服钢支撑的理论抗压刚度小的有效方法，是提高钢支撑的实际抗压刚度的手段；以钢支撑轴力设计值为参考，预加力比值与围护墙深层水平位移最大值具有负线性关系，对支撑轴力最终值的影响不显著；从施加的预加力效果看，预加力比值为40%时，经济性最佳。最后提出了低、高双向预警和对应的预加力取值方法。

Influence of Inner Steel Strut Prestress on the Retaining Wall Deformation of Deep Excavation

The measured steel strut stress is often less than the design value of steel strut prestress in deep excavation engineering. The insufficient of steel strut prestress has an important effect of the steel strut reducing the large deformation of the retaining wall of excavation. A two-dimensional numerical calculation model as a subway station case in Nanjing was established by using Midas GTS software. The suitability of the calculation model and parameters was verified by the comparison of the field monitoring data and numerical calculation results. Then the influence of the strut prestress value on the horizontal displacement of the retaining structure and the final steel strut stress was analyzed. The results show that the steel strut prestress is an effective method to overcome the small compressive stiffness of steel strut in the theory and improve the actual compressive stiffness of steel strut supporting. Taking the design value of steel strut prestress as a reference, the prestress ratio has a negative linear relationship with the maximum horizontal displacement of the wall, and insignificant influence on the final value of strut stress. The economy is the best for 40% of the prestress ratio in the effect of strut prestress. The low and high bidirectional warning method and the corresponding strut prestress ratio are also proposed on basis of the strut stress particularity.