陡峭岩面双壁钢围堰稳定性分析及风险评估

根据某长江大桥索塔基础工程施工的主要特点,综合考虑4种水中基础围堰方案的优缺点,确定该索塔基础采用锚固柱桩方案;分析现有的钢围堰计算理论,基于钢围堰的施工工艺,研究该长江大桥索塔基础的钢围堰在封底混凝土对围堰侧压力、混凝土及钢围堰重力、钢围堰刃脚摩擦力、抗滑桩及封底混凝土抗剪承载力、流水压力作用下的力学特点,基于各工况的受力特点分别建立力学模型计算公式,构建综合考虑抗滑安全系数及风险后果影响的钢围堰整体抗滑风险模型。研究结果表明:根据《建筑基坑支护技术规程》(JGJ 120-2012)要求,钢围堰在第1,2,3工况时的抗滑安全系数分别为1.607,1.716,4.684,大于规范中1.3要求;该长江大桥在钢围堰施工阶段的总体风险水平为5.6381,风险等级为3级。

Stability Analysis and Risk Assessment of Double-wall Steel Cofferdam on Steep Rock Surface

The advantages and disadvantages of four kinds of water-based cofferdam schemes were considered according to the main characteristics of the cable tower foundation construction of the Changjiang bridge; the column anchor pile scheme was finally considered for the foundation of cable tower. The theory of the existing steel cofferdam was analyzed. Based on the construction technology of steel cofferdams, mechanical characteristics of the backend concrete that provides side pressure, gravitational pull on concrete and steel, frictional force between the blade foot, shear-bearing capacity of anti-sliding piles and backend concrete, and flow pressure was studied for the Yangtze River Bridge cable tower basic steel cofferdam. A formula was set up for the mechanical model based on the working conditions of the mechanical characteristics. An overall anti-skid risk model for the steel cofferdam was constructed, while taking into account the influence of anti-skid safety factor and risk consequences. Based on the standard of Technical Specification for Retaining and Protection of Building Foundation Excavations (JTJ 120-2012), the overall stability safety factors for cases 1, 2, and 3 were 1.607,1.716, and 4.684, respectively; these values are higher than the requirement of 1.3. Considering that the risk of overall instability for steel cofferdam during the construction stage of the Changjiang bridge, as estimated by this method, is 5.639 8, the risk level is 3.