大型沉井下沉过程拉应力影响因素分析

Analysis of factors affecting tensile stress of large caisson during sinking

为研究大型沉井下沉过程中的拉应力影响因素,以五峰山长江大桥北锚碇沉井为工程背景,利用ABAQUS有限元软件建立足尺首次下沉沉井数值模型,在利用现场实测数据验证数值模型准确性的基础上,通过控制变量法分别分析初始下沉高度、开挖方式、沉井平面尺寸等因素对沉井基础混凝土拉应力的影响,并据此提出相应的拉裂防控措施。研究结果表明:在大型沉井初始下沉过程中,宽度方向混凝土拉应力往往大于其长度方向,且沉井长宽比越大,宽度方向与长度方向的拉应力比越大,故宽度方向拉应力是工程监控的重点;沉井隔墙拉应力可通过梁的相关理论近似分析,但需考虑隔墙在交点处的相互作用;初始下沉高度、开挖方式及荷载对沉井混凝土拉应力均有较大影响;沉井最大拉应力随着外荷载的增大而线性增大,八区开挖方式比大锅底开挖混凝土最大拉应力减小近90%,增大初始下沉高度可使混凝土最大拉应力减小近50%;增大初始下沉高度和调整开挖方式仅通过改变施工工序即可实现,是较为经济合理的控制井身拉应力的方法;井身混凝土强度、隔墙宽度、井壁宽度等对井身拉应力的影响较小,在沉井下沉过程中无需重点考虑。

To study the influence factors of tensile stress during the sinking process of large caissons, based on the north anchorage caisson of Wufengshan Yangtze River Bridge, the numerical model was built by ABAQUS finite element software and verified by the field measured concrete stress data. The influence factors of concrete stress for caisson foundation, such as initial subsidence height, the excavation method, the plane size of the caisson were analyzed by the control variable method, and the measures for preventing and controlling of pulling cracks of bridge caisson foundation were put forward accordingly. The results show that during the initial sinking process of large caissons, the tensile stress in the width direction of the concrete is often greater than its length direction, and the larger the aspect ratio of the caisson, the greater the tensile stress ratio in the width direction to the length direction. Therefore, the tensile stress in the width direction should be the focus of engineering monitoring. The tensile stress of the caisson partition wall can be approximately analyzed by the theory of beams, but the interaction of the partition wall at the intersection should be considered. The initial subsidence height, excavation method and external load of caisson have a great influence on the tensile stress of concrete for caisson foundations, the maximum tensile stress of the caisson increases linearly with the increase of external load, and the eight zone excavation method reduces the maximum tensile stress of the concrete by nearly 90% compared to the large pot bottom excavation. Increasing the initial sinking height can reduce the maximum tensile stress of the concrete by nearly 50%. Increasing the initial subsidence height and adjusting the excavation method can be achieved only by changing the construction process, which are more economical and reasonable methods to control the tensile stress. By contrast, the influence of concrete strength, partition wall width, side wall width, etc. on tensile stress is relative small, so there is no need to focus on them during the sinking of large caisson.3 tabs, 15 figs, 28 refs.