沉井提吊下沉锁口圈梁变形及应力响应分析

Deformation and Stress Response of Caisson Lifting and Sinking Lock Ring Beam

传统沉井施工下沉过程不可控,受土层性质及开挖方式影响大。沉井提吊下沉可对下沉状态进行主动控制,能够有效解决软土地区下沉过程突沉、超沉等一系列问题,然而,提吊下放过程中井外锁口圈梁需承受上部提吊反力,其力学行为尚不明确。依托昆山市森林公园地下智能停车库项目,针对沉井提吊下沉施工特点,建立提吊力与锁口受力力学模型,通过三维有限元模拟,探究沉井提吊下放过程锁口圈梁变形及应力变化规律。结果表明:提吊下沉施工时锁口圈梁收敛变形存在差异,沿深度方向呈上扩外缩变化,沿平面方向变形由圆形向玫瑰形过渡;下沉过程中锁口圈梁外侧边缘沉降最大,地表沉降影响范围沿提吊系统向两侧减小,影响范围为0.6~1.1倍下沉深度;由于下沉前对沉井锁口下部局部土体进行加固,与锁口梁接触角缘位置产生应力集中现象,设计时应对该处进行结构加强。

The sinking process of the traditional open caisson construction is uncontrollable and is greatly influenced by the soil stratigraphy and the excavation method.The active control of the sinking state by the lifting and sinking of the open caisson can effectively solve a series of problems,such as,sudden sinking and over sinking in the sinking process in the traditional soft soils.However,during the lifting and lowering process,the lock ring beam outside the well needs to resist the upper lifting re-action force,and its mechanical behavior is not clear.This paper presents a case history of an underground intelligent parking garage project of Kunshan Forest Park.A mechanical model of lifting and locking forces is established according to the charac-teristics of the open caisson lifting and sinking construction.By using the three-dimensional finite element simulation,the de-formation and stress changes of the lock ring beam during the lifting and lowering of the open caisson are evaluated.The results show that there are differences in the convergence deformation of the lock structure during the lifting and sinking process.It expands upward and contracts outward along the downward direction,and transits from circular to oblong shape along the ra-dial direction;During the sinking process,the settlement at the outer edge of the lock ring beam is the largest.With the sink-ing of the open caisson,the influence range of surface settlement decreases to both sides along the lifting system,and the influ-ence range is O.6~1.l times of the sinking depth;Before sinking,due to the reinforcement of the local soil at the lower part of the caisson lock,the stress concentration occurs at the contact corner edge with the lock mouth beam,the structure should be strengthened at this location in the design.