大轴力桩基托换监测分析

深圳市地铁一期工程百货广场大轴力桩基托换采用梁托换柱的结构型式,托换结构由托换大梁和两根支撑大梁的托换新桩组成,用主动托换方式,在托换大梁和新桩之间安装千斤顶,分级施加主动力。在托换的整个过程中对托换结构进行实时监测,通过反馈监测信息随时掌握托换结构和原建筑物的变形及受力状况,指导安全施工。分别用不同的测试仪测试原建筑物的沉降、梁板附加应力、梁柱接头的滑移,分析梁板附加应力、主动托换力的分配及荷载的转移规律,以及大梁的受力和变形状态。在托换新桩的桩顶垂直于梁轴线方向安装2个位移计,推测桩的沉降及大梁的偏转状况。将所有传感器集成一个自动测试系统,按照制定的监测控制标准,实施自动监测和安全控制。经过对第一根桩的全过程跟踪监测分析表明:托换结构和建筑物的变形及受力控制都在安全标准范围内;主动托换力保持在40%P时进行截桩,可使得托换前后柱的轴力变化和梁柱接头下沉达到最小。

Monitoring and Analysis of Underpinning of Heavy Load Pile Foundation

The pile foundation underpinning of Department Store Plaza in Shenzhen Metro Phase 1 was completed with an "underpinning structure", which consists of a replacing girder and two supporting girders. Active underpinning method was adopted. Between the underpinning girder and the new pile were installed jacks that applied forces in stages. During the whole underpinning process, the underpinning structure was monitored in real time. Through the feedback of monitored information, the deformation of and force application to the underpinning structure were real-time collected so that guidance can be properly given to the work. With different instruments, the original structure settlement, the additional stress of the girder plate, the displacement of the girder/pile connection were measured and the additional stress of the girder plate, the distribution of the active underpinning force, the rule of load displacement, and the forces and deformation of the girder were analyzed. 2 displacement meters were installed on the top of the new underpinning pile in the direction vertical to the girder axle to get the settlement of the pile and displacement of the girder. All sensors were integrated into an automatic testing system. According to the regulated monitoring and control standard, automatic supervision and safety control were executed. Through the monitoring, test and analysis of the full-process tracking of the first pile, it indicates that the deformation of the underpinning work and the structure and the control of forces all stay within the safety standard range. When the active underpinning force is kept at 40% P to cut the pile, the variation of the axle forces before and after the underpinning was the minimum and the settlement of the girder/pile connection was also the minimum.