高铁不同刚度桩-网复合地基工作性状差异

结合沪宁城际铁路CFG桩网复合地基试验段和京沪高铁砂桩网复合地基昆山试验段,在现场试验断面埋置土压力盒、沉降计和孔隙水压计等监测仪器,获取地基沉降、桩和桩间土压力、孔隙水压等监测数据,对比分析CFG桩与砂桩网在高速铁路地基工作性状及工后沉降控制效果中的差异。分析结果表明:CFG桩网和砂桩网联合堆载预压均可满足高速铁路无砟轨道工后沉降控制要求,CFG桩网复合地基沉降总量与沉降速率均小于砂桩网复合地基,且收敛速度快;受桩刚度差异的影响,CFG桩网复合地基与砂桩网复合地基桩土应力规律存在较大差异,前者桩土应力比随着路堤填筑加载而增大,最终趋于稳定,后者桩土应力比随荷载增加先增大后减小,再增大,呈波浪形变化;CFG桩网地基超孔压消散速率远小于砂桩桩网地基的超孔压消散速率;在施工工期较短的情况下,与砂桩网复合地基相比,CFG桩网复合地基处理技术的工后沉降控制效果更优。

Difference analysis on the performance of the pile-net composite foundations with different pile types of high speed railway

The monitoring components were put into the Shanghai-Nanjing intercity railway CFG pile-net composite foundation and Beijing-Shanghai high speed railway sand pile-net composite foundation of Kunshan test section, such as the soil pressure boxes, the settlement gauges and the pore water pressure gauges, etc., to monitor and obtain a large number of ground settlements(post construction), pile tops pressure and soil pressures, pore water pressures and other field test data in order to get variation law of properties of composite foundations. Working behavior of foundation during construction period and post construction settlement control effect were comparatively analyzed between the two different pile types (CFG pile-net and sand pile-net). The results showed that both CFG pile-net and sand pile-net preloading can meet the ballastless track of high-speed railway post construction settlement (less than 15 mm) control requirement according to the field tests. The total settlements and the velocity of settlement of CFG pile-net foundation were smaller than that of sand pile-net foundation, and its convergence speed was faster, which meant the latter requires a longer period of time to load. Affected by the pile stiffness, there was a big difference on the law of stress of pile and soil. The stress ratio of pile and soil in CFG pile-net foundation was increased with the increase of the filling of the embankment, and eventually stabilized, while that of sand pile-net foundation decreases with the increasing of load first, and then increase, presenting the wave shape change. And the CFG pile-net foundation excess pore water pressure dissipation rate was far less than the latter. In the case of short construction period, compared with the composite foundation of sand pile-net, the settlement control effect of CFG pile-net composite foundation treatment technology was more excellent.