考虑加载时序的真空堆载联合预压地基解析近似计算方法研究

Study on Analytical Approximate Calculation Method of Vacuum-surcharge Preloading Foundation Considering Loading Time Sequence

真空堆载联合预压加固软土地基理论研究滞后于实践应用。引入经典砂井地基固结方程,将单砂井地基上、下端边界假设为接近实际情况的半透水边界,考虑真空、堆载荷载的实际施加组合时序,合理界定初始边界条件,推导符合地质和施工实际情况的真空堆载联合预压工法下单砂井地基孔压、固结度及固结沉降解析解。针对一个高速铁路真空堆载联合预压加固软土地基工程项目,敲定各项参数并做简化转化,计算土体孔压时空分布规律、沉降变化规律等。计算结果与实测值对比分析表明:所获得的整个地基孔压、固结度和固结沉降计算公式,能揭示真空堆载联合预压软土地基孔压、固结度、固结沉降变化规律;可将真空堆载联合预压阶段的堆载荷载分级瞬时施加,土体的孔压、固结沉降等响应更为合理;单纯真空预压阶段,不同深度处各点孔压最终稳定在不同的恒定值;真空堆载联合预压阶段,不同深度处的各点孔压最终稳定在相同的恒定值;真空堆载联合预压阶段的堆载前期,真空荷载占主导地位,中后期堆载荷载作用才凸显出来;提出了计算参数u_(0)、u_(tt)、u_(tt)、u_(tl)概念,并开发了这些参数的合理经验取值方法,计算结果证明了方法的合理性。

The theoretical research of vacuum-surcharge preloading for strengthening soft foundation lags behind the practical application.Based on the classical consolidation equation of a sand-drain foundation,the upper and lower boundaries of a single sand-drain foundation were assumed to be impeded boundaries close to the actual permeability.Considering the actual application time sequence of vacuum load and surcharge,the initial boundary conditions were reasonably defined.The analytical solutions were deduced for the pore water pressure,consolidation degree,and consolidation settlement of a single sand-drain foundation in line with the actual geological and construction conditions.Aiming at a soft foundation strengthening project of high-speed railway,various parameters were finalized and simplified,and the temporal and spatial distribution law of soil pore pressure and settlement change law were calculated.The results show the following:the derived formulas can reveal the variation laws of pore pressure,consolidation degree and consolidation settlement of soft foundation under vacuum-surcharge preloading.The surcharge load in the stage of vacuum-surcharge preloading can be graded and applied instantaneously,with more reasonable response of pore water pressure and consolidation settlement of soil.In the single vacuum preloading stage,the pore water pressure at each point at different depths ultimately stabilizes at different constant values.In the stage of vacuum surcharge combined preloading,the pore water pressure at different depths ultimately stabilizes at the same constant value.In the early stage of vacuum-surcharge preloading,vacuum load is dominant.The effect of surcharge is prominent in the middle and late stages.The concepts of calculation parameters(u_(0)、u_(tt)、u_(tt)、u_(tl))were put forward,and reasonable empirical value method of these parameters was developed.The calculation results proved the rationality of the methods.