真空预压法中塑料排水板弯曲对固结的影响

 工程实践表明，真空预压法处理超软弱地基时因过大的地基压缩量而使塑料排水板弯曲，导致其纵向通水量减少，进而影响深层土体的加固效果。为降低这种影响，提出二次插板方案，即先对浅层土体进行处理，待其达到一定强度后，再插设较长的塑料排水板对软基进行整体加固。结合浙江省温州丁山垦区围垦造陆的真空预压工程，对不同弯曲率的塑料排水板进行纵向通水量的测试以确定其纵向渗透系数在加固过程中的变化，并基于ADINA有限元软件，开发邓肯–张本构模型，在三维有限元数值模拟中考虑排水板纵向渗透系数的变化和超软弱土中未消散的初始超孔压。分析比较数值计算结果与监测数据，结果表明，二次插板方案所产生的沉降与孔压消散值均比一次插板方案的要大，计算时考虑排水板弯曲对固结的影响比未考虑这种影响的计算值更接近实际值，所得结论可为类似工程的设计和施工提供理论支持。

EFFECTS OF BENDED PLASTIC DRAINAGE PLATES ON CONSOLIDATION CAUSED BY VACUUM PRELOADING

The practices show that the plastic drainage plates would be bended because of the large settlement of soft foundation treated by vacuum preloading，which makes the longitudinal drainage content of prefabricated vertical drains(PVDs) decreasing then impairs the improvement performance of the deeper layer soil. To decrease the influences，the scheme of twice installation of PVDs was proposed for the ultra-soft foundation，which meant that the shallow-layer soil was treated firstly then the longer PVDs would be installed to improve the whole foundation as the shallow-layer soil had certain bearing capacity. Combined with the vacuum preloading engineering in the reclamation project of Dingshan reclamation area in Wenzhou city，Zhejiang province，the longitudinal drainage content of PVDs was measured under the different bended states to estimate the variation of the vertical permeability of PVDs during the improvement. The Duncan-Chang constitutive model was developed based on the FEM program automatic dynamic incremental nonlinear analysis(ADINA)，then the permeability variation of the bended PVDs and the initial un-dissipated excess pore water pressure were considered in 3D FEM simulation. Comparing the calculated results with the field data，it showed that the settlement and reduction of pore pressure caused by twice installation of PVDs were more than that caused by once installation of PVDs，and the calculated results were more approximate to the field data when considering the influence of the bended PVDs. The conclusions can be useful for the design and construction of the similar engineering.