增压法真空预压加固机理的分析

Improvement mechanism analysis of pressurization vacuum preloading technique

本文从固结过程中有效应力和超静孔隙水压力变化角度对增压法真空预压的防淤堵、加压、卸载作用的加固机理进行分析。对于正常固结软黏土,真空预压过程中发生颗粒移动及其滤膜淤堵的可能性较小。高压充气虽能一定程度上冲刷滤膜防淤堵,但会减小塑料排水板内的真空度及真空度向深层土体传递。停止高压充气后孔压计读数迅速下降,与排水固结理论中超静孔隙水压力逐渐消散的规律存在明显的差异,增压法的高压充气不能施加额外的压力增量。高压充气会使膜下真空度降低,在某种意义上起了卸载的负面作用,导致能源浪费和延误工期。与普通真空预压相比,增压法真空预压加固后土体的孔隙比大、超固结比小、不排水抗剪强度低。

In this paper,the improvement mechanism of anti-clogging effect,pressurization effect and unloading effect is analyzed from the perspective of the change of effective stress and excess pore water pressure during consolidation process.The particle movement and clogging effect in the vacuum preloading process for normal consolidation clay are not significant.Although high-pressure inflation gas can scour the filter membrane from clogging to a certain extent,it reduces the vacuum degree in the prefabricated vertical drains and the transmission to a deep layer.The reading of pore water pressure gauge drops rapidly after stopping high-pressure inflation,which is fundamentally different from the gradual dissipation of excess pore water pressure of drainage consolidation theory.Thus,the high-pressure inflation cannot supply extra pressure increment.The inflation process reduces the vacuum degree under the membrane and plays a negative unloading role,resulting in increased energy consumption and construction period.Compared with ordinary vacuum preloading,the soil strengthened by pressurization vacuum preloading has larger void ratio,smaller over consolidation ratio(OCR)and lower undrained shear strength.