砂垫层对排水板地基固结效率的影响及设计方法

Effect of sand blanket on efficiency of ground consolidation with prefabricated vertical drains and its design method

针对排水固结软基处理技术中水平向排水砂垫层的设计方法问题,开展流-固耦合固结的三维有限元分析,研究砂垫层渗透系数、厚度和宽度对塑料排水板地基固结的影响规律,揭示固结效率取决于砂垫层参数与土性参数、塑料排水板参数的相关性。据此,将塑料排水板地基径、竖向排水固结解析解等效为纯竖向排水固结解析解,推导能够反映土性参数和塑料排水板参数对地基固结影响的等效竖向渗透系数,并将其与砂垫层参数合理组合,得到综合考虑砂垫层、塑料排水板和土体共同作用对地基固结效率影响的集总参数。通过大量的三维有限元计算,分析该集总参数与地基固结效率之间的关系。给出塑料排水板地基中砂垫层的设计步骤,并结合某工程实例的验算验证该设计方法的有效性。研究结果表明:地基固结效率随集总参数的增大呈双曲线形增加,存在一个满足最优固结效率要求的集总参数值,可作为不同土性及塑料排水板参数条件下砂垫层的设计控制指标。

Three-dimensional finite-element analyses of fluid-solid coupled consolidation were carried out to address the design issue of horizontal sand drainage blanket, which is used in preloading technique for ground improvement. The effects of the hydraulic conductivity, thickness and width of sand blanket on consolidation with prefabricated vertical drains were investigated. The efficiency of consolidation was found to be dependent on the correlations among the properties of sand blanket, soil and vertical drains. Based on this, an analytical solution for radial and vertical consolidation with prefabricated vertical drains was converted to an equivalent analytical solution for purely vertical consolidation. An equivalent vertical hydraulic conductivity was derived. It was capable of reflecting the effects of the properties of soil and drains on consolidation. By reasonably combining it with the properties of sand blanket, a lumped parameter was obtained and used to comprehensively reflect the effect of interactions of sand blanket, vertical drains and soil on the efficiency of consolidation. The relationship between the lumped parameter and the ground consolidation efficiency was analyzed by performing a large number of three-dimensional finite-element calculations. Design procedures for sand blanket in prefabricated vertical drain improved ground were proposed. The validity of the proposed design method was verified by a case study. The results show that the ground consolidation efficiency increases in a hyperbolic manner with the increase in the lumped parameter. There exists a certain value of lumped parameter for satisfying optimum consolidation efficiency. This value can be used as a controlling index for designing sand blanket on ground with various soil and drain＇s properties.