碎石桩-排水板组合型复合地基固结解析解

Analytical Solution of Consolidation of the Composite Foundation Reinforced by Stone Columns Combined with Vertical Drains

碎石桩-排水板组合型复合地基以成本低、固结速率快及加固效果好等优势被广泛应用于工程实际。虽然目前竖井地基或碎石桩复合地基固结理论已较为完善,但同时包含以上两种排水体的复合地基固结理论还鲜见报道。此外,以往固结模型中土体内孔隙水在径向仅发生单向渗流,这与实际情况存在差别。基于此,以碎石桩-排水板组合型复合地基为研究对象,考虑外荷载作用下土中孔隙水分别向碎石桩和排水板发生径向渗流,在复合地基顶面排水、底面不透水条件下建立碎石桩-排水板复合地基固结模型。利用桩体、桩周土体和竖井间流量相等的连续条件,获得该模型的解析解答。在一定条件下,该解答可退化为碎石桩复合地基固结解或竖井地基固结解,表明该解答的普适性及正确性。将该解答应用于工程实例及室内模型试验的沉降计算,计算结果与实测值吻合较好。开展大量计算研究此类复合地基不同工况下的固结性状,结果表明:在碎石桩桩间打设排水板,能有效提高复合地基固结速率,复合地基固结速率随排水板数量增加而加快;排水板渗透系数对复合地基固结速率及沉降速率的影响较大;与传统复合地基技术相比,碎石桩桩间增设排水板的工法具有更好的经济价值。

Composite foundations reinforced by stone columns and vertical drains are widely utilized in various projects due to their low cost,high consolidation rate,and effective reinforcement.Although the consolidation theory of a single vertical drain or stone column composite foundation is well-developed,reports on theories involving both types of drainage bodies are scarce.Previous models only accounted for unidirectional seepage of pore water in the radial direction,which diverges from the actual situation.Therefore,a theoretical model that accounts for bidirectional seepage of pore water under external loading in the radial direction is proposed.This model features a permeable top and an impermeable bottom,and the analytical solution is derived from the seepage continuity conditions of the stone columns,vertical drains,and surrounding soils.Under certain conditions,this solution may be simplified to the consolidation models for foundations with either a single stone column or a vertical drain,thereby demonstrating the universality and accuracy of the approach.Subsequently,the solution is applied to the settlement calculations of both an actual project and an indoor model test,with results aligning well with the measured data.The analytical solution is further employed to investigate the consolidation behavior of the composite foundation in detail.The results indicated that the consolidation rate significantly benefits from the installation of vertical drains between stone columns.Besides,the consolidation rate increases with the number of vertical drains,and the permeability coefficient of these drains greatly influences both the consolidation and settlement rates.Compared to reducing the column spacing in classical composite foundation technology,installing vertical drains between stone columns has higher economic value.