超深软土区真空预压对复合地基的影响及其防治

Influence of Vacuum Preloading on Composite Foundation in Ultra-Deep Soft Soil Area and Its prevention

在超深软土区,地块进行真空预压处理时可能会对近邻既有复合地基产生不利影响,针对性分析这种影响并寻求实用的防治方法具有重要意义。本文以某深厚软土区实际工程为原型,建立了平面应变模型,还原路侧真空预压过程,探索了复合地基受到的影响,并分析了4种对策的效果。结果表明:(1)真空预压产生的水平位移在场地边缘最大,场地边缘与复合地基之间的过渡区变形剧烈,承受了两个区域之间主要的水平和沉降变形差;(2)对于低渗透性的软土,真空预压产生的沉降主要集中在地表以下15 m范围内,深层的排水板对沉降贡献率低;(3)负压经历了从排水板向土体,从上至下的传递过程,排水板与土体之间的孔压差随着排水板深度增大而减小;(4)群桩中边桩侧向位移最大,弯矩是桩破坏的控制指标,群桩可能从边桩破坏,然后向地基中心蔓延;(5)增大场地处理边缘与路基距离、复合地基施工前先对路基进行真空预压处理、缩短地路基边缘排水板的长度以及在过渡区靠近路基一侧增加钢混支护,均是控制复合地基变形和受力的有效措施。

In the ultra-deep soft soil area,the vacuum preloading treatment may have adverse effects on the adjacent composite foundation.It is of great significance to analyze these effects and seek practical prevention and control methods.Based on the practical project in ultra-deep soft soil area,a plane strain model was established to restore the vacuum preloading process,explored the impact on composite foundation,and analyzed the effects of countermeasures.Results showed that:(1)the horizontal displacement caused by vacuum preloading was the largest at the site edge,and the deformation of the transition zone between the site edge and the composite foundation was severe,which bearded the main horizontal and settlement deformation difference between the two areas.(2)For the soft soil with low permeability,settlement caused by vacuum preloading was mainly concentrated within 15m below the surface,and the contribution of deep prefabricated vertical drain(PVD)to the settlement was very low.The negative pore pressure experienced the transmission process from the PVD to the soil,from top to bottom.(3)The pore pressure difference between the PVD and the soil decreased with the increase of the depth of the PVD.(4)The lateral displacement of side pile was the largest.The analysis of tension,bending and shear showed that bending moment was the control index of pile failure.The pile group may be damaged from the side pile and then to the foundation center.(5)Increasing the distance between the site to be treated and the subgrade,pretreatment of vacuum preloading before the construction of composite foundation,shortening the length of PVD near subgrade and adding reinforced concrete support on the roadside were all effective measures to control the deformation and stress of composite foundation.