真空荷载下超软土固结试验及土颗粒移动数值模拟研究

Consolidation test and numerical simulation of particles movement to ultra-soft soil bearing vacuum load

新近吹填超软土经真空预压浅层加固后，普遍会在排水板周围形成土体强度相对较高的小范围区域，该区域范围内的土体较密实，抗剪强度较高，而沉降较小，即所谓的“土桩”，“土桩”范围外的土体固结效果较差，造成大面积吹填淤泥现场加固不均匀现象。针对以上现象，首先进行了吹填土无砂真空预压室内模型试验，并研究土体在加固过程中颗粒组成、沉降、孔压水头高度和含水量的变化情况；其次采用颗粒流数值软件PFC^2D从微观角度进行模拟，探究土颗粒的移动情况。室内模型试验结果：真空顸压加固后，土体产生不均匀沉降，排水板处产生半径为20～25cm明显的隆起，排水板附近土体细颗粒含量和密实度明显升高，渗透系数下降，形成一个相对密实和弱透水性的“土桩”现象。数值模拟分析表明：土颗粒在土体表面负压影响下向下移动是土体固结下沉的原因，排水板附近的土颗粒在排水板负压影响下向排水板方向移动，是形成“土桩”的根本原因。

After consolidated by vacuum preloading, recently superficial hydraulic filled mud soil commonly forms a small region, which has a higher strength around the drainage plate. This zone with a higher density, greater shear strength and small settlement, is so-called the ＂soil pile＂. The poor consolidation result of the region outside the ＂soil pile＂ causes uneven reinforcement phenomenon in a large blow filled silt field. To analysis this phenomenon, we firstly conduct an indoor model test of superficial hydraulic filled mud soil under vacuum preloading to research the particle composition, settlement, pore pressure head height and water content. Secondly, we adopt numerical analysis software PFC2D to explore particle＇s forming mechanism from the micro sight. The indoor model test shows that uneven settlement is formed in soil after vacuum preloadilag. Obvious uplift is developed around the drainage plate with the radius of 20 cm to 25 cm. The content and density of fine particle gains highly, and its permeability coefficient decreases around the drainage plate, forming a relatively dense and weak permeability ＂pile＂ phenomenon. The numerical simulation indicates that under the influence of negative pressure, particles moving down results soil＇s consolidation. With the effect of negative pressure in drainage plate, soil particles nearby drainage plate move to drain board direction which result in the ＂soil pile＂.