Model tests and simulation analyses on lateral deformation characteristics of PVD-improved ground
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摘要:
为探明不同预压模式下塑料排水板（prefabricated vertical drains，PVD）处理软土地基的侧向变形特性，以指导软土地区相关工程的设计与施工，通过室内大比例模型试验对比分析堆载预压和真空联合堆载预压下PVD地基的侧向变形特性。此外，结合有限元仿真分析，系统研究真空联合堆载预压下堆载速率（LR）、堆载大小（ps）和真空压力大小（|pv|）对PVD地基侧向变形的影响规律。研究表明：真空联合堆载预压相较堆载预压可以匹配更快的堆载速率和更大的堆载，且达到最大堆载后的后续固结阶段，PVD地基的向外侧向变形并无明显增长，反观堆载预压工况，地基的最大向外侧向变形仍可增长达10%，局部深度位置侧向变形可增长超30%。真空联合堆载预压下PVD地基的侧向变形轮廓整体随ps与LR的增加及|pv|的减小而向预压区外侧移动，且地基的侧向变形速率及最大向外侧向变形（δom）深度随之增加。此外，堆载施加过程中PVD地基的向外侧向变形呈阶梯型规律增加，其最大值δom近似随ps增加而线性增大，随LR增加及|pv|减小而非线性增长。同等荷载改变量下，|pv|的改变相较于ps改变对地基侧向变形的影响更为显著。研究结果可为真空联合堆载预压处理软土地基的分析与设计提供参考。
Abstract:To explore the lateral deformation characteristics of prefabricated vertical drains (PVD)-improved soft ground under different preloading loads and provide guidance for the design and construction of relevant structures in soft deposit regions, this study analyzed the lateral deformation characteristics of PVD-improved ground under surcharge preloading and combined vacuum and surcharge preloading using large-scale model tests. The influence of loading rate (LR), surcharge load (ps), and vacuum pressure magnitude (|pv|) on the lateral deformation of PVD-improved ground under combined preloading was systematically studied using finite element analyses. The results show that the preloading under combined vacuum and surcharge could match faster loading rates and larger surcharge loads compared to surcharge preloading alone. In the subsequent consolidation stage after reaching maximum surcharge load, there is aninsignificant increase in the outward lateral deformation of PVD-improved ground under combined preloading; in contrast, the maximum outward lateral deformation of the ground under surcharge preloading could still increase by 10%, and the lateral deformation of localization depths could increase by over 30%. The lateral deformation profile of PVD-improved ground under combined preloading overall moves outward with the increase of ps and LR, and the decrease of the |pv|; meanwhile the lateral deformation rate and the depth of the maximum outward lateral deformation (δom) increase. The outward lateral deformation of PVD-improved presents step growth patterns during the surcharge loading process, and the δom increases approximately linearly with the increase of ps, but increases nonlinearly with the increase of LR and the decrease of |pv|. With the same load change, the variation in |pv| has a more significant impact on the ground lateral deformation compared to the variation in ps. This study can provide basic information for the analysis and design of soft ground improvement under combined vacuum pressure and surcharge load.
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表 1 试验工况
Table 1. Test conditions
工况 pv/kPa ps/kPa LR/（kPa·d−1） 堆载预压 工况1 0 44 2 工况2 0 44 3 真空联合堆载预压 工况3 −65 60 4 工况4 −65 60 6 注：由于真空压力（pv）为抽吸荷载，为区别于堆载荷载，因此用负值表示真空作用。 
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表 2 预压静置后模型地基的物理力学参数
Table 2. Physical and mechanical properties of model ground after preloading and resting
荷载模式 γt/（kN·m−3） $w' $ /%$w $ /%e0 H0/m POP/kPa 仅堆载 16.22 80.8 62.4 1.650 0.72 6.125 真空联合堆载 15.47 100.0 70.0 1.875 0.65 3.500 注：γt为经砝码预压静置后的地基土的初始重度； $w' $ 为填筑模型地基时所用流塑态土体的含水率；$w $ 、e0和H0分别为填筑完成并经砝码预压静置后的模型地基的初始含水率、初始孔隙比和初始厚度；POP为模型地基的先期固结压力与其自重应力的差值（即静压砝码对应的压力值）。
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表 3 模型地基的本构模型参数
Table 3. Constitutive properties of model ground
参数 γt/（kN·m−3） λ κ e0 K0 M kv/（m·d−1） kh/（m·d−1） khp/（m·d−1） POP/kPa 取值 15.47 0.2523 0.0505 1.875 0.558 1.41 2.35×10−5 3.53×10−5 1.41×10−5 3.5
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表 4 加载参数分析工况
Table 4. Simulation conditions of loading parameters
工况 pv/kPa ps/kPa LR/（kPa∙d−1） 影响因素 备注 M1 −65 60 2 LR M2 −65 60 3 M3 −65 60 4 M4 −65 60 5 加载破坏 M5 −65 48 4 ps M6 −65 52 4 M7 −65 56 4 M8 −50 48 4 pv 加载破坏 M9 −55 48 4 M10 −60 48 4
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