Performance of laterally loaded piles driven in collapsible soils

众所周知，湿陷性土壤由于含水量的增加而经历显著的体积减少，而不管负载的增加。这反过来又导致在可湿陷性土壤上的基础设计成为一个很大的问题。易塌陷的土壤包括黄土、胶结砂和粉土以及一些残积土。加拿大东部和西部、美国、东欧、中国、东南亚以及非洲北部和南部的大部分地区都发现了湿陷性土壤。随着这些地区人类活动的不断增加，与基础设计相关的问题也相应增加（Brandon et al., 1990; Lim and Miller, 2004）。使用浅基础结合土壤置换或土壤处理构成了薄湿陷土层轻型结构的经济设计。但是，对于较重的结构和较厚的可湿陷土层，可以在可湿陷土层上的合适承重层上安装桩基础。在这种情况下，基础设计人员应预测可折叠层在结构寿命内的负面作用。而在湿陷性土中打桩，由于周围土体的润湿，桩身原有的桩身阻力可能会丧失，因此桩身将承受未计算的阻力荷载。本文的目的是研究在湿陷性土壤中安装的桩在竖向和横向荷载作用下的性能。原型模型测试将在康考迪亚大学基础工程实验室进行，以模拟所述问题。该模型将能够测量部分或全部淹没时土体的体积变化。实验结果将用于验证三维有限元模型，该模型用于检查负载传递机制和控制参数的敏感性。研究结果将从设计理论的角度提出，以预测这些桩的承载力。

Collapsible soils are known to experience significant volume decreases due to an increase in moisture content, regardless of a load increase. This in turn causes the design of foundations on collapsible soils to be highly problematic. Soils susceptible to collapse include loess, cemented sand and silts, and some residual soils. Collapsible soils are found in major parts of Eastern and Western Canada, USA, Eastern Europe, China, South East Asia, and both Northern and Southern Africa. As human activities continue to increase in these regions, the problems associated to foundation design increase accordingly (Brandon et al., 1990; Lim and Miller, 2004).The use of shallow foundations combined with soil replacement or soil treatment constitute economical designs for light structures on thin collapsible soil layer. However, for heavy structures and relatively thick layers of collapsible soil, pile foundations may be installed to a suitable bearing stratum overlying the collapsible soil layer. In this case, foundation designers should forecast the negative role of the collapsible layer within the lifespan of the structure. Piles driven in collapsible soil however may lose the existing shaft resistance upon wetting of the surrounding soil, and accordingly they will experience uncalculated drag load.The objective of this proposal is to study the performance of piles installed in collapsible soils subjected to vertical and lateral loads. Prototype model tests will be conducted in the Foundation Engineering Laboratory at Concordia University to simulate the stated problem. The model will be capable of measuring the volume change in the soil mass due to partial or full inundation. The experimental results will be used to validate a three dimensional finite element model, developed to examine the load-transfer mechanism and the sensitivities of the governing parameters. The results will be presented in terms of design theory to predict the capacity of these piles.