Performance of laterally loaded piles driven in collapsible soils

已知湿陷性土壤由于含水量的增加而经历显著的体积减小，而与载荷增加无关。这反过来又导致湿陷性土壤上的基础设计存在很大问题。易发生湿陷的土包括黄土、胶结砂和粉土以及一些残积土。在加拿大东部和西部、美国、东欧、中国、东南亚以及北方和南部非洲的大部分地区都发现了湿陷性土壤。随着人类活动在这些地区的持续增加，与地基设计相关的问题相应地增加（布兰登等人，1990年; Lim和米勒，2004年）。浅基础与换土或土壤处理相结合的使用构成了薄湿陷性土层上轻型结构的经济设计。然而，对于重型结构和相对较厚的湿陷性土层，桩基础可以安装在覆盖湿陷性土层的合适的承载层上。在这种情况下，基础设计人员应预测湿陷层在结构寿命内的负面作用。然而，在湿陷性土壤中打入的桩可能会在周围土壤变湿时失去现有的轴阻力，因此它们将承受未经计算的拖曳荷载。本建议的目的是研究在垂直和横向荷载作用下安装在湿陷性土壤中的桩的性能。原型模型试验将在Concordia大学的基础工程实验室进行，以模拟所述问题。该模型将能够测量由于部分或全部淹没引起的土体体积变化。实验结果将被用来验证三维有限元模型，开发检查的负载传递机制和敏感性的管理参数。结果将在设计理论方面提出，以预测这些桩的能力。

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.