Bearing capacity and settlement behaviour of foundations in unsaturated soils

适用于饱和土体的经典土力学通常用于基础设计，即使对于半干旱和干旱地区的非饱和土体也是如此。这可能是由于缺乏可用于现场测量土壤吸力的简单工具和符合传统岩土工程实践规程的简单框架。申请人将针对这些问题开展三项不同的研究活动：(I)简单的吸力测量技术：建议使用一种简单的工具--袖珍渗透仪--估算细粒非饱和土壤中的原位吸力值(即小于500kpa，具有重要的实用价值)。这项技术是基于细粒土的渗透阻力与吸力值之间有很强关系的假设。(Ii)对非饱和土壤中地基的承载能力和沉降行为的解释：申请人提出了一种简单的技术，用于根据利用饱和土壤特性和土壤-水特征曲线进行的地基模型研究来预测粗粒和细粒土壤的承载能力。进一步研究深度、倾角、形状、大小、比例等因素对地基承载力的影响，提出非饱和土地基承载力通用计算公式。申请人提出了一种估计非饱和粗粒土中沉降行为的技术，扩展了弹性方法。对于非饱和细粒土，将采用类似的方法来估计沉降特性，使用压缩特性作为工具。(3)估算膨胀土膨胀压力和膨胀压力的简单方法：目前用于估算膨胀土膨胀压力和一维膨胀压力的方法繁琐且耗时，而膨胀土膨胀压力和一维膨胀压力是非饱和土的典型例子。申请人建议开发一种简单的技术来预测天然膨胀土的膨胀压力和隆起，只使用塑性指数和活跃区天然含水率随深度的变化。

Classical soil mechanics valid for saturated soils are conventionally used for foundation designs even for unsaturated soils of semi-arid and arid regions. This may be attributed to the lack of simple tools available for the measurement of in situ soil suction and a simple framework that is consistent with the conventional geotechnical engineering practice protocols. Three different research activities will be undertaken by the applicant to focus on these issues: (i) Simple techniques for measurement of suction: In situ suction values (i.e., less than 500 kPa, which is of significant practical interest) in fine-grained unsaturated soils are proposed to be estimated using a simple tool, pocket penetrometer. This technique is based on the assumption that there is a strong relationship between the penetrometer resistance and the suction value of fine-grained soils. (ii) Interpretation of the bearing capacity and settlement behaviour of foundations in unsaturated soils: The applicant proposed simple techniques for predicting the bearing capacity of both the coarse- and fine-grained soils based on model footings studies using the saturated soil properties and the soil-water characteristic curve. More studies will be performed to understand the influence of depth, inclination, shape, size and scaling factors to propose general bearing capacity equation for unsaturated soils. The applicant proposed a technique for estimating settlement behaviour in unsaturated coarse-grained soils extending the elasticity approach. Similar approach will be undertaken to estimate the settlement behaviour using compressibility behaviour as a tool for unsaturated fine-grained soils. (iii) Simple techniques for the estimation of the heave and swelling pressure of expansive soils: Presently used techniques are cumbersome and time consuming to estimate the swelling pressure and 1-D heave of expansive soils, which are typical examples of unsaturated soils. The applicant proposes to develop a simple technique to predict both the swelling pressure and heave of natural expansive soils using only the information of plasticity index and the variation in natural water content with respect to depth in the active zone.