Bearing capacity and settlement behaviour of foundations in unsaturated soils

即使是半干旱和干旱区非饱和土的基础设计，也通常采用适用于饱和土的经典土力学。这可能是由于缺乏可用于测量原位土壤吸力的简单工具和与传统岩土工程实践协议一致的简单框架。申请人将进行三种不同的研究活动来关注这些问题：(i)测量吸力的简单技术：建议使用一种简单的工具-口袋渗透计来估计细粒非饱和土壤的原位吸力值（即小于500千帕，这是具有重要实际意义的）。该技术是基于细粒土的渗透阻力与吸力值之间存在强烈关系的假设。（ii）解释非饱和土壤地基的承载力和沉降行为：申请人提出了简单的技术来预测粗粒和细粒土壤的承载力，基于模型基础研究，使用饱和土壤特性和土壤-水特征曲线。进一步研究深度、倾角、形状、尺寸和标度因子对非饱和土承载力的影响，提出非饱和土的一般承载力方程。申请人提出了一种非饱和粗粒土的沉降行为估计技术，扩展了弹性方法。将采用类似的方法来估计沉降行为，使用压缩性行为作为非饱和细粒土的工具。(3)膨胀土的膨胀压力和膨胀压力估算方法简单：目前使用的估算膨胀土的膨胀压力和一维膨胀压力的方法繁琐且耗时，膨胀土是典型的非饱和土。申请人建议开发一种简单的技术，仅利用塑性指数信息和活动区天然含水量随深度的变化来预测天然膨胀土的膨胀压力和隆起。

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.