Bearing capacity and settlement behaviour of foundations in unsaturated soils

传统上，即使是半干旱和干旱地区的非饱和土地基设计也采用适用于饱和土的经典土力学。这可能是由于缺乏简单的工具，可用于测量现场土壤吸力和一个简单的框架，是符合传统的岩土工程实践协议。申请人将开展三项不同的研究活动，重点关注这些问题：（一）测量吸力的简单技术：现场吸力值（即，小于500 kPa，这是显着的实际利益）在细粒非饱和土提出了估计使用一个简单的工具，口袋流量计。该技术是基于这样的假设，即细颗粒土壤的吸力值与土壤电阻率计的阻力之间存在很强的关系。(ii)解释非饱和土壤中地基的承载力和沉降特性：申请人提出了简单的技术，用于预测粗粒和细粒土壤的承载力，其基础是利用饱和土壤特性和土壤-水特征曲线进行的模型基础研究。进一步研究深度、倾斜度、形状、尺寸和比例因子对非饱和土承载力的影响，提出非饱和土承载力通用公式。申请人提出了一种技术，用于估计非饱和粗粒土壤中的沉降行为，扩展了弹性方法。对于非饱和细粒土，将采用类似的方法，利用压缩性特性作为工具来估计沉降特性。(iii)膨胀土胀缩和胀缩压力估算的简单方法：膨胀土是非饱和土的典型代表，目前常用的膨胀土胀缩和一维胀缩估算方法繁琐且耗时。申请人提出开发一种简单的技术，仅使用塑性指数的信息和天然含水量相对于活动区中的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.