3-D Characterization and Analytical Description of Desiccation Cracking

这项研究的重点是干燥开裂，以及通过开发无损检测技术或将其应用于易受强度、体积关系和水力特性等特性变化影响的细粒土中，开发裂缝几何信息的必要性。这项研究的目的是发展一种超声波无损检测技术，以确定粘土中干燥裂缝的深度，并将裂缝深度与各种粘土性质联系起来。研究人员将制定一系列与裂缝的发展和扩展有关的预测方程，例如：裂缝深度、表面裂缝密度和裂缝扩展速率作为塑性和活性、矿物学、土壤的初始含水率、压实条件和强度以及应用于土壤的干湿循环的函数。试验分析的裂缝特征包括与裂缝萌生相对应的土壤吸力、扩展深度、表面几何形状、裂缝扩展速率和通过裂缝的水分通量，重点是裂缝对土壤水力性质的影响。这项研究将通过实验确定由于存在裂缝而对流经粘土的流动的影响。超声波方法将为分析土壤中裂缝的深度提供一种创新的工具，并将与先前开发的图像分析技术一起用于确定裂缝的三维特征。这两种方法可用于分析土体中的拉伸裂缝、冻融裂缝或任何其他类型的裂缝。超声波设备也可以很容易地运输到现场进行测试，干燥过程的照片是图像分析所需的唯一输入。预测方程将允许使用基本的土壤特性数据而不是复杂的理论解来确定裂缝的程度。研究结果将应用于在易开裂的土壤上的工程结构的设计和施工，以及垃圾封存设施的建设。此外，这些结果将适用于地下水补给问题、包气带中的污染物运输以及农业问题。

This research focuses on desiccation cracking, and on the need to develop geometric information on crack geometry through the development of nondestructive testing techniques or application to fine grained soils that are susceptible to changes in properties including strength, volumetric relationships, and hydraulic properties. The objective of the proposed research is to develop an ultrasonic nondestructive testing technique to determine the depth of desiccation cracks in clay soils and to relate the depth of cracking to various clay properties. The investigators will formulate a series of predictive equations relating to the development and propagation of cracks, such as: depth of cracking, surface crack density, and rate of crack propagation as a function of plasticity and activity, mineralogy, initial water content, compaction conditions, and strength of soils, and wetting and drying cycles applied to the soils. The crack characteristics that will be analyzed experimentally include soil moisture suction corresponding to crack initiation, depth of propagation, surficial geometry, rate of crack propagation, and moisture flux through cracks, with a focus on the effects of cracking on hydraulic properties of the soils. The research will experimentally determine the modification of flow through the clay as a result of the presence of cracks. The ultrasonic method will provide an innovative tool to analyze the depth of cracking in soils, and will be used together with previously developed image analysis techniques to determine 3-D characteristics of cracks. These two methods can be applied to analyze tension cracks, freeze/thaw cracks, or any other type of crack developing in soils. The ultrasonic equipment can also be readily transported to the field for tests, and photographs of the desiccation process are the only input required for the image analysis. The predictive equations will allow for determining extent of cracking using basic soil characterization data as opposed to complicated theoretical solutions. Results of the research will apply to design and construction of engineering structures on soils susceptible to cracking and construction of waste containment facilities. In addition, the results will apply to groundwater recharge problems, contaminant transport in the vadose zone, and agricultural problems.