3-D Characterization and Analytical Description of Desiccation Cracking

本研究的重点是干燥开裂，以及通过开发无损检测技术或应用于易受强度、体积关系和水力特性等特性变化影响的细粒土壤，开发裂纹几何几何信息的需求。提出的研究目的是发展一种超声无损检测技术，以确定粘土中干燥裂缝的深度，并将裂缝的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发展和扩展有关的预测方程，例如：裂缝深度、表面裂缝密度、裂缝扩展速率（作为塑性和活动性、矿物学、初始含水量、压实条件、土壤强度以及适用于土壤的干湿循环的函数）。实验分析的裂缝特征包括与裂缝起裂相对应的土壤吸湿量、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，重点关注裂缝对土壤水力特性的影响。该研究将通过实验确定由于裂缝的存在而改变流过粘土的流量。超声波方法将提供一种分析土壤裂缝深度的创新工具，并将与先前开发的图像分析技术一起使用，以确定裂缝的三维特征。这两种方法可以应用于分析拉伸裂缝，冻融裂缝，或任何其他类型的裂缝在土壤中发展。超声波设备也可以很容易地运输到现场进行测试，并且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征数据来确定开裂的程度，而不是复杂的理论解决方案。研究结果将适用于易开裂土壤上的工程结构的设计和建造，以及废物围堵设施的建造。此外，研究结果将适用于地下水补给问题、渗透带的污染物输送问题和农业问题。

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.