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Numerical simulation of vertical crack propagation in paddy fields based on nonlinear fracture mechanics

基于非线性断裂力学的稻田垂直裂纹扩展数值模拟

基本信息

批准号：
17580218
负责人：
YOSHIDA Shuichiro
金额：
$ 2.04万
依托单位：
National Agricultural Research Organization
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

Mechanics of crack formation were described using Crack Tip Opening Angle (CTOA) measured with fractography soil were used. Fracture testing used deep-notch bend specimens formed by moulding a mixture of Ca-bentonite and silica sand, and a paddy soil at the liquid limit into rectangular bars, equilibrating to soil water suction ranging from 5 kPa to 50 kPa (with some 50kPa specimens wetted to 5kPa), and inserting a flaw 0.4 x specimen thickness. The growth and geometry of the cracks were quantified from a series of images. CTOA measured during stable crack growth decreased with drying. CTOA decreased even further when specimens equilibrated initially to 50 kPa were rewetted to 5 kPa. These results suggested CTOA was primarily governed by the stiffness, although rewetting probably altered the capillary stresses in advance of the crack tip.Vertical crack propagation was studied in a laboratory-scale model subject to shrinkage. Soil installed in a container was consolidated by compression pressure. After removing the pressure, a vertical flaw was formed at the center, and then the specimen was subject to water suction imposed to both sides made of permeable ceramics. Observed CTOA values were compared with those measured by the bending tests. CTOA values in shrinkage were similar to those in bending, suggesting it is practically sufficient to use CTOA obtained by the bending tests for the simulation of shrinkage-induced cracking.A numerical model was developed based on the coupled mechanical and hydraulic analysis of soil. The model is consists of a main program which calculates the deformation of soil due to depletion of soil water, and a module which determines progress of the crack tip by referring to current and critical CTOA. Test runs of the model proved that the predicted crack depths were practically corresponded to those measured in the field where parameters for the simulation were obtained

裂纹形成的机制，描述了裂纹尖端张开角（CTOA）测量与断口土壤被使用。断裂试验使用深切口弯曲试样，该试样通过将钙基膨润土和硅砂的混合物以及处于液限的水稻土模塑成矩形棒而形成，平衡至5 kPa至50 kPa范围内的土壤水吸力（一些50 kPa试样润湿至5 kPa），并插入0.4 x试样厚度的裂纹。从一系列图像中量化裂纹的生长和几何形状。在稳定裂纹扩展过程中测得的CTOA随干燥而降低。当最初平衡至50 kPa的试样再润湿至5 kPa时，CTOA甚至进一步降低。这些结果表明，CTOA主要是由刚度，虽然再润湿可能会改变毛细应力提前裂纹tip.Vertical裂纹扩展进行了研究，在一个实验室规模的模型收缩。土壤安装在一个容器中，通过压缩压力固结。在去除压力后，在中心处形成垂直裂纹，然后对由渗透性陶瓷制成的试样的两侧施加水吸力。将观察到的CTOA值与弯曲试验测得的CTOA值进行比较。基于土的力学-水力耦合分析，建立了数值模型。该模型由一个主程序，计算土壤的变形，由于土壤水的消耗，和一个模块，确定裂纹尖端的进展，参考当前和临界CTOA。模型的试运行表明，预测的裂纹深度与现场实测的裂纹深度基本一致，并得到了相应的模拟参数