全级配水工混凝土宏细观损伤断裂机理及断裂尺寸效应

The present project plans to adopt the combination of experimental study, theoretical analysis, and numerical simulation to conduct a deep and systematic study on such scientific problems as the size effect rule of fully-graded hydraulic concrete fracture criteria, fracture initiation mechanism, and the entire process of damage fracture. Through fracture tests of concrete members meeting different types of similarity ratios, the study will analyze the size effect rule of fully-graded hydraulic concrete macro fracture parameters, will establish a calculation method for the similarity ratio of fully-graded hydraulic concrete fracture parameters, and will ascertain the conversion formulas among fully-graded hydraulic concrete, wet screening concrete, one-graded concrete, and two-graded concrete fracture parameters. The fracture initiation state of the fully-graded hydraulic concrete will be recorded with high-speed photography to study the fracture initiation mechanism and analyze its size effect. Based on the technologies related to Digital Image Correlation, the morphological characters of the fracture process zone of the fully-graded hydraulic concrete will be quantitatively described. The whole dynamic process of extension and development of the fracture process zone of the fully-graded hydraulic concrete will be studied.The three-dimensional random defective interface spring element model will be adopted to simulate the entire microscopic fracture process of the fully-graded hydraulic concrete; consequently, the fracture size effect mechanism of the fully-graded hydraulic concrete will be explained from a microscopic perspective. The current study focuses on the similarity ratio of the fracture criteria of the fully-graded hydraulic concrete and on the evolution process of the entire fracture and mechanism processes. The micro mechanism study on fracture initiation and extension as well as the expected results can provide data for the theoretical analysis of 300 m-graded high-arch dam construction, including cracking-risk evaluation, fracture stability analysis, and safety evaluation, among others.

拟采用试验研究、理论分析、数值仿真相结合的手段，对全级配水工混凝土断裂指标尺寸效应规律、裂缝起裂机理及损伤断裂全过程等问题进行深入系统研究。通过满足不同相似比构件的断裂试验，分析全级配水工混凝土宏观断裂参数的尺寸效应规律，推求全级配与湿筛、一级配、二级配混凝土断裂参数间的换算公式。通过高速摄像记录全级配水工混凝土的起裂状态，研究其起裂机理并分析其尺寸效应。基于数字图像相关技术，定量描述全级配水工混凝土断裂过程区的形态特征，研究断裂过程区扩展与发展的动态全过程。采用三维随机缺陷界面弹簧元模型模拟全级配水工混凝土的细观断裂全过程，从细观角度解释全级配水工混凝土断裂尺寸效应机理。课题研究重点在于全级配水工混凝土的断裂指标相似关系、断裂全过程的演化过程及机理分析，预期成果可为300m级特高拱坝开裂风险评判、裂缝稳定性分析等提供理论基础。

项目采用试验研究、理论分析、数值仿真相结合的手段，对全级配水工混凝土宏细观损伤断裂机理及断裂参数尺寸效应等问题进行了深入系统研究。.提出了利用大坝施工现场拌合楼生产的混凝土拌合物浇筑试件，试验确定全级配水工混凝土真实断裂性能的方法与实施步骤。通过楔入劈拉试验，成功获取描述全级配水工混凝土试件裂缝扩展全过程状态的荷载—裂缝嘴张开口位移全曲线和荷载—裂缝尖端张开口位移全曲线，计算得到评价裂缝扩展特性的相关断裂参数。分析了龄期变化对起裂断裂韧度的影响规律；给出了起裂断裂韧度随试件尺寸的变化规律。研究确定了全级配水工混凝土断裂参数的尺寸效应规律，当试件有效高度增加到1500mm时，各断裂参数趋于稳定，若确定无尺寸效应的真实断裂参数，试件尺寸须满足韧带高度大于等于六倍骨料最大粒径。通过不同尺寸的全级配及对应的湿筛混凝土试件的试验对比分析，建立了湿筛与全级配混凝土断裂参数的换算关系，解决了由小尺寸湿筛混凝土试件的断裂参数推求大尺寸全级配水工混凝土断裂参数的关键技术难题。提出了“等效成熟度”的概念，等效成熟度为等效温度与龄期的乘积，基于不同外界条件下的全级配水工混凝土断裂试验成果及理论分析，建立了断裂参数与等效成熟度的定量关系，为有效控制大坝裂缝提供了定量判据。提出了特高拱坝悬臂高度个性化控制概念，并给出其具体实施方法；悬臂高度个性化控制有利于优化施工进度，缩短施工工期，从而按计划实现坝体挡水度汛及预期发电等关键目标。提出了由试件峰值荷载同时确定全级配水工混凝土等效断裂韧度与临界裂缝尖端张开口位移的方法，峰值荷载法只需实测各试件的峰值荷载，就可方便确定断裂参数。建立了混凝土三维正交各向异性统计损伤本构模型，可描述混凝土复杂荷载环境下的力学行为；建立了混凝土双轴压-压细观统计损伤本构模型。推导出混凝土允许损伤尺度的解析表达式。基于损伤耗散能与断裂耗散能等效原理，给出了混凝土裂缝黏聚律的求解方法，获得了大坝混凝土和湿筛混凝土的黏聚律的具体表达式。给出三维随机缺陷界面弹簧元模型模拟混凝土破坏的数值方法。考虑裂缝黏聚力的作用，基于Paris位移公式推导出混凝土三点弯曲梁裂缝扩展过程中断裂过程区上的裂缝张开位移的解析表达式，采用起裂韧度作为裂缝起裂及扩展的判断标准，提出了荷载作用下混凝土裂缝起裂、扩展及失稳破坏全过程的数值模拟方法。成果可为评价大坝开裂风险和已有裂缝扩展风险等提供科学依据。