Study On Rheological Property Of Rockfill By Meso-mechanics Simulation Based On Sub-critical Crack Expansion Theory

Under the background of the implementation and deepening of the Western Development Strategy, quite a few high rock-fill dams are being or to be built in Western China as an important part of the major engineering items such as South-to-North Water Diversion and West-to-East Power Transmission Project. With the height of dams entering the level of300meters, the rockfill particle breakage in high stress areas of a dam body is more prominent. Therefore, stress adjustment and particle location rearrangement caused by particle breakage becomes one of the controlling factors in deformation of the high rockfill dams.Deformation of the high rockfill dams during the period of filling and initial impoundment is mainly caused by particle compacting and tiny particles from breakage filling the pores. After completion and impoundment, the deformation won’t develop along with time if the rockfills do not possess rheological characteristics. However, the monitoring data of numerous built dams around the world show that the long-term deformation of a high dam would be continued after completion and impoundment, which can last for years, more than a decade or even longer. The deformation rate maintains around0.1%of the height of dam, and the maximum deformation is up to3.8%. Then, the stress and deformation behaviors of the panel are deteriorated, which result in the cracks in the face, even the risk of dam break. Unfortunately, the mechanism and observed phenomena of the long-term deformation still could not be clarified unambiguously. Therefore, the rheology behavior of rockfill has become one of the most important technical issues restricting the construction of high rockfill dams. With the support from National Nature Science Foundation of China under Grant50879007, which titled "Study on Rheological Property and Constitutive Model of Rockfill by Meso-mechanics Simulation Based on Sub-critical Crack Expansion Theory", in-depth research was conducted regarding the critical issues including the characteristics of particle breakage and rock-fill rheology mechanism from the microscopic view. The study includes:(1) Preparation of numerical samples and construction of numerical experiment platform.The simulation method for a variety of numerical particles with irregular shape is developed which aims at the characteristics of rockfill, such as irregular shape and prominent interlock behavior. Various types of generation methods for numerical samples and forming techniques for numerical particles are suggested, which can meet certain grading requirements. The numerical experiment platform is built using FISH language to lay the foundation for the next step in this research.(2) The study of particle breakage for rockfill without considering the time effect.The rockfill particle breakage can occur after filling, initial impounding or extreme geological disasters like earthquake. Under the high contact stress conditions, the main crushing modes of particles are characterized by angular breakage of particles and cleavage under high contact stress due to the changes of the external loads. Typical crushing modes are studied according to the actual failure modes of rocks in a series of indoor soil tests. In consideration of rockfill particles breaking during filling, a theoretical model of particles’ brittle crushing has been extended from two dimensions to three dimensions, and particle flow programs are introduced to conduct triaxial shear numerical study, then the microscopic mechanism of rock-fill deformation under triaxial shear is analyzed.(3) The study of sub-critical expansion of cracks and the design of particle flow program for numerical rheological test.According to the theory of sub-critical expansion of cracks, rockfill particles breakage with the time effect is caused by the extension of micro cracks. The influence on the stress intensity factor and extension of crack are studied by discussing the stress on the crack face of particles, geometrical characters of particles and cracks. In order to simulate the rheological lab test of the rockfill, the theory of sub-critical expansion of cracks has been refined, summed up and concluded, and the particle flow programs have been designed and written.(4) The uniaxial and triaxial numerical rheological tests are carried out according to the rheological lab test. The reasonable particle breakage mode is determined, and the evolution of microscopic characteristics for rockfill samples and particles breakage are presented visually during the process of numerical rheology. The relations among the rule of particles breakage, structure change of particles and rheology are synthetically analyzed. Furthermore, the microscopic mechanism of rock-fill rheology is given qualitatively.