Simulation Test Research On The Rules Of Local Deformation And Energy Evolution Of Fractured Rock

Rock mass is discontinuous media, there are large amounts of fractures and holesinside, which make rock behave anisotropic. Extension and connection among jointsand fractures under external loads not only have significant effects on rockmechanical characters, but also be the main cause of local deformation. So, correctlyanalyzing the mechanical character and local deformation process of fracture rock hasan important engineering significance. The nature of rock damage is the result ofenergy dissipation and release from the view of energy, and studying mechanicalfeatures from this point could reflect rock deformation rule factually.This thesis uses similar material to simulate basalt and makes single fracturespecimens with different fracture dip angles and double fracture specimens withdifferent distribution. Using PIV(A particle image velocimetry) to observe the test andthe YY-L600biaxial compression test system to conduct biaxial test under differentstress load ratio. Analyze mechanical character, local deformation process andfracture connecting patterns of specimen. Study energy evolution rule and energyconsumption character of specimen in load process. Main achievements as follows:(1) Sample peak intensity increases as V-shaped fissure angle distribution, theminimum angle is45°and increase as loading rate increases. Strength of the specimenfracture filling is significantly greater than open fissures sample; the strength ofoverlap specimen is the largest in double fractured sample. The stress crack initiationand crack angle of fractured rock samples variation: the initiation angle of wingcracks decrease with the increase of crack angle, and the relationship could beexpressed by index curve. The ratio of crack initiation stress by peak stress fractureshow increasing trend as loading rate increasing. Positive and negative wing anglecracks have no significant differences which is about130°.(2) the variation law of stress intensity factor of cracks: KⅠdecreases linearlyand KⅡcurve increases at first and decreases later with the increase of crack angle.Identifying fracture criterion of crack by relative stress intensity factor and the ratio of relative fracture toughness.(3) using displacement filed variance as statistical index of displacement filedcharacter, the S variance curve shows significant periodical characteristics beforespecimen failure, which could describe evolutionary process of rock deformationlocalization effectively. Combining the displacement distribution cloud could observethe deformation localization process and areas intuitively.(4) Crack propagation coalescence mode:①Single fractured rock samples: Withfissure angle increases, the failure mode of the specimen begins as tensile failuremode to tension-shear failure mode and then converted to stretch coalescence splittingfailure mode.②Double fractured rock sample: collinear and overlapping fracturedspecimens: with loading rate increases, the coalescence mode begins withtension-shear coalescence mode and shift to tensile coalescence mode, non-collinearnon-overlapping fractured specimens characterized by tension-shear failure mode.Rock Bridge coalescence mode is divided into non-coalescence, tensile coalescence,shear coalescence, tension-shear coalescence.(5) Comparative analysis is proposed to study the law of the energytransformation during the different deformation and fracture of the specimen. In thecompaction and elastic deformation stage, most of the input energy is to be stored inthe form of elastic strain energy, only a small amount of energy is dissipated in thefracture closure pressure process. In the Fracture development stage, with the crackinitiation, expansion, the absorbed energy is gradually transformed to dissipatedenergy. In the Failure stage after the peak, pre-stored strain energy can be releasedrapidly in the form of kinetic energy and surface energy, forming the macroscopicfracture surface. In addition, with the increase of fracture angle, the ratio of dissipatedenergy before the peak and total dissipated energy decreases, elastic strain energyincreases gradually; the greater the loading rate, the smaller the ratio.(6) From the analysis of crack coalescence pattern, crack coalescence istension-shear composite, during the shear crack initiation, expansion before the peak,the large amounts of energy is dissipated, plastic deformation is larger, causing a lossof strength of the specimen, and the storage rate of elastic strain energy is low beforethe peak, which is released few after peak, resulting the plastic flow through the crackcoalescence face of the specimen, the strain energy is mainly dissipated in the form offriction heat energy. Tensile cracks coalescence is wing cracks, energy dissipation islower and storage rate of elastic strain energy is higher, in the post-peak, the elastic strain energy can be released quickly and intensively, resulting the tension cracksoccur along the direction of energy release, the tension cracks of specimen wouldincrease at failure accompanied by ejection phenomenon.