Study On A Damage Model For A Rock Mass With Arbitrary Multi-cracks

At present,the study on the damage model for the cracked rock mass mainly focuses on the following two aspects.One is the geometrical damage theory only considering the geometrical properties of the crack,such as its length,inclination,spacing and so on.The other is the damage theory which can consider both the geometrical property and the mechanical one.Based on the study on the rock mass with the periodic cracks,the effect of arbitrary non-persistent crack on the rock mass mechanical behavior is studied further.The following results are obtained in this dissertation.(1)Starting from the rock mass with a single non-persistent crack,the calculation formula of the rock mass damage variable caused by one crack is deduced from the viewpoint of the energy.Then,the calculation formula of stress intensity factor(SIF)and the rock mass damage variable of a set of one or more-rowed crack tips is given by considering the interaction among the cracks.Based on the plane elastic mechanics,the calculation formula of SIF of the arbitrary multi-cracks is given,and the relationship of multiple cracks is obtained.(2)A calculation model for the SIF of multiple cracks is established.The interaction of multiple cracks is related to their relative geometrical position and the inclination.The SIF of B and C at the inner tip of the two cracks are more affected by the crack interaction than those of A and D at the outer tip.The trend of the SIF produced by the interaction of the parallel cracks with different spacing is completely consistent.With the increasing distance between the cracks,the value of the calculated SIF tends to not take that multiple cracks interacting with each other into account.(3)According to the relative geometric position and inclination of the crack,the stress field after the different superposition can produce the effect of strengthening and weakening respectively.That is,when the adjacent crack tip is in the intensified region,the SIF of the crack will become larger,otherwise less.(4)Under the compressive and shear stress,when the distance of the two cracks is close enough,the interaction of the cracks makes the stress field at the crack tip significantly enhanced,which indicates that in the same external load condition,the multi-cracked rock mass is more prone to the crack initiation and propagation,which is much easier to cause the rock mass to destruct eventually.(5)The rock damage model with two arbitrary non-persistent cracks is established,and the damage variables of two arbitrary non-persistent cracks model are calculated.The model with two arbitrary non-persistent cracks is set up as a model which has two parallel cracks with zero vertical distance,and the calculation results are in good agreement with those in the published literature.The results show that the model is rational.