Research On Multiscale Evolution Mechanism Of Rock Creep Fracture

The external load increase will bring about the deformation and rupture of rock.Due to the heterogeneity of the rock,even if the external load stops increasing,the deformation still will continue,accompanied by creep deformation.The creep rupture of rock is a multi-scale evolution process caused by the original heterogeneity inside the rock,including the micro-scale rupture,the meso-scale crack propagation and penetration,the macro-scale deformation increase and rupture.Therefore,it is necessary to study the multi-scale evolution mechanism of rock creep rupture.Based on the macro evolution experiment of rock creep rupture and the micro-and-meso scan experiment offracture,the deformation and rupture mechanism of rock specimens at different scales is analyzed by introducing the concept of endogenetic force,and the Lagrangian governing equation of dissipative problem is established with the constitutive relation of creep rupture given.On the basis of the continuous-discontinuous methods,the solution and the calculation arecarried out to simulate the evolution process of uniaxial compression creep rupture and diametral compression and tension creep rupture.The main conclusions are as follows:(1)It can be seen from the macro evolution experiment of rock creep rupture that there are no cracks on the rock surface in the initial and isokinetic creep stages,mainly the initiation and propagation of micro-and-meso cracks.With the macro rupture surface formed,it enters the accelerated creep stage in which the friction sliding occurs along the rupture surface with the rupture finally coming up.(2)Based on the analysis of micro and meso structure features and composition of typical rupture fracture,the microcomposition and the micro-and-mesostructure of rock are not uniform.The rocks consist of different minerals.The composition of mudstone is mainly quartz,potassium feldspar and mica,while sandstone is mainly quartz and kaolinite.The structural heterogeneity of micro-pores and fractures is the main cause of micro rupture and meso crack propagation.(3)From terms of energy,the driving force of crack propagation caused by the heterogeneity of rock itself is called internal force.The criterion of crack propagation based on endogenetic force is given.The cumulative failure mechanism of micro crack initiation,meso crack propagation and macro deformation is analyzed by applyingendogenetic force concept.(4)It can be seen from the numerical calculation that in the initial creep stage,due to the heterogeneity on the micro scale of the rock,the micro cracks are randomly generated,and the macro deformation continues increasing with the deformation rate decreasing gradually.In the isokinetic creep stage,the meso cracks interact,connect and cut through with each other,and the macro deformation rate remains unchanged.With the macro rupture surface forming,it enters the accelerated creep stage in which the rupture occurs along the macro rupture surface,which is consistent with the experimental results.To sum up,the heterogeneity of the rock brings about the endogenetic force that promotes the micro crack initiation,while the micro cracks intensify the heterogeneity of the rock with the new endogenetic force producing,which makes cracks further initiate and propagate with the heterogeneity degree continuously increasing.Gradually like that,a feedback loop forms.Meanwhile,when the micro crack length reaches a certain threshold,it enters the meso stage,while when the meso crack connection reaches a certain threshold,it enters the macro stage,and the crack jumps step by step.Due to the heterogeneity,coupled with the drive of the endogenetic force,the multi-scale evolution mechanism of rock creep rupture is a self-organizing feedback process with multi-scale step-by-step transition of the micro crack initiation,meso crack propagation and the macro crack connection.The study on the multi-scale evolution mechanism of rock creep rupture can provide theoretical basis and technical support for rock engineering creep deformation and disaster prevention.There are ninety-six figures,nine tables and one hundred and fifty-six references.