Study On Creep Characteristics Of Rock-Like Mass With Multiple Parallel Penetrating Flaws

The rock mass contains a large number of structural planes such as joints and fissures.The joints and fissures will weaken the mechanical properties of the rock mass and make the rock mass have stronger aging performance,which will have an impact on the stability and safety of rock mass engineering.However,the current research on rock mass creep mainly focuses on intact rock and single and double fractured rock mass,and there is little research on the creep mechanical behavior and creep failure mode of rock mass with multiple fractures.In view of this,this paper takes multiple parallel fractured rock masses as the research object,and successively carries out uniaxial compression test,graded creep test and single-stage creep test.According to the test results,the effects of different crack dip angles and different crack numbers on the mechanical properties,characteristic stress,creep properties,long-term strength and failure mode of rock mass are revealed;The strength model and rheological fracture model of open fractured rock mass based on wing crack propagation are proposed;Combined with damage mechanics and element model theory,the damage creep constitutive model of rock mass is established.The main research contents of this paper are as follows:（1）Uniaxial compression tests are carried out on fractured rock masses with different dip angles and numbers.The variation law of characteristic stress of fractured rock mass(σ_cc,σ_ci,σ_cd andσ_c)with dip angles and numbers of fractures is studied.The relationship between other characteristic stress and peak stress is analyzed.According to the crack propagation pattern of single fracture samples,a strength model of open fractured rock mass based on wing crack propagation is proposed,The test results of this paper and those of other scholars are used to verify the model.（2）Graded loading creep tests were carried out on fractured rock masses with different dip angles and numbers.The creep curve,instantaneous deformation and creep deformation of fractured rock mass with stress level are studied;The long-term strength of various fractured rock masses is estimated by steady-state creep rate method;The influence of crack dip angle and crack number on the long-term strength of rock mass is analyzed;The long-term strength value is compared with the crack initiation stress and damage stress;Finally,the relationship between long-term strength and compressive strength is studied.（3）The single-stage loading creep test of fractured rock mass with different inclination and number is carried out,and the changes of creep time,instantaneous deformation,creep deformation and steady-state creep rate with stress level are studied;The effects of crack inclination and crack number on instantaneous deformation and creep deformation are analyzed;The similarities and differences of creep characteristics between graded loading and single-stage loading are compared,the failure modes of various fractured rock masses under different loading conditions are compared and analyzed,and the typical failure modes of various fractured rock masses are summarized.（4）According to the variation of wing crack propagation with time in single fracture sample,combined with fracture mechanics and element model theory,a rheological fracture model of open fractured rock mass is proposed,and the predicted starting time of accelerated creep stage by the model is compared with the test results;Based on the principle of conservation of strain energy,a calculation method of initial damage variable is proposed.Because the accelerated creep stage appears in the tests in this paper,the reasonable and feasible damage creep model of fractured rock mass is established by comprehensively considering the initial damage and aging damage of fractured rock mass and combined with the element model theory.