Study On Expansion Law And Damage And Fracture Characteristics Of Prefabricated Fissure Rock-like Materials

Engineering rock masses contain a wide range of primary joint fractures.The structural characteristics and physical and mechanical properties of these joint fractures play a key role in controlling the stability of the rock mass.Due to the complexity of insitu tests,research on fracture propagation and damage and fracture characteristics of rock masses is generally carried out through laboratory tests.In order to study the rock expansion and damage failure characteristics under different fracture parameters,based on previous studies of rock-like materials,this paper uses cement,quartz sand,water,and additives to make a sand-like material,its physical and mechanical parameters have good similarity;The thin steel sheet is used to produce thin rock specimens with single fractures,parallel double fractures,and primary and secondary fractures through thin strip drawing method.The main monitoring methods such as resistivity test and ultrasonic test are used to study the initiation,propagation,penetration,and damage evolution of the new cracks in the test specimens with different fracture parameters under uniaxial compression.At the same time,the physical mechanical parameters such as mechanical properties,resistivity,and ultrasonic wave velocity obtained during the test were analyzed.Through research,it is found that fractured rock samples have obvious brittle failure characteristics.With the number of fractures and geometric distribution characteristics,the trend of the stress-strain curve,crack initiation stress,peak strength,elastic modulus,residual strength,etc.will produce obvious The difference is that the specimens with rough cracks have higher mechanical strength and stability,and the internal damage is severe after failure.When the vertical cracks act,it is easy to form a "multi-column" loadbearing structure effect,so the peak strength of the specimens does not vary with the number of cracks.The change fluctuates obviously;when there are multiple fissures,the fissure propagation has the dependent property.In this paper,resistivity and ultrasonic parameters are used to evaluate the damage state of rocks.Resistivity can be used as a method for intuitively characterizing rock damage.It has two sudden changes with stress-strain.The first sudden change occurs near the crack initiation stress,which is about 50%～80%of the peak stress level,and there is a slight delay in the reflection time,the second abrupt change occurs near the peak stress,which is about 90%～98%of the peak stress level;Ultrasonic test is performed on the rock fracture process,the relationship between the attenuation coefficient and the maximum amplitude is established,and the comparative analysis of the damage variables characterized by them is made.Tests show that the sensitivity of the amplitude is higher than the wave velocity.It is more accurate to predict the damage evolution during the loading process with the attenuation coefficient and the wave velocity.When the attenuation coefficient reaches 0.5cm-1,the rock mass basically enters the stage of unsteady expansion of fractures,and the rock mass is about to lose stability.