Experimental Study On Mechanical Properties Anddamage Law Of T-shaped Cracked Sample Under Multi-level Cyclic Loading

The presented cracks with different lengths are often intersected in the real jointed rock mass,and they have an important influence on the mechanical properties and damage law of the rock mass.The real jointed rock mass in the nature is not only subjected to static load,but also under cyclic load with varied characteristic.Therefore,it is necessary to study the mechanical characteristics and damage law of crossed cracks under different cyclic loading.In this paper,samples containing single crack and T-shaped crossed cracks were made by using cement mortar,and uniaxial static compression tests and uniaxial multi-level cyclic loading tests were carried out in laboratory.The shape of hysteresis curve,mechanical properties,failure mode and damage law of cracked samples with different geometric characteristics are studied.The main conclusions are as follows:The uniaxial compression test of the cracked samples with different geometric characteristics were carried out,it is found that the existence of the secondary crack isn't negative to the mechanical properties of samples,and the influence of the secondary cracks with different angle to the major crack is also varied.The strength and dynamic elastic modulus of cracked samples increases with the increase of loading frequency and strain amplitude under uniaxial multi-level cyclic loading,however,the strength and dynamic elastic modulus of cracked samples decrease with the increase of cyclc times under the same strain amplitude,and the larger the angle between the major and sccondary cracks,the more sensitive the strength of cracked samples is to the change of frequency.Under the cyclic loading with the same strain amplitude,when the dip angle of the major cracks is 45° and 90°,the larger the strain amplitude,the more obvious the reduction of strength of the T-shaped specimen with the larger angle between the major and secondary cracks after 20 cycles,but the existencc of the secondary crack with different dip angles has little effect on the strength of the sample containing major crack of 0°.The failure modes of the cracked samples with different geometric characteristics is different under the same uniaxial loading modes,but the failure modes of the same type of cracked samples under different uniaxial loading modes have little change.and the change of loading frequency has a great influence on the number of cracks generated,the larger the loading frequency,the less the number of crack developed,and the brittle failure characteristics are significant.From the viewpoint of energy,the energy dissipation ratio is use defined as the damage variable,and the total energy and dissipation energy of cracked samples with different geometric characteristics were studied,and the damage evolution equation of T-shaped cracked samples is proposed.