| In nature,there are usually some weak surfaces in rock mass,such as joints and fissures with different numbers and forms.When these joints and fissures are disturbed or changed by the external environment,the fractures will expand and penetrate,and in serious cases,they will converge into a larger rock mass fracture plane,thus causing irreversible instability of the entire rock mass,which will seriously affect people's life and property safety.Therefore,in this paper,a series of indoor model experiements are carried out on rock-like specimens with different angles of cross fractures,and numerical simulation analysis is carried out by using ABAQUS finite element software.To study the influence of cross fractures with different angles on the mechanical parameters,creep characteristics and failure rules of rocks.The main contents and conclusions of this paper are as follows:1)In this paper,on the basis of consulting and learning a lot of literature on geotechnical research,the suitable rock-like raw materials are selected: river sand,cement and water.And the ratio of river sand: cement: water =2:1:0.11 is determined.The designed fracture angles were 15°,30°,45°,60°,75°,and the cruciform fracture specimens and intact specimens.The similar specimens of sandy shale rocks with different angle were prepared by using the similarity theorem and the self-made cross fracture mold.2)Results of uniaxial compression experiment and tri-axial compression experiment that: there are also compaction stage,elastic stage,plastic stage and stress softening stage about rock-like specimens.The peak strength of specimens decreases with increasing of angle on whole,peak intensity of tri-axial compression experiment is greater than the uniaxial compression experiment,and the larger the confining pressure,the greater the peak strength.The tensile splitting failure and shear slide failure were the main failure.The splitting experiment can be divided into two installation modes: the crack is aligned to the convex bar of the test fixture and the other installation mode is perpendicular to the convex bar.The obtained tensile strength varies with the angle.3)Uniaxial creep experiment and tri-axial creep experiment with confining show pressure of 1MPa were carried out on specimens with different angles of cross fractures.The results showed that there was no accelerated creep stage in the creep curve,indicating that the loading stress did not reach the stress level of the specimen's creep failure.On the whole,the uniaxial steady creep rate decreases gradually with the increase of the angle of the cross fractures,and the tri-axial steady creep rate decreases first and then increases with the increase of the angle of the cross fractures,which fluctuates more regularly than that under the action of uniaxial creep.4)In order to better explore the influence of creep on rock-like specimens,uniaxial creep experiment and triaxial creep experiment were carried out on the cross fractured rock-like specimens with different angles and then compression experiment were carried out.After uniaxial creep preaction,the peak strength and elastic modulus of the specimens were strengthened.But tri-axial creep preaction had a deterioration effect on the specimens with cross fractures.5)Numerical simulation analysis of uniaxial creep of rock-like specimens was carried out by ABAQUS software,and it was found that stress concentration of different degrees appeared at the fracture tips of the specimens at different angles.Moreover,the equivalent creep strain is larger at the crack tip,which is consistent with the failure law of the specimen in the experiment,and the reliability of the experiment is verified laterally,which has certain reference significance for the excavation and maintenance of the actual geotechnical engineering. |
PDF Full Text Request