Experimental Study On Mechanical Properties Of Double-circular Cavity-fissure Rock Specimens

After a long period of complex geological tectonic movement,the rock mass in nature contains a large number of structural defects such as pores,cracks,bedding,joints,etc.,resulting in mechanical properties such as transverse anisotropy.A large number of research results show that:different types of structural defects have different mechanical responses to the mechanical properties and failure modes of rock masses,and the interaction between different types of structural defects will also have a greater impact on the mechanical properties and failure modes of rocks.Therefore,scientific and accurate evaluation of the mechanical properties of defective rock masses has important practical significance and application value for the construction and design of rock mass engineering.In tunnel construction,double-arch circular tunnels are generally used,and the surrounding rock of the tunnel generally contains a large number of cracks,which can theoretically be simplified as a mechanical model with double circular holes-cracks.Therefore,this paper adopts a combination of laboratory experiment,numerical simulation and theoretical analysis to study the mechanical behavior and failure mode of the double circular hole-fracture rock sample,revealing different fracture parameters(single fracture inclination angle,double fracture inclination angle And the distance between cracks and holes,etc.)on the strength,deformation characteristics,crack evolution and failure modes of rock-like specimens.The results showed that:(1)The RMT-150 rock mechanics testing machine was used to conduct uniaxial compression test and Brazilian split test on the complete and double circular hole-fracture rock samples,and the PFC numerical simulation software was used to simulate the crack evolution law,analyze its mechanical response,the results showed that:when the distance between the double circular holes remains the same and the double circular hole-fracture rock sample contains a single fracture,its elastic modulus decreases linearly with the increase of the fracture dip,and the peak strength appears first with the increase of the fracture dip.The change law of increasing after decreasing and finally decreasing again,and when the inclination of the fissure is 45°,its peak strength reaches the maximum value;the cracks of the double-circular hole-fissure-like rock sample originated around the hole,and the cracks mainly propagated along both sides of the hole,but the hole and the crack did not form a through crack.(2)When the distance between the double circular holes remains unchanged and the double circular hole-fracture rock sample contains double parallel cracks,the elastic modulus of the cracks and cavities will first decrease and then increase with the increase of the crack inclination.And when the crack inclination is 30°,its elastic modulus is the smallest,and the peak strength first increases,then decreases and then increases with the increase of the crack inclination angle,and when the crack inclination is 90°,its peak strength is the largest;the cracks started around the cracks of the specimen,and mainly expanded along the holes and cracks,and the through cracks formed by the holes and cracks.(3)When the inclination angle of the cracks in the double-circular hole-crack-like rock sample remains unchanged,and the crack center distance between the double circular holes changes,the elastic modulus of the sample first decreases and then increases with the increase of the crack center distance.The peak intensity decreases approximately linearly with the increase of the crack center distance;when the center distance of the crack is small,the cracks start around the hole and expand along both sides of the hole,but the hole and the crack of the sample do not form a through crack;as the center distance increases,the crack gradually starts to crack around the crack.And expand along the holes and cracks,the holes and cracks formed through cracks.