Study On Size Effect Of Shear Strength Of Rock Like Structural Plane Under Low Normal Force

The shear strength of the structural plane is one of the most important mechanical properties of rock mass.A large number of studies have shown that shear mechanical properties of structural plane have size effect characteristics.However,due to the nonrepeatability of rock mechanics test,it is very difficult to carry out the size effect test of shear strength on rock structural plane in laboratory.For this reason,this paper adopts 3D scanning technology and 3D printing technology to prepare structural surface molds,adopts structural plane molds to trial-produce batch structural plane with the same morphology,and conducts laboratory tests on specimens.At the same time,numerical shear tests on PFC2D joints were carried out to analyze the law of shear strength and size effect of rock structure surface and the influencing factors.First,the raw rock structural plane is scanned by the SHINING 3D white light scanner to obtain the structural plane morphology data.On this basis,five kinds of structural plane molds of different sizes(50mm~2,75mm~2,100mm~2,125mm~2,150mm~2)are made with 3D printer technology,and the structural plane are cast in the self-made steel mold.Then,shear tests were carried out under four levels of normal forces for each piece of structure plane with different sizes,and the shear mechanical parameters of the pieces with different sizes were obtained through fitting calculation.Finally,in order to make up for the lack of laboratory shear mechanics tests under low normal force,three typical Bardon joint profiles were selected to carry out PFC numerical shear mechanics tests for structural planes of different types and sizes.The results show that(1)3D scanning and 3D printing technology is an effective method to accurately realize the shear strength test and size effect test of structural plane in the room.(2)The specimen shearing process can be divided into four stages,namely,the initial stage?the shear loss stage?the peak stage and the post-peak stage.(3)The shear strength of specimens of the same size increases with the increase of normal stress.(4)Under the same normal stress,as the size of the specimen increases,its peak value tends to increase first and then decrease.Through calculation,it is concluded that the main reason for the size effect is the roughness of the structural surface.(5)Through Bardon three different types of typical joint contour cutting numerical experiment shows that the?type,?type structure,the peak shear strength increases with the size,all size effect was a first,and then negative size effect;For type?structural plane,the peak shear strength increases with the size,size effect was a first,and then negative size effect,and gradually tend to be stable.With different types of structural planes,the dividing points of positive and negative size effect correspond to different sizes.Under the same normal force,the peak shear strength of the structural plane with small roughness is smaller than that of the structural plane with large roughness.This also indicates that roughness is the main factor affecting the peak shear strength of the structural plane under low normal force.