Mechanical Properties And Failure Mechanism Of The Rock-like Anchored Brittle Samples Under The Uniaxial Compression Load Experiment

With the deep development of resource extraction and tunneling,some geological disasters,such as rockburst,can be easily caused by excavating and unloading brittle surroundings rock with complete structure buried in high ground stress environment,which seriously threats the stability of the chamber structure.At present,the main supporting methods in preventing and controlling of brittle surrounding rock disaster are anchor netting and bolt supporting both at home and abroad,but many engineering examples show that the effects in controlling brittle surrounding rock are ineffective of deep geotechnical engineering in the existing bolt support measures,and brittle surrounding rock disaster under support measures usually have the hysteresis and concealment.Based on the National Natural Science Foundation of China(No.51674116),and on summarizing the research results of brittle rock failure,this paper analyzes the mechanical properties and failure deformation of the anchored brittle rock-like samples under uniaxial compression.The main contents and conclusions are as follows:(1)According to the superficial local failure characteristics of brittle surrounding rock under bolt supporting,and the rock similarity simulation theory,the non-anchored and anchored rock-like samples are made.Based on the brittleness evaluation of the prepared samples,the mechanical properties of these samples with different bolt materials,bolt diameter under uniaxial compression are studied.The results show that the strength of the anchored rock-like samples doesn’t increase with the increase of the diameter of the bolt,the bolt material and bolt diameter as well as the surrounding rocks have a best matching during the process of bolt supporting and strengthening surrounding rock.Under the matching condition,the performance of bolt can be made to the best degree.(2)The influences of bolt on the fracture mode of brittle rock under uniaxial compression are analyzed from the perspective of macroscopic force and micro-crack propagation.The reinforcement effect of the bolt on the macroscopic can be equivalent to the lateral load of the specimen,which changes the final failure mode of the brittle rock under uniaxial compression,from the splitting failure under nonanchored condition to the shear failure under anchor condition.Based on the sliding crack model,the calculation formula of the stress intensity factor of the wing crack tip with the azimuth angle of the main crack and the variation of the crack length of the main and the wing was deduced.The results show that the nonanchor samples produced a relatively long wing crack,and the final failure form was axial fracturing.While for the anchored rock-like samples,the cracks was shorter and the fracture form was shear fracture in the process of compression.(3)Combining with acoustic emission experiment,the differences of acoustic emission characteristics signals between the brittle and non-brittle surrounding rock-like samples were contrasted during failure process.There was a relatively stable period of the acoustic emission ringing count rate before the failure of rocklike samples.The duration of the failure of brittle rock-like samples in the period is longer than that of the non-brittle rock-like samples,which can be used as an important sign to judge the damage of brittle rock in actual engineering.(4)Compared with the non-anchored rock-like samples,the acoustic emission signals of the anchored samples were more obvious.And the acoustic emission signals were increased again in the post-peak phase of the stress-strain curve.The longer the duration of the failure,the bigger the uniaxial compressive strength of the anchored rock-like samples,meanwhile the ability of the specimen to resist the external load were stronger,and the effect of the anchor was more obvious.