Study On Loading Rate Effect Of Fracture And Acoustic Emission Characteristics Of Anchored Brittle Rock

With the gradual depletion of shallow resources,rock engineering at home and abroad are developing towards deep rock mass.Under the condition of deep high geostress,many special engineering disasters such as rockburst are more prominent,and those are caused by the destruction of brittle rock mass that widely exists in many projects such as coal mine hills and non-coal mines,tunnels and slopes,which bring great challenges to the engineering design,but also seriously threatens the safety of life and property of the construction workers.Although certain supporting measures have been adopted in roadways or tunnels,the surrounding rock instability disasters are still frequent.At the same time,the characteristics of concealment and hysteresis of the surrounding rock failure under supporting measures often make it difficult to prevent and control the dynamic disasters of brittle surrounding rock such as rockburst.With the support of the National Natural Science Foundation of China(51674116),this paper systematically carried out the loading rate effect of fracture and acoustic emission characteristics of anchored sandstone under uniaxial compression.The main contents and conclusions are as follows:(1)According to the frequent instability phenomena and the superficial local failure characteristics of deep hard brittle rock mass engineering under bolt supporting,Uniaxial compression tests of anchored sandstone under five low strain rate loading conditions,ranging from 0.001mm/s to 0.1mm/s were carried out.The test results show that the anchorless specimens all show tensile and shear mixing failure under different loading rates,which is not sensitive to the change of loading rate;The anchored specimens show shear failure,and most of the anchored specimens show a single inclined shear failure in the direction of crack propagation substantially parallel to the axial direction of bolt.When the loading rate are 0.01,0.05 and 0.1mm/s,a part of the anchored specimens will have a shear failure at a certain angle with the axial direction of the bolt.(2)The influences of bolt and loading rate on the uniaxial fracture characteristics of brittle rock mass were analyzed.When the equivalent anchoring force formed by bolt anchorage is parallel to the potential shear slip surface,and the failure mode of most anchored specimens is mainly that the direction of the shear fracture plane is parallel to the bolt axis.When the bolt arrangement direction is parallel to the potential slip surface ? and passes through the potential slip surface ?.When loading rate is 0.001,0.005mm/s,resulting in the direction of the shear fracture plane is parallel to the bolt axis.When the loading rate is 0.01,0.05,0.1mm/s,leading to shear failure along the slip surface of the rock mass,which results in the phenomenon that the shear fracture plane is at a certain angle with the axial direction of the anchor when the anchored sandstone is failure.(3)Combined with the acoustic emission test,the differences in the basic characteristics of acoustic emission between the anchorless specimens and the anchored specimens were compared.Acoustic emission signals indicate that the elastic strain energy of the anchorless specimens is accumulated until the specimen is completely destroyed at each loading rate,but the elastic strain energy stored in the anchored specimens can be fully released before the stress peak.The distribution of acoustic emission RA value with time has a good correspondence with the initiation and propagation of internal cracks,and it is helpful to further understand the initiation and propagation of cracks in the rock.(4)The controlling of buckling rockburst is analyzed from three aspects of anchoring mechanism,Specimen rupture mode and energy release.The equivalent composite beam formed by bolt anchorage greatly reduces the occurrence of layer explosion,weakens and reduces the occurrence intensity and frequency of buckling rock burst.The equivalent composite beam formed by bolt anchorage greatly reduces the occurrence of layer blasting and weakens the strength and frequency of the buckling rockburst.The bolt anchorage destroys the incubation process of rockburst,so it plays a role in controlling spallation-buckling rockburst.When the anchor specimen is destroyed,the proportion of energy released from outside is reduced,which reduces the inoculation ability and intensity of the rock burst,thus achieving the effect of controlling the layer buckling type rockburst.(5)The key to the anti-shock anchoring control technology for large-section coal roadway under high ground stress is to use support systems such as bolts and anchor cables with high strength,coordinated support and anti-shock characteristics.Therefore,the strengthening support measures of "anchor belt net cable + anchor cable beam + channel steel beam with anchor cable support" are put forward.The supporting control of deep roadway shows that the surrounding rock of the roadway has no obvious damage under the control of this anti-scouring anchorage technology during excavation,which has a good support and reinforcement effect on the roadway.