Research And Application Of Stress Thresholds Of Brittle Rock

The study of the progressive failure process of brittle rock,and the mic-evolution laws of cracks initiation and propagation are key issues in rock engineering.In order to ensure the safe construction and long-term stability of large-scale rock engineering,it is necessary to carry out in-depth research on the strength,deformation and failure process of brittle rock.In this paper,the determination and application of stress thresholds in the process of brittle rock deformation and failure are studied.The advantages and disadvantages of different methods for obtaining stress thresholds of brittle rock specimens are studied by collecting experimental data of existing rock specimens and conducting rock uniaxial compression tests.And propose an optimized method.This study has certain guiding significance for the analysis of the determination of stress thresholds of brittle rock.The content of this paper is as follows:(1)This paper reviews the methods for obtaining crack closure stress,crack initiation stress and crack damage stress of rock specimens,and compares the advantages and disadvantages of different methods.Through theoretical analysis,the methods of determining the rock stress thresholds by volumetric strain method,lateral strain method and moving point regression technique have obvious subjectivity.Lateral strain response method mitigates the interference of human subjective factors,but the physical meaning of the result is not clear yet.Crack volumetric strain method reduces the subjectivity to a certain extent,but its calculation accuracy is easily affected by Poisson's ratio.Acoustic emission technology can be used to assist in determining stress thresholds by monitoring crack rupture during progressive rock failure.(2)Based on the research data of domestic and foreign researchers in laboratory experiments,the volumetric strain method,lateral strain method,crack volumetric strain method,lateral strain response method and moving point regression technique are used to analyze the stress-strain of Lac Du Bonnet granite,mica schist and limestone.The accuracy of different methods for obtaining rock stress thresholds is evaluated,and the variation of internal micro cracks is discussed.The crack volumetric strain method based on moving point regression technique is established to obtain the rock stress thresholds.The method can not only reduce the influence by rock physical and mechanical parameters to a certain extent,but also greatly reduce the interference of human subjective factors on the determination of stress thresholds,making the results more objective.(3)By comparing and analyzing the stress thresholds of rocks of the different rocks or same type rock with different internal structures,the stress thresholds of different kinds of rocks are obviously different.The mineral composition,mineral particle size and cementation state of rock samples are all important factors affecting the stress characteristics of rock.The same type of rock has different internal structure and anisotropy of rock;the difference of stress thresholds is also obvious.(4)Through the data collection and test of the ABH water diversion tunnel in Xinjiang,the in-situ stress of different depths in the tunnel was measured by the overcoring method,the stress thresholds of siliceous siltstone under uniaxial compression test are obtained.It is found that the crack closure stress and crack closure energy of rock specimens increase gradually with the increase of sampling depth,which can describe the degree of sampling damage of rock to some extent.The crack closure stress gradually increases as the in-situ stress difference increases.Acoustic emission monitoring results for some rocks indicate that acoustic emission techniques can assist in determining stress eigenvalues.