Rock burst proneness prediction by acoustic emission test during rock deformation

Rock burst is a severe disaster in mining and underground engineering,and it is important to predict the rock burst risk for minimizing the loss during the constructing process.The rock burst proneness was connected with the acoustic emission(AE) parameter in this work,which contributes to predicting the rock burst risk using AE technique.Primarily,a rock burst proneness index is proposed,and it just depends on the heterogeneous degree of rock material.Then,the quantificational formula between the value of rock burst proneness index and the accumulative AE counts in rock sample under uniaxial compression with axial strain increases is developed.Finally,three kinds of rock samples,i.e.,granite,limestone and sandstone are tested about variation of the accumulative AE counts under uniaxial compression,and the test data are fitted well with the theoretic formula.

Prediction method of rock burst proneness based on rough set and genetic algorithm

A new method based on rough set theory and genetic algorithm was proposedto predict the rock burst proneness. Nine influencing factors were first selected, and then,the decision table was set up. Attributes were reduced by genetic algorithm. Rough setwas used to extract the simplified decision rules of rock burst proneness. Taking the practical engineering for example, the rock burst proneness was evaluated and predicted bydecision rules. Comparing the prediction results with the actual results, it shows that theproposed method is feasible and effective.

A new criterion of rock burst proneness based on residual energy release rate index

The natural property of rock material,whether impact occurs,is the key influencing factor of the occurrence of rock burst disaster.To accurately assess rock burst proneness,this study focuses on typical sandstone as the research object.Uniaxial cyclic loading and unloading tests were conducted to measure the elastic strain energy accumulated in sandstone under different stress levels and a relationship between elastic strain energy and stress level was established.The results show that:(1)The peak stress under cyclic loading and unloading conditions is slightly lower than the uniaxial compressive strength.With an increase in the number of cycles,the internal damage of sandstone continues to accumulate,and the mechanical properties such as compressive strength continue to deteriorate;(2)With an increase in stress,the input strain energy,elastic strain energy,and dissipated strain energy also increase;(3)When the stress is low,the increase in elastic strain energy is large and shows a steady growth;with an increase in stress,the increase of elastic strain energy decreases;(4)The square of stress at any time has a good linear relationship with elastic strain energy.According to the relationship obtained from the test,the elastic strain energy at the peak stress time can be obtained;(5)A new criterion for assessing rock burst proneness is proposed:residual energy release rate index W_(T),which characterizes the energy release per unit time when the rock burst occurs.The intervals for evaluating the rock burst proneness of the residual energy release rate index W_(T) are as follows:W_(T)<0.025,indicating no rock burst proneness;0.025≤W_(T)<0.15,indicating weak rock burst proneness;0.15≤W_(T)<2,indicating medium rock burst proneness;W_(T)>2,indicating strong rock burst proneness;and(6)The rationality of the proposed residual energy release rate index W_(T) is verified by the multi-index method and the multi-sample method,and the proposed residual energy release rate index is used to determine the rock burst proneness of 10 kinds of rock samples.The evaluation accuracy is shown to be high,and it can reflect the actual rock burst proneness.

Strength and energy exchange of deep sandstone under high hydraulic conditions

To investigate the influence of confining pressure and pore water pressure on strength characteristics,energy storage state and energy release intensity at peak failure of deep sandstone,a series of triaxial compression tests under hydraulic coupling conditions are carried out.By analyzing the process of rock deformation and failure,the stress thresholds of the rock are obtained.The change trend of total energy density,elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration method.By comparing the dynamic energy storage level of rocks under different confining pressures,the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress,crack initiation stress,crack damage stress and peak stress is analyzed.Based on the ratio of pre-peak total energy density to post-peak total energy density,the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is studied.The experimental results show that the peak stress of sandstone increases with the increase of confining pressure,while the existence of pore water pressure can weaken the peak stress of sandstone.In the stress stage from crack closure stress to peak stress,the dynamic energy storage level of rock presents a trend of the inverse“check mark”.Meanwhile,the larger the confining pressure,the higher the energy storage level of rock.However,the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock,and the degree of dissipation is linear with pore water pressure.The increase of confining pressure aggravates the instability and failure of deep sandstone,while pore water pressure has the opposite effect.The research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.