The Study Of Disturbance Factor In Hoek-Brown Strength Criterion

The accurate determination about rock-mass mechanics parameters is an important and complex subject in rock engineering. Reduced rock mechanics parameters which are based on indoor rock tests, and compositely considered of fissures in the rock and size can meet the engineering requirements. This fact has been proved by large number of practices. Hoek-Brown strength criterion method which has been widely used in engineering practice is a better method. Because of blast loading and unloading, rock mechanical parameters are greatly reduced after blasting. In 2002, Hoek introduced disturbance factor D which considers disturbance of rock mass blasting excavation into the improved Hoke-Brown strength criterion. However, for the determination of disturbance factor D, Hoek has given notional range, which is lack of systematic research. Meanwhile, the inaccurate determination of disturbance factor D will bring down the reliability of rock mechanics parameters which is revised by Hoek-Brown strength criterion. Taking Dapingzhang copper and Jianshan phosphate slope project as the project background, using rock-mass sonic test, the paper studies and discusses disturbance factor. Procedure is as follows:(1)The turbulent mechanism of blasting excavation is described. The disturbance on rock of blasting excavation includes load disturbance and unload disturbance, which will both weaken the physical and mechanical properties of the rock mass.(2)Through the result of sonic test on the reserved slope rock mass, investigate the fracture distribution law of the rock, and evalue the integrities of rock. The results show that blasting excavation has an effect on the fracture distribution of rock and integrities. At the same time the rock block index is introduced to classify rock mass.(3)According to acoustic rock test results, use wave velocity of variation to confirm the depth of disturbance and disturbance factor D during the disturbance depth range.(4)Combining with the determined disturbance factor results, reduce the rock mechanics parameters by Hoek-Brown strength criterion. Compare the revised results with rock direct shear test results to verify the correctness of the determination of disturbance factor. Apply the revised mechanical parameters to slope stability analysis in jianshan, and to further verify the correctness of the determination of disturbance factor.(5) Rock blasting excavation disturbance is affected by many and complex factors. Using gray relational analysis method, analyze various factors. Then identify the main factors to be dose-hole, array pitch, row pitch, structural plane angle and unloading quantity.