Characteristics Of Excavation Damaged Zone In Fractured Rock Mass

A number of major projects,such as the China Jin-Ping underground Laboratory,the Baihetan hydropower station,and the nuclear waste disposal repository etc.have been carried out in recent years.Whether it is tunnel engineering,hydropower engineering or nuclear waste disposal engineering,a series of engineering and technical problems,such as collapse,water gushing,rock burst and so on,will inevitably be encountered in the process of underground chamber excavation.In fractured rock mass,these engineering problems are more serious and common.Understanding of characteristics of fractured rock mass Excavation Damaged Zone(EDZ)is the foundation of underground chamber excavation.It is of great significance for the stability analysis,support selection and reliability evaluation of the tunnel to accurately grasp the distribution and range of the damage zone in the surrounding rock.Based on Discrete Element Method(DEM)numerical simulation,the characteristics of EDZ in fractured rock mass were studied in this thesis.Combined with the BartonBandis fracture constitutive model,the identification basis of three excavation damage zones(failure zone,shear zone and open zone)in fractured rock mass in discrete element simulation was proposed.Based on the concepts of probability statistics and reliability,a method for determining the scope of EDZ in randomly fractured rock mass was proposed.The effects of Joint Roughness Coefficient(JRC)distribution,fracture dip angle distribution and anisotropy on the EDZ of fractured rock mass were studied.Through the HM and TM coupling analysis,the characteristics of EDZ under different coupling conditions were obtained.The comparison with field measured EDZ depth data of columnar fractured rock mass showed that DEM combined with Barton-Bandis fracture constitutive model is an accurate and effective tool to simulate the EDZ characteristics of fractured rock mass.The characteristics of EDZ in fractured rock mass mainly depends on the geometrical distribution characteristics of fractures,but the depth of EDZ is affected by the mean and standard deviation of JRC distribution to some extent.The range of EDZ decreases with the increasing of JRC average.As the standard deviation(discreteness)of JRC distribution increases,the depth of high-probability EDZ region increased.In view of HM coupling problem in tunnel water inrush in fractured rock mass,the influence of EDZ on seepage characteristics around the tunnel is considered.Compared with the dry fractured rock mass,the depth of EDZ increased when there was water seeping through the crack around the tunnel.With the increasing of JRC,the total water inflow into the tunnel increases as the dilation value of the crack in the critical state increases.In the process of thermal-mechanical coupling,both the heating process and the cooling process of surrounding rock will cause the expansion of EDZ to some extent,and the expansion of EDZ caused by the cooling process is more obvious.