| It is an important national strategy to push deep into the earth.A large number of key deep tunnel projects are under construction or will be built soon.Accurate evaluation of the integrity and fracture zone of deep rock mass,the evolution characteristic of deep rock mass fracture zone and the mechanism of zonal disintegration are important requirements for the construction and theoretical development of deep engineering.In this study,the integrity and initiation and development of excavation fracture zone of deep hard rock tunnel was observed using a digital borehole televiewer.The relationship between fracture distribution characteristics in the fracture zone and surrounding rock integrity and rock mass strength was found.A new evaluation method was proposed:a rock mass integrity index(RMIBT)based on high-definition digital borehole televiewer data which can be used to assess dynamically the integrity of macroscopic rock masses.The mechanism of fracture zone and zonal disintegration was revealed.An evaluation method of frcture degree of deep hard rock tunnel fracture zone(RMIBT-Z)is proposed.The specific research results are as follows:(1)When the surrounding rock mass shows no primary fracture or integrity is very poor,the fracture zone presents the single zone distribution after tunnel excavation.When the surrounding rock has good integrity and high rock mass strength,and there are 1?2 groups of primary fractures in the plastic zone of surrounding rock,the surrounding rock fracture zone will tend to be zonal disintegration.(2)A new evaluation method was proposed:a rock mass integrity index(RMIBT)based on high-definition digital borehole televiewer data.The relationship between fracture distribution characteristics in the fracture zone and surrounding rock integrity and rock mass strength was found.It was applied in multiple deep rock excavations and therefore proved to be useful,especially where core discing occurs,in specific spatial distributions of structural planes,as well as logging errors from core breakages induced by drilling.In addition,the RMIBT can be used to assess dynamically the integrity of macroscopic rock masses and the evolution of fractures in the excavation fracture zone.(3)The characteristics of fracture zone and the mechanism of zonal disintegration were revealed.The comparison of fracture zone observation based on borehole camera and damage zone test based on elastic wave shows that when the surrounding rock has good integrity and high strength,the depth of damage zone is much higher than that of fracture zone.However,when the integrity of the surrounding rock is poor and lower strength,the depth of the damaged area is basically the same as that of the fracture area.The formation and evolution of the fracture zone are concentrated between the diameter of 0.7 times between 1 times of the tunnel.The deformation of the surrounding rock increases synchronously with the development and excavation of the rupture zone,increase of new fractures or the expansion of original fractures.After the development of the rupture zone is stable,the deformation amount of the surrounding rock will continue to increase slightly.In the process of deep buried hard rock tunnel excavation,single zone fracture occurs when the surrounding rock has no primary fracture.The formation of fracture in two or three zones depends on the distribution of primary fractures.The above results are consistent with the in-situ observation results of the fracture zone.(4)An evaluation method based on rock mass integrity index using digital borehole televiewer data(RMIBT-Z)was proposed by only calculating excavation-induced fractures(initiation of new fractures,extension of primary fractures,and falling of rock blocks)in the walls of boreholes for the analysis of zonal disintegration process in the deep hard rocks surrounding the tunnels.By using the method the initiation and evolution of fractures during zonal disintegration could be quantified.The results indicate that fractured zones within intact high-strength marbles were small and exhibited a higher degree of fracturing,whereas fractured zones within low-strength,low-integrity,marbles showed fewer,yet larger,fractures. |
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