Study On Measurement Of Discontinuities And Key Block Analysis Of Surrounding Rock Mass Of TBM Tunnel

Based on the research “whether it's necessary to lining the surrounding rock mass of Class ? tunnel excavated by TBM(Tunnel Boring Machine)or not”,this paper has formed a set of integrated process,which applies Key Block Theory to analyze the stability of the surrounding rock mass of TBM tunnels.Facing with the problem of how to measure the discontinuities exposed in TBM tunnel,author presents a new approach called dual laser alignment technology based on Non-prism total station,which has been applied in the research of this subject successfully.With the aid of new approach,obtaining the geometric information of discontinuities becomes more efficient,convenient,safe and reliable.After rigorous mathematical derivation and computer calculation,the tunnel's outlet and the trace line of outcrops are reconstructed in the three-dimensional space,which creates basic conditions for further statistical analysis of rock mass structural characteristics.When applying Key Block Theory to analyze the stability of rock mass' surface excavated,the statistical theory of rock mass structure and three-dimensional network simulation technology are introduced to enhance the original stability analysis method.The combination of the methods mentioned above can not only reflect the more realistic structural characteristics of rock mass,but also generalize the geometric model of fracture network of rock mass,which makes the conditions of applying Key Block Theory more credible.In this paper,some optimized methods such as niche Pareto genetic algorithms,statistical window and scan line of orthogonal network are selected to analyze basic elements of rock mass discontinuities by statistics.By means of the JRS-3D(Joint Rock Simulation in three dimensional)program developed by Changjiang River Scientific Research Institute,the analysis results are able to simulate 3D rock mass containing definite and random discontinuities.On the basis,the Block Theory was used to seek Key blocks and analyze their stability.In the end,in order to predict the possible area that key blocks will appear and estimate emergence of the largest key blocks preliminarily,the maximum key block and the maximum removable area are computed.The research indicates that the probability of key blocks appear in the Class ? tunnel is very low.Although rock fractures are dense locally,the size of removable blocks is small and proper safety margin can be ensured.It has no unfavorable effect on surround rock mass without lining.The analysis results are in good accordance with the geological findings of large spacing and sparse distribution of exposed structural planes on the spot.