Deformation Mechanism And Classification Methods For Surrounding Rock Of Railway Tunnels

The surrounding rock grade is a comprehensive reflection of the stability of the surrounding rock, and it is also an important basis for tunnel design and construction. At present, the stability evaluation of surrounding rock is mainly based on the self-stabilization span. The method of classification of surrounding rock is also established on the basis of self-stabilization. China has a vast territory, diverse geological structure, different types of surrounding rock deformation mechanism and instability mode. The surrounding rock stability evaluation method based on the self stability span can reflect the stability of surrounding rock in a certain range, but it is not comprehensive. The stability evaluation of surrounding rock should be based on the structure type of surrounding rock,and the stability evaluation method of multi-factor should be established for different surrounding rock. The classification of the surrounding rock is based on the evaluation of the stability of the surrounding rock. At present,the classification of the surrounding rock of the railway tunnel in China is divided into six grades, and a large amount of data shows that the six sub-grades are obviously less than normal. Based on the analysis of the stability of surrounding rock, the method of surrounding rock classification should be further studied. The classification index of surrounding rock mainly includes the degree of hardness and completeness, and the span has important influence on the deformation of surrounding rock. The current grading method ignores this factor, and the construction site is more complicated to obtain the classification index of surrounding rock. Therefore, it is necessary to study how to consider the span and how to get the classification index of surrounding rock quickly.In this paper, the methods of theoretical analysis, data research and numerical analysis are used to analyze the deformation mechanism, instability mode of surrounding rock, the stability evaluation and the classification method of surrounding rock, the method of scale correction of surrounding rock and the method of quick access for surrounding rock classification index. The main conclusions are as follows:1. The deformation mechanism and instability mode of surrounding rock of different tectonic types are clarified. Firstly, on the basis of the existing types of surrounding rock, the special surrounding rock has been added, and the types of special surrounding rock are given.Thus, the classification of surrounding rock has been improved. Besides, based on the type of surrounding rock, the deformation mechanism and instability mode of surrounding rock are clarified, and the failure model of surrounding rock is concluded as three categories:local collapse, arched collapse, excessive deformation. Finally, through the combination of lithology and integrity, the deformation and failure modes of surrounding rock are obtained,which lays the foundation for the stability evaluation of surrounding rock.2. The stability evaluation and classification method of surrounding rock have been put forward. Based on the deformation and instability model of surrounding rock, three kinds of stability evaluation methods of surrounding rock are determined: self-stability span,allowable displacement and allowable support force. Based on the research of self-stabilization span, a qualitative classification method of surrounding rock based on tectonic type and including special surrounding rock is established. A method of quantitative classification of surrounding rock based on elastic wave velocity is proposed. In the studies of permissible displacement and allowable support of surrounding rock, the relationship among the classification of the surrounding rock ,the permissible displacement and the allowable support force is obtained, and the method of determining the stability of the surrounding rock based on the allowable displacement and allowable support force is established.3. The method of scale correction based on span is established. The influence rule of surrounding rock deformation with different degree of rigidity and integrity is analyzed. On the basis of the deformation of surrounding rock, The method of classification of surrounding rock considering span correction is put forward.4. The Research enriches the quick acquisition method of the classification index of surrounding rock?And the adaptability of the method of testing the hardness of the surrounding rock based on the hammer test and the correspondence between the springback value and the hardness of the surrounding rock are given in the paper; The adaptability of the method of obtaining the degree of development of surrounding rock facies based on digital imaging is also obtained through the reserch.