Study Of Property Indexes Of Rock Masses And Stability Of Underground Structures With Exceptionally Large Cross-Section

This paper relies on Badaling underground station of new Beijing-Zhangjiakou intercity railway. First, the acquisition of property indexes of rock masses for large scale and large scale engineering has been studied. Then, the appropriate calculation formulas have been selected by the comparison of different methods for obtaining parameters of rock mass mechanical parameters based on property indexes of rock masses. Finally, the stability of surrounding rock of underground structure with large cross-section including large cross-section single arch span and large section tunnel group based on the obtained mechanical parameters of rock mass. The main research contents and methods are as follows:RQD prediction method of engineering rock mass based on spatial interpolationRock quality designation (RQD) index is an important parameter for evaluating the quality of fractured rock mass. It is difficult to express the actual rock mass of the whole space region by RQD obtained from geological exploration drilling in specific location because of structural and random distribution of RQD in engineering rock mass. In order to make up the deficiency, the spatial interpolation method in statistics provides powerful means. By considering the anisotropy of RQD spatial distribution and the difficulty to describe the structure of RQD distribution in engineering coordinate system, a standard coordinate system could be established according to the space rotation matrix and zoom ratio matrix after getting the principal Hessian direction (pHd) of geological exploration drilling RQD in engineering coordinate system. Then Kriging interpolation method is introduced. Variation function is used to describe RQD structural changes in standard coordinate system, a mathematical model which is conforming to spatial variation is established and the interpolation calculation is made. At last, the prediction of RQD distribution in engineering coordinate system will be acquired by inverse transforming standard coordinate system. Using R programming language, the method is applied to engineering. The results show that this method can effectively predict the distribution of RQD in engineering rock mass, and make up the limitation of local drilling.The application of mixed-effects model in the quantification of GSI indexGSI has been chosen as the research object because of easy contacting with Hoek-Brown strength criterion by comparing with RMR and Q index. The acquisition of GSI from the chart depend greatly on subjectivity. In view of this problem, a kind of GSI quantization method determined by the RQD value and the joint conditions was proposed by E. Hoek in 2013, which was easy to operate in the operation. However, the joint condition contains 6 factors, and it is difficult to obtain all factors in practical engineering. In order to make up for this deficiency, Mixed-Effects Models with fixed parameters and random parameters has been applied in the quantification of GSI index. By comparing with the engineering examples, the feasibility of this method has been verified. Using R programming language, the method is applied to engineering.Method selection for obtaining mechanical parameters based on property indexes of rock massesHoek-Brown criterion of rock mass is widely used in geotechnical engineering. Based on the analysis of the mechanical tests including uniaxial compression, three axis compression and splitting test of the collected samples in Badaling and the combination of the results of properties indexes of rock mass, the appropriate formulas or methods have been made clear by comparison. Finally, the selection of the formulas has been summarized, the results of calculated parameters which are needed during engineering design and numerical simulation, have been output to the interactive interface by using R programming language.Calculation of Surrounding rock pressure of large span underground structure with exceptionally large cross-sectionRelying on single arch long-span side type platform scheme of Badaling underground station of new Beijing-Zhangjiakou Intercity Railway, the applicability of various traditional calculation methods of surrounding rock pressure of single arch large span underground structure with exceptionally cross-section have been analyzed. Then, numerical simulations of underground structures in different span with different geological strength index (GSI) have been carried out. Base on the analysis of comparison between numerical simulations and the formulas of surrounding rock pressure with Q index, the newly formula with the factor of span and GSI has been proposed. Comparison of surrounding rock pressures between estimated and monitoring results of underground structures with 50 examples shows that this method could provide engineers and designers with a quick way to predict rock mass pressures in the design and construction stage of underground excavations as well as researchers with a reference guide.Model test of surrounding rock stability of group tunnels with large cross-sectionRelying on four holes side type platform scheme of Badaling underground station of new Beijing-Zhangjiakou Intercity Railway, model tests were carried out on the excavation of the group tunnels. The comparison of the collection of the pressure change of surrounding rock during excavation between model test and numerical simulation has been analyzed. Then, the stability in different situations including evaluation underground structure with different proportions and spacing chambers has been studied. According to different situations (open hole room size, cavern excavation spacing) excavation of underground structures was studied. Finally, a risk assessment system of excavation of group tunnels with large cross-section was put forward by considering the influence factors on the stability of surrounding rock of underground structure on integrated group tunnel effects.