Research On Distribution Law Of Surrounding Rock Pressure And Calculation Method Of Deep-buried Tunnels With Small Clear Distance

In recent years,small-distance tunnels,as a new type of tunnel structure between ordinary separated tunnels and multi-arch tunnels,have been more and more widely used due to their good applicability and many advantages.Small-distance tunnels are in the early stages of development in China.Coupled with the particularity of their structure,the research on related theories is not as good as engineering practice.The calculation of surrounding rock pressure and its distribution law are an important basis for the design and construction of tunnel supporting structures,and it is also a difficult point in underground engineering research.Based on the literature research,this paper uses statistical analysis,theoretical analysis,numerical analysis and other methods,combined with the field monitoring data of the Badaling Great Wall Station of the Beijing-Zhangzhou Railway,to study the surrounding rock pressure of the deepburied small-distance tunnel.The main work and conclusions as follows:(1)Based on the measured data of surrounding rock from 231 deep-buried sections of 50 tunnels,explore the relationship between surrounding rock pressure and surrounding rock grade,buried depth,excavation span and span-to-height ratio.For the same surrounding rock conditions,the pressure of the surrounding rock is directly proportional to the buried depth.For the same buried depth,the worse the surrounding rock conditions are,the greater the vault pressure will be.The surrounding rock pressure of the vault is inversely proportional to the ratio of the excavation span.The pressure of the surrounding rock is distributed in a "large upper and lower lower" section.The maximum surrounding rock pressure may appear anywhere around the cave,and the arch waist and vault should be reinforced.(2)Combining the actual measurement data of the project,using three theoretical methods to calculate and compare and analyze,the results show that the calculation results of Platts theory and the railway tunnel plan are basically the same,and the calculation results of the highway tunnel plan are relatively close to the actual measured value and are conservative.The pressure inside the tunnel is greater than the outside.The excavation sequence of small clear tunnels has an impact on the surrounding rock pressure.(3)Using MIDAS GTS to simulate tunnel excavation under different buried depths,tunnel spans,clear distances and surrounding rock conditions,and analyze the distribution and change of surrounding rock stress.In general,the surrounding rock stress distribution of the two tunnels is related to the sandwiched rock The column is symmetrical,the stress of the preceding cave is slightly greater than that of the succeeding cave,and the pressure of the surrounding rock inside is greater than that of the outside.(4)From the analysis of the vertical stress ratio at the inner and outer arch toe,there is a certain bias in the tunnel with a small clear distance,and it does not change significantly with the buried depth.The span is proportional to the tunnel.The smaller the clear distance,the greater the bias in the tunnel.Obviously,the worse the surrounding rock,the less obvious the bias effect.(5)The ratio of the lateral pressure coefficient between the inner and outer sides is greater than 1,and is inversely proportional to the buried depth and proportional to the span of the cave.It generally decreases with the increase of the clear distance,and decreases with the increase of the surrounding rock grade.(6)Based on the data of numerical analysis,the simplified calculation formula of the vertical stress of the vault of the advance tunnel is obtained through multiple linear regression,and the actual engineering data is combined with the theoretical calculation result for comparison and verification.