Development And Application Of Supporting Structure Of Layered Rock And Soil Large Section Tunnel Analysis

The uneven distribution of soft and hard surrounding rocks and significant differences in surrounding rock properties in layered rock and soil strata can easily cause uncoordinated stress and deformation of the tunnel structure,resulting in instability or even collapse of the support structure.The layered rock-soil stratum construction section in the Baitashan tunnel is likely to cause uneven stress and uncoordinated deformation of the tunnel support structure.However,at present,conventional joint support methods are mostly used for tunnels in layered rock and soil strata,and its pertinence and applicability to layered rock and soil strata are not fully studied;at the same time,innovative tunnels under this special geological condition The research and development and application of supporting structures are also less.Therefore,through on-site monitoring tests combined with actual working conditions,the stress and deformation characteristics of the Baitashan layered rock-soil tunnel will be analyzed,and then an asymmetric yielding support structure for layered rock-soil tunnels will be proposed;The reliability and applicability of the model is verified by the establishment of a real tunnel model,and the numerical model of the asymmetric yield support structure is constructed by the application of the model.The main factors affecting the bearing characteristics of the new support structure are discussed;Unique advantages and good support effects under different layered rock-soil interface dip angles and complex surrounding rock conditions.The main research contents are as follows:(1)Through the analysis of on-site monitoring data of tunnels in layered rock and soil strata.In general,the pressure of the surrounding rock in the loess stratum is greater than that of the rock stratum,and it presents an asymmetric distribution pattern of "larger on the left side,smaller on the right side,larger at the upper part,and smaller at the lower part".Small deformation distribution regularity.During the change process of surrounding rock pressure,both formations showed three stages of rapid growth→slow growth→gradually stable;in the rapid growth stage,the load release rate of the surrounding rock in the rock stratum was as high as 80%;when it reached a stable state,the rock The stable time and stable distance of strata are shorter than that of loess stratum.During the construction process,the lower pilot pit was significantly affected by the tunnel construction,and the maximum change in confining pressure exceeded 50% of the total change,while the upper pilot pit was less affected by the construction of the lower pilot pit and the symmetrical side pilot pits.(2)Based on the analysis and discussion of on-site monitoring results,an asymmetric yielding support structure for tunnels in layered rock and soil strata is proposed.The structure is a tunnel support method that combines "yielding pressure,strong support,and weak support".The measures of buffering and pressure relief are adopted at the inclination of the layered rock-soil interface;at the same time,at the intersection of the layered rock-soil interface and the lower part of the tunnel,beams are used to support the arch frame on the hard rock,so as to realize the stress of the upper part of the supporting structure.Effects carried over to the lower hard rock.(3)The on-site prototype tunnel model was constructed by numerical simulation software,and the construction deformation data of the support structure in the model was obtained.Through comparative analysis with the measured data,the error of the deformation data of the two was within a reasonable range,which verified the reliability of the numerical model.A numerical model of the asymmetric yielding support structure for tunnels in layered rock and soil strata is constructed,and the main structural parameters affecting the support performance of the asymmetrical yielding support structure are discussed: the improvement of the stiffness of the double arch structure can effectively enhance the Support performance;and the improvement of the elastic modulus of the buffer layer in the buffer pressure relief device reduces the stress and deformation of the steel frame at the corresponding position,achieving the effect of buffer pressure relief.(4)Numerical models of conventional support structures and asymmetric yield support structures in different formation dip angles are established.In general,with the increase of formation dip angle,the surrounding rock deformation will increase in different support structures.By comparing the control of the support structure on the deformation of the surrounding rock and the stress and deformation of its own structure,it can be found that the asymmetric yield support structure has a higher vertical and horizontal displacement of the surrounding rock than the conventional support structure.In the comparative analysis of the force and deformation of the support structure itself,the overall force and deformation of the asymmetric yield support structure are smaller than that of the conventional support structure,which has the effect of structural strengthening.(5)By constructing the numerical model of the two support structures when the properties of different surrounding rocks are different,the support effects of different support structures are discussed and compared.With the deterioration of the surrounding rock properties of the loess strata,the deformation distribution of the surrounding rocks shows an obvious shift effect to the loess side,and the deformation of the loess side increases significantly.It can be seen from the support effect that the asymmetric yield support structure has a good effect on the deformation control of the surrounding rock.At the same time,it also promotes the uniform distribution of the deformation of the surrounding rock and weakens the phenomenon of excessive deformation in some positions.The setting of the crossbeam reduces the deformation degree of the whole support structure and improves the support capacity;the setting of the buffer and pressure relief device optimizes the local displacement of the arch by up to 13.83%,reducing the deformation of the arch.