| In recent years,with the rapid development of China’s economy,people’s demand for underground space development and utilization is getting higher and higher.However,the geological conditions in the southwestern of China are complex.Under the conditions of greater depths and high geo-stress.The construction of soft rock tunnel engineering has to face the threat of large deformation disaster of surrounding rock.The large deformation disaster of soft rock tunnel has the characteristics of high degree of damage,high treatment cost and large construction risk,resulting in various disasters such as lining cracking in the supporting system and distortion of steel arches.At the same time,the traditional strong support system has been greatly challenged in the large deformation treatment of soft rock tunnels,and it is difficult to obtain the ideal support effect.Based on this,from the idea of rational release of surrounding rock deformation energy of soft rock tunnel,it is of great significance to design a new supporting structure based on the support concept of “couple hardness with softness”.Based on the support concept of "combining rigidity with flexibility" in soft rock tunnel and the study of interaction mechanism between corrugated steel pipe(bridge)culvert and fill,the flexible corrugated steel plate is proposed as the primary lining structure of soft rock tunnel,and its suitability is studied.In view of the geological conditions and characteristics of the actual project on which the support structure is based,the corrugated steel plate with a thickness of 8 mm and a thickness of 400 mm*150 mm is selected to form the support structure on the basis of previous studies.The stress-deformation law and strength characteristics of the support structure are calculated and simulated by means of theoretical calculation and numerical simulation.Finally,based on the actual project on which it relies,the support structure is constructed.The suitability of its practical application is studied.Through the research,the results are as follows:(1)Based on the interaction mechanism between corrugated steel culvert structure and overlying soil,combined with the concepts of yielding support in soft rock tunnel,the corrugated steel primary lining structure suitable for soft rock tunnel is proposed.The corrugated steel plate is introduced into the tunnel support system to replace the traditional steel arch,which is composed of bolts,shotcrete and so on.A new support system with certain yielding function.The structure has the characteristics of high strength,good deformation performance,fast construction speed and continuous closure.The purpose of this structure is to achieve mutual balance by using the force and deformation characteristics of corrugated steel plate and the interaction with surrounding rock,so as to achieve the purpose of "timely support and yielding support".At the same time,in view of the particularity of the primary lining structure of corrugated steel,the corresponding construction process and key points are put forward.(2)From the point of view of theoretical analysis,referring to the existing methods of internal force calculation and strength checking of corrugated steel pipe(bridge)culvert,the internal force calculation and strength checking method of primary lining structure of corrugated steel are put forward based on the principle of convenience and practicability,and the concrete calculation formula is deduced.This method can serve for the preliminary design of the primary lining structure of corrugated steel and the preliminary selection of corrugated steel plate.(3)The stress law and influencing factors of the primary lining structure of corrugated steel are analyzed.Considering the influence of surrounding rock on the mechanical properties of primary lining structure of corrugated steel,a threedimensional solid model of structure-surrounding rock interaction is established by ANSYS software,and the contact relationship between surrounding rock and primary lining structure of corrugated steel is simulated by MPC contact algorithm.Using this model,the distribution and deformation characteristics of circumferential stress,axial stress and Mises equivalent stress of the primary lining structure of corrugated steel are studied.The results show that under the action of external loads,the structure distributes stresses in both circumferential and axial directions;the distribution characteristics of circumferential stresses of wave crest,wave neutral and wave trough are similar,showing that the circumferential stresses of arch foot are the highest and the circumferential stresses of arch bottom are the smallest,but there are some differences among the three stresses,and the difference between them is the same.The bending deformation state of the structure is related;in different circumferential positions,the axial stress distribution of wave crest,wave neutral and wave trough is quite different;overall,the wave trough position of the arch foot of the structure shows a high stress concentration phenomenon,which is the weak part of the structure.(4)Based on the above numerical calculation model,combined with the mechanical characteristics of tunnel support structure,the main influencing factors of structural deformation characteristics are analyzed.The effects of vertical load,horizontal lateral pressure coefficient and surrounding rock material parameters on the stress and deformation law of the primary lining structure of corrugated steel are studied.The results show that the vertical load has a linear relationship with the internal force and deformation of the structural crest and trough;the horizontal load mainly affects the circumferential stress distribution of the structure,and a certain horizontal load is helpful to improve the mechanical performance of the structure;while the internal force and deformation of the structure decrease with the increase of the elastic modulus of surrounding rock,which is relative to the stress.The effect is more obvious.On the basis of the comparison and analysis with typical pipe culvert structures,the reasons for the different mechanical responses of the two structures are obtained.(5)Based on the actual project,the suitability of the combined support composed of corrugated steel primary lining structure and bolt is studied under the actual working conditions.According to the material parameters and in-situ stress field obtained by predecessors,four representative sections are selected according to the standard of insitu stress level and surrounding rock level.A three-dimensional geological model is established by FLAC3 D software for numerical calculation.The internal force of the primary lining structure of corrugated steel in the whole process of tunnel excavation and support is obtained by simulating two steps construction.The results show that the primary lining structure of corrugated steel discussed in this paper has certain limitations in use.When the local stress level is high,the arch foot trough position of the structure enters the yield state because of the excessive stress.。 At the same time,by comparing the stress characteristics of the structure itself under four sections,it can be concluded that the in-situ stress and the surrounding rock level have great influence on the mechanical performance of the structure.In practical use,the calculation results of this paper can be referred to for further study and judgment according to the actual conditions.Finally,taking the section at the exit of the tunnel as an example,the interaction between the surrounding rock and the primary lining structure of corrugated steel during the whole construction process and the mechanical characteristics of the structure itself are analyzed. |
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