Research On Deformation Control Technology Of Continuously Passing Through Existing Roadbed In Ultra-shallow Buried Soft Rock Large-section Tunnel

In recent years,with the rapid progress of urbanization in China,the urban migrant population is increasing,and the traffic volume is also increasing sharply.In order to alleviate the pressure of urban travel,the road network system has to develop into underground space,and the condition of tunnel tunnel crossing appears more and more in the urban traffic construction.However,in order to facilitate the flow of people and take into account the development of urban planning,and limited by the urban terrain,it is often necessary to cross the soft surrounding rock area of shallow or ultra-shallow burying in order to facilitate the flow of people and take into account the development of urban planning.In the construction of ultra-shallow tunnel,in addition to ensuring the stability of its own construction,it is necessary to strictly control the settlement and deformation of roadbed and buildings when passing through the structures such as urban roads,high-speed railways,high-rise buildings etc.And because of the distance between the tunnel and the existing structure is close under the condition of ultra-shallow burying,the interaction between the ground structure and the underground tunnel construction is significant,and the mechanism of the influence needs to be studied more deeply.Based on the above research background,it is urgent for researchers and engineers to study the deformation mechanism of large section of ultra-shallow soft rock crossing existing traffic subgrade,the stability analysis of cavern and the related control measures.Based on the engineering background of an ultra-shallow buried soft rock large section tunnel project in Xiamen,this paper analyzes the deformation mechanism and influencing factors of subgrade and caverns in the construction process of subgrade under the new super shallow buried large section tunnel by means of theoretical analysis,numerical simulation,model test and field data test,and puts forward the corresponding control measures and control standards,which can be applied in another project.The main research content of this paper includes four parts.(1)The sensitivity of surrounding rock parameters to surrounding rock parameters in the construction of new super shallow buried large section tunnel is analyzed,and the influence of different surrounding rock parameters on subgrade deformation and excavation stability of caverns is obtained.(2)Based on the calculation principle of surrounding rock pressure,the definition conditions of super shallow burying of soft rock large section tunnel are calculated,the stability of subgrade and caverns excavation under different buried depths is analyzed,and the settlement formula of related pavement is modified,and the settlement calculation formula in accordance with the construction engineering conditions is obtained.(3)The stability of subgrade and caverns excavation with different penetration angles and different excavation methods is analyzed,and the related optimization suggestions are given.(4)On the basis of analyzing the necessity of advance reinforcement,the construction optimization proposal of similar projects is given,and the relevant deformation control standards are given.Through the above research,the conclusions of this paper mainly include the following aspects.(1)The deformation law of subgrade and tunnel surrounding rock under different surrounding rock parameters is analyzed by numerical simulation.It is found that soil elastic modulus and internal friction angle have great influence on subgrade and tunnel surrounding deformation,but the influence of cohesion is relatively small.It is concluded that tunnel selection design should be carried out on the basis of considering the sensitivity difference of surrounding rock parameters before construction.(2)Through theoretical analysis,numerical simulation and model test,the deformation law of subgrade and tunnel surrounding rock under different buried depths is analyzed.It is found that under the condition of ultra-shallow burying,the stability of tunnel excavation is proportional to the buried depth,and the greater the buried depth is,the smaller the influence of tunnel excavation on the ground is,but the higher the requirement of support is,so it is concluded that deep burying should be selected as far as possible in the construction design of ultra-shallow buried tunnel.At the same time,we should pay attention to the initial support in the lower arch roof and arch foot of the subgrade.(3)The calculation formula of the classical settlement is modified,and the influence factor of the buried depth is added to obtain the correction formula for the settlement calculation of the subgrade in accordance with the actual situation of the project.(4)Based on the numerical simulation and the model test,the relationship between the crossing angle and the deformation of the subgrade is analyzed,the key factors that influence the deformation of the subgrade by the crossing angle are the vertical projection area of the excavation tunnel,the larger the projected area,the greater the influence of the tunnel on the subgrade,For crossing the subgrade working conditions,a large angle crossing shall be selected.(5)Based on the numerical simulation and model test,the deformation of the subgrade and the surrounding rock of the tunnel under the construction conditions of the comprehensive method,the CRD method and the double-side wall guide pit method is analyzed,and the construction of the super-shallow-buried underground excavation tunnel in the upper part of the construction process is considered,and the CRD method and the double-side wall guide pit method are adopted to construct,The settlement of the upper subgrade is small and relatively stable,and the effect of the full-section excavation is large.Therefore,in the shallow-buried tunnel construction with poor surrounding rock conditions,it is not recommended to use the full-section for construction,and it is recommended to adopt the CRD method and the double-side wall-guide method with partial excavation and temporary support.(6)The deformation law of subgrade and tunnel surrounding rock before and after advance reinforcement is analyzed by numerical simulation.It is found that the deformation of surrounding rock and subgrade is close to 1.5 times ～2 times of that of advance reinforcement construction without advanced reinforcement,which is not conducive to construction stability.(7)The deformation standard should be controlled within 30 mm when the super-shallow-buried tunnel is considered to pass through the important road base of the city by counting the settlement value and the control standard of the similar project,and considering the condition that the smoothness of the road surface is guaranteed,the deformation standard should be controlled within 30 mm when the super-shallow-buried tunnel is considered to pass through the important road.(8)The deformation control measures of super shallow buried large section tunnel passing through subgrade are applied to Xiamen Lianyue tunnel through existing traffic subgrade engineering.Under the control methods of deep burying,advanced reinforcement,partial excavation,land subsidence prediction and so on,the deformation of subgrade and tunnel is effectively controlled,which shows that the conclusion obtained in this paper has certain engineering applicability.However,due to the limitation of route selection,the subgrade is parallel to the tunnel,so the deformation of subgrade is larger than that of the study area.