The Synergetic Principle And Design Method Of Tunnel Support System

Tunnel support system is the basic requirement to ensure the stability of surrounding rock.However,due to the great diversity of tunnel surrounding rock conditions in China,there are still many confusions in support timing selection,support parameters determination and support reliability evaluation in specific engineering design,which makes the tunnel quantitative design struggling.In general,The tunnel support system is composed of surrounding rock as subject and artificial support structures such as pre-support,primary support and secondary lining.At present,the mechanisms,objectives and technical standards of various supports are uncertain,resulting in the tunnel design theory lagging far behind practice.Therefore,starting from the essence and purpose of tunnel support,the support-surrounding rock dynamic interaction mechanism is revealed,the support demand and the stability control principle of surrounding rock are clarified.And then the mechanisms of pre-support,primary support and secondary lining are systematically studied,as well as their characteristics and adaptabilities.Finally,the synergistic design method of tunnel support system is put forward.The main work and research results are as follows:(1)A method for predicting the deformation and failure of tunnel surrounding rock is established,and the spatial and temporal evolution mechanism of the tunnel support-surrounding rock interaction is revealed.In view of the problem that the previous research on support-surrounding rock interaction mostly focused on a single support structure and could not reflect the mechanical characteristics of tunnel construction process,the prediction methods for the engineering responses of tunnel surrounding rock are established,the spatiotemporal evolution laws and influencing factors of engineering responses are analyzed.According to the mechanical principle of tunnel construction,the essential functions of tunnel support that to mobilize and to assist the bearing capacity of surrounding rock are revealed,of which the former is more efficient and should be taken as the basic principle in support design.By statistical analysis of field measured data,the staged evolution mechanism of tunnel surrounding rock deformation is revealed,the proportion and control key of each stage and are clarified.(2)The deformation control mechanism model of pre-support is established and the optimization method of pre-support parameters is put forward.In the past presupport design,only the anti-collapse function is considered and the design scheme could not meet the tunnel safety requirements.The deformation control principle of pre-support is expounded.The work efficiency of different pre-support design concepts are compared,and the peripheral reinforcement is found to be more efficient than the face reinforcement.Then,the deformation control mechanism model of pre-support is established.According to the distribution of surrounding rock plastic zone(s),different configrations as well as the surrounding rock deformation and plastic zone radius of each configration are given.On this basis,the sensitivity analysis of reinforcement parameters is carried out.Combining with the surrounding rock deformation law,the optimization method of the circumferential parameters and longitudinal range of pre-support are put forward.(3)The main bearing capacity of the primary support of the tunnel is defined,and the synergistic design method and evaluation system of the primary support system are established.According to the differences in mechanisms,the primary support is divided into anchorage system and surface primary support,whose support-surrounding rock coupling models are set up and analyzed,respectively.The effects,adaptabilities and influencing factors of different support structures are studied systematically.The determination methods of support patterns and reasonable support time are put forward.Furthermore,taking the anchorage system as the improvement of surrounding rock,a synergistic design method for the primary support system is established.An evaluation system based on surrounding rock deformation and synergy degree is proposed.In this way,the quantitative design of primary support is realized.(4)The synergistic mechanism of tunnel composite support structure is revealed and the calculation method of safety reserve coefficient of secondary lining is put forward.The connotation and realization of secondary lining as safety margin are clarified.The interaction model of composite support structure and surrounding rock is established and analyzed,the support stresses,deformations and load bearing ratios at different space positions are obtained.Based on the tunnel long-term safety,the evaluation method of synergy between composite support structure is proposed.Furthermore,the support capacity diagrams are established,and the calculation method of support reserve factor is proposed,thus the tunnel safety in service can be ensured.(5)The synergetic principle of tunnel support system is expounded,and the synergetic design method of support structure system based on multi-objective optimization is established.Based on the evolution mechanism of tunnel support-surrounding rock interaction,the synergetic principle is introduced into tunnel support design.The synergetic support system is set up,whose components,basic characteristics and research levels are clarified.Furthermore,the synergistic mechanism of tunnel support system is analyzed.Taking surrounding rock deformation,support force and support cost as the design objectives,the synergistic optimization design method of tunnel support system is established and applied in practical engineering.