Analysis Of Mechanical Effect Of Existing Tunnel Expansion On One Side And Research On Bolt And Shotcrete Support

With the continuous development of China’s highway construction industry,the upgrading and renovation of low-grade roads are being carried out on a large scale nationwide,and the problem of rebuilding and expanding existing tunnels is increasingly facing builders.At present,there is limited theoretical research specifically focused on the expansion of existing tunnels,and key issues such as tunnel excavation and anchor spray support are mainly based on the relevant theories of newly built tunnels.Due to the release of some stress in the existing tunnel,there may be many problems when referring to the design and construction experience of new tunnels.Therefore,it is particularly important to study the construction of existing tunnel expansion projects.This paper combines specific engineering examples and conducts the following work on the analysis of mechanical effects and optimization of anchor rod support parameters under the unilateral expansion method in the expansion of existing highway tunnels:1)Based on the theoretical analysis of tunnel mechanics,the stress and deformation of the surrounding rock during tunnel expansion construction,the elastic-plastic zoning of the surrounding rock,and the stress-strain of the support structure were discussed,laying a theoretical foundation for the research in this article.Based on specific engineering,collect relevant information on tunnel design and construction,consult research literature on tunnel expansion at home and abroad,and use the large-scale finite element software Midas GTS NX2020 to establish a tunnel expansion model.Calculate the theoretical values of arch settlement and peripheral convergence,and verify the rationality of the expansion tunnel finite element model by comparing it with on-site monitoring data of tunnel construction;2)Analysis of mechanical effects of unilateral excavation of existing tunnels: For Class III,IV,and V surrounding rocks,the unilateral excavation widths of 1.5 meters,3 meters,4.5meters,6 meters,and 7.5 meters were selected in order to establish a calculation model for the expansion tunnel,calculate the stress of the surrounding rock,arch settlement,and peripheral convergence.Study the influence of different levels of surrounding rock and excavation widths on the distribution of stress and displacement in surrounding rock without supporting structures,obtain the maximum values and positions of surrounding rock stress and displacement,and prepare for the optimization research of anchor spray support parameters;3)Optimization study on the parameters of single side excavation anchor spray support for existing tunnels: anchor rod lengths of 2.5 meters,3 meters,and 3.5 meters,anchor rod spacing of 0.8 meters,1.0 meters,and 1.2 meters,spraying thickness of 20 cm,25cm,and 30 cm,spraying strength of C20,C25,and C30,and 1215 finite element analysis models were established through orthogonal combination.Study the influence of anchor spray parameters on the stress and displacement of surrounding rock,and obtain the optimization sequence of support parameters.By calculating the arch settlement,peripheral convergence,anchor axial force,shotcrete tensile stress,and shotcrete compressive stress under different levels of surrounding rock and different excavation widths,the mechanical response of the surrounding rock and support structure is obtained as a function of the parameters of shotcrete support.The parameters of shotcrete support are optimized in accordance with relevant regulations and engineering economics.