Study On Stress And Deformation Characteristics Of Initial Support Of Loess Tunnel

In recent years,with the popularization of high-speed railways and highways,more and more lines have passed through the loess area.The completed high-speed railways such as Lan xin and Zheng xi have built a large number of loess tunnels with a section of about 150 m~2.The design and construction of the loess tunnel has been completed.It is an inescapable technical problem for the western transportation network.During the construction of the built loess tunnel,there have been many problems such as excessive ground subsidence,wide ground cracks,water leakage,and lining cracking.However,the large-section loess tunnel has a larger disturbance area to the soil during construction,which is prone to suddenness.Collapse and large-scale ground cracking and other disasters.The initial support is the key structure to ensure tunnel construction safety and tunnel stability.Only when the force mechanism of the initial support is truly understood and the deformation amount is effectively controlled can the construction be optimized under the premise of ensuring construction quality and safety.Method to speed up the progress of the project.Because the loess strength is small and the degree of integrity is poor,this paper uses the load-structure model as the research basis,that is,the surrounding rock pressure on the lining is applied to the model as the external load,and the structural mechanics theory is used to design the lining.The main research contents and related conclusions are as follows:(1)System bolt mechanismExploring the reinforcement of the surrounding rock by the system anchors—mainly studying the contribution of the system anchors to the elastic resistance.The combination of theoretical derivation and numerical simulation is used to find the relationship between the system anchor and the elastic resistance,and the results are corrected and improved by field test.The anchor rod can improve the elastic resistance of the loess.The smaller the elastic modulus of the surrounding rock of the loess,the more obvious the effect of the anchor rod on the elastic resistance of the surrounding rock.The anchor bolt of the shot system in this test section has a reinforcing effect of 1.4 times the elastic resistance of the surrounding rock.When the surrounding rock conditions are relatively broken,that is,the greater the influence range of the tunnel excavation on the surrounding rock,the smaller the impact strength of the same quality anchor.Increasing the length of the bolt or the circumferential spacing of the encrypted anchor when the other conditions are the same can improve the elastic resistance of the surrounding rock at this time.(2)Locking anchor pipe reasonably set angleThe deformation of the weak and broken surrounding rock is mainly based on the overall settlement.Controlling the subsidence at the arch can significantly control the deformation of the lining of the loess tunnel.Due to the insufficient bearing capacity of the loess tunnel,the control at the arch is mainly supported by the lock anchor pipe.The numerical simulation method is used to determine the reasonable installation angle of the lock anchor pipe,and the influence of different foundation bearing capacity and different quality anchor pipe on the structural force and safety is further analyzed.On the site,different lengths and different numbers of lock anchor pipes can be arranged according to the different bearing capacity of the foundation and the requirements for structural settlement.Calculate the angle of the locking foot anchor pipe is close to 80°.Due to the construction on site,the vertical locking foot anchor pipe can not be applied.Therefore,60°is selected as the reasonable shooting angle and calculated.The function of the lock anchor pipe is that the upper step is the largest,followed by the middle step,and finally the lower step.Therefore,the high-quality lock anchor pipe is decisively affected during the construction of the upper step.(3)Initial support dynamic force analysisThis section tests the early strength of the shotcrete and the variation of the surrounding rock pressure,and combines the early strength of the concrete with the steel frame to determine a reasonable steel frame form.The combination of field test and numerical simulation is used to establish the concrete strength growth curve and the surrounding rock pressure change curve.The load structure method is used to obtain the initial support structure stress and deformation at different moments,and the safety factor is calculated.When the early strength control of concrete is better,and the structure does not require much control on settlement,the grid steel frame support can be selected;otherwise,the steel frame support should be selected.Through the research and analysis of the above contents,the paper systematically discusses the system anchors,lock anchor pipes and shotcrete structures in the initial support of the loess tunnel,and proposes the corresponding supporting parameters.I hope that the research results in this paper will be similar to the loess in the future.The tunnel provides a certain reference value.