Bearing Capacity And Safety Evaluation Of Tunnel Lining Of Shuohuang Railway

In-service heavy-haul railway tunnels suffer from a variety of defects,of which lining cracking is the most common and widespread.With the increasing speed and capacity of trains,the axle weight and grouping of trains are also increasing significantly,which leads to serious lining cracks and even falling blocks.Ultimately,the safety of the structure is reduced,and driving safety is seriously endangered.Therefore,this thesis takes the Shuohuang Railway Sifujian Tunnel as a relying project and establishes a three-dimensional numerical model of the tunnel lining by means of literature research,field measurements and numerical simulations to analyse the effects of cracking on the bearing capacity,dynamic response and safety of the tunnel lining structure under both static and dynamic conditions,which has important engineering and reference values for ensuring the safe operation of heavy-haul railway tunnels under the influence of cracking.(1)Through literature research and on-site investigation,this thesis summarizes the crack morphology and causes of railway tunnel lining crack diseases.Based on these types and characteristics of lining cracks,a classification was proposed for Shuohuang Railway tunnel lining cracks according to "cause + crack direction".(2)Statistical analysis of the distribution range,orientation,length,width and depth of the lining cracks in the Sifujian tunnel was carried out through field measurements,which showed that: the longitudinal cracks accounted for the largest proportion and the most densely distributed part is the top of the arch;the crack length was generally distributed in the interval of 1～5 m,with a roughly normal distribution;the width of cracks is mainly small cracks,nearly half of the total number;the depth of cracks is mainly concentrated in the range of 5-20 cm.(3)By using the "no gravity interaction model",the thesis studied the crack damage evolution process,bearing capacity,and critical soil cover thickness of intact and cracked lining structures.The results indicate that the damage evolution process of the intact lining structure is as follows: arch crown → both sides of the inverted arch → wall foot → side wall,obtaining an ultimate bearing capacity of 2.713 MPa,and converting the obtained ultimate bearing capacity into the critical soil thickness that the lining structure can withstand,which is 118 m.For the cracked lining structure,according to the trend of the load bearing capacity discount rate,comparing the different locations of the cracks,it was obtained that when the initial cracks were preset in the top of the arch,left arch shoulder,left wall and left wall foot,the ultimate load bearing capacity decreased by 4.08%,3.67%,2.62% and 3.83%respectively compared to the intact lining structure;when the cracks were preset in the top of the arch,comparing the geometric properties,it was obtained that the depth of the cracks had a much greater effect on the tunnel lining The degree of influence of the structural load bearing capacity is much greater than that of the length and width.(4)On the basis of numerical simulation,the thesis extracts the internal force values of the lining structure under various working conditions,calculates the safety coefficient of the structure,and quantitatively judges the safety of the lining structure.The results indicate that when the crack depth is 0.5d(d is the lining thickness),the safety factor of the arch crown is only 1.91,which is lower than the standard limit value of 2.0,indicating that the structure is in a dangerous state.(5)By establishing a three-dimensional dynamic finite element model and applying train loads at the center of one of the lines,the vertical displacement and acceleration time history curves of the lining structure at different positions on the same cross-section are obtained.The results show that the vertical displacement of the inverted arch lining at the center of the left line is the largest,while the arch crown is the smallest,and the change in lining acceleration also follows the same pattern.Then,by changing the depth of the cracks at the inverted arch lining,it was found that as the depth of the cracks increased,the peak values of vertical displacement and acceleration at the inverted arch also increased.And the safety evaluation of the lining structure is carried out using the same method as the static working condition.