Analysis Of Composite Basement Settlement Control For Heavy-haul Railway Loess Tunnel

With the development of the west China and the gradual improvement of the road network,heavy-haul railway has been constrcted into the northwest loess area quickly.The northwest China is a mountainous region.In order to meet the needs of heavy-haul raiway traffic,and to complete the goal of overcoming the height difference,shortening the mileage and optimizing the linear index,the construction of the tunnel is indispensable.At present,the research on heavy-haul railway mainly focuses on the track,roadbed and the bridge,but the research on the impact of tunnel basement is scarce in home and abroad.Chinese existing heavy-haul railway tunnel basement design is lack of normative guidance.During the railway operation period,many bottoms of the tunnel turned cracking,frosting mud,subsidence and other disasters.With the increase of axle and traffic loading,this harmful phenomenon will be more obvious.Therefore,it is of great engineering significant to have study on the composite basement of heavy-haul railway loess tunnel.Taking the Liutiaoshan shallow bias tunnel in the connecting line of Datong to Jungar Banner railway and Shuozhou to Huanghua railway which is located in collapsible loess area as the projiect background,the paper have analyzed the settlement of lime soil compaction pile in the composite basement,discussed the engineering properties and mechanical parameters of remolded loess through laboratory tests,used theoretical formula and numerical simulation to calculate the settlement and variation of composite basement,and analyzed the effect from parameters of lime compaction pile on the settlement of composite basement.The main work and achievements of this paper are as follows:1.By gathering and access to literature,the paper have summed up the status of heavy-haul railway development at home and abroad,loess tunnel composite basement research and the application of lime soil compaction piles to put forward the research content and the technical route of this paper.2.Remolded loess permeability test and the triaxial shear test results showed that the elastic modulus changing with water content and dry density approxiamately linear,and cohesion changing with water content and dry density approxiamately exponential relationship.Meanwhile,the test results provide the soil mechanical parameters as numerical simulation of composite basement.3.The paper have established settlement calculation model of composite basement of the heavy-haul railway tunnel in loess,and determined the composite basement loading conditions.The composite basement additional stress was calculated by the method of corner points,and the settlement of the composite basement calculated by layerwise summation method.4.The paper have established finite element numerical analysis model in different depths of natural loess foundation and lime soil compaction pile composite foundation to analyze the influence for settlement of different stratigraphic structure and pile tip position.The maximum settlement has been determined which at the entrance of the tunnel,and the effect of lime soil compaction pile on the settlement of the tunnel basement has been studied.5.The paper combined with Liutiaoshan tunnel as engineering example to determine parameters and the reasonable range of lime soil compaction pile.Based on the orthogonal experiment design scheme to make a significant test of the parameters,the results find that the change of pile length on the settlement is the most significant effect.The paper obtained an exponential relation of composite basement settlement and parameters.Combined with the settlement law,the optimization design for Liutiaoshan tunnel composite basement has been proposed.