| This paper takes the expansive soil subgrade of the Liuzhou-Nanning Passenger Dedicated Line as the research object,obtains the relevant mechanical parameters of the subsoil through laboratory and field tests,determines the calculation method of settlement,stability and bearing capacity;takes the subgrade of manganese mining area as the research object,calculates and analyzes the bearing capacity of foundation in composite foundation reinforcement zone;analyzes and determines the representative part of the four-line parallel segment subgrade: distance between lines,drainage design,auxiliary works after station and so on;studies the design measures for karst treatment and rockfall protection under karst geomorphology.The paper analyzes the design results and summarizes the advanced experience,provides the basis for the design and construction of subgrade engineering of Liuzhou-Nanning Passenger Dedicated Line,provides reference for new railways.And the principal achievements are shown below:1.In terms of the expansive soil test,most of the expansive soil in Liuzhou-Nanning Passenger Dedicated Line is weakly expansive;The mechanical properties of soil samples under load were studied by laboratory tests,it is found that the soil samples are moderately compressive and exhibits certain softening and hardening properties;Combineed the field test results for comparison,and selected some appropriate physical and mechanical parameters.2.It can be seen from the comparison results of various calculation methods,that when calculating natural foundation settlement,using the modified proportional load method to calculate the base stress,and using the elastic soil embankment method and the fitting formula to calculate the additional stress,the results are closer to the measured values,the method is also simpler;The settlement of the composite foundation includes the reinforcement zone and the lower layer,by comparing the calculation result of traditional method and the L/3 method,it is found that the two results are similar.However,the calculation process of the L/3 method is simple,therefore,we recommend this approach.3.The stability of the expansive soil embankment was analyzed by the method of Sweden slice method,Bishop method and transfer coefficient method.By comparing and analyzing their differences and similarities in assumptions,equilibrium conditions,applicable conditions and stability analysis results,we find that the calculation process of Bishop and the transfer coefficient method are more precise and reasonable,which provide evidence for determination of stability calculation methods under different conditions.4.Through the comparative analysis of the reinforcement mechanism of composite foundations,it is learned that cement mixing piles mainly enhance the bearing capacity of foundation by hydration,cementation and compaction of pile shaft material and surrounding soil,and prestressed pipe piles are used for railway foundation reinforcement due to their high single bearing capacity and convenient construction;Gave the reinforcement scheme of the cement mixing pile and the prestressed pipe pile respectively,carried out the bearing capacity check of the composite foundation separately.5.Used the correlative specifications and data,determined the minimum line spacing between the two lines of parallel line base was 7.7m;The hydrological calculation results indicated that the drainage capacity of the line gap met the design flow requirements,and set up the auxiliary works after station economically.6.Combined with correlative data and specifications,determined the design principles of karst treatment: For the general karst area,a combination of closed backfilling and borehole grouting reinforcement is adopted;and the strong development section adapted the method of “taking the bridge to replace the road”;Made a targeted study on the protection measures of the development area of dangerous rocks and falling rocks. |
PDF Full Text Request