| The highway traffic infrastructure construction locate the basic and guiding position in the western development and "The Belt and Road" national strategy.As an important part of highway engineering,highway culvert is a large proportion in both the number of projects and the project cost.The construction of the highway culvert which early in the collapsible loess area,because of the landforms and complex geological conditions,the physical mechanical properties of collapsible loess,such as improper foundation treatment will lead to significant settlement and the foundation uneven settlement after soaking,which causes highway culvert appeared different degrees of disease which seriously affect the normal operation of highway.Therefore,it is very important to choose the suitable method for foundation treatment.For collapsible loess foundation treatment of highway culvert area,the depth of processing less than 3.0m required in the "highway bridge foundation design specification"(JDG D63-2007).For the collapsibility of loess in Longxi,the engineering practice shows that the strength of this kind of foundation treatment is weak,and it should be determined according to the features that the collapsibility of loess areas.Based on the construction of Qinghai Eastern Minhe and to Xiaoxia first level highway(III serious)two highway culverts which located on the collapsible loess area as a practical engineering background,using the indoor soil test,test pit water test on site,settlement observation of composite foundation and finite element numerical simulation method,discussed the composite foundation settlement characteristics of highway culvert collapsible loess.On the basis of the above research,the optimal design scheme of composite foundation is put forward.The main research contents and results are as follows:(1)Expound the settlement characteristics of highway culvert foundation in collapsible loess area,and sum up the disease occurring reasons that highway culvert.Induce the common methods of collapsible loess foundation treatment,analyze the reinforcement mechanism and application conditions of lime-soil replacement method and lime-soil compaction pile method.(2)On the basis of test and quantitative analysis the collapsible loess compressibility,collapsibility and permeability of the highway culvert test site:(1)The compression coefficient of two different depth highway culvert site site of collapsible loess through indoor soil test to determine the two test points,highway culverts soil showed moderate compression.(2)The field immersion test of test pit with the diameter of 20.0m,depth of test pit 50 cm,and in the pit at the bottom of laying 10~20 cm thick gravel,the site measured weight test pit in collapsible loess layer thickness of 15.0m.Immersion test of test pit at the site after injection,which happens obvious collapsibility and a funnel shape at test pit surface,and deformation different at the different positions.(3)Through the test pits of different depth and location where buried the TDR moisture probe,analysing the infiltration process of the moisture content in the test pit including vertical and horizontal direction.Experiment results showed that the permeation rate of collapsible loess in the vertical direction of the 1.7~5.9E-04 cm/s through field immersion test of test pit,the permeation rate of collapsible loess in the horizontal direction of the 1.2~4.6E-04 cm/s.(3)Experimental study on foundation treatment and foundation treatment effect of highway culvert:(1)Using the lime-soil replacement method of the foundation treatment depth of 3.0m and the lime-soil compaction pile with the depth of the foundation treatment are 6.0m,respectively.(2)Monitoringthe settlement deformation of composite foundation on site,comparative analysis of collapsible loess area of culvert foundation treatment effect.(3)Using hyperbolic curve method,three point method and Asaoka method to predict the final settlement of composite foundation of two highway culverts.(4)Comparative study on numerical simulation of composite foundation of highway culvert site:(1)MIDAS/GTS software was used to simulate the composite foundation of lime-soil replacement and lime-soil compaction pile composite foundation.(2)The comparative analysis of site monitoring that composite foundation settlement results and numerical simulation results to verify the rationality and validity of the numerical simulation.(3)Choosing the lime-soil compaction pile composite foundation model,considering the effect of pile length,pile diameter and pile spacing on the settlement of lime-soil compaction pile composite foundation,respectively.(5)Based on the settlement characteristics of the composite foundation of two highway culverts and the requirements of the existing design specifications,the paper puts forward the design scheme of the composite foundation in collapsible loess area.It is suggested that the depth of foundation treatment should be increased on the basis of the corresponding design specification in the collapsible loess area,and the depth of foundation treatment should be above 5.0m.At the same time,it is necessary to improve the highway culvert drainage function and highway culvert foundation seepage control function.The research results can provide project instance reference for the revision of the relevant provisions of the design specification. |
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