Characteristics Research On Settlement Of Expansive Soil Natural Foundation And Cfg Pile Composite Foundation Of Liuzhou-Nanning Passenger Dedicated Line

This paper researches two sections in litang test section in liuzhou of Liunan Passenger Railway, and they are D1K559+650(CFG pile foundation) and D1K559+671.52(natural foundation) in the same geological conditions and a similar filling. Comparative and analytic researches are made on the results of a series of test, such as plate loading test, static cone penetration test, standard penetration test, lateral pressure test, laboratory consolidation (compression deformation) test.settlement observation and so on. And the main research contents are summarized as follows:1. some parameters about the corresponding soils, such as bearing capacity of foundation, compression modulus (or deformation modulus), can be determined through a series of in-situ test. Through the contrast of plate loading test results between CFG pile foundation and natural foundation, its bearing capacity requirements can be meet by this reinforcement treatment. Plate loading test on a single pile may underestimate the settlement of composite foundation according to some references,so it is essential to analyze the follow-up measured data and revise the results of the test. According to analysis and comprehensive of test results in situ test, the results of compression modulus from standard penetration test and bearing capacity of soil layers from static cone penetration test are more credible.2. Whether natural or CFG pile foundation, the measured base stress increased with filling can be divided into three stages:in the early filling,the increase is not obvious; along with the continuous filling, the value increase sharply; when standing, the value remain unchanged basicly. Different from natural foundation, the stress on the top of pile may increase slowly when standing, which can explain the load transfer from soil among piles to pile top through soil arching.3. through the comparative analysis of the theoretical calculation and the measured,whether natural or CFG pile foundation,the calculations valued by the method of elastic earth and modified ratio are closer to the measured ranged the whole road shoulder,and the latter is simple and convenient. And it is necessary to analyse the follow-up measured value and determine the application in high embankment conditions.4. According to the deformation observation in filling two stages of the two sections.whether natural or CFG pile foundation.the settlement in filling can be divided into three stages,and the latter is more less.For CFG pile foundation.the value of soil among piles is greater than the top of pile,but along with filling,especially after standing,the increasement of deposition of the top of pile is greater than the soil among pile.but the difference is not great. Through the analysis of the settlement curve of the two sections, it is found that CFG pile can reduce the measured value lagerly and slow down sedimentation rate.5. Compared the theoretical calculations of additional stress, the final settlement calculated by the method of elastic earth,the formula (4-13) or the diffusion angle from method of elastic earth, are closer. And the differece between the diffusion angle and method of elastic earth decrease with the increasement of L/H,and the former is more convenient as both the two sections of the depth of the compressible soil are certain.6. According to the calculated results when choosing different parameters of natural foundation.the differences of final settlement reach greater to38%, dueing to the compression modulus.It is suggestion that the value of modulus can be determined by standard penetration test,considering the factors such as operability.feasibility and economy.7. The filling will be in three stages,so Asaoka method is used for the prediction of final settlement. The datas of the second stage is not sufficient dueing to time,leading to the difference between the predicted and the calculated is up to50mm.So it is essential to correction and optimization on the basis of the abundance follow-up datas.in order to enhance the analysis and studies about the settlement when filling,which make the predicted method more suitable for expansion of the ground.