Study On Treatment Methods And Deformation Characteristics Of Saline Soft Soil Ground Of Expressway In Xinjiang Province

Xinjiang province has the most widely saline soil distributed in our country. Saline soil has lots of harms to expressway engineering, such as dissolve falling, salt expansion, corrosion, frost boiling, deformation, etc. As a result, it is necessary to improve saline soil foundation under embankment. The dissertation describes research work on treatment methods and deformation characteristics of saline soft soil foundation of freeway in Xinjiang province. Based on indoor and in situ tests,3D numerical simulation and theoretical analysis, technology and effect of three treatment methods including gravel compaction column, dynamic replacement method and replacement method, deformation characteristics of saline soft ground are researched systematically.The main research achievements are summarized as follows:(1) Definition, classification and distribution in our country of saline soil are introduced at length. a comprehensive review is conducted on literature of origin mechanism, engineering harms and treatment methods of saline soil. The state of the art of characteristics of soft soil foundation under embankment load is also summarized. In addition, the existing problems in the literatures are discussed.(2) According to filed sampling and in-situ tests for basic physical and mechanical property of soil, engineering property of saline soft soil is studied. The results show that its formation type is lake and alluvial facie, which has middle-high compressibility and large degree of salinization. The ratio between Cl- and SO42- is 06-0.8, so sulphate is the main salt type. On the basis of informed research, how salt content effect on engineering property is induced and analyzed.(3) Design methods, construction techniques and equipments of three treatment methods including gravel compaction column, dynamic replacement and replacement method at experimental sections are summarized. Then the effect of these methods is researched based on in situ test including composite foundation loading test, cone penetration test, dynamic penetration test and compactness test etc. The results show that foundation capacity has enhanced obviously; strength of gravel compaction column and compactness of replacement layers have been all up to standards.(4) Deformation characteristics of saline soft soil foundation on embankment are studied based on in situ test. The results show that ground settlement increases as embankment height increases. Ultimate settlement calculated with hyperbola solution is only 8 mm, which meets standard requirements. The settlement of soil between columns is often bigger than column's. The typical curve of lateral deformations along the depth is bow-type. The maximum lateral displacement occurs to soft soil layer under the ground surface. Excess pore pressure increases while embankment fills, and decreases while embankment standing gradually. The value of maximum excess pore pressure is very small and dissipates rapidly(5) Deformation characteristics of saline soft foundation on embankment are studied based on 3D numerical simulation. The results show that settlements of column and soil increase as embankment rises, then stabilize gradually after embankment finishing. The differential settlement affects mechanism of distributions and diversion between columns and soils under embankment load. The column-soil differential settlement of 1 year after embankment finishing is 2.2% of the total settlement. The typical curve of lateral deformations along the depth is bow-type. Lateral deformation at different depths increase as embankment raises, then decreases gradually while embankment standing, stabilize at last while finished. The initial excess pore pressure increases as depth because of vertical gradient of excess pore pressure induced by column-soil load transferring. The closer is the distance to drainage surface; the faster excess pore pressure dissipates.