Research On Construction Technology Of Fully Weathered Granite Subgrade Of Liuyang-Liling Expressway

There are a large number of weathered granites distributed in the 15~17 contract section of Liuyang-Liling Expressway.This thesis focus on the filling technology of the fully weathered granite roadbed of Liuyang-Liling Expressway.Through investigation of relevant research results and engineering experience,combined with indoor experiments and field tests,the full-weathered granite's engineering characteristics,soil improvement technology and on-site compaction characteristics were studied,and the construction plan of the fully weathered gr anite subgrade was finally determined.The main research contents and results of this thesis include:Firstly,extensively collect the distribution of granite,natural geography and engineering environment in the highways already built in Hunan Province with the purpose of providing reference for the construction of the Liuyang-Liling Expressway.Through on-site reconnaissance and indoor geotechnical tests,the engineering characteristics of weathered granite were analyzed.Then,six on-site compaction test plans were prepared,and on-site compaction test was carried out on the 15~17 test sections.The field test results showed that the compaction degree of the 15 and 16 test sections were all lower than 93%.Only the compaction degree of the 17 contract section can meet the requirements of the specification for the embankment filling.The results of on-site settlement test show that the cumulative settlement of the 15-17 contract section with the optimal compaction scheme is 9cm,9cm and 6.3cm respectively.After that,the improvement technology of the fully weathered granite subgrade soil of Liuyang-Liling Expressway is studied.The results show that the addition of cement or lime can reduce the plasticity index of fully weathered granite soil and improve the maximum dry density and unconfined compressive strength.The relationship between the maximum dry density and the unconfined compressive strength of the modified soil with the amount of cement or lime is obtained by means of related mathematical tools.Finally,combined with economic comparison and theoretical analysis,the construction plan and quality control standard of Liuyang-Liling Expressway was finally determined: The lower embankment of the 15~17 contract section shall be constructed according to Scheme 3,Option 4 and Option 3 respectively.When construct the upper embankment,weathered granites should be replaced by strong weathered slate fiestly.And then,deflection test should be carried out.If the deflection on the top surface of upper embankment is less than 293(0.01mm),the road bed will continue to be filled with strongly weathered slate.Otherwise,soil improvement should be adopted in road bed.Thickness should be determined by the results of the deflection test.