| As an important city of the western development,Chengdu and its surrounding areas are widely distributed with Chengdu clay,also called expansive soil.Because of the montmorillonite and other mineral components,the expansive soil has the engineering characteristics of water absorption and expansion,water loss and shrinkage.With the further extension of high-speed railway to mountainous area,the subgrade filler should have higher performance and meet the requirements of sustainable development.Using lime to improve expansive soil has good effect and wide range,but it has great influence on environment.As a new type of soil curing agent,biological enzyme has a broad research prospect.In order to study whether the combined action of the two is better than that of single improver in improving the engineering properties of expansive soil,this paper carried out a study on the improvement and optimization of expansive soil in Chengdu area.Through laboratory test and theoretical analysis,the properties of expansive soil under the single and combined action of lime and biological enzymes are studied,and the variation rules of different indexes of the improved soil under various conditions are expounded in detail.The research contents and main achievements of this paper are as follows:(1)This article summarizes the related expansive soil engineering properties,lime,enzymes,the research status of compound modifier modified expansive soil,lime and other modifier can significantly improve the function of engineering properties of expansive soil,thus put forward in this paper,the research direction,and design the corresponding experiment scheme,for the study of enzyme-lime compound modified expansive soil to provide experimental basis.Test main physical and mechanical characteristics of improved expansive soil are studied,including limit moisture content,compaction test,unconfined compressive strength test,and the characteristics of expansion,including the free expansion rate,the load rate,the load expansion ratio and the expansive force,through the analysis of the test results of different modifier on the chengdu area of expansive soil.(2)The mechanical properties of expansive soil improved by a single improver of quicklime and biological enzyme in different dosage ratios were studied through indoor geotechnical tests.According to the compaction experiment it is concluded that the maximum dry density,optimum water content after finish making sample according to0.95 degree of compaction,refer to the test specification complete expected test,it is concluded that different modifier dosage under weak the strength of the expansive soil,expansion properties change rule,based on the analysis of experimental results,the single use of lime,the optimum content of expansive soil enzymes improved chengdu6%,and 0 respectively,The improvement effect of lime is better than that of biological enzyme,and the test conditions are feasible.(3)Based on the experimental basis of Chapter 3,different concentrations of biological enzyme solution were added to the lime mixing soil instead of water solution to form compound improers with different proportions.The physical,mechanical and expansion properties of the compound improved soil were studied experimentatively.The test results show that the optimum dosage of compound improver is different under different characteristic indexes,and the improvement effect is different greatly.After curing the improved soil,the free expansion rate and unconfined compressive strength of the improved soil are significantly improved.The improvement effect of composite improver is better than that of lime improver when the soil sample is subjected to overburden. |
