Study On Lime And Cement Improvement Of Loess Filler And Field Replacement Effect

Gansu Province is located in the west of the Loess Plateau.In different regions of province,the loess have great differences in collapsibility,engineering characteristics,physical and mechanical characteristics,water sensitivity and other aspects.In recent years,the mileage of expressway construction and operation in Gansu Province has increased substantially,and many highways in the province have also been planned and designed.However,the geological conditions in Gansu Province are complicated,and there are many strata through which the highway is built.This situation will brings many problems to the highway design,construction process and maintenance after opening to traffic.Therefore,it’s a key and important work for highway construction in loess area to unify the technical standards of loess area design in the province.Unified standards can improve the quality of highway construction and disaster prevention level,reduce the risk of highway diseases caused by external factors during operation,and ensure the driving comfort and operation stability of expressway.In this study,the typical loess in eastern and western Gansu Province was used as the test material to study the improvement effect of lime and cement on loess highway subgrade filler.Firstly,the physical and mechanical properties of typical loess are determined by the limit moisture content test,particle analysis test,leaching solution test and compaction test.Then,lime and cement are used as inorganic binders added into loess for improvement.By controlling the mixing ratio and curing time of inorganic binder,the strength and deformation characteristics of improved loess are studied and analyzed by using unconfined compressive test,direct shear test,limit moisture content test,mixing ratio test,freeze-thaw cycle test and other related indoor tests.In the existing specifications of highway engineering,the strength of improved soil is based on the unconfined compressive strength after curing for 7 days,which is the basis of this study.Firstly,the mixing ratio test is carried out to test the influence of different lime mixing ratios（3%～12%）and cement mixing ratios（2%～10%）on the strength of improved loess.The test results show that lime and cement,as improvers,have obvious improvement effect on loess.With the increase of mixing ratio,the strength of improved loess firstly increases obviously,then gradually slows down and then a plateau appears.According to the experimental analysis,when the lime content is 5%～8%and the cement content is 4%～6%,the improved loess has the best economy under the premise of ensuring the specified strength.In the curing test and durability test,the lime mixing ratio is 5%and 8%,and the cement mixing ratio is 4%to discuss the influence of curing time on the strength of improved loess.The results show that there is no significant relationship between the strength improvement of lime-improved loess and curing time,and the strength of improved loess has reached 80%of that of 28 days after curing for 7 days.The improved cement loess has the characteristics of high early strength,and the strength increases obviously with the curing time after curing for 28 days.And it is greatly influenced by the number of freeze-thaw cycles.After 8 freeze-thaw cycles,the unconfined compressive strength of cement-improved loess decreased the most,and the strength attenuation was basically stable after the 12th freeze-thaw cycle.The field test of lime-soil replacement was carried out in the construction section of the expressway under construction.Through the test of 5%,8%lime mixed improved loess and 4%,6%cement mixed improved loess,the technical parameters of lime-soil cushion replacement treatment method of loess foundation and the evaluation and treatment effect were summarized,the optimal mechanical combination in lime-soil replacement construction process was obtained,and the construction technology was optimized.At the same time,the portable drop weight deflectometer is used to detect the rolled subgrade surface layer,and the dynamic deformation modulus(E_vd)test value is correlated with the K value of compaction degree,and the results are highly correlated.Then,the conversion formulas of E_vd and K value of loess in different regions in Gansu Province are summarized.The verification results show that it is feasible,rapid and reliable to test the compaction quality of loess subgrade with dynamic deformation modulus tester,and the related research results of this study also provide basic data for the selection of control indexes of new technology for rapid detection of loess subgrade.