Study On Shrinkage Property Of Cement And Soil Tuff Curing Agent To Improve Highway Subgrade Soil

According to National Highway Network Planning(2013-2030),In the new era,China’s highway construction has entered an all-round development stage.Highway subgrade is an important part of highway.The shrinkage of subgrade soil not only has a direct impact on the engineering structure,but also reduces the strength of soil,which seriously affects the road performance.Zhangjiakou,an Olympic city,is located in the northwest of Hebei Province,where the temperature difference between day and night is large and silty clay is widely covered.At present,the application of traditional solidifying agents,such as cement,lime and fly ash,has a large drying shrinkage coefficient,which is liable to crack,and also causes many problems,such as environment,roadbed diseases and so on.In order to explore the shrinkage properties of highway subgrade soil in Zhangjiakou seasonal frozen area,based on the freeze-thaw cycle conditions in seasonal frozen area,a new type of solidifying agent of soil tuff(a new economic,energy-saving and environmental protection material synthesized from red mud,fly ash and other industrial wastes to solidify all kinds of soil)and a traditional cement solidifying agent were used,and two different mixing ratios were completed by using high-low temperature alternating test box and static strain gauge.The shrinkage tests of improved soils are explored,and the shrinkage properties of the two improved soils are analyzed by SPSS and MATLAB data processing software.The main research and analysis contents are as follows:(1)The basic physical properties such as particle analysis,compaction and liquid-plastic limit of soil samples are tested,and the related properties and characteristics of traditional solidifying agent cement and new solidifying agent of soil tuff are briefly described.Through the basic physical properties of soil samples,it is determined that the tested soil samples are silty clay with low liquid limit,and the optimum moisture content and maximum dry density of the improved soil are obtained under various dosages,so as to improve the shrinkage performance of soil.Relevant experiments provide parameters and research directions.(2)Drying shrinkage,temperature shrinkage and flexural-tensile tests were carried out on two kinds of improved soils with five mix ratios.Comparing and analyzing the shrinkage relationship and change trend of two improved soils under different dosage,different drying and wetting,different temperature cycle and so on,it is concluded that the shrinkage strain of the improved soils with 6% cement and 8% soil condensate is smaller,and the maximum shrinkage strain of the two improved soils appears near the optimum water loss rate,and the temperature shrinkage strain data of the two improved soils show a "spiral" change.The temperature shrinkage strain of cement and soil tuff improved soil increases gradually with the increase of content,and the new curing agent of soil tuff is superior to cement in improving the dry-temperature shrinkage performance of silty clay.(3)Using SPSS and MATLAB data processing software,two kinds of improved soils are estimated and analyzed by non-repetitive two-factor regression curve,and the relationship between dry shrinkage strain and mixing amount and time is obtained by means of multiplication and counter-evidence.The experimental and software data analysis all reflect that the key maintenance of improved soils is needed to reduce shrinkage deformation 15 days before the actual project.The mechanism of the internal change of the improved soil in the process of drying shrinkage and temperature shrinkage is further elaborated.Meanwhile,the flexural-tensile test is carried out to obtain the flexural-tensile properties of the improved soil and provide parameters for the crack resistance of the improved soil.The shrinkage and crack resistance of the two improved soils are evaluated by the crack resistance coefficients of drying shrinkage and drying shrinkage energy,temperature shrinkage and temperature shrinkage energy,and the improvement of 6% cement content and 8% soil condensate content is obtained.The crack resistance of soil is better.