Research On Application Technology Of Cement Soil Subgrade Engineering In Seasonal Frozen Area

Subgrade is the foundation of highway engineering.Good overall stability,high strength,and stable water temperature stability are the basic requirements for subgrade and the prerequisite for normal use of roads.If the mechanical properties of the subgrade soil cannot be effectively guaranteed,coupled with the repeated action of vehicle loads,the subgrade structure will be damaged and diffracted to the pavement to form cracks and congestion,which will seriously affect the normal use of the pavement structure.Along the expressway from Shuangliao to Taonan,silty sand with the characteristics of "high saltiness and low viscosity" is widely distributed,which is manifested as loose texture,low viscosity content,poor water retention,and poor compaction effect.At the same time,if the soil mass is excessively compacted,the shaped soil mass structure is easily damaged,and it is not suitable to be used directly as a subgrade filling material.In order to solve the above problems,and at the same time comply with the requirements of the current norms,such as adapting measures to local conditions,using local materials,and effectively utilizing resources,this paper proposes to use cementmodified silty sand as roadbed filler,that is,cement-modified soil.As a subgrade filler,cement-modified soil must not only meet the road performance requirements for subgrade soil in relevant specifications,but also maintain reliability under long-term cyclic vehicle loads.Therefore,this paper takes the cement-improved subgrade soil in the seasonally frozen area as the research object,and relies on the Shuangtao Expressway project in Jilin Province to systematically explore the road performance,static characteristics and dynamic characteristics of silty sand under different cement content conditions.Determine the best mix ratio of silty sand and cement.On this basis,the test road section is laid,the sensors are embedded,and the rolling construction process is continuously monitored in real time,and the subgrade filling quality is ensured by accurately controlling the compaction of the subgrade soil.This paper takes the construction of the subgrade of Shuangtao Expressway as the engineering background,through the method of laboratory test and field test,from the theoretical point of view,the engineering characteristics and application technology of cement-soil subgrade are deeply studied,in order to form the construction technical standard of cement-soil subgrade in seasonally frozen area,for the purpose of The application of cement-soil roadbed in Jilin Province and other seasonally frozen regions provides theoretical basis and practical reference.The main results of the paper are as follows:(1)The comprehensive characterization parameter PCT for the strength of cementmodified soil is proposed.PCT can better reflect the influence of factors such as watercement ratio,cement content,and curing age on the unmeasurable compressive strength of cement-modified soil.The strength and comprehensive characterization of cementmodified soil The parameter PCT has a good power function relationship,and this relationship can be used to predict the strength of cement-modified soil in practical engineering.(2)The static elastic modulus increases with the increase of the cement dosage,and decreases with the increase of the number of freeze-thaw cycles.After the cycle,the static elastic modulus tends to a constant value,and the static elastic modulus decreases the most after the first freeze-thaw cycle;the dynamic elastic modulus of cement-improved soil is positively related to the cement content and confining pressure,and is related to the cyclic deviatoric stress.was negatively correlated with the number of freeze-thaw cycles.(3)From the characterization model of dynamic resilience modulus,the summary dynamic resilience modulus of cement-improved soil is obtained,and a static resilience modulus prediction model is proposed.The static and dynamic elastic modulus conversion formula is constructed,and the fitting effect is ideal.The 2%,3%,and 4%cement content of the improved soil all meet the requirements of the specification,and the 2% cement improved soil is only slightly larger than the specification requirements.Considering the mechanical properties of materials and economic factors,it is recommended to use 3% cement.Quantitatively improved silt sand is used as subgrade soil.(4)During the rolling process of the road roller,the earth pressure has a significant attenuation along the depth direction,about 20% for the thickness of 30 cm,and about60% for the thickness of 60 cm.The highest peak value of vibration acceleration gradually decreases along the depth direction.During the first two times of rolling,the peak value of acceleration is small.After several times of rolling,the compaction degree of subgrade soil increases,and the peak value of acceleration becomes larger.The soil layer with a thickness of more than 60 cm has poor energy transfer effect,and the soil layer with a thickness of about 30 cm has a good rolling effect.Considering the project cost and construction efficiency,it is recommended to choose 30 cm thick cementmodified soil for layered filling.(5)The fitting function between the effective value of acceleration and the degree of compaction is constructed.The fitting effect of the two is good,and the fitting degree is above 94%,which proves that in the process of rolling,the effective value of acceleration after signal processing is used to predict the subgrade soil pressure.The solidity is practical and feasible,which provides a new idea for non-destructive inspection of the compaction.