| The roadbed is the foundation of the pavement structure,and the roadbed with excellent working performance can provide important support for the pavement structure to withstand driving loads for a long time.During the initial stage of service,the roadbed usually has sufficient strength and resistance to deformation.However,due to the influence of climate and environment,the humidity of the roadbed gradually increases,resulting in a gradual decrease in the roadbed modulus,which in turn leads to the deterioration of the roadbed’s working performance.Its resistance to deformation is difficult to achieve the expected goals in the initial design stage,which may lead to pavement structural diseases and a decrease in road service level.Therefore,conducting systematic research on the deformation behavior of roadbed structures under humidity has important theoretical significance and engineering value.Red clay is widely distributed in the south of China,which has excellent mechanical properties such as high bearing capacity,strong shear resistance and low compressibility,and is often used as natural subgrade filler.However,red clay is a special type of soil with strong water sensitivity.Due to adverse engineering properties such as softening and cracking due to water loss,red clay roadbed has significant engineering hazards.Therefore,this article combines the National Natural Science Foundation of China project "Calculation Method and Evolution Mechanism of Dynamic Resilience Modulus of Roadbed Structure under Driving Load and Humidity Changes"(project number:51908562),and takes the red clay roadbed filling material of the "G5513 Yiyang Changde Expressway Expansion Project" as the research object.Through indoor experiments,model tests,and numerical analysis,the basic physical and mechanical properties,water holding capacity,and We have conducted systematic research on deformation characteristics and structural deformation,and the main work is as follows:(1)The mineral composition,soil properties,and compaction characteristics of red clay samples were studied using indoor experimental methods.The experimental results show that the main mineral composition of the soil sample is mica,followed by secondary clay minerals such as quartz and kaolin,which have strong hydrophilicity,as determined by X-ray diffraction test results;According to particle screening and liquid plastic limit tests,the tested soil sample is high liquid limit clay;Through heavy compaction tests,the optimal moisture content and maximum dry density of the soil sample were determined to be 20.2%and 1.74g/cm3,respectively.(2)Through the filter paper method,experimental research was conducted on the soil water characteristic curves of red clay under different compaction degrees,and the estimation accuracy of different mathematical models was compared and analyzed.The experimental results show that different compaction degrees have a significant impact on the water holding characteristics of the test soil sample.When the moisture content is the same,the greater the compaction degree,the smaller the matrix suction;According to the predicted results of the mathematical model,if the soil sample has a high degree of compaction,there are fewer pores in the internal soil,resulting in a lower saturated water content and stronger water holding capacity of the test soil sample;By comparing the estimated results,it can be seen that the VG-3 parameter model and the Fredlund&Xing model can better describe the soil water characteristic curves of red clay under different compaction conditions,providing a theoretical basis for the subsequent calculation of moisture field in roadbed structures.(3)Through triaxial tests,the stress-strain behavior of red clay under different humidity and compaction conditions was studied,and the variation law of the initial elastic modulus of the soil sample was analyzed based on the test curve.The test results indicate that as the confining pressure increases,the maximum deviator stress of the test curve gradually increases,and the shear failure mode of the soil sample changes from "brittle failure" to "plastic failure";With the increase of water content,the shear strength of the soil sample softened,and the failure deviatoric stress gradually decreased;This study proposes an exponential prediction model for the initial elastic modulus,which can better reflect the effects of humidity and confining pressure on the elastic modulus.(4)Based on the water holding and deformation characteristics of red clay mentioned above,this paper designs a roadbed structure model test that can reflect the influence of humidity,and uses PFWD testing to study the deformation behavior of the roadbed structure under different structural layer thicknesses and humidity conditions.The research results indicate that as the thickness of the soil layer increases,the rebound deflection of the top surface of the roadbed structure gradually increases;It can be seen from the measured results of the hygrometer that after water injection at the top of the model,the soil moisture in the model gradually increases along the depth direction after the infiltration process and the moisture reaches stability,which can reflect the moisture change of the subgrade structure;Under the action of load,the stress at various points inside the roadbed structure responds to varying degrees,and the amplitude of stress change decreases with the increase of depth.(5)In order to further characterize the deformation behavior of the roadbed structure,this paper establishes a finite element model of the roadbed structure considering the humidity state,and compares and verifies it with indoor model tests.The research results indicate that compared with the deflection results of indoor models,the numerical calculation results have good correlation and can simulate the impact of changes in roadbed humidity on roadbed deformation;Compared with traditional linear elastic models,the numerical calculation method proposed in this paper can describe the non-uniformity of elastic modulus at various points within the roadbed,which is more in line with the actual situation;In subsequent calculations,the changes in humidity field under different climatic environments should be introduced to predict the deformation behavior of the roadbed structure during the service period. |
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