Analysis Of Equilibrium Density And Long-term Strength Of Silty Soil Subgrade

In recent years,the traffic volume of some pre-built highways has become increasingly saturated,and traffic pressure is increasing.In order to save land resources and reduce the adverse impact of new highways on the region and the economy,the broadening of old subgrades has become the main way to expand and renovate highways.However,the excavation and detection of the old subgrade in a large number of reconstruction and expansion projects was found that the subgrade moisture content increased and the compaction degree decreased,which were contradicted with the traditional theory of compaction settlement of subgrade soil.The attenuation of soil density and the increase of moisture content will exacerbate roadbed subsidence,instability and road surface cracking.Therefore,grasping knowledge of the actual state of the subgrade density and strength during the service period and the attenuation mechanism of the density has important theoretical and practical value for using the subgrade pavement design and engineering control rationally,using the old subgrade in the reconstruction and expansion project rationally,improving the service performance of subgrade pavement and reducing disease and maintenance cost.In response to the above questions,this article obtained the measured compaction degree and moisture content of the highway subgrade for many years of operation,analyzed the mechanism of compaction degree change by data review and on-site testing,and proposed the concept of "subgrade equilibrium density";carried out unsaturated soil humidification test and compaction soil elastic recovery test to analyze the impact of the two on compaction degree;carried out field tests to obtain the measured strength values at different depths of the roadbed based on the test road of the Jiqing Expressway K9+800;conducted remodeling soil indoor test to analyze the degree of attenuation of the subgrade strength after being completed and opened to operation for many years.The main findings are as follows:(1)The subgrade not only has equilibrium humidity,but also has equilibrium density.The decay of compaction and the increase of moisture content of highway subgrades for many years of operation are a common phenomenon.(2)The influence factors of compaction and strength are not the same at different depths of the subgrade.Therefore,the working mechanism is different.It is necessary to partition and discuss.(3)Subgrade soil wetting and elastic recovery have a certain contribution to the attenuation of compaction,and their contribution values are 1.8%and 0.5%,respectively.The attenuation of subgrade compaction caused by the two is less than the actual attenuation of subgrade compaction,the mechanism of subgrade compaction attenuation needs to be further explored.Low initial moisture content,high initial compaction,and small overburden load are more favorable for the development of elastic recovery.(4)The strength of the highway subgrade soil for many years of operation is less than the strength of the subgrade soil when it is completed and opened,and the degree of attenuation is about 68.7%.(5)Under the same working conditions,the measured strength of the on-site subgrade soil is greater than the strength of the indoor remolded soil.This is because the highway subgrade soil has formed a certain structural performance for many years of operation.