Detection And Evaluation Method Of Subgrade Service Status Based On Electrical Measurement Method

In the past two decades,the mileage of expressways in China has grown from less than 20,000 kilometers to over 140,000 kilometers.Ensuring the stability and durability of roadbeds under the influence of complex climate change and rapid traffic loads is the main direction for the future development of China’s expressways.The detection and evaluation of roadbed service status is one of the scientific problems urgently to be solved in current operations.The subgrade of the expressway is the foundation of the entire structure.Once damage occurs,its repair is much more difficult than road surface damage,which often brings huge economic losses and hidden dangers.The subgrade is a concealed project.The traditional method is mainly for pavement and shallow areas.It is difficult to detect the internal diseases and development of the subgrade.Therefore,it is particularly important to detect and evaluate the service status of highway subgrades.Based on a large number of investigations on the status of domestic and foreign research,this paper relies on literature surveys,laboratory tests and finite element numerical simulations to carry out "resistivity and polarizability-water content and compaction-roadbed deformation" for roadbed soil The study of detection indicators,based on the analysis of indicators,proposed an electrical measurement method and demonstrated its feasibility.Starting from the typical disease characteristics of highway subgrades,the common structural diseases,causes and service status of highway subgrades are analyzed.The two key indicators of water content and compaction are expounded according to the quality control mechanism of subgrades.Quantitative relationships between different dry densities,water contents,cohesion,and internal friction angles were obtained through experiments such as direct shear or fast shear tests of soil.Finally,typical roadbed problems were investigated and their causes were analyzed.Based on examples of typical subgrade surveys,a finite element calculation model of the subgrade structure was established,and simulation calculations were carried out in consideration of typical subgrade damage.Simultaneously,the compaction changes in the wet and dry cycle action areas inside the subgrade,the lateral water transfer area,and the groundwater siphon effect areas were analyzed of the rate change on the deformation of the roadbed.The influence law of subgrade soil moisture content,compaction degree and subgrade deformation is summarized.Based on the finite element numerical simulation research,the control range of subgrade performance evaluation indexes such as moisture content and compaction degree is proposed.An indoor rapid test device for soil physical parameters was developed based on the four-pole electrical measurement method.A series of laboratory tests were conducted on the resistivity and polarization changes of soil samples with different compaction degrees by changing the water content,and the correlations were obtained.And its changing trend,the influence of moisture content and compaction on electrical parameters were analyzed.For loam in North China,when the compaction is in the range of 84.47% to94.41%,and the water content changes from 15% to 20%,the resistivity decreases to 1/3 to 1/2 times the original,and the polarization rate increases to the original 1.4 to 2.3 times,and red clay in Hunan and silty clay in Yunnan also show similar rules.The related relationship was established and the calculation formulas of resistivity and polarization based on soil moisture content,compaction degree were proposed.The accuracy of the test method was verified by the drying method,and the feasibility of its engineering application was discussed.