Assessment Method Of Bearing Capacity Of Highway Subgrade In Service

Influenced by traffic load and external environment,the bearing capacity of roadbed shows deterioration and attenuation in varying degrees,which is a necessary condition for the evaluation of roadbed bearing capacity.Secondly,in order to respond to the development concept of road management and maintenance under the new situation,determine the appropriate maintenance time,give full play to the effectiveness of road pre-maintenance,while catering to the requirements of roadbed bearing capacity assessment in road reconstruction and expansion work,and minimize road closure and congestion.Furthermore,the static modulus parameters are often used to evaluate the bearing capacity of Subgrade in the past.With the drop weight deflectometer(FWD)detection method and the dynamic modulus of each structural layer of road being applied to the design code of road asphalt pavement,the dynamic inversion analysis using dynamic modulus parameters is a direction that needs to be expanded at present.Therefore,under the premise of not destroying the original structure of the road surface,it is significant to make full use of the dynamic deflection detection results of the drop weight deflectometer(FWD)to evaluate the bearing capacity of the roadbed.In this paper,according to the relevant literature of highway at all levels,and aiming at the structural combination form of domestic high-grade highway,following the analysis idea of "selecting the mechanical analysis model of road structure-constructing the theoretical deflection database of road surface-modulus regression of structural layer",and referring to the deflection data measured by relevant falling weight deflectometer(FWD),the bearing capacity of existing highway subgrade is analyzed.The research work is as follows.(1)On the basis of understanding the basic working principle of the Falling Weight Deflectometer(FWD),the sensor calibration and distance calibration of the Falling Weight Deflectometer(FWD)were carried out.Then,according to the actual measurement and research needs,nine sensor placement positions were set up,and 10 specific semi-rigid base asphalt pavement structure combination forms and material parameters were selected for domestic high-grade highways.The range of values,to a certain extent,reduces the impact of sensor accuracy on the analysis results,avoids the blindness of subgrade bearing capacity evaluation,and has a certain reference significance for most domestic high-grade highways.(2)Based on the theory of dynamic response analysis of pavement structure,a two-dimensional axisymmetric finite element model is established,and the dynamic and static finite element model is compared with the actual deflection value of road structure.The results show that the dynamic finite element mechanical response state is more in line with the actual road conditions.By creating the time history curve of deflection point with or without damping effect,it is found that the phenomenon of gradual attenuation of amplitude under damping effect coincides with the stress state of road.The modal analysis of the system is carried out,and the natural frequencies of the first and second modes are determined.Then the viscous damping coefficient alpha and structural damping coefficient bet of the system are calculated to exert resistance on the dynamic finite element model of road.The Nissan effect.In the process of ABAQUS finite element analysis,the instantaneity and repeatability of dynamic loads and the energy consumption of damping effect are in good agreement with the actual stress state of the road.This has played a positive role in promoting the analysis of dynamic deflection data by means of basic dynamic theory and the evaluation of subgrade bearing capacity.(3)The database between the modulus of each structural layer and the theoretical deflection value of the road surface is established by using the finite element model of the road structure constructed.With the help of the dynamic deflection basin parameter index(DPB),which is composed of the direct deflection of the road surface and its combination,the modulus regression formula of the asphalt pavement with high-grade semi-rigid base under different structural combination forms is analyzed,and the regression formula is carried out according to the engineering practice.The results show that the concept of modulus regression model is easy to understand,convenient and practical.It can be used to evaluate the bearing capacity of roadbed by means of non-destructive testing technology and guide the general application of Engineering practice.It has certain practical value.This paper evaluates and analyses the bearing capacity of roadbed by regression analysis method.On the one hand,it can provide theoretical support for the timing selection of the pre-maintenance technology of asphalt pavement with high-grade semi-rigid base,prolong the life cycle of road structure;on the other hand,timely evaluation and analysis of the bearing capacity of roadbed can guide the reconstruction and expansion of roads and make up for the drop-weight deflection.The vacancy of dynamic deflection value application at other locations outside the instrument load center also meets the development requirements of road non-destructive testing in a period of time.