Evaluation And Fast Detection Technology Of Operation Expressway Subgrade Performance

As the construction of expressway network in China was completed, the development of expressway has gradually shifted from construction to maintenance. Under the new situation, the development on expressway maintenance and detecting techniques has to accelerate so as to satisfy the demand of expressway development. Subgrade is the bearing subject of road, the degradation of performance caused by vehicle loads and environmental factors especially the asymmetrical vertical deformation is the main contribution to pavement surface diseases. Therefore, to strengthen the detection and evaluation on subgrade performance is of vital significance to improve the service performance and prolong the service life of expressway.Subgrade belongs to concealed work, great difficulty of detection. Poor efficiency and large-scale damages to road surface structure, traditional damage testing failure to satisfy the demand of operating expressways subgrade detecting. Accordingly, based on the major projects for science and technology of MOT (Ministry of Transport of the People’s Republic of China), this paper launches a research on the evaluation and rapid detection technology of subgrade performance for operation expressway. The main research works and achievements are as follows:(1) By the on-site survey on the subgrade defects of typical operating expressways in Hunan, obtained were the major categories, expression forms and distribution characteristics. By the excavation experiments, subgrade evaluation index and detection index were obtained.(2)By the excavation experiments, the migration rule of subgrade moisture content was obtained. According to the compaction curve of subgrade filling, the degree of compaction degradation law of subgrade was obtained. Based on the relationship of subgrade resilient modulus, compactness and moisture content, the attenuation law of resilient modulus was obtained and the degradation mechanism of subgrade performance was ultimately obtained.(3) Based on the experiment of dynamic responses of subgrade and pavement and 3D finite element calculation, the affects of traffic load and subgrade resilient modulus on the stress of subgrade and pavement was analyzed.(4) In accordance to the influence of subgrade resilient modulus on the structural stress and the fatigue lifetime of pavement, the subgrade performance evaluation method was put forward. By the experiment of bearing plates, the rule of the changes of subgrade resilient modulus with consistency under the condition of standard heavy compaction was obtained. By referring to the classification standard of the dry-wet condition of subgrade, the rationality for the evaluation method of subgrade working performance was testified.(5) According to roadbed structure characteristics and detection demand, optimization inversion algorithm of Ground Penetrating Radar was proposed, effectively enhancing speed and accuracy of retrieval data. Based on multi-sensor data fusion and joint operation, a multi-index data fusion joint interpretation algorithm under multifactor control was established, which solved the difficult problem that the ambiguity or low accuracy of retrieval result caused by the local convergence of single sensor. In addition, subgrade working performance thorough detecting was realized. Relying on data fusion joint interpretation algorithm, an integrated interpretation platform for subgrade working performance was developed and comprehensive management of testing data on subgrade working performance was achieved.(7) Based on the of abundant field tests, new conductive foam electrode and contact detectors were developed and the direct application of High-density Resistivity Method and Rayleigh Wave Method on detection of subgrade working performance of operating expressway was achieved. Besides, an integrated detection device combined by High-density Resistivity Method and Rayleigh Wave Method was obtained. The automatization of electrode, detector and hammer were realized and the rapidity of detection of subgrade working performance was achieved.