| In order to deal with the problem between the highway capacity,service level and the increasing traffic volume at the present stage,and promote the construction of China’s transportation power,the highway has entered the era of construction and expansion.At present,the experience of highway expansion project shows that it will cause excessive uneven vertical displacement on the top of subgrade,and then longitudinal cracking of pavement,and seriously come to highway disaster,if the construction method of new subgrade is unreasonable,the joint of new and old subgrade and foundation treatment measures are improper,and the uneven vertical displacement control standard is not perfect.Aiming at the problems of subgrade widening construction measures and treatment technology,this paper proposes a new construction method based on the reconstruction and expansion project of Ri-Lan expressway.The deformation characteristics,influencing factors and uneven vertical displacement control standards of the new and old subgrade in the project are explored through numerical simulation and field test,and the effect of uneven vertical displacement treatment technology is analyzed combined with laboratory test,The main research contents and conclusions are as follows:(1)Based on the loading berm effect and the effective stress path optimization theory,a new construction method,namely partial embankment filling method,is proposed.The cross-section model of subgrade widening is established on the method according to the relying project.The deformation characteristics of subgrade are analyzed by numerical simulation,and compared with the traditional method.The result shows that the vertical displacement of the old subgrade will be reduced,and the subgrade tends to be safe by the partial embankment filling method.(2)Based on the partial filling method,taking the subgrade top deformation as the index,this paper explores the influence of widening method,widening width,subgrade height,foundation modulus,subgrade modulus and subgrade weight on the uneven vertical displacement of new and old subgrade,and makes a comparative analysis with the traditional horizontal layered filling.The results show that The height,width and weight of widened subgrade are positively correlated with the uneven vertical displacement and horizontal displacement of the new and old subgrade;The foundation modulus and widened subgrade modulus are negatively correlated with the top uneven vertical displacement and horizontal displacement of the new and old subgrade;Compared with the subgrade widening filling method,the partial embankment filling method is better to reduce the uneven vertical displacement of the top surface of the old subgrade,and the wider the widening width is,the higher the widening height is,and the lower the foundation modulus is,the higher the proportion of partial embankment filling method to reduce the uneven vertical displacement is.(3)Based on the new and old pavement structure,the finite element model is established.By applying different uneven vertical displacement at the bottom of the pavement,the mechanical response of the pavement structure is analyzed.The uneven vertical displacement control standard of the pavement structure is determined and the uneven vertical displacement control grade is divided by comprehensively considering the splitting strength and allowable tensile stress of the material.The results show that under the effect of uneven vertical displacement,the old pavement surface and base bear tensile stress,and the base first reaches the failure strength,while the new pavement base and subbase are in tensile state,and the subbase first reaches the failure strength.(4)According to the established uneven vertical displacement control standard,the treatment effect of composite foundation and geogrid treatment technology on the uneven vertical displacement of new and old subgrade is analyzed by numerical simulation and laboratory test.The results show that the geogrid and cement mixing pile composite foundation treatment technology can effectively reduce the top uneven vertical displacement and horizontal displacement of new and old subgrade,and the uneven vertical displacement of pavement structure can meet the uneven vertical displacement control standard.(5)Combined with the reconstruction and expansion project of the Ri-Lan expressway,eight field test sections are selected.By burying settlement observation equipment,the dynamic monitoring of the settlement at the cross section of the base of the new road and the settlement at the corner of the new subgrade slope is carried out.The dynamic monitoring data of the field test section are compared with the finite element calculation results to verify the reliability of the calculation method... |
