Study On Subgrade Stability And Controlling Technology Of Reconstruction And Extension Project Of Binlai Expressway

With the rapid increase of traffic volume,some highways in our country can not fully meet the current status of traffic flow.Road reconstruction and expansion have become an important task in road construction.In roadbed widening project,because the settlement of the old roadbed has been completed,and the settlement of the new roadbed has not yet begun,there will be differential settlement between the new and old roadbed.When the differential settlement is too large,it will cause diseases on the roadbed and pavement,seriously affects traffic safety.In this paper,aiming at the problem of roadbed safety and stability,combined with the reconstruction and extension project of Binlai Expressway in Shandong Province,studing the engineering characteristics and construction technology of the project by means of field investigation,laboratory tests,numerical simulation and field test.The main results are as follows:(1)Establishing a roadbed numerical simulation model to study the interaction characteristics and influencing factors of new and old roadbeds during construction and operation period.The calculation shows that the new roadbed widening method will have a great impact on the interaction and engineering characteristics of the new and old roadbeds.Reasonably control the width and height of the widened roadbed can effectively reduce the differential settlement of new and old roadbeds.(2)Selecting representative sections to monitor the vertical settlement and horizontal displacement of widened sections.The test results show that the settlement of subgrade in construction period can be divided into two periods: the period of drastic change of settlement and the period of stable settlement,After construction,the settlement and horizontal displacement rate at the shoulder of new subgrade in the same period are obviously higher than that at the foot of subgrade slope,and the settlement of subgrade is mainly caused by foundation settlement..The field test results are in good agreement with the numerical simulation results.(3)Based on the analysis of pavement structure,puting forward the control standard of differential settlement of the relying engineering.Considering the ultimate tensile stress of pavement structure material and the strength attenuation of pavement material under fatigue load,3.6 cm is taken as the maximum allowable differential settlement value of new and old subgrade after construction,and the control standard of differential settlement is divided into four levels: slight,low,medium and high.After the road is opened to traffic,the corresponding maintenance and treatment measures can be made in time according to the differential settlement grade.(4)The influences of different laying methods of geogrid and the way of excavation of old roadbed on differential settlement of subgrade are analyzed.The results show that it is best to lay two layers of gratings and lay them on the bottom of the subgrade and the top of the subgrade.When the old roadbed excavates the steps,the larger the contact area of the new and old subgrade joints,the smaller the differential settlement.Based on the research results,the old roadbed excavation step height is 70 cm and the width is 100 cm.Based on the actual engineering,this paper deeply studied the deformation stability of widened roadbed.The research results can scientifically guide the design and construction of the highway,and it has certain theoretical significance and practical value.