Study On Expressway Settlement Evaluation And Profile Design Of Extension Project Based On Driving Comfort

For the expressway constructed in soft soil area, since the consolidation and secondary consolidation characteristics of soft soil ground, large settlement and uneven settlement often occur after expressway beginning servicing, which will be further exacerbated by the load of pavement overlay. Excessive settlement and uneven settlement affect road profile alignment and driving comfort. At the same time, excessive settlement and uneven settlement cause great difficulty in profile alignment design for reconstruction and extension engineering of expressways. Road settlement evaluation and profile alignment design are two important issues of expressway reconstruction and extension engineering in soft soil area.From the viewpoint of driving comfort, this paper performed theoretical analysis and experimental research on the above issues, carried out specific work in the following four aspects:Firstly, the vehicle-road interaction model with five degrees of freedom was adopted, solving the vibration acceleration by an MATLAB program compiled according to Newmark-3 method. And driving comfort evaluation was performed in accordance with ISO 2631 standard "Mechanical vibration and shock—Evaluation of human exposure to whole body vibration". On the basis of literature investigation and measured settlement results, three calculation modes of road longitudinal uneven settlement were proposed. And the laws of vehicle-road interaction under the condition of uneven settlement and the effects of vehicle calculation parameters on driving comfort were analyzed.Secondly, for two kinds of cars driving at different speeds in roadbed-bridge transition section, vibration accelerations of the seat and vehicle body were measured in field test. Compared to theoretical calculation results, the model with five degrees of freedom adopted in this paper and the laws of vehicle-road interaction are verified.Thirdly, the influence of fitting method and the interval of elevation data obtained by vehicular laser instruments were investigated. Settlement evaluation method for expressway in soft soil areas was proposed. With a kilometer as a base evaluation element, the method counts the proportion of weighted RMS acceleration caused in the range of each comfort level, calculates driving comfort index and riding quality index, estimates settlement evaluation grade and gives maintenance guidances.Fourthly, road profile alignment design indexes such as slope length, slope difference and radius of vertical curve were analyzed. The method of profile alignment design for reconstruction and extension engineering of expressways was proposed. When site conditions are limited, we can properly exceed limitation of most small slope length specified in the criteria, and design vertical alignment according to requirements of driving comfort or the vertical carve length larger than three seconds’ travel distance. At last, practical case studies of expressway reconstruction and extension projects were performed.