Engineering Behaviour Of Unconventional Subgrades And Influence On Pavement Responses

Subgrade is an integrated part of pavement structures. Insufficient subgrade support always results in premature failure and excessive distress of pavements, especially in road-widening projects and mountainous areas where unconventional subgrades such as cut-fill sections and profiles constitute one of the major reasons of pavement failure. This dissertation reports a comprehensive research of engineering behavior of unconventional subgrades and influence on pavement responses supported by the Excellent Young Teachers Program of MOE, P.R.C. This study includes 7 parts as listed below.(1) It is the first time that the concept of "unconventional subgrade" is draw in domestic. Because of the geometry and material non-uniformity, the differential settlement of part-cut part-fill subgrade will cause additional mechanical response to effect the pavement. It is of great significance to study the problem of unconventional subgrade and establish the design system.(2) Pavement distresses in several highway routes in Sichuan and Tibet area of China with unconventional subgrades were conducted. Major types of distresses in those routes including Highway 108 (Section between Guanyuan and Qipanguan), Mian-Guan Express (from Mianyang to Guangyuan), Highway 318 and Highway 109 were identified.(3) Based on the software desktop FLAC/SLOPE Version 4.0, strength reduction technique (SRT) is conducted to analyze the failure mode of part-cut part-fill subgrade. Also commercial finite difference method program FLAC~3D is conducted to analyze the dynamic behavior of part-cut part-fill subgrade under the earthquake dynamic loading.(4) Based on literature review of a large number of relevant domestic and international research findings, the technical specification and pavement analysis computer program are summarized and disadvantages in the unconventional subgrade design are discussed in details.(5) Based on elastic layer system, a plane strain finite element model, which may compute the additional stress of asphalt pavement, is drawn to analyze the influences of the asphalt pavement deformation due to the differential subgradesettlements. Such as differential settlement value; length and pavement structure parameters; including the thick and modulus of surface layer and base layer are analyzed. Furthermore some advice to avoid premature distress is advanced.(6) A computer software called KENPAVE developed by Yang H. Huang; professor of Kentucky University; written for pavement analysis and design; is conducted to analysis the portland cement concrete pavement responses over part-cut part-fill subgrade existing initial gap.(7) The principle technical methods to avoid premature distresses of unconventional subgrade and pavements are advanced. It is the first time in domestic that geocentrifuge model tests are carried out to investigate the behavior of subgrade settlement behavior in road-widening engineering.