Study On Post-construction Settlement Of High Fill Foundation In Mountainous Airport

The rapid development of airport construction in the mountainous areas in westernChina leads to increasing number of hill-fill foundations, which usually have large fillvolume, high height and original soft foundation below filler. It is an important topic topredict the settlement, especially post construction settlement, of high-fill foundations,which are encountered more and more often in the high-fill engineering in mountainousareas. However, both the calculation model and calculation method are to be studiedfurther. Presented in this study are large-scale laboratory tests, field data analysis,simplified formula calculation, numerical analysis that were systematically and deeplymade for the purpose of investigating the mechanical properties of coarse-grained soiland long-term deformation behaviors of high-fill foundation. As a result, severalreasonable simplified calculation methods are proposed for simulating the long-termdeformation of high-fill foundation. Besides, a strain hardening constitutive model thatcan well reflect classical mechanical properties of coarse-grained soil is also proposed.The rationality and feasibility of above methods and model are demonstrated bycomparisons with test results and field data. Through this thesis the followinginnovative conclusions or results are made:1. With the specially designed large-scale oedometer, compression experimentshave been conducted on specimens with different broken rock contents to investigatethe compression, rheological and wetting deformation of broken rock-soil mixture. Onthis basis, method for determining the optimal mixing ratio of broken rock-soil mixtureis seriously studied. Furthermore, the routine rheological and dry-wet cycle experimentshave been also conducted on specimens to investigate the rheological and dry-wet cycledeformation mechanism and properties of rockfills, which has been widely used inairport construction in the mountainous areas in western China.2. Through analyzing the field observed data, it is revealed for the first time thatthe post-construction settlement of high-fill foundation is mainly from the rheologicaldeformation of later filling rockfills, while the early filling rockfills, even if which havea higher level of stress after filling, have little contribution on the settlement. This ismainly because the early filling rockfills have been compressed many times and its rheological deformation has also experienced many long intermission periods duringconstruction. On this basis, the reason for differences between above observedphenomena of actual high-fill engineering and laboratory test results is reasonableexplained.3. According to composition characteristic of hill-fill foundations in the airport inmountainous areas, several distinctive simplified calculation methods are well proposed,mainly including:1) a simplified method is proposed to calculate the rheologicaldeformation of coarse-grained filler, in which load variations during rheologicaldeformation can be properly considered;2) the other simplified coupling calculationmethod, which can consider a given rainfall situation and the interaction between abovetwo deformations, is well proposed;3) another simplified method applied to calculatelong-term deformation of original soft foundation, in which construction process canalso be properly considered, is proposed. After that, a user-oriented software especiallyapplied to calculate the deformation of high-fill foundation is programmed via VBlanguage, in which above proposed simplified calculation methods are integrated, andthen using this software the practical high-fill engineering is calculated and analyzed toinvestigate the post construction settlement behaviors.4. A strain hardening model is proposed in this thesis, which can well reflectclassical mechanical properties of coarse-grained soil. Not only the nonlineardeformation behavior, nonlinear strength property, confining stress dependence ofstiffness, dilatancy of coarse grained soil, but also stress path dependence andrheological properties can well be reflected via this model. After that the rationality andfeasibility of the proposed models is demonstrated through comparison with testingresults, it is applied to the simulation analysis of practical engineering boundaryproblems, and the post construction settlement behaviors of high-fill foundations aredeeply studied again. The new models are also shown to be reasonable, effective andadvanced.