Analysis Of Foundation Deformation And Stability Of High Fill Of Airport In Mountainous Area

With “The legal protection for 1.2 million square kilometer cultivated land",the land for construction in urbanization of mountainous area and in the implement of the strategy “The Belt and Road" is mostly solved by shaving hills and filling ditches. However, the maximum height and the problem of Three Surfaces, Two Bodies and Two Water are continually refreshed in some filling projects,which causes a new series of problems in soil engineering. The most prominent core problems are that the calculation for deformation of high embankment and the analysis for stability of high fill slope. Because of the problems, through the project of high embankment of the civil airport in Chengzhou, South Gansu, and based on the methodology of mechanics of unsaturated soil, multiple study methods and high technology are adopted, and the solutions for high embankment in mountainous area are deeply explored, by which the deformation, strength, and the water holding characteristics of mixture-filled soil body are totally revealed, and the change law of spatio-temporal deformation of high embankment during and after construction is analyzed systematically. Furthermore, the problems about deformation calculation of high embankment and stability evaluation are mainly solved. Not only can the research results be used in constitution of relating criterions and standards, which are the scientific basis for similar high embankment projects, but also have the essential theoretical value and social economic benefits. The following paragraphs are the work done in this essay, the creative points and conclusions.(1) Based on a series of experiments including the filled mixture proportion experiment in test section, in-situ foundation treatment experiments, filling body compaction experiments, and dig-fill-line treatment experiments, the layer of silt clay in high embankment is found to be the relatively weak layer in the foundation,which is the key factor for the settlement and differential settlement of high embankment foundation and for the controlling foundational stability. The technology factors for dynamic compaction treatment of soft foundation with variety thickness are given and the suggestions for filling body compaction and dig-fill-line treatment and quality control are provided. The effective reinforcement range for dynamic compaction and the calculation for reinforcement influencing range are established. The compaction process monitoring system for filling body is proposed,which can provide the scientific basis for large area dynamic informatization design and construction of high embankment foundation.(2) The in-situ shear tests for the soil-stone mixing filling body and the soil around dig-fill-line were carried out. The weak area is found where there is a contact zone or a crack between the mudstone and soil, which can possibly turn to a concave-convex-shape shear plane. The slope in the dig-fill-line has a higher possibility than the slope in large filling body to have a shear failure so that the treatment should be pay more attention during the construction process. Through indoor directly shearing tests, high pressure compression tests, the suggestion for filling materials controlling in large filling construction is given, and the methods of calculating shear strength and settlement deformation when considering the initial condition of filling soil body are established. Through a series of three-axis tests, the strength, deformation and water holding characteristics of the soil from origin foundation and filling mixture are deeply revealed, which lays a theoretical foundation for the correction of constitutive model and the calculation of numerical simulation.(3) Along with the construction process, the wireless remote monitoring system was designed and installed to the high fill embankment in mountainous area for the first time, the original foundation settlement and deformation of soil mass and filling body and the space-time evolution of pore water pressure and earth pressure in the loading period and after a certain period of time were revealed, then a series of regular knowledge were achieved. Meanwhile, the routine deformation of the typical parts of the whole area was monitored. Based on field monitoring, suggestions for post-construction settlement and differential settlement control of high fill was given.Then the post-construction settlement was analyzed and predicted through the field measurement data, and it can provide the scientific basis for the reasonable begin time of airfield pavement construction and the evaluate of post-construction settlement in the service life period.(4) Based on the indoor and outdoor test, the theory expression for settlement and lateral deformation of the high fill subgrade was established, thus solved the calculation problem of high fill foundation deformation. A calculation program was written by MATLAB software, and the theory was proved to be correct and reasonable by comparison algorithm. With finite element software simulation analysis, it was found that the foundation settlement and uneven settlement of the embankment during construction should be strictly controlled; The settlement after the first year accounts for about 60% of post-construction settlement and settlement after the second year accounts for about 30% of post-construction settlement, the settlement after 3～5 years accounted for about 10% of the post-construction settlement, and post-construction settlement is not more than 20cm in total; The pavement construction should not begain after the first year of construction of the embankment,it should be placed 1～2 rainy season when conditions permit.(5) Through the monitoring and inversion analysis of high fill slope slip deformation process, it was found that the slip deformation of high fill slope is mainly subsidence and combining with obvious lateral displacement. It belongs to the typical artificial load and the pushing-type slip; The early warning criterion space-time evolution characteristics and deformation rate for mountainous area high fill in the different deformation stages of slope are put forward. Combined with modified Duncan-Chang model parameters and the strength of the unsaturated soil destroyed principles, the modulus double strength subtraction was established, the new ideas for high fill slope stability evaluation was preliminary discussed. The flexible structure was used to reinforced the instable rigid retaining wall at the first time, and the stability calculation method with dynamic and static force was derived and established.