| China has a vast territory where hills and mountains are widely distributed. Because of that embankment over sloped weak ground engineering is frequently encountered in transportation infrastructure construction. Major engineering accidents such as slump, large lateral deformation easily occur due to the particularity of sloped weak ground. Firstly, by literature review and field investigation, the latest research progress of embankment over sloped weak ground was comprehensively reviewed and commented. Secondly, through sophisticated numerical simulation technology, engineering behaviors of embankment over sloped weak ground such as deformation and stability were studied systematically by using geotechnical engineering computational mechanics software and relying on the research findings of geotechnical centrifuge model tests and field tests. Thirdly, double indexes design system based on "deformation" and "stability" was put forward according to engineering behavior of embankment over sloped weak ground. Fourthly, engineering treatment measures of embankment over sloped weak ground were summarized. The main research results obtained are as follows:(1) By combining with the highway, railway, geotechnical and other industry standards, the similarities and differences between the "sloped soft soil" and "soft soil" were compared from the causes, distribution, engineering properties etc. After that, the concept of "sloped soft soil" was defined and relevant criteria were tried to put forward.(2) By using nonlinear finite element method, building numerical analysis model of embankment over sloped weak ground, simulating embankment of staged construction, analyzing the relationship between deformation and stability on soil body, combining the results of geotechnical centrifuge model experiment, the effects of the weak surface layer and lateral slope of ground on the engineering behavior of embankment over sloped weak ground were comprehensively demonstrated. Research results show that sloped weak ground can not be simply regarded as the linear superposition of sloped ground and weak ground which are not equal-weight. The lateral displacement, vertical settlement and the shape of the potential slip plane were significantly affected by weak surface layer and lateral slope of ground which reduced the stability. Therefore, it is essential in engineering to attach great importance to the lateral displacement of toe and the treatment of weak surface layer.(3) Based on elastic-plastic plane strain finite element method, four numerical analysis models (common horizontal ground, horizontal weak ground, common sloped ground and sloped weak ground with embankment filling) were established, which could be used to simulate staged construction and get dynamic changes of ground lateral deformation and vertical settlement. Ground deformation coefficient was introduced to obtain the relationship between lateral deformation and vertical settlement, which was used to propose the theoretical basis of design principles about embankment over sloped weak ground. The design principles mainly depended on controlling lateral deformation. Ground deformation coefficient and displacement field which were obtained from geotechnical centrifuge model tests were also adopted to discuss the reinforcement mechanism of driven pile and anti-slide pile. Research results show that:Based on the monotonicity and slope of ground deformation coefficient curves, the size of ground deformation coefficient (greater than 1.0 or less than 1.0) etc., the relationships between lateral deformation and vertical settlement during the staged construction could be described scientifically by the variation of ground deformation coefficient. Reinforcement mechanisms in sloped weak ground were different between driven pile and anti-slide pile. Vertical settlement in sloped weak ground could be mainly controlled by driven pile and lateral deformation could also be restrained to a certain extent. Lateral deformation could be mainly controlled by anti-slide pile, but ineffectively in vertical settlement.(4) In order to get the deformation characters of embankment over sloped weak ground with different weak layer’s properties, numerical models were established based on nonlinear finite element method. The orthogonal design was applied to evaluate significances of influencing factors. The results show that the elastic modulus and thickness of a weak layer are the decisive factors affecting vertical settlement and lateral deformation; the lateral slope of ground is an important. factor aggravating foundation deformations; when the weaker layer locates on ground top, foundation deformations are significantly affected, especially on lateral deformation; the effect weights of each factor of weak layer’s properties on lateral deformation and vertical settlement are different. Engineering measures based on weak layer’s properties, such as foundation treatment and lateral restraint should be adopted to eliminate deformations.(5) In current technical specifications, the concepts and engineering treatment measures of embankment over sloped weak ground are not clearly defined. Or the allowable value of safety factor allowing for lateral slope of ground is corrected through tentative calculation only by adjusting a single influencing parameters. In order to obtain the relationships between deformation and stability accurately, numerical models were established based on elastic-plastic finite element method. Relying on the research findings of field tests about Chongqing-Huaihua Railway, the double indexes design system based on "deformation" and "stability" was put forward according to ground deformation coefficient and safety factor which was respectively obtained by elastic-plastic deformation and strength reduction method. The design system is proved to be scientific, operable and the applications of the design system are recommended. The results show that the stability and the deformation trends of embankment could be more truly reflected by the design system based on double indexes "deformation" and "stability". The engineering design and construction could also be effectively guided by the design system.(6) It is the core design principles of embankment over sloped weak ground that application of reinforced by concrete anti-slide pile at the corner of embankment can effectively limit lateral deformation of the foundation. By using 3D fast Lagrangian analysis of continua and comparing with the results of indoor geotechnical centrifugal model tests, numerical analysis models of embankment over sloped weak ground reinforced by anti-slide piles were built. The influence of the pile design parameters were studied, such as pile spacing, pile length, elastic modulus, cross-section dimension and the position of piles on its internal forces and deformation. Research results show that the lateral deformation of sloped weak ground could be significantly restricted by using anti-slide piles at the downhill toe of embankment. The factors, such as force, economy, construction etc., should be comprehensively considered in order to confirm the reasonable pile spacing; anti-slide piles must be penetrated potential slip surface, but with the increase of the length of pile the reinforcement effect is not significantly improved; with the increase of elastic modulus and cross section dimension of pile, the reinforcement effect is improved in some extent; anti-slide pile is suitable to be set at the middle of dypass downhill slope of the embankment.(7) The basic principles of engineering treatment about embankment over sloped weak ground were initially proposed. The main engineering treatment measures were summarized systematically from improving the overall ability to resist foundation deformation and the stability of foundation, strengthening the embankment body, applying pile-net structure or pile-plank structure and strengthening the waterproof and drainage measures etc. Scopes of application about treatment measures were also presented. |
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