| Tens of thousands of potential debris flow and debris flow widely distribute in the vast area of China’s mountains. Every year in the heavy rain season, debris flow disasters occur frequently, especially in the west. In recent years, debris flow has caused serious loss of lives and property. Thus debris flow prevention has become an urgent task, and the new debris flow control technology is to be further introduced to engineering applications. This paper carried out a research on debris flow control technology based on "Research and Demonstration on Bailong River’s Landslide and Debris Flow Control Techniques", which is a sub-project of a National Key Technology Support Program. Through on-site investigation and information collation, a new type of ground anchors buttress dam-style debris grille was first proposed. As a new debris flow control structure, its theoretical calculation method is not perfect, and the practical application is also very lacking. A comprehensive theoretical analysis and numerical simulation on the characteristics of the dam for the new grille has been carried out. The work done and the results obtained are as follows:(1) Field research has been done in debris area of the Bailong River, some under construction prevention project and in-service prevention project being investigated. Reason analysis of the success and failure in prevention and control structure has been carried out to instruct the future design, construction and maintenance of the prevention and control engineering. Through field research we have got an objective understanding of the disadvantages of a single control structure. Repeated use of the same large cross-section or buried retaining structures should be avoided, while a new landslides blocking exhaust grille dam structure is first proposed on the basis of the new ideas and new understanding, and a detailed introduction of its structure, characteristics and model selection is made.(2) The new mudslides grille dam foundation scour formula in the early and late stage is derived using energy superposition and balance principle. In employing the newly-derived formulas, we have established a new probability mathematical model of grille dam erosion and analyzed the reliability of Foundation scouring depth. We could know from the calculation:the scouring depth is relatively large according to the formula of this paper, so its early stage influence should be given enough attention in design. When ditch bed material composition and debris flow parameters under the same circumstance, new grille dam foundation ditch bed scouring depth increases with the increase of longitudinal slope gully bed; and it decreases with the increase of ditch bed material bulk density and compressive strength.(3) A formula concerning the anchor system pullout force and displacement deformation has been established and derived. Through calculation and analysis with the formula, it can be seen that:the anchor pier displacement and deformation decreases when anchor pier surrounding soil modulus increase in size; displacement deformation increases linearly when Poisson’s ratio and cable tension T increases. ANSYS finite element software is employed to simulate the displacement and deformation of anchor system and the result manifests that trapezoid anchor pier is a relatively ideal choice for it provides greater anchoring force in terms of mechanical performance.(4) A mechanical model has been established and a formula has been derived on the basis of the grille beam’s simplification to multi-span continuous beam rigidly propping up the grid columns, taking into account the two conditions:empty-reservoir overflowing and full-reservoir overflowing. Through the equivalent stiffness and embedment side processing the grid column is simplified to elastically supported cable multi-span continuous beam, then force calculation method considering elastic support is proposed. Besides, considering the overall work of the beam grille and displacement influence on new grille dam’s structural forces, respective calculation formulas have been derived; there are three circumstances in the stability calculation of the new grille dam structure: empty-reservoir overflowing, half-reservoir overflowing and full-reservoir overflowing, with each a respective stability calculation model has been established and the computing methods of stability coefficient have been put forward.(5) The general finite element software ANSYS has been employed to simulate buttresses constraints and the influence of different grille beam spacing on mechanical properties and displacement control of new grille dam structure. Simulation analysis shows that:when buttress wall is restrained it will bear a large part of the internal forces of the end-column grid, which makes the grille a more reasonable force column. In order to control the displacement of the new grille dam structure, buttresses sill burying should be considered in design to make it more consistent with buttresses bottom in constrained conditions. We recommend5m×3m as grid spacing beams which is believed the optimal design from the perspective of performance and force displacement control.(6)A new seismic dynamic model of grille-dam and a control equation have been established in accordance with the concentrated mass method. A pulse model and a stochastic ground motion model are combined to generate near-fault ground motions. The seismic response of the new grille-dam under simulated near-fault ground motions is analyzed. The calculation shows, the maximum displacement is at the top and the smallest is in the bottom; the maximum axial force is in the middle layer, the underlying minimum. Finite element software ANSYS made modal analysis and dynamic analysis for the dam structure. The results shows the first-order and second-order modal were new grille along the dam structure and the short to long to translational; the grille beam’s acceleration, displacement and peak force along the axial direction showing the trend of the big in middle and small in two sides. However, along the direction of column height the grille has amplification effects, namely, being big at the top and small at the bottom. |
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