水位变幅对地下框架结构作用效应敏感性分析

发布时间：2018-09-11 13:24

【摘要】：山区河道城市化前溪流深切,城市化后天然河流与周边地块存在较大高差,设计从防洪、水生态等多目标出发,提出了适应山区城市的双层河道建设方案:上层明渠、下层暗涵。其中,下层暗涵河道在场平过程中深埋地下,维护、检修困难且事故后果严重,因此对其结构受力特性的掌握尤为重要,在设计阶段加以考量能有效降低其事故风险。回填场区的地形、渗透特性使得强降雨条件下涵周土体内地下水环境会发生剧烈变化,土体若长时间呈沁水饱和状态,对场区的构筑物极为不利,因此考虑将外水通过涵体透水通道导入下层河道向下游排出,此时结构将会遭遇地下水水位变化这一工况。现行规范通过载荷—结构方式计算水荷载时通常进行折减或采用可能的最大水位,而涵体受力实质是与渗流—应力双场耦合作用下的涵周土体共同变形的过程,因此,研究深埋地下框架结构在地下水位变化所产生的流固耦合效应作用下的受力特性具有重要的工程应用价值。本文依托工程实例建立了地下框架结构三维有限元模型,主要研究内容如下:(1)从基本理论有效应力原理和达西定律出发,推导了应力场、渗流场的控制方程:应力平衡方程和非稳定饱和渗流连续方程,并给出相应的定解条件。根据两场相互作用的的影响方式,得到了多孔介质土体渗流场应力场耦合的数学模型并给出了耦合状态下的有限元矩阵格式和求解方式。阐述了三维有限元模型建立过程中的要点,并依托实例工程地勘报告和相应土工实验成果给出模型参数。(2)模拟分层回填施工过程,其涵顶存在应力集中现象,此为深埋框架结构所特有的受荷形式;模拟水位下降固结过程,其有效应力的增长由产生明显水位降前(主要)、明显水位降落过程、涵侧水位降落过程三阶段阶段的孔压溢出、沉降差(35)h产生的应力集中共同贡献,此时水位降幅快慢并不适用来衡量内力变化的趋势。固结排水过程使得沉降加剧、内力增大,结构受荷破坏的风险相应增大。(3)回填材料对涵体受荷以及内力响应影响较大的因子为弹性模量E以及渗透系数k,不考虑涵背回填、涵侧排水工程措施时,仅存在土石混合料的单参数作用下,场区回填料弹性模量E_m越大、渗透量级较高时渗透系数K_m相对越小结构越有利;反之,引入涵背砂砾石回填料,其弹性模量E_s、渗透系数k_s,在多参数作用下,E_m越小、E_s越大、K_m大于并接近k_s、k_s越小时,对结构越有利,其中,在相同的变化量级范围内,E_m比E_s更敏感,k_s比K_m更敏感。总体来说,在涵侧土体范围内采用相应工程措施能有效减小结构受荷及内力大小,且更为经济高效。
[Abstract]:Before the urbanization of mountain rivers, the rivers are deep, and there is a great difference in height between the natural rivers and the surrounding land blocks after urbanization. From the multi-objectives of flood control and water ecology, this paper puts forward the construction scheme of the double-layer river channels suitable for mountain cities: the upper open canal, the open channel in the upper layer, and so on. The lower culvert. Among them, the underground is buried deeply in the course of the hidden culvert in the course of site leveling, the maintenance is difficult and the accident consequence is serious. Therefore, it is very important to master the mechanical characteristics of the structure, and the risk of the accident can be effectively reduced by considering it in the design stage. The topography and permeation characteristics of backfill site make the groundwater environment of culvert surrounding soil change dramatically under heavy rainfall. If the soil is saturated with water for a long time, it will be very unfavorable to the structure of the field area. Therefore, it is considered that the external water will be discharged from the lower river through the culvert permeable channel, and the structure will be subjected to the condition of groundwater level variation at this time. In the current code, the maximum water level is usually reduced or the maximum water level is adopted when calculating the water load by load-structure method, and the stress of culvert is essentially the process of deformation of soil around culvert under the coupling of seepage and stress, so, It has important engineering application value to study the mechanical characteristics of deep buried underground frame structure under the effect of fluid-solid coupling caused by the change of groundwater level. In this paper, a three-dimensional finite element model of underground frame structure is established on the basis of engineering examples. The main research contents are as follows: (1) the stress field is derived from the basic theory of effective stress principle and Darcy's law. The governing equations of seepage field are stress balance equation and unsteady saturated seepage continuity equation, and the corresponding definite solution conditions are given. According to the influence mode of the interaction of two fields, the mathematical model of the coupling of seepage field and stress field in porous media is obtained, and the finite element matrix format and the solution method under the coupling state are given. The main points in the process of establishing 3D finite element model are expounded, and the model parameters are given based on the geological prospecting report of practical engineering and the corresponding geotechnical experiment results. (2) the stress concentration phenomenon exists in the culvert top of the culvert when the construction process of layered backfill is simulated. This is the special loading form of the deep buried frame structure, and the increase of effective stress is caused by the pore pressure overflow in the three stages of the water level descending process, the obvious water level falling process and the culvert side water level falling process, and the increase of the effective stress in the simulated water level descending consolidation process is mainly caused by the obvious water level drop (mainly). The stress concentration caused by the settlement difference (35) h contributes together, and the water level decline is not suitable to measure the trend of internal force change at this time. During consolidation and drainage process, settlement intensifies, internal force increases, and the risk of structural damage under loading increases accordingly. (3) the factors which have a great influence on the response of culvert and internal force are elastic modulus E and permeability coefficient k, and the backfill is not considered. In culvert drainage engineering measures, under the action of only one parameter of earth-rock mixture, the larger the elastic modulus E _ m of backfill in field area is, the more favorable is the structure of permeability coefficient km _ m when the order of permeability is higher; The smaller the ESM is, the bigger the KSM is, the smaller it is and the smaller it is, the smaller the structure is, the more favorable the structure is to the structure. In the same range of variations, Em is more sensitive than ES, and KS is more sensitive than KM. In general, using the corresponding engineering measures in the range of the culvert soil can effectively reduce the load and internal force of the structure, and it is more economical and efficient.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV31

【参考文献】