群桩—承台—桥墩竖向动刚度特性研究

发布时间：2018-10-13 07:18

【摘要】：随着我国高速铁路和重载铁路的发展,客运列车既有线提速及货运列车轴重的提升都会引起桥墩基础承载力安全储备的降低。目前我国采用的桥梁检测的相关方法和规程主要针对桥梁上部结构和横向振动,对于桥墩基础竖向承载力的无损检测评估方法尚不完善。以群桩-承台基础为例,传统的静载试验和高应变测桩法均无法满足对既有桥墩基础承载性能快速普查的无损检测需求。因此,发展一套用于评价桥墩基础竖向承载能力的动力无损检测方法就显得尤为重要。目前,用于桥桩竖向承载力评价的动力无损检测方法主要有两类,除高应变测桩法外,另一种是以机械阻抗法为测试手段发展而来的动刚度综合评价法。当桥桩承载力由变形控制时,动刚度与静刚度之间通过动静对比系数加以换算。既有实验研究表明,采用动刚度作为评价指标时,动刚度与桩基竖向承载力之间存在正相关关系。然而,以往研究对象多以单桩为主,并没有考虑承台和桥墩对动刚度的影响。对于广泛使用的群桩-桥墩结构系统,采用动刚度指标评价是否仍具有可靠性,尚缺乏系统的研究。基于此,本文通过室内原理性试验和数值模拟,对群桩-承台-桥墩系统竖向动刚度的影响因素及其特征进行了系统的研究分析,主要工作如下:(1)基于瞬态机械阻抗法的基本原理,建立了群桩-承台-桥墩的原理性试验模型。采用木材和石膏两种材料分别对桩基缺陷、桩径、桩周有效摩擦面积和墩身高度对群桩-承台-桥墩系统竖向动刚度的影响以及单桩与群桩-承台系统竖向动刚度之间的关系进行了测试研究;(2)结合现场模型桩的动静检测数据,验证了所建立的桩-土三维有限元分析模型参数的合理性,并从材料因素(混凝土弹模、泊松比,土体的弹模和土层变化等)和几何因素(单桩、单桩-承台和群桩-承台,桩长,墩身以及桩体几何缺陷等)两个角度对群桩-承台-桥墩系统竖向动刚度的影响及其特征进行了研究。本文由以上工作得到结论如下:(1)与完整桩相比,扩径桩竖向动刚度值明显偏大,而缩径桩和短桩(桩基实际长度不满足设计要求)则与扩径桩情况相反;缺陷桩的缺陷部位越接近承台底面,对群桩-承台系统竖向动刚度值影响越大;桩基竖向动刚度与桩径成正相关;群桩-承台结构系统竖向动刚度随着桩周有效摩擦面积的减小而减小;随着墩身的增高,群桩-承台-桥墩系统竖向动刚度呈减小的趋势。(2)群桩-承台系统竖向动刚度值与结构混凝土弹性模量和泊松比成正比;随着桩周土层动弹性模量的增大,群桩-承台系统竖向动刚度值也随着增大,其中摩擦桩对桩周土体的变化较端承桩敏感。随着桩基周围土层等厚度降低,系统竖向动刚度值下降百分比逐渐减缓。(3)群桩-承台系统竖向动刚度值介于n-1倍和n倍单桩-承台系统竖向动刚度值之间(其中n为承台下桩基的数量);摩擦桩系统竖向动刚度值随着桩长的增大呈现增大,端承桩系统竖向动刚度值随着桩长的增大呈现减小,在桩长为20m时系统竖向动刚度值趋于稳定。
[Abstract]:With the development of high-speed railway and heavy haul railway in our country, both the speed-up of the passenger train and the lifting of the freight train will cause the reduction of the safety reserve of the pier foundation bearing capacity. At present, the related methods and regulations of bridge detection adopted by our country are mainly aimed at the superstructure and lateral vibration of the bridge, and the nondestructive detection and evaluation method for the vertical bearing capacity of the pier foundation is not perfect. On the basis of group pile-bearing platform, the traditional static load test and the high strain gauge pile method can not meet the requirement of nondestructive testing for rapid census of existing pier foundation bearing performance. Therefore, it is very important to develop a set of dynamic nondestructive testing methods for evaluating the vertical bearing capacity of pier foundation. At present, there are two kinds of dynamic nondestructive testing methods for the evaluation of vertical bearing capacity of bridge piles. In addition to the high strain gauge pile method, the other is the dynamic stiffness comprehensive evaluation method developed by the mechanical impedance method as the test means. When the bearing capacity of bridge pile is controlled by deformation, the dynamic stiffness and static stiffness are converted by dynamic and static contrast coefficient. There is a positive correlation between dynamic stiffness and vertical bearing capacity of pile foundation when dynamic stiffness is used as the evaluation index. However, the previous research objects are mainly single-pile, and do not consider the influence of bearing platform and pier on dynamic stiffness. For a widely used group pile-pier structure system, the dynamic stiffness index evaluation is used to evaluate whether it still has the reliability, and the research on the system is still lacking. Based on this, the influence factors and their characteristics of vertical dynamic stiffness of pile-bearing platform-pier system are analyzed by indoor principle test and numerical simulation. The main work is as follows: (1) The basic principle of transient mechanical impedance method is given. The principle test model of pile-bearing platform-pier was established. The relationship between pile foundation defect, pile diameter, effective friction area of pile and pier height on vertical dynamic stiffness of pile-bearing platform-pier system and the relationship between single pile and vertical dynamic stiffness of pile-bearing platform system were studied by using two kinds of materials of wood and gypsum respectively. (2) According to static and static detection data of the on-site model pile, the rationality of the parameters of the established pile-soil three-dimensional finite element analysis model is verified, and the material factors (concrete elastic modulus, shear modulus, elastic modulus of soil body and soil layer change, etc.) and geometric factors (single pile) are verified. The influence of single-pile-bearing platform and pile-bearing platform, pile length, pier body and geometric defect of pile body on vertical dynamic stiffness of pile-bearing platform-pier system are studied. The results obtained from the above work are as follows: (1) Compared with the complete pile, the vertical dynamic stiffness value of the enlarged diameter pile is obviously larger, while the diameter pile and the short pile (the actual length of the pile foundation do not meet the design requirement) are opposite to the case of the enlarged diameter pile; the closer the defect part of the defect pile is closer to the bottom surface of the bearing platform, The influence of vertical dynamic stiffness value of pile-bearing platform system is larger, the vertical dynamic stiffness of pile foundation is positively related to pile diameter, the vertical dynamic stiffness of pile-bearing platform structure decreases with the decrease of effective friction area of pile, The vertical dynamic stiffness of pile-bearing platform-pier system is decreasing. (2) The vertical dynamic stiffness value of the pile-bearing platform system is directly proportional to the elastic modulus and Poisson's ratio of the structural concrete; with the increase of the dynamic elastic modulus of the soil layer of the pile, the vertical dynamic stiffness value of the pile-bearing platform system increases with the increase, among which the friction pile is sensitive to the change of soil body at the end of the pile. As the thickness of surrounding soil layer of pile foundation decreases, the decrease percentage of vertical dynamic stiffness value of the system gradually decreases. (3) The vertical dynamic stiffness value of the pile-bearing platform system is between n-1 times and the vertical dynamic stiffness value of the n-fold single pile-bearing platform system (where n is the number of pile foundation below the bearing table); the vertical dynamic stiffness value of the friction pile system increases with the increase of the pile length, The vertical dynamic stiffness value of the end bearing pile system decreases with the increase of pile length, and the vertical dynamic stiffness value of the system tends to be stable when the pile length is 20m.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U441

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