碾压混凝土拱坝温控仿真研究

发布时间：2018-08-08 20:25

【摘要】：随着碾压混凝土筑坝技术的迅速发展，国内外兴起了各类碾压混凝土拱坝的建设，但随之出现了大坝在运行后的坝体开裂问题。碾压混凝土拱坝的裂缝大多数是由于温度应力引起，因此，如何在施工过程中通过温度控制措施防止裂缝成为了碾压混凝土拱坝发展的重要课题。碾压混凝土拱坝的温度应力和温控措施都有自己的特点，与常态混凝土相比碾压混凝土在材料参数和施工方法上有较大的区别，加之拱坝不同于重力坝，不能解除其在坝轴线方向坝体温度变形所受到的约束，坝内将产生较大的温度应力。本文以ANSYS有限元软件为平台，，综合考虑拱坝施工过程及外界因素的影响，对碾压混凝土拱坝的几种温控措施进行仿真研究，主要成果如下：（1）以某碾压混凝土双曲拱坝为依托工程，计算过程中考虑外界气温、水温、混凝土水化热及夏季停工度汛等多种因素，运用有限元数值分析法研究碾压混凝土拱坝从开始浇筑到蓄水运行的整个过程中的温度场；综合考虑施工过程中坝体自重、混凝土弹模和蓄水过程中水压力的变化，模拟大坝浇筑施工运行全过程，得到温度场主要影响下应力场的发展过程。（2）依据碾压混凝土拱坝温度及应力控制标准，分析大坝在无温控措施下出现的问题，讨论大坝可能出现裂缝的位置及原因。研究表明：未采取温控措施时，坝体内部温度较高，在整个施工期最高温度都超过28℃，而外表面受外界因素的影响温度较低，内外温差超过控制标准；分期施工形成的新老混凝土结合面附近因间歇时间长且过水而产生较大的上下层温差；大坝出现较大拉应力的位置在中上部拱端处，因自重作用和两侧基岩的约束使两坝肩受拉，尤其在分期施工的结合面附近出现施工过程中最大的拉应力1.7MPa；坝体出现较大压应力且长期受压的位置在靠近底层基岩的拱两端，但最大压应力值小于容许压应力。（3）针对上述问题制定相应的温控措施，按不同影响因素拟定方案进行仿真分析，对比研究温度随时间的变化规律和温控效果，总结各措施温控特点，找到最佳温控方案。结果表明：采取上下游面保温措施可使坝体表面温度升高13℃左右，可有效减小内外温差，降低表面裂缝发生的几率；对分期施工形成的新老混凝土结合面上采用聚乙烯泡沫塑料板进行保温隔热，可有效降低上下层温差；采取坝内水管冷却措施后，坝体各部位最高温度降低5~10℃，有效地控制了温度，有利于减小内外温差及温度应力；最直接有效的温控方法是降低混凝土浇筑温度，每降低2℃，可使坝内最高温度降低0.2~0.9℃。（4）综合上述四种温控措施的最佳方案进行仿真计算，得到坝体温度、应力分布规律，结果显示坝体最高温度降低了11℃，最大拉应力降低了0.47MPa，Mises等效应力分布均匀，平均降低0.2MPa，组合温控措施使各种温差及应力均控制在标准范围之内。对比各措施温控效果，组合温控措施最大拉应力在各时段平均降低22.27%，水管冷却措施在各时段效果都很显著，表面保温措施在停工度汛期间效果最佳。
[Abstract]:With the rapid development of RCC damming technology, the construction of all kinds of RCC arch dams has been developed at home and abroad, but the problem of the cracking of the dam after the operation has appeared. Most of the cracks in the RCC arch dam are caused by the temperature stress. So, how to prevent the crack through the temperature control measures during the construction process. For the development of roller compacted concrete arch dam, the temperature stress and temperature control measures of RCC arch dam have its own characteristics. Compared with normal concrete, the roller compacted concrete has a great difference in material parameters and construction methods. Besides, the arch dam is different from the gravity dam. It can not relieve the deformation of the dam body temperature in the axis direction of the dam. In this paper, the ANSYS finite element software is used as the platform. Considering the influence of the construction process and the external factors of the arch dam, several temperature control measures of the RCC arch dam are simulated and studied. The main achievements are as follows:
(1) taking a RCC Double Curved Arch Dam as the support project, the temperature field, water temperature, water temperature, concrete hydration heat and summer stop flood are considered in the calculation process, and the temperature field in the whole process of RCC arch dam from starting to water storage is studied by the finite element method. The water pressure changes in the body weight, the concrete elastic modulus and the water storage process. The whole process of dam construction operation is simulated, and the development process of the stress field under the main influence of the temperature field is obtained.
(2) according to the temperature and stress control standard of the roller compacted concrete arch dam, the problems of the dam under no temperature control measures are analyzed, and the location and reasons of the possible cracks are discussed. The study shows that the temperature of the dam is higher when the temperature control measures are not taken, and the highest temperature in the whole construction period is over 28 degrees, and the outer surface is affected by the external factors. The temperature difference is lower and the internal and external temperature difference exceeds the control standard. The temperature difference between the upper and lower layers of the new and old concrete composite surface formed by stage construction is due to the long interval of intermittent time and over water. The large tensile stress of the dam is located at the arch end of the middle and upper parts, and the two dam shoulder is pulled by the self gravity action and the constraints of the two sides of the bedrock, especially in stages. The maximum tensile stress 1.7MPa in the construction process is found near the joint surface, and the dam body has large compressive stress and the long compression position is located at both ends of the arch near the base rock, but the maximum pressure stress is less than the permissible pressure stress.
(3) according to the above problems, the corresponding temperature control measures are formulated, and the simulation analysis is made according to the different influence factors. The temperature control and temperature control are compared and studied. The temperature control characteristics of various measures are summarized and the best temperature control scheme is found. The results show that the temperature of the upper and lower surface heat preservation can increase the surface temperature of the dam body to about 13 degrees. It can effectively reduce the internal and external temperature difference and reduce the probability of surface cracks. Thermal insulation can effectively reduce the temperature difference between the upper and lower layers by adopting polyethylene foam board on the new and old concrete combination surface formed by installment, and the highest temperature of each part of the dam is reduced by 5~10 C after adopting the cooling measures of the inner water pipe of the dam, and the temperature is effectively controlled. It is beneficial to reduce the internal and external temperature difference and the temperature stress, and the most direct and effective temperature control method is to reduce the pouring temperature of concrete, and the maximum temperature in the dam can be reduced by about 0.2~0.9 C by each reduction of 2 degrees C.
(4) the optimum scheme of the above four temperature control measures is simulated, and the temperature and stress distribution of the dam body are obtained. The results show that the maximum temperature of the dam is reduced by 11, the maximum tensile stress is reduced by 0.47MPa, the equivalent stress distribution of the Mises is uniformly distributed, the average reduction of 0.2MPa is reduced, and the combined temperature control measures are controlled in the range of temperature and stress in the standard range. Within the temperature control effect of each measure, the maximum tensile stress of the combined temperature control measures is reduced by 22.27% on average in each period. The water pipe cooling measures are very significant in each period, and the effect of surface insulation is best during the shutdown period.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV642.4

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