基坑冻土挡墙强度及温度测控系统的研究

发布时间：2018-07-05 11:21

本文选题：基坑 + 冻土挡墙　；参考：《吉林大学》2015年博士论文

【摘要】：国家经济不断腾飞，社会发展速度不断加快，大型建筑、大型基建项目正不断的上马，但与此同时带来了地下工程支护的诸多问题。已有的支护方案不仅造成后续工程的无法顺利进行，同时由于支护的原因，造成大量的建筑废弃物，如土钉墙、桩锚支护中的钢筋无法取出再使用，而且在支护前的大量降水止水过程，不仅改变了地下水位的位置，由于钢筋的腐蚀也造成了地下水的污染。因此，地下支护的改变成为了十分突出的问题。基坑冻土挡墙在支护过程中不受地质条件限制，只需通过人工冻结技术使土体冻结，就可以使土体的抵抗外力的能力增强，在强度上达到设计要求。基坑冻土挡墙不仅可以起到支护作用，而且冰可以有效的阻挡水的渗流，起到止水的效果。基坑冻土挡墙具有的诸多优点，保证了在不改变地下水条件下，仍可以保证基础施工的顺利进行。在冻土的自然融解后，恢复原有的地层情况。由于没有建筑废弃物的存在，不会对地下水产生污染，另外不会影响周围的地下管线，不会对建筑物周围的建设造成后期的影响，且可以循环使用，不会造成经济上的浪费。对比以往的支护方案，基坑冻土挡墙的优势非常明显，越来越成为施工人员选择的施工方法。然而，不论是施工人员还是设计人员，对于该施工方法不甚了解。尽管在矿井建设上已经使用人工冻结技术多年，并且形成的理论相当成熟，但作为基坑支护的一种施工方法使用还是很少。原因是基坑冻土挡墙在基坑中的支护缺少理论研究，不能为基坑冻土挡墙做理论支持。比如冻土挡墙强度理论的贫乏、冻土温度场发展规律计算复杂、冻土温度场计算机辅助时人为因素过多影响模型性质、制冷循环系统的温度控制以及远端无线操控的研究等。本文通过现场模拟试验、数值模拟分析等方法对基坑冻土挡墙强度的影响因素进行理论分析及数值分析，找到强度的变化拐点，以能量守恒定律为基础，利用数值分析的方法研究基坑冻土挡墙冷冻半径的发展规律，自制较为简单的温度测控系统。以下是研究的主要内容及主要成果：（1）通过冻结试验装置进行模拟试验，分析了粉质粘土在不同含水率下，冻结强度与深度、径向距离、冻结时间、冻结温度间等的强度变化规律。基坑冻土挡墙的强度在含水率和冻结温度上都存在拐点。含水率低于拐点值时，冻土挡墙的抗压强度、抗拉强度、抗剪强度及压入硬度都随温度的降低而增高，但含水率高于拐点值时，变化趋势相反或变化不大。当含水率一定时，冻土的压入硬度在土体温度低于拐点值时不再继续增高或增高缓慢，冻土挡墙的抗压强度、抗拉强度及抗剪强度在土体温度低于拐点值时，反而随温度的降低而降低。（2）以能量守恒定律为基础，对冻土温度场进行数值模拟研究，得到运算简单、精度更高的基坑冻土挡墙冻土温度场发展规律的数学模型。模型解决了传热学温度场冻土模型建立的困难和对复杂偏微分方程组的求解；解决了采用ANSYS有限元分析法时，由于在冻土建模时控制参数选取受到人为主观因素的影响较大而经常出现分析解算结果与实际不符的情况。通过与现场试验得到的数据对比分析，模拟的冻土温度场变化规律的发展拟合曲线走势大致与试验数据所得到的拟合曲线相近，吻合度较高。（3）以主处理器AT89S52为核心制作单片机，建立温度测控系统。温控系统包含测温系统与温度控制系统。经过对多个单探头测温传感器与温度测温系统的测试对比分析，该套温度测试系统在温度自动采集的使用中可行，且准确率较高。利用测温系统对温度进行采集，把温度信号传送到温度控制系统，通过温度控制系统对工作泵进行控制，在温度达到要求是关闭工作泵，停止输送制冷液，温度超过范围时，自动打开工作泵，，制冷液开始循环流动。通过现场试验，该设备可准确的控制工作泵运转。以无线通信传输模式为基础，通过无线通讯协议制作无线传输设备，并把无线设备与自动温控系统连接，然后通过接口软件把无线传输设备与计算机进行连接，编写计算机软件，利用计算机在远端无线控制自动测温系统，通过现场试验效果良好。
[Abstract]:The national economy is constantly soaring, the speed of social development is speeding up, large buildings and large infrastructure projects are coming up continuously, but at the same time it brings many problems in the support of underground engineering. The existing support schemes not only cause the failure of the follow-up projects, but also cause a large amount of construction waste, such as soil nails, due to the reasons of support. The steel bars in the pile and anchor support can not be taken out and reused, and a large number of precipitation and stopping processes before the support not only change the position of the groundwater level, but also cause the pollution of the groundwater. Therefore, the change of underground support has become a very prominent problem.
The frozen soil retaining wall in the foundation pit is not restricted by the geological conditions in the supporting process. The soil can be frozen by artificial freezing technology, which can enhance the ability of the soil to resist external force and meet the design requirements. The frozen soil retaining wall can not only play a supporting role, but also can effectively block the seepage of water and play an effective way to stop the water. There are many advantages of the permafrost retaining wall, which ensures the smooth progress of the foundation construction without changing the ground water conditions. After the natural melting of the frozen soil, the original formation situation will be restored. Because there is no construction waste, it will not be contaminated with groundwater, and the surrounding underground pipelines will not be affected. The influence on the construction around the building, and it can be used circulate, will not cause the waste of economy. Compared with the previous support scheme, the advantages of the frozen soil retaining wall in the foundation pit are very obvious, and more and more become the construction methods chosen by the constructors.
However, the constructors and designers are not very familiar with the construction method. Although artificial freezing technology has been used for many years in the mine construction, and the theory is quite mature, the use of a construction method as a foundation pit support is still very few. The reason is that the support for the frozen soil retaining wall in the foundation pit is lack of theory. The research can not provide theoretical support for the permafrost retaining wall of the foundation pit, such as the lack of the permafrost wall strength theory, the complexity of the temperature field development of the permafrost, the overabundance of artificial factors, the temperature control of the refrigeration cycle system and the research on the remote wireless manipulation of the refrigeration cycle system. Theoretical analysis and numerical analysis on the influence factors of the strength of frozen soil retaining wall in foundation pit are analyzed and analyzed by numerical simulation analysis, and the changing inflection point of strength is found. Based on the law of conservation of energy, the development law of frozen radius of frozen soil retaining wall in foundation pit is studied by means of numerical analysis, and the simple temperature measurement and control system is made by ourselves. The following is the research of the temperature measurement system. The main contents and main achievements of the study are as follows:
(1) through the simulation test of the freezing test device, the strength changes of the freezing strength and depth, the radial distance, the freezing time and the freezing temperature are analyzed under the different water content. The strength of the frozen soil retaining wall in the foundation pit is in the inflection point at the water content and the freezing temperature. The compression of the frozen soil retaining wall is lower than the water cut point. Strength, tensile strength, shear strength and indentation hardness increase with the decrease of temperature, but when the water content is higher than the inflection point, the change trend is opposite or little. When the water content is certain, the compressive hardness of the frozen soil no longer increases or increases slowly when the soil temperature is lower than the inflection point, and the compressive strength, tensile strength and resistance of the permafrost retaining wall. When the soil temperature is lower than the inflection point, the shear strength decreases with the decrease of temperature.
(2) on the basis of the law of conservation of energy, the mathematical model of the temperature field of frozen soil is numerically simulated to obtain the mathematical model of the development law of frozen soil temperature field in frozen soil retaining wall with simple operation and higher precision. The model solves the difficulty of establishing the frozen soil model in the heat transfer temperature field and solving the complex partial differential equations, and solves the problem of using ANSYS. In the finite element analysis method, the control parameter selection is greatly influenced by the subjective factors in the frozen soil modeling, and the analysis results are often inconsistent with the actual conditions. Through the comparison and analysis of the data obtained from the field test, the trend of the simulation curve of the simulated temperature field variation of frozen soil is roughly with the experimental data. The fitting curves are close, and the degree of anastomosis is high.
(3) the temperature measurement and control system is set up with the main processor AT89S52 as the core. The temperature control system includes the temperature measurement system and the temperature control system. After comparing and analyzing the test of the temperature measuring system with a number of single probe sensors, the temperature measurement system is feasible in the use of temperature auto acquisition, and the accuracy is high. The temperature measurement system can collect the temperature, transmit the temperature signal to the temperature control system and control the working pump through the temperature control system. When the temperature is reached, the working pump is closed, the refrigerating liquid is stopped and the temperature exceeds the range. The working pump is opened automatically and the refrigeration liquid begins to circulate. Through field test, the equipment can be accurate. Control work pump operation. Based on wireless communication transmission mode, wireless transmission equipment is produced by wireless communication protocol, and wireless devices are connected with automatic temperature control system. Then wireless transmission equipment is connected to computer through interface software, computer software is written, and automatic temperature measurement is used by computer in remote wireless control. The system has a good effect through the field test.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU476.4

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