【作者】 张婷；

【导师】 杨平；

【作者基本信息】 南京林业大学 ， 森林工程， 2013， 博士

【摘要】 修建地铁隧道，盾构机的安全始发与接收是盾构法关键所在。水平杯型冻结技术在盾构进出洞端头加固中具有止水、保持土体自立性、环保等特点，而冻结温度场随时间的可变性、冻胀变形对周围环境的影响程度等制约着水平杯型冻结壁的进一步推广应用。基于上述问题，本文结合南京地铁二号线逸仙桥车站盾构出洞水平杯型冻结工程，通过室内试验、现场实测、理论分析与数值模拟方法，对水平杯型冻结温度场及地表冻胀位移进行了较系统研究，主要研究成果如下：1）南京地区淤泥质黏土、粉质黏土、粉砂三种典型地层的起始冻结温度随含水率增加近似线性升高，随盐份浓度增加直线降低，水质对起始冻结温度有较大影响，干密度和冻融循环对此影响不大。常温土导热系数随含水率及干密度增加而增大，且冻土导热系数大于常温土导热系数。土中水分迁移受温度影响较大，水分迁移程度与土质、冻结时间、含水率和干密度有关。2）通过南京地铁二号线逸仙桥车站温度场实测对水平杯型冻结壁温度场数值模拟方法的可行性进行了验证；研究了盐水温度、冻结管直径、地层热参数及冻结时间对水平杯型冻结壁温度场的影响规律；在各因素取值范围内，冻结40d时杯型冻结壁短管底部最小厚度可达30～54cm，圆筒壁厚度可达80～140cm；内圈管间冻结壁最早交圈，杯型冻结壁的“杯底”和“杯壁”交接处最晚交圈。3）研究分析了影响地层冻胀的因素，通过有限元计算，研究了不同因素变化对水平杯型冻结引起地表冻胀位移的影响规律。结果表明：不管是垂直或是沿着隧道轴线方向上，距离隧道轴线或是地下连续墙（围护结构）越近，地表冻胀位移越大，低温盐水温度、隧道半径、隧道埋深及冻胀率变化对地表最大冻胀位移的位置未产生明显影响，随板块厚度增加，该位置朝远离地下连续墙方向移动；在各因素取值范围内，距离冻结壁区域越远，地表冻胀位移呈衰减性规律减小，其中低温盐水温度、隧道直径、隧道埋深对地表冻胀位移的影响较为显著；考虑各种建筑物对地基变形的要求，确定距离隧道洞门20m以内为盾构进出洞水平杯型冻结加固端头的地表变形监测范围。4）建立了水平杯型冻结壁稳定性计算模型，研究结果表明杯底厚度、圆筒壁厚度及长度变化对引起的应力与位移均大大小于其允许值，隧道直径越小，越有利于地层稳定性。水平杯型冻结时合理的杯底厚度宜取2.0～2.5m，常规地铁隧道的圆筒壁长度取值与盾构机壳体长度相当，圆筒壁厚度宜取1.0～1.2m，隧道埋深越大，需要的冻结壁尺寸越大，具体隧道埋深与与冻结壁尺寸的选择和地层物理力学性质密切相关。研究结果解决了水平杯型冻结壁应用中的参数选取、温度场发展及地表冻胀程度预测等问题，对水平杯型冻结壁在盾构进出洞端头加固工程中的推广应用具有重要的科学意义和应用价值。更多还原

【Abstract】 The safety start technique and arrival of shield machine are crucial to the shield methodwhen an underground railway tunnel is built. The artificial horizontal cup-shaped freezingtechnique has the benefits such as stopping water, keeping the subsistence of soil andenvironmental protection, but it is also restricted to be spread and exploited further because ofthe variability of temperature field with time during the formation of artificial freezing wall andthe frost heaving deformation influence on the surrounding. Based on the problems above, Inthis paper, the application of horizontal cup-shaped freezing wall in shield constructiontechniques for pass out of working pit engineering was presented by instances and the authormade a systematic study on the temperature field and the earth’s surface frost heavingdeformation during the formation of horizontal cup-shaped freezing wall by laboratoryexperiment, field survey, theoretical analysis and numerical simulation. The main conclusionsfor this paper were listed as follows:1）The results of laboratory experiment indicate that the initiative freezing temperature ofthe three kinds of typical soil layers in Nanjing region silt mass clay, silt clay and sandapproximately linearly increase when moisture content increase and temperature decreasewhen the Salt concentration increase. That’s more, water quality has great influence on theinitiative freezing temperature, but dry density and freezing and thawing cycle have littleinfluence on it. According to the test results coefficient of thermal conductivity increases withmoisture content and dry density increasing, and the frozen soils’ is greater than the normaltemperature soils’. Moisture migration extent is relevant to several factors, such as soil texture,freezing time, moisture content, dry density and so on and the moisture content influentsgreater.2) After establishing the computational model of the horizontal cup-shaped freezing walltemperature field, the model’s practicability is verified by the temperature field test result inNanjing metro line2Yixian Bridge subway station.This paper studies the effects of subzero saltwater temperature, thermal physics parameter andfreezing time on the horizontal cup-shaped freezing wall temperature field. Among the differentfactors’ value range, the short freezing pipe bottom’s freezing wall thickness can be30-54cm,the cup’s thickness can be80-140cm while freezing. The results of the closure of freezing wallshow that interior circle freezing pipes close the earliest, the part between the bottom of the cupand the cup’s wall close at the latest. 3) According to the finite element analysis, different factors which have influence on theground level displacement are researched. The results show that: horizontal or along axial oftunnel the nearer to the axial and sub-continued wall the ground level frozen deformation isgreater. What’s more, temperature of saline water, radius of tunnel, buried depth of tunnel andfrozen ratio have little influence on the position of the greatest displacement, but with thethickness of plates increase, the position is near to the sub-continued wall. Among thedifferent factors’ value range, the further the distance to frozen wall, the displacement of groundlevel decrease attenuatly. Based on the influence of temperature of saline water, parameter oftunnel, buried depth of tunnel about frozen displacement is greater and taking the requirementsof kinds of architecture into consideration,20m away from the tunnel portal and export isdetermined to be monitored.4) With establishing the stability model of horizontal cup-shaped freezing wall,the resultssuggest that the stress and displacement caused by changes of the thickness of cup bottom andcylinder are much less than allowable value, and the diameter of tunnel is smaller of thestability of formations. In addition, the reasonable thickness of cup bottom can be2.0~2.5m,and the length of cylinder is almost the length of shield machine. The last but not least, thethickness of cylinder can be1.0~1.2m, the deeper the tunnel, greater the thickness, and thespecific thickness and buried depth will be determined by the physical and mechanicalproperties of formations.The researches solve several problems such as parameter selection, development oftemperature field, prediction of ground level deformation ect. And the researches haveimportant significance on application and spread of horizontal cup-shaped freezing in shield’sturnover.更多还原