【作者】 蔡德钩；

【导师】 何华武； 王澜； 叶阳升；

【作者基本信息】 中国铁道科学研究院 ， 岩土工程， 2011， 博士

【摘要】 我国高速铁路在本世纪初进入快速发展期,并迅速成为世界高速铁路强国。高速铁路对路基工后沉降提出十分严格的控制要求,各种地基处理方法应运而生。桩网支承路基结构(简称桩网结构,GRPS)是一种有效、经济的新型地基处理方法,适用于硬土层或基岩上有深厚的软弱层、施工期较紧及总沉降和不均匀沉降要求严格等情况。尽管桩网结构已在工程中大量应用,但其理论研究远落后于工程实践,国内尚无相应的设计规范,国外现有计算方法的假设条件也存在较大差异,在工程应用中造成极大的盲目性。正值当前我国大规模开展基础设施建设,在充分吸收国内外成果的基础上,对桩网结构中最为复杂的加筋网垫工作机理开展系统研究,建立适应我国国情的加筋网垫计算方法十分必要。论文以桩网结构的路基土拱效应、加筋网垫索膜效应和边坡推力效应为主线,通过有限元仿真、模型试验、现场试验和理论分析相结合的方法,对动静荷载在桩网结构路基的传递特性及其引起加筋网垫加筋体受力变形、边坡推力效应引起的加筋体拉力等问题进行研究。首先,调研分析国内外桩网结构加筋网垫的研究成果,对比分析现有4个国外规范的假设条件和计算方法;其次,采用ABAQUS有限元软件建立桩网支承路基结构的三维模型,分析关键参数对其受力变形的影响特性;再次,通过12组室内模拟试验、1组现场静态路基填筑试验和1组现场动态激振试验,全面分析加筋网垫在桩网结构中荷载传递和加筋体受力变形特性;最后,结合我国塑料格栅蠕变特性分析,提出适合我国国情的加筋网垫计算方法。主要研究结论如下:(1)现有设计规范对比分析表明,加筋网垫承担竖向荷载的计算假设和方法存在差异,主要在于路基成拱形式和外荷载的考虑方式不同;竖向荷载引起加筋体拉力的计算方法均采用悬索理论,但简化方法、格栅变形控制变量及地基反力的考虑方式不同。(2)土拱效应分析表明,加筋网垫上方的竖向应力为加筋网垫与桩间土承担的竖向应力之和,与采用球形拱假设的计算结果较为接近,加筋网垫下方桩间土承担着部分荷载。粘性土路基成拱效率略低于砂土路基,格栅的初始松紧状态对土拱成拱效率有一定的影响。(3)索膜效应分析表明,两桩帽间格栅竖向变形近似呈现悬索形状,桩帽间的格栅拉力大于桩间土格栅,位于桩帽之间并垂直于桩帽边的格栅拉力大于平行于桩帽边的格栅拉力。计算竖向应力引起的加筋体拉力时,应考虑地基反力和加筋体初始形状的影响。(4)边坡推力效应分析表明,实测主动土压力的合力明显大于由边坡推力效应引起的格栅拉力,在计算边坡推力效应引起的格栅拉力时,应考虑基底摩擦反力的影响。(5)动荷载在低矮路基中的传递分析表明,经过550万次模拟动荷载作用后的土拱基本处于稳定状态,路基动态应力传递与静态应力存在明显差异,动应力在路基土拱中基本按照均质体进行传递。论文有以下创新点:①提出了考虑地基反力和加筋体初始形状的悬索理论计算加筋网垫加筋体拉力的方法;②提出了考虑基底摩擦力的边坡推力效应引起加筋体拉力的计算方法;③提出了采用Boussinesq公式分析动荷载在桩网支承路基中传递的计算方法;④提出了考虑蠕变的塑料土工格栅长期强度的确定方法;⑤建立了适合我国国情的加筋网垫在桩网支承路基中的计算方法。更多还原

【Abstract】 High-speed railway in China have reached a rapid development period in the 21st century and quickly became powers of high-speed railway of the world. Since the post-construction settlement of subgrade is strictly restricted for high-speed railway, all sorts of foundation treatment methods emerge as the times require. Geosynthetics reinforced and pile supported embankment structure (hereinafter referred to as the pile supported embankment, GRPS) is an effective and economic new method for treating foundation, it is suitable for such conditions as deep weak layer on hardpan or bed-rock, short in construction period and strictly demanding for total settlement and uneven settlement. Although the pile supported embankment structure has been widely used in engineering, but its theoretical research is far behind the engineering practice, there is no corresponding design specification in our country, the existing foreign theory of computing methods also occurred obvious difference, this will have the direct effect of great blindness in engineering application. Current China is just at the period of large-scale developing infrastructure construction, therefore, on the basis of fully absorbing the achievements of domestic and foreign, to research on working mechanism systematically and establish the calculation method of reinforced bedding which adapts to the situation of China is necessary.Taking the subgrade soil arching effect of pile supported embankment structure, cable-membrane effect of reinforced bedding and slope thrusting effect as the main line, adopting the finite element simulation, model tests and field tests, to combine with theoretical analysis, such problems as the transfer characteristics of dynamic and static loads in pile supported embankment structure, reinforced bedding tensile force caused by which and force caused by slope thrusting effect are studied. Firstly, a survey and analysis on reinforced bedding of domestic and foreign GRPS is presented and the existing four foreign codes with the assumptions and calculation method are compared and analyzed. Secondly, the three-dimensional model of pile supported embankment structure is established by ABAQUS finite software and the effects of key parameters on its stress and deformation are analyzed. Then, through 12 groups experiments, 1 group field static test and 1 group field dynamic excitation test, the load transfer characteristics of reinforced bedding and tensile characteristics of geosynthetics on pile supported embankment structure are analyzed comprehensively. And finally, combined with the geosynthetics creep characteristics, the calculation method of reinforced bedding which adapts to the situation of China is presented. The main research conclusions are as follows:(1) The comparison and analysis of existing design specification show that the calculation method and hypothesis of vertical load of reinforced bedding occurred difference, which mainly lies in the different subgrade arching form and the loading consideration. The calculation method for vertical load caused by geosynthetics tensile all adopts suspension of cable theory, but the simplified method, control variables of geosynthetics deformation and foundation counterforce are all considered in a different way.(2) The analysis of arching effect shows that the vertical stress upon reinforced bedding is the sum of stress bearing by reinforced bedding and the soil among piles, the results approaches to which using spherical arch theory basis on German standard, the soil among piles under reinforced bedding undertakes partial load. Soil arching efficiency of subgrade filling with cohesive soil is slightly less than that with silt soil, the initial tightness state of geosynthetics effects on soil arching efficiency to a certain extent.(3) The analysis of cable-membrane effect shows that the vertical deformations of geosynthetics between the pile caps approximately present the shape of suspended-cable, the geosynthetics tension between the pile caps is greater than that of soil among piles, and the geosynthetics tension perpendicular to the edge of pile cap is greater than that parallel to the edge of pile cap. The influence of foundation counterforce and geosynthetics initial deflection shape should be considered when calculating geosynthetics tensile caused by vertical stress.(4) The analysis of slope thrusting effect shows that the measured resultant force of active earth pressure is significantly greater than the geosynthetics tension caused by the slope thrusting effect. So the basal friction counterforce influence should be considered in the calculation of geosynthetics tension caused by the slope thrusting effect.(5) The transmission of dynamic loads in lower embankment indicates that the soil arch is basically in stable after the action of 5.5 million times simulated dynamic loads, the transmission of dynamic stress in subgrade is obviously different from the static stress, and its transmission in soil arch is generally considered as homogeneous substance.The paper has put forward the following innovative points:(1) Propose a calculation method of suspended-cable theory for geosynthetics tensile of reinforced bedding considering foundation counterforce and initial deflection shape of geosynthetics.(2) Propose a calculation method for geosynthetics tensile caused by slope thrust ing effect which considering basal friction.(3) Propose a calculation method for analyzing the transmission of dynamic loads in pile supported embankment structure by Boussinesq formula.(4) Propose the method to determine the long-term strength of plastic geosynthetics considering the creep deformation.(5) It is for the first time to establish the calculating method of reinforced bedding in the geosynthetics reinforced and pile supported embankment of China.更多还原