【作者】 李懿；

【导师】 王连俊；

【作者基本信息】 北京交通大学 ， 道路与铁道工程， 2014， 博士

【摘要】 我国的铁路建设进入了跨越式发展时期,施工工期紧、路基不均匀沉降大及土地资源紧缺等问题日益突出。在借鉴钢筋混凝土挡土墙和箱梁设计思路的基础上,本文提出了一种新型路基结构——悬臂式U型结构路基,它具有刚度大、变形小、整体性好和不均匀沉降小等优点；也解决了常规放坡路基占用土地面积大以及地基处理面积大的问题。基于此,本文对U型结构路基荷载下垫层参数、桩体参数(桩长、桩径和桩间距)及路基高度对复合地基的沉降、附加应力、桩的应力及桩土应力比的影响,及车辆轨道—U型结构路基—复合地基耦合系统的动力响应进行了系统深入的研究,主要研究内容和成果如下：(1)U型结构路基与地基是一个整体,两者间相互协调,共同作用。地基系数是影响U型结构路基的变形和内力的最关键因素,地基系数达到6000kN/m3时,U型结构路基的沉降、底板的差异沉降及结构的次应力都趋于稳定；U型结构路基的高度应控制在5m左右,并应在出现应力集中区域采取加密布置箍筋或布置加强钢筋的构造措施；增大U型结构的厚度和提高U型结构混凝土强度等级都可以增大结构的刚度,提高抗挠曲变形能力,混凝土的强度等级比结构厚度对于结构内力的影响小,混凝土的强度等级宜取C30。(2)垫层在U型结构路基复合地基中具有分担桩土荷载的重要作用,厚度建议取0.4m,过厚的垫层使桩承担的荷载减少且不经济；桩长对U型结构路基复合地基的沉降和应力特性有显著的影响,桩身长度应取15m,穿透软土压缩层,进入承载力高、压缩量小的土层；减小桩间距和增大桩径都可以增大复合地基的置换率,减小复合地基沉降,桩间距的影响比桩径显著,选用细桩密布方案,桩间距取3.5m,桩径取0.5m。(3)在车辆轨道—U型结构路基—复合地基耦合系统中,行车荷载通过钢轨、轨道板、U型结构路基、垫层传递到复合地基,在传递过程中,能量被各种介质吸收,各动力响应指标值逐渐衰减。钢轨振动远大于轨道板,从轨道板到支承层再到U型结构路基振动逐渐衰减,但相差不大；再通过垫层传递到复合地基,衰减达90%左右。双向同时行车或单侧行车时,U型结构路基复合地基均能满足列车高速运行时平稳性和稳定性的要求。(4)钢轨、轨道板、U型结构路基和复合地基各动力指标的时程曲线均有明显的轮对效应、叠加效应,从上部钢轨传递到复合地基的深部,轮对效应逐渐减弱。行车速度对U型结构路基复合地基的动力学性能的影响较大,列车运行速度的提高会加剧钢轨的振动和动力冲击效应,需要合理控制行车速度,保证行车安全。(5)以M-B联合解析法为基础,采用C语言编写U型结构路基复合地基的附加应力程序,结合分层总和法得出的复合地基沉降结果与有限元模拟结果有相似的变化规律,此方法计算U型结构路基复合地基的沉降可行。更多还原

【Abstract】 Railway construction is entering leap-forward development period, while the problems of short construction period, large uneven settlement and shortage land resources are increasingly outstanding. Based on the design ideas of reinforced concrete retaining wall and box beam, this paper proposes a new type of subgrade structure—U-shaped structure subgrade in cantilever-type, which has the merits of large rigidity, small deformation, good integrality and little uneven settlement. The new type structure subgrade solves problems, such as the large land area of occupation on general slope subgrade and foundation treatment area. In this paper, the influence of settlement and mechanics property of composite foundation in U-shaped structure subgrade with different parameters of composite foundation, and the dynamic response of railway track-U-shaped structure subgrade-composite foundation coupling system are deeply and systematically investigated. The main research contents and achievements are as follows:(1) U-shaped structure subgrade and foundation are considered as a whole. It has the common action between them. Foundation coefficient is the most important factor influencing the deformation and inner force of U-shaped structure subgrade. When the foundation coefficient is6000kN/m3, the settlement of U-shaped structure subgrade, the differential settlement of slab and secondary stress of structure are tended to be stable. The height of U-shaped structure subgrade should control about5meter, and more stirrup or reinforcement steel bar is necessary in the stress concentration regions. Enlarging the thickness of U-shaped structure and enhancing the concrete strength grade can enhance the rigidity of structure and improve the capacity of resist flexure deformation. The concrete strength grade has larger influence to structure internal force than the thickness of structure, C30is the best strength grade of concrete.(2) Cushion is important to the pile-soil load distribution in U-shaped structure subgrade composite foundation, and reasonable value is0.4m. Cushion over thickness decreases the load pile sharing and diseconomy. Pile length has a significant impact on settlement and mechanics property of U-shaped subgrade structure on composite foundation, and reasonable value of pile shaft is15m, which should penetrate soft soil compressed layer, and insert soil layer with high load-bearing capacity and little compression amount. Decreasing the pile spacing or enlarging the pile diameter can increase the replacement ratio and decrease the settlement of composite foundation. Pile spacing has more influence than pile diameter, and the scheme of thin pile is optimal. The value of pile spacing is3.5m, and the value of pile diameter is0.5m.(3) In spatial coupling dynamics model of vehicle model-U-shaped structure subgrade-composite foundation, train loads transmit to composite foundation through steel rail, track slab, U-shaped structure subgrade and cushion. During the process of transmission, energy is absorbed by kinds of medium, and the value of each dynamic response indicators is damping gradually. The vibration of steel rail is larger than that of track slab. The vibration is attenuating gradually from track slab to supporting layer and U-shaped structure subgrade, but the difference is little. When the vibration transmits from cushion to composite foundation, the damping of each dynamic response indicators is about90%. Under the condition of single-direction and two-direction railway, U-shaped structure subgrade composite foundation can meet the stationarity and stability requirements of train high-speed running.(4) The time-history curve of each dynamic response indicators of steel rail, track slab, U-shaped structure subgrade and composite foundation have obvious wheel set and additive effect. The wheel set effect is receding gradually from steel rail to the deep composite foundation. The train speed has large influence on the dynamics property of U-shaped structure subgrade composite foundation. Increasing the train speed can aggravate the vibration and dynamic impact effect of steel rail, so the reasonable running speed is needed to meet the requirement of running safety.(5) Based on the M-B combining analytical method, programming the additional stress of U-shaped structure subgrade composite foundation using C programming language, and then we get the settlement of composite foundation combining with layer-wise summation method. The results have similar changing tendency to the conclusion drawn by finite element simulation, so the calculating method is feasible.更多还原