路堤荷载下沉管灌注筒桩复合地基性状

随着我国经济建设的快速发展,在深厚软土地基上修建高等级公路越来越多,沉管灌注筒桩(简称筒桩)作为软土路基处理的一种新型技术,吸收了预应力管桩、振动沉管桩的技术优点,具有混凝土使用方量少,造价低,承载力高,施工方便的特性,在路堤下软土地基处理中具有广泛的应用前景。为此本文开展了对筒桩及路堤下筒桩复合地基的理论研究。 首先对筒桩进行简单的介绍,并对目前桩基及复合地基理论进行概况分析。 其次,介绍筒桩桥头软土处理的现场试验并对测试成果进行分析,包括成桩质量、单桩及群桩承载力试验、成桩前后地基土性的改变、桩问土和桩顶土压力、分层沉降、侧向位移和孔隙水压观测。分析结果表明筒桩施工工艺成熟,施工质量可靠,筒桩联合土工格栅处理桥台软基,可以很好的解决桥台的跳车问题。 第三,考虑桩土界面的摩擦接触,采用轴对称平面有限元方法对竖向荷载作用下筒桩单桩进行数值模拟,分析筒桩内、外侧摩阻力、桩端阻力及各项荷载分担比的变化规律和土塞的性状,提出筒桩单桩极限承载力的计算公式。 第四,采用典型段三维有限元方法模拟路堤下筒桩复合地基,并且考虑桩土界面的摩擦接触、挚层中的土工格栅以及填土的分层加载,以使计算模型在力学概念上更为合理,对复合地基变形、荷载传递机理的影响因素做了研究。计算表明路堤填土中的土拱效应、土工格栅的拉膜效应或多层格栅垫层的梁效应保证了大部分荷载由筒桩承担,有效的减少了复合地基总沉降和不均匀沉降。 第五,将现场实测成果与本文的有限元方法进行对比分析,表明有限元方法对筒桩单桩及路堤下筒桩复合地基的工作性状分析是可行的。
活动房
With the fast development of the national economy, more and more highway is constructed on thick soft clay ground. As a new foundation treatment technique, driven cast-in-place tubular pile (DCTP) combine both advantages of pre-stressed tubular pile and buffeting-sunk pile, and have the properties of less concrete quantity, low cost, high bearing capacity and suitable for construction. Therefore, it has a good application perspective in soft clay ground treatment. Theoretical study of the DCTP and the DCTP composite foundation below the embankment is carried out in this thesis.First, DCTP is introduced briefly. A general analysis of the current pile foundation and composite foundation theory is followed.Secondly, in-situ experimentation of DCTP soft clay treatment located in bridgehead is introduced. Results obtained are analyzed, specifically include: pile quality, test of the bearing capacity of single-pile and multi-piles, variation of ground property before and after pile construction, top and pile-to-pile soil pressure, delamination settlement, horizontal displacement and pore water pressure observation. Results show that craftwork for DCTP is applicable, and construction quality is tenable. In addition, it is found that DCTP combining the geogrid to perform bridgehead soft ground treatment is able to solve the car-jump problem.Thirdly, pile-ground interface friction touch is considered. Axis-symmetrical in-plane finite element method is used to perform numerical simulation of single DCTP under vertical loading. The inner and outer friction forces of DCTP, pile-end resistance force and variation of loading share ratio and performance of soil plug are analyzed. A formulation to perform computation of single pile utmost bearing capacity is proposed.Fourthly, DCTP composite foundation is simulated using typical three-dimensional finite element model. Pile-ground interface friction touch, geogrid of underlayer and layered loading of earthfilling is considered, so that the computational model is morerational. The deformation of composite foundation and the basic principle of influential factors on the load transformation are also studied. It is found that most part of the load is undertaken by the pile due to the soil arching effect in embankment soil, tensioned membrane effect in geogrid or beam effect in multi-layer grid underlayer. Thus, the total settlement and uneven settlement of the composite foundation is reduced effectively.Lastly, the numerical results obtained by finite element analysis are compared with those obtained by in-situ experimentation. Results show that performance analysis of the single DCTP and under embankment DCTP composite foundation using finite element method is applicable.