外文翻译---粘土中的桩的承载力

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1、 1 X 外文资料译文 粘土中的桩的承载力 桩通常是传递上部结构荷载至各种地基土的最可靠基础形式。包括含有软弱下卧层（例如：软粘土）和在不利环境（例如：海岸）下的地基土。大部分现有的桩的设计方法是从计算单桩的竖向承载力着手。当无可靠的持力层存在时，端阻力是相对较小的，主要的承载力来自于沿着桩身的侧摩阻力。因此，保证一定的侧摩阻力 fs，是粘土中的桩在设计中要首先注意的问题。 在某一地区范围内摩擦桩的 fs是一经验值。这些通过在相似地层之上的由桩的载荷实验反算 得来的 fs（侧摩阻力 ）值和土层的一些假定的相关原始特征值之间的关系得到。实际需要考虑的 事项要求这些相关特征值的测得或估算必须具有良

2、好的可靠性，它们可以通过勘探、试验和目前 土木工程技术上其他的有效分析方法得到。对粘土层，大部分研究假定和原状土相关的特点是它 的不排水剪切强度 cu 或用垂直有效应力来描述他的有效应力情况。因此存在三种用经验估算 fs 的方法：（ 1）总应力法，通过经验参数知 fs 和不排水强度有关；（ 2）有效应力法，通过经验参数 知 fs和最初过大的有效应力有关；（ 3）混合法，在经验参数存在情况下 fs结合 cu 和在 考虑 了 经验因数 的情况下。 在最近的十年，有关离岸建筑的土木工程技术遭遇了难题，并且其他要求包括了在粘土中的 长摩檫桩。这导致考虑评价现存计算 fs 的经验方法和试图发现更多现存的

3、估算方法的研究结果难 以得到。由于桩间土的相互干扰很复杂，并且取决于很多因素，包括位置（地层图、土的工程性 质、地下水位表等），桩的特点（直径、长度、材料、表面粗糙度等），打桩的设备和步骤（闭口 式或开口式、钻孔时间、轴心荷载等级等）。结果学习处理现有经验方法不能通过一般位置，桩 特点，钻孔和荷载条件确定它们的可靠性。这成果限于用来比较另一个不同的方法和桩载荷试验结果。这些研究指出现有经验法一般偏向于安全设计，这些方法提供保守技术意见用来挑选适当的的土参数值（或不排水强度 cu）和经验侧摩系数值。提供一套桩的设备和地层条件，利用这方法可估算 fs并能容易的把二者区分开来。由于现存的方法计算桩的

4、轴向强度可靠性有限，将通过有效应力原则结合它们隐匿处的适应性和不同状态下的其他的重要成就来预测合理的 fs值。推理法估算 fs通常称为有效应力法。需要通过围绕桩身的压力和土的特性和贯穿围绕桩身的不同土层 及不同的桩来估算。（ 1）优先考虑打桩过程； （ 2）钻孔影响和打桩的干扰；（ 3）桩打入后桩周土的固结；（ 4）剪切导致了过大的单轴轴向荷载。这篇文章提供了一个国家通行的系统的方法。这方法用来说明和预测在粘土中摩檫桩的轴向承载力。为了简单明了，这方法在次被限于用来描述穿透统一的含有适度超固结土沉积层，并从属于正常状态下的圆柱形刚性单桩。这种处理方法也处理：（ 1）桩穿透了有孔隙水移动的土层（

5、比如，不排水模式）；（ 2）足够的安装时间（在设备就位后），剩余孔隙应力（在施轴向荷载之前）被允许完全发散，并且从此得到所有的土 层条件；（ 3）过大的单桩轴向荷载迅速进入使毛细水无法移动，此后再利用土的不排水剪切因素。这些精简假定描述了足够的现实条件和轴向荷载。在的结果是正常的。在这个深度总的垂直应力包括原位垂直孔隙压力值。横向压力传感器是一种典型的测桩仪器。直径为 37.8mm 的桩在麻省理工学院被研究过了，为了在打桩的不同阶段同时测量作用于圆柱桩桩身的总水平应力，孔隙压力， u，平均剪切应力和轴向荷载。图 1（ a）和（ b）演示了典型的测量方法，当仪器在 60圆锥的尖端之后填料 1m，

6、防入一定深度的波士顿蓝粘土层内，图 1（ a）显示测量过大的孔 隙压力，“超过”总的水平应力，并且水平有效应力随着时间 t，在放入 30m 深的波士顿蓝粘土时， OCR 值约为 1.3。在图 1（ a）里设计的最初阶段它们描述足够现实条件导致讨论（最小值） fx和峰值是可信赖的。 vo宜春学院物理科学与工程技术学院毕业设计 1 外文资料原文 Shaft Resistance of Piles in Clay Piles often provide the only foundation system that can reliably transmit structural loads to

7、the foundation soils in cases involving weak surficial deposits and hostile environments . Most existing methods of pile design start with estimating the axial capacity of a single pile. When no competent end bearing layer exists, the point resistance is relatively small and the major portion of pil

8、e capacity is derived form skin friction along the shaft. Therefore, the limiting skin friction, fs, that can be provided by the soil is of primary importance in pile design. The design of friction piles at a given site currently relies on empirical methods to estimate fs. This is achieved by means

9、of correlations established in “similar” deposits between values of fsbackfigured from pile load tests and some assumed “relevant” in situ characteristic(s) of these deposits. Practical considerations require that this relevant characteristic(s) must be measured and/or estimated with a satisfactory

10、level of reliability by means of exploration, testing, and analysis methods available in current geotechnical practice. For clay deposits, most investigators postulate that the relevant characteristics of the in situ soil are its undrained shear strength, cu , and/or its effective stress state as de

11、scribed by the vertical effective stress, Therefore, existing empirical methods for estimating fs can be broadly classified into three categories:(1)Total stress approaches, where fs is correlated to the undrained shear strength, cu , through the empirical parameter ；(2)effective stress approaches,

12、where fs is correlated to the initial effective overburden stress, through the empirical factor ；and (3)mixed approaches, where fs is correlated to a combination of cu and as in the case of the empirical parameter,.Challenges encountered by the geotechnical profession during the last decade in offsh

13、ore construction, and other applications involving long friction piles in clays, resulted in considerable research efforts to evaluate existing empirical methods for estimating fs and in attempting to develop more evaluation of existing methods is difficult to achieve, due to the complicated nature

14、of pile-soil interaction and its dependence on many factors including site conditions (stratigraphy, soil properties, water table, etc.),pile characteristics (diameter, length, material, surface roughness, etc.),installation procedures(closed versus open-ended, time after driving, rate of axial load

15、ing, etc.). As a result, studies conducted on existing empirical methods could not establish their reliability under general site and pile characteristics, driving and loading conditions. Instead, efforts were limited to comparing predictions of various methods with one another and./or with results

16、of pile load tests. These studies indicated that existing empirical methods generally lead to safe designs, provided that conservative engineering judgement is exercised in selecting appropriate values of soil parameters ( or cu) and empirical skin-friction coefficients ( ). For a given set of pile

17、and site conditions, estimates of fs can easily differ by a factor of two, depending on the methods utilized. In view of the limited reliability of existing empirical methods for calculating the shaft capacity of piles and the difficulties associated with their adaptability to mew and different situ

18、ations other significant efforts were dedicated to the problem of predicting fs rationally (i.e., based on accepted rational methods of analysis) through effective stress principles. Rational methods for estimating fs, often called effective stress methods, require that stresses and properties of th

19、e soil surrounding the pile shaft be estimated throughout vo or,宜春学院物理科学与工程技术学院毕业设计 2 the various stages in the soil surrounding the various stages in the pile:(1) The initial conditions prior to pile installation； (2)pile-driving effects and installation disturbances； (3)consolidation of the soil a

20、round the shaft after installation； and(4)shearing due to monotonic axial loading to failure. This paper proposes a national and systematic methods, the method for elucidating and predicting the axial capacity of friction piles in clays. For purposes of simplicity and clarity, the method described h

21、erein is limited to single cylindrical rigid piles driven in uniform saturated deposits of moderately overconsolidated clays(OCR4)that obey normalized behavior. The treatment also assumes that (1)Pile penetration takes place without significant pore-water migration in the soil (i.e., an undrained mo

22、de )；(2)sufficient set-up time (after installation) is allowed (before axial loading) for full dissipation of excess pore pressures caused by installation, and thus achieve complete soil consolidation； and (3)monotonic axial pile loading to failure takes place rapidly enough to allow no pore-water m

23、igration and hence., imposes undrained shearing conditions in the soil. These simplifying assumptions represent sufficiently realistic conditions and axial loading are believed to represent sufficiently realistic conditions leading to critical (minimum) vales of fx that are of primary interest in de

24、signs. The piezo-lateral stress (PLS) cell is an instrumented model pile. 37.8mm in diameter, that was developed at Massachusetts Institute of Technology (MIT) in order to provide simultaneous measurements of the total horizontal stress, the pore pressure, u ,and the average shear stress , ,acting on a cylindrical pile shaft during the various stages from installation to axial loading. Fig.1(a) and (b) preset typical measurements when the PLS