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1.
基于天津于家堡南地下车库工程扩底桩抗拔极限承载力试验,结合数值模拟手段对扩底桩抗拔承载特性、破坏模式和受力机制开展了分析研究。计算分析表明,扩底桩（有效桩长19 m）相比等截面桩抗拔极限承载力提高约50%,材料增加仅8.5%,扩底桩扩大头周边土体提供的抗力显著提高了抗拔承载力;荷载较小时抗拔力主要由等截面段侧摩阻力提供,扩头段抗拔力占桩顶加载的比值随加载近似呈线性增加;扩底桩等截面段沿桩土界面先发生剪切破坏,扩头段周边土体后发生受压破坏,抗拔承载力达到极限;扩头段位于同一土层时,不同桩长扩头段提供的极限抗拔力相差不大,桩长越长,扩头段抗拔力贡献率越低;扩头段抗拔力主要由自重、扩头段法向力竖向分力和侧摩阻力组成,其中法向力竖向分量提供了扩头段的主要抗拔力,占扩头段总抗拔力约70%。 相似文献
2.
静钻根植竹节桩是由预制竹节桩和桩周水泥土所构成的一种新型组合桩基,它主要通过桩周水泥土改善桩-土接触面摩擦性质以及桩端水泥土扩大头改善桩端承载性能。通过现场静载试验对静钻根植竹节桩桩端承载性能进行研究,并采用传统桩端沉降计算公式对其桩端沉降进行计算;通过模型试验对竹节桩桩端与水泥土扩大头相对位置不同的试桩桩端承载性能进行研究。结合现场和模型试验可以得到：桩端水泥土扩大头可以改善静钻根植竹节桩桩端承载性能;当竹节桩桩端位于水泥土扩大头中间位置时,静钻根植竹节桩桩端承载性能最好;可以用传统桩端沉降计算公式对静钻根植竹节桩桩端沉降进行计算,且当竹节桩桩端位于水泥土扩大头中间位置时,理论计算与实测曲线几乎完全吻合。 相似文献
3.
Ali Bouafia 《Geotechnical and Geological Engineering》2003,21(4):389-398
Nine Static vertical pile loading tests were carried out in Abu-Dhabi, the United Arab Emirates in order to assess the end bearing capacity and settlement of piles bored in slightly silty sands overlying soft rocky horizons like sandstone and calcarenite. The paper is aimed at presenting the results of interpretation of the pile tests in order to estimate the end bearing capacity in correlation with the unconfined compressive strength R
c
and the rock quality designation (RQD). Load-settlement behaviour is also studied through an analysis by the elastic methods commonly used in pile design. 相似文献
4.
通过海洋环境条件下大直径管桩的垂直和水平荷载试验,分析了管桩在垂直和水平荷载作用下的受力特点,得到了管桩的垂直极限承载力、侧摩阻力及端承力、轴向反力系数等结果,以及水平荷载作用下桩顶位移和转角关系、弯矩分布、土抗力、水平地基反力系数的比例系数和最大弯矩点等参数。试验结果表明：垂直荷载作用下,极限承载力可达12000kN,在沉桩过程中部分桩有一定程度的闭塞;大直径管桩能够抵抗水平荷载的作用,弹性长桩的受力性质主要受上部土层的影响。根据试验结果计算的水平地基抗力比例系数m值,对本工程及同类地质条件的桩基设计具有参考价值。 相似文献
5.
J. R. Omer 《Geomechanics and Geoengineering》2015,10(3):223-233
A new computer program “PILESET” is developed for use in predicting the bearing capacity and load-settlement behaviour of axially loaded single piles. The program can analyse almost any soil profile and accommodates (a) displacement piles (b) replacement (c) friction piles, (d) end-bearing piles, (e) under-reamed piles and (f) partially sleeved piles. A variety of soil input data can be used, including: (i) standard penetration tests, (ii) cone/piezo-cone tests, (iii) pressure-meter tests and (iv) laboratory tests. The above data types can be combined, if desired, for pile analysis by PILESET. The program calculates the shaft and base capacities of a pile based on 23 methods published in design guides in over 10 European countries. PILESET also predicts the pile load-settlement curve using five published methods, which include two modified load transfer (t-z) approaches formulated by the author. To demonstrate the capabilities of the program, analysis is carried out for case study involving seven full-scale screw piles formed in sand and tested to failure. In each case, the load-settlement curve computed using the author’s modified method in PILESET is found to be in excellent agreement with the actual pile test results. 相似文献
6.
软土地区土体工程性质较差,土体所能提供桩侧摩阻力和桩端阻力较小,预制桩桩身材料强度无法充分发挥。在预制桩压入土体过程中灌入砂石能够改善桩周土体性质,提高桩-土接触面摩擦性能,从而提高桩基的抗压极限承载力。为了研究填砂竹节桩的抗压承载性能,进行了一组现场静载试验和ABAQUS三维建模计算,通过对试验和计算结果的分析可以得出以下结论：软土地基中填砂竹节桩的抗压承载性能相比常规等截面管桩有了显著提高;填砂竹节桩桩身轴力在竹节节点处减少幅度较大,竹节节点能够提高桩侧承载性能;软土地基中填砂竹节桩桩侧承载性能相比常规等截面管桩有了显著提高,且侧阻增大系数为1.15～1.40。 相似文献
7.
为进一步研究沉箱-桩复合基础的水平向承载性能,开展粉质黏土中单桩、沉箱-桩复合基础在水平向荷载和竖向及水平向组合荷载作用下的系列试验,对沉箱-桩复合基础的水平荷载与位移关系、桩身弯矩、位移及土抗力分布规律及群桩效应等进行了研究。结果表明,在水平荷载作用下沉箱对桩顶的约束使桩身弯矩分布较桩顶自由情况要更均匀,并能有效地降低桩身弯矩、位移及土抗力,提高了基础水平承载能力;在同时作用有竖向和水平向组合荷载时,沉箱底摩擦力参与抵抗水平力作用、桩顶竖向力也有利于进一步提高基础水平承载力;试验获得了不同桩数、桩顶约束、荷载作用条件下的沉箱-桩复合基础群桩效应系数,对于桩距为6倍桩径的情况,桩与桩之间的相互影响很小。 相似文献
8.
Osterberg-Cell (O-Cell) tests are widely used to predict the load–settlement behavior of large-diameter drilled shafts socketed in rock. The loading direction of O-Cell tests for shaft resistance is opposite to that of conventional downward load tests, meaning that the equivalent top load–settlement curve determined by the summation of the mobilized shaft resistance and end bearing at the same deflection neglects the pile-toe settlement caused by the load transmitted along the pile shaft. The emphasis is on quantifying the effect of coupled shaft resistance, which is closely related to the ratios of pile diameter to soil modulus (D/Es) and total shaft resistance to total applied load (Rs/Q) in rock-socketed drilled shafts, using the coupled load-transfer method. The proposed analytical method, which takes into account the effect of coupled shaft resistance, was developed using a modified Mindlin’s point load solution. Through comparisons with field case studies, it was found that the proposed method reasonably estimated the load-transfer behavior of piles and coupling effects due to the transfer of shaft shear loading. These results represent a significant improvement in the prediction of load–settlement behaviors of drilled shafts subjected to bi-directional loading from the O-Cell test. 相似文献
9.
桩端压浆对超长大直径桩侧阻力的影响研究 总被引：11，自引：2，他引：9
桩端压浆可大幅提高超长大直径桩侧阻力,且桩侧阻力的提高成为桩承载力提高的主要原因。桩土间存在一个软弱层（泥皮层）,浆液在压力作用下总是沿着软弱面向上运动,并对桩侧土产生挤压,在使桩径扩大的同时,亦对桩周土体进行加固,从而使桩侧摩阻力提高。根据超长大直径桩工程实例的静载荷试验、标贯试验及CT检测结果证明,压浆后在桩端以上一定范围内桩周土强度提高,桩侧阻力提高12.39 %～52.87 %,侧阻力增量占总增量比例达56 %～88 %。 相似文献
10.
A new type of micropile, the waveform micropile, has been developed to provide improved load-bearing capacity compared with that of a conventional micropile. The waveform micropile has a wave-shaped grout with a partially enlarged shear key formed by the jet grouting method on the cylindrical shaft of the micropile. Previous research has determined that the waveform micropile can be installed faster than the conventional micropile and that the bearing capacity increases as the wave-shaped grout provides additional shaft resistance between the ground and the grout. In this study, a series of centrifuge model tests were conducted on the waveform micropile model with various wave-shaped grouts to analyze the relationship between the arrangement of the shear key and the load-bearing mechanism of the waveform micropile. The load–settlement relationship and the load-transfer mechanism were analyzed based on the test results of six test micropiles, including three waveform micropiles with a single shear key at various depths, one waveform micropile with a multiple shear key along the pile depth, and two micropiles with only a cylindrical shape. The test results showed that the ultimate bearing capacity of the waveform micropile was over two times greater than that of the conventional micropile. The rate of increase in the bearing capacities of each waveform micropile differed with the shape of the shear key. Furthermore, the characteristics of the load-sharing ratio due to the shaft resistance and end bearing varied depending on the shape of the waveform micropiles.
相似文献11.
Load displacement response and ultimate resistance of piles in sand under uplift load are predicted by load transfer approach.
The pile is divided into number of segments and assigned geometrical and material properties according to actual soil pile
situation. The shaft resistance is obtained analytically in accordance with existing studies. The proposed method takes into
account the length, diameter and relevant surface characteristics of pile and soil properties. The load displacement characteristics
and the value of uplift capacity of vertical piles from field test have been predicted. Reasonable agreement has been found
out between predicted and observed values of uplift capacity. Load transfer mechanism is capable of predicting the nonlinear
variation of load-displacement response of piles. 相似文献
12.
Large-scale pile tests in Mercia mudstone: Data analysis and evaluation of current design methods 总被引：3，自引：0，他引：3
J. R. Omer R. B. Robinson R. Delpak J. K. C. Shih 《Geotechnical and Geological Engineering》2003,21(3):167-200
Full-scale load tests were carried out on six instrumented large diameter bored, cast in-situ piles formed in Mercia mudstone, as part of the design of a new Viaduct in Cardiff, UK. In this paper, the results from six
test piles and extensive data from 218 ground investigation boreholes are systematically processed in order to study the load
transfer and resistance mechanisms in Mercia mudstone. Data from strain gauges embedded in each pile are first analysed to
calibrate the load-deformation relationship of each pile as-built, taking into account (i) the non-linearity of concrete and
(ii) the effect of partial steel encasement on pile stiffness at various levels. The shaft and base capacity of the piles
are each predicted using 10 calculation methods belonging to the four basic categories: (i) Undrained analysis, (ii) Drained
analysis, (iii) Mixed approach and (iv) Empirical correlation. It is found that the shaft capacity prediction methods are
moderately consistent. The standard deviations of the ratio Q
sp/Q
sm of predicted to observed shaft capacity lies in the range 0.06–0.24. However, 8 of these methods are over-conservative, giving
Q
sp/Q
sm values in the range 0.29–0.67. The remaining two methods yield Q
sp/Q
sm = 1.01 and 1.49. In contrast, the prediction methods for base capacity are found to be much less consistent. The ratio Q
bp/Q
bm of predicted to measured base capacity falls in the interval 0.52–1.93, with corresponding standard deviations of 0.16–0.82.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
人工挖孔桩桩端土承载力的确定 总被引：2，自引：0，他引：2
城市建设中高层建筑越来越多．基础大多采用单桩承栽能力很高的人工挖孔灌注桩。既保证桩基工程的安全．又能节省工程造价．桩端土承栽力参数的确定在基础工程设计中是十分重要的。本文提出了应用深层平板栽荷试验方法能够较准确的提供桩端土承栽力参数．并在不同地质条件下进行了试验．积累了本地区的一些经验;同时认为在桩端土为中粗砂、泥岩时,应用效果很好;桩端土为粘性土时,应用效果较差。 相似文献
14.
大直径超长钻孔灌注桩荷载分层传递特性试验分析 总被引：3，自引：2，他引：1
基于＂上海市虹桥综合交通枢纽交通中心工程西交通广场＂工程现场静载荷试验和桩身应力测试结果,分析竖向荷载作用下大直径超长钻孔灌注桩在成层土中的荷载传递特性。本工程试桩已加载至破坏,对此试验结果进行分析,能为深入研究大直径超长钻孔灌注桩的承载性状提供有价值的工程参考。本次试验结果表明：1）大直径超长钻孔灌注桩桩端承载力所占比例较低,荷载-沉降关系为陡降型,存在明显拐点;2）桩侧与桩端阻力非同步发挥且相互影响,而上下土层侧阻力系先后发挥至极限;3）根据试桩实测数据,土层埋深对桩周具有相似物理力学性质土层的侧摩阻力影响较大。 相似文献
15.
随钻跟管桩施工不能完全清除桩底岩土沉渣,从而影响桩基端承力。为揭示桩底沉渣对随钻跟管桩承载力的影响机制,开展了考虑桩底沉渣影响的随钻跟管桩竖向承载特性模型试验研究。试验结果表明:在密砂地层中,具有桩端水泥土扩大头的随钻跟管桩,其桩顶荷载-沉降曲线为缓降型,而模拟试验的其他管桩均为陡降型;桩底沉渣降低随钻跟管桩的极限承载力在22%以内,且其桩顶荷载主要由桩侧摩阻力承担,承担占比超过90%;与存在一定厚度沉渣的钻孔灌注桩相比,随钻跟管桩的桩底沉渣对降低承载力的影响相对较小;靠近桩端的轴力随着沉渣厚度的增加而减小,沉渣越厚,减少的幅度越明显;桩端水泥土扩大头施工可提高随钻跟管桩约37%的承载力,且桩端阻比均小于15%。现场原位测试(桩长为15.5 m,长径比为15.50)和室内模型试验(桩长为1 m,长径比为15.87)结果均表明:存在桩底沉渣时,随钻跟管桩是以发挥侧摩阻力为主的端承摩擦型桩。研究成果有助于进一步加深对随钻跟管桩承载性状的认识。 相似文献
16.
桩基础研究的核心问题是桩承载力和桩-土相互作用,包括桩周土的变形和饱和土中孔隙水压力的变化。通过离心模型试验的方法,利用竖向压桩设备把桩压入土体,研究饱和及非饱和粉质黏土中单桩的竖向承载力,以及加载过程中桩周土体的变形和孔隙水压力的变化。粉质黏土饱和后,桩基的承载特性表现出软化的特点,且桩基的承载能力比非饱和粉质黏土中的桩基小,非饱和粉质黏土的压桩试验中桩基没有出现明显的极限承载力。桩基的加载特性与桩周土的变形响应具有显著的相关性,桩的加载过程对桩周土体变形的影响有一定范围,超过这个范围,土体的变形可以忽略不计。饱和粉质黏土中桩基的加载对桩周土体孔压的变化也有一定的影响范围,与桩周土体的变形范围体现出类似的规律。距离桩较近时,桩周土的变形较大;距离桩越远,土体的变形受到桩的影响越小。 相似文献
17.
Field tests were conducted to study the effect of compressive loading on the uplift capacity of single piles embedded in silty
sand. The test program consists of four instrumented cast in situ axial pile load tests in compression, pure tension and tension
with 25 and 50% of compressive load of ultimate capacity in compression. The experimental results indicate that the net ultimate
uplift capacity of single pile decreases with increase in compressive load. The shaft friction is non linear in nature. It
observed that as the compressive load increases the shaft friction along the length of pile decreases. 相似文献
18.
为研究珊瑚砂地基下膨胀混凝土桩竖向承载特性,开展了室内单桩竖向静载模型试验,分析了膨胀混凝土桩的单桩荷载-位移曲线以及轴力、桩侧摩阻力等沿桩长分布特性,与PLAXIS 3D软件数值模拟结果进行对比并探究了线膨胀率对承载特性的影响。结果表明：珊瑚砂中膨胀混凝土桩的荷载位移曲线呈现缓变型,在加载过程中,荷载主要由桩侧摩阻力承担,轴力随着深度的增加而减小,桩侧摩阻力随深度先增加后逐渐减小,随荷载的增加逐渐发挥作用。随着膨胀剂用量的增加,桩身线膨胀量逐渐增加,桩-土相互作用更加明显。添加25% HCSA型膨胀剂可提高近20%的极限承载力和56%的极限侧阻力,提高桩体线膨胀率可以有效提高桩的极限承载力和侧摩阻力。该研究可为珊瑚砂桩基工程设计提供参考。 相似文献
19.
珊瑚地层是钙质砂和礁灰岩的统称。在珊瑚地层中开展预应力高强度混凝土管桩（PHC桩）的原位堆载测试,分析了桩?珊瑚地质的相互作用规律。采用光纤光栅传感技术采集加载过程中的试桩桩身应变,由计算获取桩身轴力,分析加载过程中珊瑚地层中PHC桩基础的承载特性。试验结果表明,（1）桩?土响应处于线弹性阶段;（2）桩的承载发挥状态与入土深度显著相关,且入土深度超过15倍桩径时桩端阻力发挥峰值;（3）桩的安装方式几乎不影响其在珊瑚地层中的承载性能,但贯入能量的大小则显著影响;（4）入土深度和贯入能量的大小,影响珊瑚地质的破碎程度,颗粒破碎显著影响珊瑚地质中桩的承载发挥特性。通过原位测试可知在珊瑚地质中在贯入深度在15倍桩径以内,入土深度与桩端阻力正相关,与桩侧摩阻力反相关。 相似文献
20.
This paper presents the results of three-dimensional, finite element analyses performed with an advanced, two-surface-plasticity, constitutive sand model to investigate the response of non-displacement piles to axial loading. The analysis domain is carefully meshed such that the formation and evolution of shear bands next to the pile shaft and near the pile base can be properly captured. Analyses considering various soil profiles and pile geometries show that the mobilized lateral earth pressure coefficient K along the pile shaft increases with increasing relative density and decreasing initial confining stress. The ultimate unit base resistance is independent of pile diameter, increasing with increasing relative density and increasing initial confining stress at the pile base. Based on the analysis results, design equations are proposed to estimate the limit shaft resistance and ultimate base resistance of non-displacement piles in sandy soil. In proposing these relationships, the pile slenderness ratio is considered. The effect of layer proximity to the base of the pile or pile base embedment in a layer is also considered. 相似文献