Prediction of ground-borne vibration induced by impact pile driving:numerical approach and experimental validation

Deep foundations are currently used in engineering practice to solve problems caused by weak geotechnical characteristics of the ground.Impact pile driving is an interesting and viable solution from economic and technical points of view.However,it is necessary to ensure that the environmental drawbacks,namely ground-borne vibration,are adequately met.For this purpose,the authors propose an axisymmetric finite element method-perfectly matched layer(FEM-PML)approach,where the nonlinear behavior of the soil is addressed through an equivalent linear methodology.Given the complexity of the problem,an experimental test site was developed and fully characterized.The experimental work comprised in-situ and laboratory soil characterization,as well as the measurement of vibrations induced during pile driving.The comparison between experimental and numerical results demonstrated a very good agreement,from which it can be concluded that the proposed numerical approach is suitable for the prediction of vibrations induced by impact pile driving.The experimental database is available as supplemental data and may be used by other researchers in the validation of their prediction models.

Improved plane layout of stabilizing piles based on the piecewise function expression of the irregular driving force

The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway landslide, the piecewise function is used to calculate the irregular driving force by dividing the landslide into several sub-areas.Furthermore, the reasonable layout range and pile spacing can be obtained based on the piecewise function expression of the irregular driving force and on relevant research results of the plane layout for stabilizing piles. Therefore, an improved plane layout of stabilizing piles is presented in consideration of a piecewise function expression of the irregular driving force. A highway landslide located in eastern Guizhou Province, China, is analyzed as a case study using the proposed method. The results demonstrate that the theory presented in this paper provides improved economic benefits and can reduce the requirednumber of stabilizing piles by 28.6% compared with the conventional plane layout scheme.

Ground-borne vibrations induced by impact pile driving: experimental assessment and mitigation measures

Impact pile driving is an interesting technique for the construction of deep foundations from a practical and economical point of view.However,the generalization of this technique can be restricted due to the excessive vibration levels that can be generated,which can be especially problematic in residential areas.However,different mitigation measures can be applied to prevent excessive vibration levels inside buildings located near construction sites.To compare its efficiency through a numerical prediction tool,two experimental test sites are first presented and characterized.From the results obtained,it was found that the construction of an open trench near the impact source can be used as an efficient mitigation measure to reduce the maximum vibration levels evaluated in this study.

ON THE DRIVING BEHAVIOR，VARIABLE－DIAMETEREFFECT AND BEAKING CAPACITY OF DRIVENCAST－IN－SITU PILE WITHFLAT

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Difficulties and measures of driving super long piles in Bohai Gulf

Long piles of the ocean oil platform are usually manufactured as the integration of several segments, which have to be assembled one by one during installation. During pile driving, excessive pore pressure will build up in such a high level that hydraulic fracturing in the soil round the pile may take place, which will cause the soil to consolidate much faster during pile extension period. Consequently, after pile extension, the soil strength will recover to some extent and the driving resistance will increase considerably, which makes restarting driving the pile very difficult and even causes refusal. A finite element （FE） analysis procedure is presented for judging the risk of refusal by estimating the blow counts after pile extension, in which the regain of soil strength is considered. A case analysis in Bohai Gulf is performed using the proposed orocedure to exolain the nile refusal phenomenon.

The Influence of Water-Jet Modification of Soil Conditions on Reduction of Vibrations during Sheet Pile Driving in the Subsoil

Vibratory driving is the most efficient method of sheet pile installation. The elimination or at least reduction of harmful consequences of sheet pile vibratory driving becomes an increasingly important and often the decisive factor in the selection of the excavation protection technology. In difficult soil conditions with strength soil parameters, pressure water jetting precedes sheet pile driving. This technique changes the soil properties, destroying its existing structure near the installed sheet pile. Unfortunately, the results and achievements of contractors using this technique are very often held confidential or simply remain in the records and it is difficult to find papers on this subject. This article features a detailed description of jet-assisted sheet pile driving, including a prefabrication description for the sheet pile toe used to jet water through, water pressure and quantity data and the results with regard to reduce vibrations and noise, as well as to the increase in sheet pile vibratory driving performance.

Selection of the Proper Hammer in Pile Driving and Estimation of the Total Driving Time

There are various methods for analyzing pile driving process such as dynamic formulas, wave equation analyses and dynamic measurements. The programs of the two latter methods are relatively expensive to purchase and also require trained engineers to interpret the data it collects. Meanwhile, the use of the site specific empirical formulas based on the real cases of pile driving and output analyses of the wave equation analysis programs can be beneficial. In the current study, pile driving data from three sites in the south of Iran were collected. Using the data of these cases and one-dimensional wave equation analysis program GRLWEAP, couple of experimental formulas which determine the proper range of hammer＇s ID for driving a pile, are proposed. Finally, due to the importance of the time in marine projects, another experimental formula is also proposed for estimation of the total driving time.

Dynamic and Field Analysis of Pile Driving in Cameroun

Complexity and implementation of design norms in Cameroon required a proven foreign expertise, but nowadays local engineers are mastering modern construction techniques. They are turning to pile foundations to solve the problem of construction sites on weak soils. The objective of this work is to present the trend of the country pile-driving capacity of some foundations design and construction companies. The proposed analytical method is based on Finite Element Method and on the theory of wave＇s propagation and transmission along the pile taking into account experimental data on the construction site. The proposed method is validated through recorded data during the construction of the Mungo Bridge in Cameroon, and obtained analytical results are in agreement with experimental results.

海上风电桩基础打桩过程中桩周土强度弱化模型试验研究

在海上风电桩基础的打桩过程中,桩周土体强度会产生明显的弱化现象,为明确桩周土体强度弱化影响因素以及弱化规律,开展模型试验模拟打桩过程,研究在不同锤击能量下,不同桩体尺寸情况下,桩身侧摩阻力随着贯入深度的变化规律,建立描述土体强度弱化规律的弱化公式,并通过打桩软件对多个海上风电桩基础工程中大直径及超大直径钢管桩的打桩实测数据进行打桩分析。研究结果表明:在打桩过程中,桩周土体强度的弱化同时受到桩体质量以及锤击能量的影响,桩基质量和锤击能量越大,土体强度弱化程度越高。在打桩的可打入分析中,采用该文所建立的弱化公式可模拟出不同尺寸桩体沉桩时土体强度的折减规律。

层状土中静压桩连续贯入现场试验与数值模拟

为探讨层状土中静压桩连续贯入过程的沉贯特性,依托上海市某桩基工程开展静压桩贯入过程现场试验,探究沉桩阻力随贯入深度的演变规律,并结合ABAQUS数值模拟,明确静压桩贯入过程中沉桩阻力、桩周土体竖向应力、径向应力以及径向位移的变化规律。结果表明:层状土的软硬程度制约着沉桩阻力的大小;当桩端贯入浅部粉质黏土层和淤泥质黏土层时,沉桩阻力增长较慢甚至出现减小趋势,当桩端贯入到深部砂质粉土层、粉质黏土层和粉砂层时,沉桩阻力增长较快,其中在砂质粉土层中增长率最高可达174%;桩周土体中竖向应力和径向应力与土层性质密切相关,竖向应力和径向应力最大值均出现在桩端贯入至黏质粉土层时,分别为558.0、1 178.0 kPa,当桩端贯入到下部较软的淤泥质黏土层时,最大竖向应力和径向应力均出现明显退化现象,径向应力退化率达到52%;径向位移随径向距离的增加而减小,其变化规律基本反映了土层性质的变化特征。

带扩大桩靴桩侧同步灌浆桩成桩过程试验研究

针对新型带扩大桩靴桩侧同步灌浆预制桩基础的施工成桩过程,开展透明土模型的试验研究.相较于传统预制桩,新桩型成桩完成后,端部扩大桩靴结构及桩周固化后的水泥浆液可以明显提升基桩端阻力和侧摩阻力,使得该新桩型具有较高的抗拔能力.通过透明土材料Laponite RD模拟软黏土施工环境,分别针对常规预制桩、带扩大桩靴预制桩及带扩大桩靴桩侧同步灌浆预制桩开展对比模型试验,采用粒子图像测速(PIV)技术进行成桩施工过程的可视化后处理,以探明该新桩型的成桩过程机理,为新桩型的进一步推广应用提供理论支撑.研究结果表明,新桩型施工挤土位移场的分布形式不同于常规预制桩,呈涡旋状,挤土位移的影响范围小于桩靴同直径的预制桩. X、Y方向的位移云图显示,扩大桩靴结构和同步灌浆施工技术使得桩周土体表面及内部施工扰动的影响范围更小,这对于挤土型桩基施工而言是十分有益的.

砂土地基中钻进比对螺旋桩安装性能和抗拔承载性能的影响

螺旋桩在输电线路杆塔和光伏支架等工程基础中获得了推广应用,然而沉桩速率对螺旋桩沉桩效应和承载力特性的影响机制尚不明确。通过开展砂土地基中螺旋桩沉桩与抗拔承载性能模型试验,分析了螺旋桩钻进比与扭矩、下压力之间的关系,建立了考虑承载力-扭矩-下压力相互影响的极限抗拔承载性能相关系数K'_(t)的计算方法。与既有文献试验结果及理论计算方法进行了对比分析,验证了所建立的计算方法的可靠性。研究结果表明:钻进比与螺旋桩的沉桩扭矩和下压力呈线性关系,钻进比对沉桩扭矩的影响幅度大于下压力;降低沉桩过程中钻进比可有效提高螺旋桩的抗拔承载力,钻进比为0.6工况下的抗拔极限承载力可达到钻进比为2工况下的2.9倍;所建立的砂土地基螺旋桩抗拔极限承载力-扭矩-下压力相关系数计算方法,计算误差小于30%,具有较好的准确性和适用性。

海上风电打桩系统动力学建模与冲击动力特性分析

基于LS-DYNA建立3500 kJ海上风电打桩系统拒桩工况下的有限元模型,基于应力波原理分析打桩系统内部能量的传递和各部件的动力学响应。同时基于牛顿碰撞理论建立打桩系统的集中参数模型,该模型综合考虑各部件的质量和刚度,和有限元模型的分析结果较吻合。从而在该集中参数模型的基础上,分别分析替打刚度、替打和锤质量比、替打环刚度对打桩系统冲击力的影响规律,表明冲击力的主要影响参数为替打刚度。

无封装FBG应变传感器在不同布设方式下的标定试验研究

【目的】光纤光栅(FBG)应变传感器作为一种新型测量应变的仪器逐渐运用到土木工程领域中,其能运用的关键在于传感器的布设以及根据不同的使用要求和环境对灵敏度系数进行标定。为了确定表面直接粘贴和开槽植入两种光纤光栅应变传感器布设方法的测量精度。【方法】提出了一种用于沉桩试验的无封装FBG灵敏度系数的标定方法,并通过采用圆形无缝钢管作为基体对两种布设方法进行标定试验研究。【结果】在逐级加载阶段,开圆形凹槽植入粘贴法所得到的标定系数比表面直接粘贴更小,而表面直接粘贴法更接近理论值,开槽植入和表面粘贴法所得到的标定系数与理论值相比最大误差分别为2.84%和0.33%;在逐级卸载阶段,两种布设方法光纤的中心波长存在一定的滞后,但标定系数与加载阶段相差不大。【结论】在FBG使用过程中需要根据试验环境情况以及在试验允许误差范围内选择合理的光纤光栅布设方案及标定方法。

复合断面隧道受侧方沉桩影响的模型试验研究

打桩施工产生的冲击荷载和挤土效应可通过地层传递到隧道结构,需进行控制和监测来保证地铁隧道的正常运营。基于青岛地区的地层工况,采用室内模型试验研究复合断面隧道受旁侧沉桩施工的影响。试验中考虑了单桩、群桩、沉桩深度与桩隧间距等因素,研究沉桩对既有隧道附加弯矩和振动效应的影响。结果表明:随着桩隧间距的增大,隧道的附加弯矩逐渐减小,附加弯矩的分布形态基本呈现出了隧道顶部和底部远离中心点位、左右两端靠近中心点位的趋势。当沉桩深度超过某一定值时,沉桩深度和桩隧间距对隧道振速有明显的影响。模型试验揭示了复合地层中沉桩施工对临近既有隧道的受力变形和动力响应规律,研究成果可为类似工况下隧道监测提供参考。

考虑群桩土体运移的浅海隔水导管变形分析

浅海隔水导管作为海上油气田井筒的最外层结构,在海底硬土层中时常遭遇打桩受阻与管体变形问题,从而阻碍钻头通过,导致井槽浪费。结合渤海A区块海底土质,深入探讨了隔水导管锤入过程中的挤土效应、土塞效应、群桩效应以及往复锤击载荷的影响。通过有限元模拟,揭示了隔水导管群桩布局中土体的运移规律,明确了导管在拒锤后由于应力集中使得局部最大应力超出DH36钢的屈服强度,导致导管端部横向偏移以及缩径变形。基于研究结果,提出了针对性的优化方案,即通过优化隔水导管的壁厚尺寸来有效预防形变的发生。本项研究成果为特殊海底土质区域隔水导管的安全下入提供了有力支持,可为海上油气田的勘探与开发提供保障。

组合沉拔桩施工方法在船坞续改建工程中的应用

在船坞续改建工程中,若能将原坞墙结构中的CAZ组合钢板桩重复利用,则会大幅减少工程成本,带来可观的经济效益。因此,在保障施工质量的前提下,如何将既有坞墙结构的CAZ组合钢板桩拔出、加工、再打入设计标高位置处是船坞续改建施工中的一个重要问题。结合某船坞的续改建工程施工进行深入研究,详细介绍了使用组合沉拔桩施工方法进行既有坞墙组合钢板桩拔出、加工以及再打入土体的施工步骤,并针对提高施工速度和保障施工质量提出了措施建议。

海上风机单桩基础沉桩施工工艺与应用

[目的]海上风力发电因其年均发电量高和发电稳定等优势,逐渐在全球能源结构转型中得到广泛应用。然而,由于海上风机建设在复杂多变的海洋环境中,这给海上风机基础的施工工艺和技术方案带来了巨大的障碍。[方法]文章以某海上风电场的建设项目为背景,具体分析了沉桩施工船舶、稳桩平台和液压打桩锤的选型标准与可行性。同时依据风机基础沉桩的施工要求,重点阐述了作业前的准备工作、稳桩平台的施工方案以及主-副吊船协同配合的风机基础沉桩作业,并进一步分析了风机基础沉桩中垂直度的控制与纠偏措施。[结果]钢管桩沉桩施工工艺可以有效地保障工程质量和进度预期,经济效益明显且安全可靠。在沉桩过程中,需对垂直度精度控制完成初调和终调。[结论]对海上风机基础沉桩施工技术的研究,将为类似的海上风机工程提供有益的参考和借鉴。

基于CFD的浅水条件下工程船水阻力快速预报方法

为准确预报工程船的流阻力,以杭州湾铁路桥施工中的“水欣麒”号打桩船为研究对象,参考同类型船的阻力系数试验值,采用计算流体力学(CFD)方法对考虑锚泊约束的打桩船阻力进行预报。数值计算结果表明:在深水条件下,相比采用悬链线约束船舶得到的船舶阻力,完全限制船舶运动的计算误差不超过1.52%;在浅水条件下,锚泊无法完全限制船舶运动,船舶升沉、横倾和横摇对船舶阻力计算的影响较大,此时不考虑船舶运动得到的阻力相比悬链线约束条件下的阻力计算结果偏小,其误差最大达到26.6%;完全放开船舶的升沉和横摇自由度之后,计算得到的船舶横倾和横摇值比锚泊约束下的结果更大导致船舶兴波更剧烈,兴波阻力变大导致计算得到的总阻力偏大;考虑到不同锚泊方案对船舶运动的限制程度不同,从安全性的角度考虑,进行较为保守的阻力修正是有必要的。

南城商贸金融大厦项目基础设计

南城商贸金融大厦地上44层,结构高度为197.3 m;地下4层,基础埋深约19 m。结合项目的地质情况及特点,对基础型式进行多方案比较设计,塔楼投影范围采用钻孔灌注桩基础,持力层为中风化或微风化岩层;纯地下室范围采用天然地基筏板基础,持力层为粉质黏土或全风化土层,采用抗浮锚杆进行抗浮。为了满足工程进度要求,本项目先施工基坑支护和开挖基坑,工程桩在坑底施工。其基坑支护型式为内支撑,在内支撑下面的桩只能在6 m净高的空间内施工。因此,灌注桩优先选用人工挖孔桩较为合理。由于基坑临近地铁轨道线,二者外墙之间最近仅间隔14.5 m,加之基坑开挖深度较深,在基坑开挖的过程中,随着开挖深度的加深,周边地下水位的变化对地铁工程的变形有较大影响。为减小项目基坑开挖和基础施工对地铁工程变形的影响,桩基础改用钻孔灌注桩。常规旋挖机不具备在内支撑下的6 m操作空间内施工,为此对旋挖机进行改装,采用超低空旋挖钻孔机器进行桩基施工,这也是本项目基础设计的重要影响因素。