Experimental study and numerical analysis on bearing behaviors of super-long rock-socketed bored pile groups

A centrifuge modeling test and a three-dimensional finite element analysis（FEA）of super-long rock-socketed bored pile groups of the Tianxingzhou Bridge are proposed.Based on the similarity theory,different prototypical materials are simulated using different indicators in the centrifuge model.The silver sand,the shaft and the pile cap are simulated according to the natural density,the compressive stiffness and the bending stiffness,respectively.The finite element method（FEM）is implemented and analyzed in ANSYS,in which the stress field during the undisturbed soil stage,the boring stage,the concrete-casting stage and the curing stage are discussed in detail.Comparisons in terms of load-settlement,shaft axial force distribution and lateral friction between the numerical results and the test data are carried out to investigate the bearing behaviors of super-long rock-socketed bored pile groups under loading and unloading conditions.Results show that there is a good agreement between the centrifuge modeling tests and the FEM.In addition,the load distribution at the pile top is complicated,which is related to the stiffness of the cap,the corresponding assumptions and the analysis method.The shaft axial force first increases slightly with depth then decreases sharply,and the rate of decrease in rock is greater than that in sand and soil.

Effect of sediment on vertical dynamic impedance of rock-socketed pile with large diameter

Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedance function transfer method. Firstly, the sediment under rock-socketed pile was assumed to be fictitious soil pile with the same sectional area. The Rayleigh-Love rode model was used to simulate the rock-socketed pile and the fictitious soil pile with the consideration of the lateral inertial effect of large-diameter pile. The layered surrounding soils and bedrock were modeled by the plane strain model. Then, by virtue of the initial conditions and boundary conditions of the soil pile system, the analytical solution of the vertical dynamic impedance at the head of rock-socketed pile was derived for the arbitrary excitation acting on the pile head. Lastly, based on the presented analytical solution, the effect of sediment properties, bedrock property and lateral inertial effect on the vertical dynamic impedance at rock-socketed pile head were investigated in detail. It is shown that the sediment properties have significant effect on the vertical dynamic impedance at the rock-socketed pile head. The ability of soil-pile system to resist dynamic vertical deformation is weakened with the increase of sediment thickness, but amplified with the increase of shear wave velocity of sediment. The ability of soil pile system to resist dynamic vertical deformation is amplified with the bedrock property improving, but the ability of soil-pile system to resist vertical vibration is weakened with the improvement of bedrock property.

Ultimate end bearing capacity of rock-socketed pile based on generalized nonlinear unified strength criterion

In order to study the mechanism of bearing behavior at the tip of a pile embedded in rock, the generalized nonlinear unified strength criterion and slip line principle for resolving the differential equation systems which govern the stress field were applied to derive the ultimate end beating capacity based on some reasonable hypothesis and failure plane model. Both numerical simulation and test results were compared with the theoretic solution. The results show good consistency with each other and verify the validity of the present approach. The depth effect with respective to embedment ratio and other influence factors like geological strength index, intermediate principal stress, overburden factor, and damage on end bearing capacity were discussed in the analytical solution. The results show that the proposed yield criterion can be much better for investigating the ultimate end bearing performance of rock-socketed pile. The end bearing capacity increases with embedment ratio and the increasing degree is influenced intensely by the above parameters. Furthermore, ignoring intermediate stress effect would underestimate the strength properties of the rock material and lead to a very conservative estimation value.

Buckling analysis of super-long rock-socketed filling piles in soft soil area by element free Galerkin method

In order to discuss the buckling stability of super-long rock-socketed filling piles widely used in bridge engineering in soft soil area such as Dongting Lake, the second stability type was adopted instead of traditional first type, and a newly invented numerical analysis method, i.e. the element-free Galerkin method (EFGM), was introduced to consider the non-concordant deformation and nonlinearity of the pile-soil interface. Then, based on the nonlinear elastic-ideal plastic pile-soil interface model, a nonlinear iterative algorithm was given to analyze the pile-soil interaction, and a program for buckling analysis of piles by the EFGM (PBAP-EFGM) and arc length method was worked out as well. The application results in an engineering example show that, the shape of pile top load-settlement curve obtained by the program agrees well with the measured one, of which the difference may be caused mainly by those uncertain factors such as possible initial defects of pile shaft and the eccentric loading during the test process. However, the calculated critical load is very close with the measured ultimate load of the test pile, and the corresponding relative error is only 5.6%, far better than the calculated values by linear and nonlinear incremental buckling analysis (with a greater relative error of 37.0% and 15.4% respectively), which also verifies the rationality and feasibility of the present method.

自升式钻井平台插拔桩技术发展现状及趋势

针对自升式钻井平台在插桩和拔桩过程中面临的土工问题,系统地梳理插桩和拔桩涉及的关键技术。分析插桩过程中的土工试验技术、土体破坏机理、上硬下软地层承载力和桩脚滑移问题;阐述拔桩过程中的拔桩阻力计算方法和减小拔桩阻力方法的研究进展情况。在此基础上,根据目前面临的新挑战,提出今后自升式钻井平台插拔桩技术研究的重点,并预测其发展趋势。

预制装配墩柱-桩基础承插节点冲切性能研究

承插连接由于具有整体性能好、施工工序简单和拼装容许误差大等优点,成为预制装配桥墩节点的有效连接方式之一。为探明桩基础承插节点的冲切失效模式及承载力计算方法,采用ABAQUS有限元软件建立预制装配墩柱-桩基础承插节点数值计算模型,通过UHPC-NC直剪试验和墩柱-桩基础轴压试验进行了数值模型校验,研究了底板、接缝和承插连接参数对预制装配墩柱-桩基础承插节点的冲切传力机制、承载能力和失效模式的影响规律,提出了预制装配墩柱-桩基础承插节点冲切承载力计算公式。数值模拟结果表明,预制装配墩柱-桩基础承插节点的传力路径沿墩柱底部到桩的顶部;峰值荷载过后,承台底部混凝土开裂失效;接缝承载力和UHPC与混凝土之间的接触面积呈正相关,承台的冲切承载力与底板高度呈正相关。此外,当承插深度与底板高度之比由0.60增大到2.08时,接缝承载力提升了80.2%,而承插连接以及底板承载力分别降低了27.7%、52.9%,承插连接参数与底板参数具有相同的变化趋势,且底板承载力对承插连接承载力的占比较大,说明底板对承插节点承载力的贡献起主导作用。通过对已有试验和数值模拟分析,将底板和接缝的贡献系数分别取为1.00和0.92,为类似预制装配墩柱-桩基础承插节点冲切承载力的计算提供了依据。

褶皱逆深地带机械冲孔桩施工技术

在传统桥梁工程桩基础施工中,大直径深孔桩常采用机械成孔桩法。云南红河州逆深大断裂地带为褶皱与断层交织地质,该地质形成年代晚,地质结构复杂、地理环境高差达440m。在以上条件限制下,常规深孔桩冲孔施工方法难以实现。以元江至蔓耗高速公路土建项目桩基工程为背景,总结褶皱逆深地段25~40m深孔机械成孔桩施工技术,主要从技术特点、工艺原理、施工工艺流程及操作要点、材料设备及质量控制等方面进行详述。

桩基选型及冲孔灌注桩施工控制

针对冲孔灌注桩施工过程中的桩基选型、控制措施以及施工完成后的桩身质量检测问题,分析了不同地质的桩基选型以及冲孔桩的施工控制措施,并从声测管的埋设数量以及声测管的安装两方面优化超声波透射法检测过程,以实时检测桩基的状态变化。

边坡加固的冲孔灌注桩基质量多法融合检测技术研究

地灾区域的边坡塌陷问题会直接影响该地区的长期安全性和稳定性,对该地区的灾后重建工作形成较大负面影响。针对地灾区域边坡塌陷加固作业工程中质量检测方面存在的问题,研究以某地灾区域边坡塌陷加固作业工作为例,对该类型工程中开展冲孔灌注桩施工的桩基质量进行检测分析。结果表明,相比于单一的检测方法,将采用低应变法、超声波透射法和钻芯法等相互结合的检测方法可以更为精准地发现桩基结构完整性描述,超声波-低应变联合法具有检测效率适中、破坏性小、检测精度理想等优势。

单桩水平静载试验在万州体育中心工程中的应用

对万州体育中心工程的3根机械冲孔灌注桩进行单桩水平静载试验,在桩身强度和水平位移两种控制工况下,确定其单桩水平承载力特征值、水平极限承载力,并推定地基土抗力系数的比例系数m值。试验结果验证了特殊地质条件下的桩基施工工艺,给出了桩基水平承载力与位移的计算参数,并为类似桩基工程的设计与施工提供了基础试验数据。

提高岩溶桥梁桩基质量的应用研究

广西区域喀斯特地貌的特殊地质,其中溶洞、地下河、暗湖、石钟乳、石笋对于桥梁桩基的影响尤为严重,溶洞良好的处理及桩基的完整性是整个线性工程中桥梁质量把控中关键的一环;桥梁桩基的质量决定了桥梁整体的稳定性及安全性。利用合理的施工工艺及溶洞处理方式方法来提高岩溶桥梁桩基的成桩质量合格率及施工效率,同时达到降本增效的目的。

复杂地质条件下钢板桩引孔施工技术研究与应用

本文以某项目工程为例,通过了解该项目地质特性,确定施工方案,重点从旋挖引孔、引孔灌砂、插打钢板桩、承台施工及钢板桩拆除等具体施工技术进行论述,最后对钢板桩围堰稳定性进行验算及监测,结果显示各杆件稳定性均符合要求,基坑水平位移监测数据达标,验证了该工艺的可行性。

公路桥梁冲孔灌注桩施工技术与质量控制措施研究

冲孔灌注桩具有操作简便、适用性强、经济性好、单桩承载力大等优势,在公路桥梁建设中被广泛应用。为研究冲孔灌注桩成桩工艺与技术特征,文章以巴中市巴州区新建Z桥为工程背景,基于理论知识应用和实践经验总结,分析冲孔灌注桩施工要点,提出了质量控制措施,成桩后经质量检测,Ⅰ类桩占比为94.4%,Ⅱ类桩占比为5.6%,无Ⅲ类桩和Ⅳ类桩,施工效果达到工程预期。

防洪工程冲孔灌注桩常见施工问题分析

为了探究防洪工程冲孔灌注桩施工问题及处理措施,以福建省三明市沙溪流域防洪工程为例进行分析,并对该工程部分冲孔灌注桩进行超声波透射检测。结果显示,HH0+518.39号桩和HH0+619.29号桩的声速分别为5.2和5.5km/s,波幅分别为1 200和1 180pV,且二者的功率谱密度均未发生变化,表明HH0+518.39号桩和HH0+619.29号桩均不存在缺陷,为Ⅰ类桩。而其他桩的声速、波幅及功率谱密度均在相应位置发生突变,表明其他桩均存在一定缺陷。

喀斯特地区冲孔灌注桩施工特点及质量控制要点

冲孔灌注桩是一种常用的基坑支护和地基处理技术,被广泛应用于建筑、桥梁、隧道、码头等各类土木工程。冲孔灌注桩通过冲入基槽内的橡胶管道灌注钢筋混凝土,形成一个坚固的桩身,起到支撑和加固土体的作用。冲孔灌注桩作为一种有效的地基处理和基坑支护技术,施工过程需要严格按照设计要求和施工规范进行,以确保桩身的质量和整体工程的安全性。文章结合实际案例,主要探讨了喀斯特地区冲孔灌注桩施工特点及质量控制要点,旨在为同类工程项目的开展提供参考和借鉴。

高速公路软基路堤改扩建若干问题与建议

基于大量高速公路改扩建工程实践,对软基路堤改扩建的若干问题给出建议。水塘路段不能在塘底进行地基处理施工时宜采用搅拌桩,采用刚性桩时宜按桩承堤设计。既有边坡下软基处理工作面宜采用削陡边坡或钢板桩支护等方式形成。拼宽路堤沿其与既有路堤的界面滑动稳定性满足要求时,可不设置台阶。普通土拼宽路堤台阶壁宜倾斜、平台宜水平或轻微外倾。竖壁台阶高度大于44cm时会在台阶壁附近形成虚土区,需利用液压夯实或冲击碾压等对虚土进行压实,台阶高度大于2m时可利用注浆将虚土胶结。轻质土拼宽路堤不应用作挡土墙,应设置易于施工的排水设施,以避免轻质土拼宽路堤后面积水。轻质土拼宽路堤滑动稳定分析时,应只考虑斜坡范围内的交通荷载。除长螺旋桩机施工的钻孔桩外,其他桩帽之间不必设置连梁。

Experimental study on load bearing behavior of large-scaled caps with pile groups

The objective of this investigation was to study the behavior of deep pile caps and the ultimate load-carrying capacity. Four 1/10 scaled models of nine-pile caps were cast and tested on vertical loads to failure. The destruction shapes of pile caps,the correlation between load and displacement,and the internal stresses were analyzed systematically. The results demonstrated that the failures of all the four models are resulted from punching shear; the internal flow of the forces in nine-pile caps can be approximated by "strut-and-tie" model. Furthermore,the failure loads of these specimens were predicted by some of the present design methods and the calculated results were compared with the experimental loads. The comparative results also indicated that the "strut-and-tie" model is a more reasonable design method for deep pile caps design.

埕岛油田反复插拔桩区域就位风险及预防措施

胜利埕岛油田位于现代黄河水下三角洲,海底地层复杂,沉积物粉土、粉质黏土互层变化大.近年来,动平台作业在同一井口或相近井口反复插拔桩作业次数越来越多.海上动平台反复插拔桩区域存在滑桩、穿刺、液化下沉风险,在该类型区域插桩存在较大隐患.针对该风险进行预防措施分析,降低动平台插桩风险.

冲孔灌注桩技术在建筑工程施工中的应用分析

冲孔灌注桩技术依托自身所具有的灵活性强、负面影响小和单桩承载力大等优势,得以在建筑工程施工实践中广泛应用。在冲孔灌注桩技术应用阶段,受到多重因素影响,容易诱发一系列问题,影响建筑工程施工效果。基于此,该文对冲孔灌注桩技术于建筑工程施工中的应用予以研究,在简单介绍冲孔灌注桩技术内涵、优势和应用流程基础上,引进具体的工程案例,结合案例探讨冲孔灌注桩技术应用,并针对性构建质量控制措施,期望以此提升冲孔灌注桩技术应用水平,从整体上强化建筑工程施工质量,在一定程度上也可为后续阶段建筑工程施工中冲孔灌注桩技术的应用提供参考。

冲孔灌注桩施工常见问题分析及解决对策

冲孔灌注桩是建筑工程中普遍应用的一种桩基施工工艺,具有施工操作方便灵活、场地环境适应性强、承载力大、桩端穿透力强等优点。文中结合实际工程案例分析了冲孔灌注桩施工工艺,提出施工存在的常见问题及解决办法,仅供参考。