Numerical modelling for predicting corrosion initiation life of reinforced concrete square piles under reverse-seepage pressure

Square piles of reinforced concrete(RC)in marine environments are susceptible to chloride-inducedcorrosion.A novel reverse-seepage technique(RST)is applied to square piles to block the intrusion of chlorides.Thisresearch introduces a computational model designed to predict the lifespan of corrosion initiation in reinforced concretesquare piles when applied reverse-seepage pressure.The model considers the impacts of chloride binding and the tripletime-dependence property among the permeability,the corrected surface chloride concentration,and the diffusioncoefficient.The proposed numerical model is solved using the alternating direction implicit(ADI)approach,and itsaccuracy and reliability are evaluated by contrasting the computational outcomes with the analytical solution andexperimental results.Furthermore,the primary factors contributing to the corrosion of reinforced concrete square pilesare analyzed.The results indicate that applying RST can decrease the chloride penetration depth and prolong the lifespanof corrosion initiation in square piles.The water-cement ratio and reverse seepage pressure are the most influentialfactors.A water pressure of 0.4 MPa can double the life of concrete,and the durable life of concrete with a water-cementratio of 0.3 can reach 100 years.

Centrifuge model tests on pile-reinforced slopes subjected to drawdown

Piles are generally an effective way to reduce the risk of slope failure.However,previous approaches for slope stability analysis did not consider the effect of the piles coupled with the decrease of the water level(drawdown).In this study,a series of centrifuge model tests was performed to understand the deformation and failure characteristics of slopes reinforced with various pile layouts.In the centrifuge model tests,the pile-reinforced slopes exhibited two typical failure modes under drawdown conditions:across-pile failure and through-pile failure.In the through-pile slope failure,a discontinuous slip surface was observed,implying that the assumption of the slip surface in previous stability analysis methods was unreasonable.The test results showed that drawdown led to instability of the piles in cohesive soil,as the saturated cohesive soil failed to provide sufficient constraint for piles.The slope exhibited progressive failure,from top to bottom,during drawdown.The deformation of the piles was reduced by increasing the embedment depth and row number of piles.In addition,the deformation of soils outside the piles was influenced by the piles and showed a similar distribution shape as the piles,and the similarity degree weakened as the distance from the piles increased.This study also found that the failure mechanism of unreinforced and pile-reinforced slopes induced by drawdown could be described by coupling between the deformation localization and local failure,and it revealed that pile-reinforced slopes could reduce slope deformation localization during drawdown.

Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

Study on Interface mechanical behavior of steel tube reinforced concrete composite pile

Currently for the steel tube reinforced concrete composite pile research, although predecessors make a comprehensive research on the composite pile beating performance, design technology, but there are still many problems have not been solved, such as the steel tube reinforced concrete pile composite interracial force learn performance research is still in the initial stage. In this paper, we mainly discuss the research methods of several interface mechanical properties and propose the possibility of studying the mechanical properties of the steel tube reinforced concrete composite pile by using the principle of ultrasonic speckle.

Flexure-Compression Testing of Bridge Timber Piles Retrofitted with Fiber Reinforced Polymers

The adequacy of using Fiber Reinforced Polymer (FRP) retrofit technique to restore the flexure-compression behavior of deteriorated bridge timber piles is examined experimentally in this paper. Sixteen specimens are tested monotonically under eccentric compressive loading. The specimens are first tested in their unretrofitted condition to determine their elastic properties. Each specimen is then cut and connected (posted) using the proposed FRP retrofit technique, and retested. The results show that the retrofitted specimens are capable of reaching same or higher strengths than that of the unretrofitted specimens with minimal reduction in their stiffness. Based on the experimental results, a design equation is presented to compute the volumetric ratio of FRP needed for retrofitting bridge timber piles under eccentric load.

Quantitative analysis of magnetic anomaly of reinforcements in bored in-situ concrete piles

We quantitatively study magnetic anomalies of reinforcement rods in bored insitu concrete piles for the first time and summarized their magnetic anomaly character. Key factors such as measuring borehole orientation, borehole-reinforcement distance, and multiple-section reinforcement rods are discussed which contributes valid and quantitative reference for using the magnetic method to detect reinforcement rods. Through tests with model piles, we confirm the accuracy of theoretical computations and then utilize the law discovered in theoretical computations to explain the characteristics of the actual testing curves. The results show that the Za curves of the reinforcement rod reflect important factors regarding the reinforcement rods, such as rod length, change of reinforcement ratio, length of overlap, and etc. This research perfects the magnetic method for detecting reinforcement rods in bored in-situ concrete piles and the method has great importance for preventing building contractor fraud.

High-Rise Residential Reinforced Concrete Building Optimisation

In the last few decades structure optimisation has become a main task in a civil engineering project. As a matter of fact, due to the complexity and particularity of every structure, the great amount of variables and design criteria to considerate and many other factors, a general optimisation’s method is not simple to formulate. As a result, this paper focuses on how to provide a successful optimisation method for a particular building type, high-rise reinforced concrete buildings. The optimization method is based on decomposition of the main structure into substructures: floor system, vertical load resisting system, lateral load resisting system and foundation system;then each of the subsystems using the design criteria established at the building codes is improved. Due to the effect of the superstructure optimisation on the foundation system, vertical and lateral load resisting system is the last to be considered after the improvement of floor. Finally, as a case example, using the method explained in the paper, a 30-story-high high-rise residential building complex is analysed and optimised, achieving good results in terms of structural behaviour and diminishing the overall cost of the structure.

预应力混凝土管桩桩端侧后注浆理论及承载特性研究进展综述

意义管桩后注浆可有效改善桩-土接触界面物理力学性质,在提高管桩摩阻力、减少上部结构沉降等方面发挥着重要作用。进展通过对管桩后注浆工艺、后注浆理论、管桩注浆后的承载性能、管桩-注浆体-土接触界面剪切性能等进行综述,展望了管桩后注浆的发展方向。结果表明:(1)后注浆对提高中小直径管桩承载力有一定作用;注浆后,中掘法管桩的承载力一般超过了4 000 kN、静钻根植竹节桩的承载力可提升20%以上、随钻跟管桩承载力普遍超过20 000 kN。(2)现有的注浆理论推动了注浆技术的发展,虽然相关研究成果与工程实践存在差异,但可以给出浆液扩散的初步轮廓和扩散范围,为注浆设计和工程应用提供科学指导。(3)桩-浆-土接触界面的研究大多以剪切试验为载体,研究浆-土接触界面剪切性能这一宏观表象,很少涉及注浆液以注浆根系、爪牙和毛细爪牙的形式伸入土体并与土体进行关键离子交换从而提高桩-浆-土接触界面黏结强度的宏微观扩散本质。(4)现有注浆研究大多止步于注浆结果分析,较少涉及注浆机理,对浆液在地层中的流动扩散规律认识不够清晰。结论与展望桩侧注浆液渐进性流动过程可视化分析、注浆体三维尺寸定量表征、管桩注浆过程智能化监测、新型管桩桩侧注浆工艺研发是未来管桩桩侧后注浆发展的重要方向。

非平衡建筑超载下软弱地层地铁深基坑变形特性及加固方案研究

软弱地层中某地铁深基坑外侧作用有建筑物偏压超载,对深基坑开挖存在较为不利影响。为研究外部建筑物偏压超载对软弱地层中基坑支护结构的变形影响,确定合理的隔离桩及基底加固方案,采用有限元方法进行了不同加固方案下基坑开挖模拟计算,并与实测结果对比分析。结果表明:临近深基坑的外部建筑物超载将对基坑支护结构产生明显的偏压效应,偏压超载对坑底软弱地层范围内支护结构影响最为明显;基坑外侧设置隔离桩加固,可有效减小地下连续墙水平位移,隔离桩变形在软弱地层范围最大,增加桩长可使桩底产生支点约束效应,但不能有效减小支护结构位移及支撑轴力;同样,改变隔离桩刚度对支护结构位移及支撑轴力影响较小;仅采用基底加固方案,可减小坑底范围内支护结构位移,但对上部支护结构变形影响较小,采用隔离桩+基底加固组合方案可有效减小支护结构变形及支撑轴力,降低了偏压荷载对基坑的不利影响,具有较好的加固效果。

JC/T 934-2023《预制钢筋混凝土方桩》标准解读

为便于JC/T 934—2023《预制钢筋混凝土方桩》的使用方准确理解标准条款的具体含义,正确贯彻实施标准条款的具体要求和规定,简述了该标准的编制背景、编制目的和意义,解释说明了标准条文的具体内容,并指出了标准实施过程中应注意的事项。

盾构隧道近距离穿越高速桥桩保护方案研究

深圳地铁某共建管廊盾构隧道近距离侧穿高速公路桥桩工程,施工扰动容易造成桥桩基础变形,严重时桥梁结构受损,影响车辆通行使用。通过对方案进行设计、数值模拟、现场应用及监测分析等手段,研究采用合理的预加固技术,并设置盾构掘进参数,使得桥桩基础变形能满足设计要求,盾构施工顺利安全穿越。研究表明:(1)数值模拟分析表明采用隔离桩及注浆加固能有效降低盾构施工对桥桩的扰动;(2)设置试验段进行盾构参数优化有利于控制周边土体变形;(3)监测结果表明预加固方案和合理的盾构掘进参数能有效控制桥桩基础变形,满足桥梁结构变形控制要求。

悬臂式抗滑桩桩身位移及内力变化影响因素分析

针对抗滑桩桩身结构与桩周岩土体之间的应力传递及桩体受力影响因素不明确问题,以某碎石土堆积体边坡为研究对象,基于土拱效应相关理论,采用颗粒料数值模拟软件揭示抗滑桩设计参数对桩体受力变形的影响,得出以下结论:(1)不同抗滑桩截面尺寸下,桩身水平位移随深度的变化规律基本一致。即在桩顶处取得最大位移值,随着桩深增大,位移值逐渐减小,桩顶以下12m时桩体位移趋于0。(2)不同抗滑桩截面尺寸下,弯矩均呈凸型分布,弯矩极值点出现在滑面以下1m位置。

软土地质坑中坑钢板桩免支撑加固技术研究

通过对施工方案、图纸设计及材料选型进行反复论证优化,对比放坡土钉墙基坑支护形式、钢板桩+钢支撑基坑支护形式与钢板桩+钢丝绳基坑支护形式三者优缺点,得出最适合流塑性淤泥质土基础底板工程的施工工艺并形成指导方案。最终项目采用钢丝绳加钢板桩的坑中坑支护形式,该技术通过解放坑中坑中部施工空间的方式,较大提高了施工效率,总结包括在淤泥质土质背景下钢板桩免支撑支护形式的安装等具有指导性的施工技术,旨在更好地促进建筑项目工程技术的发展。

码头防护堤坝搅拌桩防渗加固设计探究

采用搅拌桩对码头防护堤坝进行加固,可以有效提升码头防护堤坝与码头运营与建设的安全性和稳定性。依据堤坝不同部位的特点,进行防渗加固设计,设定合理的参数。在施工时,严格依照要求与工艺进行操作,恰当选择搅拌设备的功率,精确控制下钻和提钻的技术,科学、合理地确定安全监测的范围、频次和预警值。研究成果可以为码头防护堤坝工程提供科学、有效的解决方案,从而保障工程的安全建设。

碎石桩加固软土路基沉降特性分析

通过工程实例,采用有限元分析软件建立碎石桩加固软土路基数值模型,分析桩身模量、桩身直径、桩身长度和桩间距等不同碎石桩参数下软土路基沉降变化规律,并通过监测碎石桩加固前后路基竖向沉降、水平位移、竖向应力值等重要指标变化情况,评价碎石桩加固软土路基的改善效果,揭示碎石桩加固软土路基的改良机制。研究结果表明,采用碎石桩加固软土路基后,路基竖向沉降值、水平位移值均有效降低,路基竖向应力值为加固前的3.05倍,碎石桩能够起到很好的加固作用;增大碎石桩桩身模量、桩身直径、桩身长度和减小桩间距能有效改善软土路基沉降;在距离路基中心10 m范围内采用碎石桩加固效果更为显著。

桩筏互补加固技术在软土地区厂房中的应用

软土地区厂房基础多采用预制桩、灌注桩,由于上部软弱土及施工质量存在缺陷,通常会造成厂区地坪凹陷、开裂等质量问题。通过对某大型厂房项目的不均匀沉降、底板脱空原因研究分析,采用桩筏互补加固技术,大幅度提高了深厚软土区地基承载力,有效减小沉降,同时解决了加固施工过程中涉及的厂区设备多作业空间小,施工不影响厂区正常生产等技术难题,该技术对于深厚软土区、狭小空间加固具有一定的参考意义。

多向加芯搅拌桩技术在软土地基处理中的应用

基于珠海市鹤洲至高栏港高速公路一期软基处理工程,介绍多向加芯搅拌桩技术的基本原理、施工工艺和应用效果。通过设计参数优化、施工工艺改进和质量控制,多向加芯搅拌桩技术能够有效提高软土地基承载力,减少工后沉降,提高施工效率,具备经济实用性,有良好的应用前景,并对多向加芯搅拌桩技术提出进一步优化和推广建议。

富水复合地层盾构下穿CFG群桩开仓换刀技术

根据不同的地层条件选择不同的刀具是保证盾构高效、顺利掘进的关键。郑州地铁5号线农—心区间,针对富水复合地层并下穿CFG群桩工况,设计了不同的盾构刀具配置方案,提出换刀区混凝土桩加固联合降水的常压换刀方案。对比了换刀前后各部分刀具的磨损值及磨损状态,说明刀具更换的科学性及必要性。本工程所提出的辅助作业方案有效保证地表变形在预警值范围内、掌子面稳定,常压换刀顺利实施。

高压旋喷桩技术应用于坑底加固的实效研究

为有效应对深基坑工程中出现的沉降挑战,以玉环万达广场的大型商业综合体建筑为例,采用高压旋喷法技术进行坑底加固处理。首先通过坑底加固设计计算确定桩长为3.5m、桩径0.55m、桩间距为1.124 m,加固区域总共布置64根。然后从钻机就位、钻孔施工、灰浆制备及旋转喷浆对高压旋喷桩施工工艺流程进行全面的分析。最后对该建筑项目的沉降进行了监测,对比两个季度的数据得出高压旋喷桩在深基坑工程中的加固效果显著。这一系统性的监测与分析流程,旨在全面评估高压旋喷法的实施效果,为类似工程提供宝贵的经验参考。

抗滑桩结合复合地基在软土路基滑坡整治中的应用

结合西南地区某高速公路斜坡软基高填工点滑塌整治设计实例,提出反压护道结合复合地基、抗滑桩结合复合地基两种方案,从施工、造价、社会影响角度进行对比分析,确定选用抗滑桩结合复合地基方案,并通过三维数值模拟方法对该方案进行评估。采用该方案对路基整治处理后,其沉降变形控制效果显著。