Testing Analysis of Composite Ground with Grouting Piles and Deep Mixing Piles

This paper discusses a new technique to improve soft ground with grouting piles and deep mixing piles. The bearing capacity of composite ground and the stress ratio between piles and soil is discussed by means of the static test. Based on Mindlin solution and Boussinesq solution, the additional stress and settlement of the composite ground are acquired.Compared the practical value with calculation, a better calculating method is confirmed.

Probabilistic limit state design methodof the axial resistance of post grouting pile

The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.

Mechanical Behaviors and Deformation Properties of Retaining Wall Formed by Grouting Mould-Bag Pile

The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.

Numerical Analysis of the Settlement of Composite Foundation Reinforced with Crushed Stone Grouting Pile and Rigid Bearing Plate

This paper deals with a new type of crushed stone grouting pile with a rigid bearing plate. The load transfer characteristics were analyzed, and a settlement model of the composite foundation reinforced with crushed stone grouting pile and rigid bearing plate was built by FEM program. The effects of replacement ratio of capping plate, replacement ratio of pile, replacement ratio of grout diffusion zone, pile-soil modulus ratio, and serous-soil modulus ratio, on the composite foundation settlement were discussed. It is concluded that the proposed crushed stone grouting pile with a rigid bearing plate is effective in decreasing the settlement of composite foundation.

Calculation method of composite foundation sedimentation of grouting pile with cover plate under embankment load

Grouting pile is a new soft soil foundation treatment method with characteristics such as no vibration, no noise, no soil compaction, light construction machines and quick construction velocity and so on. At present, study on reinforcement mechanism and design calculation method of composite foundation of grouting pile is initially started without design specifications, so it is usually required to draw on design specifications of stump pile when designing composite foundation of grouting pile while grouting pile has its characteristics and difference although reinforcement mechanisms and construction processes of two types of piles are similar. Sedimentation formula of composite foundation of grouting pile with cover plate is educed and a suitable deformation mode is proposed by aiming to deformation characteristics of composite foundation of grouting pile with cover plate under embankment load on basis of relevant sedimentation theories of composite foundation by combination of characteristics of composite foundation of grouting pile. The sedimentation calculation formula of grouting pile with cover plate under embankment load is educed according to balance relation of force and displacement coordination conditions by elastic theory and sedimentation calculation model established is validated by sedimentation monitoring documents of one expressway in China.

Pressured Grouting Method (PGM) in Pile Engineering

Application of pressured grouting method (PGM) in pile engineering can tackle problems encountered during construction of bored piles. Bearing capacity of piles can be increased through compaction of subsoils around piles. This paper reports research efforts of this technique by the pile research team in Southwest Jiaotong University in last decade with respect to the construction process, test findings, and primary research conclusions. The social-economical benefits of this method and application market in pile engineering are also analyzed.

The Effect of Jet Grouting on Enhancing the Lateral Behavior of Piled Raft Foundation in Soft Clay(Numerical Investigation)

Soft clay soils cannot usually support large lateral loads,so clay soils must be improved to increase lateral resistance.The jet grouting method is one of the methods used to improve weak soils.In this paper,a series of 3D finite element studies were conducted using Plaxis 3D software to investigate the lateral behavior of piled rafts in improved soft clay utilizing the jet grouting method.Parametric models were analyzed to explore the influence of the width,depth,and location of the grouted clay on the lateral resistance.Additionally,the effect of vertical loads on the lateral behavior of piled rafts in grouted clay was also investigated.The numerical results indicate that the lateral resistance increases by increasing the dimensions of the jet grouting beneath and around the piled raft.Typical increases in lateral resistance are 11.2%,65%,177%,and 35%for applying jet grouting beside the raft,below the raft,below and around the raft,and grouted strips parallel to lateral loads,respectively.It was also found that increasing the depth of grouted clay enhances lateral resistance up to a certain depth,about 6 to 10 times the pile diameter(6 to 10D).In contrast,the improvement ratio is limited beyond 10D.Furthermore,the results demonstrate that the presence of vertical loads has a significant impact on sideward resistance.

Grouted Pile and Its Bearing Capacity

The grouting method applied in bored pile is an improvement to the conventional bored pile. Load tests have proved that grouting under the bored pile tip is an effective method to enhance the bearing capacity of the pile and to reduce the pile settlement. In this paper, the grouting technology is described and pile load test results are discussed. In order to put the grouting method into design practice, the authors analyze the working mechanism of soil compaction. And, based on the theory of cavities expansion in soil mass, approximate formulae are proposed for estimating the bearing capacity of the grouted pile. The theoretical prediction agrees well with the load test results.

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。

复杂地层超长桩后压浆施工工法探究与实践

在复杂地质环境下,超长桩施工难度大、造价高,基桩的单桩承载力特征值无法满足设计要求。后压浆灌注技术可以通过在施工灌注桩时预先安装注浆管,极大提高桩端承载力及桩与土之间的摩阻力。以广东省深圳市南山某一项目为例,探讨了在复杂地质条件下抗拔桩的后压浆施工工艺,桩基承载能力得到大幅提升,在有限桩长下满足了设计要求。

不同灌浆效果下黏土海床导管架桩基础的竖向承载特性离心试验

在40~60 m水深海域,海上风力发电机多使用导管架基础作为主要支撑结构.导管架通过水下高强灌浆与桩基础顶部连接,形成顶端密封段,共同承载竖向荷载.针对桩基顶部灌浆正常、灌浆不足、灌浆不良存在通孔3种不同灌浆效果开展离心模型试验,分析极限状态下基础的竖向承载力及灌浆段与桩身段的承载力分担比,并与现有理论计算方法进行对比.结果表明,灌浆密封顶盖的承载力取决于密封效果.对于灌浆密封顶盖灌浆正常和灌浆不足的基础,灌浆密封顶盖的承载力约占基础总承载力的25%~30%;灌浆不良存在通孔时,基础灌浆段承载力发挥较早且很快达到极限,其分担比远低于其他两者承载力.试验结果可为导管架桩基础设计中的灌浆段承载力计算提供参考依据.

灌注桩后注浆施工技术在建设工程施工中的应用

传统钻孔灌注桩容易出现泥皮、沉渣等问题,影响灌注桩的成桩质量。为提升钻孔灌注桩的承载力与整体质量,灌注桩后注浆施工技术得到了广泛应用。文章首先阐述了灌注桩后注浆施工技术的原理;然后分析了灌注桩后注浆技术的参数设定方法;最后选取某建设工程为研究对象,研究了灌注桩后注浆施工的工艺流程及施工要点,同时提出了施工质量控制措施,为后续类似工程建设提供了借鉴。

旁压试验在软岩地区单桩承载力估算中的应用

目前软岩地区桩基承载力估算多数依赖于勘察单位的工程经验,存在较大不确定性。限于国产旁压设备试验压力较低,现行《地基旁压试验技术标准》(JGJT 69-2019)未给出基于旁压试验成果估算岩石地区桩基承载力的经验公式。本文依托某工程实例,采用适用于软岩的进口旁压试验设备,并结合国内外研究成果,总结提出通过Menard旁压试验成果估算软岩地区的后注浆灌注桩桩基竖向抗压承载力的计算方法,对比分析了基于勘察报告参数及后注浆增强系数修正的国内规范法、欧洲规范Eurocode 7公式法、Baguelin-彭柏兴修正公式法计算结果,并与静载荷试验双曲线法极限承载力预测结果进行对比验证,结果表明:(1)进口TEXAM型预钻式旁压试验仪,其最大试验压力可达8.0 MPa,用于软岩地区桩基承载力评价具有良好的适用性;(2)基于旁压试验成果,采用Baguelin-彭柏兴修正公式计算的单桩承载力极限值与实测曲线的预测极限值相比误差在5%以内;采用欧洲规范公式计算会高估单桩承载力约8%~15%;(3)采用基于勘察报告经验参数的国内规范方法计算结果较为保守,约有24%~32%的安全富余度。相比于基于勘察报告经验参数的国内规范方法,采用Menard旁压试验原位测试方法并结合Baguelin-彭柏兴修正公式,可充分挖掘软岩地区单桩竖向抗压承载力。

重复压浆钢管桩在既有建筑基础加固中的应用

本文通过某盖挖顺做既有建筑地基基础加固项目钢管桩现场试验,验证了一种可在深厚砂层中施工超深钢管桩的小型化设备施工工法。该工法具有承载力大、低净空施工等特点。同时,通过对比两种不同施工工艺的单桩承载力,验证了重复注浆钢管桩较泥浆护壁成孔钢管桩的优势,并给出重复注浆钢管桩承载力的估算方法。通过后期实际工程的施工及监测,证明重复注浆施工工艺的可靠性,为今后同类型项目施工提供一种可靠的施工方案。

灌注桩后注浆技术在大型商场施工中的应用研究

研究对灌注桩后注浆工艺中的几个重要环节进行了详细分析,其中包括注浆孔的布设,灌浆参数的确定和灌浆的监测。在钻孔灌注桩中灌注水泥浆,使其承载力及稳定性得到了显著提高。通过对注浆材料质量、注浆压力及注浆量等技术指标进行分析,明确了施工质量的控制方法,保证了工程安全,并提高了工程质量。

声波透射法与钻芯法结合在灌注桩缺陷的应用分析

阐述了声波透射法与钻芯法的测试原理与特点,介绍灌注桩常见的质量缺陷,并通过对某实际工程中灌注桩缺陷的检测和影响因素分析,结合实际情况探讨声波透射法与钻芯法结合在灌注桩缺陷的应用。结果表明,采用这两种方法可以准确可靠地检测出灌注桩内部的缺陷位置和性质。

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference（FE-FD） analysis is conducted to investigate the settlement and the excess pore water pressure（EPWP） of a piled-raft foundation due to cyclic high-speed（speed： 300km/h） train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer（No-9 layer） has better effect on reducing the settlement.

黏性土中桩侧后注浆单桩抗压承载性能室内模型试验研究

后注浆技术的应用能有效减少桩周土体扰动和泥皮等造成的不利影响,从而提高钻孔灌注桩的承载力。目前有关后注浆技术的研究多集中于桩端后注浆,少有涉及桩侧后注浆,影响了桩侧后注浆技术进一步推广应用。根据桩侧后注浆工艺,开展单桩抗压室内试验,以研究桩侧后注浆量对单桩抗压承载性能的影响。结果表明:在荷载水平较大的工况下,相较于桩侧后注浆量为1 L的单桩,注浆量为2、3 L时单桩极限抗压承载力分别提高18.2%和66.0%,提高幅度与注浆量呈正相关,并且可以在很大程度上减小桩顶沉降量;桩侧后注浆桩桩身轴力在侧注浆点位附近减小较快,在整个加载过程中桩端附近处桩身轴力值均比较低,单桩受压表现为摩擦桩;水泥浆液同时存在上返和下劈扩散,在室内试验条件下,两者扩散高度均约为14倍桩径,在浆液扩散段桩侧摩阻力得到显著提高,且越靠近注浆点位提高程度越明显。

浅埋偏压黄土隧道地表旋喷桩加固工艺参数研究

在黄土隧道修建过程中,其洞口段因浅埋偏压、围岩软弱破碎等通常需要进行加固处理。地表旋喷桩法具有适用范围广、加固效果好等优点,被广泛应用于隧道浅埋偏压段软弱围岩地表加固工程。以浅埋偏压黄土隧道进口段初期支护侵限为研究背景,介绍了现场地表旋喷桩加固的施工过程;建立了侵限段三维加固模型并分析了地表旋喷桩加固前后的变形控制效果,说明了处治措施的合理性;对比分析了现场监控量测结果,验证了数值模拟的准确性;开展了地表旋喷桩的工艺设计参数优化分析。结果表明:由于偏压作用,地表最大沉降值偏离隧道中心线,且拱顶中心线处沉降>右拱肩处沉降>左拱肩处沉降;施加地表旋喷桩对于减小地表沉降十分有效,地表最大沉降值减小了45.5%;采用地表旋喷桩加固处理后,拱顶处加固效果最为显著,较加固前沉降减小了57.9%,同时加固后左、右拱肩沉降差值减小了17.4%;建议隧道浅埋偏压段地表旋喷桩加固工艺设计参数:桩直径为0.4~0.6 m、桩间距为1.2 m、横向加固范围为1.5~2倍洞径、竖向加固范围为洞身两侧旋喷桩与隧道拱底平齐。

基于水平旋喷桩处置优化的地铁隧道施工变形控制分析

为研究富水砂层隧道中水平旋喷桩+超前小导管组合预加固的效果,以青岛地铁某区间段隧道为依托,采用有限元数值模拟方法,对比分析了无预加固、单独使用水平旋喷桩及旋喷桩配合超前小导管组合预加固三种工况的加固效果。结果表明,与无预加固方案相比,单独使用水平旋喷桩预加固可使地表沉降、拱顶沉降、掌子面纵向位移分别相应减少约61%、59%、38%;而水平旋喷桩与超前小导管组合预加固方案可使地表沉降、拱顶沉降、掌子面纵向位移分别相应减少约66%、77.6%、38.9%,典型开挖断面处与拱脚处地下水渗流量分别减少93.4%、96.7%,预加固效果与止水效果显著。