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.

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。

多维度深水浅层建井方式优选方法研究

深水钻井作业具有海洋环境多变、地质条件复杂、作业风险大和日费率高等特点,深水浅层建井的方式难以选择。针对海底土质强度、建井质量、作业时效、经济性、风险控制等因素,根据现场作业工程数据,分别对不同建井工艺的适应性进行了分析,建立了单维度的适应性分级机制,并借助雷达图进行定量可视化,形成了多维度深水浅层建井方式优选方法。研究结果表明,水深500~1500 m的南海北部海域,单井作业时,喷射法一般为浅层建井最优方法,作业效率相比钻入法可提高50%以上。该方法已在中国南海几十口深水井取得良好应用效果,可为深水复杂地层建井方式选择提供定量评价方法。

修正Mohr-Coulomb准则下倾斜基岩中桩端极限承载力研究

为计算倾斜岩面浅嵌岩桩极限承载力,本文基于修正Mohr-Coulomb强度准则提出了倾斜岩面浅嵌岩桩桩端承载力计算方法。采用特征线法构建了桩端面以下塑性发展区,考虑岩面倾斜角几何关系,推导了倾斜岩面位移滑移场;进一步通过黎曼不变量控制方程,求解了倾斜岩面浅嵌岩桩基极限承载力公式。分析了倾斜岩面坡角、岩体完整性参数以及岩体内摩擦角等因素对桩端承载力的影响。结果表明:浅嵌岩桩基嵌入深度达到极限嵌入比时,桩基达到极限承载力;当嵌入比大于极限嵌入比时,桩端承载力系数不受倾斜坡角和嵌入比影响,此时可按平地桩基进行分析计算;极限嵌入比随倾斜坡角的增大呈幂函数增大,且在岩石完整性较差时,极限嵌入比随岩体内摩擦角的增大而显著增大;当嵌入比小于极限嵌入比时,桩端承载力系数随倾斜坡角的增大近似线性减小,需考虑岩面倾角对桩基承载力的影响。

浅覆盖层深水钢栈桥桩基设计与施工

浅覆盖层深水条件下,钢栈桥施工难度大、造价高、安全风险大,合理的方案设计及施工监测对于其工期及成本控制至关重要。本文所涉钢栈桥施工过程受汛期和库区蓄水、长江岸坡侵蚀地貌和冲沟侵蚀等不利的水文地质影响,有效作业时间有限,作业场地受限,施工组织难度大。本文按车辆荷载的不同分为5种工况进行钢栈桥及浅覆土层钢管桩承载力设计计算。同时设计合理的施工工序及施工监测技术,有效确保了浅覆土层钢管桩施工的安全性,并缩短工期、降低成本。

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。

咬合桩围护结构在桥梁浅基加固中的应用——以陇海线坝河大桥加固工程为例

为探究咬合桩围护结构在浅基础加固中的力学特性,以陇海线坝河大桥为工程背景,选用Mohr-Coulomb本构方程,通过有限元软件MIDAS/GTS建立三维仿真模型,分析桩侧土体冲刷掏空对结构的影响,研究结构同一断面在不利工况下位移和内力的分布规律,并分析Ⅱ序桩的种类、冠梁布置、桩径对加固效果的影响。结果表明:土体冲刷后控制位移发生在桩顶长边方向且方向向内;土体冲刷掏空后土压力达到峰值且桩底弯矩为零,同时桩顶产生一定弯矩且反弯点位于桩基中部偏下;左、右侧面与迎水面背水面在受力和变形上均对称;在Ⅱ序桩为有筋桩时,其刚度对结构位移起到较大作用,无筋桩较有筋桩水平位移提高了2.75倍;冠梁作为边界约束对结构位移产生数量级影响,未冠梁较设冠梁水平位移提高43倍;咬合桩桩径与结构水平位移成反比,桩径对结构位移起到较大作用,桩径由0.8 m增加到1 m,桩径顶位移由0.18 mm增加到0.41 mm。

深厚软土地基浅层固化技术应用

本文介绍了浅层固化技术在珠海富山某地块软土地基特别是淤泥地基中的应用和效果,该技术具有处理大面积地基、经济效益高、处理工期短、处理效率高等优点。地基经该技术处理后,具备大型施工设备、车辆在场地里行走和作业条件,显著增强水泥搅拌桩的固结效果和强度,承台开挖中能防止管桩偏位、倾斜等,避免发生淤泥翻涌现象。通过工程实例分析该技术在道路基础和桩基础施工中的作用和效果,为此类地质条件的工程提供参考。

低应变法检测工程基桩浅部缺陷的波形实例分析

结合工程现场实例,简要论述了低应变反射波检测方法的原理和工程中常见的浅部缺陷桩,并详细分析了实际检测工作中典型浅部缺陷的低应变反射波形曲线。根据实测波形资料,总结了检测工作中常见的各种浅部缺陷桩的波形特征和技术要点,为判别基桩缺陷性质提供借鉴。通过对基桩浅部异常波形曲线的详细分析,避免实际检测工作中的错判或漏判。

复合地层隧洞中隔离桩对围岩位移的控制效果分析

设置隔离桩作为一种控制城市隧洞开挖引起围岩变形的有效手段,在“上软下硬”复合地层中的作用效果还罕有研究。依托滇中引水工程龙泉隧洞,采用FLAC^(3D)软件,分析隔离桩桩位、桩径、桩长及桩顶埋深等参数对隧洞衬砌及地表建筑物变形控制效果的影响。结果表明:设置隔离桩能够阻隔地层应力的传递,合理的设计参数是充分发挥隔离桩阻隔作用的关键;同等条件下,隔离桩对地层位移的限制作用在水平方向优于竖直方向;隔离桩距离隧洞越近、桩径越大,控制变形效果越好;隔离桩只有穿过地层滑移面并嵌入下层土体时,才能够较好控制由隧洞开挖引起的隧洞衬砌以及地表建筑物位移,建议嵌入下层土体深度为隔离桩长度的1/4;适当设置桩顶埋深能够降低隔离桩对于土体的牵引作用,建议桩顶埋深深度为隔离桩长度的1/5。研究成果可为隔离桩在城市浅埋复合地层隧洞工程中的应用提供参考。

浅埋桩基的高密度电法数值模拟与探测

在已拆除建筑的地块上重新拟建新建筑时,为方便基桩施工和基坑的开挖需要对地块内遗留的建筑基础进行清除,在缺失相关资料的情况下,对地块内基桩的探查一直是个难题。该文采用有限差分技术建立相应的数学模型,并进行高密度电法的正演模拟。在正演模拟的基础上采用高密度电法对地下基桩进行探测,对判定的基桩位置采用钻孔磁梯度法进行验证,通过磁梯度验证,表明在无基础资料的条件下高密度电法探测浅埋桩基础是可行的。

深水区浅覆盖层锚桩法钢栈桥设计及施工

从钢栈桥的设计理念出发,结合具体的工程案例,对深水区浅覆盖层区域钢栈桥的设计施工进行了探讨,对照使用区域的实际情况,采用锚桩法栈桥施工技术。经计算,栈桥的强度和刚度能够满足工程的施工要求,栈桥整体的稳定性可以得到保障。对钢栈桥锚桩法的施工流程和技术要点进行了讨论,顺利实现了施工目标。

滨海浅埋深厚软土条件下高等级公路地基处理方案研究

为了解决滨海地区软土地基不稳定及承载力差的问题,以甬台温高速公路某互通至S218省道连接线工程为案例,深入研究了滨海浅埋深厚软土条件下高等级公路地基处理的有效方案。论文深入探讨了就地固化+预应力混凝土管桩处理方案的设计要点,对就地固化强度和深度、管桩桩长和间距的确定、预应力管桩路堤桩基承载力及沉降和稳定计算、提高处理路段稳定性的措施等方面提出了建议。

浅坑堆栽法在黄葛树古树抢救性移栽中的运用

为保护白鹤滩水电站影响安置区7株黄葛树古树,对黄葛树古树进行了抢救性移栽,即对原生地立地因子进行认真调查,就近选择移植地点。结合黄葛树生物学、生态学特性,运用“浅坑堆栽法”进行移栽。结果表明:移栽存活率为100%,1年后移栽保存率100%。古树抢救性移栽原则上要坚持近地移植,在移栽中要采取根、冠修剪、伤口处理及带土球移栽等树体处理措施,并在移栽后切实加强管理,尤其是“浅坑堆栽法”满足了黄葛树需要充分的透气的生理需求,是黄葛树古树移栽中最关键的技术措施。

跨栈桥煤仓的基础设计及施工

为保证新建跨栈桥籽煤仓施工过程的安全,同时保证施工过程中选煤厂现有系统的正常生产,通过将新建籽煤仓范围内现有产品栈桥的部分土建结构拆除,并利用新建钢桁架将现有产品带式输送机托起,从而完成了跨栈桥煤仓的基础设计与施工。结果表明:该设计方法可在选煤厂不停产的情况下完成新建跨栈桥煤仓基础的安全施工,有效缩短了施工工期,使选煤厂如期达产,减少了企业的停产损失,同时也降低了建筑工程投资,增加了企业的经济效益;此外提出了部分无埋深筒仓的基础设计方法,可为选煤厂厂房或筒仓的设计提供一定借鉴。

浅覆盖层地质条件下海上钢平台施工关键技术

本文结合依托项目的实际工况,围绕近岸段裸岩浅覆盖层地质条件、桩位临近沉箱基础常规平台搭设方式无法进行海上钢平台搭设的情况,提出适用于不同工况复杂条件下海上钢平台施工关键技术,通过合理优化平台结构形式,借助于桩位相邻的沉箱及胸墙扩建现有平台形式,增加袋装混凝土等相应稳桩措施,保证平台结构的整体稳定性,对码头栈桥钢平台搭设技术的发展具有重要意义。

前撑式注浆钢管桩技术在基坑工程中的应用研究

以上海浦东新区某项目为例,研究前撑式抗压注浆钢管桩支护技术在超大浅基坑工程中的应用,以及目前存在的问题。通过对设计方案、现场施工工艺以及监测数据分析,前撑式抗压注浆钢管桩代替了原混凝土或钢内撑方法,极大地减少了内支撑的成本支出,大幅度提高了挖土效率,节省了工期,并指出当前仍然存在钢管支撑轴力不足、钢管桩插入比较大等问题。该方法的提出为今后“双碳”环境下的超大浅基坑工程提供新的设计思路,具有重要的推广意义。