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.

Study on the Effect of Occlusion Rate on the Deformation of Non-Vegetarian Occlusal Piles

In order to investigate the force characteristics of the occlusal pile, this paper takes the underground garage support project of Nanchang Bayi Square as the research background and studies the bending moment of the occlusal pile after the excavation process of the foundation pit through the model test. The test results show that the bending moment of the pile increases and then decreases with the increase of soil depth under horizontal load, and the bending moment reaches the maximum near the excavation surface of the foundation pit;the test results can provide a reference for the design of occluded pile body in practical engineering.

塑性混凝土咬合桩防渗墙变形机理研究

以大连湾沉管隧道南岸港池临时围堰工程监测数据为基础,建立了塑性混凝土咬合桩防渗墙数值计算模型,通过实测数据验证了模型的准确性,分析了不同影响因素下咬合桩防渗墙的变形演化规律,结论表明:水压力相比土压力对咬合桩变形和内力的影响更为显著,水压力增大导致桩身变形和弯矩增大,扰动临时围堰土体;土体坡度的影响较小,但土体坡度应逐渐放缓,不小于1∶1.5;桩长的变化对变形影响较大,较短的桩身未嵌固在岩石中,较长的桩身在桩顶出现最大位移;随着桩径增大,桩顶变形和最大弯矩逐渐增大,弯矩分布较为一致。

基于ABAQUS的咬合桩支护深基坑数值分析

基于ABAQUS数值分析软件,利用刚度等效原则对咬合桩支护深基坑进行等效.对基坑开挖卸荷过程中坑底隆起变形、支护结构位移及支撑轴力变化进行分析,并与实际监测数据进行对比验证.研究结果表明:采用刚度等效原则进行咬合桩支护分析能够反映基坑的变形特征,数值分析得出的支护结构和周围环境的变形结果与实际监测值具有良好的一致性,可作为基坑实际施工的指导.

管板组合结构拉森型锁扣咬合数值模拟研究

针对管板组合结构振打施工过程中的拉森型锁扣容易被撕裂的问题,依托管板组合桩结构形式的尼日利亚莱基深水港码头工程,采用有限元方法对管板组合桩拉森型锁扣拉伸、扭角、倾斜3种咬合情况进行受力仿真研究。结果表明:管板锁扣咬合精度越低,锁扣咬合应力越大,对拉森型锁扣产生越不利的影响,并提出管板锁扣在不同咬合状态下偏移、扭角、垂直度等精度参考限值。最后建议加强对管-板桩沉桩工艺的研究,提高沉桩精度控制与监测,降低锁扣不利的咬合应力,减小锁扣撕裂风险。精度参考限值可为管板组合结构施工技术标准提供依据,以及为提高管板组合结构施工质量提供重要参考。

跨海高速铁路桥梁超长钢管桩锤击沉桩机理探究

针对跨海高速铁路桥梁超长钢管桩试验匮乏、桩基设计参数等问题,文中依托杭州湾跨海铁路大桥工程,对超长钢管桩开展初打和复打高应变测试及静载试验,分析钢管桩承载力性能、贯入特性等沉桩机理,验证桩基设计参数,为大范围沉桩作业提供依据。结果表明,(1)在该试桩区地质条件下,采用YC80液压锤和HHD1000液压锤,能量传递效率为63%~84%,满足同类型工程桩的沉桩要求;(2)高应变检测法对于超大直径单桩基础承载力的评估存在偏于保守现象,其承载力值与静载试验值相比减少了18.35%;(3)试桩SZ-1、SZ-2轴向抗压承载力恢复系数为1.37和1.56,钢管桩沉桩后承载力存在显著的时间效应。(4)试桩SZ-1、SZ-2实测土塞效应系数为0.71和0.3,超长钢管桩存在显著的土塞效应。

锚碇基坑地下连续墙围护结构作永久受力结构的应用研究

随着地下建设空间的进一步利用,地下连续墙应用范围不断向下拓展。目前,地下连续墙已经作为永久受力结构应用于建、构筑物主体结构中。基于上海远方相关地下连续墙锚碇基坑实践,对地下连续墙作永久受力结构的应用进行探讨,并针对框架式地下连续墙、桩-墙咬合式地下连续墙、圆形地下连续墙施工关键技术进行阐述。结果表明,作永久受力了的地下连续墙结构通常较为特殊,部分为特殊结构形式,部分包含特殊接头形式,在目前的施工技术下是可以实现地下连续墙作永久受力结构的。用集约高效,推进城市功能复合。创建“就近职住、功能复合”的现代城市,在规划及设计中进行街道一体化设计。

新型桩-墙咬合圆形基坑支护施工技术探析--以S253远松线当阳市河溶大桥危桥改造工程为例

文中以S253远松线当阳市河溶大桥危桥改造工程为例,对新型桩-墙咬合圆形基坑支护施工技术进行探析,后续基坑变形监测显示,连续墙体的最大侧移为15.1 mm,旋喷桩的最大侧移为10.5 mm,周边的最大沉降量为25.4 mm,满足工程设计的要求。

基于ABAQUS的深大基坑支护体系模拟分析

深大基坑工程具有地质条件复杂和变形隐蔽等特点,其安全性和稳定性对工程建设至关重要。以中国铁建华南总部大厦基坑咬合桩支护工程为例,结合ABAQUS软件,对多工况下咬合桩支护体系进行了模拟分析与位移计算。结果表明:支护前期,咬合桩桩体受土压力和桩体强度影响,咬合桩中部产生偏移,顶部和底部受拉伸的影响产生最大位移;支护中期,随着混凝土强度增加及中部拉杆固定,拉伸位移逐渐减小;支护后期,除边界咬合桩和底部支撑具有较大位移外,其余桩体均保持稳定;模拟位移与实测结果一致,具有较高的可靠性。

复杂地质下咬合桩施工技术研究

基坑支护技术在项目施工阶段扮演着重要角色,伴随地质环境变化,其施工难度也将受到一定影响。在复杂地质条件下,咬合桩施工质量可以决定基坑是否发挥自身实际作用,基于此,以南方科技大学附属医院(校本部)项目为研究对象,通过分析基坑支护技术特点,总结项目施工重难点,针对硬咬合桩施工方法、放坡、插筋、挂网喷锚以及冠梁、连梁支撑体系施工等所应用基坑支护技术进行了详细论述,以降低基坑变形、坍塌等事故发生概率,保证施工安全性。

旋挖咬合灌注桩在基坑支护工程中的应用

结合传统的钻孔咬合桩和旋挖钻机全套管钻进技术,形成了一种新的围护结构施工工法——旋挖咬合灌注桩工法。旋挖咬合灌注桩具有传统咬合桩的所有优点,且施工速度快、造价低、占用场地空间小。结合工程实例,简单介绍了旋挖咬合灌注桩的原理、施工工艺、施工技术要点和事故处理措施。通过实践证明,旋挖咬合灌注桩作为一种新型围护结构施工工法是合理可行的。

深基坑钻孔咬合桩特点及关键施工技术

在基坑工程中,钻孔咬合灌注桩是一种新型的围护结构。除岩层以外,钻孔咬合灌注桩可适用于任何土层,尤其适用于淤泥、流沙、地下水富集等不良条件的沿海地区软土地层。它具有防渗效果好、经济适用等优点。

钻孔咬合桩——地铁工程围护结构新型式

文章就深圳地铁一期工程会购区间隧道明挖段围护结构之钻孔咬合桩施工方案的比选 ,施工作业流程 ,施工关键技术 ,应用条件及经济、环保价值等作了详细论述。

全套管钻孔咬合桩在临近地铁基坑工程中的应用

以苏州某商业大楼咬合桩的施工为例,介绍全套管钻孔咬合桩在临近地铁基坑支护工程中的应用情况以及咬合桩施工技术要点。施工结果表明,全套管钻孔咬合桩对周围环境影响小,对地层扰动小、施工快、造价低,在苏州软土及高水位土层基坑支护中具有广阔的应用前景。

南京某地铁深基坑围护结构方案的比选研究

针对南京某地铁深基坑工程的地层和承压水特性,对全套管咬合桩围护、地下连续墙围护及组合式围护等三种围护方案进行了比选研究,并就推荐方案通过离心模型试验研究其技术可行性。研究表明全套管咬合桩围护结构能较好的适应该地层深基坑工程,同时由于其造价低廉,是一种在类似工程中值得推广的围护结构。

咬合桩止水帷幕在PBA暗挖隧道中的应用研究

结合北京地铁某线暗挖隧道咬合桩落底式止水帷幕试验工程,研究洞桩法暗挖隧道洞内有限空间条件下,塑性混凝土与钢筋混凝土咬合桩止水帷幕施工技术可行性,采用数值模拟、抽水试验等手段验证咬合桩帷幕的止水效果。结果表明:咬合桩渗透系数k=8.6×10^(-7)cm/s,满足设计要求,有良好的止水效果;帷幕实施前后稳定涌水量由2129 m^(3)/d变为6.8 m^(3)/d,止水效果明显;抽水试验前后外观测井水位标高无明显变化,现场开挖无渗水。研究成果验证了该技术方案及施工工艺满足工程建设需要,可为今后类似工程的设计和施工提供借鉴。

邻近地铁的深基坑咬合桩结合内支撑支护体系施工及监测

在邻近地铁隧道且周边建筑密集的深基坑施工中采用咬合桩结合内支撑的支护形式,作用在咬合桩上的水土压力可由内支撑有效传递和平衡,构造简单、受力明确。支撑材料选用钢筋混凝土,其刚度大、整体性好、布置灵活。对在营运中的地铁隧道实施机器人24h全天候进行监测,减少了人工进入隧道测量的不安全性,采用计算机软件自动生成、进行数据处理、数据分析、报表输出及提供图形,同时还有自动报警功能。