CFG桩的几种方法综合检测

采用CFG桩处理的地基,具有承载力提高幅度大、工后地基变形小以及施工方便快捷等特点。本文通过比较几种检测方法的适用性,提出了几种方法的检测次序、侧重点和局限性,从而总结出,几种方式配合起来,综合使用,可以对CFG桩进行经济、有效且准确的检测。     

CFG桩复合地基在福建省建筑工程中的应用

通过在具有强腐蚀性的填海区域、溶洞十分发育的岩溶地区、存在严重液化的冲洪积河床等不同地质情况下进行建设的三个典型工程的实例分析,介绍了CFG桩复合地基在福建省建筑工程中应用情况;实践应用表明,CFG桩复合地基具有施工设备简单、速度快、沉降变形小、造价省、质量可靠等优点,并为复杂地质基础处理提供了一种有效地基处理方法,值得在全省推广应用。     

Numerical and experimental assessment of thermal performance of vertical energy piles: An application

A district space heating and cooling system using geothermal energy from bearing piles was designed in Shanghai and will be installed in two years before 2010. This paper describes the pile-foundation heat exchangers applied in an energy pile system for an actual architectural complex in Shanghai, 30% of whose cooling/heating load was designed to be provided by a ground-source heat pump (GSHP) system using the energy piles. In situ performance tests of heat transfer are carried out to figure out the most efficient type of energy pile and to specify the design of energy pile system. Numerical investigation is also performed to confirm the test results and to demonstrate the medium temperature variations along the pipes. The averaged heat resistance and heat injection rate of different types of energy piles are calculated from the test and numerical results. The effect of pile type, medium flow rate and inlet temperature on thermal performance is separately discussed. From the viewpoint of energy efficiency and adjustability, the W-shaped underground heat exchanger with moderate medium flow rate is finally adopted for the energy pile system.     

热轧U型钢板桩精轧过程金属流动行为的有限元分析

针对热轧U型钢板桩(SY390BZ/%:0.23C、1.60Mn、0.44Si、0.18V,0.18Ti、0.05Nb)轧制过程中产生翘曲缺陷,采用有限元分析软件ABAQUS显式动力学算法,结合实验室试验测量参数,对钢板桩的精轧过程进行了仿真计算。在仿真计算的基础上,根据轧制平面内节点位移矢量分布情况,分析了轧件横向和纵向断面内金属流动规律。模拟结果显示轧件断面在孔型轧制的压下方向上存在零位移线,表明U型钢板桩轧制中坯料翼缘和锁口处在轧制压力方向上轧件内金属流动存在位移中性面,并伴有轧件锁口凸缘处金属流动过快,腹板处金属流动较慢而产生翘曲的现象。     

Uncertainties in Geologic Profiles versus Variability in Pile Founding Depth

How the design and actual founding depths of foundations correspond to the variability of geological conditions has long been a concern. This paper evaluates the spatial variability characteristics of as-built and estimated founding depths of driven steel H piles with reference to the spatial variability characteristics of geologic profiles at a weathered soil site in Hong Kong. Spatial variability characteristics are evaluated in terms of variance and scale of fluctuation. The variability of three founding depth indicators, i.e., the depth of Grade-III bedrock, the depth of standard penetration test blow count “N” of 200 blows/0.3 m (SPT-200), and the depth of completely decomposed granite over the site was estimated. It is found that pile founding depths exhibit greater variations than those of the geologic profiles due to the presence of design model errors, judgment errors, and construction effects. The as-built founding depths are mostly between the SPT-200 profile and the Grade-III bedrock profile. The variances of as-built pile length are similar to those with depth of SPT-200 but less than those with depth of Grade-III bedrock. The scale of fluctuation of as-built pile length is on the order of 20 m when kriging is used and 10 m when kriging is not used, which are less than those with depths of SPT-200 and Grade-III bedrock.     

Theoretical Study on Pile Length Optimization of Pile Groups and Piled Rafts

Pile groups are frequently designed with equal or similar pile lengths. However, the significant interaction effects among equal-length piles imply that this may not be the optimized configuration. This paper presents the optimization analyses of piled rafts and freestanding pile groups, where pile lengths are varied across the group to optimize the overall foundation performance. The results of the analyses are applicable in cases where the piles derive a majority of the capacity from the frictional resistance. It is demonstrated that, with the same amount of total pile material, an optimized pile length configuration can both increase the overall stiffness of the foundation and reduce the differential settlements that may cause distortion and cracking of the superstructure. The benefits of the optimization can be translated to economic and environmental savings as less material is required to attain the required level of foundation performances. The reliability of the optimization benefits in relation to construction-induced variability is also discussed.     

Increased Lateral Abutment Resistance from Gravel Backfills of Limited Width

Lateral pile cap tests were performed on a pile cap with three backfills to evaluate the static and dynamic behavior. One backfill consisted of loose silty sand while the other two consisted of 0.91- and 1.82-m-wide dense gravel zones between the pile cap and the loose silty sand. The 0.91- and 1.82-m-wide dense gravel zones increased the lateral resistance by 75 to 150% and 150 to 225%, respectively, relative to the loose silty sand backfill. Despite being thin relative to the overall shear length, the 0.92- and 1.82-m-wide gravel zones increase lateral resistance to approximately 54 and 78%, respectively, of the resistance that would be provided by a backfill entirely composed of dense gravel. The dynamic stiffness for the pile cap with the gravel zones decreased about 10% after 15 cycles of loading, while the damping ratio remained relatively constant with cycling. Dynamic stiffness increased by about 10 to 40% at higher deflections, while the damping ratio decreased from an initial value of about 0.30 to around 0.26 at higher deflections.     

Reduction Factor for the Unloading Point Method at Clay Soil Sites

Full-scale testing can be an integral component of quality control/quality assurance for projects involving construction of deep foundations. Rapid load tests are being used in the deep foundation industry as a method for assessing the axial static behavior of deep foundations. Since rapid load tests involve dynamics, inertial and damping forces must be considered in analyzing measured pile response to estimate the static pile response. The unloading point method (UPM) is typically used for this purpose. Generally considered a consequence of load rate effects in clays, results from the UPM must be further modified by a reduction factor to obtain a reasonable estimate of the static pile response. A reduction factor of 0.65 applied to the UPM for clay soil sites has been recommended by others. However, a review and analysis of readily available literature reporting static and rapid pile load test results at sites predominantly consisting of clay soils indicate that an average reduction factor of 0.47 is more appropriate. Rapid load testing should be used judiciously. When using the UPM to estimate static pile capacity from rapid load tests in clay, static load tests should be performed to validate the reduction factor used to interpret rapid load tests.     

Field-Measured Response of an Integral Abutment Bridge with Short Steel H-Piles

Integral abutment bridges (IABs) with short steel H-pile (HP) supported foundations ( ? 4?m of pile depth) are economical for many environmentally sensitive sites with shallow bedrock. However, such short piles may not develop an assumed, fixed-end support condition at some depth below the pile cap, which is inconsistent with traditional pile design assumptions involving an equivalent length for bending behavior of the pile. In this study, the response of an IAB with short HP-supported foundations and no special pile tip details such as drilling and socketing is investigated. Instrumentation of a single-span IAB with 4-m-long piles at one abutment and 6.2- to 8.7-m-long piles at the second abutment is described. Instrumentation includes pile strain gauging, pile inclinometers, extensometers to measure abutment movement, earth pressure cells, and thermistors. Pile and bridge response during construction, under controlled live load testing, and due to seasonal movements are presented and discussed. Abutment and pile head rotations due to self-weight, live load, and seasonal movements were all found to be significant. Measured abutment movements were likely affected by both temperature changes and deck creep and shrinkage. Based on the field study results presented here, moderately short HPs driven to bedrock without special tip details appear to perform well in IABs and do not experience stresses larger than those seen by longer piles.     

Current Design and Construction Practices of Bridge Pile Foundations with Emphasis on Implementation of LRFD

The Federal Highway Administration (FHWA) mandated the use of the load and resistance factor design (LRFD) approach in the U.S. for all new bridges initiated after September 2007. This paper presents the bridge deep foundation practices established through a nationwide survey of more than 30 DOTs in 2008. Highlighted by this study are the benefits of the LRFD as well as how the flexibility of its usage is being exploited in design practice. The study collected information on current foundation practice, pile analysis and design, pile drivability, pile design verification, and quality control. Since this is the first nationwide study conducted on the LRFD topic following the FHWA mandate, the status on the implementation of LRFD for bridge foundation design was also examined. The study found that: (1) more than 50% of the responded DOTs are using the LRFD for pile design, while 30% are still in transition to the LRFD; and (2) about 30% of the DOTs, who use the LRFD for pile foundations, are using regionally calibrated resistance factors to reduce the foundation costs.