碎石桩复合地基检测分析

结合南京钢铁集团新钢铁厂碎石桩复合地基工程实例，从桩身的密实性和连续性、桩体周围土的隆起量以及桩间土挤密效果3个方面对碎石桩复合地基进行检测分析。     

复合注浆法在基础加固中的应用

复合注浆法是将静压注浆法和高压旋喷注浆法进行时序上的结合，分别发挥两种注浆加固方法各自的优点，又可克服各自的技术和工艺缺陷的一种基础加固新方法，它可以较好地对既有建筑物地基和新建建筑基础出现质量问题进行加固处理。简述了复合注浆法的加固作用机理、设计及计算模型，在此基础上通过工程实例介绍其施工技术并分析其加固效果和经济性。     

Marine and limnic radiocarbon reservoir corrections for studies of late- and postglacial environments in Georgia Basin and Puget Lowland, British Columbia, Canada and Washington, USA

Models of late-glacial environmental change in coastal areas are commonly based on radiocarbon ages on marine shell and basal lake sediments, both of which may be compromised by reservoir effects. The magnitude of the oceanic reservoir age in the inland waters of the Georgia Basin and Puget Lowland of northwestern North America is inferred from radiocarbon ages on shell-wood pairs in Saanich Inlet and previously published estimates. The weighted mean oceanic reservoir correction in the early and mid Holocene is −720±90 yr, slightly smaller than, but not significantly different from, the modern value. The correction in late-glacial time is −950±50 yr. Valley-head sites yield higher reservoir values (−1200±130 yr) immediately after deglaciation. The magnitude of the gyttja reservoir effect is inferred from pairs of bulk gyttja and plant macrofossil ages from four lakes in the region. Incorporation of old carbon into basal gyttja yields ages from bulk samples that are initially about 600 yr too old. The reservoir age declines to less than 100 yr after the first millennium of lake development. When these corrections are accounted for, dates of deglaciation and late-glacial sea-level change in the study area are pushed forward in time by more than 500 yr.     

Scattering of plane SV waves by cylindrical canyons in saturated porous medium

On the basis of Biot dynamic theory, an analytic solution of two-dimensional scattering and diffraction of plane SV waves by circular cylindrical canyons in a half space of saturated porous media is presented in this paper for the first time. The solution is obtained by employing the Fourier–Bessel series expansion technique. Parametric studies had been carried out, which includes: the angle of incidence, the frequency of the incident SV wave, the porosity of saturated porous medium and the stiffness and Poisson's ratio of the solid-skeleton. All the outcomes are useful for the seismic analysis of the surface topography conditions.     

垫层对CFG桩复合地基影响的分析

对CFG桩复合地基垫层进行分析 ,探讨了垫层厚度和模量对桩土应力比、桩侧摩阻力、沉降变形、承载力的影响 ,并得出一些规律     

桩基筒形翼状钻头的改进设计及应用

针对浙江省温州市世贸中心大厦桩基施工中硬岩钻进时出现的堵管、卡钻和效率低等问题,从所钻地层和钻头的磨损分析出发,提出了钻头的改进设计方案.改进型筒形翼状钻头比原先使用的平底滚刀钻头增加了18个孕镶金刚石-针状硬质合金复合式钻齿和3个钎头,并按受力特点进行了合理分布.实际钻进效果表明改进型钻头应用于超深、大直径钻孔的钻进效率较高、钻进过程平稳.针对钻头的实际磨损情况提出了钻头进一步改进设计的建议.     

高压旋喷桩复合地基在高层住宅楼中的应用

以郑州市某高层住宅楼工程为例,介绍了高压旋喷桩复合地基的设计计算和施工方法,经静荷载试验和建筑物沉降观测,复合地基的承载力可以满足设计要求,说明高压旋喷桩复合地基可以成功地用于高层住宅楼的建筑中.     

复杂条件下深圳汝南大厦基础工程方案的优选与实践

位于复杂地质条件和环境条件下的深圳汝南大厦在基坑支护的施工过程中出现钻进困难,必须重新选择基础工程施工方案.结合场地特殊地质和环境条件在对人工挖孔桩、换填法、树根桩法、旋喷桩复合地基等8种基础工程施工方案进行分析与优选的基础上,借助模糊决策理论进行方法优选验算,最终选定了人工挖孔桩加部分钻(冲)成孔灌注桩的方案.采用该方案在深圳市汝南大厦的施工实践表明其施工效果良好.     

现浇薄壁管桩复合地基非线性有限元分析

现浇薄壁管桩是处理大面积软土地基的一项新技术,目前已在沿海软土地区高速公路建设中得到了一定的应用,但其产生的时间较短,开展的研究相对较少,利用Plaxis岩土工程有限元软件对现浇薄壁管桩（PCC桩）的工作特性、荷载传递规律及其影响因素、加固机理等方面进行了详细的分析,结果表明,桩外壁摩阻力随桩深近乎呈线性分布,桩内壁摩擦力只在桩下端一定长度内有所发挥,桩芯土体具有较好的闭塞效应,研究成果具有较大的指导意义.     

Seasonal records of climatic change in annually laminated tufas: short review and future prospects

Many Recent and fossil freshwater tufa stromatolites contain millimetre‐scale, alternating laminae of dense micrite and more porous or sparry crystalline calcites. These alternating laminae have been interpreted to represent seasonally controlled differences in the biotic activity of microbes, and/or seasonally controlled changes in the rate of calcification. Either way, couplets of these microbially mediated alternating calcified laminae are generally agreed to represent annual seasonality. Combined stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg, Sr, Ba) geochemistry from Recent tufa stromatolites show that seasonal climatic information is available from these calcites. Variability in δ¹⁸O (and in one case Mg concentration) has been shown to be controlled primarily by stream temperature change, usually driven by solar insolation. In arid climates, seasonal evaporation can also cause δ¹⁸O enrichment by at least 1‰. Variability in δ¹³C results potentially from: (1) seasonal change in plant uptake of ¹²C‐enriched CO₂; (2) seasonal change in degassing of ¹²C‐enriched CO₂ in the aquifer system; and (3) precipitation of calcite along the aquifer or river flow path, a process that increases δ¹³C of dissolved inorganic carbon (DIC) in the remaining water. Mechanisms 2 and 3 are linked because calcite precipitates in aquifers where degassing occurs, e.g. air pockets. The latter mechanism for δ¹³C enrichment has also been shown to cause sympathetic variation between trace element/Ca ratios and δ¹³C because trace elements with partition coefficients much greater than 1 (e.g. Sr, Ba) remain preferentially in solution. Since degassing in air pockets will be enhanced during decreased recharge when water saturation of the aquifer is lowest, sympathetic variation in trace element/Ca ratios and δ¹³C is a possible index of recharge and therefore precipitation intensity. High‐resolution geochemical data from well‐dated tufa stromatolites have great potential for Quaternary palaeoclimate reconstructions, possibly allowing recovery of annual seasonal climatic information including water temperature variation and change in rainfall intensity. However, careful consideration of diagenetic effects, particularly aggrading neomorphism, needs to be the next step. Copyright © 2005 John Wiley & Sons, Ltd.