Local geoid determination combining gravity disturbances and GPS/levelling: a case study in the Lake Nasser area, Aswan, Egypt

 The use of GPS for height control in an area with existing levelling data requires the determination of a local geoid and the bias between the local levelling datum and the one implicitly defined when computing the local geoid. If only scarse gravity data are available, the heights of new data may be collected rapidly by determining the ellipsoidal height by GPS and not using orthometric heights. Hence the geoid determination has to be based on gravity disturbances contingently combined with gravity anomalies. Furthermore, existing GPS/levelling data may also be used in the geoid determination if a suitable general gravity field modelling method (such as least-squares collocation, LSC) is applied. A comparison has been made in the Aswan Dam area between geoids determined using fast Fourier transform (FFT) with gravity disturbances exclusively and LSC using only the gravity disturbances and the disturbances combined with GPS/levelling data. The EGM96 spherical harmonic model was in all cases used in a remove–restore mode. A total of 198 gravity disturbances spaced approximately 3 km apart were used, as well as 35 GPS/levelling points in the vicinity and on the Aswan Dam. No data on the Nasser Lake were available. This gave difficulties when using FFT, which requires the use of gridded data. When using exclusively the gravity disturbances, the agreement between the GPS/levelling data were 0.71 ± 0.17 m for FFT and 0.63 ± 0.15 for LSC. When combining gravity disturbances and GPS/levelling, the LSC error estimate was ±0.10 m. In the latter case two bias parameters had to be introduced to account for a possible levelling datum difference between the levelling on the dam and that on the adjacent roads. Received: 14 August 2000 / Accepted: 28 February 2001     

浅谈超声波透射法在灌注桩检测中的应用

目前国内外对于钻孔灌注桩水下混凝土质量检测的方法很多,如低应变反射波法、高应变动测法、单桩竖向静载抗压试验、钻芯法、超声波透射法等,每种检测方法都有它的适用范围和局限性。超声波透射法与其他检测法相比,该方法检测精度高,结果直观可靠,适合大直径桩、超长桩的基桩检测,故在钻孔灌注桩的完整性检测中,得到了广泛的运用,尤其在桥梁灌注桩中,超长、大直径桩几乎都采用了超声波透射法检测。本文对某工地大直径桩进行了超声波透射法检测,通过波形与照片对比,更好地验证了超声波透射法测试超长、大直径取得的效果。     

电感耦合等离子体质谱法测定铅合金中的微量杂质元素镉和锡

铅合金中的镉和锡由于含量较低,国家标准方法均为单一元素分析,步骤繁琐,检出限高,难以达到理想的检出要求。本文建立了应用电感耦合等离子体质谱法(ICP-MS)测定铅合金中微量级(μg/g级)杂质元素镉和锡的分析方法。采用单一的低浓度硝酸溶解铅合金,用低温慢溶的方式使样品溶解更加完全,减少了多离子对仪器的干扰;通过铅基体匹配和加入酒石酸保证了标准与样品介质的一致性,同时避免了锡的水解;以~(103)Rh作为内标元素,~(111)Cd和~(118)Sn作为测量同位素克服了质谱干扰。方法检出限为镉0.05 ng/g、锡0.04 ng/g,比国家标准方法的检出限(1~6μg/g)低,精密度小于4%。该方法试剂用量少,减少了处理样品的复杂性,实现了合金中微量级元素的准确测定。     

黄土斜坡地震动时程分析

应用地震危险性分析理论和地震动人工合成技术，给出Newmark法中所需的地震动时程，解决了斜坡稳定性分析Newmark法中难以选取合适地震动时程的难题。通过对黄土斜坡实例计算，给出了坡体中地震动峰值加速度与深度的关系；在计算坡体位移时，提出了等效峰值加速度的概念；对比了使用地面地震动时程和使用坡体内等效地震动时程的计算结果。     

药用滑石粉酸中可溶物测定方法考察

考察药用滑石粉酸中可溶物测定方法的重复性、耐用性 ,分析主要影响因素。比较酸溶物提取液滤过介质对测定结果差异的影响 ;采用重量法随机测定酸溶物含量和室间差异。两种滤过介质处理对测定结果没有显著差异 ;室间测定结果没有显著差异 ;30批样品平行测定结果的 RSD值范围为 0 %～ 18.2 %。酸中可溶物测定法存在重复性和耐用性不佳的问题 ,应相应调整酸中可溶物含量限度     

A new analytical solution of tidal water table fluctuations in a coastal unconfined aquifer

This paper presents a new perturbation solution of the non-linear Boussinesq equation for one-dimensional tidal groundwater flow in a coastal unconfined aquifer. Built upon the work of Parlange et al. [Parlange, J.-Y., Stagnitti, F., Starr, J.L., Braddock, R.D., 1984. Free-surface flow in porous media and periodic solution of the shallow-flow approximation, J. Hydrol., 70, 251–263], the solution adopts a new perturbation parameter that is by definition less than unit, and thus is applicable to a wider range of physical conditions within the constraint of the Boussinesq approximation. This approach avoids a secular term in the third-order perturbation equation of Parlange et al. (1984), enabling the derivation of the third- and higher-order solutions. In comparison with a numerical (“exact”) solution, the new perturbation solution is shown to be slightly more accurate than that of Parlange et al. (1984) with the second-order approximation. The obtained third-order solution exhibits considerable improvement in accuracy. In relatively simple analytical forms, the present perturbation solution will help to understand better the non-linear characteristics of tidal water table fluctuations in as modeled by the non-linear Boussinesq equation coastal unconfined aquifers.     

利用混合法构建三维数字岩心(英文)

在弹性波有三维数字岩心描述了岩石的微观孔隙结构。X射线CT扫描是获取三维数字岩心最准确和直接的方法,但实验成本高。本文结合沉积过程模拟和模拟退火算法,提出了重建三维数字岩心的混合法,基于岩石二维图像重建三维数字岩心。利用岩石颗粒沉积算法构建初始数字岩心,作为模拟退火算法的初始状态。运用模拟退火算法调整岩石颗粒和孔隙的相对位置,使三维数字岩心与岩心二维图像具有相似的自相关函数,从而建立三维数字岩心。与传统模拟退火算法相比,该方法计算时间明显减小。运用局部孔隙度理论定量比较了重建数字岩心和岩心X射线微CT图像,两种数字岩心具有相似的均质性和孔隙连通性。利用有限元方法和格子玻尔兹曼方法分别模拟了重建三维数字岩心的地层因素和渗透率,数值模拟结果与实验结果相符。相比传统模拟退火算法,混合法重建数字岩心的传导特性更接近真实岩心的传导特性。     

贵州省六盘水市钟山区地质灾害危险性模糊评判

贵州省六盘水市钟山区为地质灾害典型区,但以往地质灾害研究方面工作程度相对较低,影响了该区地质灾害的有效防治和社会发展规划的有序进行。本文在钟山区地质灾害规划现状调查的基础上,总结了该区地质灾害形成原因和影响因素,最终选取地形坡度、岩组结构、植被覆盖率、人类工程活动、降雨量、地震共六个主要地质灾害影响因素作为评价因素集,利用灰色关联度法确定各影响因子的权重,运用模糊综合评判方法对钟山区内每个网格单元进行模糊综合评判,根据最大隶属度原则得出每个网格单元的隶属度值作为危险性评价结果,按照地质灾害危险性等级对该区进行危险性定量区划。此区划评价结果可供今后该区地质灾害防治、发展规划参考。     

航空矢量重力测量水平分量的带限直接地形影响

基于第二类Helmert凝聚法的级数展开式,独立推导了航空矢量重力测量水平分量带限直接地形影响的计算公式。在中国西部山区选取了两条沿纬圈方向4000m航线高度上的航线,采用 的数字高程模型基于解析核计算了水平分量的直接地形影响,经低通滤波后与基于带限公式计算的地形影响进行了比较。数值计算结果表明,二者吻合较好,本文给出的带限地形影响公式可用于航空矢量重力测量水平分量的地形归算。     

基于"山西2015速度模型"的定位方法对比研究

为了确定山西台网基于“山西2015速度模型”的相对固定的定位方法,选择2010~2016年最大空隙角小于45°、参与定位台站数大于40的103个地震事件,分别采用单纯形法、Hypo2000、Hyposat结合PTD等3种方法重新测定。结果显示,单纯形法和Hyposat结合PTD测定的残差以及网缘地震的震中距两方面均优于Hypo2000;在震源深度方面,Hyposat结合PTD的结果较为可信。综合分析认为,基于“山西2015速度模型”定位地震时,山西台网应固定使用Hyposat结合PTD的方法。