振动切槽防渗墙施工技术

近年来出现了很多修筑防渗墙的新技术,振动切槽就是其中之一。介绍了成墙原理、工艺、设备等。该方法简单实用,效率高,质量稳定,在砂层、土层施工中,已初露锋芒,有着广阔的应用前景。     

D型耗能器偏心支撑结构的抗震性能试验研究

偏心支撑结构是一种高烈度地震区高层建筑钢结构合理的抗侧力体系,本文针对目前偏心支撑结构存在的不足,提出一种新型的框架支撑形式——耗能器偏心支撑;并将该单斜杆(D型)耗能器偏心支撑与支撑斜杆上不加设耗能器的D型偏心支撑结构进行了对比试验。验证了该新型框架支撑形式不仅可以减少耗能梁段吸收的地震能量,而且可以减小耗能梁段的破坏程度,从而减少震后修复工作量;它具有很好的变形能力和足够的抗侧移能力。文中同时给出了设计方法,并提出了改进措施。     

A Method for Analyzing the Self-Supported Earth-Retaining Structure Using Stabilizing Piles

The self-supported earth-retaining structure using stabilizing piles (SSR is used from here) has the advantages of less deformation and less internal force compared with conventional cantilever retaining structure. It is easier to conduct the excavation when SSR is used for an excavation instead of using braced excavation with struts. The SSR is better than other methods to the 10 m shallow excavation depth in terms of economical and constructional efficiency when the ground is not very soft. However, this SSR method lacks a theoretical basis in terms of geotechnical engineering. The objective of this study is to develop a method of analysis by laboratory model tests. A variety of model tests were performed in order to analyze the behavior of SSR and the ground, and to measure the stress acting on stabilizing piles relative to excavation steps and earth pressures on the wall. The analysis reveals the failure mechanism of a wedge and then suggests a method for calculating a virtual supported point. These findings were incorporated into a method for analyzing retaining wall, stabilizing piles, and beams connecting two structures. Future research is geared toward developing a design program that uses the analytical methodology for this SSR.     

Estimation of base motion in instrumented steel buildings using output‐only system identification

A procedure to estimate the seismic motion at the base of a building from measured acceleration response at two or more floors is presented. The proposed method is comprised of two steps. In the first step, the dynamic characteristics of the building are inferred by using an output‐only system identification procedure. In the second step, the motion of the base of the building is estimated by using the transfer function of a simplified building model consisting of a shear and flexural continuous beam together with dynamic properties obtained in the first step. The proposed method is validated first with an analytical model subjected to the 1940 El Centro ground motion and then with an instrumented building in California that experienced the 1994 Northridge earthquake, and the ground motions at the base of the building are available. It is shown that the proposed method is capable of providing very good estimates of the motion at the base. The use of the proposed method is finally illustrated on an instrumented building, where the sensor at the base of the building did not function during the 1994 Northridge earthquake. Copyright © 2013 John Wiley & Sons, Ltd.     

Gabor‐frame‐based Gaussian packet migration

We present a Gaussian packet migration method based on Gabor frame decomposition and asymptotic propagation of Gaussian packets. A Gaussian packet has both Gaussian‐shaped time–frequency localization and space–direction localization. Its evolution can be obtained by ray tracing and dynamic ray tracing. In this paper, we first briefly review the concept of Gaussian packets. After discussing how initial parameters affect the shape of a Gaussian packet, we then propose two Gabor‐frame‐based Gaussian packet decomposition methods that can sparsely and accurately represent seismic data. One method is the dreamlet–Gaussian packet method. Dreamlets are physical wavelets defined on an observation plane and can represent seismic data efficiently in the local time–frequency space–wavenumber domain. After decomposition, dreamlet coefficients can be easily converted to the corresponding Gaussian packet coefficients. The other method is the Gabor‐frame Gaussian beam method. In this method, a local slant stack, which is widely used in Gaussian beam migration, is combined with the Gabor frame decomposition to obtain uniform sampled horizontal slowness for each local frequency. Based on these decomposition methods, we derive a poststack depth migration method through the summation of the backpropagated Gaussian packets and the application of the imaging condition. To demonstrate the Gaussian packet evolution and migration/imaging in complex models, we show several numerical examples. We first use the evolution of a single Gaussian packet in media with different complexities to show the accuracy of Gaussian packet propagation. Then we test the point source responses in smoothed varying velocity models to show the accuracy of Gaussian packet summation. Finally, using poststack synthetic data sets of a four‐layer model and the two‐dimensional SEG/EAGE model, we demonstrate the validity and accuracy of the migration method. Compared with the more accurate but more time‐consuming one‐way wave‐equation‐based migration, such as beamlet migration, the Gaussian packet method proposed in this paper can correctly image the major structures of the complex model, especially in subsalt areas, with much higher efficiency. This shows the application potential of Gaussian packet migration in complicated areas.     

Observations of the electric fields that accelerate auroral particles

Electric fields accelerate electrons and ions in the auroral zone at altitudes below 8000 km to produce several distinctive particle distributions. The electric field of electrostatic shocks and double layers produces the inverted-V precipitating electron and up-flowing ion beams. Electrostatic ion cyclotron waves heat ion beams. The electric field in low frequency plasma waves and electrostatic shocks produces ion conics and field-aligned or counterstreaming electrons. Relationships between electric fields and particle distributions are illustrated with data from the S3-3 satellite.     

JSN-2B型泥浆净化机振筛系统的优化设计

JSN2B型泥浆净化机是地勘单位普遍使用的泥浆处理设备,在实际使用过程中,由于振筛系统采用的是电机皮带传动带动偏心块产生振动的方式,维修设备和更换筛网不方便,影响净化机的正常使用。经研究分析,采用振动电机及复合筛网对其进行改造,改造后经过1年的实际应用,使用效果良好,维修保养方便,效益显著提升。