Assessment of various CPT based liquefaction severity index frameworks relative to the Ishihara (1985) H1–H2 boundary curves

The objective of the study presented herein is to develop an understanding of the predictive trends of four different liquefaction severity index frameworks, with emphasis on the utility of the frameworks for assessing liquefaction vulnerability in Christchurch, New Zealand. Liquefaction induced land damage was widespread following the four major earthquakes in Christchurch (M_w 5.9–7.1) between 4 September 2010 and 23 December 2011. As part of the rebuilding effort, a major focus, to date, has been on assessing/developing approaches for evaluating vulnerability to liquefaction induced damage in future events. The four liquefaction severity index frameworks that are evaluated herein are: the one-dimensional volumetric reconsolidation settlement (S_V1D), the Liquefaction Potential Index (LPI), and two new liquefaction severity indices developed following the major earthquakes in Christchurch, namely the Ishihara inspired LPI (LPI_ISH) and the Liquefaction Severity Number (LSN). To assess the predictive trends of the four severity index frameworks, the H₁–H₂ boundary curves developed by Ishihara (1985) are used as a reference of comparison. In large part, the severity index frameworks serve the same purpose as the Ishihara boundary curves, but they alleviate some of the difficulties in implementing the Ishihara boundary curves for assessing the highly stratified soil profiles that underlie much of Christchurch. A parametric study was performed wherein relatively simple soil profiles are evaluated using all the procedures and contour plots of calculated S_V1D, LPI, LPI_ISH, and LSN values were superimposed onto the Ishihara boundary curves. The results indicate that the LPI_ISH and LSN indices yield similar trends as the Ishihara boundary curves, whereas the S_V1D and LPI indices do not. Furthermore, little field data is available to assess the severity indices for the scenarios where the trends in the LPI_ISH and LSN indices differ.     

Vibration control of piled-structures through structure-soil-structure-interaction

This paper deals with the vibration control of existing structures forced by earthquake induced ground motion. To this aim it is proposed for the first time to exploit the structure–soil–structure mechanism to develop a device, hosted in the soil but detached from the structure, able to absorb part of the seismic energy so to reduce the vibration of neighbourhood structures. The design of the device is herein addressed to protect monopile structures from earthquake induced ground motion. By modelling the ground motion as zero-mean quasi-stationary response-spectrum-compatible Gaussian stochastic process, the soil as visco-elastic medium and the target monopiled-structure as a linear behaving structure the device, herein called Vibrating Barrier (ViBa), has been designed through an optimization procedure. Various numerical and experimental results are produced to show the effectiveness of the ViBa. Remarkably, a significant reduction of the structural response up to 44% has been achieved.     

Isogeometric analysis of THM coupled processes in ground freezing

An isogeometric analysis (IGA) based numerical model is presented for simulation of thermo-hydro-mechanically (THM) coupled processes in ground freezing. The momentum, mass and energy conservation equations are derived based on porous media theory. The governing equations are supplemented by a saturation curve, a hydraulic conductivity model and constitutive equations. Variational and Galerkin formulation results in a highly nonlinear system of equations, which are solved using Newton-Raphson iteration. Numerical examples on isothermal consolidation in plane strain, one-dimensional freezing and heave due to a chilled pipeline are presented. Reasonably good agreements were observed between the IGA based heave simulations and experimental results.     

利用MERIS水汽数据改正ASAR干涉图中的大气影响

大气对流层对雷达信号的传播延迟是制约重复轨道InSAR高精度测量应用的重要因素之一.本文描述了MERIS水汽数据用于ASAR干涉图大气改正的方法;并以美国南加州地区为例,选取4对ENVISAT ASAR数据进行了大气改正的研究.结果显示对这4幅干涉图,经过MERIS水汽数据改正后InSAR与GPS差异的RMS分别〖JP2〗降低了41.7%,65.2%,19.3%和39.4%.平均改善程度达41.4%.更重要的是,经过MERIS水汽改正后,从2005~2007年〖JP〗干涉图和2004~2007年干涉图中,能清楚地识别出三处形变最明显的区域：Long Beach-Santa Ana 盆地、Pomona-Ontario和San Bernardino,其形变速率从-8 mm/a到-28 mm/a,大部分在-20 mm/a左右,与这些地区2003年以前的历史形变速率基本一致.因此,采用无云条件下的MERIS水蒸汽数据改正同步获取的ASAR干涉图,可以显著地降低大气水汽对干涉图相位的影响,从而更真实地反映地表形变等地球物理信号.     

强地震前乾陵台地倾斜短临暂态异常图像特征研究

系统整理分析了1983—2008年乾陵台地倾斜仪记录到的暂态异常图像,发现其与周围4000km以内6．5级以上强震有一定的对应关系。异常图像以渐变、突变阶跃、畸变及脉动为主要特征,异常出现时间为震前0-40天,主要集中在震前4天。     

Nonlinear 3D finite element analysis of soil–pile–structure interaction system subjected to horizontal earthquake excitation

The dynamic response of a seismic soil–pile–structure interaction (SSPSI) system is investigated in this paper by conducting nonlinear 3D finite element numerical simulations. Nonlinear behaviors such as non-reflecting boundary condition and soil–pile–structure interaction modeled by the penalty method have been taken into account. An equivalent linear model developed from the ground response analysis and the modified Drucker–Prager model are separately used for soil ground. A comparison of the two models shows that the equivalent linear soil model results in an underestimated acceleration response of the structure under this ground shaking and the soil behavior should be considered as a fully-nonlinear constitutive model in the design process of the SSPSI system. It was also observed that the dynamic response of the system is greatly affected by the nonlinearity of soil–pile interface and is not sensitive to the dilation angle of the soil. Furthermore, the effect of the presence of pile foundations on SSPSI response is also analyzed and discussed.     

An explanation of the large PGA value of 2013 Ms7.0 Lushan earthquake at 51BXD station through topographic analysis

In Ms7.0 Lushan earthquake, a large amount of strong ground motion recordings were collected. In this paper, we analyze the recordings carefully. The abnor- mality of ground motion recordings is identified through a log linear regression. In the station of 51BXD, the PGA value has exceeded 1 g, which is the biggest peak ground acceleration （PGA） value obtained from all recordings in this earthquake. The log linear relation shows the PGA value in this station is abnormally large. As this station is located on the footage of a hill, the topographic amplifi- cation factor is explored in order to explain this abnor- mality. Through 3D numerical modeling using spectral element method with transmitting boundary conditions, the amplification factor is quantized. In this station, the topo- graphic amplification is highly polarized in the direction of East-West which agrees with the empirical recordings. This research result suggests us in future directionality of topographic amplification should be considered in the aseismic design.     

Ground motion prediction equation considering combined dataset of recorded and simulated ground motions

Himalayan region is one of the most active seismic regions in the world and many researchers have highlighted the possibility of great seismic event in the near future due to seismic gap. Seismic hazard analysis and microzonation of highly populated places in the region are mandatory in a regional scale. Region specific Ground Motion Predictive Equation (GMPE) is an important input in the seismic hazard analysis for macro- and micro-zonation studies. Few GMPEs developed in India are based on the recorded data and are applicable for a particular range of magnitudes and distances. This paper focuses on the development of a new GMPE for the Himalayan region considering both the recorded and simulated earthquakes of moment magnitude 5.3–8.7. The Finite Fault simulation model has been used for the ground motion simulation considering region specific seismotectonic parameters from the past earthquakes and source models. Simulated acceleration time histories and response spectra are compared with available records. In the absence of a large number of recorded data, simulations have been performed at unavailable locations by adopting Apparent Stations concept. Earthquakes recorded up to 2007 have been used for the development of new GMPE and earthquakes records after 2007 are used to validate new GMPE. Proposed GMPE matched very well with recorded data and also with other highly ranked GMPEs developed elsewhere and applicable for the region. Comparison of response spectra also have shown good agreement with recorded earthquake data. Quantitative analysis of residuals for the proposed GMPE and region specific GMPEs to predict Nepal–India 2011 earthquake of Mw of 5.7 records values shows that the proposed GMPE predicts Peak ground acceleration and spectral acceleration for entire distance and period range with lower percent residual when compared to exiting region specific GMPEs.     

The Influence of Surface Building's Relative Position on the Seismic Response of Subway Structures

By using the finite element method and viscoelastic artificial boundary,a soil-structure interaction system is established to simulate the influence of surface buildings on the seismic response of subway structures.The conditions of different relative positions between ground building and subway structure are analyzed.The results indicate that when considering the existence of surface buildings,the relative story displacements and internal forces of subway structures are changed greatly.Further the influence of surface buildings on subway structure changes as the distance increases.     

Novel integrated system calibration method for impulse ground penetrating radar

This paper proposes a new method of integrated system calibration that uses the transmitting and receiving signals from the impulse ground penetrating radar itself. In order to eliminate the influence from each subsystem or part including antenna, transmitter, receiver, signal processing circuits and transmission cables, two new calibration parameters that are different from the conventional S-parameters are introduced. The characteristic and influence of all parts in the transmitting and receiving channels are incorporated into the calibration equation through the new parameters. The calibration results of the radar detection data show that the new integrated system calibration can improve the quality of the data greatly in many aspects. It removes direct coupled waves, suppresses wave distortion and tail oscillation, and improves the quality of waveform and signal-clutter-ratios. It also compresses the pulse width and enhances resolution.