Cyclic strength of imperfectly saturated sands and analysis of liquefaction

The simplified method of analysis to assess liquefaction potential of a given sand deposit is briefly introduced in the first part of this paper. Then, recent advances in the laboratory testing for evaluating liquefaction resistance are described with a particular emphasis on the sand partly saturated with water. As a means to identify the degree of saturation which is applicable for both field deposits and laboratory samples, the use of the longitudinal wave (P-wave) is proposed based on a suite of data obtained from the triaxial tests in the laboratory. It is recommended that the non-destructive P-wave measurements be carried out first to determine the degree of saturation, and then the cyclic triaxial tests involving large destructive strains should be performed to determine the cyclic strength on the same sample of the sand. In order to demonstrate usefulness of the proposed approach, two sets of undisturbed samples were secured from two sites; one is located in Sakai-minato city which has suffered severe liquefaction at the time of the 2000 Tottoriken-Seibu earthquake and the other site is located in Koshigaya city, Saitama, where likelihood of liquefaction to occur in a future earthquake is of major concern. Penetration tests and in-situ velocity logging were also conducted at these two sites. By adjusting the P-wave velocity of the undisturbed samples in the laboratory so as to have the same velocity in the field, the in-situ state of saturation was reproduced in the laboratory samples. Then, the cyclic loading tests were conducted to determine the cyclic strength of intact samples. The results of the laboratory tests as above were incorporated into the simple method of liquefaction analysis described in the first section of this paper. The analysis seems to yield results which are in reasonably good agreement with what was observed at the time of the earthquake.     

Multiple X‐ray approaches to discriminate the origin of liquefied sand erupted during the 2012 Emilia Romagna earthquake

Geochemical, mineralogical and sedimentological analyses were carried out on sands erupted from sand volcanoes and soil cracks during the 2012 Emilia earthquakes with the aim of determining their origin and depth of provenance in a complex stratigraphic plain generated by different fluvial contributions. Geochemical, mineralogical and sedimentological analyses were performed by wavelength dispersive X‐ray fluorescence, X‐ray powder diffraction and Sedigraph and Settling tube, respectively. Distinct textural features, as well as Ni/MgO and Cr/Al₂O₃ ratios, allow discriminating two populations: an A‐area located close to San Carlo village and a B‐area nearby Scortichino village. Sediments from A‐area show chemical and mineralogical characteristics well comparable with those of the sediments derived from the Apennine rivers, whereas sands from B‐area have strong similarities with the sediments from the Po river. In the earthquake crater area most of the liquefaction phenomena were related to superficial sandy deposits (fluvial ridges, paleochannels and crevasse splays) generated by Apennine rivers. The Po river sediments in the B‐area derive from a layer at a depth at which liquefaction phenomena were excluded, because of the greater lithostatic load. These sediments thus shed a new light on the mechanisms that may induce liquefaction during an earthquake or even without a seismic triggering. It is suggested that a gas phase (mainly methane), which is commonly found below the Po plain, could have been dissolved in the water, near to the saturation threshold or already exsolved, increasing the interstitial overpressure and facilitating the liquefaction and the eruption of the sandy sediments. Copyright © 2015 John Wiley & Sons, Ltd.     

The correlations between the saturated and dry P-wave velocity of rocks

Sometimes engineers need to estimate the wet-rock P-wave velocity from the dry-rock P-wave velocity. An estimation equation embracing all rock classes will be useful for the rock engineers. To investigate the predictability of wet-rock P-wave velocity from the dry-rock P-wave velocity, P-wave velocity measurements were performed on 41 different rock types, 11 of which were igneous, 15 of which were sedimentary and 15 of which was metamorphic. In addition to the dry- and wet-rock P-wave velocity measurements, the P-wave velocity changing as a function of saturation degree was studied. Moreover, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann’s and Wood’s theory and it was seen that the measured data did not fit the theories. The unconformity is due to the fact that the theories are valid for high-porosity unconsolidated sediments at low frequencies. Gassmann’s equation was modified for the rocks except high-porosity unconsolidated sediments.

The dry- and wet-rock P-wave velocity values were evaluated using regression analysis. A strong linear correlation between the dry- and wet-rock P-wave velocities was found. Regression analyses were repeated for the rock classes and it was shown that correlation coefficients were increased. Concluding remark is that the derived equations can be used for the prediction of wet-rock P-wave velocity from the dry-rock P-wave velocity.     

土壤Cd含量实验室与野外DS光谱联合反演

土壤重金属高光谱遥感建模理论上能够大大降低传统化学分析测定所需成本,正逐步发展为有效探查土壤污染空间分布与开展污染土壤综合防治的关键技术。然而土壤重金属高光谱遥感调查技术目前多局限于稳定可控条件下的实验室光谱模型,野外诸多因素（光照、湿度、土壤粗糙度等）影响下野外原位光谱模型的有效性已成为困扰该项技术大范围推广亟待突破的关键科学问题。以湖南衡阳市某矿区为例,分别利用ASD地物光谱仪和等离子发射光谱法测定46个土壤样品350~2 500 nm的实验室光谱和Cd含量,并在土壤取样时同步测量样品野外原位光谱。在运用DS（direct standardization）转换算法处理野外光谱的基础上,融合实验室光谱先验知识,基于主成分逐步回归建模方法开展了土壤Cd含量实验室与野外原位DS光谱联合反演实验,交叉验证了模型的稳定性。同时为深入探究实验室与野外原位DS光谱联合反演模型的有效性,将其与基于实验室光谱、野外原位光谱、野外原位DS光谱、实验室与野外原位光谱联合建立的主成分逐步回归模型开展了对比分析。结果表明：野外原位光谱反演模型精度（R2=0.56）明显低于实验室光谱反演模型（R2=0.64）,野外原位DS光谱反演模型与之相比精度有所提升（R2=0.66）;在野外原位光谱DS转换校正基础上,联合实验室光谱先验知识的土壤Cd含量反演模型精度最高,R2可达0.72。与此同时,实验室与野外原位DS光谱联合反演模型揭示482,565,979和2 206 nm波段对研究区土壤Cd含量有较好指示性,此结果与实验室光谱反演模型所识别的特征波段一致,两者物理意义相同。研究结果证实了实验室光谱先验知识以及DS转换算法能够提升野外原位光谱模型的可靠性,可为发展土壤Cd含量野外原位高光谱遥感探测提供重要的提供理论与方法支撑。     

The fluctuation property of blown sand particles and the wind-sand flow evolution studied by numerical method

Sand particles blown by wind cause serious environmental problems and many researchers are trying to understand the dynamic properties of blown sand better. But the existing numerical approaches have not been able to simulate many important characteristics of wind-sand flow. In this paper, the evolution and fluctuation properties of blown sand at a dynamic steady state are investigated by using a more effective method. Using the LES (large eddy simulation) method for air phase movement and the DEM (discrete element method) for solid phase movement along with the existing particle-bed splashing function, we have characterized the whole movement property of the wind-sand system. The results indicate that the saturation time decreases with the inlet friction velocity, and it gradually reaches the shortest saturation time of about 1s; the saturation length, which is about 14 m at the usual wind velocity, first increases with wind velocity and then reaches a plateau; within the saturation length, the sand transport rate at different positions varies with time; the sand transport rate of the stable wind-sand flow is non-uniform with distance downwind and time, and has a notable correlation with the inflow friction velocity.     

Experimental study of different modes of block sliding along interface. Part 1. Laboratory experiments

This paper is the first part of an experimental work on studying the formation of different deformation modes of rock discontinuities under laboratory and field conditions. The formation conditions of different sliding modes were studied under laboratory conditions for several types of discontinuities, such as rigid surface contact and cracks filled with quartz sand, talc, and clay. A wide range of shear deformation modes were experimentally reproduced—from dynamic slip with a maximum velocity of tens of mm/s to stable sliding with a velocity of 1 µm/s. The behavior of a crack with a clay-containing gouge drastically changes after its wetting. The larger is the content of clay, the longer is the slip duration. The motion of a block consists of a long phase (~100 s) in which displacement velocity smoothly increases, and a retardation phase of almost the same duration in which displacement velocity decreases down to a few tens of µm/s. The used sensors detected no acoustic emission prior to the beginning of block sliding as well as on all stages of block motion until its full stop. It is shown that slow slip events have all stages typical for stick-slip motion: acceleration, long sliding, retardation, arrest, and quiescence. The conducted laboratory experiments substantiate the earlier statement that all types of deformation processes in the Earth’s crust produce a common range of phenomena.     

Polarization of plane wave propagating inside elastic hexagonal system solids

Based on the reported physical parameters for hexagonal system solids,we have calculated the effects of anisotropy on polarization of plane P-wave propagation.Herein we report the results of calculations and the newly observed physical phenomena.It is found that,for a given propagation,if the polarization is parallel to the wave vector,so also to the Poynting vector.In such a case,the phase velocity is identical to the energy velocity;the quasi P-wave degenerates to a pure P-wave along the propagation.It is also noted that if the polarization is parallel to the Poynting vector but not to the wave vector,the propagating wave cannot be a pure P-wave.Furthermore,the polarization in a quasi P-wave may deviate from the wave vector for more than 45°,but the deviation from the Poynting vector is always less than 45°.The energy velocity of a quasi SV-wave can be larger than that of the quasi P-wave in some propagation directions,even though the phase velocity of a quasi SV-wave may never be larger than either the phase velocity or energy velocity of the quasi P-wave.Finally,in case of parameters ε=0 and δ*≠0,the polarization of a quasi P-wave has an observed symmetry at a 45°phase angle.The anisotropy of a hexagonal system solid determines if a pure P-wave can be created and what the propagation direction is for a plane wave propagating inside such a hexagonal system solid.     

Simulation of triaxial response of granular materials by modified DEM

A modified discrete element method(DEM)with rolling effect taken into consideration is developed to examine macroscopic behavior of granular materials in this study.Dimensional analysis is firstly performed to establish the relationship between macroscopic mechanical behavior,mesoscale contact parameters at particle level and external loading rate.It is found that only four dimensionless parameters may govern the macroscopic mechanical behavior in bulk.The numerical triaxial apparatus was used to study their influence on the mechanical behavior of granular materials.The parametric study indicates that Poisson’s ratio only varies with stiffness ratio,while Young’s modulus is proportional to contact modulus and grows with stiffness ratio,both of which agree with the micromechanical model.The peak friction angle is dependent on both inter-particle friction angle and rolling resistance.The dilatancy angle relies on inter-particle friction angle if rolling stiffness coefficient is sufficiently large.Finally,we have recommended a calibration procedure for cohesionless soil,which was at once applied to the simulation of Chende sand using a series of triaxial compression tests.The responses of DEM model are shown in quantitative agreement with experiments.In addition,stress-strain response of triaxial extension was also obtained by numerical triaxial extension tests.     

钢筋混凝土靶板在弹丸冲击及爆炸载荷下响应的数值模拟

 采用HJC混凝土损伤本构模型及LS-DYNA的流固耦合算法,分别对钢筋混凝土靶板在弹丸冲击和爆炸载荷作用下的响应进行了有限元数值模拟,其中模拟参数由实验数据拟合重新获取。将模拟结果与实验结果和经验公式进行对比分析,结果表明：数值模拟再现了弹体贯穿靶板过程中的开坑、隧道及漏斗碎裂区,计算得到的弹体弹道极限及残余速度与实验数据吻合较好;此外,数值模拟也很好地再现了炸药爆炸后冲击波的传播过程以及爆炸载荷作用下混凝土的破坏情况,模拟结果与实验现象具有良好的一致性。     

重塑砂质含气沉积物的声响应特性与模型预测分析

海洋沉积物中气泡的存在对沉积物的声学特性有显著影响.为实现在实验室内对不同初始应力条件下含气沉积物的声学特性测量,研制了一套可用于土工三轴仪的双探针声学测量系统,基于CT扫描试验获得重塑含气砂样品中气泡群的尺寸分布,确定其共振频率范围.试验结果表明:细砂沉积物声速随气体含量的增加呈指数型降低,衰减系数随气体含量的增加呈...     

Ionospheric Disturbance in the Near-Field Area of the Epicenter of the September 25, 2003 Hokkaido Earthquake

A method which we developed for spatio-temporal data processing is employed to yield the source coordinates of the September 25, 2003 Hokkaido earthquake (magnitude 8.3), the switch-on time, and the propagation velocity of the earthquake-induced ionospheric disturbance. Distribution of total electron content (TEC) variations obtained from the GPS sites located in the near-field area of the earthquake epicenter is used for the data analysis. Parameters calculated in this paper are in good agreement with the real location of the earthquake epicenter, the real shock time (seismic data), and the results obtained earlier for ionospheric disturbances due to strong earthquakes. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 4, pp. 299–313, April 2005.     

The Δ- Method for the Boltzmann Equation

A new numerical method is proposed to solve the Boltzmann equation. A frame is set up by using a discrete velocity approximation in the infinite velocity space, but by considering only those distribution function points which are not too small. The distribution function points may occur anywhere in the infinite discrete velocity space and are not constrained to a pre-specified region. A fourth-order finite difference is used for the convection terms. A Monte Carlo-like method is applied to the discrete velocity model of the collision integral. The effort of the method is proportional to the number of discrete points. Numerical examples are given for the full Boltzmann equation and results for some benchmark problems are compared with analytical or prior solutions.     

Application of multivariate statistical methods to classify archaeological pottery from Tel‐Alramad site,Syria, based on x‐ray fluorescence analysis

Radioisotope x‐ray fluorescence (XRF) analysis has been utilized to determine the elemental composition of 55 archaeological pottery samples by the determination of 17 chemical elements. Fifty‐four of them came from the Tel‐Alramad site in Katana town, near Damascus city, Syria, and one sample came from Brazil. The XRF results have been processed using two multivariate statistical methods, cluster and factor analysis, in order to determine similarities and correlation between the selected samples based on their elemental composition. The methodology successfully separates the samples where four distinct chemical groups were identified. Copyright © 2006 John Wiley & Sons, Ltd.     

Selection of dune shapes and velocities Part 1: Dynamics of sand, wind and barchans

Almost fifty years of investigations of barchan dunes morphology and dynamics is reviewed, with emphasis on the physical understanding of these objects. The characteristic quantities measured on the field (shape, size, velocity) and the physical problems they rise are presented. Then, we review the dynamical mechanisms explaining the formation and the propagation of dunes. In particular a complete and original approach of the sand transport over a flat sand bed is proposed and discussed. We conclude on open problems by outlining future research directions. Received 22 December 2001 / Received in final form 31 May 2002 Published online 31 July 2002     

Mechanism for propagation of a positive leader

A model of leader breakdown in air is considered. The channel is formed due to heating of the streamer trace in the field of the streamer zone. A previous model of a streamer is generalized with allowance for recombination of charged particles. A mathematical model of heating of the streamer trace is developed. It is demonstrated that, at a given potential, the ignition of the channel is provided by streamers that possess a certain charge and the corresponding propagation velocity. This velocity determines the propagation velocity of a steady leader. The dependence of the leader velocity on the cloud potential is found. The results obtained are compared with the data from in-situ observations and laboratory studies.     

ICF平面冷冻靶制备中充气速率效应

基于自主研制的平面冷冻靶打靶系统及微管注入法充气/冷冻技术,探讨了不同充气速率对平面冷冻靶制备的影响。研究表明:随着充气速率的减小,靶盒内氢气压强的变化速率越小,液化过程越明显,并且持续的时间越长;充气速率越小,越能准确测量液氢在该温度下的饱和蒸气压。同时,确定了最佳充气速率,建立了利用饱和蒸气压标定液氢温度的方法。研制的平面冷冻靶已经成功提供ICF物理实验。     

Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X‐ray diffraction study

Naturally irradiated violet fluorite, a cubic CaF₂ mineral, is a rare historic pigment. Its documented usage in Europe stretches from ca. 1450 to ca. 1550. The intensely coloured violetish black naturally irradiated fluorite is commonly called antozonite, which is only vaguely defined based on its dark colour and specific odour emanated during grinding. In the published literature, there have been some discrepancies about its Raman spectrum. Therefore, sixteen samples of antozonite were analysed by Raman (micro‐)spectroscopy using five different excitation laser wavelengths (445, 532, 633, 780 and 1064 nm), which revealed specific bands located below 500 cm⁻¹ probably related to radiation‐caused defects. Their intensity increased with increasing violet colour saturation, thus providing a specification for antozonite's definition. Spectra excited at 445 and 780 nm contained also numerous broad bands above 500 cm⁻¹, which seem to be caused by the presence of rare earth elements. The structural damage of antozonite samples has been assessed by X‐ray diffraction and related to their lightness using analysis of image histograms. The obtained results have been applied in the analysis of micro‐samples of a Late Gothic altarpiece located in an Italian Court in UNESCO city Kutná Hora, Czech Republic, which contained exceptionally large grains of deep violet fluorite identified as antozonite. Copyright © 2015 John Wiley & Sons, Ltd.     

Theory, Design, and Operation of Large-Orbit High-Harmonic Gyroklystron Amplifiers

The high-harmonic gyroklystron is a compact RF amplifier which relies on the synchronous interaction between large-orbit axis-encircling electrons and high-order azimuthal cylindrical cavity TEn11 modes. Because of this unique structure, it offers the promise of moderate- to high-millimeter-wave output power. Experimental results for a fifth-harmonic two-cavity device are compared to both small-signal analytic theory and large-signal numerical calculations which assess gain, bandwidth, sensitivity to longitudinal velocity spread, self-oscillation, and saturation characteristics. Principal theoretical results include the transition to infinite gain as the start-oscillation current threshold is reached as well as the demonstration of the insensitivity of the small-signal gain to parallel velocity spread. The required high-energy rotating electron beam is provided through gyroresonant RF acceleration. To date, over 20 dB of small-signal gain has been achieved at 11.3 GHz in a 1.3-kG magnetic field. The design of a four-cavity configuration is also presented along with simulation of its gain, bandwidth, amplitude modulation (AM) and phase modulation (PM) sensitivity, dependence upon guiding-center spread, and large-signal saturation characteristics. This device has been constructed and initial tests have yielded a gain of 30 dB. Gain in excess of 50 dB is predicted.     

Preheat-induced signal enhancement in the infrared stimulated luminescence of young and bleached sediment samples

Natural and laboratory bleached surface and young samples of potassium feldspar sand separates and polymineral silt had their infrared stimulated luminescence (IRSL) signal measured before and after preheating at 220°C for 10 min or 160°C for 16 h. For both preheats, the laboratory bleached sand samples underwent a signal enhancement which was stable with laboratory storage. The youngest samples also showed natural signal enhancement. The silt sample showed no recuperation of bleached signal on preheating, but some in the natural signal. A range of filtered bleaches was applied to one surface sand sample. Signal levels before and after preheating were reduced by filtering out the UV from the bleaching spectrum. The unfiltered bleach, however, most closely reproduced the behaviour of the natural sample.     

Anomalous change of groundwater radon concentration monitored at Nakaizu well in 2011

An anomalous increase in radon concentration was measured at the Nakaizu observatory on the Izu Peninsula prior to the 2011 Tohoku earthquake using a custom-made radon counter. Since the increase was more than three times the standard deviation of radon concentration variations over 35 years of recorded data, it is considered likely that it is a precursor to the earthquake. Following the earthquake, the radon concentration decreased exponentially to the background level. The anomalous increase is explained using a modified volatilization model containing three important aquifer parameters: the groundwater saturation ratio, the fracture surface area per unit volume, and the porosity. The modified model can also explain the radon concentration behavior prior to the 1978 Izu-Oshima-Kinkai earthquake.