共查询到20条相似文献，搜索用时 31 毫秒
1.
George D. Bouckovalas Achilleas G. Papadimitriou Dimitrios G. Niarchos Yannis Ζ. Tsiapas 《Soil Dynamics and Earthquake Engineering》2011
This paper revisits the seminal work of Seed and Booker (1977) [21] on the design of infinitely permeable drains for liquefaction mitigation. It is shown that their basic mathematical assumption for the rate of earthquake-induced excess pore pressure generation overlooks sand fabric evolution effects during cyclic loading and eventually leads to underestimation of the drain effectiveness. This is because such effects cause peak excess pore pressures to be attained at the early stages of partially drained shaking, followed by a gradual attenuation even if shaking continues undiminished, a response feature not predicted by the original formulation. In addition, special emphasis is given to the analytical relation describing the excess pore pressure build-up until liquefaction in undrained tests. This relation was considered unique in the original work, for reasons of simplicity, thus neglecting sand fabric evolution effects that may differentiate it for various sands, densities and loading conditions. Hence, a revised analytical formulation is proposed, which takes into account both above effects of sand fabric evolution. The paper provides a quantitative assessment of their influence on drain effectiveness and establishes a new set of charts for drain design. Experimental measurements from shaking table tests, as well as robust numerical simulations are shown, which underline the necessity for the revised solution and design charts. 相似文献
2.
Correlation of shear wave velocity with liquefaction resistance based on laboratory tests 总被引：4，自引：0，他引：4
According to the results of cyclic triaxial tests on Hangzhou sands, a correlation is presented between liquefaction resistance and elastic shear modulus. Material-dependent but independent of confining stress, shows the linear relation of (σd/2)1/2 with Gmax. For its application to different soils, a method proposed by Tokimatsu [Tokimatsu K, Uchida A. Correlation between liquefaction resistance and shear wave velocity. Soils Found 1990:30(2):33–42] is utilized to normalize the shear modulus with respect to minimum void ratio. A simplified equation is established to evaluate the liquefaction potential by shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the peak horizontal ground surface acceleration during earthquakes. The equation proposed in this paper is compared with previous methods especially the procedure proposed by Andrus [RD Andrus, KH Stokoe. Liquefaction resistance of soils from shear-wave velocity. J Geotech Geoenviron Eng 2000:126(11):1015–25]. The results show its simplicity and effectiveness when applied to sands, but more validation or modification is needed for its application to sand with higher fines content. 相似文献
3.
Floods play a critical role in geomorphic change, but whether peak magnitude, duration, volume, or frequency determines the resulting magnitude of erosion and deposition is a question often proposed in geomorphic effectiveness studies. This study investigated that question using digital elevation model differencing to compare and contrast three hydrologically distinct epochs of topographic change spanning 18 years in the 37-km gravel–cobble lower Yuba River in northern California, USA. Scour and fill were analysed by volume at segment and geomorphic reach scales. Each epoch's hydrology was characterized using 15-min and daily averaged flow to obtain distinct peak and recurrence, duration, and volume metrics. Epochs 1 (1999–2008) and 3 (2014–2017) were wetter than average with large floods reaching 3206 and 2466 m3/s, respectively, though of different flood durations. Epoch 2 (2008–2014) was a drought period with only four brief moderate floods (peak of 1245 m3/s). Total volumetric changes showed that major geomorphic response occurred primarily during large flood events; however, total scour and net export of sediment varied greatly, with 20 times more export in epoch 3 compared to epoch 1. The key finding was that greater peak discharge was not correlated with greater net and total erosion; differences were better explained by duration and volume above floodway-filling stage. This finding highlights the importance of considering flood duration and volume, along with peak, to assess flood magnitude in the context of flood management, frequency analysis, and resulting geomorphic changes. 相似文献
4.
In this paper,the seismic effectiveness of a density-variable tuned liquid damper(DVTLD) with a sloping bottom is experimentally investigated through a series of shake table tests on a 1/4-scale,3-story frame structure and numerically simulated by a new semi-analytical model.Special attention was given to reducing the fi rst peak and maximum response under near-and far-fi eld ground motions,and the robustness of a density-variable control system consisting of multiple DVTLDs with closely-spaced frequencies.... 相似文献
5.
Malcolm Newson 《地球表面变化过程与地形》1980,5(1):1-16
The occurrence of two ‘rare’ floods (August 1973, August 1977) in the Plynlimon experimental catchments has confirmed the susceptibility of small upland catchments to summer flooding and provided clues to complications in the geomorphological interpretation of floods in terms of their magnitude and frequency. Magnitude may be treated both in terms of work and effectiveness; the emphasis here is on effectiveness, as revealed by simple surveys. The first Plynlimon flood was more effective on slopes and the second in channels, despite peak discharges of similar return periods and almost identical rates of work revealed by bedload trapping. Effectiveness/frequency studies are likely to require a much more detailed approach, subdividing both the characteristics of the flood and the spatial elements of the affected catchments; a simple slope/channel subdivision is found to be suitable for accounts of effectiveness found in the literature on British floods this century. Effectiveness studies also require regular surveys throughout the recovery period following major flooding; in upland catchments these surveys should concentrate on identifying threshold phenomena and illustrating the relationship between effectiveness and work assessments of magnitude. 相似文献
6.
Summary The spectra of Matsushiro micro-earthquakes were studied using a spectrum analyser and discussed in relation to their magnitude and the epicentral distance. It was found that the spectra of seismic waves by Matsushiro micro-earthquakes did not depend upon the epicentral distance since the sonagrams showed a peak around 5 cps at Matsushiro as well as Suzaka. The spectrum also failed to show any distinct peak for micro-earthquakes of magnitude lower than 1.0 due to the decrease of signal to noise ratio. 相似文献
7.
经研究发现热弛豫模型的衰减比BISQ模型大得较多,与地球介质相比衰减量也过大;反演与实验结果相比在虚模量的低频(或低温)端和高频(或高温)端相差较大,仅在峰值附近符合较好.针对上述不足,将Arrhenius关系直接引进Biot模型,替换原模型引进的峰值点的频率对数和温度关系,并重新调整了模型参数.这样既改善了原模型衰减量过大,又克服了模型反演中虚模量峰值曲线两侧差异较大的缺点.进行了P波和S波的波传播分析,仍然在频率谱和温度谱上获得热弛豫峰和Biot峰.分析显示热弛豫峰导致波速随频率升高而上升的普遍规律,Biot峰导致波速随温度升高而上升的异常现象.在相同条件下对Biot模型,BISQ模型和热弛豫模型的P波波速和衰减进行了对比.热弛豫模型得到的速度频散更强,频散范围更宽,所得的衰减峰值频率比BISQ模型要低,衰减幅度比BISQ模型稍大.这些结果与实验结果相近,更符合实际. 相似文献
8.
Self-centering seismic retrofit scheme for reinforced concrete frame structures: SDOF system study 总被引：1，自引：1，他引：0
This paper presents the results of a parametric study of self-centering seismic retrofit schemes for reinforced concrete (RC) frame buildings. The self-centering retrofit system features flag-shaped hysteresis and minimal residual deformation. For comparison purpose,an alternate seismic retrofit scheme that uses a bilinear-hysteresis retrofit system such as buckling-restrained braces (BRB) is also considered in this paper. The parametric study was carried out in a single-degree-of-freedom (SDOF) system framework since a multi-story building structure may be idealized as an equivalent SDOF system and investigation of the performance of this equivalent SDOF system can provide insight into the seismic response of the multi-story building. A peak-oriented hysteresis model which can consider the strength and stiffness degradation is used to describe the hysteretic behavior of RC structures. The parametric study involves two key parameters -the strength ratio and elastic stiffness ratio between the seismic retrofit system and the original RC frame. An ensemble of 172 earthquake ground motion records scaled to the design basis earthquake in California with a probability of exceedance of 10% in 50 years was constructed for the simulation-based parametric study. The effectiveness of the two seismic retrofit schemes considered in this study is evaluated in terms of peak displacement ratio,peak acceleration ratio,energy dissipation demand ratio and residual displacement ratio between the SDOF systems with and without retrofit. It is found from this parametric study that RC structures retrofitted with the self-centering retrofit scheme (SCRS) can achieve a seismic performance level comparable to the bilinear-hysteresis retrofit scheme (BHRS) in terms of peak displacement and energy dissipation demand ratio while having negligible residual displacement after earthquake. 相似文献
9.
利用《中国地震动参数区划图》采用的地震动参数衰减关系,以及《中国地震动参数区划图》中地震动峰值加速度和地震动加速度反应谱特征周期反推不同设防烈度和设计地震分组对应的震级和震中距,再根据《建筑抗震设计规范》中各设防水准的峰值加速度确定对应的震级和震中距,进而根据地震动强度包线参数与震级和震中距关系计算地震动强度包线参数的取值,为基于强度包线函数生成人工地震动提供参考,并讨论强度包线参数的取值规律：(1)随着设防烈度的提高,加速度时程曲线上升段持续时间t1和平稳段持续时间ts减小,下降段衰减指数c增大;(2)随着地震水准和设计地震分组的提高,加速度时程曲线上升段持续时间t1和平稳段持续时间ts增加,下降段衰减指数c减小;(3)在生成人工地震动时,除考虑峰值加速度和设计地震分组影响外,还需要考虑设防烈度影响。 相似文献
10.
断层气动态变化特征及其与地震活动的关系 总被引：7，自引：2，他引：7
本文介绍了白浮断层气观测点的监测研究结果，表明在一些地震前观测的断层气（特别是Ｈｇ）的异常变化。其异常特征是震前出现异常高值突跳，异常幅度大、时间短，而震后一般变化不大，同时本文还讨论了断层气的变化特征与气象因素的关系。 相似文献
11.
Ali M. Rajabi M. Khamehchiyan Mohammad R. Mahdavifar V. Del Gaudio 《Soil Dynamics and Earthquake Engineering》2010
Arias intensity is considered as a shaking parameter suitable for characterizing earthquake impact on ground stability. Within the framework of a study aimed at providing tools for the assessment of hazards related to earthquake-induced slope failures, Arias intensity attenuation relations were determined for the Zagros Mountains region, an active tectonic belt elongated NW–SE in the western and south-western part of Iran. The calculation of relation coefficients was based on strong-motion data of earthquakes located in the Zagros area and recorded by Iranian stations managed by the Building and Housing Research Center of Iran (BHRC). Five models of attenuation relation were considered and their coefficients were estimated through a least-square regression analysis. The relations obtained were then applied to a data sample different from that used for regression and the root mean square (RMS) of residuals was examined in order to compare effectiveness of different relations in probabilistic estimates. Furthermore a comparison made with attenuation relations obtained for Alborz and the central part of Iran showed significant differences possibly related to structural differences. 相似文献
12.
《国际泥沙研究》2022,37(6):715-728
Rainfall-induced floods may trigger intense sediment transport on erodible catchments, especially on the Loess Plateau in China, which in turn modifies the floods. However, the role of sediment transport in modifying floods has to date remained poorly understood. Concurrently, traditional hydrodynamic models for rainfall-induced floods typically ignore sediment transport, which may lead to inaccurate results for highly erodible catchments. Here, a two-dimensional (2D) coupled shallow water hydro-sediment-morphodynamic (SHSM) model, based on the Finite Volume Method on unstructured meshes and parallel computing, is proposed and applied to simulate rainfall-induced floods in the Zhidan catchment on the Loess Plateau, Shaanxi Province, China. For six historical floods of return periods up to 2 years, the numerical results compare well with observations of discharge hydrographs at the catchment outlet. The computed runoff-sediment yield relation is quantitatively reasonable as compared with other catchments under similar geographical conditions. It is revealed that neglecting sediment transport leads to underestimation of peak discharge of the flood by 14%–45%, whilst its effect on the timing of the peak discharge varies for different flood events. For 18 design floods with return periods of 10–500 years, sediment transport may lead to higher peak discharge by around 9%–15%. The temporal pattern of concentrated rainfall in a short period may lead to a larger exponent value of the power function for the runoff-sediment yield relation. The current finding leads us to propose that incorporating sediment transport in rainfall-induced flood modeling is warranted. The SHSM model is applicable to flood and sediment modeling at the catchment scale in support of risk management and water and soil management. 相似文献
13.
Earthquake Researeh in Ch一na461 .METHODLet R be some value measured or estimated as a sequenee ina’‘Past”time interval(一丁,O)(I)万‘月,=(RI,…,R。),R,之R。,R=nlaX l二f匕11(RI,…,R,,) Values(l)eould have an arbitrary Physieal nature.BelowweshalleonsiderEq.(l)asearthquakemagnitudes in a given seismic aetive region or logarithms of seismie Peak ground aeeelerations at习given site.Ro isa而nimum eutoff value;it 15 defined by Possibilities of registration systems or wasehosen as the … 相似文献
14.
Mingguo ZHENG Qiangguo CAI Qinjuan CHENG 《国际泥沙研究》2007,22(3):208-217
The relation between runoff volume and sediment yield for individual events in a given watershed receives little attention compared to the relation between water discharge and sediment yield, though it may underlie the event-based sediment-yield model for large-size watershed. The data observed at 12 experimental subwatersheds in the Dalihe river watershed in hilly areas of Loess Plateau, North China, was selected to develop and validate the relation. The peak flow is often considered as an important factor affecting event sediment yield. However, in the study areas, sediment concentration remains relatively constant when water discharge exceeds a certain critical value, implying that the heavier flow is not accompanied with the higher sediment transport capacity. Hence, only the runoff volume factor was considered in the sediment-yield model. As both the total sediment and runoff discharge were largely produced during the heavy-discharge stage, and the sediment concentration was negligibly variable during this stage, a proportional function can be used to model the relation between event runoff volume and sediment yield for a given subwatershed. The applicability of this model at larger spatial scales was also discussed, and it was found that for the Yaoxinzhuang station at the Puhe River basin, which controls a drainage area of 2264km2, a directly proportional relation between event runoff volume and sediment yield may also exist. 相似文献
15.
16.
本文基于笔者采用过的同时考虑房屋层数和场地类别时烈度到水平向地面峰值转换的基本思路,统计研究了烈度与竖向地面峰值的对应关系,明确指出了不同烈度下竖向与水平向峰值的比值应该是有所不同的,并给出了建议的比值,给果可供一般工程抗震设计参考使用。 相似文献
17.
研究不同高径比橡胶基底隔震储罐的频率特征,探讨储罐隔震体系3种不同振动频率随支座隔震频率变化规律.分析在不同频谱特性地震波激励下,隔震体系各振型组分对地震响应(基底剪力、支座位移和晃动波高)的影响,以及响应峰值随支座隔震频率和阻尼比的变化特点.研究表明,基底剪力峰值与场地地震波频谱特性密切相关.支座隔震频率不能完全反映减震机理的实质,隔震振型频率是影响基底剪力的重要参数.在软弱场地上隔震储罐的减震效率低,有效隔震频率范围窄.晃动波高峰值是储罐自振特性和地震波频谱特性等多种因素导致的结果,隔震系统设计时需特别考虑晃动波高增大的影响. 相似文献
18.
Maryna Voyevoda Wolfgang Geyer Peter Mosig Eva M. Seeger Sibylle Mothes 《洁净——土壤、空气、水》2012,40(8):817-822
The effectiveness of different remediation procedures for decreasing the amount of TPH (total petroleum hydrocarbons) in contaminated groundwater was evaluated at the site of a former refinery. The investigations were carried out on samples taken from several gravel based HSSF (horizontal subsurface flow) constructed wetlands (CW) which differed in relation to their filter material additives (no additive, charcoal, and ferric oxides additives) and examined the potential effect of these additives on the overall treatment efficiency. Samples of the following gravel based HSSF CW were investigated. No filter additive (system A), 0.1% activated carbon (system B), 0.5% iron(III) hydroxide (system C), and the reference (system D). Systems A–C were planted with common reed (Phragmites australis), whereas system D remained unplanted. In addition, the influence of seasonal conditions on the reduction of these hydrocarbons and the correlation between the amounts of TPH and BTEX (benzene, toluene, ethylbenzene, and xylene isomers), on the one hand, and methyl tert‐butyl ether, on the other, was investigated. The study was carried out by using a modified GC‐FID approach and multivariate methods. The investigations carried out in the first year of operation demonstrated that the effectiveness of the petroleum hydrocarbon removal was highest and reached a level of 93 ± 3.5% when HSSF filters with activated carbon as a filter additive were used. This remediation method allowed the petroleum hydrocarbon content to be reduced independently of seasonal conditions. The correlation between the reduction of TPH and BTEX was found to be R = 0.8824. Using this correlation coefficient, the time‐consuming determination of the BTEX content was no longer necessary. 相似文献
19.
四川地区地震动峰值衰减规律研究 总被引：4，自引：1，他引：3
基于四川省地震监测台网27个基岩台站,2008年5月12日——2008年6月10日105次地震（震级ML=4.0——6.4,震中距△=26——623km）的8505条宽频带速度记录,利用实时仿真方法得到了相应的加速度记录,进而对数据进行回归分析,获得了四川地区基岩场地中小地震峰值加速度和峰值速度的衰减关系,并用最近发生的一次4.8级地震对该规律进行了验证．通过四川台网的记录,提出了符合四川地质条件的衰减关系 相似文献
20.
A recent approach relates the shift of the frequency peak of the Ground Penetrating Radar (GPR) spectrum with the increasing of the moisture content in the soil. The weakness characterizing this approach is represented by the needs of high resolution signals, whereas GPR spectra are affected by low resolution. The novelty introduced by this work is twofold. First, we evidence that clay content information is present in the location where the maximum amplitude of the GPR spectra occurs. Then, we propose three super resolution methods, namely parabolic, triangular, and sinc-based interpolators, to further refine the location of the frequency peak. In fact, it is really important to be able to find this location quite precisely, to obtain accurate estimates of clay content. We show that the peak location can be found best through sinc-interpolation in the frequency domain of the measured data. Our experimental results confirm the effectiveness of the proposed approach to resolve a frequency shift in the GPR spectrum, even for a small amount of clay. 相似文献