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1.
为了研究地下空间结构对场地地震反应的影响，以一个三层地下商场结构为原型，设计并开展了土?地下空间结构动力相互作用振动台模型试验，研究了在6条不同卓越频率输入地震波在不同峰值加速度下场地地震反应的变化规律。试验研究结果表明：（1）地表水平加速度放大系数以结构中轴线为对称轴呈对称分布，地下结构显著影响上方及邻近场地的地表水平加速度。同时，由于地下空间结构的局部场地效应影响，即使在水平地震输入下也将导致场地产生竖向振动，地表竖直加速度放大系数呈M形分布。地下空间结构的影响范围可达到其两侧各一倍宽度距离。（2）地表加速度放大系数受输入地震波卓越频率的影响明显，且随着输入地震波的峰值加速度（PGA）的增大而降低，但空间放大系数随着PGA的增大而增大。（3）地表加速度Fourier谱的峰值频率受输入地震波的卓越频率、场地水平方向的固有频率和竖向固有频率的综合影响。 相似文献
2.
Influence of vertical ground motion on seismic-induced displacements of gravity structures 总被引：1，自引：0，他引：1
Andrzej Sawicki W&#x;odzimierz Chybicki Marek Kulczykowski 《Computers and Geotechnics》2007,34(6):485-497
A method enabling assessment of seismic-induced movements of gravity block is proposed. This method is based on dynamic analysis of the block subjected to both horizontal and vertical ground accelerations, and resultant forces acting on the block. There are two kinds of the motion. The first one is trivial, as it is a common motion of the block and subsoil. The second is a relative motion of the block with respect to subsoil, depending on combination of ground accelerations and the resultant of horizontal forces. Attention is focused on the influence of vertical ground motion on seismic-induced displacements of the structure. Experimental investigations performed in order to validate a numerical algorithm are described, and then experimental data are compared with numerical predictions. A good agreement is obtained. Then, the dynamics analysis of the block is presented for harmonic and pseudo-stochastic ground motions in order to illustrate the algorithm proposed. The results of computations show that, for some typical data and ground accelerations corresponding to strong earthquakes, large permanent displacements of the block take place, as observed in real conditions. 相似文献
3.
Multilinear Regression Analysis for Seismic Response and Engineering Properties of Liquefiable Coromandel Coastal Soil Deposits 总被引：1，自引：0，他引：1
S. Senthamilkumar C. Natarajan K. Muthukumaran 《Geotechnical and Geological Engineering》2009,27(3):439-453
This paper investigates the seismic characteristics and geotechnical properties with respect to the liquefaction potential
of the deposits in the Coromandel coastal line of Nagapattinam town, Tamilnadu, India. A series of field tests were conducted
using standard penetration test, cone penetration test and plate load test. Laboratory tests were conducted on the collected
samples. From the results, a microzonation map was developed for the liquefaction potential and settlements. Some multilinear
regression models between permeability, fines content, relative density, coefficient of curvature, coefficient of uniformity,
mean particle size, factor of safety, settlement, standard penetration test values and cone penetration test values were developed.
The shear wave velocity and shear modulus were calculated from the field penetration tests and correlations between the normalized
values of peak ground accelerations, velocities and displacements, which were obtained from the equivalent linear ground motion
analysis using SHAKE software, with other parameters of soil. From the results, it was found that at some of the areas are
vulnerable to high amplification of waves even for small earthquake. 相似文献
4.
V. S. Phanikanth Deepankar Choudhury G. Rami Reddy 《Geotechnical and Geological Engineering》2011,29(6):1109-1126
Any earthquake event is associated with a rupture mechanism at the source, propagation of seismic waves through underlying
rock and finally these waves travel through the soil layers to the particular site of interest. The bedrock motion is significantly
modified at the ground surface due to the presence of local soil layers above the bedrock beneath the site of interest. The
estimation of the amplifications in ground response due to the local soil sites is a complex problem to the designers and
the problem is more important for mega cities like Mumbai in India, where huge population may get affected due to devastations
of earthquake. In the present study, the effect of local soil sites in modifying ground response is studied by performing
one dimensional equivalent-linear ground response analysis for some of the typical Mumbai soil sites. Field borelog data of
some typical sites in Mumbai city viz. Mangalwadi site, Walkeswar site, BJ Marg near Pandhari Chawl site are considered in
this study. The ground responses are observed for range of input motions and the results are presented in terms of surface
acceleration time history, ratio of shear stress to vertical effective stress versus time, acceleration response spectrum,
Fourier amplitude ratio versus frequency etc. The typical amplifications of ground accelerations considering four strong ground
motions with wide variation of low to high MHA, frequency contents and durations are obtained. Results show that MHA, bracketed
duration, frequency content have significant effects on the amplification of seismic accelerations for typical 2001 Bhuj motion.
The peak ground acceleration amplification factors are found to be about 2.50 for Mangalwadi site, 2.60 for Walkeswar site
and 3.45 for BJ Marg site using 2001 Bhuj input motion. The response spectrum along various soil layers are obtained which
will be useful for designers for earthquake resistant design of geotechnical structures in Mumbai for similar sites in the
absence of site specific data. 相似文献
5.
India is prone to earthquake hazard; almost 65 % area falls in high to very high seismic zones, as per the seismic zoning map of the country. The Himalaya and the Indo-Gangetic plains are particularly vulnerable to high seismic hazard. Any major earthquake in Himalaya can cause severe destruction and multiple fatalities in urban centers located in the vicinity. Seismically induced ground motion amplification and soil liquefaction are the two main factors responsible for severe damage to the structures, especially, built on soft sedimentary environment. These are essentially governed by the size of earthquake, epicentral distance and geology of the area. Besides, lithology of the strata, i.e., sediment type, grain size and their distribution, thickness, lateral discontinuity and ground water depth, play an important role in determining the nature and degree of destruction. There has been significant advancement in our understanding and assessment of these two phenomena. However, data from past earthquakes provide valuable information which help in better estimation of ground motion amplification and soil liquefaction for evaluation of seismic risk in future and planning the mitigation strategies. In this paper, we present the case studies of past three large Indian earthquakes, i.e., 1803 Uttaranchal earthquake (Mw 7.5); 1934 Bihar–Nepal earthquake (Mw 8.1) and 2001 Bhuj earthquake (Mw 7.7) and discuss the role of soft sediments particularly, alluvial deposits in relation to the damage pattern due to amplified ground motions and soil liquefaction induced by the events. The results presented in the paper are mainly focused around the sites located on the river banks and experienced major destruction during these events. It is observed that the soft sedimentary sites located even far from earthquake epicenter, with low water saturation, experienced high ground motion amplification; while the sites with high saturation level have undergone soil liquefaction. We also discuss the need of intensifying studies related to ground motion amplification and soil liquefaction in India as these are the important inputs for detailed seismic hazard estimation. 相似文献
6.
A series of centrifuge shaking table model tests are conducted on 4?×?4 pile groups in liquefiable ground in this study, achieving horizontal–vertical bidirectional shaking in centrifuge tests on piles for the first time. The dynamic distribution of forces on piles within the pile groups is analysed, showing the internal piles to be subjected to greater bending moment compared with external piles, the mechanism of which is discussed. The roles of superstructure–pile inertial interaction and soil–pile kinematic interaction in the seismic response of the piles within the pile groups are investigated through cross-correlation analysis between pile bending moment, soil displacement, and structure acceleration time histories and by comparing the test results on pile groups with and without superstructures. Soil–pile kinematic interaction is shown to have a dominant effect on the seismic response of pile groups in liquefiable ground. Comparison of the pile response in two tests with and without vertical input ground motion shows that the vertical ground motion does not significantly influence the pile bending moment in liquefiable ground, as the dynamic vertical total stress increment is mainly carried by the excess pore water pressure. The influence of previous liquefaction history during a sequence of seismic events is also analysed, suggesting that liquefaction history could in certain cases lead to an increase in liquefaction susceptibility of sand and also an increase in dynamic forces on the piles. 相似文献
7.
凸起地形对铁路环境振动的影响分析 总被引：1，自引：0，他引：1
建立了列车作用下路基-凸起地形的二维有限元计算模型,研究了凸起地形宽度、形状、高宽比以及地基土性质对铁路环境振动的影响规律。结果表明,凸起地形减弱了铁路环境振动的地面加速度,明显放大了水平振动位移,对竖向振动位移的影响不明显;随凸起地形宽度、高宽比的增大,水平振动位移的放大效应更为显著;高宽比越大,竖向、水平两个方向地面加速度减小越明显;半圆形、梯形凸起地形对铁路环境振动的影响较为一致,但三角形凸起地形的水平地面加速度在凸起地形顶部出现明显的局部放大,水平振动位移的放大效应较半圆形、梯形地形要明显;地基愈软弱,凸起地形的影响效应越显著。 相似文献
8.
以京沪高速铁路液化土地基加固为背景,利用大型堆叠式剪切变形模型箱,进行了模型比例1:10的CFG桩桩网结构地基加固饱和粉土地基的振动台模型试验,得出各级加载情况下地基路基响应加速度幅值放大系数的分布以及响应加速度幅值放大系数与各级加载加速度幅值的关系,分析了CFG桩桩网结构地基加固饱和粉土地基在地震作用下的加速度传递规律,得到了以下结论：（1）在加载加速度小于0.101g时,地基路基响应加速度幅值基本不放大,且加速度放大系数云图呈现水平状分布;（2）当加载加速度为0.161g时,桩间土的液化引起地基路基的响应加速度幅值放大系数的较大增加;（3）当加载加速度为0.210g时,桩间土液化的同时部分CFG桩发生剪断破坏,从而引起了地基路基的各响应加速度幅值放大系数的增大;（4）当加载加速度为0.324g和0.363g时,地基整体刚度的大幅度减小,在一定程度上降低了桩网结构地基传递振动的能力,从而导致加速度幅值放大系数相对前一级加载时减小;（5）整个加载过程中,粉土层的放大效应显著,而黏土层对加载加速度几乎没有放大作用。 相似文献
9.
Zhenming Wang 《Journal of Earth System Science》2008,117(2):749
Microzonation is an effort to evaluate and map potential hazards found in an area, urban area in particular, that could be induced by strong ground shaking during an earthquake. These hazards include: ground motion amplification, liquefaction, and slope failure. The microzonation maps, depicting ground-motion amplification, liquefaction, and landslide potentials, can be produced if the ground motion on bedrock (input) and the site conditions are known. These maps, in combination with ground-motion hazard maps (on bedrock), can be used to develop a variety of hazard mitigation strategies such as seismic risk assessment, emergency response and preparedness, and land-use planning. However, these maps have certain limitations that result from the nature of regional mapping, data limitations, generalization, and computer modeling. These microzonations show that when strong ground shaking occurs, damage is more likely to occur, or be more severe, in the higher hazard areas. The zones shown on the hazard maps should not serve as a substitute for site-specific evaluations. 相似文献
10.
地震动强度对斜坡加速度动力响应规律的影响 总被引：1，自引：0，他引：1
依托大型振动台试验成果,采用加速度响应峰值PGA及其放大系数相结合的分析方法,系统地探讨了上硬、下软和上软、下硬两种岩性组合结构斜坡模型,分别在正弦波和天然地震波作用下坡面各高程点的水平向和竖直向加速度响应随震动强度增大的变化规律。试验结果分析表明：①在天然波作用下两斜坡模型的水平向和竖直向PGA均随震动强度增大而增大,而放大系数则随震动强度增大到一定程度时,逐渐减小并趋于稳定;②在正弦波作用下两斜坡模型的水平向和竖直向PGA亦随震动强度增大而增大,然而竖直向PGA放大系数随震动强度增大亦有所增大,说明竖直向加速度响应表现出了相对于水平向响应较弱的非线性特征;③在水平向和竖直向地震力作用下加速度响应沿高程表现出的放大效应分别体现在斜坡模型的上段和下段。此外,斜坡模型的加速度响应沿坡面在坡脚、坡中和坡肩等特殊部位出现了多个极值区;④在水平向地震力作用下低频的地震波作用要强于高频地震波,且加速度在上硬、下软岩性组合结构斜坡模型中的响应要强于上软、下硬岩性组合斜坡模型;在竖直向地震力作用下则呈现相反结果。其研究结果对高地震风险山区的防震减灾及灾后重建都具有指导和借鉴意义。 相似文献
11.
为研究近断层脉冲地震动中竖向加速度对砂土场地液化的影响,基于有限元平台OpenSees开发的边界面塑性本构模型,建立了动单剪单元试验模型和饱和砂土三维有限元模型。选取台湾Chi-Chi地震中10条具有速度脉冲特性的地震波,对比分析了水平双向脉冲波与三向脉冲波作用下土柱竖向位移、循环应力比、孔压比及等效循环周数的差异性,继而明确了脉冲地震动中竖向加速度对砂土液化的影响规律。研究表明,三向脉冲地震波中竖向加速度分量对场地永久位移值影响较小,但使永久位移的发展持时明显增大;土柱循环应力比受竖向地震动影响较小,因此分析脉冲地震动对场地剪切特性的影响时,可将三向脉冲地震动简化为水平双向地震动;考虑竖向地震动的三向脉冲地震波引起的孔压比变化幅度较大,孔压消散时间较长;三向脉冲地震波对应的等效循环周数较大,地震动发展持时长,可认为竖向加速度对场地液化有促进作用。 相似文献
12.
Alvarado Patricia Christiansen Rodolfo Gregori Salvador Daniel Saez Mauro 《Natural Hazards》2020,102(3):1011-1031
Natural Hazards - The present study has investigated site amplification effects from the analysis of peak ground accelerations (PGA) and spectral accelerations (SA) of the last two major crustal... 相似文献
13.
Upper bound solutions of bearing capacity of strip footing by pseudo-dynamic approach 总被引：1，自引：0，他引：1
Priyanka Ghosh 《Acta Geotechnica》2008,3(2):115-123
This paper presents the pseudo-dynamic analysis of seismic bearing capacity of a strip footing using upper bound limit analysis.
However, in the literature, the pseudo-static approach was frequently used by several researchers to compute the seismic bearing
capacity factor theoretically, where the real dynamic nature of the earthquake accelerations cannot be considered. Under the
seismic conditions, the values of the unit weight component of bearing capacity factor N
γE are determined for different magnitudes of soil friction angle, soil amplification and seismic acceleration coefficients
both in the horizontal and vertical directions. The results obtained from the present study are shown both graphically as
well as in the tabular form. It is observed that the bearing capacity factor N
γE decreases significantly with the increase in seismic accelerations and amplification. The results are thoroughly compared
with the existing values in the literature and the significance of the present methodology for designing the shallow footing
is discussed. 相似文献
14.
Sergio A. Sepúlveda William Murphy Randall W. Jibson David N. Petley 《Engineering Geology》2005,80(3-4):336-348
The 1994 Northridge earthquake (Mw = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (Mw = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses. 相似文献
15.
Priyanka Ghosh 《Computers and Geotechnics》2009,36(1-2):342-351
This paper presents the pseudo-dynamic analysis to determine the seismic vertical uplift capacity of a horizontal strip anchor using upper bound limit analysis. However, in the literature, the pseudo-static approach was used by few researchers to compute the seismic vertical pullout resistance, where the real dynamic nature of earthquake accelerations cannot be considered. Under the seismic conditions, the values of the unit weight component of uplift factor fγE are determined for different magnitudes of soil friction angle, soil amplification, embedment ratio and seismic acceleration coefficients both in the horizontal and vertical directions. It is observed that the uplift factor fγE decreases significantly with the increase in seismic accelerations and amplification but increases with the increase in embedment ratio. The results are compared with the existing values in the literature and the significance of the present methodology for designing the horizontal strip anchor is discussed. In presence of vertical earthquake acceleration and amplification of vibration, the present values of fγE compare reasonably well with the existing pseudo-static values obtained by modifying the horizontal acceleration coefficient. 相似文献
16.
The study is concerned with the influence of various factors on vibro compaction in calcareous soils, This include effect
of carbonate content, and influence of pore water pressures in sand, settlements during vibrocompaction, vibroaccelerations
during sand column installation compared to earthquake accelerations and finally the liquefaction design based on average
CPT parameters. Previous experiences with calcareous sands and literature review confirm the necessity to apply a correlation
factor for calcareous material to the raw cone penetration resistance CPT values obtained in the field. Because of the very
fragile grains of the Dubai calcareous sands the penetration resistance will be influenced by crushing and grinding. To accommodate
for effect of calcareous sands on measured CPT values, a best fit correlations formula called here “correlation factor” is
developed. A parametric dynamic triaxial liquefaction testing programme has been executed on representative samples with loose
and dense zones. Representative testing parameters for field conditions and earthquake design accelerations have been applied
indicating that ground improvement is necessary. It was observed during the dynamic triaxial tests that the whole soil mass
consisting of dense columns and looser zones in between behaves jointly, and therefore compaction control using an average-CPT
approach is possible. 相似文献
17.
Tatyana Novikova Gerassimos A. Papadopoulos Vassilios Karastathis 《Natural Hazards》2007,40(3):537-552
In the present paper we analyze the effect of local geology on ground motion by means of numerical calculations (numerical
models) using total (TS) and effective stress (ES) methods. These numerical calculations have been applied to the site of
Itea, Corinth Gulf, which was chosen based on liquefaction susceptibility criteria and field inspection. Data from seismic
refraction experiments and cone penetration test N-values as well as selected records of ground motion in nearby areas were
used to construct the input file for the numerical model. By means of␣dynamic analysis such characteristics of ground motion
as acceleration time histories, response spectra, and amplification function were evaluated. A one-dimensional soil amplification
effect was clearly shown. Liquefaction probability at the Itea site was predicted based on the safety factor and the calculation
of the induced settlement at the test site. Results of the TS and ES modeling lead us to conclude: (1) the presence of soft
soil at Itea caused significant amplification (almost 2.5-fold higher magnitude) of the underlying bedrock motion and, therefore,
can contribute to damage; (2) the area of Itea is highly susceptible to liquefaction due to presence of silty sand deposits
at depths between 2.48 m (the position of the water table) and 12 m that demonstrate the rapid growth of the excess pore water
pressure (EPWP) ratio with an increase in peak ground acceleration values. 相似文献
18.
Responses of municipal solid waste (MSW) landfills during earthquakes are gaining worldwide importance due to the devastating nature of earthquake on landfills. Apart from the post-earthquake safety and serviceability issues which pose environmental and public health problems, other important concerns are related to the behavior of closed landfills during and after earthquake. In present study, one dimensional (1-D) equivalent-linear analysis was carried out to model the behaviour of MSW landfills subjected to seismic base accelerations using the DEEPSOIL software. Influence of foundation types, height and stiffness of MSW landfills and seismic base accelerations on the seismic responses in terms of surface accelerations, normalized stresses (i.e., shear stress/effective vertical stress) and spectral amplification are evaluated. The results showed that height and stiffness of landfills, type of foundation and amount of seismic base acceleration and period play important role in evaluating the seismic responses of MSW landfills. Assumption of constant unit weight and shear wave velocity for landfills underestimates maximum horizontal acceleration (MHA), normalized shear stresses and spectral amplification at the top of landfills. Landfill models with smaller heights (up to 40 m high) showed higher amplification ratio for low seismic base accelerations with mean period near to that of soil and landfill resonance for all sites. A complex behavior was observed at higher seismic base accelerations due to non-linear behavior of landfill materials. 相似文献
19.
Loose saturated cohesionless soils are most susceptible to liquefaction, however there are strong historical evidence suggesting that soils containing fines such as silty sands are also prone to liquefaction during earthquakes. The liquefaction of silty sands has been observed in a number of recent case studies. This paper presents the effects of fine silts on liquefaction potential of sandy soil. Tests have been conducted on the vibration table at different accelerations and pore water pressure is measured. During the lab investigation, locally (Roorkee, India) available Solani Sand and Dhanauri Silt have been used. The soil samples have been prepared by varying silt content and the initial relative density. The results of the study performed are used to clarify the effects of non-plastic fines content on the Solani sand. As the silt content increases, the number of cycles required to produce maximum pore water pressure increases. For a particular level of excitation, rate of pore water pressure generation is maximum at critical silt content. It is observed that critical silt content to generate maximum pore water pressure is different for different accelerations. Further, effect of silt content is very much dependent on relative density. 相似文献
20.
This paper highlights the seismic microzonation carried out for a nuclear power plant site. Nuclear power plants are considered to be one of the most important and critical structures designed to withstand all natural disasters. Seismic microzonation is a process of demarcating a region into individual areas having different levels of various seismic hazards. This will help in identifying regions having high seismic hazard which is vital for engineering design and land-use planning. The main objective of this paper is to carry out the seismic microzonation of a nuclear power plant site situated in the east coast of South India, based on the spatial distribution of the hazard index value. The hazard index represents the consolidated effect of all major earthquake hazards and hazard influencing parameters. The present work will provide new directions for assessing the seismic hazards of new power plant sites in the country. Major seismic hazards considered for the evaluation of the hazard index are (1) intensity of ground shaking at bedrock, (2) site amplification, (3) liquefaction potential and (4) the predominant frequency of the earthquake motion at the surface. The intensity of ground shaking in terms of peak horizontal acceleration (PHA) was estimated for the study area using both deterministic and probabilistic approaches with logic tree methodology. The site characterization of the study area has been carried out using the multichannel analysis of surface waves test and available borehole data. One-dimensional ground response analysis was carried out at major locations within the study area for evaluating PHA and spectral accelerations at the ground surface. Based on the standard penetration test data, deterministic as well as probabilistic liquefaction hazard analysis has been carried out for the entire study area. Finally, all the major earthquake hazards estimated above, and other significant parameters representing local geology were integrated using the analytic hierarchy process and hazard index map for the study area was prepared. Maps showing the spatial variation of seismic hazards (intensity of ground shaking, liquefaction potential and predominant frequency) and hazard index are presented in this work. 相似文献