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1.
We analyse aftershocks of the 26 January 2001 Bhuj earthquake, India, that were recorded for 10 weeks following the mainshock. We calculate undrained or instantaneous pore pressure and change in Coulomb stress due to the earthquake and their poroelastic relaxation in the following 10 weeks period. Almost all aftershocks occurred in the region of coseismic dilatation. In the subsequent period, pore pressure increased through relaxation in the dilatation region which further modified coseismic Coulomb stress. Maximum increase in pore pressure is estimated to be about 0.7 MPa in 60 days time following the mainshock. Correlation between the zones of increased pore pressure and postseismic Coulomb stress with that of aftershocks, suggests a definite role of fluid diffusion in their delayed triggering. 相似文献
2.
The Bhuj, India, earthquake of 26 January 2001, Ms 7.9, caused dams built on alluvium to sustain damage ranging from cosmetic to severe. Major damage was caused almost entirely by soil liquefaction in the alluvium. The critical factor was the level of earthquake ground motion.
The Bhuj earthquake showed that peak horizontal accelerations (PHAs)≤0.2 g were generally safe. PHAs>0.2 g were hazardous, when unconsolidated granular foundation soils were water saturated. N values of <20 are indicative of susceptibility to soil liquefaction. The Bhuj experience showed that alluvial foundation soils, subject to a PHA>0.2 g, must be evaluated over the full area beneath a new dam and all soils deemed susceptible to liquefaction must be either removed or treated. For remediating an old dam, reliable options are removal and replacement of liquefiable alluvium beneath upstream and downstream portions of the dam, combined with building berms designed to provide stability for the dam should there be a strength loss in soils beneath the dam. 相似文献
3.
Analysis of earth dams affected by the 2001 Bhuj Earthquake 总被引：3，自引：0，他引：3
An earthquake of magnitude of 7.6 (Mw 7.6) occurred in Bhuj, India on January 26, 2001. This event inflicted damages of varying extents to a large number of small to moderate size multi-zone earth dams in the vicinity of the epicenter. Some of the distress was due to the liquefaction of saturated alluvium in foundation. Liquefaction was relatively localized for the majority of these dams because the earthquake struck in the middle of a prolonged dry season when the reservoirs behind these dams were nearly empty and shallow alluvium soils underneath the downstream portions of the dams were partly dry. Otherwise, liquefaction of foundation soils would have been more extensive and damage to these dams more significant. Six such dams have been examined in this paper. Four of these facilities, Chang, Shivlakha, Suvi, and Tapar were within the 50 km of epicenter region. These dams underwent free-field ground motion with peak ground accelerations between 0.28g to 0.52g. Of these Chang Dam underwent severe slumping, whereas Shivlakha, Suvi, and Tapar Dams were affected severely especially over the upstream sections. Fatehgadh Dam and Kaswati Dam were affected relatively less severely. Foundation conditions underneath these dams were first examined for assessing liquefaction potential. A limited amount of subsurface information available from investigations undertaken prior to the earthquake indicates that, although the foundation soils within the top 2.0 to 2.5 m underneath these dams were susceptible to liquefaction, Bhuj Earthquake did not trigger liquefaction because of lack of saturation of these layers underneath the downstream portions of these dams. These dams were then analyzed using a simple sliding block procedure using appropriate estimates of undrained soil strength parameters. The results of this analysis for these structures were found to be in general agreement with the observed deformation patterns. 相似文献
4.
The extent of damage and affected areas in Bhuj earthquake (26th January 2001) has provided a unique opportunity to evaluate
a wide range of geotechnical issues. A large area in the Rann of Kutch experienced massive liquefaction resulting in ground
subsidence and lateral flow. A large number of dams in the Kutch district suffered moderate to severe damages. Many buildings
were damaged and collapsed in the city of Ahmedabad situated on the bank of the Sabarmati River. In this paper, the ground
response studies at a site in Ahmedabad City along with observations of geotechnical aspects such as ground cracking, sand
volcanoes and liquefaction of soils associated with the Bhuj earthquake are discussed. The ground response studies indicate
that the varying degree of damage to multistorey buildings in Ahmedabad in the close proximity of Sabarmati river area was
essentially due to the collapse and undesirable settlement of partly saturated silty sand deposits. Large settlements are
attributed to amplification of the ground and the near resonance condition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
6.
小坡度海底土层地震液化诱发滑移分析方法 总被引：1，自引：0，他引：1
地震可使海底砂质、粉质土层液化并导致上部土层的滑移。基于有效应力有限元动力分析方法和Newmark刚性滑块理论,提出了一种计算海底小坡度（≤5o）土层地震液化引起侧向滑移的简化方法。该方法将波浪荷载简化为海底恒定的上覆压力和初始孔压,忽略了海水粘性对海底土层地震反应的影响,利用改进的Seed孔压模型进行动力分析和液化判别,用Newmark滑块理论计算了土层侧向滑移。通过算例和对比分析,研究了海水深度和土层坡度对侧向滑移的影响,表明该方法的有效性,可为近海工程场地地震地质灾害评价提供参考数据。 相似文献
7.
海港工程中防波堤地震残余变形的预测以及震损机制的分析是较复杂的问题。采用定义在应变空间中考虑土体动主应力轴方向偏转影响的多重剪切机构塑性模型,分别从砂性土的黏粒含量和标贯击数2个主要影响因素对防波堤地震变形的变化机制进行了有效应力分析,得出防波堤较大的残余变形是由于地震作用下土体中孔隙水压力的升高致使土体软化而产生的。然后,采用液化度单一指标从物理本质上来间接表征防波堤的残余变形,得到防波堤残余变形与液化度之间的函数预测关系,预测值与震害调查值以及数值分析值基本相符,表明所得液化度预测公式具有一定的可靠性。残余变形的液化度预测法可为类似防波堤地震灾害设计与评价提供参考依据。 相似文献
8.
A. Janalizadeh Choobbasti Mohammad Javad Vahdatirad M. Torabi S. Firouzian A. Barari 《Arabian Journal of Geosciences》2012,5(4):545-554
Paying special attention to geotechnical hazards such as liquefaction in huge civil projects like urban railways especially in susceptible regions to liquefaction is of great importance. A number of approaches to evaluate the potential for initiation of liquefaction, such as Seed and Idriss simplified method have been developed over the years. Although simplified methods are available in calculating the liquefaction potential of a soil deposit and shear stresses induced at any point in the ground due to earthquake loading, these methods cannot be applied to all earthquakes with the same accuracy, also they lack the potential to predict the pore pressure developed in the soil. Therefore, it is necessary to carry out a ground response analysis to obtain pore pressures and shear stresses in the soil due to earthquake loading. Using soil historical, geological and compositional criteria, a zone of the corridor of Tabriz urban railway line 2 susceptible to liquefaction was recognized. Then, using numerical analysis and cyclic stress method using QUAKE/W finite element code, soil liquefaction potential in susceptible zone was evaluated based on design earthquake. 相似文献
9.
D. Ramakrishnan K. K. Mohanty S. R. Nayak R. Vinu Chandran 《Geotechnical and Geological Engineering》2006,24(6):1581-1602
The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000
lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused
significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a
part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the
areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral,
spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index
(LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum
are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after
the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic
Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values
are in agreement with liquefaction susceptible criteria and observed LSI (R
2 = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the
liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified
into three susceptibility classes. 相似文献
10.
常剪应力路径下含气砂土的三轴试验 总被引：1，自引：0，他引：1
天然气水合物完全分解时,产生的气体使得能源土孔隙压力急速增加,有效应力减小,进而引起土体液化破坏。此时深海能源土斜坡的应力状态与静力液化失稳过程可简化为含气土在常剪应力排水(或不排水)应力路径下的破坏问题。以此为背景,提出了制备含气砂土试样的改进充气管法,并开展了含气砂土的常剪应力路径三轴试验。22组试验结果表明:同一孔隙比的含气密砂在不同围压与常剪应力下具有相同的失稳线;含气砂土试样失稳时的应力比和体变均随初始相对密实度的增大而增大;含气密砂在常剪应力路径下饱和度对失稳特征影响的规律性在排水与不排水条件下均不明显,但在不排水条件下含气砂土的孔压(或体变)对变形的敏感性降低;含气密砂在常剪应力路径到达失稳点之后,排水条件下是瞬变的液化鼓胀破坏,不排水条件下是渐变的剪切破坏。 相似文献
11.
Widodo Lilik E. Prassetyo Simon H. Simangunsong Ganda M. Iskandar Irwan 《Hydrogeology Journal》2022,30(6):1877-1898
Soil liquefaction on 28 September 2018 in Palu, Indonesia, included one of the largest soil movements ever, where objects on the ground surface moved hundreds of meters away and settlements sank into the mud. Some preliminary studies show that in addition to a strong earthquake, there are strong indications that a confined aquifer in the Palu valley worsened the liquefaction. The role of the confined aquifer can be recognized early on from one of various signs, namely the presence of massive surface inundations suspected due to groundwater expulsion which is thought to originate mostly from the confined aquifer. This paper describes the mechanism of the soil liquefaction in Palu from the perspective of earthquake hydrogeology, focusing on the groundwater expelled from an unconfined aquifer and especially from the underlying confined aquifer through hydraulic inter-connection between the two, which is possible due to simultaneous interaction of excess pore pressure dissipation and enhanced permeability driven by an earthquake in the near field. If this hypothesis proves to be strong, there are implications for engineering practices because the evaluation of potential soil liquefaction carried out currently in the geotechnical engineering field generally only involves the role of shallow groundwater and/or the unconfined aquifer and the role of soil layers not deeper than 30 m from the ground surface. It may be necessary to complement current evaluation practice with an evaluation of the deep groundwater response to earthquakes, especially if the deep groundwater is artesian and productive, with a relatively thin confining layer.
相似文献12.
M. G. Thakkar Bhanu Goyal D. M. Maurya L. S. Chamyal 《Journal of the Geological Society of India》2012,79(4):367-375
The liquefaction attributes and crater geometry related to 2001 Bhuj earthquake has been reconstructed by trenching along large known craters formed near Umedpar in Kachchh. The study characterises the liquefied sediments in a large reactivated crater and distinguishes it from a non-reactivated crater located nearby. These characteristics can help in the interpretation of large paleocraters formed as a result of earthquake induced liquefaction. 相似文献
13.
Experimental Study of Undrained Shear Strength of Silty Sand: Effect of Fines and Gradation 总被引：2，自引：1，他引：1
Mostefa Belkhatir Ahmed Arab Noureddine Della Tom Schanz 《Geotechnical and Geological Engineering》2012,30(5):1103-1118
Two strong earthquakes occurred in the region of Chlef (north western part of Algeria) during the last century. From the geological context, there were several great masses of sandy soil ejections on to the ground surface level and severe damages to civil and hydraulic structures. These damages were due to the soil liquefaction phenomenon. The objective of this laboratory investigation is to study the effect of low plastic fines and gradation characteristics on the undrained shear strength (liquefaction resistance) response of sand-silt mixture samples. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with different fines content ranging from 0 to 50?% at two initial relative densities (Dr?=?20 and 91?%). The initial confining pressure was kept at 100?kPa. The evaluation of the data indicates that the undrained shear strength at the peak (qpeak) can be correlated to the undrained residual strength (Sus), the excess pore pressure (Δu), the fines content (Fc) and the intergranular void ratio (es). The test results indicate also that the undrained shear strength at the peak decreases with the increment of the coefficient of uniformity and fines content as well as with the decrement of the mean grain size in the range of 0–50?% fines content for both relative densities (Dr?=?20 and 91?%). 相似文献
14.
Postseismic relaxation due to Bhuj earthquake on January 26, 2001: possible mechanisms and processes
C. D. Reddy P. S. Sunil Roland B��rgmann D. V. Chandrasekhar Teruyuki Kato 《Natural Hazards》2013,65(2):1119-1134
Earthquakes cause static stress perturbations in the nearby crust and mantle. Obeying rheological laws, this stress relaxes in a time frame of months to years with the spatial extent of few km to hundreds of km. While postseismic relaxation associated with major inter-plate earthquakes is well established, there have been few opportunities to explore its occurrence following intraplate earthquakes. The M w 7.6 Bhuj earthquake on January 26, 2001 in western India is considered to be an intraplate event and provided a unique opportunity to examine post-earthquake relaxation processes sufficiently away from plate boundaries. To study the characteristics of transient postseismic deformation, six Global Positioning System campaigns were made at 14 sites. The postseismic transients were delineated after removing plate motions from the position time series. Postseismic deformation has been observed at all the sites in the study area. During 2001?C2007, the site closest to the epicenter exhibited postseismic deformation of about 30 and 25?mm in the north and east components, respectively. Time series of the NS and EW components of the postseismic transients can be fitted to both logarithmic and exponential functions. Close to the epicenter, the logarithmic function fits well to the initial transient, and an exponential function fits well to the later phases. The remaining sites (located east and west of the epicentral region) exhibited significantly diminished north?Csouth relaxation. Rapidly decaying afterslip and poroelastic mechanisms seem to be responsible for postseismic relaxation in the vicinity of epicenter during the initial period subsequent to the Bhuj earthquake. Postseismic relaxation by viscoelastic flow below the seismogenic zone seems to affect displacements across the entire Bhuj region. This paper presents the characteristics of postseismic transients and deformation processes in the scenario of the highly heterogeneous crust in the Bhuj region. 相似文献
15.
3-D seismic structure of the Kachchh,Gujarat, and its implications for the earthquake hazard mitigation 总被引：3，自引：2，他引：1
Several pieces of studies on the January 26, 2001, Bhuj earthquake (Mw 7.6) revealed that the mainshock was triggered on the
hidden unmapped fault in the western part of Indian stable continental region that caused a huge loss in the entire Kachchh
rift basin of Gujarat, India. Occurrences of infrequent earthquakes of Mw 7.6 due to existence of hidden and unmapped faults
on the surface have become one of the key issues for geoscientific research, which need to be addressed for evolving plausible
earthquake hazard mitigation model. In this study, we have carried out a detailed autopsy of the 2001 Bhuj earthquake source
zone by applying three-dimensional (3-D) local earthquake tomography (LET) method to a completely new data set consisting
of 576 local earthquakes recorded between November 2006 and April 2009 by a seismic network consisting of 22 numbers of three-component
broadband digital seismograph stations. In the present study, a total of 7560 arrival times of P-wave (3820) and S-wave (3740)
recorded at least 4 seismograph stations were inverted to assimilate 3-D P-wave velocity (Vp), S-wave velocity (Vs), and Poisson’s
ratio (σ) structures beneath the 2001 Bhuj earthquake source zone for reliable interpretation of the imaged anomalies and
its bearing on earthquake hazard of the region. The source zone is located near the triple junction formed by juxtapositions
of three Indian, Arabian, and Iranian tectonic plates that might have facilitated the process of brittle failure at a depth
of 25 km beneath the KRB, Gujarat, which caused a gigantic loss to both property and persons of the region. There may be several
hidden seismogenic faults around the epicentral zone of the 2001 Bhuj earthquake in the area, which are detectable using 3-D
tomography to minimize earthquake hazard for a region. We infer that the use of detailed 3-D seismic tomography may offer
potential information on hidden and unmapped faults beneath the plate interior to unravel the genesis of such big damaging
earthquakes. This study may help in evolving a comprehensive earthquake risk mitigation model for regions of analogous geotectonic
settings, elsewhere in the world. 相似文献
16.
The 2010–2011 Canterbury earthquake sequence in New Zealand exposed loess-mantled slopes in the area to very high levels of seismic excitation (locally measured as >2?g). Few loess slopes showed permanent local downslope deformation, and most of these showed only limited accumulated displacement. A series of innovative dynamic back-pressured shear box tests were undertaken on intact and remoulded loess samples collected from one of the recently active slopes replicating field conditions under different simplified horizontal seismic excitations. During each test, the strength reduction and excess pore water pressures generated were measured as the sample failed. Test results suggest that although dynamic liquefaction could have occurred, a key factor was likely to have been that the loess was largely unsaturated at the times of the large earthquake events. The failure of intact loess samples in the tests was complex and variable due to the highly variable geotechnical characteristics of the material. Some loess samples failed rapidly as a result of dynamic liquefaction as seismic excitation generated an increase in pore water pressure, triggering rapid loss of strength and, thus, of shear resistance. Following initial failure, pore pressure dissipated with continued seismic excitation and the sample consolidated, resulting in partial shear strength recovery. Once excess pore water pressures had dissipated, deformation continued in a critical effective stress state with no further change in volume. Remoulded and weaker samples, however, did not liquefy and instead immediately reduced in volume with an accompanying slower and more sustained increase in pore pressure as the sample consolidated. Thereafter, excess pressures dissipated and deformation continued at a critical state. The complex behaviour explained why, despite exceptionally strong ground shaking, there was only limited displacement and lack of run-out: dynamic liquefaction was unlikely to occur in the freely draining slopes. Dynamic liquefaction, however, remained a plausible mechanism to explain loess failure in some of the low-angle toe slopes, where a permanent water table was present in the loess. 相似文献
17.
液化自由场地震响应大型振动台模型试验分析 总被引：1，自引：0，他引：1
开展了含上部黏土层、饱和砂土层、密实砂土层的可液化自由场地在水平地震动激励下的大型振动台模型试验研究,分析了地震动激励时饱和砂土液化后场地加速度、位移、孔压比时空响应等动力响应。试验结果表明：在小震激励时,场地动力反应较小,加速度反应自下而上不断放大,各深度处孔压比均较小,模型地基整体处于弹性反应阶段;0.3g汶川地震卧龙台地震记录输入时,孔压积累迅速,可液化土体最上部土层孔压比达到1,饱和土体液化,模型地基表现出明显的非线性反应特征,加速度反应在饱和砂土层中未有明显放大,土体卓越周期对应的反应加速度自下而上有不断增大趋势。该研究是土-群桩-上部结构体系大型振动台系列试验中可液化自由场动力反应部分,可供今后做对比分析和验证数值模拟参考。 相似文献
18.
For numerical studies of geotechnical structures under earthquake loading, aiming to examine a possible failure due to liquefaction, using a sophisticated constitutive model for the soil is indispensable. Such a model must adequately describe the material response to a cyclic loading under constant volume (undrained) conditions, amongst others the relaxation of effective stress (pore pressure accumulation) or the effective stress loops repeatedly passed through after a sufficiently large number of cycles (cyclic mobility, stress attractors). The soil behaviour under undrained cyclic loading is manifold, depending on the initial conditions (e.g. density, fabric, effective mean pressure, stress ratio) and the load characteristics (e.g. amplitude of the cycles, application of stress or strain cycles). In order to develop, calibrate and verify a constitutive model with focus to undrained cyclic loading, the data from high-quality laboratory tests comprising a variety of initial conditions and load characteristics are necessary. The purpose of these two companion papers was to provide such database collected for a fine sand. The database consists of numerous undrained cyclic triaxial tests with stress or strain cycles applied to samples consolidated isotropically or anisotropically. Monotonic triaxial tests with drained or undrained conditions have also been performed. Furthermore, drained triaxial, oedometric or isotropic compression tests with several un- and reloading cycles are presented. Part I concentrates on the triaxial tests with monotonic loading or stress cycles. All test data presented herein will be available from the homepage of the first author. As an example of the examination of an existing constitutive model, the experimental data are compared to element test simulations using hypoplasticity with intergranular strain. 相似文献
19.
The paper provides a new analysis procedure for the assessment of the lateral response of isolated piles/drilled shafts in saturated sands as liquefaction and lateral soil spread develop in response to dynamic loading such as that generated by the earthquake shaking. The presented method accounts for: (1) the development of full liquefaction in the free-field soil that could trigger the lateral spread of the overlying crust layer; (2) the driving force exerted by the crust layer based on the interaction between the pile and the upper non-liquefied soil (crust) layer; and (3) the variation of the excess pore water pressure (i.e. post-liquefaction soil strength) in the near-field soil with the progressive pile deflection under lateral soil spread driving force. A constitutive model for fully liquefied sands under monotonic loading and undrained conditions is developed in order to predict the zone of post-liquefaction zero-strength of liquefied sand before it rebounds with the increasing soil strain in the near-field. The analytical and empirical concepts employed in the Strain Wedge (SW) model allow the modeling of such a sophisticated phenomenon of lateral soil spread that could accompany or follow the occurrence of seismic events without using modifying parameters or shape corrections to account for soil liquefaction. 相似文献
20.
通过固结不排水三轴压缩试验,分析了围压、固结比和干密度等因素对饱和粉土静态液化特性的影响。试验结果表明,在干密度较小时,饱和粉土的偏应力-应变曲线呈现明显的硬变软化型,随轴向应变增大超静孔隙水压力增加、有效应力减小而发生静态液化,当干密度达到1.58 g· cm-3时,饱和粉土的偏应力-应变曲线表现出硬变硬化现象,超静孔隙水压力为负值或接近0,饱和粉土不再发生静态液化,即饱和粉土存在静态液化的干密度临界值;其他条件不变,随着围压、固结比或干密度的增大,偏应力峰值和残余强度均增大,静态液化势降低;根据有效应力路径建立了流滑面以作为饱和粉土稳定区与非稳定区的分界面。 相似文献