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1.
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   

2.
Recurrence of torsional failure of elevated water tanks in past earthquakes (including 1952 Kern County and recent 1993 Killari earthquakes) has highlighted the importance of this problem. It is established that these structures may have amplified torsion-induced rotation if their torsional-to-lateral natural period ratio τ is close to 1 and amplified displacement of structural elements due to the coupled lateral-torsional vibration if τ is within the critical range 0.7<τ<1.25. The present study aims to estimate the range of variation of τ for usually constructed reinforced concrete elevated water tanks with frame-type stagings for assessing their torsional vulnerability. Closed-form expressions for torsional and lateral stiffness of tank stagings are derived and verified by standard finite element software. These expressions are used for studying the variation of τ for feasible ranges of influencing parameters. It is seen that a very large number of such tanks may have τ within the said critical range. Closed-form expressions for moments and shear forces of columns and beams under torsion and that under lateral force are also derived. It is also seen with the help of these expressions that the frame stagings of these tanks normally designed for seismic lateral force, may yield through formation of plastic hinges simultaneously in all columns instead of in beams if they are subjected to large rotational response for having τ possibly very close to 1. Such a pattern of yielding generally converts the whole system suddenly into a mechanism causing immediate collapse. Therefore, torsional coupling seems to be a potential cause of failure for these structures.  相似文献   

3.
Flow liquefaction and cyclic mobility are two different phenomena that are encountered during strong earthquakes. Flow liquefaction is associated with the contractive behavior of loose granular materials and cyclic mobility is associated with the dilative response of both loose and dense granular materials at low confining stresses. These two types of response pertain to the same material and therefore should be modeled in a consistent manner. Whether a soil in a given state exhibits contractive or dilative behavior is dependent on its dilatancy, d=dvp/dqp. A form of the dilatancy d=d(η,ψ,C) is proposed, where η=q/p is the stress ratio, and ψ and C denote the internal state variables and the intrinsic properties, respectively. It has been shown that such a state-dependent dilatancy is effective in describing both the contractive and dilative behavior. This allows the soil behavior associated with flow liquefaction and cyclic mobility during earthquakes to be modeled in a unified way.  相似文献   

4.
Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p0<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress.  相似文献   

5.
For transient, high frequency, and pulse like excitation of structures in the near field of strong earthquakes, the classical design approach based on relative response spectrum and mode superposition may not be conservative. For such excitations, it is more natural to use wave propagation methods. In this paper (Part I), we review several two-dimensional wave propagation models of buildings and show results for theoretical dispersion curves computed for these models. We also estimate the parameters of these models that would correspond to a seven-story reinforced concrete building in Van Nuys, California. Ambient vibration tests data for this building imply vertical shear wave velocity βz=112 m/s and anisotropy factor βx/βz=0.55 for NS vibrations, and βz=88 m/s and βx/βz=1 for EW vibrations. The velocity of shear waves propagating through the slabs is estimated to be about 2000 m/s. In the companion paper (Part II), we estimate phase velocities of vertically and horizontally propagating waves between seven pairs of recording points in the building using recorded response to four earthquakes.  相似文献   

6.
Semi-empirical procedures for evaluating the liquefaction potential of saturated cohesionless soils during earthquakes are re-examined and revised relations for use in practice are recommended. The stress reduction factor (rd), earthquake magnitude scaling factor for cyclic stress ratios (MSF), overburden correction factor for cyclic stress ratios (Kσ), and the overburden normalization factor for penetration resistances (CN) are discussed and recently modified relations are presented. These modified relations are used in re-evaluations of the SPT and CPT case history databases. Based on these re-evaluations, revised SPT- and CPT-based liquefaction correlations are recommended for use in practice. In addition, shear wave velocity based procedures are briefly discussed.  相似文献   

7.
The aging of the hydrothermal plume over the Endeavour segment of the Juan de Fuca Ridge was estimated by measuring the222Rn3He ratio in the plume as it dispersed. Despite uncertainties in the source function of hydrothermal input, it wa determined that the relative sequence of removal from the plume isH2 > Δc >222Rn>CH4 Mn, whereΔc is a measure of particle concentration and the mean life of222Rn is 5.5 days. H2 is removed from the plume within hours of input while Mn is not removed within the two-week timescale of the radon-helium clock.Entrainment of bottom water within the buoyant plume may introduce additional chemical signatures into the spreading effluent layer over that which would be introduced by hydrothermal discharge alone. This is particularly significant for those chemical species which are not greatly enriched in the vent fluids relative to bottom water concentration and which display a nutrient-like profile in the deep ocean. Thus we found that significant fractions of the Si and226Ra anomalies in the plume were not of hydrothermal origin but were derived from entrained bottom water which has a higher concentration of these elements than ambient water at plume height.  相似文献   

8.
Although the bulk moduli (KT0) of silicate melts have a relatively narrow range of values, the pressure derivatives of the isothermal bulk modulus (KT0′) can assume a broad range of values and have an important influence on the compositional dependence of the melt compressibility at high pressure. Based on the melt density data from sink/float experiments at high pressures in the literature, we calculate KT0′ using an isothermal equation of state (EOS) (e.g., Birch–Murnaghan EOS and Vinet EOS) with the previously determined values of room-pressure density (ρ0) and room-pressure bulk modulus (KT0). The results show that best estimates of KT0′ vary considerably from ~ 3 to ~ 7 for different compositions. KT0′ is nearly independent of Mg # (molar Mg/(Mg + Fe)), but decreases with SiO2 content. Hydrous melts have anomalously small KT0′ leading to a high degree of compression at high pressures. For anhydrous melts, KT0′ is ~ 7 for peridotitic melts, ~ 6 for picritic melts, ~ 5 for komatiitic melts, and ~ 4 for basaltic melts.  相似文献   

9.
Partial reflection differential absorption and differential phase observations have been used to systematically study collision frequencies (ν) in D-region of the lower ionosphere. The observations made with the large MF radar located at Buckland Park (35°S, 138°E) near Adelaide in the period September 1996–December 2000 show ν values larger than predicted by previously used models. The new estimates are compared with values calculated using new collision frequency momentum cross-sections for N2(σ) measured in the laboratory. The two types of measurements are found to be in good agreement, with a moderate seasonal variation of ν at a constant height. No change due to solar cycle variations is found.  相似文献   

10.
The liquefaction database describing the response of the Christchurch area in the 2010–2011 Canterbury Earthquake Sequence (CES) provides a unique basis for evaluating the regional application of various liquefaction analysis procedures, from liquefaction triggering analyses through to liquefaction vulnerability parameters. This database was used to compare the Robertson and Wride [17], Moss et al. [15] and Idriss and Boulanger [7] liquefaction triggering procedures as well as evaluate the impact of the 2014 versus 2008 Cone Penetration Test (CPT)-based liquefaction triggering procedure by Idriss and Boulanger on four liquefaction vulnerability parameters (SV1D, LPI, LPIISH and LSN), the correlation of those parameters with observed liquefaction-induced damage patterns in the CES, and the mapping of expected damage levels for 25, 100 and 500 year return period ground motions in Christchurch. The effects on SV1D, LPI, LPIISH and LSN were small relative to other sources of variability for the majority of the affected areas, particularly where liquefaction was clearly severe or clearly not. Nonetheless, considering the separation of the land damage populations as well as consistency between the events, the the IB-2008 liquefaction triggering procedures appears to give a slightly better fit to the mapped liquefaction-induced land damage for the regional prediction of liquefaction vulnerability for the Christchurch soils. The Boulanger and Idriss [1] triggering procedure produces improved agreement between the liquefaction vulnerability parameters and observations of damage for: areas south of the Central Business District (CBD) where there tends to be higher soil Fines Content (FC), and localized areas that experienced liquefaction during the smaller Magnitude (M) earthquake events. Implementation of the 2014 liquefaction triggering procedure for mapping of expected liquefaction-induced damage at 25, 100 and 500 year return period ground motions is shown to require use of representative Peak Ground Acceleration (PGA)-M values consistent with the de-aggregation of the seismic hazard. Use of equivalent magnitude-scaled PGA-M7.5 pairs, where the equivalency relates to previously published MSF relationships, with the 2014 liquefaction triggering procedure is shown to be unconservative for certain situations.  相似文献   

11.
Three methods that follow the general format of the Seed-Idriss simplified procedure for evaluating liquefaction resistance of soils are compared in this paper. They are compared by constructing relationships between penetration resistance and small-strain shear–wave velocity (VS) implied from cyclic resistance ratio (CRR) curves for the three methods, and by plotting penetration-VS data pairs. The penetration-VS data pairs are from 43 Holocene-age sand layers in California, South Carolina, Canada, and Japan. It is shown that the VS-based CRR curve is more conservative than CRR curves based on the Standard Penetration Test (SPT) and Cone Penetration Test (CPT), for the compiled Holocene data. This result agrees with the findings of a recent probability study where the SPT-, CPT-, and VS-based CRR curves were characterized as curves with average probability of liquefaction of 31, 50, and 26%, respectively. New SPT- and CPT-based CRR equations are proposed that provide more consistent assessments of liquefaction potential for the Holocene sand layers considered.  相似文献   

12.
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.  相似文献   

13.
WIND observations of coherent electrostatic waves in the solar wind   总被引：4，自引：0，他引：4  
The time domain sampler (TDS) experiment on WIND measures electric and magnetic wave forms with a sampling rate which reaches 120 000 points per second. We analyse here observations made in the solar wind near the Lagrange point L1. In the range of frequencies above the proton plasma frequency fpi and smaller than or of the order of the electron plasma frequency fpe, TDS observed three kinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waves with frequencies f ≃ fpe, coherent wave packets with frequencies in the ion acoustic range fpi ≥ f ≥ fpe, and more or less isolated non-sinusoidal spikes lasting less than 1 ms. We confirm that the observed frequency of the low frequency (LF) ion acoustic wave packets is dominated by the Doppler effect: the wavelengths are short, 10 to 50 electron Debye lengths λD. The electric field in the isolated electrostatic structures (IES) and in the LF wave packets is more or less aligned with the solar wind magnetic field. Across the IES, which have a spatial width of the order of ≃25D, there is a small but finite electric potential drop, implying an average electric field generally directed away from the Sun. The IES wave forms, which have not been previously reported in the solar wind, are similar, although with a smaller amplitude, to the weak double layers observed in the auroral regions, and to the electrostatic solitary waves observed in other regions in the magnetosphere. We have also studied the solar wind conditions which favour the occurrence of the three kinds of waves: all these e.s. waves are observed more or less continuously in the whole solar wind (except in the densest regions where a parasite prevents the TDS observations). The type (wave packet or IES) of the observed LF waves is mainly determined by the proton temperature and by the direction of the magnetic field, which themselves depend on the latitude of WIND with respect to the heliospheric current sheet.  相似文献   

14.
Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio （ec）eq and equivalent interfine void ratio （ef）eq, proposed in a companion paper （Thevanayagam, 2007） as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio （e）, liquefaction resistance of silty sand decreases with an increase in fines content （Cv） up to a threshold value （Crth）. This is due to a reduction in intergrain contact density between the coarse grains. Beyond Crth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a fttrther increase in silt content. Beyond a limiting fines content （CrL）, the liquefaction resistance is controlled by interfine contacts only. When Cr〈Crth, at the same （e）eq, the liquefaction resistance of silty sand is comparable to that of the host clean sand at a void ratio equal to （ec）eq. When CF〉CFth, at the same （ef）eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to （ef）eq.  相似文献   

15.
The relationship between the auroral electrojet indices (AE) and the ring current magnetic field (DR) was investigated by observations obtained during the magnetic storm on 1–3 April 1973. During the storm main phase the DR development is accompanied by a shift of the auroral electrojets toward the equator. As a result, the standard AE indices calculated on the basis of data from auroral observatories was substantially lower than the real values (AE’). To determine AE’ during the course of a storm main phase data from subauroral magnetic observatories should be used. It is shown that the intensity of the indices (AE’) which take into account the shift of the electrojets is increased substantially relative to the standard indices during the storm main phase. AE’ values are closely correlated with geoeffective solar wind parameters. A high correlation was obtained between AE’ and the energy flux into the ring current during the storm main phase. Analysis of magnetic field variations during intervals with intense southward IMF components demonstrates a decrease of the saturation effect of auroral electrojet currents if subauroral stations magnetic field variations are taken into account. This applies both to case studies and statistical data. The dynamics of the electrojets in connection with the development of the ring current and of magnetospheric substorms can be described by the presence (absence) of saturation for minimum (maximum) AE index values during a 1-h interval. The ring current magnetic field asymmetry (ASY) was calculated as the difference between the maximum and minimum field values along a parallel of latitude at low latitudes. The ASY value is closely correlated with geoeffective solar wind parameters and simultaneously is a more sensitive indicator of IMF Bz variations than the symmetric ring current. ASY increases (decreases) faster during the main phase (the recovery phase) than DR. The magnetic field decay at low latitudes in the recovery phase occurs faster in the afternoon sector than at dusk.  相似文献   

16.
Effects of inertial and kinematic forces on pile stresses are studied based on large shaking table tests on pile-structure models with a foundation embedded in dry and liquefiable sand deposits. The test results show that, if the natural period of the superstructure, Tb, is less than that of the ground, Tg, the ground displacement tends to be in phase with the inertial force from the superstructure, increasing the shear force transmitted to the pile. In contrast, if Tb is greater than Tg, the ground displacement tends to be out of phase with the inertial force, restraining the pile stress from increasing. With the effects of earth pressures on the embedded foundation and pile incorporated in, pseudo-static analysis is conducted to estimate maximum moment distribution in pile. It is assumed that the maximum moment is equal to the sum of the two stresses caused by the inertial and kinematic effects if Tb<Tg or the square root of the sum of the squares of the two if Tb>Tg. The estimated pile stresses are in good agreement with the observed ones regardless of the occurrence of soil liquefaction.  相似文献   

17.
δ87Sr values and Ca/Sr ratios were employed to quantify solute inputs from atmospheric and lithogenic sources to a catchment in NW Germany. The aquifer consists primarily of unconsolidated Pleistocene eolian and fluviatile deposits predominated by >90% quartz sand. Accessory minerals include feldspar, glauconite, and mica, as well as disperse calcium carbonate in deeper levels. Decalcification of near-surface sediment induces groundwater pH values up to 4.4 that lead to enhanced silicate weathering. Consequently, low mineralized Ca–Na–Cl- and Ca–Cl-groundwater types are common in shallow depths, while in deeper located calcareous sediment Ca–HCO3-type groundwater prevails. δ87Sr values and Ca/Sr ratios of the dissolved pool range from 7.3 to −2.6 and 88 to 493, respectively. Positive δ87Sr values and low Ca/Sr ratios indicate enhanced feldspar dissolution in shallow depths of less than 20 m below soil surface (BSS), while equilibrium with calcite governs negative δ87Sr values and elevated Ca/Sr ratios in deep groundwater (>30 m BSS). Both positive and negative δ87Sr values are evolved in intermediate depths (20–30 m BSS). For groundwater that is undersaturated with respect to calcite, atmospheric supplies range from 4% to 20%, while feldspar-weathering accounts for 8–26% and calcium carbonate for 62–90% of dissolved Sr2+. In contrast, more than 95% of Sr2+ is derived by calcium carbonate and less than 5% by feldspar dissolution in Ca–HCO3-type groundwater. The surprisingly high content of carbonate-derived Sr2+ in groundwater of the decalcified portion of the aquifer may account for considerable contributions from Ca-containing fertilizers. Complementary tritium analyses show that equilibrium with calcite is restricted to old groundwater sources.  相似文献   

18.
According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of G max (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (e min). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests. Foundation item: State Natural Science Foundation (59678020) and Natural Science Foundation of Zhejiang Province (RC9609).  相似文献   

19.
This paper presents a simple dynamical model for melting and trace element distribution in the Hawaiian mantle plume. I model the plume as a partially molten stagnation point flow against the oceanic lithosphere, and obtain solutions for the temperature, melt migration rate, and trace element concentration within it. Trace element concentrations in the melt exceed simple batch melting predictions by up to 70%. The magnitude of this effect depends strongly on the solid-melt partition coefficientK. Trace elements with differentK therefore experience a “dynamical fractionation” within the plume, and incompatible trace element ratios such asLa/Ce always exceed the batch melting predictions. I suggest a simple model for plume-lithosphere interaction in which melts from these two sources mix in proportions determined by thermodynamic constraints. The model can explain the composition of basalts from Haleakala if the degree of melting of the lithosphereF1 decreases with time from roughly 10% for tholeiites to 2% for alkalic basalts. These values are considerably higher than previous estimates ofF1 < 1%, and imply correspondingly smaller and more realistic values ( 10 km) for the thickness of the melted part of the lithosphere. Partial melting of additional depleted sources such as the asthenosphere is therefore not required by the Haleakala data. Estimates ofF1 are highly sensitive to the values chosen for the partition coefficients, however, and should therefore be interpreted with caution.  相似文献   

20.
The gravimetric parameters of the gravity pole tide are the amplitude factor δ, which is the ratio of gravity variations induced by polar motion for a real Earth to variations computed for a rigid one, and the phase difference κ between the observed and the rigid gravity pole tide. They can be estimated from the records of superconducting gravimeters (SGs). However, they are affected by the loading effect of the ocean pole tide. Recent results from TOPEX/Poseidon (TP) altimeter confirm that the ocean pole tide has a self-consistent equilibrium response. Accordingly, we calculate the gravity loading effects as well as their influence on the gravimetric parameters of gravity pole tide at all the 26 SG stations in the world on the assumption of a self-consistent equilibrium ocean pole tide model. The gravity loading effect is evaluated between 1 January 1997 and 31 December 2006. Numerical results show that the amplitude of the gravity loading effect reaches 10−9 m s−2, which is larger than the accuracy (10−10 m s−2) of a SG. The gravimetric factor δ is 1% larger at all SG stations. Then, the contribution of a self-consistent ocean pole tide to the pole tide gravimetric parameters cannot be ignored as it exceeds the current accuracy of the estimation of the pole tide gravity factors. For the nine stations studied in Ducarme et al. [Ducarme, B., Venedikov, A.P., Arnoso, J., et al., 2006. Global analysis of the GGP superconducting gravimeters network for the estimation of the pole tide gravimetric amplitude factor. J. Geodyn. 41, 334–344.], the mean of the modeled tidal factors δm = 1.1813 agrees very well with the result of a global analysis δCH = 1.1816 ± 0.0047 in that paper. On the other hand, the modeled phase difference κm varies from −0.273° to 0.351°. Comparing to the two main periods of the gravity pole tide, annual period and Chandler period, κm is too small to be considered. Therefore, The computed time difference κL induced by a self-consistent ocean pole tide produces a negligible effect on κm. It confirms the results of Ducarme et al., 2006, where no convincing time difference was found in the SG records.  相似文献   

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