This paper represents a predictive model for the earthquake-induced displacement of slopes using a coupled stick-slip-rotation approach recently proposed by the authors in a preceding paper. A ...collection of 1363 strong motion records associated with 25 worldwide earthquakes was used to generate the model on the basis of results of sliding block analyses. The proposed model predicts sliding displacement in terms of yield acceleration coefficient ratio (ky/kmax), period ratio (Ts/Tm), and slip length (L). The regression analysis indicates that dividing the results into the smaller intervals of period ratio can provide a noticeable higher degree of accuracy. Probable bias of the residuals versus the input variables is examined in detail. Predictions of the developed equation are compared with some available sliding block equations which similarly assumed a flexible sliding mass. The proposed model can be simply used to estimate landslide hazard in seismic prone regions.
•We presented a predictive model for seismic sliding displacement of earth slopes.•The model was developed based on the results of coupled stick-slip-rotation analyses.•Numerous earthquake records with a variety of effective parameters were incorporated.•Comparison was made with available models recently proposed for sliding displacement.
AbstractDownward movement of sliding soil mass in earthquake-induced earth slopes may gradually improve the system's stability. Hence, significant change in critical (or yield) acceleration of the ...slope is anticipated. The existing simplified coupled procedures, however, assume a constant critical acceleration in stick-slip sliding analysis. Fully coupled sliding block analyses with continuously increased critical acceleration were conducted to estimate earthquake-induced permanent displacement of earth slopes. The sliding mass was assumed as a flexible chain moving along the planes with gradually gentler inclinations. The measured data of a slope failure test in a shaking table were used to validate performance of the model. The proposed approach was compared with the previous procedures, which ignored critical acceleration changes due to downward movement of the sliding mass. Accordingly, earth slopes with smaller slip length were more influenced by the downward movement modification, especially in small amounts of initial yield acceleration. A semi-empirical equation is presented based on more than 425,000 modified-coupled analyses of several hundred strong ground motion records. An equation was then developed as a function of acceleration ratio, period ratio, slip length, peak ground velocity, Arias intensity, and earthquake magnitude. Predictions of the developed equation were compared with the available equations, which ignore the role of increased critical acceleration. It is shown that a majority of the previous models predict conservative estimates of seismic permanent displacements compared with that of new equation. The proposed semi-empirical model can be used as an alternative equation of seismic displacement for deterministic and probabilistic evaluations of earthquake-induced landslide hazard.
AbstractPore-water pressure buildup strongly affects seismic permanent displacement of the slopes constituted from saturated soils. Previous attempts simulating the generation of excess pore ...pressures (or decrease in soil strength) have been applied in the sliding block models, but the models assumed a rigid block. In the present study, a simplified procedure is presented to account for this effect in sliding block analysis. A correlation between excess pore pressure ratio and cumulative absolute velocity is obtained through the fully coupled solid-fluid effective stress analysis of level ground. The effect of pore-water pressure variation on critical acceleration is investigated in this paper, and the available Newmarkian sliding block methods, such as the rigid block, decoupled, and coupled approaches, are modified to estimate seismic permanent displacement in the presence of excess pore pressure buildup. The present study is original because the method not only simulates the generation of excess pore pressures but also considers the coupled procedure. In addition, centrifuge test results of lateral spreading in the infinite sloping ground are used to demonstrate that the proposed modification considerably improves prediction of seismic sliding displacement. The results clearly demonstrate that ignored pore-water pressure buildup in sliding block procedures can lead to unconservative estimates of seismic permanent displacements during seismic loading.
Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit. There are examples of this phenomenon in past major earthquake events. ...In this study, the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests. The research has focused on the buried depth of the tunnel, tunnel diameter, tunnel weight, liquefaction extent, uplift mechanism, and factor of safety against liquefaction-induced uplift. According to the test results, the shallow buried depth, larger diameter, and lower weight can intensify the tunnel uplift, so the displacement in post-liquefaction time continues at the same rate as during the shaking time. Due to the shear-induced dilation, pore water pressure generation around the tunnel was reduced compared with that of the free field. The excess pore water pressure dissipation in the soil overlying the uplifted tunnel was significant, which leads to suction in the soil deposit. Furthermore, the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field. However, the soil acceleration response around the tunnel without uplift was similar to the base motion.
A strong earthquake occurred on November 12, 2017, in Sarpol-e Zahab city, western Iran, with the moment magnitude (
M
w
) of 7.3 and a focal depth of 18 km. The maximum horizontal peak ground ...acceleration of 0.69 g was recorded at the Sarpol-e Zahab station. Significant damages were observed in frame and masonry buildings, while the damage distribution was non-uniform throughout this small city. The preliminary site reconnaissance revealed that numerous engineering structures collapsed or considerably damaged in some regions, contrary with those non-structural masonry buildings in other regions which remained intact during earthquake. This paper represents a preliminary reconnaissance report prepared through the site visit done by the authors, a few days following the earthquake occurrence. Then, the data recorded by the strong ground motion stations in the affected city and the surrounding regions together with the geotechnical data gathered from the available boreholes in Sarpol-e Zahab are incorporated for probabilistic seismic hazard and local site effect analyses. The observed response spectra at two stations and distance-dependency of ground acceleration are compared with those predicted by some attenuation models. The results of probabilistic seismic hazard analysis in the return periods of 475 and 2475 years are compared with the observed ground response and the design spectra recommended by the Iranian seismic code (for site classes Types I and II). Several geotechnical boreholes from the previous works in the affected area were analyzed through the equivalent-linear site response approach in order to obtain the seismic response at the soil surface. The results are then compared with the code design spectra for the site classes of Types III and IV. It is demonstrated that the calculated response spectra are generally larger than those recommended by the Iranian seismic code, especially for the 4–7 stories buildings.
This paper presents a new empirical model to predict the mean period (Tm) as a frequency-content parameter of earthquake record using the strong ground motions recorded in Iran during 1975–2019. An ...updated earthquake databank containing 2281 horizontal acceleration records was employed to develop the empirical model through a systematic fitting procedure. A simple functional form for the model was found as a function of epicentral distance (R), moment magnitude (Mw), and the shear wave velocity averaged at the top 30 m of the recording sites (Vs30). The proposed model is compared with three existing predictive models and the results are discussed in terms of magnitude, source-to-site, and site dependencies.
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•A new GMPE for Tm based on an extensive database of earthquake records is presented.•More than 4500 Iranian strong ground motions were used.•We compared the predictive model with the models recently proposed to predict Tm.•The presented equation is applicable is earthquake engineering practice
Small-strain dynamic properties of sands are commonly estimated through the correlations basically developed by the experimental results of isotropically consolidated specimens. In reality, however, ...the in-situ stress state of soils is not necessarily isotropic. Several resonant column tests were conducted on reconstituted samples of a coastal siliceous-carbonate sand in a variety of initial relative density and consolidation stress. The results indicate that despite the noticeable effect of initial stress anisotropy on the values of maximum shear modulus Gmax, the values of minimum damping ratio Dmin are almost independent of initial stress ratio. In a preceding paper, the authors proposed a correction factor for two siliceous and calcareous sands which correlates the shear modulus in anisotropic stress condition to the isotropic shear modulus. It is demonstrated herein that the proposed formula is precise for the siliceous-carbonate sand of the present study. The proposed empirical relationship is then compared with a correction factor proposed by others for shear modulus of sands in stress anisotropy condition.
•Isotropic and anisotropic dynamic properties of a siliceous-carbonate sand are compared.•The effect of stress anisotropy on the Dmin and Gmax is investigated.•A correction factor is presented to capture the effect of stress anisotropy on Gmax.
A new attenuation model is proposed to estimate the cumulative absolute velocity (CAV) of strong ground motions based on an updated earthquake database of the earthquakes occurred in Iran. The strong ...ground motion database is comprised from 4562 acceleration records of horizontal components associated with 574 earthquakes recorded in Iran during 1975–2019. A multiple regression procedure is used to develop the functional form of the predictive model as a function of the average soil shear wave velocity at the top 30 m (
V
s30
) of the recording stations, the moment magnitude (
M
w
), and the epicentral distance (
R
). Performance of the presented attenuation relationship is investigated by a parametric study and compared with some selected local-scale models recently proposed for CAV. Assessment of the model demonstrates that the magnitude-dependency of CAV is significant across all epicentral distances. The distance-dependency of CAV is particularly pronounced for
M
w
> 5.5. The influence of
V
s30
becomes particularly prominent at extended epicentral distances exceeding ⁓50 km. The estimation of the liquefaction-induced lateral spreading is presented as an application of the proposed model for a typical site in Iran. The seismic sliding displacement is predicted ⁓31 cm, diminishing to ⁓2.5 cm when pore water pressure buildup is excluded from the calculations.
In this study, drained and undrained triaxial tests under isotropic and anisotropic consolidations were conducted on reconstituted samples of Babolsar sand, which underlies a densely populated, ...seismic region of the southern coast of the Caspian Sea, Mazandaran, Iran. It was demonstrated that the sand experienced all possible states of liquefiable soil： flow failure, limited flow, and dilation. The steady-state and flow liquefaction lines of this sand were presented and compared with previously tested sands. It is shown that the initial stress anisotropy can affect the potential of volume change and pore pressure generation. The steady-state line （SSL）, however, remains identical for the isotropically and anisotropically consolidated specimens under drained and undrained conditions. The tests data were then analyzed in order to investigate the liquefaction susceptibility of this sand in terms of parameters such as the state parameter, relative state parameter index, and lateral earth pressure ratio at failure.
Lateral deformation of liquefiable soil is a cause of much damage during earthquakes, reportedly more than other forms of liquefaction-induced ground failures. Researchers have presented studies in ...which the liquefied soil is considered as viscous fluid. In this manner, the liquefied soil behaves as non-Newtonian fluid, whose viscosity decreases as the shear strain rate increases. The current study incorporates computational fluid dynamics to propose a simplified dynamic analysis for the liquefaction-induced lateral deformation of earth slopes. The numerical procedure involves a quasi-linear elastic model for small to moderate strains and a Bingham fluid model for large strain states during liquefaction. An iterative procedure is considered to estimate the strain-compatible shear stiffness of soil. The post-liquefaction residual strength of soil is considered as the initial Bingham viscosity. Performance of the numerical procedure is examined by using the results of centrifuge model and shaking table tests together with some field observations of lateral ground deformation. The results demonstrate that the proposed procedure predicts the time history of lateral ground deformation with a reasonable degree of precision.
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