Search

It has been widely recognised that near-fault ground motions can be distinctly different from far-fault ground motions, in terms of their amplitudes and spectral characteristics, and there are a number of studies investigating the effects of near-fault ground motions on the structural response. However, only a few studies focus on underground tunnels, and most of them consider vertically incident seismic waves, neglecting the wave passage effect which is critical for long tunnels. This paper investigates the consequences of near-fault pulse-like ground motions on the seismic tunnel response, with an example of a tunnel embedded in saturated poroelastic soil. The input motions are represented by obliquely incident P1 waves, and the wave passage effect along the longitudinal direction is considered by a 2.5D modelling technique. The seismic tunnel response for near-fault pulse-like and far-fault ground motions is compared. Additionally, artificial ground motions, which have consistent acceleration response spectra with the near-fault pulse-like ground motions, but without velocity pulses, are generated to gain further insight into the contribution of velocity pulses. It is shown that the near-fault pulse-like ground motions can noticeably increase the tunnel internal forces, due to large seismic energy associated with the velocity pulses. For pulse-like ground motions with similar acceleration response spectra, the fling-step velocity pulse can be more detrimental to the tunnel than the forward-directivity velocity pulse. Moreover, the amplification effect of the near-fault pulse-like ground motions on the tunnel internal forces tends to be more prominent for large vertical angles of incidence, highlighting the significance of considering the oblique incidence case for seismic design. • Interaction of the tunnel and saturated poroelastic soil for obliquely incident seismic waves. • The longitudinal tunnel response due to the wave passage effect. • Near-fault pulse-like ground motions tend to increase internal forces in the tunnel lining. • Effects of forward-directivity and fling-step velocity pulses. • Influences of pulse-like ground motions are more prominent for large vertical angles of incidence. [ABSTRACT FROM AUTHOR]

Segmented tunnels are widely used nowadays. However, most existing studies on the seismic response of underground tunnels are based on the model of continuous linings, without considering the segment joints. This paper presents a numerical study aiming to investigate the factors that affect the seismic response of segmented tunnels, with a step further than previously, considering obliquely incident seismic waves. The numerical simulation is carried out by a 2.5D coupled finite element-boundary element (FE-BE) model, which can properly simulate the soil-tunnel interaction for obliquely incident seismic waves and predicts both the transverse and longitudinal seismic responses of the tunnel. It is shown that the joint distribution is one of the critical factors that determine the seismic responses of the segmented tunnel, and the influence of the segment joints tends to be more pronounced when they are located near the positions of large transverse bending moments in the tunnel lining. Compared with the homogeneous tunnel, the reduction in the transverse bending moment and axial force of the segmented tunnel is significant, while it is minor in the longitudinal bending moment and axial force, and the effect of the segment joints highly depends on the soil-tunnel relative stiffness. In addition, the influence of the spectral characteristics of the input motions on the tunnel responses is highlighted. • Dynamic soil-segmented tunnel interaction for 3D obliquely incident seismic waves. • The segment joints lead to smaller tunnel internal forces while larger deformations. • The effects of the segment joints on the tunnel longitudinal internal forces are small. • The effects of the segment joints highly depend the soil-tunnel relative stiffness. • Input motions with significant long-period spectral accelerations cause large tunnel responses. [ABSTRACT FROM AUTHOR]

For some crucial engineering projects, a compatible time history of ground motions is required as a loading input for seismic dynamic analysis. The compatibility with multi-damping design spectra is critical to make sure the high reliability of analysis results. In previous methods, ground motions were hard to be tuned highly compatible with multi-damping design spectra. Hence we propose a method to optimize the compatibility of a seed ground motion history, which is either obtained from actual seismic records or generated from previous methods, by superimposing adjusted ground motions in the time domain through the L ∞ norm minimization. The optimization process makes the influences of the superimposed ground motions to the response spectra be under control by constraining objective variables. The high precision of the method is demonstrated by a concrete example, in which the max difference between the response spectra of the optimized ground motions and the design spectra for RG1.60 data [1] is 5.06% under five different damping ratios, and all response spectra envelope the design spectra. [ABSTRACT FROM AUTHOR]

Application of local artificial boundary conditions in high-efficient spectral element method (SEM) is a problem that needs further study, where difficulties focus on how to design an appropriate numerical scheme of artificial boundaries that is in good accordance with the unequally-spaced grid nodes and high-order property of the element. Liao's local artificial boundary, i.e. multi-transmitting formula (MTF), provides a convenient way of implementing arbitrary-order displacement-type boundaries because it is defined directly in discrete form and can be transformed into numerical schemes by using merely some interpolation approaches. A new set of numerical schemes of MTF is developed and its accuracy and stability are thoroughly discussed in the application of spectral-element simulation of 1D and 2D seismic wave propagation. The new MTF scheme cannot be written into a binomial form like the traditional one does. This fact has a significant influence on numerical properties of high-order boundary, but merely slightly affects the performance of lower-order boundaries which are daily used in practical simulations. Numerical examples compared with viscous-spring or perfectly matched layer (PML) boundary exhibits that stable and quite good accuracy can be achieved by using the proposed method. • A set of numerical schemes of MTF boundary are proposed for spectral-element simulation of seismic wave propagation. • It is a method of implementing displacement-type artificial boundaries in unequally-spaced spectral-element grid. • Spectral-element MTFs don't have the binomial form as traditional MTFs, leading to a slight reduction on accuracy. • Compared to viscous-elastic and PML boundaries, 2nd- or 3rd-order MTFs are much simpler and can give quite good results. • Seismic wave input through artificial boundaries can be easily achieved by using the MTF boundary. [ABSTRACT FROM AUTHOR]

Baseline correction in time series of ground motion is a challenging problem in research pertaining to strong ground motion. In previous studies in this area, numerous methods have been proposed to identify baseline drift. However, there is no systematic approach to verify the proposed methods. In this paper, we propose a vision-based approach to evaluate baseline correction methods quantitatively. In addition, for our proposed baseline correction method based on L1-norm optimization, we analyze the method in detail and provide a thorough analysis of the method based on experimental data. From the comparison, our method shows good performance in recovering the baseline. • A new baseline correction method based on L1-norm has be proposed. • Using vision-based displacement to verify the new method. • The proposed new method can improve the accuracy of earthquake displacement remarkably. [ABSTRACT FROM AUTHOR]

Lateral variations of shear wave velocity (V S) profile and time-averaged shear wave velocity in the upper 30 m (V S 30) are important indicators of site condition and significant contributors to uncertainty in earthquake ground motion and seismic hazards. Few previous studies involved in quantifying these lateral variations, especially at short distances, due to limited data at closely spaced sites. This study quantitatively investigated the lateral variation of V S profile and V S 30 over plain and piedmont terrains, focusing on short distances ranging from hundreds of meters to several kilometers. 2510 plain and 749 piedmont borehole profiles from the mainland China borehole profile database were employed to examine these variations using the variogram as the geo-statistics tool. The main findings include: 1) Over plain terrain, the variation in site conditions between sites does not significantly increase with separation distance within a certain range (typically from 1 km to 3–5 km). Over piedmont terrain, site condition variation steadily increases with distance. 2) The variation of site condition over piedmont terrain is higher than that over plain terrain. Nonetheless, for both terrains, the dispersion of site condition between sites at distance of <1 km is engineering negligible, and the correlation of site conditions between sites within 5 km remains strong; 3) For both terrains, the lateral variation of V S in deeper layers is higher than that in shallower layers. The study outcomes emphasize the importance of incorporating the information of nearby measurements in site condition estimations. The study outcomes can also be utilized in the optimization of borehole sampling design for microzonation projects and the evaluation of site condition dispersion at inferred sites. • Lateral variations of V S profile & V S 30 over plain & piedmont terrains were modeled. • The study focuses on lateral variations at short distance, down to < 1 km scale. • For gentle terrains, site conditions within short distance are strong correlated. • Plain has lower site condition variation than piedmont, with distinct properties. [ABSTRACT FROM AUTHOR]

In this paper, we collect and process free-field strong motion recordings from 70 earthquakes for 4.2 ≤ M W ≤ 7.9 at 0 < R rup < 300 km between 2008 and 2018 in the active tectonic regions of southwest China, and then establish a dataset containing 1324 average horizontal ground motion (ROTD50) and corresponding metadata such as parameters of the earthquake source, distance, and site. A new ground motion prediction equation (GMPE) for the average horizontal component of peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped acceleration response spectra at periods ranging from 0.033 to 8.0 s (SA (T = 0.033–8.0 s)) is introduced. This GMPE considers multiple influencing factors such as magnitude and distance saturation effect, geometric attenuation, style-of-faulting, hanging-wall effect, linear/nonlinear site response, and anelastic attenuation. The residual evaluation and median ground motion are presented. The predicted ground motions using the new GMPE are compared with predictions from the GMPE in western China and five NGA-West2 GMPEs, and the observed ground motions of strong earthquakes which occurred in southwest China. The results show that the proposed GMPE can better reflect the influence of the earthquake source characteristic, propagation media, site effect on the ground motion attenuation characteristic in southwest China, and works well versus independent strong motion data of earthquakes in southwest China, and well reflects the general feature of ground motions for the Wenchuan and Lushan earthquakes that is rich at short-period and weak at long-period. The new GMPE shows outstanding performance estimating the horizontal ground motion of the earthquakes in southwest China for M W 4.2–7.9 (related to style-of-faulting) and R rup = 10–200 km, at sites with V S30 = 140–1130 m/s. • A new GMPE considering multiple influencing factors in southwest China is presented. • Our GMPE can reflects the hanging-wall effect of the reverse and normal faulting. • Our GMPE can reflects captures the nonlinear mean effect of soil. • Our GMPE works well versus independent strong motion data in southwest China. [ABSTRACT FROM AUTHOR]

River valley terrain can lead to local amplification effects of site seismic responses and significant spatial variation of strong ground motions. This paper presented a semi-analytical solution for the scattering of incident plane P-waves by a saturated river valley with arbitrary shapes containing water, using the moment method and the wave function expansion method. The influence of factors such as valley geometry shapes, soil porosity, wave incident angle and frequency on the seismic response of valley topography is further investigated. Parameter analysis shows that these factors have a significant impact on the site seismic response. Soil porosity has a greater impact on the horizontal response of the site than on the vertical response. Moreover, the soil porosity is directly related to the amplitude of the pore pressure, while the incidence angle and frequency of the incident wave determine the distribution position of the pore pressure amplitude. This semi-analytical solution can be seen as an attempt to solve the scattering problem of incident P wave by saturated river valleys of arbitrary shapes containing water. The purpose of this paper is to provide a reference and a possible way for subsequent scholars to study the analytical solution to this problem. The conclusions drawn from the parameter analysis in this paper can also serve as a theoretical basis for seismic fortification in saturated valley areas. • Semi-analytical model for plane P waves scattering by saturated river valley with arbitrary shapes containing water. • Moment method is applied to obtain the semi-analytical solution to system response. • Influence of the water, medium porosity, and incident wave on ground surface displacement is investigated. [ABSTRACT FROM AUTHOR]

Sand liquefaction is one of the leading causes of severe earthquake damage. In this study, shaking table tests were carried out to investigate the dynamic interaction between the saturated sand and the irregular subway stations. In this test, a method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. Typical test results were interpreted, including the development and spatial distribution of pore pressure, surface subsidence, acceleration, deformation, and dynamic earth pressure. Results show that the spatial distribution of excess pore water pressure is changed by the irregular underground structure, and the liquefiable soil below the bottom plate of the structure can be divided into I, II, and III areas based on the degree of liquefication. The surface subsidence is significantly related to Arias intensity and is concentrated within the range of 5 %–95 % of the intensity. The structural floating is synchronized with the liquefaction of the saturated sand, and the uneven floating and inclination of the underground structure are remarkable, anti-flotation design of underground structures should take into account differences in section forms. During the liquefaction of saturated sand, the foundation soil has conspicuous lateral deformation, especially in the deep soil layer. The shape of the dynamic earth pressure increments turns from triangular to linear, when the foundation soil changes from non-liquefied to liquefied. Compared with the limiting values of the elastic inter-story drift ratio, the maximum inter-story drift ratio of the structure is smaller. The tensile strain responses on the columns, particularly in the lower layer, are more prominent than those at the slabs and side walls. • Shaking table model test is designed on the saturated sand-underground structure interaction system. • Dynamic interaction between irregular-section underground structures and saturated sand is researched, including the different liquefaction states for saturated sand. • A method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. • The liquefiable soil below the bottom plate of the structure can be divided into three areas based on the degree of liquefaction. • Differences in cross-section forms should be considered in the anti-floating design of underground structures. [ABSTRACT FROM AUTHOR]

The seismic performance of liquefied natural gas (LNG) tanks is significantly influenced by Soil-Foundation-Structure Interaction (SFSI). It is essential to investigate the effect of the SFSI on isolated LNG tank, particularly on a deep soil site. This study aims to examine the impact of the SFSI on the seismic performance of an isolated LNG tank located on the deep soil site. The impact of foundation type, pile length, and the frequency content on the primary seismic responses of the LNG tank were thoroughly examined in this study. These seismic responses include the acceleration of the outer tank, the height of the sloshing wave, and the shear force and bending moment of the inner tank. Additionally, the seismic force along the pile foundation, such as shear force, lateral displacement, and bending moment, was also analyzed. The results indicate that for isolated LNG tanks, it would be dangerous without considering the SFSI, while for the pile foundation, it may be beneficial when considering the SFSI. The pile foundation types did not considerably affect the seismic response of the isolated LNG tank in the deep soil site. Additionally, the seismic response appears to be highly sensitive to the frequency characteristics of the seismic excitation, especially the low-frequency content. • The impact of SFSI on the seismic performance of an isolated LNG tank located on the deep soil site was researched. • The pile foundation types, and the frequency domain of seismic excitation were assessed. • Comprehensive modeling technology was used. [ABSTRACT FROM AUTHOR]

This paper presents shaking tests conducted on a 1/30-scale utility tunnel model employing a multi-shaking table array system. The model utility tunnel-soil system was subjected to input motions simulating near-fault ground motions with and without velocity pulse. The test data were collected and analyzed including acceleration, strain and displacement of the soil bed and model tunnel responses. The soil data analysis indicated that the boundary effect of the model soil box used in the test was negligible. The observed small soil settlements confirmed that the physical and mechanical properties of the model soil did not change significantly in tests. The results also demonstrated that, in general, the transverse dynamic responses of the utility tunnel and surrounding soil under near-fault ground motion with velocity pulse were much greater than the case without velocity pulse. Therefore, the effect of velocity pulse should be considered in the design of utility tunnels. • Near-fault ground motions with and without velocity pulses were selected. • A series of scaled model tests were conducted by using a shake table array. • Transverse dynamic response of the utility tunnel model is analyzed through the test data and the result is given. [ABSTRACT FROM AUTHOR]

Strong ground-motion records from the mainshocks and aftershocks of the 2008 Wenchuan (Ms 8.0) and 2013 Lushan (Ms 7.0) earthquakes, within 300 km from the faults, were used for horizontal-to-vertical spectral ratio (HVSR) analysis. The HVRSs of the S-wave show that the predominant site frequency decreases with increasing ground-motion level, a characteristic of nonlinear dynamic soil response. We applied diffuse field theory and Monte Carlo search in the model space to produce an inverted shear-wave velocity profile using the HVSRs of weak S-wave motions. The inverted velocity structures are significantly different from the initial ones derived from in-situ measurements. We also applied 1-D equivalent-linear site-response analysis to derive the spectral ratios (i.e., transfer function) for the original and inverted soil models, and compared the results with the observed HVRSs of the S-wave motions. The comparisons showed that the spectral ratios from 1-D simulation for the inverted soil models agree quite well with the observed HVRSs. In other words, this study suggests that the HVSR from observed earthquake ground motion resembles the empirical transfer function of nonlinear site-response. [ABSTRACT FROM AUTHOR]