Influence of the variability of soil profile properties on weak and strong seismic response

Gobbi, Stefania; Lenti, Luca; d’Avila, Maria Paola Santisi; Semblat, Jean‐François; Reiffsteck, Philippe

doi:10.1016/j.soildyn.2020.106200

Cited by 9 publications

(3 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the article [2], for the stochastic study of seismic risk, the variability of the V s was considered, and in [5], the effects resulting from the choice of three different ways of considering the V s were discussed. In [6], the Monte Carlo method was applied. The parameters that substantially influence the surface seismic amplification depend on the deformation in a non-linear way [7] (among many others).…”

Section: Introductionmentioning

confidence: 99%

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

2023

View full text Add to dashboard Cite

The values of the physical–mechanical properties of any soil are affected by uncertainties both due to experimental measurements and the impossibility of knowing them, in detail, at every point of the spatial domain. Accordingly, this work focuses on uncertainty in shear wave velocity (Vs) and its impact on the seismic response. The Monte Carlo method, based on pseudo-random number generation, was selected. To understand which random distributions could identify the site’s real conditions, the Fourier spectrum frequencies were calculated for each realization and were compared with the predominant natural site frequency. The experimental range data were used to calculate the spectral average acceleration and the horizontal amplification factors. The simulations were performed and interpreted by a modified version of VisualQ4M software based on 2D Quad4M, including the generation of pseudo-random numbers and pre- and post-data processing. A site at a small scale, in the territory of the city of L’Aquila (Italy), was selected as the test case. This paper demonstrates, from a numerical point of view, that both a simple local topographic modification due to excavation and the uncertainties of the numerical values, even of the shear wave velocity alone, can have an important impact on the local seismic amplification.

show abstract

Section: Introductionmentioning

confidence: 99%

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

2023

View full text Add to dashboard Cite

show abstract

“…Ground response analysis is a key tool in seismic hazard assessment, as the reference ground motion (i.e., at the outcropping bedrock with a flat surface) can be different from that recorded at a nearby site in terms of frequency content, amplitude, duration and polarisation due to local topographic and stratigraphic conditions (e.g., [1]). Previous seismic site response investigations have focused on: (i) the heterogeneity of the deposit with depth and the soil nonlinearity (e.g., [2][3][4][5][6][7]), (ii) the variability of the soil mechanical properties and input motion characteristics (e.g., [8][9][10][11][12][13][14][15][16][17]), (iii) the ground surface topography (e.g., [18][19][20][21][22][23][24][25][26][27]), (iv) the buried morphologies (e.g., [28][29][30]) and (v) the numerical code and approach employed in the simulations (e.g., [31][32][33][34][35][36][37][38]).…”

Section: Introductionmentioning

confidence: 99%

Investigating the Influence of a Pre-Existing Shear Band on the Seismic Response of Ideal Step-like Slopes Subjected to Weak Motions: Preliminary Results

2023

View full text Add to dashboard Cite

The assessment of slope susceptibility to seismically-induced displacements receives wide attention in the geotechnical earthquake engineering field, but the alteration of the seismic wave inside the slope and at the ground surface due to the presence of a shear band confining a quiescent landslide body is rarely investigated. This paper describes the preliminary results of the numerical analysis of two step-like FE models, reproducing a gentle slope and steep cutting subjected to weak earthquakes, thus focusing on seismic wave amplification processes only. The results show that the higher the thickness of the weakened zone, the higher the maximum value of the amplification factors predicted at the ground surface. For gentle slopes affected by a landslide body confined by a thick shear band, the highest amplification factors are expected in the longer period range of 0.7–1.1 s, while the highest level of amplification is achieved in the intermediate period interval of 0.4–0.8 s in the case of steep slopes. In addition, the parasitic vertical component of acceleration can be considerably amplified beyond the crest and at the toe of the slope for increasing band thickness, especially in the case of steep topography, for which the effects of the shear band morphology enhance those related to the topographic profile. Finally, the fundamental frequency of the sloping deposit is not particularly affected by the presence of the shear band, while the amplitude of the amplification function at the fundamental frequency is clearly related to its thickness.

show abstract

“…Gobbi et al [19] performed 1D simulation of site response analysis with a set of 40 earthquake records for stochastically generated horizontally layered soil profiles. They concluded that amplification factors are best predicted as a function of V s30 in conjunction with the dominant period of the site and the shear wave velocity gradient.…”

Section: Introductionmentioning

confidence: 99%

Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

2021

View full text Add to dashboard Cite

Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow (<30 m) across the island, bedrock shear wave velocities have a significant influence on the impedance contrast and amplifications. Bedrock shear wave velocity is usually very variable due to the differences in rock formations, level of weathering and fracturing. The level of this uncertainty is shown to be greatly decreased when rock quality designation (RQD) data, common information when bore hole data are logged, is available since it is highly correlated with both shear and compression wave velocities. The results are used to derive region-specific site amplification factors as a function of both Vs30 and site fundamental frequency and compared to those of the National Building Code of Canada (2015). The results of the study indicate that there are large uncertainties associated with these parameters due to variability in soil profiles, soil properties and input seismic ground motions. Average and confidence intervals for the mean and for predictions of amplification factors are calculated for each site class to quantify this uncertainty. Amplifications normalized relative to class C are obtained by accounting for the correlation between site class amplifications for given ground motions. Non-linearity in the analysis of equivalent linear 1-D site response is taken into account by introducing the non-linear G/Gmax and damping ratios curves. In this method, it is assumed that the shear strain compatible shear modulus and damping ratio values remains constant throughout the duration of the seismic excitation. This assumption is not fully applicable to a case when loose saturated soil profile undergo heavy shaking (PGA > 0.3 g). In this study, all simulations with input motion PGA >0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.

show abstract

Influence of the variability of soil profile properties on weak and strong seismic response

Cited by 9 publications

References 32 publications

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

Investigating the Influence of a Pre-Existing Shear Band on the Seismic Response of Ideal Step-like Slopes Subjected to Weak Motions: Preliminary Results

Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

Contact Info

Product

Resources

About