Abstract

Surface wave tomography is a feasible method to provide complementary data to better understand the continuity of soil strata. It may also be used to determine best locations for invasive testing. Surface wave tomography methods are frequently used to delineate soil-rock interface and determine average shear wave velocity for seismic site class determination. Delineation within the soils layers where the change in seismic velocity within the soil layers are relatively small requires higher resolution data collection and enhanced processing methods than those used historically in surface wave tomography. This study uses a patented imaging and monitoring system based on the passive seismic interferometry technique augmented by active seismic sources at known locations. A dense nodal array of MEMs accelerometers were deployed at a site where known saturated loose materials exist. This paper presents shear wave velocity (Vs) data deduced from surface wave measurements where various, compression wave velocity (Vp) to Vs ratios were considered, especially showing the effect of Vp/Vs ratio, on the Vs data. This ratio which was traditionally assumed can have a significant effect on the inferred Vs. This paper also presents the comparison of deduced Vs data to measured Vs data by seismic cone penetration test and makes some recommendations for how to improve the methods to determine shear wave velocity in soft/loose soils.

Abstract

The determination of reliable shear-wave velocity models using Multichannel Analysis of Surface Waves (MASW) has increased importantly for site characterisation studies due to their use in geotechnical studies and regulations. The standard MASW approach is commonly based on the analysis of vertical component of Rayleigh waves, which can result in inaccurate and potentially erroneous interpretations by personal bias. Thus, we present the joint analysis of different and independent multi-component data based on Rayleigh and Love waves to obtain 2D Vs sections for site characterization. Those seismic data were recorded using a landstreamer consisting of 8 triaxial 4.5Hz geophones. To generate Rayleigh waves, the blows were given vertically on a plate, and for the Love waves the blows were given laterally on a horizontal wooden beam. A joint analysis of Rayleigh and Love waves data was conducted on seismic data recorded from the metropolitan area of Granada city (Spain) to generate their dispersion curves. This new approach enabled a proper identification of fundamental- and higher-mode surface waves facilitating the reliable reconstruction of subsurface Vs profiles through a robust joint inversion process. The MASW 1D Vs versus depth models were corroborated at several test sites by the information obtained from boreholes. Thus, the main geological formations could be inferred from MASW 2D Vs sections down to a depth of 30 meters, as well as the Vs30 parameter to perform a reliable seismic microzonation of the study area. This methodology provides a very well constrained inversion procedure capable of providing a robust subsurface Vs model for site characterization.

Abstract

This paper discusses two ratios involving penetration resistance and shear-wave velocity (VS) that have been proposed for quantifying the influence of microstructure in aged and cemented soils for liquefaction assessment. The first ratio is the small-strain shear modulus (Gmax) divided by the cone penetration test tip resistance (qc). Because Gmax/qc is dimensionless, it can be expressed as a ratio of measured VS divided by a function of qc with velocity units. The second ratio is the measured VS divided by an estimated VS from penetration resistance-VS relationships for relatively young sand deposits (MEVR). The advantages and limitations of both ratios are discussed. The influence of various fines content (𝐹𝐹𝐹𝐹) corrections on 𝑉𝑉𝑆𝑆, penetration resistance-𝑉𝑉𝑆𝑆 relationships, and a relationship between MEVR and the liquefaction cyclic resistance ratio correction factor for microstructure (𝐾𝐾𝐷𝐷𝐷𝐷) is evaluated using two published datasets. The results show the 𝐹 𝐹𝐹𝐹 correction to 𝑉𝑉𝑆𝑆 is minimal in the range for which the correction was derived. The 𝐹𝐹𝐹𝐹 corrections to qc and standard penetration test blow count are significant for silty soils, having a net effect of lowering the penetration resistance-𝑉𝑉𝑆𝑆 relationships and increasing the slope of the 𝑀𝑀𝑀𝑀𝑉𝑉𝑀𝑀-𝐾𝐾𝐷𝐷𝐷𝐷 predictive relationship

Abstract

Non-linear soil behaviour adds complexity in accurate parameter selection for numerical modelling. One of these parameters is the small-strain shear stiffness. This parameter depends strongly on the soil mass density and the shear wave velocity; the latter can be determined through in-situ tests or laboratory tests. The paper focuses on training various machine learning models to predict shear wave velocity estimates based on raw data from cone penetration test soundings. Three decision tree algorithms are considered for the analysis: XGBRegressor, HistGradientRegressor, and RandomForest. Various data preprocessing approaches are investigated, including noise removal and outlier identification, to assess their impact on the model performance. The results indicate that different data preprocessing approaches yield significant differences in the model performances. When applied to unseen raw data from a sand site of the Norwegian GeoTest Site, the model demonstrates promising predictive capabilities and is in a good agreement with well-known correlations. This study underlines the importance of data quality and preprocessing for reliable machine learning models. To enhance transparency and reproducibility, a GitHub repository with all the used files is made available online.

Abstract

This work presents both a summary of its implementation at two post-seismic sites: the island of Cephalonia (Greece), and the Petrinja (Croatia) along the Kupa river. In the first case, the main objective was to characterize the surface formations of the Koutavos plio-quaternary sedimentary basin to propose a 1D model of the surface soil column and assess the influence of the variability of these surface formations on the amplification of seismic motion. The second experimental campaign in Croatia was aimed at identifying the soil layers that had been liquefied following the events of 2020, as well as highlighting the different soil models obtained by geophysics or constructed from instrumented variableenergy DCP. For each investigated site, additional geophysical and geotechnical tests were carried out. The data collected with this new technology were compared with those obtained previously with other geophysical methods (MASW), in order to assess the shear wave velocity obtained in particular.

Abstract

We evaluated the feasibility of existing fibre optic telecommunication cable as a Distributed Acoustic Sensors (DAS) for shallow ground characterization alongside railways and using the running trains as seismic source. We utilized 5 km of fibre optic cable alongside a railway segment localized in the Hanzelijn corridor in the Netherlands. For almost a week, we recorded strain generated by passing trains that was utilized to retrieve coherent and multimodal Rayleigh waves at various soil conditions. The data was recorded in a continuous mode, using a channel spacing of 1.0 m and a sampling frequency of 1,250 Hz. The DAS interrogator was set to a gauge length of 2.0 m to reach the highest possible spatial resolution. We captured at least 60 train passages (running alongside the fibre optic cable) per day. We extracted Rayleigh waves by utilizing seismic interferometry method. The seismic interferometry processing provided virtual broad-band shot-gathers with coherent and clear surface waves trends. The computed phase velocity spectrum at frequencies as high as 30 Hz and wavelength as short as 6 m. The retrieved dispersion curves allowed us to determine S-wave velocity profile at a minimum depth of exploration of 2.0 m. The measured Rayleigh waves and calculated S-wave velocities are comparable to reference values measured with standard Geophone and geotechnical data available at the test segment.

Abstract

In 2022, a new set of probabilistic shear wave velocity (𝑉𝑆) based liquefaction triggering curves was developed for gravelly soil by Rollins et al., using a dataset of 96 liquefaction and 78 no liquefaction case histories from 17 earthquakes in seven countries. Although these curves provide liquefaction assessment based on direct field performance, they suffer from the fact that there are relatively few case histories for high 𝐶𝑆𝑅 and high 𝑉𝑆 values to define the shape of the upper branch of the triggering curves. Thus, we made shear wave velocity measurements at three sites in Valdez, Alaska where liquefaction did not occur in the Mw 9.2 1964 Great Alaska earthquake. The Multi-channel Analysis of Surface Wave (MASW) technique was used to develop several median Vs profiles at each site that account for uncertainty in the experimental dispersion data and inversion parameterizations. 𝑉𝑆-based liquefaction evaluations were then made at each site, using the 𝑉𝑆 profiles derived from each solution. Results from previous Dynamic Cone Penetrometer (DPT) tests were then used in selecting the most reasonable velocity interpretation. Based on this VS profile, the layer most likely to liquefy was selected and used to define 𝑉𝑆1 and 𝐶𝑆𝑅7.5 at the middle of this critical layer, obtaining three points of no liquefaction, that could change the shape of the upper branch of the existing VS-based liquefaction triggering curves. These preliminary results suggest that it might be necessary to shift the triggering curves to the left or steepen their slope to provide better agreement with observed performance.

Abstract

The N-value by the standard penetration test (SPT) is commonly used for site characterisation in geotechnical engineering. S-wave velocity, typically estimated by borehole measurement or seismic survey, is also indicative of the strength of the ground. Many researchers attempted to find precise relationships between these parameters. However, N-values estimated from S-wave velocity using these formulae are subject to substantial errors, and the errors are inevitable due to the different nature of the parameters. The formula for pseudo-N value was first proposed in 2011 as (Suto, 2011). This is a simplified formula derived from the formulae found by the previous authors. By using this simple formula as a common practice, with understanding of existence of error, the results can be compared from site to site. This presentation first compares the N-value and S-wave velocity in their natures, methods, practice and cost. Then it examines the previously published formulae and proposed formula of pseudo-N value. Some examples of use of the pseudo-N values are also presented at the end.

Abstract

A new geotechnical site investigation has been conducted in the southern breakwater basin of the Port of Barcelona, for which hundreds of in-situ and lab tests have been performed. Among these tests, this study focuses on the evaluation of triple points. That is, at the prospected locations, there are results from seismic dilatometer Marchetti test (SDMT), cone penetration tests (CPTu), and laboratory tests based on soil samples. Based on this information, the probabilistic distribution of the dynamic and geometrical properties of the soil profiles can be properly characterized. Eleven closely spaced boreholes have been used to characterise the statistical properties of the input variables. The objective of this article is twofold. First, the probabilistic generation of one-thousand soil profiles, which are statistically compatible with the data provided by the eleven aforementioned boreholes. Secondly, to analyse how the elastic properties of the generated soil profiles evolve once seismic waves have passed through them. To do so, a large set of ground motion recorded in hard soils have been employed. Results show that the dynamic response of the soil can be properly parametrized if considering intensity measures extracted from the ground motions acting at the bedrock level. From the results obtained, fragility functions have been derived for risk assessment purposes.

Abstract

The definition of the shear wave velocity profile is a fundamental step for the seismic characterization of a site in the context of Eurocode 8 and for the conduction of earthquake geotechnical engineering efforts such as site response analysis. Shear wave velocity profiles can be obtained: (1) directly from seismic geophysical and seismic geotechnical tests; or (2) indirectly, from “static” in-situ geotechnical tests such as dilatometer tests (DMT) and cone penetration tests (CPT). In the latter approach, shear wave velocity is estimated by using transformation models which are typically derived from data collected at other sites. This paper illustrates the procedures and main results of the comparative assessment of the performance of existing DMT-based and CPT-based transformation models to estimate shear wave velocity at two adjacent spatial locations in a rural site in the region of Tuscany in central Italy. Model-predicted shear wave velocity profiles were compared with direct measurements obtained by geophysical seismic dilatometer (SDMT) testing. The comparative assessment involved the definition, calculation, and assessment of quantitative performance statistics. The paper provides a critical analysis and a discussion of the outcomes with respect to soil type.