Abstract

In recent decades, microtremor and surface wave explorations have been widely applied for geotechnical investigations to estimate the S-wave velocity profile. The estimated S-wave velocity profile provides essential information for site characterization. Since we need to solve an inverse problem with the observed phase velocity of the surface waves to estimate the S-wave velocity profile, acquiring high-quality data is the most critical part. To ensure the data quality and the corresponding results, ISO 24057:2022, array measurement of microtremors to estimate shear wave velocity profile, was developed in 2022. The document specifies appropriate equipment, procedures, data analysis, and reporting for the array measurement of microtremors as a passive geotechnical survey. Since we cannot control the frequency contents in ambient noises, the frequency range with the high power may be limited in the microtremor explorations. In this situation, surface wave exploration can supplement this shortcoming. An example of combining the two results shows that it gives us a dispersion curve in a wide frequency range to estimate the S-wave velocity profile from shallow to deep subsurface structure. Developing a new ISO standard for surface wave explorations by following the microtremor exploration enhances the quality of the estimated S-wave velocity profile. Accordingly, we expect non-destructive and cost-effective investigations to be widely accepted worldwide.

Abstract

In recent years, there has been a global trend towards increasing the commercial speed of high-speed rail lines (HSLs) to cope with expected demand problems. Examples include the new HSLs projects for the UK and California, where the design speed reaches 400 km/h. Therefore, one of the biggest challenges currently faced by the railway sector is the determination of the critical speed value of railway sections. This is true both for future HSLs, due to their high design speeds, and for existing rail lines, due to the intended increase in commercial speed. The critical speed is that train speed that produces a dynamic amplification in the medium underlying the track, causing an amplification of the vertical movement of the track components and the supporting ground such that the stability of the infrastructure and the safety of passengers is compromised. This work sets out the methodology necessary to experimentally study the critical speed of a railway section by in situ applying surface wave spectral analysis techniques, SASW and MASW. The critical speed is determined by the lowest phase velocity of the local minima of the modal dispersion curves, or by the minimum of the apparent dispersion curve. Both methods are equivalent. This paper also presents the results obtained on some Spanish HSLs, both on tracks under construction and in operation. In the cases studied, the ballast layer is the one that presents the lowest shear wave velocity and the minimum of the dispersion curve, so it is the layer that determines the critical speed.

Abstract

The South and Southeast Kazakhstan regions exhibit notable seismicity due to intricate tectonic interactions, albeit experiencing infrequent catastrophic earthquakes. Proximate to the convergence of the Eurasian and Indian plates, this region witnesses frequent seismic activity, particularly in cities like Almaty near mountainous terrain. Given the significant seismic activity, comprehensive site characterization is imperative. Traditionally, evaluating dynamic soil properties relies on conventional borehole logging techniques. However, the emergence of the multi-channel analysis of surface waves (MASW) offers advantages in cost, time efficiency, and non-invasiveness. Despite its benefits, MASW remains underutilized in Kazakhstan and is absent from local building codes, unlike neighboring CIS countries. This study aims to demonstrate the applicability of the MASW method for site characterization in Kazakhstan's seismic regions. Through extensive work, shear wave velocity (𝑉𝑠) values were estimated and compared with reference data obtained from seismic refraction and dilatometer testing. The results showed significant agreement, highlighting the suitability and effectiveness of the MASW method in Kazakhstan.

Abstract

The multi-channel analysis of surface waves (MASW) is a widely employed surface wave method. The fundamental mode inversion is the usual scheme in MASW, because separating the fundamental mode from other high modes is feasible with an adequately long array. However, the extracted fundamental mode represents only part of the dynamic characteristics, it may deviate from the theoretical fundamental mode due to truncation effect, and part of it may correspond to another higher mode or leaky mode, resulting in mode misidentification. Conversely, the spectral analysis of surface waves (SASW) method features a more rigorous inversion scheme by matching the effective mode, but it may suffer from the tricky phase-unwrapping in the dispersion data reduction. This study introduces an improved dynamic response solution for elastic-layered media subjected to vertical loads. The proposed dynamic response solution is fast and accurate, facilitating the full wavefield inversion in terms of the frequency-velocity spectrum. The MASW frequencyvelocity spectrum inversion considers testing configuration and comprehensively models all wave phenomena, including near-field effect, truncation effect, and leaky waves. The MASW frequency-velocity spectrum inversion merges the convenience of MASW dispersion analysis with the rigorous inversion scheme adopted by SASW. The new MASW frequency-velocity spectrum inversion is compared with the SASW effective mode inversion and MASW fundamental mode inversion. The results show that both SASW effective mode inversion and MASW frequency-velocity spectrum inversion produce better inverted results than the MASW fundamental mode inversion, while the process of MASW frequency-velocity spectrum inversion is more convenient and robust. Finally, a field example is used to demonstrate the applicability of frequency-velocity spectrum inversion.

Abstract

New legislation in Brazil requires that all upstream tailings dams must be closed. However, understanding the characteristics of the foundation and deposits of these dams can be complex, and conventional investigations may not be sufficient. Geophysical methods can complement conventional approaches and provide a better understanding of geotechnical structures. The objective of this investigation is to comprehensively characterize residual soil from a tailings dam foundation by integrating data from direct and indirect approaches. Data from CPTu, SCPTu, SPT, geophysical profiles, and MASW were analyzed. The results were compared with empirical correlations for other soil types, and it was found that the equations are not effective to represent the materials. The study discusses the advantages and limitations of using these empirical equations.

Abstract

Analysis of shallow foundations, pavements, and slabs-on-grade requires adequate site characterization of the nearsurface soils. Key properties required for the above are the soil stiffness and its nonlinearity. In this paper, we present the results of field site characterization at a coastal aeolian sand site located in Villa El Salvador, Peru, where large storage tanks are being proposed to be supported on concrete slabs-on-grade and shallow ring foundations. The site characterization included standard penetration tests (SPT), dynamic cone penetrometer (DCP) tests, lightweight deflectometer (LWD) testing, and geophysical tests such as multichannel analysis of surface waves (MASW), seismic refraction, and electrical resistivity. The paper focuses on estimating elastic soil stiffness (Es) values on the main bearing layer of the tanks. The observed large variability of Es estimates was associated with inherent soil variability at the site, the in-situ test method, and the use of empirical correlations between Es and different in-situ tests. Good elastic soil stiffness estimates for the bearing layer (Upper SP sand) were required to make reliable estimates of absolute and differential settlements for the tanks. Due to soil nonlinearity, the elastic stiffness values from the different methods decreased with increasing levels of shear strains associated with each test. Accordingly, the highest elastic stiffness values were from the MASW, followed by the LWD, and the lowest from SPT-based correlations. The soil stiffness estimates using SPT-based correlations yielded the highest variability due to the high uncertainty and low confidence of the empirical correlations between Es and SPT field values.