
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

The Journal of the Acoustical Society of America

Cours d'economie politique

Today, surface-wave analysis is widely adopted for building near-surface S-wave velocity models. The surface-wave method is under continuous and rapid evolution, also thanks to the lively scientific debate among different disciplines, and interest in the technique has increased significantly during the last decade. A comprehensive review of the literature in the main scientific journals provides historical perspective, methodological issues, applications, and most-promising recent approaches. Higher modes in the inversion and retrieval of lateral variations are dealt with in great detail, and the current scientific debate on these topics is reported. A best-practices guideline is also outlined.

/pdf/surface-wave-analysis-for-building-near-surface-velocity-39ze2co0if.pdf

Surface-wave analysis for building near-surface velocity models — Established approaches and new perspectives

With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions along different hydro-mechanical paths.

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

The electrical conductivity of a soil can be related to the electrical conductivity of its solid and fluid constituents by means of theoretical and empirical relationships, taking into account the effect of porosity, saturation degree, fabric and clay content. Hence monitoring the evolution of the electrical conductivity inside a soil sample can provide useful information concerning the progress of hydro-chemo- mechanical processes and the subsequent effects on both soil skeleton and pore water. With this aim a laboratory apparatus for 3D electrical resistivity tomography has been recently developed. Some applications of this apparatus to the monitoring of different geotechnical processes in which the knowledge of the water content and of ionic concentration is particularly relevant are presented.

/pdf/hydro-chemo-mechanical-processes-in-soil-samples-monitoring-3hkhaa7mbx.pdf

Hydro-chemo-mechanical processes in soil samples: monitoring through electrical resistivity tomography

Preliminary analyses of an innovative soil improving system by sand/gravel injections–Geotechnical and geophysical characterization of a first test site

Ambient vibrations recorded on potentially-unstable rock slopes show that the temporal variations in the spectral content and in the correlation of seismic noise can be related to both reversible and irreversible changes within the rock mass. In this work, we analyzed the seismic recordings acquired at the potentially-unstable granitic cliff of Madonna del Sasso (NW Italy) from October 2013 to November 2014. The spectral content of noise systematically highlighted clear energy peaks at specific frequencies on the most unstable sector, interpreted as resonant frequencies of the investigated volume. Horizontal ground motion at the fundamental frequency was moreover found to be orthogonal to the main fractures observed at the site and consequently parallel to the potential direction of collapse. Cross-correlation was computed between the recordings of the sensors placed in the prone-to-fall compartment and a stable reference station. Both the temporal variations of the resonant frequencies and the results of cross-correlation showed seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from damage processes within the rock mass, were detected during the monitored period.

/pdf/spectral-analysis-and-correlation-of-ambient-seismic-noise-1ww4sok49f.pdf

Spectral analysis and correlation of ambient seismic noise. The case study of Madonna del Sasso (NW Italy)

A borehole thermal energy storage living lab was built nearby Torino (Northern Italy). The aim of this living lab is to test the ability of the alluvial deposits of the north-western Po Plain to store the thermal energy collected by solar panels. Monitoring the temperature distribution induced in the underground and the effectiveness of the heat storage in this climatic context is not an easy task. For this purpose, different temperature evolution strategies are compared in this paper: Local temperature measurements, numerical simulations and geophysical surveys. These different approaches were compared during a single day of operation of the living lab. The results of this comparison allowed to underline the effectiveness of time-lapse 3D electric resistivity tomography as a non-invasive and cost-effective qualitative heat monitoring tool. This was obtained even in a test site with unfavorable thermo-hydrogeological conditions and high-level anthropic noise. Moreover, the present study demonstrated that, if properly calibrated with local temperature values, time-lapse 3D electric resistivity tomography also provides a quantitative estimation of the underground temperature.

https://www.mdpi.com/2076-3263/9/4/167/pdf

Cesare Comina

Papers

Hydro-chemo-mechanical processes in soil samples: monitoring through electrical resistivity tomography

Preliminary analyses of an innovative soil improving system by sand/gravel injections–Geotechnical and geophysical characterization of a first test site

Spectral analysis and correlation of ambient seismic noise. The case study of Madonna del Sasso (NW Italy)

Time-Lapse 3D Electric Tomography for Short-time Monitoring of an Experimental Heat Storage System

Effective Vs and Vp characterization from Surface Waves streamer data along river embankments