
 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.

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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

Accurate characterization of the mechanical behavior of geomaterials at depth is a fundamental need for geologic and engineering purposes. Laboratory tests on samples from well cores provide the material characterization in terms of mechanical response and other relevant properties. Representativeness of a sample data set with respect to the in situ conditions at depth is a key issue, which needs to be addressed to extrapolate the laboratory response to the whole rock mass. We have developed a procedure aimed at quantitatively evaluating the representativeness of laboratory samples. The methodology is based on joint processing of laboratory ultrasonic tests and wellbore sonic logs. A structural index is used to quantify the difference between the average structure of the laboratory sample and the structure of the formation at the wellbore scale. This index could be used to identify different causes of discrepancies between the behavior of the cored samples and the behavior of the rock formation as documented by well logs. Then, it could also be used to integrate laboratory data for the construction of a reliable geomechanical model with reference to the real in situ state. The methodology was applied to three different experimental data sets, showing the effectiveness of the method.

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Assessment of the structural representativeness of sample data sets for the mechanical characterization of deep formations

Laboratory scale electrical resistivity measurements to monitor the heat propagation within porous media for low enthalpy geothermal applications

We discuss a paper dealing with the effect of surface wave solution non-uniqueness on 1D seismic site response analysis. We address some issues on the numerical simulations of seismic site response, specifically the correct definition of input motion. If a consistent framework is adopted, the solution non-uniqueness has negligible effect in amplification and acceleration response spectra for the presented dataset, confirming previous studies on the same topic.

/pdf/comment-on-effect-of-surface-wave-inversion-non-uniqueness-1lvxl57pei.pdf

Comment on "Effect of surface wave inversion non-uniqueness on 1D seismic ground response analysis" by Roy et al

Surface waves play a fundamental role in the propagation of vibrations caused by blasting. Indeed, active and passive surface wave tests, which are widely used techniques in engineering and geophysical exploration to infer model parameters for soils and rocks, can be profitably applied for the prediction of ground motion from blasting supplying relevant information on subsurface mechanical properties and source parameters (patterns of propagation and dominant wavelengths). In this respect, monitoring systems for ground vibrations can be conceived in order to use the collected data also for ground characterization purposes. Moreover, the interpretation of surface wave data can lead to an estimate of shear modulus and damping ratio (quality factor) as a function of depth. This information can be used to build a numerical model to simulate wave propagation and predict ground vibrations evaluating the performances of vibration mitigation systems. For preliminary assessments of ground vibrations induced by blasting, the information from surface wave tests can be used to improve the predictive capability of attenuation relationships. In particular in the present work reference is made to a recently proposed relationship based on energy spreading in the form of Rayleigh wave propagation. Data from a case history will be presented to exemplify the relevant aspects in the proposed methodology

The role of surface waves in prediction of ground vibrations from blasting

Monitoring electrolyte movements in porous media has numerous applications in civil and environmental engineering, but new techniques are needed that can provide global spatial distribution and local properties of the pore fluid. Different imaging techniques have been proposed. Magnetic resonance imaging and X-ray computed tomography provide very high resolution. But they are very expensive, not widely available, and can be applied only in laboratory experiments.

Cesare Comina

Papers

Assessment of the structural representativeness of sample data sets for the mechanical characterization of deep formations

Laboratory scale electrical resistivity measurements to monitor the heat propagation within porous media for low enthalpy geothermal applications

Comment on "Effect of surface wave inversion non-uniqueness on 1D seismic ground response analysis" by Roy et al

The role of surface waves in prediction of ground vibrations from blasting

Monitoring 3D diffusion processes with high-speed electric tomography