Simplified Theoretical Analysis of the Seismic Response of Artificially Compacted Gravels

Despite extensive use of gravely materials for the construction of big earthworks, theoretical prediction of their seismic response is often based on very simple schemes, unable to reproduce most of the important features observed at sample scales. Theoretical models capable of simulating the effects of artificial compaction on the stress-strain response of these soils under complex static and dynamic loading conditions would be particularly useful for designing more cost effective solutions in the construction of large embankments. This paper is aimed to fill this gap by reporting the results of a simplified theoretical study on the seismic response of an artificial deposit of gravels compacted at different densities. A previously defined critical state multiple yielding elasto-plastic constitutive model, validated with the results of a large variety of triaxial tests on gravels (measurement from small to large strains, samples compacted at different initial soil densities, monotonic and cyclic loading conducted at largely different stress levels), is here adopted to calculate the shear stiffness and the damping an equivalent visco-elastic model. These results form the input of a finite differences one dimensional analysis implemented to study the propagation of shear waves into horizontally layered gravel deposits subjected to variable motion of their underlying bedrock. Analyses are performed in the frequency and time domains by varying the maximum amplitude of the base acceleration to evaluate the filtering and amplification effects of the deposit. The results of this study are parametrically reported in terms of free surface accelerations and amplification ratios, to show how artificial compaction affects the response of gravel

Analysis of Dam Behaviour After Eighty Years of Service

The paper reports on the behaviour of a masonry dam built in the Italian Alps in the early twenties of the last century and still in operation for electric power supply. The dam is 31 m high and its waterproofing is ensured by a multi-layered impervious facing, a concrete cut-off and a grout curtain protruding into the foundation soils. The geological location of the dam is rather complex, because its left abutment is located on a rock formation while the right one rests on a thick moraine deposit. Since its first impounding, large downstream water flows and significant movements of the dam and of its moraine abutment were observed. A comprehensive investigation has thus been conducted in order to understand the overall behaviour of the reservoir, after eighty years of service. For this purpose, historical documents have been first reviewed in order to reconstruct the design assumptions, construction operations and early observations on site. Experimental investigations of the moraine deposit have then been conducted, in order to estimate the subsoil properties. Seepage flow rates and reservoir impoundment levels, recorded for more then twenty years, have also been analysed, showing the correlation existing between these two variables. More recently, a system for monitoring the displacements of the dam and the moraine has been implemented and the recorded data have been examined. All the available observations have been evaluated and a reasonable interpretation of the coupled hydraulical-mechanical behaviour of the dam and of its moraine abutment has been inferred. Numerical calculations have finally been conducted, in order to verify such explanation

Experimental Evidence of the Effectiveness and Applicability of Colloidal Nanosilica Grouting for Liquefaction Mitigation

AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purpo..

Strength of sandy and clayey soils cemented with single and double fluid jet grouting

Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency of the jets, with the aim of creating larger columns and increasing the productivity of construction sites. Relatively little attention has been paid to the consequences of the grouting system on the mechanical properties of the formed material. This paper investigates this aspect by analysing the results of two field trials carried out in both sandy and clayey soils, where single and double fluid jet grouting were simultaneously performed, with varied grout composition and injection parameters. Parallel uniaxial compressive tests on samples cored from the columns show that the material formed with the double system is systematically lower in strength than the material formed using the single fluid system. The mineralogical composition of samples cored from the columns was analysed by performing parallel Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analyses (TGA) to determine the reasons for this difference. A lower proportion of cementitious products, an accelerated carbonation of portlandite and a less homogeneous distribution of cement hydration products was found on the surface of the soil particles of the double samples than for the single fluid columns

insights into bedrock paleomorphology and linear dynamic soil properties of the cassino intermontane basin central italy

Abstract Seismic amplifications are dictated by the depth of the bedrock and the stratigraphy and dynamic properties of the soil deposits. Quantifying these properties, together with their uncertainty, is a necessary task to perform a reliable assessment of the seismic risk at an urban scale. In this paper, a multidisciplinary analysis is presented, where information of different nature is combined. Borehole logs, geophysical, geological and geotechnical surveys are interpreted with the aid of analytical, numerical and geostatistical techniques to characterise the complex shape of the bedrock and the linear dynamic properties of the sedimentary deposits filling the Cassino basin, a Quaternary intermontane basin located in central Italy. The regional and local seismic hazard is firstly identified with geological surveys that reveal an active seismogenic fault capable of producing earthquakes with estimated magnitudes up to 6.5. Boreholes reaching depths variable up to a maximum of 180 meters and microtremor measurements, revealing the sharp impedance contrast at the transition between the sedimentary/arenaceous bedrock and the soft Quaternary infilling, are combined to identify the depth of the bedrock and the linear dynamic properties of soil deposits. These are one of the key factors governing the propagation to the ground level of seismic waves, and their assessment represents the first step for the seismic hazard characterisation of the plain

Cosesimic liquefaction phenomena from DInSAR after the May 20, 2012 Emilia earthquake

In this paper, we have investigated the capability of Differential Interferometry Synthetic Aperture Radar (DInSAR) technique to detect the ground effects induced by liquefaction phenomena occurred during the May 20, 2012 Emilia earthquake. To this aim, a set of COSMO-SkyMed (CSK) SAR images covering the coseismic phase has been used. The detected surface effects have been related to liquefaction of deep sandy layers. Thanks to the geological/geotechnical data in the area and a liquefaction susceptibility analysis of the subsoil, it has been identified a sandy layer between 9 and 13 m in deep, which probably liquefied during the earthquake. The estimated vertical displacements due to liquefaction are comparable with the values measured by DInSAR.Published5-95T. Sismologia, geofisica e geologia per l'ingegneria sismicaN/A or not JC