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This paper presents the results of an experimental research carried out in laboratory aimed at establishing a relationship between cyclic liquefaction resistance (CRRfield) and corrected shear wave velocity (VS1) of carbonate sands. Two carbonate skeletal sands, namely Quiou and Dubai, were investigated together with a carbonate non-skeletal sand from Kenya. The programme included also tests on two silica sands prepared and tested in similar conditions for comparison purposes. The research was based on undrained cyclic simple shear tests and bender element tests in triaxial cell performed on reconstituted specimens of sand at different initial density and stress states. The results obtained highlight that data points for carbonate sands are all located to the right of the currently used cyclic liquefaction resistance vs. shear wave velocity curves suggested for silica sands, implying that the latter curves should be considered non-conservative when applied to carbonate crushable sands. An insight into the effect of the initial effective vertical stress on liquefaction susceptibility of carbonate sands was presented and a stress normalization procedure was also proposed.

The influence of non-plastic fines on undrained monotonic behaviour of sand was investigated over a wide range of fines content (FC = 0–40%), global void ratio and initial mean effective stress ($$ p_{0}^{\prime } $$ = 100 kPa to 500 kPa), by performing triaxial compression tests with isotropic and anisotropic consolidation. For the sand–silt mixtures, steady-state line in the e − log(p′) space was found to be dependent on fines content with the existence of a limiting fines content, which defines the transition from a “fines in sand” to a “sand in fines” soil fabric. It is demonstrated that by means of the concept of equivalent granular void ratio, e*, all steady-state/critical state data points can be well described by a unique relationship in the e* − log(p′) space called the equivalent steady-state line (EG-SSL), regardless of fines content. The equivalent granular state parameter (ψ*), defined in terms of e*, and the EG-SSL can be effectively adopted for predicting the undrained monotonic behaviour of sand–silt mixtures and the onset of static instability, irrespective of fines content and initial state of the sand–silt mixtures.

An extensive experimental program of constant-volume (undrained) cyclic simple shear tests was undertaken on Ticino, Italy, sand with different contents of nonplastic fines, ranging from 0%...

Sustainable development principles aim to re-utilize wastes to reduce their impact on the environment. In this context, the present contribution shows preliminary results on the preparation of innovative synthetic lightweight aggregates, starting from biomass-derived fly ash and high-density polyethylene (HDPE), to be used in geotechnical applications. The present work focuses on the manufacturing process of aggregate blends (including the selection of the right proportions of the two components) as well as on the relative determination of (i) physical&ndash, chemical properties (i.e., chemical composition, morphological analysis, mineral leachability, water absorption, specific gravity, grain size distribution), (ii) permeability features and (iii) mechanical properties (one-dimensional compression and shear strength behavior). The results, gathered from the new synthetic lightweight aggregates and compared with the corresponding ones obtained in a previous study conducted on natural and synthetic lightweight aggregates, appear promising for a potential utilization in geotechnical engineering.

The paper provides insight into factors affecting the prediction of seismic pore-water pressure build up in clean sands and sand–silt mixtures for modeling purposes. Laboratory pore pressure measurements were conducted using stress-controlled undrained cyclic simple shear (CSS) tests carried out on both reconstituted and undisturbed specimens of silty sands under different initial conditions (density state, effective vertical stress, initial fabric and fines content). Test results were interpreted by using a damage concept-based model which is actually implemented for clean sands in non-linear time domain site response analysis codes. In the present work, such a model was properly modified for sands having fines contents higher than 35%. The general applicability of the modified procedure for predicting pore water pressure response of silty sands under irregular shear stress loading using data from stress-controlled CSS tests was also verified and all factors affecting calibration parameters of the model were throughly analyzed.

An extensive experimental study was undertaken to investigate the influence of non-plastic fines on pore water pressure generation and undrained cyclic shear strength of sand–silt mixtures. For this purpose, stress-controlled undrained cyclic simple shear ( CSS ) tests were carried out on reconstituted specimens of Ticino silica sand under different combinations of fines content ( FC ) and global void ratios ( e ). The applicability of several models suggested in literature for predicting cyclic residual excess pore water pressure generation in non-plastic silty soils was analyzed, and revised correlations for assessing model parameters were proposed. Finally, the study confirmed that the equivalent granular void ratio ( e* ) is an effective and appropriate parameter for characterizing the behavior of sand with fines up to a threshold value of fines content of sand-silt mixtures, and cyclic resistance ratio ( CRR ) of the mixtures can be well correlated with e*, irrespective of their fines contents and void ratios.

The progressive bond breakage of artificially cemented sands induced by shear straining was investigated through conventional isotropically consolidated drained triaxial compression tests. Sand specimens were prepared with a low degree of cementation by adopting a chemical grout. Test results were interpreted in terms of two stress–dilatancy theories for cohesive-frictional materials proposed in literature. The influence of debonding on the stress–dilatancy behaviour of cemented sands was analysed with particular emphasis on the ‘delayed dilatancy’ phenomenon. A bonding degradation curve was determined for each test relating the interparticle cohesion (c) to the magnitude of the total plastic strain vector (ed) and a bond degradation rate factor (Dc) was assessed from each curve. The maximum value of interparticle cohesion (c0) before the onset of bond degradation under shearing was found to correspond with a sharp decrease in the soil stiffness of the specimens. The influence of the effective con...

The paper presents a study aimed at evaluating the effect of non-plastic fines on undrained static liquefaction and instability behavior of silty sands considering two different state variables: (global) void ratio (eo) and equivalent granular void ratio (e*). The last parameter was introduced as an alternative index for mixed soils with a “sand-dominated” fabric. Undrained monotonic triaxial tests were carried out on Ticino sand-silt mixtures (FC = 0–30%) for a wide range of initial void ratios and mean effective confining stresses. The study provides evidence that, when the (global) void ratio is used as the comparison basis, the effect of fines is to cause an increase in the degree of contractiveness and higher susceptibility to collapse. Nevertheless, when the comparison is made at constant equivalent granular void ratio, undrained shear behavior and collapsibility of the silty sands are closely related to e*, which appears an effective index for unifying the response of mixed soils with varying fines content.

The performance of silty soils in Emilia Romagna, Italy, during the 2012 earthquake offers an interesting opportunity for understanding their response under cyclic loading and susceptibility to liquefaction. A comprehensive investigation based on both in situ tests and laboratory tests (undrained cyclic simple shear tests) was performed for evaluating the cyclic strength of these low plasticity silty soils and thus analyzing data in light of the screening criteria for liquefaction triggering susceptibility. The laboratory results indicate that the soils are susceptible to liquefaction, whereas some types of interpretation approaches based on in situ tests appear to overestimate the liquefaction resistance of soils when applied to sands containing non plastic or low plasticity fines, thus suggesting a revision of the existing methods of analysis.

The aim of this paper is to provide an insight into the effects of a previous cyclic history “triggering” full liquefaction on the subsequent undrained cyclic behaviour of a moderately cemented grouted sand in terms of strength, deformability and pore pressure response. The research was conducted on sand specimens stabilized by a commercial mineral based chemical grout (“Silacsol”), capable of imparting unconfined compression strength (UCS) values ranging between 500 kPa and 700 kPa. Monotonic shear strength parameters of treated specimens were preliminary assessed through a series of isotropically consolidated drained triaxial tests (TX-CID). Afterwards, stress-controlled undrained cyclic simple shear (SS) tests were conducted on both treated and untreated sand specimens in order to evaluate the improvement provided by the grout on the liquefaction resistance of the sand. A significant beneficial effect of the grout was observed, regardless of the initial density of the pure sand. Finally the influence of a cyclic large preshearing on the undrained cyclic behaviour of the grouted sand was investigated by subjecting the specimens to a sequence of two cyclic loadings with the same stress ratio (CSR). After the first loading in which specimens were brought to full liquefaction, they were allowed to reconsolidate in approximately K 0 conditions and then subjected to the second loading. An increase in liquefaction resistance induced by cyclic history was clearly apparent on treated specimens. Excess pore pressures build-up during the first cyclic loading on treated specimens followed a different trend compared to that observed on untreated ones. A significant difference was also observed on the excess pore pressure trends developed in the second loading compared to that developed in the primary loading. A simple model for the prediction of pore water pressure build-up of grouted sands during cyclic loading is proposed.

The purpose of this paper is to investigate mechanical and hydraulic properties of sands treated with mineral-based grouts through the results of a laboratory test programme consisting of unconfined compression tests (UCS), triaxial bender element tests (BeT) and constant flow permeability tests in triaxial apparatus. An improved apparatus was set up for obtaining high quality, multiple grouted specimens from a single column. Two selected natural sands having different grain sizes were grouted with two mineral-based silica grouts, resulting in different levels of improvement. The behaviour of the sands treated by mineral grouts, in terms of strength, initial stiffness and permeability, was compared with that exhibited by more traditional silicate grouts. The results of this study indicate that sands treated with mineral grouts result in higher strengths, higher initial shear modulus and lower permeability values than the sands treated with the silicate solution. The effect of grout type, effective confini...

In the present study, a series of undrained cyclic simple shear (CSS) tests were performed on clean Ticino sand (TS) and TS mixed with 10% of non-plastic fines content (FC) under two values of static horizontal shear stress ratio (α = 0 and 0.1) to simulate level ground and sloping ground conditions before earthquake loading, respectively. The results in terms of cyclic resistance were analyzed assuming the global void ratio (e) as control parameter. One of the most significant findings is that the liquefaction resistance of silty sand is lower than that of clean sand due to the presence of fines and this detrimental effect is even more evident in presence of static shear stress. The concept of equivalent granular void ratio \( \left( {e^{ * } } \right) \), proposed earlier to take into account the simultaneous effect of void ratio and fine content based on symmetrical cyclic tests on silty sand, is valid for non-symmetrical tests as well.

Low plasticity sand-silt mixtures are very common in Italy either in natural depositional environment or in man-made earth-fill, hence the knowledge of their behavior is a crucial aspect in many practical applications. Due to higher compressibility features, significant strains and strength loss may be triggered by earthquakes. The results of a laboratory-based investigation undertaken on undisturbed samples of low plasticity silty-sandy soils recovered from a bank stretch after the 2012 Emilia Romagna earthquake in Italy, when serious damages and widespread liquefaction events were observed, are herein presented. Special emphasis was given to susceptibility to liquefaction and pore water pressure response in presence of an initial static shear stress. As part of the present work, the results of undrained cyclic simple shear (CSS) tests carried out on reconstituted specimens of sand-fines mixtures, covering a range of non plastic fines contents from 0% to 40%, were used for predicting undrained cyclic resistance through the concept of equivalent granular void ratio, e* . The conceptual framework based on e* appears appropriate for streamlining the effect of fines on cyclic liquefaction resistance of these intermediate soils, provided that fines content is less than a limiting value. Since an important stage in the assessment of liquefaction potential is to predict excess pore water pressure during cyclic loading, the results of CSS tests were also utilized for analysing pore water pressure generation models of silty sands over a wide range of fines contents.

This paper describes the results of a laboratory investigation performed on clean sand and low-plasticity silty sands, recovered at different locations of the bank stretch at Scortichino, which was affected by serious damages following the 2012 Emilia Romagna earthquake in Italy. A comprehensive cyclic simple shear (CSS) testing program was undertaken to evaluate the liquefaction potential and pore pressure response of silty sand layers, which form the subsoil at the site. A series of undrained CSS tests were carried out on undisturbed samples by applying an initial static driving shear stress before cyclic loading (nonsymmetrical tests), with the aim of gaining a better understanding of the role played by a static preshearing on the observed liquefaction phenomena. The results obtained prove that, in nonsymmetrical cyclic loading tests, low-plasticity silty sands tend to be more susceptible to liquefaction than in symmetrical cyclic loading tests. The onset of liquefaction occurs by large shear s...

An experimental comparative study of a silicate-grouted sand is presented. The experimental procedure adopted for preparing high-quality treated samples is accurately described together with test procedures. The overall experimental investigation comprises unconfined compressive strength (UCS) tests, undrained monotonic simple shear (SS) tests, undrained cyclic simple shear and triaxial (TX) tests. A gain in strength due to the sodium-silicate grout is apparent from both undrained monotonic and cyclic test results. The influence of loading mode on undrained cyclic stress–strain–strength behaviour of treated sand samples is explored based on a comparison between simple shear and conventional triaxial stress conditions. The simple shear device is properly adopted to allow a reliable assessment of liquefaction resistance improvement in untreated sand samples. The paper highlights that, regardless of test conditions, similarities exist between the behaviour of loose-treated samples and that of dense- untreate...

The paper deals with an experimental study of the undrained cyclic behavior of a natural coarse sand and gravel deposit located in Gioia Tauro, a town situated on the continental side of the Messina Strait in Italy. The study was conducted through cyclic undrained triaxial tests carried out on both undisturbed and reconstituted samples. Undisturbed samples were recovered by an in situ freezing technique and the sample quality was carefully assessed. Reconstituted samples were prepared by using two different reconstitution methods, namely air pluviation (AP) and water sedimentation (WS), and tested under the same in situ initial relative density and effective overburden stress. Tests were carried out on both isotropically and anisotropically consolidated specimens. The results obtained from this study provide direct evidence that cyclic liquefaction resistance obtained from water sedimented samples closely approximates that exhibited by undisturbed samples in both isotropically and anisotropically consolidated tests. Conversely, AP leads to a marked underestimation. Since the investigated deposit is considered to have been formed by the marine water environment, these results can be regarded as proof that WS closely replicates the in situ fabric of the investigated deposit allowing the substitution of the expensive undisturbed samples with their reconstituted counterparts. Anisotropically consolidated specimens respectively exhibit "cyclic liquefaction" or "cyclic mobility" depending on whether or not they are loaded under the shear stress reversal mode.

An unprecedented transformation in the design, deployment, and application of short-range wireless devices and services is in progress today. This trend is in line with the imminent transition from third- to fourth-generation radio systems, where heterogeneous environments are expected to prevail eventually. A key driver in this transition is the steep growth in both demand and deployment of WLANs/WPANs based on the wireless standards within the IEEE 802 suite. Today, these short-range devices and networks operate mainly standalone in indoor home and office environments or large enclosed public areas, while their integration into the wireless wide-area infrastructure is still nearly nonexistent and far from trivial. This status quo in the short-range wireless application space is about to be disrupted by novel devices and systems based on the emerging UWB radio technology with the potential to provide solutions for many of today's problems in the areas of spectrum management and radio system engineering. The approach employed by UWB radio devices is based on sharing already occupied spectrum resources by means of the overlay principle, rather than looking for still available but possibly unsuitable new bands. This novel radio technology has received legal adoption by the regulatory authorities in the United States, and efforts to achieve this status in Europe and Asia are underway. This article discusses both the application potential and technical challenges presented by UWB radio as an unconventional but promising new wireless technology.

The paper will offer insights regarding the effects of cyclic prestrain history on the undrained behaviour of an uncemented carbonate sand (Quiou sand) through a modified NGI simple shear (SS) apparatus. Tests were carried out on specimens reconstituted at two void ratios (loose and dense) by using the water sedimentation method. The influence of cyclic undrained pre-shearing was investigated by applying both small and large limiting shear strains; after reconsolidation, the specimens were again subjected to the same cyclic phase as before, until the sample liquefied. The pattern of post-cyclic behaviour of the tested sand showed the relevant role assumed by the phase transformation line obtained from monotonic tests on virgin specimens. For both loose and dense specimens a threshold value of cyclically induced pre-shear strain was found at which the positive effect of previous cyclic loading history on liquefaction resistance disappears or starts to reverse. A normalising criterion, capable of providing ...

This paper deals with pre- and post-liquefaction behaviour of a silica sand tested under simple shear (SS) loading conditions. Post-liquefaction response was investigated taking into account two main features: evaluation of liquefaction-induced volumetric strains resulting from the dissipation of pore water pressures; assessment of re-liquefaction characteristics of sand which has previously experienced liquefaction under the first loading. To this purpose, loose and dense reconstituted specimens were subjected to a first cyclic loading in undrained conditions. After reconsolidation, cyclic shear stresses with the same amplitude were again applied to the specimens (second loading or re-loading). With respect to the first liquefaction, a relationship between the normalized cyclic shear stresses and the normalized phase transformation strength obtained from monotonic tests was established regardless of relative density of material. The liquefaction-induced deformations obtained after re-consolidation were found to be well in agreement with those predicted by other approaches proposed in literature. Finally, it was also found that the change in liquefaction resistance of liquefied sand was affected by the relative density of the tested sand.

A standard NGI type Direct Simple Shear (DSS) apparatus has been modified to enable the application of unidirectional simple shear monotonic and cyclic loading through an automated electro-mechanical control system. Two algorithms were implemented in a computer control software, one for constant height control during the undrained shearing phase and the other for controlling the horizontal load or horizontal displacement in cyclic stress and strain controlled tests, respectively. It is shown that the adopted automated electro-mechanical control system represents a valid solution for low frequency cyclic tests under constant volume conditions. Typical cyclic test results under both stress and strain-controlled conditions are also presented in connection with the development of laboratory methods for the analysis of seismic pore water pressure build up and liquefaction at level ground.

This paper presents field trials carried out with a low data rate location tracking ultra wide band impulse radio testbed developed within the project PULSERS. Ranging measurements have been conducted -as a reference- in an anechoic chamber, then in line of sight office environments and non-line of sight intra room propagation conditions. Results show ranging performance better than 50 cm in the 1- sigma point with un-encoded and raw data. Filtering can be applied to improve further performance leading to a very accurate short-range distance measurement system.

This paper reports an experimental study concerning the frictional behavior of sand-solid structure interfaces. The study was performed using a constant normal stiffness (CNS) direct shear box. Three natural silica sands and four aluminium plates with different roughnesses were investigated. A comparison between constant normal load (CNL) and CNS tests is reported. The influence of the main factors controlling the frictional behavior of the investigated materials such as constant normal stiffness, roughness of solid surface, particle size, and relative density, and initial effective normal stress are analyzed and discussed.

The paper presents a study of the undrained behaviour of an uncemented carbonate sand (Quiou sand) under simple shear loading conditions. The experimental study was conducted through cyclic and monotonic undrained/constant volume simple shear tests carried out on reconstituted specimens prepared by using the sedimentation in water (WS) method. Tests were carried out on specimens reconstituted at two void ratios (i.e. loose and dense) and different effective consolidation stresses. Furthermore, to account for the effect of non-zero mean shear stress level, cyclic simple shear tests were performed under both symmetrical and non-symmetrical cyclic loading. Two types of failure modes have been observed in cyclic tests, that is ‘cyclic liquefaction’ or ‘cyclic mobility’, depending on whether or not they were conducted under shear stress reversal conditions. A unified framework seems to exist whereby undrained monotonic and cyclic response can be comparatively analysed. In particular, normalising the cyclic liquefaction resistances obtained from symmetrical tests by phase transformation strengths determined in corresponding monotonic tests, provides a cyclic liquefaction resistance curve which was found to be unique, irrespective of initial void ratio and vertical effective stress. Undrained cyclic shear strength of the tested sand appears to be affected by the presence of a non-zero mean shear stress, following a pattern of behaviour, which is similar for both loose and dense specimens. Furthermore, the normalised stress–strain curves of the cyclic tests show back-bone curves that are practically coincident with the equivalent monotonic curves.

La sequenza sismica che ha colpito la pianura padana emiliana nel 2012, con scosse principali il 20 e 29 maggio, ha prodotto diffusi ed estesi dissesti in alcuni rilevati arginali che, in qualche caso, hanno determinato l’inagibilità di edifici e la chiusura di strade. Uno degli argini maggiormente colpiti è quello del canale diversivo in località Scortichino, frazione del Comune di Bondeno, sede di oltre 400 tra unità abitative e produttive, molte delle quali classificate inagibili proprio a causa dei dissesti verificatisi nell’argine. La Regione Emilia-Romagna, su richiesta dell’Amministrazione Comunale, ha costituito un Gruppo di Lavoro in cui l’Associazione Geotecnica Italiana, con diversi gruppi di ricerca già coinvolti nella rete di laboratori ReLuis, ha affiancato i tecnici della Regione con l’obiettivo di analizzare la risposta sismica dell’argine durante la sequenza sismica del 2012, comprendere le cause dei dissesti osservati e suggerire le necessarie azioni di mitigazione ed eventuali interventi di messa in sicurezza nei confronti di terremoti futuri. A questo scopo è stata condotta un’ampia campagna sperimentale di indagini in sito, sia geofisiche che geotecniche, e di prove di laboratorio, finalizzate alla ricostruzione di un accurato modello geotecnico per la valutazione delle condizioni di stabilità dell’argine in condizioni sismiche, portando in conto anche l’eventuale insorgenza di fenomeni di liquefazione nei terreni sabbiosi superficiali costituenti la fondazione del corpo arginale. La presente memoria intende dare conto delle attività del Gruppo di Lavoro e sintetizzare i principali risultati conseguiti.