R. Bellotti, M. Jamiolkowski, D. C. F. Lo Presti and D. A. O'Neill anisotropy of small strain stiffness in ticino sand

P. Negro, G. Verzeletti, J. Molina, S. Pedretti, D. Lo Presti e S. Pedroni

LARGE-SCALE GEOTECHNICAL EXPERIMENTS ON SOIL-FOUNDATION INTERACTION (TRISEE TASK 3)

Special Publication No. I.98.73, European Commission, Joint Research Centre, Ispra (VA), Italy.

This report provides: 1) a general description of the experimental work carried out at the ELSA laboratory (JRC Ispra) in the framework of the activities of the research project TRISEE (3D Site Effects of Soil-Foundation Interaction in Earthquake and Vibration Risk Evaluation), funded by the European Commission under the Environment and Climate Programme, Contract n° ENV4-CT96-0254; 2) the necessary post processing of the test results and the comparative analysis, from the point of view of the assessment of the permanent deformations and the ultimate bearing capacity for the soil-foundation system.

The large dynamic interaction experiments were designed to investigate the non-linear interaction between shallow foundations of building structures and the supporting soil during strong seismic loading. A shallow foundation resting on cohesionless soil of known properties and excited by a time varying horizontal force and moment, which simulate the inertial forces transmitted to the foundation by the superstructure, was considered. The wave propagation effects in the soil were neglected with respect to the dynamic structural inertia forces transmitted by the foundation.

The results of thsi program will be used to improve the current design practice and to validate non-linear constitutive models implemented in the numerical tools developed as a part of the activities of TRISEE (AHNSE codes), or in other codes.

Two large size tests were envisaged with two different soil relative densities (about 45 and 85 %). The tests were intended as representative of high density and low density soil conditions respectively for the practical design of shallow foundation.

D.C.F. Lo Presti, M. Barla, G. Barla, O. Pallara, A. Plescia e A. Grigore

DEVELOPMENT AND USE OF A TRIAXIAL CELL FOR SOFT ROCKS

The Geotechnics of Hard Soils-Soft Rocks, Napoli12-14 Ottobre 1998, Balkema, Vol. 1, pp. 259-265.

The stiffness of sedimentary soft rocks was determined by means of compression loading triaxial tests. These tests were performed on two different kinds of sedimentary soft rocks: i) specimens retrieved from a Miocene (23 million years) geologic formation (S. Raffaele Cimena, Italy) which consists mainly of clay shales interbedded with sandstones and ii) specimens of mudstone from Sagamihara (Japan) (Kim et al. 1994, Hayano et al. 1997). The Sagamihara sedimentary soft mudstone have been deposited in the late Pliocene to the early Pleistocene epochs. These deposits of mudstone are well cemented and most of them are unweathered and continuous (Hayano et al. 1997). The tests were performed with a specially devised triaxial apparatus (Hayano et al. 1997, Tatsuoka 1988) having the following peculiar characteristics: i) very low apparatus compliance; ii) accurate, local measurements for the axial and radial strains; iii) high resolution of the actuator; iv) sliding mechanism at bottom of pedestal.

D.C.F. Lo Presti and M. Jamiolkowski

DISCUSSION ON "SPT-N-VALUE AND S-WAVE VELOCITY FOR GRAVELLY SOILS WITH DIFFERENT GRAIN SIZE DISTRIBUTION

Soils and Foundations, 1999, Vol. 39, No. 2, pp. 142-144.

The authors present a great number of high quality experimental data concerning the shear wave velocity ( and the SPT N-value of reconstituted gravels which were tested in a Calibration Chamber. Data interpretation shows several interesting features, such as the influence of grading on the void ratio function and a new correlation between Vs and N. In particular, the authors show that, for a given level of the consolidation pressure, different kinds of granular soils exhibit the same V and N values at the maximum void ratio. However, the writers would like to have some more details concerning the experiments in order to better evaluate the relevance of the findings. Moreover the writers would like to compare their own data to those of the authors. Thus, the discussion deals with the following points:

a) Request for additional information

b) Comparison between authors' and writers' data

A. Cavallaro, D.C.F. Lo Presti, M. Maugeri and O. Pallara

STRAIN RATE EFFECT ON STIFFNESS AND DAMPING OF CLAYS

Italian Geotechnical Review, 1998, Vol. XXXII, n. 4, pp. 30-49.

This paper describes the results of a laboratory study which was carried out in order to determine the stress-strain behaviour of two italian clays (Augusta and Pisa clays), with special attention being paid to the variation of stiffness parameters and damping ratio with strain rate. The experimental study was carried out using a Resonant Column/Torsional Shear appparatus and a triaxial cell. Monotonic loading torsional shear tests (MLTST), cyclic loading torsional shear tests (CLTST, Resonant Coumn tests (RCT) and mononic compression loading triaxial tests (TX) were performed on specimens of Augusta and Pisa clays. The obtained results showed a little influence of strain rate on stiffness parameters in the small strain range. While the stiffness parameters for medium and large strains are strongly influenced by the strain rate. The neasured damping ratio values resulted to be influenced by strain rate much more than stiffness. A comparison of the stress-strain curves obtained from monotonic and cyclic tests allowed one to verify the effectiveness of a modified second Masing rule (Tatsuoka et al. 1993).

V. Fioravante, M. Jamiolkowski, D.C.F. Lo Presti, G. Manfredini e S. Pedroni

ASSESSMENT OF COEFFICIENT OF EARTH PRESSURE AT REST FROM SHEAR WAVE VELOVITY MEASUREMENTS

Géotechnique, 1998, Vol. 48, No. 4, pp. 1-10.

The paper presents an attempt to evaluate the feasibility to predict the value of the coefficient of earth pressure at rest (Ko) of natural soil deposits on the basis of the measured velocities of the seismic shear waves. The experimental data presented have been obtained from seismic tests performed in the calibration chamber (CC) on laboratory prepared specimens of seven granular materials with grade ranging from fine sand to gravelly sand. The relationship between Ko and shear wave velocity established by means of the CC results was used successfully to predict K at two well documented sites where both Cross-Hole Seismic (CH) and Seismic Piezocone Penetration (SCPTU) tests are available.

F. Tatsuoka, R. Jardine, D.C.F. Lo Presti, H. Di Benedetto e T. Kodaka

TESTING AND CHARACTERISING PRE-FAILURE DEFORMATION PROPERTIES OF GEOMATERIALS

Theme Lecture Session 1, XIV ICSMFE, Hamburg September 1997, Balkema, Vol. 4, pp. 2129-2164.

Recent developments in the characterisation of geomaterial prefailure deformation properties are reviewed, focusing on the data required to predict ground deformations and structural displacements at working loads. Descriptions are given of the deformation characteristics developed at very small to intermediate strains of a variety of geomaterials, in testing using modern laboratory and field techniques. The relationships between static and dynamic experiments, between laboratory and field techniques, and between testing and field full-scale behaviour are discussed. Important features that are highlighted include: kinematic yielding, effects of recent stress-time history, anisotropy, structuration and destructuration, non-linearity by strain and pressure and effects of cyclic, loading. Careful distinctions are made between elastic, plastic and viscous properties.

D.C.F. Lo Presti

STRESS-STRAIN BEHAVIOUR OF UNDISTURBED CLAYS IN THE LABOTRATORY

Panel Discussion Session 1.1, XIV ICSMFE, Hamburg September 1997, Balkema, Vol. 4, pp. 2183-2186.

This Panel presentation concerns the stiffness assessment of undisturbed clays in the laboratory and summarises the research activity undertaken at the writers' University over the last five years. the main purpose of this research was to define reliable test procedures in order to determine the stiffness of geomaterials to be used for settlement analysis under working loading conditions.

D.C.F. Lo Presti

COMPORTAMENTO DEI TERRENI IN CONDIZIONI DINAMICHE E CICLICHE

Ingegneria Geotecnica nelle aree sismiche. 1999, CISM, Udine, pp: 109-146

Il presente lavoro analizza i recenti sviluppi riguardanti la determinazione delle caratteristiche sforzi-deformazioni dei terreni con particolare attenzione ai parametri necessari per l'analisi della risposta sismica di un deposito di terreno e per gli studi di interazione dinamica terreno-struttura. Vengono presi in considerazione i risultati ottenuti mediante recenti tecniche di indagine in laboratorio e in sito. Il lavoro descrive le caratteristiche di deformabilità a piccole e medie deformazioni ed i fenomeni di degradazione ciclica a grandi deformazioni per un'ampia varietà di terreni.

A. Cavallaro, D.C.F. Lo Presti, M. Maugeri e O. Pallara

A CASE-STUDY (THE SAINT NICOLÒ CATHEDRAL) FOR DYNAMIC CHARACTERIZATION OF SOIL FROM IN SITU AND LABORATORY TESTS

Earthquake Resistant Engineering Structures II. 1999, pp: 769-778.

The Saint Nicolò Cathedral of Noto was damaged by a post-seismic structural collapse on March 13th 1996 and is now under repair and restoration. The city of Noto is located near Siracusa on the east coast of Sicily and actually is object of a seismic microzonation (level II) study. Assessment of the seismic risk of Saint Nicolò Cathedral by means of analytical computation is also under way. To this end, in situ and laboratory investigations have been carried out in order to determine the soil profile with special attention being paid to the variation shear modulus and damping ratio with depth. This paper is aimed at providing information about the Saint Nicolò Cathedral site characerisation for seismic analysis.

D.C.F. Lo Presti, A. Cavallaro, M. Maugeri e O. Pallara

NON LINEAR STRESS-STRAIN MODELLING OF GEOMATERIALS UNDER STABLE AND UNSTABLE CYCLIC LOADING.

Proceedings of the 2nd International Conference on Earthquake Geotechnical Engineering, Lisbona 21-25 June 1999, Balkema, Vol. 1, pp. 29-34.

The paper shows that a modified 2nd Masing rule is capable of well reproducing the experimental stress-strain curve of natural clays during cyclic loading. The modified 2nd Masing rule assumes that the scale amplification factor for the unload-reload branches (n) is not necessarily equal to two as postulated by the original 2nd Masing rule. In particular, it was found that n=6 in the case of stable cycles. When degradation phenomena occur, n decreases. The limited experimental data did not allow the authors to determine the dependence of n on shear strain (γ) and number of loading cycles (N). On the other hand the degradation parameter (t) proposed by Idriss et al. (1978) was computed according to the procedure suggested by Lin & Chen (1991). The values of t resulted to be much higher than those available in literature.

D.C.F. Lo Presti, O. Pallara, A. Cavallaro e M. Jamiolkowski

INFLUENCE OF RECONSOLIDATION TECHNIQUES AND STRAIN RATE ON THE STIFFNESS OF UNDISTURBED CLAYS FROM TRIAXIAL TESTS

Geotechnical Testing Journal, GTJODJ, Vol. 22, No. 3, September 1999, pp. 211-225.

This paper concerns the stiffness assessment of undisturbed clays from triaxial tests. The paper summarises the research activity undertaken at the authors' Universities over the last five years by means of triaxial cells equipped with local gauges for axial and radial strain measurements and with piezoceramic bender elements for the measurement of the propagation velocity of differently polarised shear waves. The main purpose of this research was to define reliable test procedures in order to determine the stiffness of geomaterials to be used for settlement analysis under working load conditions. In particular the paper deals with four different topics: i) evaluation of sample disturbance by means of different methods, ii) assessment of the reconsolidation techniques which minimise the sample disturbance effects, iii) influence of strain rate on the stiffness of undisturbed clays iv) stiffness anisotropy of undisturbed clays at small strains.

D.C.F. Lo Presti, O. Pallara, M. Jamiolkowski e A. Cavallaro

ANISOTROPY OF SMALL STRAIN STIFFNESS OF UNDISTURBED AND RECONSTITUTED CLAYS

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 3-10.

This paper concerns the assessment of the elastic shear modulus of reconstituted and undisturbed clays by means of seismic measurements performed during triaxial compression tests. The experiments were performed by means of a triaxial cell equipped with local gauges for axial and radial strain measurements and with piezoceramic bender elements for the measurement of the propagation velocity of differently polarised shear waves. The tests were performed on reconstituted specimens of Fujinomori (Japan) clay and on intact specimens of two Italian clays (Pisa and Augusta). Seismic tests were performed during saturation process, consolidation and shearing. These measurements allowed to determine the small strain shear modulus in the vertical and horizontal plane . In particular the paper deals with the following topics: i) assessment of the stiffness anisotropy at small strains, ii) assessment of the decay of Go during shearing in order to define the sensitivity of this parameter to sample disturbance.

D.C.F. Lo Presti, M. Jamiolkowski, O. Pallara e M.L. Tordella

ASSESSMENT OF SAMPLE DISTURBANCE IN THE LABORATORY

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 11-19.

This paper concerns the assessment of sample disturbance in the laboratory by means of several methods. In particular, the degree of disturbance of Pisa clay was evaluated. Pisa clay samples were retrieved by means of Laval, Begemann and Osterberg samplers. Possible countermeasures for mitigating the negative effects of disturbance due to sampling and handling the soil specimens in the laboratory are also considered. The following reconsolidation techniques have been compared to evaluate possible beneficial effects: i) dry vs. wet setting ii) reproducing in the laboratory a known stress-history. Undisturbed Pisa and Augusta clay and reconstituted Fujinomori clay samples were used to assess the effectiveness of such procedures.

M. Barla, G. Barla, D.C.F. Lo Presti, O. Pallara e N. Vandebussche

STIFFNESS OF SOFT ROCKS FROM LABORATORY TESTS

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 43-50.

The stress-strain-strength properties of various soft rocks have been evaluated by means of tests performed with a specially devised triaxial apparatus having the follwong characteristics: i) very low compliance; ii) accurate local measurements for the axial and radial strains; iii) high resolution of the actuator; iv) sliding mechanism at the bottom of the pedestal. The samples tested were taken from two sedimentary soft rocks: i) Miocene silty marl interbedded with sandstone (S. Raffaele Cimena, Italy) and ii) late Pliocene to early Pleistocene mudstone (Sagamihara, Japan), well cemented and mostly unweathered and contonuous. Moreover, two tests were performed on specimens of highly tectonised carbonatic Breccia (Giaglione Site, Italy). In particular, the following aspects have been considered: i) the influence of CaCO3 content on strength and stiffness in the case of S. Raffaele Cimena sandstone; ii) the importance of local strain measurements; iii) the importance of end capping; iv) the comparison of the stiffness inferred from in situ and laboratory tests, as well as from rock mass rating systems in the case of carbonatic Breccia.

A. Cavallaro, M. Maugeri, D.C.F. Lo Presti e O. Pallara

CHARACTERISING SHEAR MODULUS AND DAMPING FROM IN SITU AND LABORATORY TESTS FOR THE SEISMIC AREA OF CATANIA

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 51-58.

The paper shows the dynamic characterisation of three different sites of the city of Catania which is one of the most seismically active areas of Italy. The results of in situ and laboratory investigations are described and compared. Moreover, normalised laws are proposed to consider shear modulus decay and damping ratio increase with strain level. Special attention is paid to the variation of shear modulus and damping ratio with strain level and depth. The deposit under consideration consist of different type of soils and represnt the geotechnical variability in the municipal area of Catania.


A. Cavallaro, M. Maugeri, D.C.F. Lo Presti e O. Pallara

STRAIN RATE EFFECTS ON THE YOUNG MODULUS OF AUGUSTA CLAY

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 353-340.

An experimental study was carried out using a triaxial cell in order to determine the undrained stress-strain behaviour of Augusta clay, with special attention being paid to the dependence of Young modulus on strain rate. A particulra attention was paid to the stiffness assessment at small strains, for which the deformation of specimen in triaxial compression was measured locally over the central part with an accuracy of the strain measurement of about 0.001 %. The results obtained showed in the small strain range a little influence of strain rate on Young modulus. The results obtained from triaxial tests were compared to those obtained from monotonic loading torsional shear tests (MLTST) performed in undrained conditions. Rate effects were evaluated by means of an empirical parameter. The rate dependence of the pore pressure increase in undrained monotonic, triaxial compression tests and MLTST was carefully examined.

M. Jamiolkowski, D.C.F. Lo Presti, I. Puci, P. Negro, G. Verzeletti, J.F. Molina, E. Faccioli, S. Pedretti, S. Pedroni e P. Morabito

LARGE SCALE GEOTECHNICAL EXPERIMENTS ON SOIL-FOUNDATION INTERACTION

Proc. of 2nd Int. Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Torino 27-30 September 1999, Balkema, Vol. 1, pp. 749-758.

This paper describes two large-scale load tests performed on a square rigid foundation, 1 m by side, resting on a sand bed 4.6 by 4.6 m in plan and 3 m deep. Two samples of Ticino sand were reconstituted at two different relative densities (DR and 85 %). In the case of the low-density sample a maximum vertical pressure of about 100 kPa was applied. For the high-density sample the maximum vertical pressure was equal to about 300 kPa. The observed settlements have been compared to those inferred from conventional computation methods (Schmertmann 1970). The load displacement curves were used to determine the soil stiffness. The obtained values were compared to those inferred from plate load tests performed in Calibration Chamber on a circular, rigid, deep foundation resting on reconstituted Ticino sand samples (Ghionna et al. 1994).

D.C.F. Lo Presti, S. Pedroni e F. Froio

RIGIDEZZA DEI TERRENI A GRANA GROSSA DA PROVE TRIASSIALI ESEGUITE IN UNA CELLA DI GRANDI DIMENSIONI

XX Convegno Nazionale di Geotecnica, Parma 22-25 Settembre 1999, Pàtron Editore Bologna, pp. 149-153.

La caratterizzazione meccanica dei materiali a grana grossa che trovano un diverso impiego nell'Ingegneria Civile (materiale di fondo per pavimentazioni stradali flessibili, massicciate ferroviarie, rockfill, ecc.) richiede appropriate tecniche sperimentali. Questa nota descrive una cella triassiale in grado di alloggiare un provino con diametro di 300 mm e rapporto altezza diametro pari a 2 e che è stata sviluppata nell'ambito di una collaborazione di ricerca tra l'ENEL PIS di Milano e il Politecnico di Torino. Le caratteristiche principali di questa cella triassiale vengono confrontate con altre apparecchiature simili. L'apparecchiatura è stata utilizzata per eseguire delle prove di compressione triassiale di tipo CID su alcune sabbie e su un ghiaietto. Il confronto tra i risultati relativi alle sabbie e quelli del ghiaietto ha consentito di verificare che i parametri delle correlazioni empiriche normalmente utilizzati per le sabbie non sono del tutto adeguati nel caso delle ghiaie. In particolare è emerso, nel caso delle ghiaie, una più pronunciata non linearità ed una maggiore influenza dell'indice dei vuoti sul modulo iniziale

A. Cavallaro, D.C.F. Lo Presti, M. Maugeri e O. Pallara

CARATTERISTICHE DI DEFORMABILITÀ DEI TERRENI DA PROVE DILATOMETRICHE: ANALISI CRITICA DELLE CORRELAZIONI ESISTENTI

XX Convegno Nazionale di Geotecnica, Parma 22-25 Settembre 1999, Pàtron Editore Bologna, pp. 47-53.

La determinazione del profilo del modulo di taglio a piccole deformazioni risulta particolarmente importante negli studi di interazione terreno-struttura soprattutto in quelle aree ove è possibile il verificarsi di eventi sismici. Nel presente lavoro sono criticamente analizzate le correlazioni disponibili per la determinazione di Go da prove dilatometriche in sito. In particolare, si sono utilizzati i risultati di prove dilatometriche eseguite nel sito Le saline di Augusta per determinare, con le correlazioni disponibili in letteratura, il profilo di G. I valori così ottenuti sono stati confrontati da quelli ricavati da prove Cross-hole in sito e da prove di colonna risonante e taglio torsionale eseguite in laboratorio su campioni indisturbati prelevati con campionatori Osterberg e Shelby.

D.C.F. Lo Presti, A. Cavallaro, M. Maugeri, O. Pallara e F. Ionescu

MODELLING OF HARDENING AND DEGRADATION BEHAVIOUR OF CLAYS AND SANDS DURING CYCLIC LOADING

12WCEE, Auckland 30 Jan. to 4 Feb. 2000, paper No. 1849/5/A

It is demonstrated that the stress-strain response in both undrained and drained cyclic loading conditions is of the hardening type until the shear strain is smaller than the so called volumetric threshold. On the contrary, beyond this limit, degradation phenomena occur. In this paper, the possibility of modelling the hardening and degradation behaviour of clays and sands with a simple law is examined. In particular, the case of one-dimensional loading is considered. Experimental data on reconstituted Toyoura sand specimens and undisturbed specimens of three Italian clays (Pisa, Augusta and Catania) have been used

A. Cavallaro., D.C.F. Lo Presti e M. Maugeri

DYNAMIC GEOTECHNICAL CHARACTERIZATION OF SOILS SUBJECTED TO UMBRIA AND MARCHES EARTHQUAKE

12WCEE, Auckland 30 Jan. to 4 Feb. 2000, paper No. 2509/10/A/ST3

The Umbria and Marches regions, in central Italy, were severely damaged by the seismic sequence initiated on September 26, 1997. After that event, Local Authorities, GNDT and Servizio Sismico Nazionale (SSN) have promoted and supported some Grade 3 microzonation studies in those areas, in order to reduce the seismic risk and to rationalise the land use. A Grade 3 seismic microzonation of the city of Fabriano is under way. This paper presents the results of in situ and laboratory investigastions performed in typical deposits of Fabriano area with the main purpose of obtaining representative shear modulus and damping ratio profiles.