MODELLING OF PILED RAFT FOUNDATIONS IN SAND

A piled raft is a composite foundation in which the piles are used as settlement reducers and they share, with the raft, the load from the superstructure. The applied load is transferred from the raft to the shallow soil and to the pile heads, and from the piles it is diffused through the shaft and the base to deeper soil. The pile–raft and pile–pile interactions represent the distinctive aspect of the piled raft foundations since they modify the load–bearing behaviour of each foundation component, compared to an analogous isolated element, thus determining the overall foundation behaviour. The main aim of this thesis is to highlight the effects of the raft–soil–pile interactions on the resistance and stiffness of axially loaded piled raft foundations in sand. A series of centrifuge tests on models of rigid circular piled rafts in loose saturated sand has been performed to this end, employing both non displacement and displacement piles. The raft settlement and the load transmitted to the pile heads and bases were monitored during the tests, which also included unpiled raft and isolated pile tests. The test results have been analysed in terms of bearing capacity and stiffness; the former according to a load efficiency method, the latter by comparing the values obtained from centrifuge tests with those evaluated through a simplified analytical method. ii Modelling of Piled Raft Foundations in Sand D. Giretti In order to clarify the effect of the pressure transmitted by the raft to the soil on the behaviour of a single capped pile, some of the centrifuge tests were simulated via finite element numerical analyses, using an elasto–plastic strain hardening constitutive model for the sand. The geometry and the dimensions of the numerical models corresponded to those of the physical ones and the simulations were carried out applying an accelerated gravitational field to the mesh. The influence of a granular layer, interposed between the raft and the pile heads, on the load transfer mechanism has also been analysed, through an additional series of centrifuge tests which was performed on square rigid raft models on displacement piles in dry dense sand

Walkable urban environments. An ergonomic approach of evaluation

The salutogenicity of urban environments is significantly affected by their ergonomics, i.e., by the quality of the interactions between citizens and the elements of the built environment. Measuring and modelling urban ergonomics is thus a key issue to provide urban policy makers with planning solutions to increase the well-being, usability and safety of the urban environment. However, this is a difficult task due to the complexity of the interrelations between the urban environment and human activities. The paper contributes to the definition of a generalized model of urban ergonomics and salutogenicity, focusing on walkability, by discussing the relevant parameters from the large and variegated sets proposed in the literature, by discussing the emerging model structure from a data mining process, by considering the background of the relevant functional dependency already established in the literature, and by providing evidence of the solutions’ effectiveness. The methodology is developed for a case study in central Italy, with a focus on the mobility issue, which is a catalyst to generate more salutogenic and sustainable behavior

Walkable urban environments: An ergonomic approach of evaluation

Background. The salutogenicity of urban environments is significantly affected by their ergonomics, i.e., by the quality of the interactions between citizens and the elements of the built environment. Measuring and modelling urban ergonomics is thus a key issue to provide urban policy makers with planning solutions to increase the well-being, usability and safety of the urban environment. However, this is a difficult task due to the complexity of the interrelations between the urban environment and human activities. The paper contributes to the definition of a generalized model of urban ergonomics and salutogenicity, focusing on walkability, by discussing the relevant parameters from the large and variegated sets proposed in the literature, by discussing the emerging model structure from a data mining process, by considering the background of the relevant functional dependency already established in the literature, and by providing evidence of the solutions’ effectiveness. The methodology is developed for a case study in central Italy, with a focus on the mobility issue, which is a catalyst to generate more salutogenic and sustainable behaviors

Analisi predittive del comportamento idro-meccanico di un modello di argine fluviale in condizioni di flusso transitorio

Il frequente manifestarsi di eventi alluvionali per collasso di opere in terra costituisce un problema di particolare rilevanza nella valutazione del rischio idrogeologico e della pianificazione territoriale. In questo contesto risulta cruciale un’accurata stima delle condizioni di stabilità che tenga conto dello stato di parziale saturazione dei terreni costituenti il rilevato. Altrettanto importante è tenere conto delle condizioni di flusso transitorio che si instaurano negli argini e nei terreni di fondazione a seguito delle continue variazioni del livello idrometrico dei corsi d’acqua. Tutto ciò influenza notevolmente la risposta idro-meccanica delle opere in parola. In tale prospettiva la nota illustra uno studio numerico, basato sull’approccio agli elementi finiti e sul metodo dell’Equilibrio Limite, per l’analisi del comportamento di un argine fluviale rappresentativo delle opere di difesa idraulica degli affluenti alpini e appenninici del fiume Po. Lo studio proposto tiene debito conto delle condizioni di parziale saturazione del corpo arginale interessato da un moto di filtrazione in regime transitorio. Le analisi numeriche proposte costituiscono parte integrante della progettazione di una prova in centrifuga geotecnica su un modello fisico in scala ridotta, finalizzata a investigare la vulnerabilità delle infrastrutture arginali nei confronti di eventi di piena

Analisi sperimentale per lo studio del comportamento idromeccanico di un terreno costipato

La valutazione delle condizioni di stabilità delle opere in terra rappresenta una difficoltà spesso sottovalutata nella pratica ingegneristica e, viceversa, di attualità della ricerca scientifica in geotecnica. Infatti, è certamente vero che il contenuto d’acqua dei terreni costituenti tali opere e la distribuzione della pressione interstiziale nelle strutture in terra variano nel tempo a causa dei mutevoli effetti delle condizioni idrometriche e climatiche al contorno, cosa che influenza significativamente le condizioni di stabilità dell’opera. In questo lavoro è presentata una procedura per la caratterizzazione del comportamento idromeccanico di una miscela di sabbia e limo al variare dell’energia di costipamento. I dati sperimentali vengono discussi al fine di contribuire allo studio del comportamento in esercizio delle opere in terra

Earthquake Geotechnical Engineering Aspects of the 2012 Emilia-Romagna Earthquake (Italy)

On May 20, 2012 an earthquake of magnitude ML=5.9 struck the Emilia Romagna Region of Italy and a little portion of Lombardia Region. Successive earthquakes occurred on May 29, 2012 with ML=5.8 and ML=5.3. The earthquakes caused 27 deaths, of which 13 on industrial buildings. The damage was considerable. 12,000 buildings were severely damaged; big damages occurred also to monuments and cultural heritage of Italy, causing the collapse of 147 campaniles. The damage is estimated in about 5-6 billions of euro. To the damage caused to people and buildings, must be summed the indirect damage due to loss of industrial production and to the impossibility to operate for several months. The indirect damage could be bigger than the direct damage caused by the earthquake. The resilience of the damaged cities to the damage to the industrial buildings and the lifelines was good enough, because some industries built a smart campus to start again to operate in less of one month and structural and geotechnical guidelines were edited to start with the recovering the damage industrial buildings. In the paper a damage survey is presented and linked with the ground effects. Among these, soil amplification and liquefaction phenomena are analyzed, basing on the soil properties evaluation by field and laboratory tests. Particular emphasis is devoted to the damaged suffered by the industrial buildings and to the aspects of the remedial work linked with the shallow foundation inadequacy and to the liquefaction mitigation effects

Modellazione fisica in centrifuga di un argine fluviale soggetto a forzanti idrauliche

In questo lavoro sono riportati i risultati sperimentali di una prova in centrifuga su un modello di argine fluviale soggetto ad una progressiva sollecitazione idraulica. Le misure di pressioni neutre e di suzione nell’argine mostrano che il fronte di saturazione raggiunge il lato campagna attingendo la condizione stazionaria solo dopo una persistenza irrealistica dell'evento di piena simulato. Pertanto svolgere la progettazione o la valutazione delle condizioni di sicurezza di un argine fluviale con proprietà simili a quello testato nel presente lavoro, assumendo l'ipotesi semplificata di un regime stazionario di filtrazione potrebbe risultare in molti casi un approccio eccessivamente conservativo e, comunque, poco significativo

Load transfer mechanisms of piled raft foundations

Within an extensive research programme on piles as settlement reducers, multi-g centrifuge tests have been performed on models of piled rafts with the piles arranged in two configurations: in direct contact with the raft and separated from the raft by a granular fill layer, introduced to create a uniform pressure distribution on the raft bottom and to reduce constraint reactions between the piles and the slab. The aim of this paper is to present some of the observations concerning the load transfer mechanisms which take place within a mixed foundation and to evidence the influence of a granular cushion, inserted between the raft and the pile heads, on the foundation load – settlement behaviour

Unidirectional cyclic resistance of Ticino and Toyoura sands from centrifuge cone penetration tests

The evaluation of the undrained cyclic resistance of sandy deposits is required to forecast the soil behaviour during an earthquake (liquefaction, cyclic mobility); due to the difficulties in obtaining undisturbed samples of most liquefiable soils, it is usually deduced from field test results such as cone penetration tests. This paper proposes a methodology to evaluate the undrained cyclic resistance from normalised cone resistance of two wellstudied silica sands (Ticino and Toyoura), with different mineralogy, one mainly composed of feldspar, the other of quartz. The etermination of the cyclic resistance of Ticino and Toyoura sands was achieved through undrained cyclic triaxial tests on reconstituted specimens. The tip resistance was deduced from CPTs performed in centrifuge with a miniaturised piezocone on homogeneous reconstituted models. Both the undrained cyclic and tip resistances were correlated with the state parameter w. Results of centrifuge and triaxial tests were combined through w to deduce the cyclic resistance ratio CRR directly from the normalised cone resistance. The shape of the curve relating CRR to the normalised cone resistance resulted unusual respect to all the recognised curves widespread in the geotechnical literature. The aim of the proposed correlations is to provide a useful instrument to improve the actual knowledge on liquefaction and to give a contribution based on the critical state soil mechanics framework to the development of refined correlations between the cyclic resistance of a sand and the results of cone penetration tests

Physical Modeling of Raft on Settlement Reducing Piles

The paper presents the results of extensive centrifuge tests modeling rigid circular piled rafts laying on a bed of loose very fine silica sand. The tests were aimed at investigating the behavior of rafts on settlement reducing piles. The testing program included: an unpiled raft, rafts on 1, 3, 7 and 13 piles. In each test, some model piles were instrumented with load cells to determine the distribution of load along the shaft. Beneath the rafts, two types of model piles, close-ended and free headed were installed: quasi displacement (QD) and quasi-non displacement (QND) piles. The obtained results permitted figuring out the role of piles in terms of their effectiveness as settlement reducers and to quantify the load sharing mechanism between piles and the raft-soil contact. The tests were aimed at investigating the load transfer mechanisms adopted in the design approach, and in particular at validating a numerical code which can be used in engineering practice. The paper describes the details of experiments undertaken, the adopted procedures and some of the results; where not specified, all the experimental data given in this paper referred to model scale. The adopted numerical code is briefly described and its validation, via test results on quasi-non displacement piles, is also reported