Vincenzo Fioravante

Contact versus noncontact piled raft foundations

In the last few decades there has been a rapid increase in the number of piled foundations where the piles have been employed as settlement reducers; in some recent projects, the piles have been separated from the raft by a granular layer, which creates a more uniform pressure distribution on the raft bottom and reduces constraint reactions in the soil, foundation, and superstructure. A series of centrifuge model tests has been performed to investigate the load transfer mechanisms between a square rigid raft and a group of instrumented piles jacked in dry dense sand, in direct contact with the raft or separated from the raft by an interposed granular layer. The test results have shown that contact piles act as settlement reducers by diffusing the load applied to their heads to greater and deeper volumes of soil. The insertion of a deformable layer between a raft and pile heads does not ensure displacement compatibility, and the pressure diffused by the granular fill acts partly on the pile heads and partl...

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.

Seismic Stability Analyses of the Po River Banks

The Po River is the major Italian watercourse. Over half its length is controlled with embankments as protection measures against heavy floodings. Recently, the Italian Government has funded a project for the evaluation of the seismic stability of about 90 km of embankments of the Po River. The project mainly aims at the seismic stability analyses of the river banks, with assessment of local site response and evaluation of the liquefaction potential. Hundreds of geotechnical investigations within the study area were performed and the water level variations in the embankment and subsoil were investigated using piezometers. This paper describes the methodology and the main results of the analyses. The safety of 43 significant sections in static and seismic conditions was investigated using limit equilibrium analyses. Dynamic effects in the seismic condition were considered using the pseudostatic method. Local seismic hazard and effects of site conditions on the ground motion are taken into account in the definition of the expected seismic action. Eventually, the analysis results are summarized in a static and seismic stability map of the investigated area, a useful tool for the local Authority in the prevention and mitigation.

Validation of In-Situ Probes by Calibration Chamber Tests

This paper describes the ISMGEO Large Calibration Chamber and its application for the validation of in-situ testing probes such as Cone Penetration, Nuclear Cone Penetration, geophones for seismic wave propagation. The calibration chamber is active since the 1980s, during this period thousands of tests have been carried out demonstrating the effectiveness of such experimental facility.

ISMGEO Large Triaxial Apparatus

The design of earth and rockfill dams is focused on ensuring the stability of the structure under a set of combined mechanical and hydraulic conditions that may occur both during construction and operative life of the dam. The prediction of the hydro-mechanical behavior of construction materials (which range from clayey soils to rockfill) is therefore fundamental. The most important characteristics to be studied are static and dynamic shear strength, shear stiffness at small and intermediate strain and compressibility of the construction materials. Testing of these properties is typically performed using the triaxial apparatus. However, testing large size materials such as rockfill requires the use of large triaxial specimens, whose diameter depends on the particles maximum dimension. Facilities capable of testing large grain size materials are few and sometimes neither the largest apparatuses are big enough to test particles as large as cobbles and boulders. ISMGEO large triaxial apparatus allows the execution of static and cyclic test on 300 mm diameter samples. The maximum particle dimension is 50 mm. Originally designed for testing the gravelly foundation soils of the Messina strait bridge, the apparatus has been recently up-graded in order reach a cell pressure of 2.5 MPa, thus allowing to reproduce the in situ stress conditions within particularly tall earth and rockfill dams.

Soil Liquefaction Tests in the ISMGEO Geotechnical Centrifuge

Operational since 1988, the ISMGEO geotechnical centrifuge is a 240 g-ton centrifuge with a nominal radius of 2.2 m. The centrifuge can spin up a model of 400 kg up to 600 g. Since 2010 the centrifuge is equipped with a 1D shaking table able to reproduce real earthquake signals under an acceleration field up to 100 g. The special design of this centrifuge allows keeping the shaking table permanently installed on the rotating arm, while the model is driven on the shaking table during the spin-up phase. Physical models are submitted to 1D seismic shear waves, the typical free-field boundary conditions are reproduced by an equivalent shear beam box recently manufactured for dynamic applications.

A correlation to evaluate cyclic resistance from CPT applied to a case history

A methodology to evaluate the undrained cyclic resistance of sandy deposits from cone penetration tests through the state parameter is applied to the case history of the village of San Carlo (Italy), where widespread liquefaction phenomena occurred during the 2012 Emilia earthquake. The mechanical behaviour of the sand retrieved in the area of San Carlo was characterised within the framework of critical state soil mechanics via a series of monotonic and cyclic triaxial tests carried out on both undisturbed and reconstituted samples. Centrifuge cone penetration tests were also performed on reconstituted models of the same material. The results of centrifuge and undrained cyclic triaxial tests were interpreted through the state parameter to calibrate a direct correlation between the cone resistance, qc and the undrained cyclic resistance ratio (CRR). CRR profiles were deduced from the CPTs performed at sites in San Carlo where liquefaction took place using the correlation calibrated herein and a liquefaction assessment was carried out. The results of the proposed method was compared to a well-known simplified approach.