Sebastiano Rampello

Capacity Design of Retaining Structures and Bridge Abutments with Deep Foundations

This paper examines a seismic capacity design approach for retaining structures with piled foundations, which assumes full-strength mobilization in the soil and in the foundation piles during the earthquake. The plastic mechanism activated by the seismic forces consists of a horizontal movement of the structure, involving plastic hinging in the piles. This mechanism is triggered when the seismic inertial forces acting within the structure and the soil mass equal the overall strength of the soil-pile foundation system. The paper describes an iterative procedure for evaluating the critical seismic acceleration that activates the plastic mechanism. The seismic performance of the structure is expressed by its permanent displacements and the corresponding curvature ductility demand in the foundation piles. With reference to an idealized bridge abutment, this procedure is expressed in a fully consistent nondimensional form and is applied to a reference case, to show its potentiality and to discuss the influence of a number of key parameters, such as the soil strength and the foundation geometry on the seismic performance of the structure.

An Approach to Evaluate the Efficiency of Compensation Grouting

AbstractCompensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magn...

Seismic Performance of Geosynthetic-Reinforced Earth Retaining Walls Subjected to Strong Ground Motions

There is general evidence that the good performance of geosynthetic-reinforced earth retaining walls (GRWs) observed after strong seismic events can be attributed to their capacity to redistribute seismic-induced deformations within the reinforced zone, provided that the reinforcements are characterised by adequate extensional ductility. Therefore, it is desirable to promote the activation of internal (or local) plastic mechanisms, involving the reinforcement strength, since the design phase. In this study, the seismic performance of two earth retaining walls is compared. Specifically, a pseudo-static approach is adopted to conceive a GRW with a seismic resistance, expressed by the critical seismic coefficient kc, that involves activation of an internal plastic mechanisms, and a conventional retaining wall, in which the same critical seismic coefficient kc is attained for an external (or global) plastic mechanism. Finite difference dynamic analyses are carried out to evaluate the seismic performance of the two walls. In the analyses, a real acceleration time history is applied at the base of the models. The results of the dynamic analyses show that, compared to the wall in which external plastic mechanisms develop, the wall designed to activate internal plastic mechanisms exhibits a better seismic performance, with lower permanent displacements computed at the end of the seismic event.

Predicting the seismic behaviour of the foundations of the Messina Strait Bridge

This paper presents some of the geotechnical studies carried out for the seismic design of the one-span suspension bridge across the Messina Strait, that is to connect Sicily with mainland Italy. These studies included advanced geotechnical characterisation, through in situ and laboratory tests, estimate of site stability involving both liquefaction analysis and submerged slope stability, evaluation of soil-foundation stiffness for spectral analysis of the superstructure, 3D FE static calculations, evaluation of anchor block performance under seismic conditions, and full dynamic analyses of the soil–structure interaction. The paper summarises the main results obtained from the geotechnical characterisation of the foundation soils, reports the approach adopted for evaluating the seismic performance of the anchor blocks through a modified Newmark-type calculation, and presents the study of the soil–structure interaction carried out through a series of two-dimensional, plane strain numerical analyses. In these analyses, in addition to the embedded foundation elements, the models included a simplified structural description of the bridge towers specifically designed to reproduce their first vibrations modes, that were deemed to have the most significant influence on the system’s dynamic response. The illustration is limited to the foundation systems of the bridge located on the Sicily shore.