Ad hoc analytical equations and probabilistic treatment of uncertainties for the seismic assessment and amelioration of a XVI Century retaining wall in central Rome

This paper presents a study aiming at assessing the seismic safety and developing the rehabilitation design of a masonry retaining wall, known as Bastione Farnesiano, and placed around the Palatinum hill, in the central archeological area of Rome, in Italy. It is a singular artifact of its kind and hardly identifiable with known stereotypes or constructive models. The phase of survey, together with both the material and degradation analyses, showed the impossibility to define with certainty some features, even geometrical, of the monument, necessary to reach a judgment about its safety. Therefore, it was necessary to formulate the risk assessment problem by taking into due consideration all uncertainties and evaluating them in probabilistic terms. A simple mechanical model, considering different and alternative collapse modes, was developed and, after characterizing the uncertain parameters in probabilistic terms, Monte Carlo simulations were carried out. Based on the obtained results: a) the value of the current risk index has been determined, and b) a sensitivity analysis has been performed in order to identify the parameters that mostly affect the monument safety. This sensitivity analysis has provided useful information that has allowed to orient the seismic amelioration design strategy by acting on one of the parameters that have greater impact on the risk reduction.