Numerical and experimental investigation on the effects of filling shallow cavities beneath an urban area



The hazard posed by a number of shallow cavities in the tuff formation beneath the densely populated city of Napoli (Italy) has given rise to a research program aimed both to study their static conditions and to set forth a list of preservation interventions and remedial measures. Among the latter, when dealing with cavities in bad static conditions and of no artistic or historical value, complete filling of the cavity with a suited material is by far the most simple and definitive way to solve the problem. In fact, the filling material (foamed concrete) ensures a confining action on both the walls and the roof. However, an undesired effect can arise, due to a soft made ground which often exists on the bottom of the cavity. Such a soft material settles upon filling and shear stresses arise on the cavity walls and pillars. The resulting sum of confining pressure and shear stresses on the cavity walls is such that the mobilized shear stress in the rock mass increases at thc depth of the

cavity floor. In the paper, some numerical analyses have been carriedkont to quantify such undesired interaction, taking into account in a simplified manner the effect of continuous curing of the concrete mass poured into the cavity. The results indicate that, depending on the filling procedure, on the stiffness of the made ground under the cavity floor and on the dimensions of the cavity, the amount of applied load carried by the cavity walls can be very large. A trial field was then carried out, where settlements of the cavity floor and strains in the cavity walls were monitored. Numerical back analyses were in fair agreement with monitoring results, showing that in this case as much as 63% of the weight of the filling material was acting on the cavity. Based on these numerical and experimental results, indications on the best procedure for cavity filling are finally given, which depend on the relevant concern to be considered.

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AUTORI: De Sanctis F., Evangelista A., Flora A., Lirer S., Lombardi G.
Numero di pagine: 9

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