PSI - Issue 78

Marco Peroni et al. / Procedia Structural Integrity 78 (2026) 2110–2117

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The following stratigraphy of the terrain was obtained: • A subsurface layer: around ten meters thick, made up of prevalently clayey-silty soils, dry and tending to be well consolidated by pedogenesis • An intermediate layer: at a depth of approximately ten to twenty meters, made up of tending to be silty and silty sandy soils that are partially saturated and of medium consistency. • A deep layer: from depths of around twenty meters, corresponding with the stratified “pseudo-rock” bedrock lithotypes (Marly-Arenaceous Formation). The basement level of the walls and pillars of the Church was obtained following a topographical levelling; it is therefore geologically differentiated between the upstream and downstream sides, and the foundations of the downstream side were, quite rightly, deeper (and in fact we find them more than 2m deep from ground level). As far as the underground hydrogeology of the area is concerned, in December 2015 the depth of the first water level was measured at approximately -14m, but it is likely that this level on the one hand has certainly been shallower in the past and on the other hand has been lowered in recent years as a result of recurring drought periods. However, it is also to be considered, again with regard to subterranean hydrogeology, that due to the contrast in permeability between the relatively loose and permeable topsoil and the clayey and poorly permeable soils immediately below, it is possible that periodic subsurface water stagnation and seepage may have occurred (possibly also accentuated by seepage). Basically, the precariousness of the hydrogeological equilibrium of the foundations is identified as a predisposition to possible volumetric settlements of the foundations that could partially justify the lesions to the Church's structures, in order to remedy which, as we shall see, the need to build deep foundations (at -20m from ground level) on compact soils and, above all, ‘untied’ with respect to the sub-surface hydrogeological equilibrium is considered reasonable. 3. Observed damage and possible causes Following several inspections carried out in recent years, the last of which was in August 2022, a widespread crack pattern was found in the right chapel on the south side of the building complex. The cracks are present both in the masonry elevations and in the internal vault, and are also present in the interior flooring of the church, denote, as noted in the geological report, the triggering of a mechanism of base subsidence undoubtedly attributable to the significant drought in recent years, with the drying up of the clayey soil under the foundations and the consequent instability due to loss of support. Testimonies recovered from locals also revealed that there was an old water drainage hole near the foundation of the portion in question, which had then fallen into disuse, but which had leaked profusely over time and caused quite a few moisture problems for the neighboring buildings.