Academic Article
Caratteristiche geo-meccaniche e problemi di instabilità della falesia di Porto Miggiano (Puglia)
- Title
- Caratteristiche geo-meccaniche e problemi di instabilità della falesia di Porto Miggiano (Puglia)
- Date
- 1991
- Is Part Of
- Geologia Applicata e Idrogeologia
- Volume
- 26
- Pages
- 273-291
- Language
- ita
- Abstract
- The coast ot Apulia includes a number of stretches of coastal cliffs which, due to their geo-structural character and the relentless wave action of the sea, reveal clear phenomena of mass movement. The cliffs of Porto Miggiano (south-est Apulia) are considered in this work their conditions of stability are evaluated in relation to the geo-mechanical characteristics of the rock outcrops and to the effective state of mass movement found. The stratigraphic sequence of the area is formed by a paleocenic carbonatic basement known as the Formation of Castro Limestone, on which in transgression calcarenitic rocks are found known in the literatures as «Calcarenites of Salento», A detailed study of the calcarenitic lithofacies has made it possible to sub divide the calcarenitic formation into two parts. The lower, oft Calabrian origin, is formed by calcarenites in which intercalations of marly-clayey silts are present towars the top. The upper part, of tyrrhenian origin, is formed by cross bedded calcarenites which rest on silts below with marked angular discordance. The analysis of the tectonic and geo-structural character of the area made it possible to hypothesize the presence of two direct faults running respectively NW-SE an d NNE-SSW, which can be traced to Plio-quaternary neo-tectonics, and also to define the geometry of the discontinuity families which affect the rock mass. The determination of the physical parameters of the pleistocenic calcarenites allows some hypotheses to be made about the environment of formation of the silty partss; while, in agreement with what emerges from the geo-physical survey, the parameters ot mechanical resistence obtained show the poor quality of the rock. The state of mass movement found on the stretch of coast studied is almost exelusively confined to the tyrrhenian calcarenites and is due to the mobilization phenomena of falls toppling, breaks along newly formed shear planes and sliding of wedges. The verification ot sliding and toppling stability carried out with the graphic methods proposed by J.T. Markland, E. Hoek & J.W. Bray, and R.E. Goodman, have given safety factor levels generally below the limit value of Fs = 1, thus confirming the correspondence between the instability deduced from the calculation and that actually found in situ. Finally, the comparison of the safety factors obtained shows the substantial equivalence between the verification methods employed.
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