Microstructural features and compressibility of volcanic deposits from Central Italy

Large areas of Central and Southern Italy are covered by pyroclastic materials, at the border between weak rocks and granular soils, which pose various problems in modelling their mechanical behaviour for geotechnical design. The paper reports the results of a comparative experimental study of the microstructural features and compressibility of three pyroclastic deposits from Central Italy, namely two pozzolanas from the Colli Albani Volcanic Complex, located immediately south-east of the city of Roma, and one pozzolana from the Vulsini Volcanic Complex, forming the slab on which the historical town of Orvieto is founded. The compressibility was investigated by means of conventional laboratory techniques, such as one-dimensional and isotropic compression tests, performed on natural and reconstituted samples. However, due to the pyroclastic nature of the materials, special non-standard procedures had to be developed for the preparation of natural samples, including coring of frozen samples. At the same time, an investigation of the microstructural features of the materials was undertaken by means of optical and electron scanning microscopy. The paper discusses the results of the experimental activity in order to find out common features and differences of behaviour of the three materials and to try and connect the primary and secondary compressibility characteristics to the observed microstructural features