Transparent consolidants and GFRP anchors as aesthetic solution for soft-rock stabilization

Soft rock geostructures composed of carbonate rocks (such as chalk and calcarenites) and volcanic (tuff), due their weak bonds, suffer much more than other rocks the weathering effect causing structural instability. Because of the carbonate rich geology, geohazards such as sinkhole and cliff instabilities are a real threat for inland and coastlines regions. The areas affected by such threat often coincide with cultural heritage sites because of their evocative landscape and they represent important nation landmarks. The Apulian region (SE Italy) is characterized by many anthropic underground cavities in calcarenite. In the last decade the number of sinkholes in correspondence of such caves as dramatically increased because of hydro-chemo-mechanical weathering mechanisms induced by long term exposure to water, increased lithostatic loads, absence of ventilation or approximate excavation geometries. In this work an experimental study demonstrating an approach to stop and reverse the micromechanical weathering mechanism is proposed. A rock consolidation intervention using sustainable materials, with low environmental impact and preserving the beauty of the site is proposed. After the characterization of untreated rocks, a set of transparent chemical consolidants (nanosilicates and impregnating resins) is explored experimentally. It is shown how the UCS strength of treated samples can be increased up to 50%. To stabilise fractured rock masses, a set of laboratory pull-out tests of fiberglass anchors in calcarenite is also performed. The obtained show that GFRP anchors are an interesting alternative to steel when stabilizing high historical-aesthetic value areas.