Hazards related to open pit quarries in the karst environment of Apulia, south-eastern Italy

The Murge plateau (in the Apulia region of south-eastern Italy) is characterized by a Mesozoic sedimentary succession of regularly stratified fine-grained limestones. These materials exceed 6000 m in thickness, and are overlain by Plio-Pleistocene transgressive calcarenites. The peculiar geologic setting, and especially the widespread presence of carbonate rocks, determined the intense development of karst processes. Great part of the region is in fact characterized by karst morphology and the presence of a complex network of underground cavities and caves. Many carbonate rocks in the area have been extracted in the past for construction purposes and as building materials. The intense extractive activity was principally localized in open pit quarries. Today, several quarries are still active, while, on the other hand, a number of them has been abandoned. Although Italian legislation provides quarry restoration at the end of exploitation, many of the abandoned quarries cause relevant environmental alteration and damages, and high hazards as regards slope instability problems and pollution. This paper deals mostly with the analysis of the factors controlling the different types of landslides (slides, falls, topples, etc.) in selected abandoned quarries of the Murge plateau. In particular, an effort will be made to evaluate the influence of the textural and geostructural features on slope stability in carbonate rock masses which are intensely affected by karst processes. Examples of rock slope failure mechanisms are illustrated at different scales. A new rock mass classification method for engineering design and a simple theoretical model for slope stability assessment is proposed

Qualitative Assessment of the Cliff Instability Susceptibility at a Given Scale with a New Multidirectional Method

This paper aims to present a new predictive method for the assessment of rocky cliff instability susceptibility at a given scale in carbonate environment. The method (CISA, Cliff Instability Susceptibility Assessment) entails in situ specific geomechanical and morphological surveys, laboratory geotechnical tests, analysis of meteo-marine data together with human-related variables controlling cliff recession potential. The first step of the method consists of the subdivision of the coastal stretch in sectors based above all on morphological and geological criteria. Then, according to an heuristic approach, 28 conditioning parameters were divided in four categories (geomechanical, morphological, meteo-marine and anthropogenic) and weighted on the basis of a multifactor spatial GIS analysis using physical geographically-based measures. For each parameter 5 classes of rating were proposed; the cliff classification, in terms of cliff instability susceptibility, was obtain from the total rating which represents the summation of the single rating of the individual parameter. An application of the CISA method was here presented through a case study along the Murgia coastline South of Bari (Apulia, SE Italy). The stretch of coastline considered in this study is entirely in the territory of the municipality of Polignano a Mare, between the localities of San Vito and Largo Ardito; it is made up of cliffs, up to 20 m high, and shore platforms interrupted by small pocket beaches. The coastal outcrops consist of Mesozoic carbonate rocks, mainly white-greyish calcilutites well stratified and, moderately to highly fractured and karstified, which are overlain by massive PlioPleistocene calcarenites

The effects and importance of anthropogenic changes on karst environment

This paper describes a case study in the Murge karst (Apulia, southern Italy) in a site in which the role exerted by anthropogenic activity, in the course of the time, has caused significant damage to the natural landscape and environment, also in terms of loss of human life. Recently, in the night between 22 and 23 October, 2005, exceptional rainfalls (160 mm in a few hours, in an area where the mean annual rainfall is about 600 mm), hit the city of Bari and the neighbouring towns, belonging to the same catchment area. The heavy rainfall caused a flood event with disastrous results: six dead and the destruction of roads, railways and bridges. The whole area is characterised by a low-relief karst very rich in natural cavities and slightly incised valleys, the latter locally called “lame”. These karst valleys act as water flow channels only during and immediately after heavy rainstorms and, in the coastal area, generally, reach the shoreline. Karst morphology is very well developed due to widespread outcrops of Cretaceous carbonate rocks of the Apulian foreland. In recent years, urbanization, land use change and quarrying produced irreversible degradation and serious consequences for the the integrity of the fragile natural landscape. Starting from medium-term in situ observations, detailed surface surveys, historic and bibliographic data (archival terrestrial photographs and scientific papers), and aerial photograph analysis, this study provides a description of the main factors influencing the geomorphologic processes affecting a typical karst area including hydrological, geological and anthropogenic control on landscape development

Landslide processes and stability assessment in weathered carbonate rock cliffs

Many sites of the Apulian coast (southern Italy) consist of carbonate rock cliffs affected by intense erosion and development of slope instabilities. Present morphology of the coastal cliffs was mostly produced by the quaternary tectonics, and the severe and selective action of erosion by sea waves. In addition, due to the carbonate nature of rock masses, the role exerted by development of karst processes has to be considered. The cliffs are involved in different types of landslides, with several, complex mechanisms of rock slope failure. Assessment of the overall slope stability, and evaluation of the potential hazard, are related to the morphologic, lithologic, and structural characteristics of the rock cliffs, and to local meteomarine condition and erosion by sea waves as well. This article provides a critical review of the common modes of failure in weathered and soft carbonatic rocks; the different theoretical formulations that allow predictions about the behavior of rock slopes are also examined. Examples of slope hazard indicators and mass movement typologies are in particular illustrated along a typical apulian area (stretch of Murgia coastline south of Bari)

Deterioration of the ornamental stones from Apulia (SE Italy) caused by thermal stresses

Mesozoic carbonate rocks cropping out in Apulia, SE Italy, represent today, as in the past, a fundamental artistic and communicative mean for the local culture. For their physico-mechanical and aesthetic properties, these sedimentary rocks have always found a large application both as ornamental stones and as simple construction materials, particurarly in military architecture and worship buildings during the Middle Ages. The Apulian “marbles” are characterised by high strength and durability, nevertheless outdoors exposure often involves significant changes in their technical properties and state of conservation caused by weathering. The effects of thermal stresses on the material performances, due to diurnal and seasonal temperature fluctuations, constitute a topic of particular interest in the assessment of durability problems associated to long-term exposure. In this work, a study about changes in technical properties of the Apulian ornamental limestones and dolostones induced by thermal stresses is presented. Direct and indirect evaluations concerning index properties, mechanical strength, deformability, textural characteristics and chromatic features, on samples subjected to thermal cycles, were used for providing a comprehensive perspective about deterioration, from the mesoscopic scale to the microscopic one. In a muffle fornace, the samples were subjected to thermal cycles ranging from 100 to 700C. At the end of each cycle, mass and volume determinations, mercury porosimetry measurements, sclerometric tests, ultrasonic tests, thin section observations and chromatic evaluations through image analysis and Munsell charts were performed. The proposed methodology took into account only non-destructive or semi-destructive tests, in order to highlight the qualitative and quantitative characteristics of decay related to thermal stresses exclusively. In this way a constant comparison among the results of different experimental tests was carried out

Degree of decay and weathering mechanisms in the ancient walls of Castro (Salento, southern Italy)

The ancient centre of Castro is located on a hill ridge along the coastal area of Salento (southern Italy). It is known for the beautiful landscape and historic heritage date back to the Upper Palaeolithic (wall-paintings inside the coastal cave, locally called “Grotta Romanelli”). The medieval walls surrounding the ancient centre are now in a deteriorated state owing to weathering by wind action, marine aerosols and meteoric water precipitations. The historic structure is, in fact, exposed to marine environment. Calcarenite rocks, which outcrop along the coastal stretch about 5 km N of the historic centre, constitute the building stones of the ancient walls. These rocks are very soft and porous and show a reduced ability to maintain their characteristics of strength, appearance, and resistance to decay over a considerable period of time. In order to evaluate the degree of decay of the building stones, petrophysical and mechanical analysis were performed on both fresh (from original quarry) and deteriorated specimens. The study involves, particularly, microtextural analysis on thin sections using optical petrographic microscopy, and evaluation of index parameters by means of standard geotechnical laboratory tests. Particular attention is given to pore size distribution by mercury intrusion porosimetry, effective porosity and degree of saturation by water absorption determinations, grain size frequency distribution by traditional sieve and sedimentation analysis on disaggregated materials

Ultrasound velocity test to decay evaluation on decorative stone after different artificial ageing treatments

Ultrasound propagation velocity depends on several physical properties, for instance density, porosity and textural discontinuities within stones. These properties are strongly influenced by state of conservation of materials and their modification can be considered decay markers; therefore, ultrasound velocity measurement represents a non-destructive technique to evaluate the decay underway on employed stone. In this study, samples of the Avorio variety, an Apulian limestones, were processed to artificial ageing treatments, in particular thermal shocks, extreme thermal exposure at high temperatures between 200 and 600C, and cycles of immersion of rock samples into saline solution alternating with drying phases in muffle furnace. Effects of induced deterioration were examined by comparing p-wave ultrasound velocity values, visual appearance and mass loss with water absorption values and capillarity test results. This research suggests first that the ultrasound velocity test can be considered a valuable non-invasive technique to assess the state of decay of decorative and building stones. Furthermore, in order to simulate dangerous and extreme environmental conditions and study their influence on the stone decay patterns, new considerations and suggestions about ageing test and procedures were proposed

On the applicability of geomechanical models for carbonate rock masses interested by karst processes

Rock mass classification and geomechanical models have a particular importance for carbonate rocks, due to their peculiar fabric, variability of the main features, and scarce availability of experimental data. Carbonates are particularly sensitive to syn-depositional and post-depositional diagenesis, including dissolution and karstification processes, cementation, recrystallisation, dolomitisation and replacement by other minerals. At the same time, as most of sedimentary rocks, they are typically stratified, laminated, folded, faulted and fractured. The strength and deformability of carbonate rock masses are, therefore, significantly affected by the discontinuities, as well as by their pattern and orientation with respect to the in situ stresses. Further, discontinuities generally cause a distribution of stresses in the rock mass remarkably different from those determined by the classical elastic or elasto-plastic theories for homogeneous continua. Goal of this work is the description of the difficulties in elaborating geomechanical models to depict the stress–strain behavior of karstified carbonate rock masses. Due to such difficulties, a high degree of uncertainty is also present in the selection of the most proper approach, the discontinuum one or the equivalent continuum, and in the numerical model to be used within a specific engineering application as well. The high uncertainty might cause wrong assessments as concerns the geological hazards, the design costs, and the most proper remediation works. Even though recent developments in the application of numerical modeling methods allow to simulate quite well several types of jointed rock masses, as concerns carbonate rock masses many problems in representing their complex geometry in the simulation models still remain, due to peculiarity of the structural elements, and the presence of karst features. In the common practice, the improper use of the geomechanical models comes from a superficial geological study, or from the lack of reliable geological and structural data that, as a consequence, bring to erroneous evaluations of the influence of the geological-structural features on the in situ stress state and the stress–strain rock mass behavior

Influence of weathering, textural and geostructural features in slope stability analyses for limestone open pit quarries

The Murge plateau (Apulia, south-eastern Italy) is characterised by a Mesozoic sedimentary succession (exceeding 6000 m in thickness) of regularly stratified fine-grained limestones overlain by Plio-Pleistocene transgressive calcarenites deposited in shallow and agitated marine waters. This particular geologic setting has favored today, as in the past, an intense extractive activity, principally localized in open pit quarries. Although Italian legislation provides quarry restoration at the end of exploitation, many quarries were abandoned causing relevant environmental alteration and damages, and high risk situation for slope instability. Factors controlling the different types of landslides (slides, falls, topples, etc.) are described. In particular, the influence of textural and geostructural features on slope stability in carbonate rock masses affected by karst are analysed. Examples of rock slope failure complex mechanisms are illustrated at different scales. A new rock mass classification method for engineering design and a simple theoretical model for slope stability assessment is proposed

Shallow landslides in weathered soils: a case study from the Apennine chain in southern Italy

Stability conditions in an area located at the eastern Daunia Mts. are presented in this study. The Daunia Mts. belong to the outermost part of the southern Apennine chain, which consists of a Neogene thrust belt resulting from the deformation of the Apulian continental margin. In particular, the study area, in the territories of Alberona, Volturara Appula and San Bartolomeo in Galdo, is located at the north-western boundary of Apulia (southern Italy) in one of the most seismic zones of Italy. It is characterised by low structural and topographic elevation, only locally exceeding 1000 m above sea level. The geological setting is very complex and represented by a series of tectonically deformed turbiditic formations of pre-Pliocene age covered by discontinuous Quaternary and Holocene deposits, including terraced alluvial deposits and colluvial slope sediments. The outcropping units are rich of weathered argillaceous deposits in chaotic setting and prone to landsliding. The area is affected by intense landslide activity, mostly related to periods of heavy and prolonged rainfalls (mean annual rainfall is above 600 mm). The most common types of mass movement are shallow slips, flows and complex landslides consisting of rotational slumps evolving to flows. They are mainly re-mobilisations of shallow landslides involving weathered clayey soils. This study presents the site characterisation, including geology and hydrogeology, assessment of the pore pressures and soil properties, especially shear strength parameters for both drained and undrained conditions, mechanics of sliding, and analysis of stability, slope hazard and deformations pre- and post-failure. In particular, an attempt will be made to evaluate the weathered characteristics of the formations involved in landsliding