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Abstract The "Chaotic Complex" is a mélange largely present in the Northern Apennines (Italy). It resembles both sedimentary, olistostromes, and tectonic mélanges, which geostructural assemblage ranges from "broken formation" to "scaly fabric". The Chaotic Complex (CC) is characterized by a clayey matrix including calcareous rock blocks which size can range from coarse sand to boulders and huge fragments of a formation. In this paper its geomechanical characterization has been faced with these criteria: Classical geotechnical approach; GSI approach; Bimrock approach. In general it results that Mohr-Coulomb data from GSI cover a wider range than those from lab tests, while the Bimrock approach resulted into higher values of friction angle and lower values of cohesion. 1 Introduction The Chaotic Complex (hereafter called as CC) is widely present in the Northern Apennines orogenic chain, Italy. It is a redefinition (Abbate & Sagri 1970) of the classical term "Argille Scagliose" introduced by Salmojraghi (1881) in a paper facing the geological concerns encountered by the "new" Napoli- Foggia rail-line, Southern Apennines, where it is also largely present and known as "Varicoloured Shales". Since that experiences, which led to the introduction of the classical "Italian Method" to drive a tunnel through complex squeezing and swelling rock-mass, many tunnels, large mine and civil excavations were executed into the CC, every time with severe concerns (short-term response in terms of strong swelling and squeezing) regarding both the stability of the excavations and how to face that problems by a correct rock-mass characterization and parameters definition. In almost all those experiences, the classical geotechnical approach, which implies the definition of the mechanical parameter of the shaly component of the CC on reconstructed samples, was applied. Recently, the Bimrock (Medley 1994) and GSI (Hoek et al. 1998, Marinos & Hoek 2001) approaches were introduced in order to define the rock-mass parameters to be used in the design for tunnels and large civil and mine excavations. In this paper, on the basis of published data and personal experience, we compare results from these three different approaches in order to outline the advantages and difficulties in defining the best approach suitable to be used for CC in tunnelling and excavations.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral (0.96)
- Geology > Structural Geology > Tectonics (0.91)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.50)
ABSTRACT: The Northern Apennine chain in Italy is characterised by scattered outcrops of many oligo-miocenic clay-limestone melanges. The Shale-Limestone Chaotic Complex (SLCC) is one of these melanges and it outcrops in the Valdarno Basin, eastern part of Tuscany. From a geotechnical point of view the SLCC represents a typical bimrock, made up of a highly sheared and tectonized, scalyfabric, clayey matrix containing marly-calcareous blocks from a few millimetres to tens of meters in size, randomly distributed. In this paper focus is given to high artificial slopes (a few hundred meters) of a dismissed pit-mine cut in the SLCC bimrock. An accurate characterization of the block size distribution in the matrix was carried out by means of photographic surveys on natural and artificial outcrops, that allowed a high number of georeferenced images to be collected. Images were analyzed with an image processing technique, providing important indications about the block-size distribution in the studied bimrock. 1. INTRODUCTION The Shale-Limestone Chaotic Complex (hereafter called as SLCC) is a typical melange widely outcropping in the Northern Appennine chain in Italy. It is made up of a highly tectonized clayey matrix containing heterometric, randomly distributed, marly-calcareous blocks in a typical block-in-matrix fabric. The SLCC forms wide mined slopes in the Santa Barbara dismissed pit-mine (Fig. 1), located near San Giovanni Valdarno, Tuscany. Fig. 1. Panoramic view of the SLCC slopes in the Santa Barbara dismissed pit-mine. A1 and A2 are two of the investigated outcrops discussed later in this paper.(available in full paper) The slopes, with a total length of 1.5 km and a total height of 180 m, underwent since the beginning of their excavation large mass movements and rotational landslides. The Santa Barbara mine complex is a property of ENEL S.p.A., the largest power company in Italy, which is promoting a research study on the geological and geomechanical characterization of the SLCC in order to properly characterize the mechanical behavior and to assess the stability of the slopes. This paper presents the first results of this research study, conducted at the Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna. A detailed geological and geomechanical characterization of the SLCC was carried out by means of field surveys and bibliographic research. The activity is now focusing on the marlycalcareous block-size distribution in the SLCC, according to the bimrocks theory [1, 2, 3, 4, 5, 6]. The investigation was carried out by means of photographic surveys and an image analysis technique. 2. GEOLOGICAL CHARACTERIZATION OF THE SLCC The SLCC represents one of the many melanges extensively mappable in Tuscany. Tuscan melanges are interbedded in the oligo-miocenic turbiditic formations, like the Macigno of the Tuscan Nappe, and their origin is still under debate in the geological community [7, 8, 9, 10]. Some authors attribute the origin of Tuscan melanges to sedimentary submarine mass movements, like debris-flows and mud-flows [7, 8]. These phenomena generate huge chaotic accumulation of hheterogeneous and heterometric material (i.e. olistostromes) deriving from preexisting formations. The scaly fabric of the clayey matrix shows that the deposition and diagenesis of the sedimentary body took place in a context of tectonic activity during the formation of the Northern Appennine chain [7, 8, 11].
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.91)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Power Industry (0.89)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.56)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (0.56)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.47)
- Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (0.34)
ABSTRACT: Six non conventional in situ shear tests were carried out in order to investigate the strength properties of the Shale Limestone Chaotic Complex bimrock at the Santa Barbara disused open-pit mine. The testing procedure ensures that the failure surface is free to develop in a tortuous way along block/matrix contacts, thus allowing for the evaluation of the bimrock strength parameters by taking into account the influence of blocks, and ultimately to overcome the size limitation of laboratory specimens. The evaluated operative strength parameters show an overall larger friction angle and a lower cohesion compared to that of the clayey matrix, in agreement with the common bimrock mechanical behaviour. 1 INTRODUCTION The Shale-Limestone Chaotic Complex bimrock (hereafter referred as SLCC) outcrops over a wide slope in the Santa Barbara disused lignite open-pit mine (Italy). During the past years, in fact, the SLCC has been the object of several studies that assumed it as a homogeneous body governed by the mechanical properties of the clayey matrix only (D'Elia et al., 1988; Tommasi, 1996; D'Elia et al., 2006). In order to overcome the inadequate size of laboratory specimens and namely to take into account the influence of blocks, six non conventional in situ shear tests were carried out on specimens of 0.3m3 in volume. The testing procedure ensures that the shear plane is free to develop inside the specimen and to negotiate in a tortuous way along the block/matrix boundaries; thus differing from the ISRM Suggested Method for In Situ Shear Tests (ISRM, 2007). This aspect has a very important role in shear tests performed on bimrocks: the main consequence for the presence of blocks, in fact, is an increase in tortuosity of the shear plane that causes the increase in shear strength.
- Asia (0.70)
- North America (0.69)
- Europe > Italy (0.51)
- Geology > Geological Subdiscipline > Geomechanics (0.99)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.46)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.46)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Metals & Mining (0.89)
In Situ Large Size Non Conventional Shear Tests For the Mechanical Characterization of a Bimrock In The Santa Barbara Open Pit Mine (Italy)
Coli, N. (Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna) | Berry, P. (Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna) | Boldini, D. (Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna) | Bruno, R. (Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna)
Abstract A high mine slope in the disused Santa Barbara open pit mine (Tuscany, Italy) is cut in the Shale-Limestone Chaotic Complex (SLCC), which is a typical bimrock made up of a scaly-fabric clayey matrix including heterometric calcareous blocks. The slope shows evidence of instability phenomena: mainly rotational landslides and toppling countercracks. In order to characterize the mechanical behaviour of the SLCC bimrock, in situ large size non conventional shear tests were performed. The aim of in situ tests is to overcome the size limitation of laboratory specimens and namely to take into account the influence of calcareous blocks on the strength of the bimrock. Bimrock’s strength parameters under natural conditions can be evaluated by means of a limit-equilibrium analysis taking into account shear test data and the geometry of the sliding surface. 1. INTRODUCTION The Shale-Limestone Chaotic Complex (SLCC) is a mélange formation of the Northern Apennines mountain belt, which, from a geomechanical point of view, represents a typical block-in-matrix rock (bimrock) [1, 2, 3, 4]. The SLCC forms a wide mine slope (with a maximum height of 200 m and a planar extension of about 1300 m x 400 m) in the disused Santa Barbara lignite open pit mine (Tuscany, Italy) (Fig. 1). Since the beginning of its excavation, the slope suffered from a diffuse instability phenomena characterized by rotational landslides and toppling countercracks. Gravitational movements must be considered as still active: rotational landslides show evidence of reactivation due to intense precipitation while toppling countercracks has displayed a net slip up to a meter, over the last two years. In the past, during mine activity, several stability analyses were carried out, assuming the SLCC as an homogeneous material governed by the only mechanical properties of the clayey matrix, without taking into account the influence of calcareous blocks on the mechanical behaviour of the bimrock [5, 6, 7]. On the other hand, recent advances in the understanding of bimrock’s mechanical properties have pointed towards a strong influence of the blocks on the strength of the bimrock [8, 9, 10, 11, 12]. For this reason, a research study on the geomechanical characterization of the SLCC according to modern bimrock theories is being carried out. (Figure in full paper) The research is conducted by the Department of Chemical, Mining and Environmental Engineering (DICMA), University of Bologna. In the first step of the research program the geometrical properties and spatial variability of calcareous blocks were investigated by means of advanced image and geostatistical analyses [13, 14]. The activity is now focusing on defining the mechanical behaviour of the SLCC. In order to investigate the actual strength of the bimrock, non conventional in situ shear tests are being carried out on large-sized material specimens (80 cm x 80 cm x 50 cm). The tests are performed with the financial and logistical support of ENEL Santa Barbara Department. 2. GEOTECHNICAL CHARACTERIZATION OF THE CLAYEY MATRIX In order to characterize the SLCC clayey matrix from a geotechnical point of view.
- North America > United States (1.00)
- Europe > Italy > Tuscany (0.45)
- Europe > Italy > Emilia-Romagna > Bologna > Bologna (0.25)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.45)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.45)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.95)
An Integrated Geostatistical-geomechanical Approach For the Characterization of a Bimrock
Coli, N. (Department of Civil, Environmental and Material Engineering (DICAM), University of Bologna) | Berry, P. (Department of Civil, Environmental and Material Engineering (DICAM), University of Bologna) | Bruno, R. (Department of Civil, Environmental and Material Engineering (DICAM), University of Bologna) | Boldini, D. (Department of Civil, Environmental and Material Engineering (DICAM), University of Bologna)
ABSTRACT Bimrocks are structurally complex formations made up by a fine-grained matrix including heterometric hard-rock fragments which deeply influence their mechanical behavior. A new approach for characterizing the morphological and spatial variability of rock fragments in bimrocks is introduced, based on the geostatistical analysis of bimrock outcrop pictures through a single-scale variogram analysis of the rock fragment indicator variable IB (x, y). The analysis indicated the presence, all over the field, of a nested structure characterized by three or four common elementary variogram models, each taking into account the variability of a specific size range of the rock fragments. A first attempt was also made in order to investigate the possible correlations between the bimrock strength parameters, obtained through in-situ non-conventional shear tests (BimTests), and the geostatistical indexes, which quantify specific spatial and morphological properties of the fragments, by means of a Cross- Covariance study of non-isotopic regionalized variables (ReV). 1. INTRODUCTION Bimrocks [1] are structurally complex formations characterized by a fine-grained soil, the “matrix”, which includes, in a typical block-in-matrix fabric, hard-rock fragments of variable dimensions. The presence of rock fragments above a critical threshold size, namely the block/matrix (B/M) threshold, deeply influences the mechanical behaviour of bimrocks [2, 3, 4, 5, 6, 7]. The B/M is not an absolute property of bimrocks but is related to a specific engineering scale of interest (i.e. several B/M can be identified depending on the working scale of the problem under investigation). Due to their complex structure, an exhaustive mechanical characterization of bimrocks requires some special investigations to be carried out. In particular a nonconventional in-situ large size test (namely BimTest) was developed by the Authors in order to properly take into account the presence of rock fragments and their interactions with the soil matrix [8]. The main advantage of BimTest is that that the shear plane is free to develop inside the specimen, thus allowing for an increase in tortuosity of the shear plane, leading to an increase in the bimrock shear strength compared to that of the only clayey matrix. However, the in-situ characterization through BimTests could result in a quite expensive and time-consuming task, especially when large volumes of the formation are involved. For this reason, the possibility to integrate the mechanical tests with an indirect method of characterization was investigated. The analysis aimed at correlating the strength parameters with 2D geostatistical indexes obtained through a single-scale variogram analysis of the rock fragment indicator variable IB (x, y), performed on digital pictures of outcrop exposures. The present study was carried out on a wide slope located in a dismissed open-pit mine in Tuscany, Italy, characterized by a wide exposure (about 345.000 m2) of an Oligo-Miocenic olistostrome of the Tuscan Nappe. The formation is constituted by a dark-grey clayey matrix containing rock fragments of micritic and arenitic limestone [9] (Fig. 1). 2. THE BIMTEST Six BimTests were performed over the investigated area, on specimens of 0.3 m3 (80x80x50 cm) [8].
- Europe > Italy (0.70)
- Europe > Norway > Norwegian Sea (0.45)
- North America > United States > California (0.29)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type (0.90)