Tunneling in heterogeneous rock masses with a block-in-matrix fabric

Napoli, Maria Lia; Barbero, Monica; Scavia, Claudio

doi:10.1016/j.ijrmms.2021.104655

Cited by 30 publications

(17 citation statements)

References 23 publications

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“…These results confirm previous findings from the literature, which highlight that the presence of the blocks provides little geomechanical advantage for low VBP values (i.e. 25% VBP) with respect to the matrix-only model, while for higher rock contents the SFs increase significantly (Lindquist 1994;Medley and Sanz Rehermann Napoli et al 2018aNapoli et al , 2019Khorasani et al 2019b).…”

Section: Resultssupporting

confidence: 90%

“…In order to investigate the factors influencing the overall mechanical behaviour of these complex formations, much research has been conducted in the last decades. The results of these studies have shown that the strength, deformability and failure mode of these geomaterials mainly depend on the volumetric block proportion (VBP), when this parameter falls between 25 and 75% (Lindquist and Goodman 1994;Sonmez et al 2004Sonmez et al , 2006Barbero et al 2012;Coli et al 2012;Afifipour and Moarefvand 2014;Napoli et al 2018aNapoli et al , 2021Napoli 2021). Moreover, the importance of taking blocks into account in the planning, designing and construction phases of any engineering work has also been underlined.…”

Section: Introductionmentioning

confidence: 99%

“…More rigorous, statistically based FEM analyses were carried out by a few authors, who investigated the effects of VBPs on safety factors (SFs), volumes involved and failure surfaces tortuosity of slopes in bimsoils (Khorasani et al 2019b, a) and bimrocks (Napoli et al 2018b, a). In order to take the inherent variability of bimrocks and bimsoils into account, these authors analysed ten configurations for each VBP considered.…”

Section: Introductionmentioning

confidence: 99%

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Effects of block shape and inclination on the stability of melange bimrocks

Napoli

Barbero

Scavia

2021

Bull Eng Geol Environ

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A wide range of heterogeneous geological units composed of strong rock blocks enclosed in a bonded matrix of fine texture exists worldwide. Such geomaterials belong to geotechnically complex formations and are often referred to as bimrocks (block-in-matrix rocks) or bimsoils (block-in-matrix soils), as a function of their matrix characteristics and the interface strength between the matrix and blocks. Stability problems occurring in such complex geomaterials have been analysed almost exclusively by means of deterministic approaches and with the aim of investigating the effects of variable block contents on their mechanical behaviour. However, bimrocks and bimsoils can present very different internal block-in-matrix arrangements and properties according to their forming process and, consequently, significantly dissimilar mechanical behaviours. Therefore, the aim of this paper was to statistically investigate and compare the stability of theoretical slopes in the most widespread bimrock formations, i.e. sedimentary and tectonic melanges. These formations are characterised by substantial differences in their rock inclusion geometry. To this aim, a great number of 2D slope models were generated to enclose blocks with variable shapes, dimensions, arrangements, inclinations and contents. To obtain statistically based results, fifteen configurations were analysed for each block content and geometrical configuration considered. The results obtained indicate that block shapes and orientations significantly affect the stability of slopes in bimrocks only when the block contents are greater than 40%. Moreover, it is demonstrated that blocks inclined 0° to the horizontal provide the most tortuous and irregular failure surfaces and, consequently, the highest safety factors.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of block shape and inclination on the stability of melange bimrocks

Napoli

Barbero

Scavia

2021

Bull Eng Geol Environ

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“…Due to the erratic variability of the mechanical properties of mélanges, considerable difficulties may arise in their sampling, testing and characterisation [10][11][12][13][14][15][16]. Moreover, the design and execution of geotechnical works in/on these geomaterials, such as tunnel excavations or landslide repairs, have proven to be extremely challenging [1,10,11,[17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Preliminary Characterisation of an Italian Soft Rock with a Block-in-Matrix Fabric

et al. 2022

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Mélanges are heterogeneous geological deposits and represent the most widespread bimrock (block-in-matrix) formations. This paper presents the efforts undertaken to characterise an Italian mélange composed of a clayey-marly matrix enclosing strong calcareous blocks. Due to its low uniaxial compressive strength, this geomaterial can be classified as a soft rock. The weak nature of the marly matrix and its water sensitivity, as well as the presence of rock inclusions, made the collection and preparation of intact specimens extremely complex and time-consuming operations. The difficulties encountered during these phases are described in detail; the various non-conventional procedures considered and developed to overcome these problems are also presented. The potential of the solutions proposed lies in the fact that they can be conveniently applied to other soft rocks with a block-in-matrix internal arrangement, such as the Italian mélange. To characterise the Italian mélange, point load and uniaxial compressive tests were carried out. From the results of these tests, a conversion factor equal to 14 is proposed to correct the point load strength index in order to estimate the uniaxial compressive strength of soft rocks, such as the mélange under study. Moreover, to estimate local strains and the deformability of the geomaterial, the non-destructive digital image correlation technique was applied.

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“…Soil-rock mixtures (S-RMs) are extremely inhomogeneous geomaterials typically composed of rock blocks with various sizes and a fine-grained soil matrix (Xu 2008). They are widespread worldwidely over natural slopes (Medley 1994;Li et al 2004;Sonmez et al 2006;Coli et al 2011;Minuto and Morandi 2015;Napoli et al 2021) and are also used as construction materials in embankments and fills (Calseira and Brito 2014;Zhang et al 2016a, b;Cen et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Influence of Block form on the Shear Behaviour of Soft Soil–Rock Mixtures by 3D Block Modelling Approaches

et al. 2022

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The influence of block forms on the shear behaviour of soil–rock mixtures with soft blocks (soft S–RMs) can be efficiently investigated by the discrete element method (DEM) on the basis of accurate 3D models accounting for the block breakage. This paper proposes a novel modelling approach, based on the spherical harmonics series, for the generation of 3D block geometries with different forms but same convexity and angularity. An already existing non-overlapping modelling approach was improved, characterized by a reduced computational cost, for the set-up of 3D block DEM models accounting for the block breakage. A number of soft S–RM DEM samples, subjected to numerical direct shear tests, were generated to analyze the influence of block forms and volumetric block proportion VBP on the mesoscopic and macroscopic behaviours. The results showed that the breakage degree is maximum for the spheroidal blocks, followed by the oblate, prolate and blade ones, due to the combined influence of the block frictional sliding and rotation. The shear strength of soft S–RMs is mainly controlled by the block interlocking and breakage, being maximum in the case of spheroidal block samples when the applied normal stress is low and in the case of prolate and blade ones for a high normal stress. It was found that a nonlinear Mohr–Coulomb criterion can provide a good description of the shear strength envelope of soft S–RMs. Soft S–RMs are characterized by a higher friction angle if composed by spheroidal and prolate blocks when the VBP is 40%, due to their elevated block interlocking, and in the case of prolate and blade blocks when the VBP is 60% at the higher normal stress, due to their lower block breakage degree.

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Tunneling in heterogeneous rock masses with a block-in-matrix fabric

Cited by 30 publications

References 23 publications

Effects of block shape and inclination on the stability of melange bimrocks

Effects of block shape and inclination on the stability of melange bimrocks

Preliminary Characterisation of an Italian Soft Rock with a Block-in-Matrix Fabric

Influence of Block form on the Shear Behaviour of Soft Soil–Rock Mixtures by 3D Block Modelling Approaches

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