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Un modello teorico per lo studio del fenomeno di imbarcamento in rivestimenti di marmo soggetti a cicli termici
No full textIntergranular Microcracking Due To Anisotropic Thermal Expansion In Calcite Marbles
No full textMarble slabs are frequently used as façade panels to externally cover buildings. In some cases bowing of such façade panels after a certain time of environmental exposure is experienced. The bowing is generally accompanied by a progressive reduction of strength. In the present paper, a theoretical model to calculate the progressive bowing and the thermal fatigue of marble slabs submitted to temperature cycles is presented. The model, developed within the framework of fracture mechanics, takes into account the mechanical microstructural characteristics of the marble as well as the actual cyclic temperature field in the material. The slabs are subjected to a thermal gradient along their thickness (due to different values of temperature between the outer and inner sides of the slab) as well as to thermal fluctuation on the two sides of the slab due to daily and seasonal temperature excursions. This thermal action causes a stress field which can locally determine microcracks due to decohesion of calcite grains. Stress intensification near the cracks occurs and leads to crack propagation in the slab. Such crack propagation under thermal actions is evaluated and the corresponding bowing is calculated
In situ stress measurements interpretations in large underground marble quarry by 3D modeling
No full textThis paper describes the studies and the in situ stress measurements carried out to support the stability
analysis of underground ornamental stones quarries. In particular, this paper describes the findings,
evidence and analysis carried out at the Ravaccione and Fantiscritti quarries, which are located in the
Carrara basin, Italy. Themain activities carried out during the study are starting with the characterization of
the rock mass which has been done through the interpretation of data obtained from in situ geostructural
surveys, combining the geometrical and mechanical characteristics of the discontinuities with the
mechanical features of the rock matrix in order to assess the proper rock index in accordance with the
more diffused classification systems. Further consideration regarding the tectonic stress orientation are
done through the observation of kinematic indicators on brittle structures-such as faults, fractures s.l.
(joints s.s., and fractures with no evidence of movement) and systems of conjugated fractures, in order to
evaluate the tectonic stress main orientation for the studied area. Then several in situ measurements of
actual state of stress on various location inside the Ravaccione and Fantiscritti quarries where carried out
using CSIRO cells. This preliminary work lead to the geometric reconstruction of the rock mass, carried out
using the computer code Resoblocks. This phase allowed, once the current excavation geometry was given,
to define the geometry of a discontinuous rock mass model on which, thereafter, a numerical simulations
was carried out using the computer code 3DECs. At last, the comparison between the numerical model
results and the in situ tests allowed the back analysis of the site and lead to a most satisfying model
calibration to be used for the provisional analysis of further excavation development
Studio tridimensionale del rivestimento di prima fase in spritz-beton di gallerie profonde
No full textIn this work the behaviour of shotcrete preliminary linings for tunnel construction has been analysed. This problem is quite complicated, due to the complexity of tunnel modelling and material nonlinearity. Few constitutive models able to describe the actual mechanical behaviour of the lining are available in technical literature. In most cases, material nonlinearity and the stress and strain distribution along the thickness of shotcrete lining are ignored and the design of lining thickness and reinforcement is frequently based on semi-empirical methods.
In order to investigate the influence of reinforcement type on shotcrete behaviour, a series of NLFE analyses simulating the conventional procedure of tunnel excavation and lining have been carried out. The attention has been mainly focused on deep tunnels excavated in rock, considering different opening geometries and initial stress distributions. The local behaviour of shotcrete has been modelled through the PARC constitutive model, which is able to describe the behaviour up to failure both of ordinary and fibre reinforced concrete structures
Numerical study of the role of fibres in the preliminary lining of tunnels
No full textThe design of preliminary lining has a fundamental role in the stabilization of tunnel working, before the completion with the final concrete lining. Among the several types of lining, shotcrete is one of the most widespread, but since its limited tensile strength it is usually reinforced using welded steel fabric or coupled with steel ribs and anchorage systems in the soil. Nowadays, the designers, instead of using welded steel fabric, prefer more and more often the use of standard concrete reinforced with steel and/or synthetic fibres, which are usually added during material mixing.
Recent studies [1] have shown that the use of fibres, considering proper volumetric percentages, fibre lengths, aspect ratios and bond properties, also mixing, if necessary, different types of fibres (hybrid fibres), has a positive effect on all FRC mechanical properties, and particularly on its tensile strength, ductility, workability and shrinkage. As the material shows a larger toughness, the presence of fibres especially improves the properties which are typically related to the post-cracking behaviour; so fibres are often used instead of traditional reinforcement in several applications.
In this work the attention will be focused on preliminary lining realised using shotcrete. A series of numerical analyses aimed to determine the role of fibres with respect to traditional welded steel mesh on the structural behaviour of preliminary lining will be carried out by performing transversal and longitudinal bidimensional tunnel finite element models having different kind of lining (concrete, traditionally and fibre reinforced concrete.
In order to perform realistic simulations, the local behaviour of concrete reinforced by fibres and ordinary bars must be properly modelled to realistically describe the soil-structure interaction forces, stress and strain fields of the single materials as well as crack pattern and failure modes of structural elements. To this scope the PARC [2, 3] constitutive model, which is able to describe the behaviour up to failure both of ordinary and fibre reinforced concrete structures, will be adopted to perform non linear finite element analyses
Confronto tra prove quasi statiche e dinamiche di assorbimento di energia di strutture di protezione
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