Dr Anna Giacomini

© 2017, Springer International Publishing Switzerland. Roof collapses during the constructions of underground excavations in weak rocks is a serious problem. In particular, excavations in shallow depths and in incompetent rocks may initiate the caving of the overburden materials and sinkhole formation. Sinkholes have significant environmental impacts and more importantly, they threaten the stability of surface and subsurface infrastructures above the excavations. This study investigates the formation of sinkhole subsidences in shallow excavations in poor and problematic rocks. The progressive collapse and sinkhole subsidence in the Dolaei road tunnel is considered as a case history. Understanding the geological and geotechnical characteristics of rocks is the fundamental step for analysing the mechanisms of instability. Rock mass characteristics are reviewed, and the most effective factors impacting on the tunnel¿s stability are identified and discussed. The role of the method of excavation and support in controlling ground movements are assessed through numerical modellings. The effect of pre-support as a practical technique for controlling ground movements and preventing sinkhole formation in weak rocks is also discussed. Outcomes of this study indicate that the rock mass surrounding the Dolaei tunnel consists of highly tectonised and foliated metamorphic rocks. Schistosity and foliation considerably impact on the strength and deformability of the rock mass. This study shows that the geological characteristics of the rocks in the Dolaei tunnel had substantial effect on the collapse and sinkhole formation. The numerical findings also reveal that employing pre-supporting techniques, particularly forepoling, using a staged excavation and applying composite support systems (consisting of rock bolts and reinforced shotcrete) are practical remedies to prevent the progressive collapse, and to avoid the formation of sinkholes during excavation in weak rocks in shallow depths.

© 2016 Informa UK Limited, trading as Taylor & Francis Group. This paper presents a new methodology for estimating the expected energies and first impact distances at the base of a rock cliff, subject to the geometry and properties of the cliff and the representative block being known. The method is based on a sensitivity analysis, conducted by means of kinematic simulations and carried out for a large range of input parameters and their combinations, taking into account the uncertainty associated with their estimate. The proposed approach is validated by comparing predictions to experimental data and shows great potential for a quick qualitative hazard assessment.

© 2014, Springer-Verlag Wien. In rockfall science, the bullet effect refers to the perforation of a rockfall mesh by a small block traveling at high speed. To date, there is still no comprehensive experimental data set investigating the underlying mechanisms of such effect. The bullet effect illustrates the fact that the capacity of a rockfall mesh depends on the size and speed of the impacting block. This paper presents the results of an experimental study on the effect of block size and mesh geometry (aperture and wire diameter) on the mesh performance. The results clearly show that the amount of energy required to perforate the mesh drops as the blocks get smaller. They also suggest that the mesh performance reaches a maximum and reduces to zero when the mesh cannot sustain the static load imposed by very large blocks. The outcome of the first series validates an analytical model for mesh perforation, making it the first simple model capturing the bullet effect. A second series of tests focused on the effect of mesh geometry and it was found that decreasing the mesh aperture by 19¿% improves the performance by 50¿% while only an extra 30¿% could be gained by increasing the wire diameter by 33¿%. The outcomes of the second series were used to discuss and redefine a dimensionless geometrical parameter G* and to validate a simple power type equation relating the mesh characteristics and the mesh performance.

From a consideration of the concepts of geological weathering and structure, it can be expected that rockfall hazards should be characteristically different in different geological environments. This paper tests this idea by looking at the geometric characteristics of rock fragments formed on natural slopes in four different geological environments in Eastern Australia, where rockfall phenomena are often characterised by rolling of pre-detached debris. By measuring the three principle dimensions and making a systematic assessment of the shape characteristics of samples of rock debris in significant geological environments, it is found that the distributions of size and shape for the surface debris are statistically different. From the results, it is shown that the size and shape of debris is directly controlled by the rock type, its weathering characteristics and the structure of the parent rock mass. The severity of rockfall hazards is shown to be relatively lower in areas of Tertiary basalt, as the size of rolling fragments is limited by closely spaced fracturing inherited from its formation and the tendency to deteriorate further as it weathers deeply and rapidly. It is also lower in areas of Palaeozoic volcanics, since these tend to produce relatively angular fragments with higher proportions of fragments that are inherently more resistant to rolling. By contrast, thickly bedded sandstones form larger blocks with a larger proportion of shapes that are more prone to rolling. The size distribution of fragments is shown to be well approximated by a log-normal statistical distribution, and using the data provided in this study, it is possible to generate the size and shape data needed to undertake a stochastic assessment of rockfall trajectories in different geological environments. © 2013.

This paper reports an analysis procedure for the evaluation of the features of the motion of blocks detaching from a steep rock wall and traveling down the slope below. Starting from the execution of real scale rock fall tests, carried out on two slopes having different morphology and lithology, the paper describes the methodology used for test interpretation and a procedure for the evaluation of the parameters best suited to the description of rock fall motion. The influence of the parameters assessed on the prediction of the rock fall trajectory was also investigated using two-dimensional and three-dimensional numerical models. These models were calibrated by means of a back analysis of the in situ tests, which also allowed the evaluation of the uncertainties involved in the parameters experimentally estimated.

This paper investigates the factors affecting the shear strength of granular materials by means of the tilt box test. The test involves the titling of a specifically designed split-box and measuring the angle at which the upper half of the box slides off. This angle can be interpreted as the peak friction angle of the sample for a low stress state. Experimental tests and numerical analyses using the Discrete Element Method (DEM) are carried out and compared. The study is carried out for two different materials, a rounded and an angular aggregate. It is shown that rolling resistance is needed to match the experimental results if only spheres are used but this is not the case for non-spherical particles. © 2015 Taylor & Francis Group, London.

This work consists of a preliminary numerical study on the impact behaviour of rock blocks on muckpiles using the Discrete Element Method (DEM). A contact law using a linear hysteresis model for normal contacts and a Mohr-Coulomb model for tangential contacts is used. In addition, two dissipative laws are introduced consisting of a moment transfer law and normal viscous damping law. One of the aims of this study is to investigate if the contact law enables a realistic modelling of the rebound characteristics of a block during impact on a muckpile. A parametric study is carried out in order to investigate the influence of the constitutive model parameters and the presence of clumps. Numerical predictions are compared to experimental results. It is shown that clumps in the muckpile are essential to reproduce realistic results. © 2015 Taylor & Francis Group, London.

This paper presents a discrete modelling approach which allows the simulation of rockfalls behind drapery systems. The falling rock is represented by a rigid assembly of spheres whereas the slope is represented by triangular elements. Energy dissipation during impact on the slope is considered via friction and viscous damping. The drapery is represented by a set of spherical particles which interact remotely. The numerical model is used to investigate the efficiency of a drapery system. Various simulations with two different block sizes are performed and the numerical predictions of simulations with drapery are compared to simulations without drapery in order to assess the performance of the protection system.

The paper investigates the soil-structure interaction between a clay embankment of the new high speed railway network Milan-Naples (Italy) and its clay foundation reinforced with different length driven concrete piles and geotextile. The embankment has been placed next to the old railway line. A monitoring system has been installed in a section of the embankment from the beginning of the construction of the new line. Numerical simulations describing both the old and new embankments (for a given section) have been carried out, by using Abaqus computer code, in order to back analyse the monitoring data. The analysis has been carried out in effective stress conditions, referring to long term conditions, to analyse the engineering problem to reduce the final embankment settlement. The results of the numerical simulations put into evidence that the model can reproduce the experimental data regarding the settlements below the new embankment and the interaction between the new embankment supported by piles and the old railway line embankment. © 2007 Taylor & Francis Group.