Preliminary 3-D finite element analysis of the triggering mechanism of an occasional reactivation of a large landslide in stiff clays

In December 2013 a large landslide occurred along a clay slope located at the south-western outskirts of the Montescaglioso village (Basilicata, Southern Italy) as a consequence of intense and prolonged rainfalls that presumably caused a significant increment of the pore water pressures in the slope. The slope is formed of stiff clays belonging to the formation of the Subappennine Blue Clays, which are over-consolidated and characterized by medium plasticity. According to aerial photos dating back to 1950s, the slope was already affected by previous landslide processes, so that the examined landslide process can be classified as an occasional reactivation according to the well-known classification of Cruden & Varnes (1996). Also, during the last decades several man-made actions in the area resulted in strong changes in the original water surface network that could have played some role in the slope reactivation. Based on displacement data, obtained from a monitoring system installed few days after the phenomenon, and still in function, at present the landslide does not show relevant signs of activity. Preliminary 2-D and 3-D finite element analyses have been carried out to investigate the factors that controlled the mechanism of reactivation of the landslide. The numerical model has been setup based on the available topographical, geological and geomorphological information, the geotechnical properties of the involved soils and the information concerning the piezometric regime in the slope. The results indicate that the mobilized shear strength of the clays ranges between the typical post-peak and residual values for this type of material and confirmed that the strong increment of the pore water pressures in the slope induced by the exceptional rainfalls occurred in the previous days can be identified as the main triggering factor of the reactivation

Stability charts based on the finite element method for underground cavities in soft carbonate rocks: validation through case-study applications

Abstract. The stability of man-made underground cavities in soft rocks interacting with overlying structures and infrastructures represents a challenging problem to be faced. Based upon the results of a large number of parametric two-dimensional (2-D) finite-element analyses of ideal cases of underground cavities, accounting for the variability both cave geometrical features and rock mechanical properties, specific charts have been recently proposed in the literature to assess at a preliminary stage the stability of the cavities. The purpose of the present paper is to validate the efficacy of the stability charts through the application to several case studies of underground cavities, considering both quarries collapsed in the past and quarries still stable. The stability graphs proposed by Perrotti et al. (2018) can be useful to evaluate, in a preliminary way, a safety margin for cavities that have not reached failure and to detect indications of predisposition to local or general instability phenomena. Alternatively, for sinkholes that already occurred, the graphs may be useful in identifying the conditions that led to the collapse, highlighting the importance of some structural elements (as pillars and internal walls) on the overall stability of the quarry system

Sinkhole susceptibility assessment of underground caves in soft rocks by means of FEM-based charts.

The presence of man-made underground caves in soft carbonate rocks susceptible to degradation processes due to weathering nowadays induce high risk conditions in the Apulia region (Southern Italy) which is characterised by a huge number of caves spread in the territory. In recent years, several collapses affected some of these cavity systems, involving structures and roads located at the ground surface and, therefore, inducing high risk for human life and properties. In order to comply with this problem at the regional scale, Perrotti et al., 2018, have proposed specific charts aimed at assessing at a preliminary stage the stability conditions of a cave along with a safety margin with respect to the occurrence of failure. The charts have been defined upon the results of a large set of parametric two-dimensional finite-element analyses of ideal cases of underground cavities that account for the typical geometrical features of the caves and the range of mechanical properties of these rocks. The relationships obtained in terms of plots representing the ratio between the strength mobilized at failure and the vertical stress at the cavity roof against the ratio between cave width and roof thickness identify mechanically-based threshold envelopes for stability. In this paper, applications of the stability charts to case studies of man-made underground caves of soft carbonate rocks, either subjected to failure in the past or still stable, are discussed. In the first case the applications proposed show the role of specific structural elements, as pillars and walls, on the general stability of the examined quarry system, while in the second case an indication on the safety factor of the cave with respect to instability has been derived. Therefore, the proposed stability charts have been verified to provide a reliable method to assess in a preliminary way the stability of underground cavities in soft carbonate rocks, so that, for those situations where the safety margin results to be low, more detailed and sophisticated numerical models need to be developed

Stability charts based on the finite element method for underground cavities in soft carbonate rocks: validation through case-study applications

The stability of man-made underground cavities in soft rocks interacting with overlying structures and infrastructures represents a challenging problem to be faced. Based upon the results of a large number of parametric twodimensional (2-D) finite-element analyses of ideal cases of underground cavities, Accounting for the variability both cave geometrical features and rock mechanical properties, specific charts have been recently proposed in the literature to assess at a preliminary stage the stability of the cavities. The purpose of the present paper is to validate the efficacy of the stability charts through the application to several case studies of underground cavities, considering both quarries collapsed in the past and quarries still stable. The stability graphs proposed by Perrotti et al. (2018) can be useful to evaluate, in a preliminary way, a safety margin for cavities that have not reached failure and to detect indications of predisposition to local or general instability phenomena. Alternatively, for sinkholes that already occurred, the graphs may be useful in identifying the conditions that led to the collapse, highlighting the importance of some structural elements (as pillars and internal walls) on the overall stability of the quarry system

Analysis of the Displacement Field of Soft Rock Samples During UCS Tests by Means of a Computer Vision Technique

The measurement of rock sample displacement during laboratory testing is generally carried out by means of instrumental devices, which are capable of detecting average or local sample displacements, but are subjected to various error measurements; instrumental errors especially increase when localization takes place in the rock sample and macro-cracking develops. Photogrammetric techniques and, more recently, computer vision techniques based on non-contact digital image change detection propose an interesting alternative in this field, since they allow for detecting, with high precision, the visible displacement field of the rock sample external surface. This work is aimed at presenting the results of the application of an advanced computer vision technique to the assessment of the evolving displacement field of soft calcarenite samples subjected to uniaxial compression test. The corresponding results confirm that the technique is capable of detecting, with high level of accuracy, both the pre-failure displacement evolution, when continuity conditions still exist in the sample, and in the post-failure state, when large fissuring occur and a clear failure mechanism develops in the sample. A comparison between the results obtained from the technique here proposed and those resulting from a more conventional digital image correlation technique is also provided, highlighting a clear improvement in terms of accuracy of the images and capability of detecting the failure mechanisms of the samples

Developing mechanically-based charts to address the assessment of underground cave stability

Natural or anthropogenic sinkholes threaten diffuse areas of the italian territory. A specific research project aimed at defining an overall methodology for susceptibility analysis and risk mitigation of underground cave sinkholes, from cave identification to modelling failure mechanisms and defining mitigation interventions, has been recently developed. Based on two levels at different scale of analysis, i.e. urban area and single cavity scale, the methodology at the first level is aimed at defining quantitative procedures to assess in a preliminary way the stability of underground caves at the urban area scale. As a matter of fact, when dealing with a large number of cavities, single-cavity scale investigations can be time- and cost-consuming, resulting in huge economical investments. Therefore, a preliminary approach to detect those caves that are characterized by relatively high failure susceptibility level is necessary to make choices for investing more sophisticated analyses. In particular, the project has furtherly developed a methodology already proposed by Perrotti et al. (2018, 2019) aimed at assessing the stability conditions of underground caves by using charts based on the results of parametric finite element analyses. The use of such stability charts is straightforward since they are based only on simple information regarding the cave geometry and the geo-mechanical parameters. An advanced version of the charts has been proposed in the aforementioned project, which includes also the quantitative assessment of a safety factor range. The enhanced version of the stability charts has been also validated against field data.The methodology is not intended to replace proper site-specific stability analyses and models implementing the actual cave geometry and the rock mass stress-strain state and should be considered only for speditive preliminary stability assessment

Clinical and radiographic mid-term outcomes after shoulder resurfacing in patients aged 50 years old or younger

Purpose: Humeral resurfacing is a treatment option to conventional shoulder arthroplasty, conferring the advantages to preserve the bone stock and the normal joint geometry. Aim of the current study was to report clinical and radiographic mid-term outcomes in a population of 60 patients, aged 50 years or younger, who underwent shoulder resurfacing in osteoarthritis. Methods: The mean age was 48 ± 8.4, 36 were male and 24 female, dominant arm in 43 cases. Glenoid arthritis was treated in 36 cases (60 %) using a meniscus allograft in 22 cases, biologic patch in 4 cases and microfractures in 10 cases. Clinical and radiographic assessment was performed with Constant-Murley score and standard X-ray. Results: At an average follow-up of 44 months, the mean values of the constant score increased of 30 points (p < 0.05), the pain decreased of 4.56 points (p < 0.05) and the Simple Shoulder Test increased of 4.3 points (p < 0.05). We found lower scores (p > 0.05) in 9 patients (15 %) treated for glenoid arthritis using homologous meniscus (7 cases) and biologic patch (2 cases). A significant narrowing of joint space (5.92 mm postoperative versus 1.65 mm at 37 months) (p < 0.05) was found in the 22 cases treated with meniscus interposition. In 4 cases with type A2 preoperative glenoid morphology and in 9 cases type B1, we registered significantly lower scores compared with the overall study population (p < 0.01). Five unsatisfied patients (7 %), underwent to meniscus removal and glenoid reaming in 3 cases and conversion in total shoulder arthroplasty in 2 cases. Conclusions: Resurfacing arthroplasty is an effective device in young patients with advanced glenohumeral arthropathy; however, the high rate of postoperative glenoid erosion and the failure of biologic allograft lead us to consider glenoid replacement as the best option to improve clinical outcomes. © 2013 Istituto Ortopedico Rizzoli

Influence of brittleness of soft calcarenites in cliff stability problems: insights from FEM-DEM modelling

For soft rocks, brittle behavior occurring under low confinement stresses is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of rocky cliffs. In these cases, modelling approach should take directly into account processes such as the material detachment as well as crack opening and propagation, following fracture mechanics and rock brittleness concepts. This work is aimed at highlighting the role of post-peak brittleness in cliff stability problems involving soft calcarenites by means of the application of a hybrid finite-discrete element method (FDEM), which allows for a proper simulation of the brittle rock behavior and the related mechanism of fracture propagation. In particular, the paper presents the simulations performed for an ideal vertical cliff formed of soft calcarenites belonging to the Calcarenite di Gravina Fm. (Upper Pliocene - Lower Pleistocene) and largely outcropping in Apulia (Southern Italy). The numerical results highlight the impact of calcarenite brittleness in the stability assessment, the influence of the mesh dependency on the same results and the role of the combination of rock brittleness with joint sets to generate failure mechanisms in the cliff