3D Numerical Modelling of the Application of Cemented Paste Backfill on Displacements around Strip Excavations

This article presents laboratory and spatial numerical modeling of cemented paste backfill. The first part of the research concerned laboratory tests of a mixture of sand, water, and variable cement content (5%, 10%, and 15%). The density and curing time of the mixture were determined. Moreover, cylindrical samples with a diameter of 46 mm and a height of 92 mm were constructed, for which compressive and tensile strength were calculated after one, two, three, and four weeks. The second part of the research concerned 3D numerical modeling with the use of RS3 software. For the exploitation field with dimensions of 65 m × 65 m, a strip-mining method was designed. The main objective of the research was to determine the changes in displacements around the haulage room and transportation roadway located in the immediate vicinity of the exploitation field. For the first time in numerical modeling, a two-sided strip method was used for the four stages of mining the ore deposit where the post-mining space was filled with a cemented paste backfill. Based on this research, the compressibility coefficient was determined.

An investigation of longwall failure using 3D numerical modelling – A case study at a copper mine

It is well-known that the longwall mining method (with roof caving) is widely used in underground mining extraction for bedded deposits (e.g. coal) due to its numerous advantages. Generally, this method is not commonly applied for ore deposits such as copper deposit. In Poland, the longwall mining method has been tested for thin copper deposits at the Polkowice-Sieroszowice copper mine (KGHM). Various failure modes were observed during longwall operation in the 5A/1 panel. This paper aims to examine these occurred failures. To do so, an analysis has been conducted using 3D numerical modelling to investigate the failure mode and mechanism. Based on the 3D numerical modelling results with extensive in situ measurements, causes of failure are determined and practical recommendations for further copper longwall operations are presented.

Ground deformation mechanism due to deep excavation in sand: 3D numerical modelling

In densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing structure. Inadequate support systems have always been major concern as excessive ground movement induced during excavation could damage to neighbouring structure. A detailed parametric analysis of the ground deformation mechanism due to excavation with different depths in sand with different densities (Dr=30%, 50%, 70% and 90%) is presented. 3D finite element analyses were carried out using a hypoplastic model, which considers strain-dependent and path-dependent soil stiffness. The computed results have revealed that the maximum settlement decreased substantially when the excavation is carried out in the sand with higher relative density. This is because of reason that sand with higher relative density possesses higher stiffness. Moreover, the depth of the maximum settlement of the wall decreases as the sandbecome denser.The ground movement flow is towards excavation in retained side of the excavation. On the other hand the soil heave was induced below the formation level at excavation side. The maximum strain level of 2.4% was induced around the diaphragm wall.

Investigation of piled behaviour due to an adjacent excavation: 3D numerical modelling

Zameer Ahmed Channaret al.,InternationalJournal of Emerging Trends in Engineering Research, 9(6), June 2021, 683–689683ABSTRACTIn congested cities, excavations are unavoidably constructed adjacent to high rising building supported by piled raft foundations which reduces differential settlements in the buildings. Since the excavations inevitably induce soil movement and stress changes in the ground, it may cause differential settlements to nearby piled raft foundation. In this numerical study, a 3D coupled consolidation numerical analysis (using a hypoplastic model, which considers strain dependent and path-dependent soil stiffness) was conducted to investigate a (2×2) piled raft responses to an adjacent 25-m deep excavation in saturated clay. The computed results have revealedthat the rate of piled raft settlement increased significantly beyond excavation stage h/He=0.5. This is because of the degradation of stiffness of clay with strain due to excavation-induced stress release. Differential settlement (i.e. tilting) was induced in the piled raft due to non-uniform stress release.Owing to separation of the raft from the ground due excavation, some of the working load was transferred to the four piles. The maximum positive bending moment was 200 kNm at Z/Lp=0.67. However, no any bending moment was induced in both the piles at the toes.

Load capacity of the mixed bench and slab foundation. Numerical simulations and analytical calculation model

The paper presents results of a numerical investigation on load capacity of the mixed bench and slab shallow foundations (often used in the process of the modernization of the old, antique buildings, which are suffering from lack of the load capacity). The main trouble with use of existing analytical approaches is a non-unique foundation level of the bench and slab, they could even be founded on different geotechnical layers. Proposed analytical model based on Brinch Hansen (EC-7) approach could deal with such a problem. Results of 2D and 3D numerical modelling (ultimate load of the foundation) are compared to the obtained by using the proposed approach. Influence of the soil above the foundation level is also investigated. Different width to length ratios of the foundation are analyzed (from “short” to “long” foundations). Usability of the proposed analytical model in engineering practice is proved by numerical simulations; the obtained results are on the safe side with quite acceptable margin of additional safety.

Climate change and cryosphere in high mountains: updates from the Capanna Margherita hut study case (Punta Gnifetti, Monte Rosa Massif, Pennine Alps)

<p>Mountain glaciers and permafrost are among the most evident geomorphological tracers of climate change. In the last decades, they showed a growing and faster response also at very high elevations, leading to increased instability of the Alpine landscape. In the meanwhile, they became of great interest also for their possible interactions with human activities and infrastuctures.</p><p>On the highest massif of the Alps, as for example the Monte Rosa, this interaction is mainly represent by the one with mountaineering activities. The top of Gnifetti Peak (4554 m a.s.l.), with the Capanna Margherita hut (the highest in Europe), is under investigation to better understand the effects of global warming on hut stability and mountaineering routes safety. Thanks to the cooperation between the Italian Alpine Club (CAI), University of Turin (UniTo), Politecnico di Milano (PoliMi) and IMAGEO srl, a first assessment of geological and glacial settings of hut surroundings have been performed on 2019. Data collection continued on 2020, by means of comparative analyses designated to: a) identify the relevant geomechanical features for rock mass stability; b) verify permafrost related instabilities; c) reconstruct the ice-covered morphology of the Punta Gnifetti peak; d) calculate rock-building interactions. Here below the related results:</p><p>1) A 3D model of the area has been obtained by integrating helicopter-borne photogrammetry with terrestrial laser scanner surveys.</p><p>2) Glacier thickness at the Colle Gnifetti has been established thanks to GPR survey.</p><p>3) From the comparison of a large number of historical pictures a first multi-temporal stability analysis highlighted sector of greater instability. Results of this work are freely available on the website www.geositlab.unito.it/capanna .</p><p>4) The geomechanical features of the rock mass below and around the hut have been retrieved from the analysis of the dense point cloud provided by terrestrial laser scanner integrated with direct field investigations.</p><p>5) Constructive drawing of the hut have been obtained from the terrestrial laser scanner point cloud integrated with manual measurements taken inside the structure.</p><p>6) 3D numerical modelling are going to be applied in order to simulate the interactions between the hut and the foundation rock on the base of the above data.</p><p>The ongoing activities are addressed to a detailed study of more vulnerable sectors of the Punta Gnifetti to better understand morphodynamics and possible interactions with mountaineering activities. This will be performed through a two-way investigation. On one hand, a link with alpine guides and mountain hut keepers has been established, in order to have “sentries” ready to report instabilities and detect new hazards and risks. On the other hand, a monitoring network will be installed around Capanna Margherita in order to collect data on weather, glacier and permafrost conditions.</p>

Advanced rockfall modelling for risk mitigation: tree impact and fragmentation

<p>Despite their centrality to rockfall risk management, two issues are frequently overlooked: the role of forests in rockfall dynamic and the fragmentation phenomenon. To investigate the importance of these issues we have developed advanced modelling case studies in two representative sites that have been recently affected by rockfall events in the Aosta Valley Region (Western Italian Alps). In the Saint Oyen case study, about 17,500 m3 of rock detached in March 2019 and reached a service road and the sport center in the lower part of the slope, passing through a mature fir forest. The presence of the forest has significantly influenced the rocks distribution along the slope, increasing the lateral dispersion of trajectories and reducing the mobility. For the design of defensive works, 3D rockfall models of three future potential risk scenarios were therefore performed by using the tree-impact algorithm of the code HY-STONE (Frattini et al., 2012). This algorithm provides the location of impacts on trees, the absorbed energy, and the deviation angle. The input parameters (i.e., the value of diameter at breast height and the forest density) were based on direct measurements of the fir forest. Compared with a traditional simulation without the protective role of forests, the results of 3D numerical modelling with tree-impact algorithm show a decrease in the number of blocks impacting the barriers (91%), no variations in the bouncing heights (for 95<sup>th</sup> percentile), and an increase in the kinetic energies due to a filter effect by the forest (85% for 95<sup>th</sup> percentile). In the Roisan case study, about 1,050 m3 of rock toppled in October 2019. While the main body of the rockfall stopped in a relatively flat area close to the failure, two blocks were exceptionally able to reach the foot of the slope causing the interruption of a municipal road. An attempt to back-calibrate this event with HY-STONE showed difficulties to describe the behaviour of these isolated blocks with respects to the main landslide body. A possible explanation for this behaviour is that the detached volume fragmented soon after impacting the slope, giving rise to flying fragments with higher mobility. To test this hypothesis we accounted for fragmentation through a specific algorithm of HY-STONE that fragments the falling blocks when their energy overcomes a certain threshold and simulate the behaviour of the resulting fragments. This approach allowed to accurately replicate the rockfall event. We therefore adopted this approach for defensive-works design, simulating all the unstable volumes overhanging the municipal road. Compared with a traditional simulation, the results of 3D numerical modelling with fragmentation algorithm show an increase in the number of blocks impacting the barriers (86%) and in the bouncing heights (96% for 95<sup>th</sup> percentile), with a decrease of the kinetic energy due to comminution (39% for 95<sup>th</sup> percentile). These two case studies demonstrate the importance of accounting for the forest or for fragmentation in the design of cost-effective defensive works.</p><p> </p><p>Frattini P, Crosta GB, Agliardi F (2012) Rockfall characterization and modeling. Landslides: types, mechanisms and modelling 22:267-281</p>