Applicability of Constitutive Models to Describing the Compressibility of Mining Backfill: A Comparative Study

The compressibility of mining backfill governs its resistance to the closure of surrounding rock mass, which should be well reflected in numerical modeling. In most numerical simulations of backfill, the Mohr–Coulomb elasto-plastic model is used, but is constantly criticized for its poor representativeness to the mechanical response of geomaterials. Finding an appropriate constitutive model to better represent the compressibility of mining backfill is critical and necessary. In this paper, Mohr–Coulomb elasto-plastic model, double-yield model, and Soft Soil model are briefly recalled. Their applicability to describing the backfill compressibility is then assessed by comparing numerical and experimental results of one-dimensional consolidation and consolidated drained triaxial compression tests made on lowly cemented backfills available in the literature. The comparisons show that the Soft Soil model can be used to properly describe the experimental results while the application of the Mohr–Coulomb model and double-yield model shows poor description on the compressibility of the backfill submitted to large and cycle loading. A further application of the Soft Soil model to the case of a backfilled stope overlying a sill mat shows stress distributions close to those obtained by applying the Mohr–Coulomb model when rock wall closure is absent. After excavating the underlying stope, rock wall closure is generated and exercises compression on the overlying backfill. Compared to the results obtained by applying the Soft Soil model, an application of the Mohr–Coulomb model tends to overestimate the stresses in the backfill when the mine depth is small and underestimate the stresses when the mine depth is large due to the poor description of fill compressibility. The Soft Soil model is recommended to describe the compressibility of uncemented or lightly cemented backfill with small cohesions under external compressions associated with rock wall closure.

Study on the mechanism of hydrate adhesion on the surface of rocks and minerals

Natural gas hydrate is mainly enriched in the low temperature and high pressure environment such as the extremely cold permafrost zone and the polar continental shelf, which is a renewable energy with great development value. The analysis of the adhesion mechanical properties of gas hydrate on the surface of rock and mineral is of great significance for the correct evaluation and effective control of the influence of gas hydrate on sedimentary layers. In this paper, an experimental device for visualizing the adhesion of hydrate wall under atmospheric pressure was built to directly test the adhesion strength of hydrate on the rock wall. The influence mechanism of the microstructure of rock wall and the types of rock minerals on the adhesion strength of hydrate was studied. It was found that the adhesion strength of hydrate on the sandstone wall was greater than that of carbonate rock salt. The higher the surface roughness of rock and mineral, the higher the adhesion strength of hydrate.

Rock hardness identification based on optimized PNN and multi-source data fusion

To solve the problem that it is difficult to identify the cutting rock wall hardness of the roadheader in coal mine, a recognition method of cutting rock wall hardness is proposed based on multi-source data fusion and optimized probabilistic neural network. In this method, all kinds of cutting signals (the vibration signal of cutting arm, the pressure signal of hydraulic cylinders and current signal of cutting motor) are analyzed by wavelet packet to extract the feature vector, and the multi feature signal sample database of rock cutting with different hardness is established. To solve the problems of uncertain spread and complex network structure of probabilistic neural network (PNN), a PNN optimization method based on differential evolution algorithm (DE) and QR decomposition was proposed, and the rock hardness was identified based on multi-source data fusion by optimizing PNN. Then, based on the ground test monitoring data of a heavy longitudinal roadheader, the method is applied to recognize the cutting rock hardness, and compared with other common pattern recognition methods. The experimental results show that the cutting rock hardness recognition based on multi-source data fusion and optimized PNN has higher recognition accuracy, and the overall recognition error is reduced to 6.8%. The recognition of random cutting rock hardness is highly close to the actual. The method provides theoretical basis and technical premise for realizing automatic and intelligent cutting of heading face.

Theropod tracks from the Jurassic–Cretaceous boundary, Tuchengzi Formation, Chengde, China: Review and new observations

Previously known theropod dinosaur footprints preserved as natural casts in the Tuchengzi Formation, on a rock wall beside the railway in Nanshuangmiao Village, Shangbancheng Town, Chengde City, were originally assigned to ichnogenus Anchisauripus and tentatively attributed to oviraptosaurs. The assemblage was restudied in more detail by examining the entire assemblage of 55 tracks associated with two horizons. The size range of the 27 measured tracks suggests a more diverse grallatorid–eubrontid assemblage and potentially greater diversity of theropod trackmakers. The label Anchisauripus, which has fallen into disuse in some recent literature, implies trackmakers of medium shape and size in the grallatorid–eubrontid morphological spectrum. However, given the presence of other theropod ichnotaxa in the Jurassic to Early Cretaceous strata of the Tuchengzi Formation and time equivalent units we suggest that explicit reference to the Grallator-Anchisauripus-Eubrontes (GAE) plexus, or simply the term Grallator-Eubrontes plexus be confined to Lower Jurassic assemblages as originally defined and intended. Further study centered on the 16 known Tuchengzi assemblages and older theropod ichnfaunas is necessary to confirm or refute the degree to which grallatorid–eubrontid assemblages from these different epochs are similar or convergent. Even if the tracks are morphologically very similar inferences regarding trackmaker identity are problematic because the same theropodan trackmaker species, genera or even families were not present in both epochs.

Investigation of a cold-based ice apron on a high-mountain permafrost rock wall using ice texture analysis and micro-14C dating: a case study of the Triangle du Tacul ice apron (Mont Blanc massif, France)

The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.

Surface temperatures and their influence on the permafrost thermal regime in high-Arctic rock walls on Svalbard

Permafrost degradation in steep rock walls and associated slope destabilization have been studied increasingly in recent years. While most studies focus on mountainous and sub-Arctic regions, the occurring thermo-mechanical processes also play an important role in the high Arctic. A more precise understanding is required to assess the risk of natural hazards enhanced by permafrost warming in high-Arctic rock walls. This study presents one of the first comprehensive datasets of rock surface temperature measurements of steep rock walls in the high Arctic, comparing coastal and near-coastal settings. We applied the surface energy balance model CryoGrid 3 for evaluation, including adjusted radiative forcing to account for vertical rock walls. Our measurements comprise 4 years of rock surface temperature data from summer 2016 to summer 2020. Mean annual rock surface temperatures ranged from −0.6 in a coastal rock wall in 2017/18 to −4.3 ∘C in a near-coastal rock wall in 2019/20. Our measurements and model results indicate that rock surface temperatures at coastal cliffs are up to 1.5 ∘C higher than at near-coastal rock walls when the fjord is ice-free in winter, resulting from additional energy input due to higher air temperatures at the coast and radiative warming by relatively warm seawater. An ice layer on the fjord counteracts this effect, leading to similar rock surface temperatures to those in near-coastal settings. Our results include a simulated surface energy balance with shortwave radiation as the dominant energy source during spring and summer with net average seasonal values of up to 100 W m−2 and longwave radiation being the main energy loss with net seasonal averages between 16 and 39 W m−2. While sensible heat fluxes can both warm and cool the surface, latent heat fluxes are mostly insignificant. Simulations for future climate conditions result in a warming of rock surface temperatures and a deepening of active layer thickness for both coastal and near-coastal rock walls. Our field data present a unique dataset of rock surface temperatures in steep high-Arctic rock walls, while our model can contribute towards the understanding of factors influencing coastal and near-coastal settings and the associated surface energy balance.

Botanical curiosities of Prodarjeva Grapa gorge in the upper Bača Valley (western Slovenia) / Botanične posebnosti Prodarjeve grape v zgornji Baški dolini (zahodna Slovenija)

We researched the vegetation of the protected lower part of the Prodarjeva Grapa gorge in the foothills of Mt. Porezen in the upper Bača Valley. Its botanical curiosities are the localities of protected or rare species Moehringia villosa, Pri­mula auricula,Pinguicula vulgarisand Carex frigida. All four occur (but are not limited to) on the rocky and gra­velly shady area in the lower part of the gorge with a distinctly cold local climate. The relief, climate and parent material (platy limestone with admixture of marlstone and chert) are the decisive factors that allow for the occurrence of the previously unknown community of wet spring areas, which we classify into the new association Pinguiculo vul­garis-Cari­cetum frigidae, alliance Cratoneurion commutatiand class Montio-Cardaminetea, in this area. It is syndynamically connected with surrounding communities of wet screes and rock crevices. Screes under the rock wall are partly overgrown with a community of Molinia arundinaceaand Adeno­styles glabra (Adenostylo glabrae-Molinietum arundinaceanom. prov.), on the fringes in places also with an open low-growth hop-hornbeam and manna ash forest (Palustriello commutati-Ostryetum carpinifoliaenom. prov.). Key words: vegetation, synsystematics, Carex frigida, Moehringia villosa, Pinguicula vulgaris, Primula auricula,Bača Valley, Porezen, Natura 2000 Izvleček Raziskali smo rastje spodnjega, zavarovanega dela Prodarjeve grape v prigorju Porezna v zgornji Baški dolini. Njene botanične posebnosti so nahajališča zavarovanih ali redkih vrst: Moehringia villosa, Primula auricula,Pinguicula vulgarisin Carex frigida. Vse štiri med drugim rastejo v skalnatem in gruščnatem osojnem območju v spodnjem delu grape z izrazito hladnim krajevnim podnebjem. Relief, podnebje in geološka podlaga (ploščasti apnenec s primesjo laporovca in roženca) so odločilni dejavniki za tukajšnje uspevanje do zdaj nepoznane rastlinske združbe vlažnih povirij, ki jo uvrščamo v novo asociacijo Pinguiculo vulgaris-Caricetum frigidae,v zvezo Cratoneurion commutatiin v razred Montio-Cardaminetea. Sindinamsko je povezana z okoliškimi združbami vlažnih melišč in skalnih razpok, pri čemer se melišča pod steno deloma zaraščajo z združbo trstikaste stožke – Adenostylo glabrae-Molinietum arundinaceanom. prov., na robovih tudi z vrzelastim nizkim gozdom črnega gabra in malega jesena – Palustriello commutati-Ostryetum carpinifoliaenom. prov. Ključne besede: vegetacija, sinsistematika, Carex frigida, Moehringia villosa, Pinguicula vulgaris, Primula auricula, Baška dolina, Porezen, Natura 2000

Permafrost in monitored unstable rock slopes in Norway – New insights from rock wall temperature monitoring, geophysical surveying and numerical modelling

The warming and subsequent degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. The unstable and monitored slopes of Mannen (Møre and Romsdal, southern Norway) and Gámanjunni-3 (Troms and Finnmark, northern Norway) were classified as high-risk sites by the Norwegian Geological Survey (NGU). Failure initiation has been suggested to be linked to permafrost degradation, but the detailed permafrost distribution at the sites is unknown. Rockwall (RW) temperature loggers at both sites have measured the thermal regime since 2015, showing mean rock surface temperatures between +2.5 °C and −1.6 °C depending on site and aspect. Between 2016 and 2019 we conducted 2D and 3D electrical resistivity tomography (ERT) surveys on the plateau and directly within the rock wall back scarp of the unstable slopes at both sites. In combination with geophysical laboratory analysis of rock wall samples from both sites, the ERT soundings indicate wide-spread permafrost areas, especially at Gámanjunni-3. Finally, we conducted 2D thermal modelling to evaluate the potential thermal regime. Rockwall temperatures, together with ERT measurements and modelling of the ground thermal regime strongly indicate, at least locally, the presence of permafrost. Displacement rates show a seasonality, with higher velocities during spring and early summer than the rest of the year, possibly related to snow melting.