Rock Walls Research Articles

Responses of Acidophilic Communities in Different Acid Mine Drainages to Environmental Conditions in Nanshan Mine, Anhui Province, China

Acidophiles play a vital catalytic role in the formation of acid mine drainage (AMD). In this study, acidophilic communities in a stream, two lakes and five ponds in Nanshan Mine, Anhui Province, China were comparatively investigated. Among the three types of AMDs, the stream which originated from a rock wall had the strongest acidity (pH 2.30–2.42), while the ponds (pH 2.35–2.60) formed in mine dump and the two large-scale AMD lakes (pH 2.66–3.05) were less acidic. The chemolithotrophic iron-oxidizer Leptospirillum dominated at the stream starting point with the lowest pH and highest Fe content. However, with streamflow, pH increased and Fe concentration decreased dramatically, and the dominance of Leptospirillum was replaced by the less acid-resistant iron-oxidizer Ferrovum. In contrast to the stream, prokaryotic communities in the ponds were mostly dominated by chemoheterotrophic Acidiphilium because of the abundant organic matter from surrounding mine waste. Both chemolithotrophic Ferrovum and chemoheterotrophic Acidiphilium were abundant in the AMD lakes, which may form a symbiotic relationship around the carbon cycle. Statistical analyses indicated that pH was the predominant environmental factor influencing the prokaryotic communities. As for the eukaryotic communities, the microeukaryotes in the stream were mostly uncultured groups. Both photoautotrophic algae Chrysonebula and chemoheterotrophic fungi were abundant in the ponds, while the two AMD lakes were only dominated by photoautotrophic algae Coccomyxa and Ochromonas.

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)

AbstractThe 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

Abstract. 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.

Response analysis of yielding structures coupled to rocking walls with supplemental damping

AbstractGiven that the coupling of a framing structure to a strong, rocking wall enforces a first‐mode response, this paper investigates the dynamic response of a yielding single‐degree‐of‐freedom oscillator coupled to a stepping rocking wall with supplemental damping (either hysteretic or linear viscous) along its sides. The full nonlinear equations of motion are derived, and the study presents an earthquake response analysis in terms of inelastic spectra. The study shows that for structures with preyielding period s, the effect of supplemental damping along the sides of the rocking wall is marginal even when large values of damping are used. The study uncovers that occasionally, the damped response matches or exceeds the undamped response; however, when this happens, the exceedance is marginal. The paper concludes that for yielding structures with strength less than of their weight, the use of supplemental damping along the sides of a rocking wall coupled to a yielding structure is not recommended. The paper shows that supplemental damping along the sides of the rocking wall may have some limited beneficial effects for structures with longer preyielding periods (say ). Nevertheless, no notable further response reduction is observed when larger values of hysteretic or viscous damping are used.

Expansion of intertidal mussel beds following disease-driven reduction of a keystone predator

Disease shapes community composition by removing species with strong interactions. To test whether the absence of keystone predation due to disease produced changes to the species composition of rocky intertidal communities, we leverage a natural experiment involving mass mortality of the keystone predator Pisaster ochraceus from Sea Star Wasting Syndrome. Over four years, we measured dimensions of mussel beds, sizes of Mytilus californianus, mussel recruitment, and species composition on vertical rock walls at six rocky intertidal sites on the central California coast. We also assessed the relationship between changes in mussel cover and changes in sea star density across 33 sites along the North American Pacific coast using data from long-term monitoring. After four years, the lower boundary of the central California mussel beds shifted downward toward the water 18.7 ± 15.8 cm (SD) on the rock and 11.7 ± 11.0 cm in elevation, while the upper boundary remained unchanged. In central California, downward expansion and total area of the mussel bed were positively correlated with mussel recruitment but were not correlated with pre-disease sea star density or biomass. At a multi-region scale, changes in mussel percent cover were positively correlated with pre-disease sea star densities but not change in densities. Species composition of primary substrate holders and epibionts below the mussel bed remained similar across years. Extirpation of the community below the bed did not occur. Instead, this community became limited to a smaller spatial extent while the mussel bed expanded.

Shaking table test of a frame structure retrofitted by externally-hung rocking wall with SMA and disc spring self-centering devices

An innovative externally-hung rocking wall (ERW) with shape memory alloy (SMA) and disc spring self-centering devices for retrofitting existing structures was proposed in this paper. By arranging steel corbels on the columns of an existing structure, the rocking walls were connected to the corbel using H-shaped connectors. Two types of self-centering devices, using disc spring and SMA separately, were installed between rocking wall and foundation to prevent collision damage, and can provide self-centering capability for the structure. The seismic performance characteristic of the ERW structure was studied via a shaking table test. For comparison, an unretrofit control (UC) structure was also tested. The UC structure was severely damaged and nearly collapsed after PGA = 1.2 g test cases: some steel bars at the bottom of the beam were fractured, and concrete at the beam end and column foot were crushed. For the ERW structure, the damage was significantly reduced after PGA = 1.5 g test cases: there were some cracks appeared in the structure, and concrete at the column foot were slightly crushed. However, no obvious damage was observed in the self-centering devices. The maximum story drift and residual deformation of the ERW structure are reduced 86.7% and 91.2%, respectively, relative to the UC structure.

Nanomaterials for subsurface application: study of particles retention in porous media

The ability to transport nanoparticles through porous media has interesting engineering applications, notably in reservoir capacity exploration and soil remediation. A series of core-flooding experiments were conducted for quantitative analysis of functionalized TiO2 nanoparticles transport through various porous media including calcite, dolomite, silica, and limestone rocks. The adsorption of surfactants on the rock surface and nanoparticle retention in pore walls were evaluated by chemical oxygen demand (COD) and UV–Vis spectroscopy. By applying TiO2 nanoparticles, 49.3 and 68.0 wt.% of surfactant adsorption reduction were observed in pore walls of dolomite and silica rock, respectively. Not surprisingly, the value of nanoparticle deposition for dolomite and silica rocks was near zero, implying that surfactant adsorption is proportional to nanoparticle deposition. On the other hand, surfactant adsorption was increased for other types of rock in presence of nanoparticles. 5.5, 13.5, and 22.4 wt.% of nanoparticle deposition was estimated for calcite, black and red limestone, respectively. By making a connection between physicochemical rock properties and nanoparticle deposition rates, we concluded that the surface roughness of rock has a significant influence on mechanical trapping and deposition of nanoparticles in pore-throats.

Combined Use of Rocking Walls and Inerters to Improve the Seismic Response of Frame Structures

AbstractThis paper investigates the possibility to enhance the seismic response of a frame structure by the combined use of an external rocking wall and some inerters attached to both the frame and...

Biosurfactant as an Environmental Remediation Agent: Toxicity, Formulation, and Application in the Removal of Petroderivate in Sand and Rock Walls

The exploitation and transportation of petroleum products are important reasons for environmental concern since they are the major causes of accidents involving oil spills. Therefore, the biosurfactant produced by the bacterium Bacillus cereus UCP1615 was applied in the removal of motor oil from sand and stones from coastal regions. Bioassays carried out with the microcrustacean Artemia salina and three vegetables' seeds showed that the biosurfactant has reduced toxicity. The application of the biosurfactant in crude and isolated form, as a removal agent, was carried out in static and kinetic tests using sand contaminated with motor oil, in packed columns, and in flasks under orbital agitation, respectively. The results showed that the biosurfactant removed 63.0 ±2.1% of the hydrocarbon in the static test and 84.0 ±2.2% in the dynamic test. In tests using rock wall samples, the removal rates reached 69.0 ±2.0%. Conservation tests carried out during 120 days demonstrated that the surfactant activities were maintained, especially in the presence of the preservative potassium sorbate. The B. cereus biosurfactant has proven to be a biocompatible, effective, and stable alternative for applications in environments contaminated with hydrophobic compounds and can be industrially stored for application in the event of possible environmental disasters.

Drained Triaxial Compressive Shear Response of Cemented Paste Backfill (CPB)

Cemented paste backfill (CPB) has been widely used as local and regional underground support to reduce host rock wall closure in mined-out areas and also to reduce rockfall and rockburst incidents. However, analyzing the rock mass—CPB interactions in the first month after backfill placement must account for the CPB’s time-dependent strength, stiffness, and volume change characteristics during binder hydration. This article presents the first such comprehensive study made for CPB from the Williams mine in Ontario, Canada. Monotonic isotopically consolidated drained compressive triaxial tests were conducted on cured CPB specimens using the lubricated-ends test technique. The specimens had 3.0–7.5% Cement Content (CC); Curing Times (CTs) were from 3 to 28 days; and the confining stress ranged from 25 to 350 kPa. During shearing, all tests exhibited an initial contractive phase leading to a Characteristic State (CHS or point of volumetric strain reversal) followed by dilation with a maximum dilation rate corresponding to peak stress at the Failure State (FS). Both CHS and FS are adequately described by the Mohr–Coulomb criterion and a framework formulation was proposed to predict the evolution of CHS and FS based on CC and CT. Furthermore, the volumetric strains at CHS and FS can be defined as linear functions of the respective axial strains at the CHS and FS. Quantification of the observed behaviors through these functional relationships can help develop future constitutive models that better represent CPB’s transient response to triaxial stress loading while curing, which is essential to understanding as-placed backfill properties and its interaction with surrounding rock mass.

Study on the effect of dynamic disturbance on creep behavior of frozen fractured red sandstone

The freezing method is an effective water shut-off method for shaft construction in water-rich Cretaceous strata in Northwest China. Blasting is an efficient excavation method for vertical shafts crossing the frozen stratum. The frozen rock wall is usually composed of ice and fractured rock mass and is influenced by both the in situ stress and blasting disturbance. To study the creep behavior of fractured rock masses under subzero temperatures and dynamic disturbances, a series of conventional triaxial creep and creep-disturbance tests were carried out. The results show that the flaw dip angle and dynamic disturbance had a significant influence on the creep failure characteristics of the specimens. The creep rate and failure strain of the accelerated creep stage of the specimens under dynamic disturbance were significantly greater than those of the specimens that did not undergo dynamic disturbance. Dynamic disturbance closed and recombined the microcracks, improved the short-term bearing capacity, increased the total creep time, and reduced the creep rate of the specimens. When the load or disturbance intensity reached a certain value, the crack propagation rate and creep rate of a specimen increased, the disturbance energy stored in the rock mass was released, and the specimen suddenly failed. Therefore, this disturbance creep phenomenon must be considered when constructing freezing vertical shafts in Northwest China. Moreover, timely support should be provided for exposed ice-filled fractured rock masses to guarantee construction safety and rock mass stability.

Stability analyses of side-exposed backfill considering mine depth and extraction of adjacent stope

Pillar recovery requires stable backfill upon side exposure in open stoping mining methods. Until now, the solutions used to estimate the required strength of side-exposed backfill are mainly based on a wedge model where the effect of rock-wall closure was neglected. In this paper, the influence of mine depth and adjacent extraction on the stability of side-exposed backfill is analyzed through numerical modeling with FLAC3D. The failure mechanism and cohesion at failure (cf) of backfill are investigated. Results show that the governing failure mechanism can be sliding or crushing, depending on the magnitude of rock-wall closure. When the mine depth and rock-wall closure are small, sliding failure is dominant and rock-wall closure has effect to improve the stability of exposed backfill. The values of cf can become even smaller than those obtained with immobile rock walls solutions. When the sliding failure is dominant, the cf decreases with the increase of mine depth, fill stiffness, rock pressure coefficient, and fill-rock interface strength (friction angle and adhesion). Increasing rock mass stiffness, stope height and width leads to an increase in cf. When mine depth and rock-wall closure are large, the crushing failure is dominant. The cf increases with the increase of mine depth, stope height and length, fill stiffness and rock pressure coefficient. It decreases with the increase of stope width and rock mass stiffness, and is insensitive to the variation of fill-rock interface strength. In all cases, the stability of side-exposed backfill is improved by increasing its internal frictional angle.

Unbonded Post-tensioned Precast Concrete Walls With Rocking Connections: Modeling Approaches and Impact Damping

Over the past two decades, precast concrete members have been utilized in seismically resilient structures. In developing these structures, different techniques have been used for connecting the precast members to the foundation. In building construction, unbonded post-tensioning (PT) tendons can anchor a precast wall to the foundation, resulting in the so-called rocking wall system. The rocking wall system develops a dry connection with the foundation and provides moment resistance by means of the PT tendons. The PT tendons remain elastic when the wall is subjected to design-level ground motions to preserve the re-centering capability of the wall. Moreover, the structural damage is concentrated near the wall toes and can be minimized with proper detailing of the toes. Rocking wall systems can consist of a Single precast Rocking Wall (SRW), which uses no supplemental damping, or walls with supplemental damping in the form of viscous or hysteretic energy dissipating devices. In addition to the supplemental damping, rocking walls dissipate the seismic energy through their impacts on the foundation base, their inherent viscous damping, and the hysteresis of concrete near the wall base. While the investigation of rocking walls continues to gain interest, there is no widely accepted means of modeling their dynamic behavior. This paper investigates two popular approaches for modeling rocking walls with and without supplemental damping: the finite element method and analytical modeling. The ability of the two approaches to capture the local and global responses of the walls is evaluated against shake table tests of walls with multiple-level intensity base motions. Next, the behavior characteristics of the two modeling approaches and their ability to simulate impact damping are discussed.

Laws of gas and water flow and mechanism of reservoir drying in tight sandstone gas reservoirs

The reservoir permeability of tight sandstone gas reservoirs is low, which makes it difficult to carry out displacement flow experiments on real cores underground conditions, so the microscopic flow mechanism can be hardly studied. Based on the lattice Boltzmann method (LBM), this paper simulated the flow process of formation water displaced by tight gas under the simulated reservoir conditions of high temperature and high pressure to clarify the distribution of bound water in the reservoir. Then, reservoir drying was experimentally studied using the laser etching model, and numerical simulation of reservoir drying was simplified by referring to the visualization results of the experiment. Finally, the influence of reservoir drying on the seepage capacity of tight gas was studied by means of numerical simulation. And the following research results were obtained. First, when the lattice Boltzmann model is used for high temperature and high pressure reservoirs, it satisfies the Laplace law and its numerical solution of two-phase Poiseuille flow rate is basically consistent with the analytical solution, which indicates that this model can be used to simulate gas–water immiscible displacement under reservoir conditions. Second, tight gas preferentially breaks through in large porous media connected channels, and after the breakthrough, the displacement rate of formation water decreases significantly. Third, the contact angle between formation water and rock wall has a significant influence on gas–water two-phase flow. The stronger the water wettability of the rock is, the lower the displacement rate is. Fourth, the bound water in tight sandstone gas reservoirs can be classified into four types, including adsorbed water film, blind end pore water, dead pore water and trapped water. In porous media, a large number of connected micro-channels are occupied by trapped water and adsorbed water film and the phenomenon of “water lock” is obvious, which seriously influences the seepage capacity of tight gas in the porous media of reservoir. Fifth, drying agent can react with bound water to produce a large number of bubbles, which will consume adsorbed water film, trapped water and blind end pore water, so as to improve the gas seepage capacity. Sixth, in the “water lock” regions formed by trapped water, the gas seepage capacity can be effectively improved by increasing the drying strength. On the whole, the tight gas permeability increases with the increase of drying strength, but its increase amplitude decreases gradually when the drying strength exceeds a certain degree.

Optimization for Connected Steel Plates of Single-Layer Shaft Wall under Blasting Excavation by Numerical Simulation Method

In order to increase the cross-section utilization rate of the deep shaft, a new type single-layer wall with connected steel plates has been invented. The numerical simulation method is used to analyze the coupling interaction between the steel plate and the concrete. The results show that: there are four vibration strengthening regions in each formwork wall. The order from strength to weakness for the regions is as follows: the concrete outside of vertical steel plate > the concrete at the interface between shaft wall and rock wall > the concrete on the upper side of each formwork > the concrete on the lower side of each formwork. There are two potential leakage channels in the vicinity of the connected steel plate, and the channel under the inclined steel plate is a controlled channel. The thickness of steel plate has an important influence on the damage degree and range of concrete. The concrete damage is affected by vertical steel plate, inclined steel plate and thickness combination of themselves. When the project takes the inclined steel plate 10 mm and the vertical steel plate 6 mm, the phenomenon of crack and leakage of the concrete wall is greatly reduced, and the quality of the project is good.

Elucidating suspended sediment dynamics in a glacierized catchment after an exceptional erosion event: The Djankuat catchment, Caucasus Mountains, Russia

Suspended sediment yields from glacierized catchments are often among the highest in the world, and their sediment dynamics can be highly variable. This study was undertaken in the 9.1 km2 glacierized catchment of the Djankuat River located in the Russian part of the Northern Caucasus. The outlet of the study catchment is a hydrological gauging station located at an altitude of 2635 m a.m.s.l. (‘N43°12′31.71″, E42°44′05.93″). The catchment includes a temperate valley glacier (area = 2.42 km2) and three smaller hanging glaciers, several moraine deposits, rock walls, and a large and expanding proglacial area. The main goal of our study was to assess the impact of an exceptional erosion event on 1st July 2015 (with an annual exceedance probability of less than 0.1%) on suspended sediment yields and the relative contributions of various sediment sources The work combined direct suspended sediment discharge measurements at the gauging station during five ablation seasons (2015–2019) with geomorphic mapping techniques based on detailed field observations and sediment source fingerprinting. Results show that mean annual suspended sediment yields reached 1118 t km−2 year−1 which is one of the highest measured estimates for any of the glacierized mountain rivers globally. About half of the annual suspended sediment flux was exported during a limited number (1–12% of the annual events) of extreme hydrological events. The sediments mobilized by bank and riverbed erosion within the new lower reach of a tributary channel which appeared after the breakthrough of a lateral moraine became the primary sediment source. It contributed over 50% of the suspended sediment on days with extreme rainfall. Contributions to the suspended sediment load from the glacier source were event-dependent and were only dominant (c. 60–70%) in the upper reaches of the proglacial area (first 800 m). The proglacial part of the study catchment with buried ice was the main sediment source (79%) during non-rain days.

4D quantification of alpine permafrost degradation in steep rock walls using a laboratory‐calibrated electrical resistivity tomography approach

ABSTRACTThe warming of rock permafrost affects mechanical stability and hydro‐cryostatic pressures in rock walls. The coincident decrease in slope stability frequently affects infrastructure by creep and subsidence and promotes the generation of rockfalls and rockslides. The increasing hazard posed by warming permafrost rock walls and the growing exposure of infrastructure and individuals create a demand for quantitative monitoring methods. Laboratory‐calibrated electrical resistivity tomography provides a sensitive record for frozen versus unfrozen bedrock, presumably being the most accurate quantitative monitoring technique in permafrost areas where boreholes are not available. The data presented here are obtained at the permafrost‐affected and unstable Steintaelli Ridge at 3100 m a.s.l. and allow the quantification of permafrost changes in the longest electrical resistivity tomography time series in steep bedrock. Five parallel transects across the rock ridge have been measured five times each, between 2006 and 2019, with similar hardware. Field measurements were calibrated using temperature‐resistivity laboratory measurements of water‐saturated rock samples from the site. A 3D time‐lapse inversion scheme is applied in the boundless electrical resistivity tomography (BERT) software for the inversion of the data. To assess the initial data quality, we compare the effect of data filtering and the robustness of final results with three different filters and two time‐lapse models. We quantify the volumetric permafrost distribution in the bedrock and its degradation in the last decades. Our data show mean monthly air temperatures to increase from −3.4°C to −2.6°C between 2005‒2009 and 2015‒2019, respectively, while simultaneously permafrost volume degraded on average from 6790 m3 (±640 m3 rock in phase‐transition range) in 2006 to 3880 m3 (±1000 m3) in 2019. For the first time, we provide a quantitative measure of permafrost degradation in unstable bedrock by using a temperature‐calibrated 4D electrical resistivity tomography. Our approach represents a fundamental benchmark for the evaluation of climate change effects on bedrock permafrost.

Deformation and cyclic buckling capacity of external replaceable hysteretic dampers for unbonded post-tensioned precast concrete walls

This paper proposes and validates a type of external replaceable hysteretic dampers to be mainly applied to unbonded post-tensioned (UPT) precast walls. The main aim of the proposed damper was to provide the UPT walls with large energy dissipation without significant buckling. To evaluate the efficiency of these dampers, a cyclic test was conducted. The damper specimens consisted of a mild steel round bar with a reduced diameter over a fused length and an additional threaded length at each side, for installation purposes. Moreover, a round steel tube was installed over the fused length and filled with grout to delay the buckling. The proposed dampers, with different geometries and conditions, were subjected to cyclic loads to evaluate their deformation capacity and fracture mechanism. The specimens displayed a regular and stable hysteretic curve until strains of 9%, after which a flexural buckling was observed at the ends of the fused length. However, this flexural buckling did not affect the energy-dissipating capacity in any specimen. Consequently, this type of damper is considered suitable for applications in self-centering rocking walls. Furthermore, the proposed dampers fractured by a combination of low-cycle fatigue and excessive rotations at the transition length. In addition to the experimental validation, an extensive numerical investigation was conducted on the proposed damper to complement the experimental data and to provide analytical tools for design.

An Elastic Solution for Twin Circular Tunnels’ Stress in Hydrostatic Stress Field

In order to present an elastic solution for twin circular tunnels’ stress distribution in hydrostatic stress field, based on the complex variable theory and the superposition principle, the stress field of twin tunnels under static hydraulic pressure is decomposed into two parts: the original stress field and the secondary stress field. According to the symmetry of the structural form and the load distribution, the secondary stress filed can be simplifyed into a half-plane model. Therefore, the stress filed can be analyzed with the complex variable theory conveniently. Finally, the elastic solution of the twin tunnels under static hydraulic pressure is demonstrated by the superposition of the original stress field and the secondary stress field. In order to verify the analytical solution, a finite element model is adopted as the comparative test.. The result of the finite element simulation shows that the stress concentration at the middle rock wall is most obvious. And the stress concentration factor keeps increasing when the twin tunnels’ spacing distance and supporting pressure are decreasing. Besides, the maximum tangential stress appears at the tunnel boundary. The farther away from the tunnel’s boundary, the tangential stress gets lower. Furthermore, the supporting pressure leads to the increasing of radial stress and the decreasing of tangential stress. The analytical results are highly consistent with the numerical results with finite element method.

The Soldier Ghaut Petroglyphs on Montserrat, Lesser Antilles

Only five years ago, Montserrat was a blank spot on the distribution map of islands in the Lesser Antilles where petroglyphs were known. In January 2016, hikers in Soldier Ghaut, a deeply incised watercourse in the northwest of the island, came upon a panel of nine petroglyphs engraved on a nearly vertical wall of volcanoclastic tuff. Soon afterward the petroglyphs were documented by the Survey and Landscape Archaeology on Montserrat project (SLAM). Then in January 2018 an additional petroglyph was spotted on a large slab of rock, detached from the rock wall on the opposite side of the ghaut. At the invitation of the Montserrat National Trust (MNT) and with European Union funding, Susana Guimarães and Christian Stouvenot traveled to Montserrat in 2018 to assist in further studies at the site. They conducted photogrammetric documentation and photography under enhanced lighting conditions and inspected the petroglyphs and their context in detail in order to advise MNT about their conservation and provisions for public access. This report presents this new group of petroglyphs and their landscape setting and considers questions of dating and interpretation.