Unstable Rock Research Articles

Prediction of Seismic Wave Intensity Generated by Bench Blasting Using Intelligence Committee Machines

In large open pit mines prediction of Peak Particle Velocity (PPV) provides useful information for safe blasting. At Sungun Copper Mine (SCM), some unstable rock slopes facing to valuable industrial facilities are both expose to high intensity daily blasting vibrations, threatening their safty. So, controlling PPV by developing accurate predictors is essential. Hence, this study proposes improved strategies for prediction of PPV by maximum charge per delay and distance using the concept of Intelligent Committee Machine (ICM). Besides the Empirical Predictors (EPs) and two Artificial Intelligence (AI) models of ANFIS and ANN, four different ICMs models including Simple and Weighted Averaging ICM (SAICM and WAICM) and First and Second order Polynomial ICM (FPICM and SPICM) in conjunction with genetic algorithm, proposed for the prediction of PPV. Performance of predictors was studied considering R2, RSME and VAF indices. Results indicate that ICM methods have superiority over EPs, ANN and ANFIS, and among the ICM models while SAICM, WAICM and FPICM performing near to each other SPICM overrides all the models. R2 and RSME of the training and testing data for SPICM are 0.8571, 0.8352 and 11.0454, 12.3074, respectively. Finally, ICMs provides more accurate and reliable models rather than individual AIs.

The Use of Gigapixel Photogrammetry for the Understanding of Landslide Processes in Alpine Terrain

The work in this paper illustrates an experimental application for geosciences by coupling new and low cost photogrammetric techniques: Gigapixel and Structure-from-Motion (SfM). Gigapixel photography is a digital image composed of billions of pixels (≥1000 megapixels) obtained from a conventional Digital single-lens reflex camera (DSLR), whereas the SfM technique obtains three-dimensional (3D) information from two-dimensional (2D) image sequences. The field test was carried out at the Ingelsberg slope (Bad Hofgastein, Austria), which hosts one of the most dangerous landslides in the Salzburg Land. The stereographic analysis carried out on the preliminary 3D model, integrated with Ground Based Synthetic Aperture Radar Interferometry (GBInSAR) data, allowed us to obtain the main fractures and discontinuities of the unstable rock mass.

Landslides near Enguri dam (Caucasus, Georgia) and possible seismotectonic effects

Abstract. The Enguri dam and water reservoir, nested in the southwestern Caucasus (Republic of Georgia), are surrounded by steep mountain slopes. At a distance of 2.5 km from the dam, a mountain ridge along the reservoir is affected by active deformations with a double vergence. The western slope, directly facing the reservoir, has deformations that affect a subaerial area of 1.2 km2. The head scarp affects the Jvari–Khaishi–Mestia main road with offsets of man-made features that indicate slip rates of 2–9 cm yr−1. Static, pseudostatic and Newmark analyses, based on field and seismological data, suggest different unstable rock volumes based on the environmental conditions. An important effect of variation of the water table is shown, as well as the possible destabilization of the slope following seismic shaking, compatible with the expected local peak ground acceleration. This worst-case scenario corresponds to an unstable volume on the order of up to 48±12×106 m3. The opposite, eastern slope of the same mountain ridge is also affected by wide deformation affecting an area of 0.37 km2. Here, field data indicate 2–5 cm yr−1 of slip rates. All this evidence is interpreted as resulting from two similar landslides, whose possible causes are discussed, comprising seismic triggering, mountain rapid uplift, river erosion and lake variations.

Passive radio-frequency identification ranging, a dense and weather-robust technique for landslide displacement monitoring

Ground deformation monitoring at a local scale requires accuracy, along with dense spatio-temporal resolution. Radio-Frequency Identification (RFID) technology is proposed as an alternative to classical geodetic methods for monitoring displacements of a landslide. Passive RFID tags allow for a very dense resolution, both in time and space, at the scale of a 100-m-long surface. By deploying 19 passive RFID tags on a landslide for 5 months, this study validates the technique by comparison with laser total station and wire extensometer data. The accuracy of the RFID technique was 1 cm during normal weather and up to 8 cm during snow events. The results demonstrate that RFID tag tracking can monitor landslide displacements with multiple sensors at low cost, providing dense spatio-temporal data. This technique could potentially be used for other applications such as monitoring volcanic activity, buildings, unstable rocks or snow cover.

A study of the distribution ratio for combined spore-anchor supporting of unstable rocks based on FLAC3D

For the question of distribution ratio for combined spore-anchor supporting of unstable rock engineering, taking the unstable rock W32 in Shouli Mountain, Wanzhou City, this paper carried out the simulation study on the distribution ratio for combined spore-anchor supporting by means of monitoring displacement. It can be concluded that stability coefficient, displacement cloud and displacement gradients of monitoring points of unstable rock W32 indicated its instability, which was controlled by bedding surface and unloading plane; The maximum displacement at 500 kN of supporting spore reduced by 87.2% compared with no supporting, meanwhile, the maximum displacement at 500 kN of anchor reduced by 84.0% compared with no supporting, thus, supporting spore and rock anchor both nicely supported the stability of unstable rock. However, the supporting spore could lose its advantage of controlling displacement, but rock anchor could give play to its advantage of controlling displacement. The maximum displacement at 500 kN of conbined spore-anchor reduced by mora than 95% compared with no supporting, which indicated better supporting effect than that of the single supporting spore or rock anchor. Simultaneously, this paper analyzed that the best distribution ratio of conbined spore-anchor was 6:4 based on monitoring displacement.

Ambient vibration classification of unstable rock slopes: A systematic approach

In this paper, we are comparing the seismic response of 25 different rock slope instabilities with diverse geological properties, activity level, failure mechanism, fracturing and volumes. We classify them according to their dynamic behaviour. In the dataset, we found two main classes of unstable rock slopes: depth-controlled sites and volume-controlled sites.For depth-controlled instabilities, the seismic wavefield is controlled by horizontally propagating surface waves in the highly fractured and weathered material. At such sites, surface-wave dispersion curves can be retrieved and inverted into velocity profiles of the underground. The lateral borders of depth-controlled instabilities are not obvious and the seismic properties mainly change with depth.The seismic response of volume-controlled sites is dominated by the eigenvibrations of the rock mass itself. Such instabilities have clear lateral and vertical borders and show highly amplified ground motion in limited frequency bands. The observed polarisation of the ground motion is perpendicular to deep open fractures that do not allow surface waves to propagate. A special case of the volume-controlled sites is represented by tower-like rock masses showing strong amplification and directionality. Their dynamic behaviour might not only be related to the internal structure, but also to their geometry that is similar to high-rise buildings.Another type of rock instabilities is represented by block structures, which are difficult to identify by the proposed ambient-vibration methods.A clear relation between geological properties and seismic response was not found.

ПОВЫШЕНИЕ ЭФФЕКТИВНОСТИ ПОДЗЕМНОЙ РАЗРАБОТКИ ЗОЛОТОРУДНЫХ МЕСТОРОЖДЕНИЙ ВОСТОЧНОЙ СИБИРИ

Vein deposits of gold in Eastern Siberia are located in remote areas with a severe sharp-continental climate and are characterized by complex conditions of geological environment. This fact jeopardises the profitability of production. The task of increasing the efficiency of ore underground mining in the development of these deposits is relevant. The purpose of the conducted researches is to solve the problems of improving the development efficiency of vein gold deposits. Research methods are based on the profound study of gold ore body occurrence conditions and the geomechanical state of the rock massif using field observations and measurements, mathematical modeling, laboratory and industrial tests. As a result of this, the mining order of inclined gold-bearing veins in technologically separated contours of reserves with the division into production zones (working, stoping, localization) and subsequent backfilling of voids by controlled caving was substantiated and proposed. When this technology was introduced in Russian gold mines, an explosion-proof hydraulic support and vacuum stoping of ore were used for the first time. A structure of the flexible system of stope drift location has been created for a sublevel development system in order to provide the effective excavation of steeply dipping veins. The rock massif was supported from stope drifts. The rocks were supported using rope anchors. This enabled the effective extraction of ore in unstable rocks. It is proposed to mine the balance reserves of thin steeply dipping veins by sublevel ore breaking with combined overhand-underhand stoping and support work. The carried out works directed at the improvement of the development technology of vein deposits allowed significant reduction in the costs of metal production at the mines.

Probabilistic estimate of rock mass static and dynamic demands for underground excavation stabilisation

Excavation damage under high in situ stress depends largely upon the potential block size associated with any violent ejection. The size and shape of the dynamic instability are largely controlled by the location, orientation and extent of the pre-existing geological discontinuities. A new methodology is presented in which the rock mass demand can be expressed in terms of the mass in tonnes of unstable rock that is ejected per unit area of the excavation surface where failure occurs. A probabilistic approach has been implemented to estimate the potential rock mass instabilities and their associated static and dynamic demands. The new methodology considers that the strain energy released by the rock mass during violent stress-driven failure is largely converted into kinetic energy of ejection for blocks. The estimated dynamic demand has been favourably compared with observations of rock mass damage in a number of underground excavations.

Performance Assessment of Arch-shaped Primary Lining during Construction in Weak Rock Shallow-buried Tunnel

Tunnels excavated through weak rock masses using the Shallow Tunneling Method (STM) call for rigid lining support to withstand and constrain the mobility of the unstable rock where its performance needs to be assessed with field measured data in case of potential failure. For fear of any further hazards after the occurrence of a rock fall at chainage km 86,685 m in the Longsheng Tunnels, the monitoring plan was specially modified to accurately obtain the relative vertical and horizontal displacements of the steel rib component in the arch-shaped composite rigid primary lining that was simply placed on the heading. In this paper, the weak rock masses’ interaction with the rigid lining is treated as unknown distributed loads divided into radial and tangential directions, where the influence line theory is applied to better understand the response of the lining so as to facilitate a displacement-based back analysis for unknown rock mass loads and the resultant stress outcome. By comparing the back analyzed stress outcome with the measured one, the proposed performance assessing method for the unclosed arch-shaped lining was proven to be time efficient with acceptable accuracy, which is of considerable application potential and can provide a reference for similar engineering.

HVSR Analysis of Rockslide Seismic Signals to Assess the Subsoil Conditions and the Site Seismic Response

Many Italian rock slopes are characterized by unstable rock masses that cause constant rock falls and rockslides. To effectively mitigate their catastrophic consequence thorough studies are required. Four velocimeters have been placed in the Torgiovannetto quarry area for an extensive seismic noise investigation. The study area (with an approximate surface of 200×100 m) is located near the town of Assisi (Italy) and is threatened by a rockslide. In this work, we present the results of the preliminary horizontal to vertical spectral ratio analysis of the acquired passive seismic data aimed at understanding the pattern of the seismic noise variation in case of stress state and/or weathering conditions (fluid content and microfracturing). The Torgiovannetto unstable slope has been monitored since 2003 by Alta Scuola of Perugia and the Department of Earth Sciences of the University of Firenze, after the observation of a first movement by the State Forestry Corps. The available data allowed an extensive comparison between seismic signals, displacement, and meteorological information. The measured displacements are well correlated with the precipitation trend, but unfortunately no resemblance with the seismic data was observed. However, a significant correlation between temperature data and the horizontal to vertical spectral ratio trend of the seismic noise could be identified. This can be related to the indirect effect of temperature on rock mass conditions and further extensive studies (also in the time frequency domain) are required to better comprehend this dependency. Finally, the continuous on-line data reveal interesting applications to provide near-real time warning systems for emerging potentially disastrous rockslides.

Complex rock slope deformation at Laxiwa Hydropower Station, China: background, characterization, and mechanism

An unstable rock slope called the Guobu landslide, observed in granite with a maximum cumulative displacement of 45 m, located on the upper stream of the dam of the Laxiwa Hydropower Station, China, and directly threatening the safety of the dam and the people living downstream, was investigated. Detailed field surveys, geological structure investigations, remote sensing image analysis, and GPS displacement monitoring were carried out to investigate the deformation characteristics of the slope after reservoir impoundment, historical deformation, ancient landslide reactivation, the influence factors of the large deformation of the slope, and the mechanism. Based on the results of the above analyses, it was seen that there is a clear geological structural dependence of the failure mechanisms in the study area, and that the complex failure mechanisms include toppling, subsiding wedge failure, rockfalls, and tension cracking in deep-seated rock masses. Moreover, analysis of the remote sensing images indicated that the ancient landslide had been reactivated between 2005 and 2008. Detailed field displacement monitoring data showed that the whole slope was deforming significantly and continuously with the increase of the water level in the reservoir. The displacement rate had a positive correlation with the variation of the reservoir water level, increasing and decreasing as the the latter rose and fell, respectively. The vulnerable geological conditions, water infiltration, and the reservoir impoundment were the main factors causing the large deformation of the Guobu landslide. Water infiltration was the driving force resulting in the reactivation of the ancient landslide, and the reservoir impoundment accelerated the slope deformation. The mechanism of the large deformation of the rock slope was a combination of the upper pushing deformation induced by wedging and toppling, due to the ancient landslide reactivation, and the lower traction deformation due to the reservoir impoundment.

Numerical and analytical simulation of the structural behaviour of fully grouted cable bolts under impulsive loading

Designing reliable yielding support system to mitigate the effect of the kinetic energy in burst-prone conditions in mining and tunneling excavations is one of the challenges for geotechnical engineers. A combination of the support elements can be used to increase rock strength and minimise the displacement of unstable rock mass. It is important to understand how the support system works to ensure the stability of underground excavations. Cable bolts have been commonly used as an effective underground support system and an element of reinforcement to improve rock stability. Cable bolts are usually considered to be subjected to static loads under relatively low stress environments, however, in burst-prone conditions, they might be subjected to dynamic loads. Cable bolts as well as other support elements are used in burst-prone conditions to absorb the kinetic energy of the removed rock to avoid sudden and violent failures. This paper develops numerical and a novel analytical simulation technique for cable bolts to assess their structural behaviour under static and dynamic loading conditions. The numerical and analytical models are then validated against experimental observations reported in the literature, which demonstrates the reliability of the proposed models.

DEM Simulation of the Evolution of an Unstable Rock Face: A Modelling Procedure for Back Analysis of Rockslides

The evolution of unstable rock slopes is a discontinuous process that is typically characterised by a succession of discrete events, each one giving rise to a new configuration of the rock face. If these events are put in a wider time frame, they can be seen as a local step contributing to the overall process. The advances in recognition systems, such as laser scanning or georadar techniques, allow to build numerical models of higher and higher precision, where the topographic and geostructural configurations may be precisely reconstructed. These improved capabilities open the possibility for defining highly representative numerical models that can be used for back analysis purposes or the design of risk mitigation works. One possible drawback of such approaches is that they superimpose structural and topographic data, whose compatibility is not independent of the mechanical behaviour of the rock mass. In fact, the initial geometry depends on the (usually complex) rock slope history, which has a twofold relationship with the whole set of structural and mechanical features of the rock mass. In order to investigate this point, a series of distinct element analyses of an unstable rock face located in Bolzano province is performed. The model is characterised by a very simple geometry, and slope evolution is studied by adopting the strength reduction technique. Structural and mechanical information is obtained from an extensive in situ survey. The aim of the simulations is to show how a model based on the available geomechanical information and a minimum amount of topographic data can be used to reproduce the main topographic features of the rock slope, and to perform a back analysis of a selected case history.

Case study of a rockfall in Chongqing, China: movement characteristics of the initial failure process of a tower-shaped rock mass

Tower-shaped rock masses are particularly susceptible to failure, via fracture and disintegration, due to their inherently large height-to-diameter ratio. A rockfall event at the Zengziyan Cliff, in Chongqing, China, was selected for a case study. Based on video footage, the movement characteristics of the initial failure processes were analyzed in three movement stages: initiation, acceleration and deceleration. The failure process began at the bottom of the tower-shaped unstable rock mass and manifested itself in the form of fissure extension followed eventually by disintegration. The acceleration curve presented a continuous negative fluctuation associated with buffering in the deceleration stage. At the same time, the movement characteristic curves at different measurement points displayed significant time-dependent differences, proving that cracking, collisions and disintegration occur in the failed rock mass during the initial failure process. The results of this analysis provide a reference for the early identification of similar rockfalls and for analysis of their mechanisms.

O abatimento mecanizado de rochas instáveis e segurança no trabalho em mina subterrânea de ouro

Nos últimos anos, a introdução de um equipamento chamado de scaler buscou controlar a exposição ao risco de acidentes durante a atividade de abatimento de “choco”. Os objetivos deste artigo são analisar as vantagens e limitações da tecnologia de abatimento mecanizado de rochas instáveis; identificar as dificuldades e os riscos para os operadores e as estratégias utilizadas no desempenho da atividade. Realizou-se pesquisa qualitativa, combinando análise documental e entrevistas com seis trabalhadores durante quatro sessões coletivas, utilizando roteiro prévio. O uso do scaler trouxe benefícios para a segurança e minimizou o esforço físico necessário na atividade. Fatores organizacionais e a concepção do equipamento agravam a situação, uma vez que não levam em conta as características físicas e psicológicas dos operadores e a gestão implicada na atividade.

Paraglacial Rock Slope Adjustment Beneath a High Mountain Infrastructure—The Pilatte Hut Case Study (Écrins Mountain Range, France)

Landslides triggered by shrinking glaciers are an expected outcome of global climate change and they pose a significant threat to inhabitants and infrastructure in mountain valleys. In this study we document the rock slope movement that has affected the Pilatte hut (2572 m a.s.l.) in the Ecrins range (French alps) since the 1980s. We reconstructed the geometry of the unstable rock mass using Terrestrial Laser Scanning and quantified the unstable volume (~ 400,000 m3). Field observations and annual crack surveys have been used to identify the dynamics of past movements. These movements initiated in the late 1980s and have accelerated since 2000. The current trend seems to be towards a relative stabilization. Reconstruction of the glacier surface using past images taken since 1960 and ‘Structure from Motion’ photogrammetry showed that the glacier probably applied stresses to the rock slope during its short-lived advance during the 1980s, followed by debuttressing caused by rapid surface lowering until the present day. The relationship between observed crack propagation and glacier surface change suggests that the rock slope instability is a paraglacial response to glacier surface changes, and highlights that such responses can occur within a decade of glacier change.

Numerical modeling of rockburst near fault zones in deep tunnels

Many factors that influence rockburst damage have been identified but the mechanism that drives rockburst is not fully understood. Weak planes such as faults and shears have been observed near excavation boundaries in many rockbursts and these structures must have played a role in these rockburst events. In this paper, the role of weak planes around tunnels in rockburst occurrence and damage was studied. A heterogeneous Abaqus2D explicit code was used to simulate dynamic rock failure in deep tunnels. Firstly, rock failure near the excavation boundary of a tunnel without any adjacent weak plane was modeled. Then a fault with different lengths, inclinations, and distances to the tunnel was added to the model and its effect on rock failure was simulated. The velocity and the released kinetic energy of failed rocks, the failure zone around the tunnel, and the deformed mesh were studied to identify stable and unstable rock failures. The simulation results showed that the presence of a fault near a tunnel could induce rockburst if the fault is positioned and oriented in such a way that it promotes high stress and low mine system stiffness. Finally, a rockburst occurred in the Jinping II drainage tunnel with an observed nearby fault was simulated. The modeling results captured the field observation of rockburst damage and confirmed that the presence of weak planes in the vicinity of deep tunnels is a necessary condition for the occurrence of rockburst. The presented methodology in this paper can be useful for rockburst anticipation and control during mining and tunneling in highly stressed grounds.

Influence of strain energy released from a test machine on rock failure process

Rock instability occurs if the energy supplied to the rock failure process is excessive. The theoretical analysis on the energy transfer in the process of rock failure revealed that the rock failure process is a result of the strain energy released from the test machine or the surrounding rock masses of wall rock, plus the additional energy input from an external energy source if the deformation of the rock is continued and driven by the external energy source. The strain energy released from the test machine is the focus in this study because it is responsible for some of the unstable rock failures in laboratory testing. A finite element method (FEM)-based numerical experiment was carried out to study the strain energy released from test machines under different loading conditions of loading system stiffness (LSS). The modeling results demonstrated that depending on the LSS of a test machine, the strain energy released from the test machine alone without additional energy supply can drastically affect the rock failure process. The insight gained from this study can explain unstable rock failure in laboratory tests and the mechanism of some delayed rockbursts that occurred sometime after the excavation of the openings.

Suitability of structure from motion for rock‐slope assessment

AbstractThis study examines three sites in Alaska with unstable rock slopes that were surveyed using both terrestrial laser scanning (TLS) and structure‐from‐motion (SfM) techniques. The datasets were acquired simultaneously and linked to a rigorous survey control network. An accuracy evaluation of the SfM‐derived surface models was performed using the TLS data and numerous reflectorless total station observations collected across the rock slopes. A quality evaluation was conducted to examine differences in point density, model completeness and distributions of morphological properties between the SfM and TLS datasets. The results indicate that SfM is a viable option for unstable rock‐slope assessment when a sufficient number of images with adequate overlap are acquired and the reconstruction is tied to a survey control network. The best results, in terms of accuracy and completeness, were achieved when combining both unmanned aerial vehicle (UAV) and terrestrial imagery for the SfM reconstruction. However, issues such as over‐smoothing and geometric inconsistencies bring into question the suitability of SfM for the detection of small changes over time.

SPLASH: semi-empirical prediction of landslide-generated displacement wave run-up heights

Abstract Displacement waves (or tsunamis) generated by sub-aerial landslides cause damage along shorelines over long distances, making run-up assessment a crucial component of landslide risk analysis. Although site-specific modelling provides important insight into the behaviour of potential waves, more general approaches using limited input parameters are necessary for preliminary assessments. We use a catalogue of landslide-generated displacement waves to develop semi-empirical relationships linking displacement wave run-up ( R in metres) to distance from landslide impact ( x in kilometres) and to landslide volume ( V in millions of cubic metres). For individual events, run-up decreases with distance according to power laws. Consideration of ten events demonstrates that run-up increases with landslide volume, also according to a power law. Combining these relationships gives the SPLASH equation: R = a V b x c , with best-fitted parameters a = 18.093, b = 0.57110 and c = −0.74189. The 95% prediction interval between the calculated and measured run-up values is 2.58, meaning that 5% of the measured run-up heights exceed the predicted value by a factor of 2.58 or more. This relatively large error is explained by local amplifications of wave height and run-up. Comparisons with other displacement wave models show that the SPLASH equation is a valuable tool for the first-stage preliminary hazard and risk assessment for unstable rock slopes above water bodies.