Behavior Of Slope Research Articles

Application of Remote Sensing to the Investigation of Rock Slopes: Experience Gained and Lessons Learned

The stability and deformation behavior of high rock slopes depends on many factors, including geological structures, lithology, geomorphic processes, stress distribution, and groundwater regime. A comprehensive mapping program is, therefore, required to investigate and assess the stability of high rock slopes. However, slope steepness, rockfalls and ongoing instability, difficult terrain, and other safety concerns may prevent the collection of data by means of traditional field techniques. Therefore, remote sensing methods are often critical to perform an effective investigation. In this paper, we describe the application of field and remote sensing approaches for the characterization of rock slopes at various scale and distances. Based on over 15 years of the experience gained by the Engineering Geology and Resource Geotechnics Research Group at Simon Fraser University (Vancouver, Canada), we provide a summary of the potential applications, advantages, and limitations of varied remote sensing techniques for comprehensive characterization of rock slopes. We illustrate how remote sensing methods have been critical in performing rock slope investigations. However, we observe that traditional field methods still remain indispensable to collect important intact rock and discontinuity condition data.

Monitoring of displacement evolution during the pre-failure stage of a rock block using ground-based radar interferometry

As a typical abrupt geological hazard, rockfalls are widely distributed and occur frequently. It is often difficult to predict the occurrence, and therefore record and monitor the whole failure process of rockfalls. In this study, with the combined use of terrestrial laser scanning (TLS) and ground-based radar interferometry (GB-InSAR) technologies, a typical small collapse in the Hongshiyan post-earthquake rock slope was monitored. An accurate TLS three-dimensional (3D) rock slope model of the study area was established with high-resolution geometry and morphology information, the discontinuity sets and their orientations and distributions were visually identified and analyzed by means of an automatic discontinuity identification algorithm. A perspective view of the whole dynamic failure process of the small collapse was achieved; the displacement behavior during critical sliding stage was revealed by integrating the high-accuracy (millimetric) GB-InSAR monitoring results into the TLS 3D model. It can be used for a complete analysis of the failure behavior and stability assessment of the rock slope during a phase of emergency. The unstable rock block on the slope exhibited a rapid growth of displacement. The dynamic failure process of the rock block underwent three obvious accelerating periods. There was a correspondence between the spatial expansion of the moving area and the process of cracking propagation of rock bridges. The stability of the perilous rock above the tafoni was controlled by the connectivity of rock bridges. Thanks to monitoring, early warning and preventive measure were taken, which avoided a possible undesirable event. This typical case study can provide a reference for the monitoring of an unstable rock slope and the understanding of the evolution of rock block kinematics before collapse.

Implication of kinetic Alfvén waves to magnetic field turbulence spectra: Earth’s magnetosheath

In the present paper, we investigate the power-law behaviour of the magnetic field spectra in the Earth’s magnetosheath region using Cluster spacecraft data under solar minimum condition. The power spectral density of the magnetic field data and spectral slopes at various frequencies are analysed. Propagation angle, $\theta_{kB}$ , and compressibility, $R_{\|}$ , are used to test the nature of turbulent fluctuations. The magnetic field spectra have the spectral slopes, $\alpha$ , between −1.5 to 0 down to spatial scales of $20\rho_{i}$ (where $\rho_{i}$ is ion gyroradius), and show clear evidence of a transition to steeper spectra for small scales with a second power-law, having $\alpha$ between −2.6 to −1.8. At low frequencies, $f_{sc} <0.3 f_{ci}$ (where $f_{ci}$ is ion gyro-frequency), $\theta_{kB}\sim 90^{ \circ} $ to the mean magnetic field, $B_{0}$ , and $R_{\|}$ shows a broad distribution, $0.1 \le R_{\|} \le 0.9$ . On the other hand at $f_{sc} >10 f_{ci}$ , $\theta_{kB}$ exhibits a broad range, $30^{ \circ} \le \theta_{kB} \le 90^{ \circ} $ , while $R_{\|}$ has a small variation: $0.2 \le R_{\|} \le 0.5$ . We conjecture that at high frequencies, the perpendicularly propagating Alfven waves could partly explain the statistical analysis of spectra. To support our prediction of kinetic Alfven wave dominated spectral slope behaviour at high frequency, we also present a theoretical model and simulate the magnetic field turbulence spectra due to nonlinear evolution of kinetic Alfven waves. The present study also shows the analogy between the observational and simulated spectra.

Reflectance spectra of seven lunar swirls examined by statistical methods: A space weathering study

Higher magnetic field in lunar swirls is believed to deflect majority of incoming charged particles away from the lunar-swirl surfaces. As a result, space weathering inside and outside swirls should be different. We wanted to evaluate these differences, therefore we have examined seven swirl areas on the Moon (four mare and three highland swirls). We applied the Modified Gaussian Model to statistical sets of the Moon Mineralogy Mapper spectra. Using Principal Component Analysis (PCA), we were able to distinguish the old (weathered) material from both the fresh crater and swirl materials. The swirls did not follow the same behavior as the fresh material, nor were they fully separable. Additionally, we could distinguish between the mare and highland swirls (mare/highland dichotomy) based on the PCA and histogram plots of the albedo and strength of the 1000-nm absorption band. The mare/highland dichotomy can partially be caused by different FeO content in maria and highlands, which points to the existence of a threshold value that changes the spectral evolution due to space weathering. Slope behavior seemed to be dependent on whether the swirl was on the near- or far-side of the Moon, likely due to shielding of lunar nearside by Earth's magnetotail. Our results thus favor the solar wind stand-off hypothesis in combination with the fine dust transport hypothesis and point to the fact that micrometeoroid impacts generally do not reproduce the same weathering trends as all the space weathering effects together.

Use of geophysics for site investigations and earthworks assessments

Site investigations for various infrastructure is traditionally done using boreholes drilled through various strata, logging of boreholes, sampling of strata and laboratory testing to assess engineering properties and infer behaviour of slopes, soft soils, embankments and foundations. Geophysics is still not used as a standard tool by most engineers due to the perception that it is not well-established science or that the results are unreliable. This paper outlines how Engineering and Geophysics can be integrated by having a well-balanced team with all the team members understand the fundamentals of each area. This is demonstrated by case histories for site investigations and earthworks quality assessment. The variety of geophysical methods available for site investigations, their applications, interpretations are presented. The paper describes how cost of investigations can be reduced and the risk of ground variations can be reduced by applying geophysics in geotechnical investigations.

Three-Dimensional Physical and Numerical Modelling of Fracturing and Deformation Behaviour of Mining-Induced Rock Slopes

Fracturing behaviour of jointed rock mass subjected to mining can significantly affect the stability of the rock structures and rock slopes. Ore mining within an open-pit final slope would lead to large-scale strata and surface movement of the rock slope. Rock mass structure, or more specifically, the strength, spacing and distribution of rock joints, are the controlling factors that govern the failure and deformation mechanisms of the final slope. Two-dimensional (2-D) physical modelling tests have been conducted in the literature, but in general, most of them have simplified the geological conditions and neglected some key features of rock mass structure in the field. In this study, new three-dimensional (3-D) physical modelling methods are introduced, with realistic modelling of mechanical behaviour of rock mass as well as identified properties of predominant rock joint sets. A case study of Yanqianshan iron mine is considered and the corresponding 1:200 model rock slope was created for studying the rock joint effects on the strata movement and the subsidence mechanism of the slope. The physical model test results are subsequently verified with 3-D discrete element numerical modelling. Due to the presence of the predominant joints, the observed well-shaped strata subsidence in Yanqianshan iron mine was successfully reproduced in the 3-D physical model. The failure mechanism of rock slopes differs from the trumpet-shaped subsidence observed in unconsolidated soil. Due to the formation of an arching mechanism within the rock mass, the strata deformation transferred gradually from the roof of the goaf to the slope surface.

Slope monitoring system for nuclear power plants

Because of increases in both the intensity and frequency of localized heavy rainfalls in Korea, slope failures are frequently occurring throughout the country. Subsequently, the possibility of a slope failure at NPP has become a major concern for the nuclear power industry. KHNP (Korea Hydro & Nuclear Power Co., Ltd.) has been regularly carrying out inspections of the slopes at NPP sites. However, because most of the inspections have been performed by naked eye, inspectors cannot figure out small or invisible deformation. A new slope monitoring system, termed K-SLOPE system (KHNP SLOPE Maintenance & Management System), is developed for more systematic and quantitative measurement of slope behavior by installing a series of monitoring devices.

Formulation of landslide risk scenarios using underground monitoring data and numerical models: conceptual approach, analysis, and evolution of a case study in Southern Italy

Understanding the mechanism of a landslide and its evolution is of fundamental importance in the risk management process. This work introduces an articulated approach to the problem, applying it to a specific case in the south of Italy where a gravitational movement insists on a section of an important highway. In recent years, the site has been investigated from a geomorphological and a lithological point of view, and a comprehensive geomechanical characterization has been carried out by means of on-site and laboratory tests. The area has been instrumented with a monitoring system composed of automatic inclinometers, piezometers, a rainfall station, and time domain reflectometry (TDR) cables. These sensors have monitored the deformation processes and their correlation with groundwater fluctuation. A 2D finite differences model (FDM) of the slope has been created, calibrated, and validated through back analysis, carried out using the monitoring data available. A secondary creep phenomenon, barely influenced by the water level rise due to occasional rainfall, has been identified and modeled using the Burgers viscoelastic constitutive model. Variations in the piezometric level were introduced and their effect accounted for the numerical model refinement. Once the improvements had been completed together with the reproduction of past events, a predictive analysis was carried out in order to forecast the most probable slope behavior relative to the incoming year. At the end of this phase, the infrastructure supervisor should have information about possible deformations to be compared with the near real-time monitoring outcomes and design assumptions. This procedure allows real-time monitoring of the compatibility of slope deformations with highway safety.

Influence of Initial Conditions on Unsaturated Groundwater Flow Models

Slope failure in unsaturated soils is common in tropical countries due to the seasonal pattern of abundant rainfall preceding a period of prolonged drying. Much research has been undertaken to understand the behaviour of unsaturated slopes and reduce the number of catastrophic failures. The initial conditions are important factors in numerical modelling of the groundwater flow yet rarely considered in detail in the literature. This paper presents a parametric study of the initial conditions at a slope in Bukit Timah, Singapore. The intensity and duration of rainfall are varied to assess the effect on the pore-water pressure in the slope. The generated pore-water pressure profile is compared with field measurements and previous numerical studies. It is discovered that a low rainfall, with an intensity of 1x10-7 m/s over a period of 62 days, results in initial pore-water pressure which is consistent with data recorded at the field. Unlike the duration, changes in the rainfall intensity are shown to have a significant effect on the pore-water pressure in the slope. This study, therefore, demonstrates the importance of determining appropriate initial conditions in unsaturated groundwater flow analysis.  Â

An Experimental Investigation on the Progressive Failure of Unsaturated Granular Slopes

Slope failure is a complex process which depends on several factors concerning nature and properties of soil, slope morphology and structure, past stress history, groundwater regime, boundary conditions, and their changes. As a consequence, the mechanism of slope failure is typically characterized by the development of a highly non-uniform strain field, which does not allow an easy prediction of the failure conditions. Usually, the process which will bring the slope to final collapse starts with local soil failure, which then leads to formation and propagation of a shear zone, and finally to general slope failure. This mechanical process is called progressive failure. However, in spite of the progresses in the knowledge of the slope behavior, a complete framework about the progressive failure is still missing; in particular, information about the response of granular unsaturated sloping soils is very poor. This paper reports the results of a couple of small-scale experiments on slopes reconstituted with unsaturated pyroclastic soils and subjected to continuous rainfall. The use of miniaturized sensors and optical fibers provided useful data to read some aspects of the mechanics of failure.

Seismic Stability of a Fissured Slope Based on Nonlinear Failure Criterion

In this study, the kinematic approach of limit analysis is employed to investigate the seismic stability of slopes with cracks on the basis of a nonlinear failure criterion. Quasi-static representation is adopted to consider the seismic effect using a non-dimensional coefficient named as horizontal seismic coefficient. The maximum crack depth is determined by requiring that the crack profile can keep stable. Of many cracks present in the upper part of the slope, only one that has the most unfavorable influence on the slope stability is involved. The critical height of slopes is determined and expressed using a stability factor. The minimum stability factor is sought by optimization. Numerical results are obtained to analyze the parametric effects. The obtained results indicate that accounting for the presence of cracks and seismic effect results in a more conservative result so they cannot be overlooked in the design of slopes, and that soil strength nonlinearity has a great impact on the slope stability. This paper considers a more realistic service behavior of slopes where the effects of cracks, soil strength nonlinearity and seismic actions are taken into account, and presents an effective solution for estimating the stability of such slopes.

Characteristics of weathered mudstone with X-ray computed tomography scanning and X-ray diffraction analysis

Large-scale deformation on a cut slope composed of mudstone from the Neogene was observed over time during excavation of the powerhouse area at the Rajamandala Hydroelectric Power Plant in Indonesia. This paper discusses the characteristics of the mudstone and the mechanisms of slope behavior. As a part of detailed research into the mudstone, X-ray Computed Tomography scanning (CT scanning) and X-ray diffraction (XRD) analysis were applied to core samples. The purpose of CT scanning was to visually observe inside the core samples in three dimensions. The CT scanning image, which was a set of numbered CT scans, exhibited a color tone corresponding to the soundness of the core samples and this can be an indicator of weathering grade. The extent of weathering of each core sample was classified quantitatively by the CT scanning image and CT number. The extent of weathering maintains objectivity in the engineering classification of rock mass, which is generally assessed by core sample observation and hammer impacts. XRD analysis is commonly applied to dried samples in order to clarify their mineral components, especially the content of swelling clay minerals such as smectite. This paper discusses, in addition, XRD analysis for field-wet samples, because it is considered that a number of interlayer water molecules in smectite may have changed while preparing dried samples. Smectite, because of the relatively high quantity of interlayer water molecules, could likely cause swelling and slaking.

Small- and large-scale analysis of bearing capacity and load-settlement behavior of rock-soil slopes reinforced with geogrid-box method

This paper presents an investigation on bearing capacity, load-settlement behavior and safety factor of rock-soil slopes reinforced using geogrid-box method (GBM). To this end, small-scale laboratory studies were carried out to study the load-settlement response of a circular footing resting on unreinforced and reinforced rock-soil slopes. Several parameters including unit weight of rock-soil materials (loose- and dense-packing modes), slope height, location of footing relative to the slope crest, and geogrid tensile strength were studied. A series of finite element analysis were conducted using ABAQUS software to predict the bearing capacity behavior of slopes. Limit equilibrium and finite element analysis were also performed using commercially available software SLIDE and ABAQUS, respectively to calculate the safety factor. It was found that stabilization of rock-soil slopes using GBM significantly improves the bearing capacity and settlement behavior of slopes. It was established that, the displacement contours in the dense-packing mode distribute in a broader and deeper area as compared with the loose-packing mode, which results in higher ultimate bearing load. Moreover, it was found that in the loose-packing mode an increase in the vertical pressure load is accompanied with an increase in the soil settlement, while in the dense-packing mode the load-settlement curves show a pronounced peak. Comparison of bearing capacity ratios for the dense- and loose-packing modes demonstrated that the maximum benefit of GBM is achieved for rock-soil slopes in loose-packing mode. It was also found that by increasing the slope height, both the initial stiffness and the bearing load decreases. The results indicated a significant increase in the ultimate bearing load as the distance of the footing to the slope crest increases. For all the cases, a good agreement between the laboratory and numerical results was observed.

Expectation Formation in the Treasury Bond Market

I document that subjective bond risk premia implied by survey forecasts of future Treasury yields are acyclical at the one-year horizon. This is in stark contrast to large countercyclical variation in objective risk premia fitted from in-sample predictive regressions of future bond excess returns. This difference in risk premia implies a wedge between subjective and objective expectations of future short rates, which I show is predictable by trend and cycle components of macroeconomic forecasts. I show that these empirical findings can be explained with a learning model in which the agent filters latent trend and cycle components of fundamentals in real time, while an econometrician analyzing the data ex-post has full knowledge of the data-generating processes. The model also yields predictions, consistent with the data, on the joint behavior of the unconditional yield curve slope, the cyclicality of short-rate and macroeconomic expectation wedges, and the cyclicality of objective risk premia. My results suggest that equilibrium models of bond risk premia should target acyclical subjective risk premia and expectation formation, rather than ex-post in-sample fitted risk premia from predictive regressions.

Assessment on the hydrogeological condition of an open pit mine based on piezometric measurements

Understanding groundwater and flow pattern behavior in a given mine site is generally based on accepted theory related to flow through porous granular media. The existence of discontinuities within the rock mass alters the accepted hydraulic behavior being the joint profile and aperture variability a challenge when designing an open pit mine. In this regard, groundwater interaction with the rock mass is the key variable that influences mining slope design and monitoring. This manuscript studies and analyses the geotechnical perspective of an open pit mine and carries out a comprehensive assessment on the groundwater behavior of an open pit mine in a hard rock environment. The analysis is carried out using data gathered from piezometers and correlating the findings with the structural model of the mine. A comparison of the analysis with the results of previous investigations like hydraulic testing and mapping of the mine site are presented comprehensively. The authors propose the concept of receding time for a better understanding of the drainage capability of a given discontinuity (or a set of them) and its importance in assessing groundwater behavior of the pit slope. Discussions are also made on how groundwater flow can be locally modified by slope scale structures and what are the potential consequences there may have for overall slope stability.

Examination of Rainfall-Induced Landslide Failure Mechanisms via a Centrifuge Physical Simulation Test

Rainfall is one of the most important factors contributing to landslides, and gentle bedding incline, high-rainfall induced landslides are common throughout the world. Field observations and theoretical analyses have been used to assess slope instability caused by permeability variation. In this study, the influence of rainfall infiltration on gentle bedding incline slope behaviour was investigated using a centrifuge physical simulation test. The magnitude, pattern and development of pore water and earth pressure at the interface; the shear failure surface features; and the corresponding deformation and failure processes were considered. A model with interbedded sand and mud was created, and a centrifuge was used to simulate both natural and rainfall conditions. The weak intercalation was composed of single-material silty clay, and the landslide mass was composed of red-bed sandstone. A combination of photography, pore water pressure measurements and earth pressure measurements were used to examine the relationship between the pore water pressure, earth pressure and failure modes. When the slope experiences overall instability, the curves of the earth pressure and pore water pressure dramatically decrease. The results reveal that the failure shear surface largely depends on the differential creep caused by the properties of the rock mass and the rainfall infiltration.

Modelling the Stability of the Aleksotas Hill Slope in Kaunas

Main causes of slope failures in soils are: geological activities (earthquakes), hydrological influence (rise of the groundwater table), topographical features, weathering processes (a rainy season, snowmelt), human activities (vibrations from explosions, machinery, road and air traffic, loading the slope crest, etc.) and vegetation and climatic conditions. As a result, the shear strength of the soil decreases and factor of safety of the slope reduces to a low value that may trigger failures. The slope of the Aleksotas Hill was sliding in 2015. To protect the slope from future landslides, the reconstruction work began in 2018. Geotechnical modelling software SLOPE/W was used for determination of the factor of safety. Model with three modifications (variants) was created by SLOPE/W software for the slope behaviour modelling. The Aleksotas Hill slope stability calculations of original (natural) slope and excavated slope with constructing subsurface drainage was performed in order to evaluate the solutions proposed in the reconstruction project.

Stability analysis of the north-eastern slope of Daralou copper open pit mine against a secondary toppling failure

Secondary toppling failures have complicated mechanisms. In these instabilities, some natural or manmade external factors motivate and overturn a rock mass. One of the most common types of secondary toppling failures is slide-toe-toppling mode. When a blocky or layered rock mass is overlaid by a soil or weak rock mass, the combination of a toppling failure in the rock at the toe and a circular or non-circular sliding in the soil or weak rock in the top leads to this hybrid failure. In 2015, such failure occurred in north-eastern slope of Daralou copper open pit mine. During this instability, the slope consisted mainly of two 10-m benches and one 4-m semi-bench. Since it was supposed to excavate the slope to the depth of 54 m, experts were worried about the project facing a similar larger failure in the future. Hence, a widespread investigation was carried out on the failure. Firstly, the mechanism of this instability was clarified with geological and geotechnical surface and subsurface investigations. Next, existing analytical solution which had been presented for analysis of static slide-toe-toppling failure was modified and some new equations were obtained for analysis of the failure under dynamic condition. Then, a computer code was developed based on the new equations for evaluation of the instability. In the next step, the failed slope was analyzed using the code and finite element method, and outcomes of these analyses were compared with real conditions. The comparison showed that there was satisfactory agreement between the analytical, numerical and actual results. Therefore, these methods were used to predict the behavior of the final slope in static and dynamic conditions. These evaluations indicated that if displaced materials are completely excavated and removed from the mine and overall dip of the slope is reduced, the final slope will be stable against slide-toe-toppling failure. This paper summarizes the results and concludes that both the modified analytical approach and finite element method are able to analyze a slope against the secondary toppling mode. Furthermore, the research proves that re-sloping and unloading are two adequate methods which can be used for stabilization of the failure.

Stratified slopes, numerical and empirical stability analysis

Urbanisation means that many natural slopes in and around cities are often subjected to cuts resulting in dramatic changes in the geometry of slope faces mostly by increasing slope angle, which could lead to failures with catastrophic consequences. As most natural slopes are of non-homogeneous layered nature, understanding the stability behaviour of such slopes will be of utmost importance. The current practice in analysing slopes of complicated nature, geometrically and materially, is mostly to apply simplifications sacrificing accuracy leading to use of large factors of safety (FoS), which could undermine analytical and economic feasibility of projects. In this research study, limit-equilibrium and finite-element methods are used by the Oasys slope and Plaxis 2D software programs, respectively, empirically and numerically to model and analyse geometrically non-homogeneous stratified slopes with the aim of understanding the effects of non-homogeneity of geometry and materials on stability under various inclination angles of slope face. The analysis included determination of FoS as well as a sensitivity analysis looking into the combined effects of contributing parameters.

The Influence of Slope Geometry on its Stability: Spatial and Plane Analysis

Abstract The paper presents the results of numerical calculations of the stability and deformation process of several idealized slopes performed by the elasto-plastic finite difference method, using the commercial codes FLAC3D and FLAC2D. The results of 3D analysis of these slopes are compared with those obtained by the 2D method. The behaviour of slopes of different shapes and inclinations was analyzed. The calculations were carried out for flat, concave and convex slopes inclined at 30°, 45° and 60°, taking into account the influence of the lateral constraints of the slope. Two variants of the medium were analysed, i.e. the mass with no friction and with no cohesion. A comparison of 3D calculation results with those obtained by the 2D limit equilibrium analysis indicates that the 3D approach produces almost always higher safety factors than does the 2D method.