Hazardous Rock Research Articles

FACETS : A CLOUDCOMPARE PLUGIN TO EXTRACT GEOLOGICAL PLANES FROM UNSTRUCTURED 3D POINT CLOUDS

Abstract. Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (http://cloudcompare.org/ ) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects.

Quantifying weather conditions for rock fall hazard management

Relationships between weather conditions and rock fall occurrences have been acknowledged in the past, but seldom have such relationships been quantified and published. Rock falls are frequent hazards along transportation corridors through mountainous terrain, and predicting hazardous rock fall periods based on weather conditions can enhance mitigation approaches. We investigate the relationship between weather conditions and rock fall occurrences along a railway section through the Canadian Cordillera. Monthly weather-rock fall trends suggest that the seasonal variation in rock fall frequency is associated with cycles of freezing and thawing during the winter months. The intensity of precipitation and freeze–thaw cycles for different time-windows was then compared against recorded rock falls on a case-by-case approach. We found that periods when 90% of rock falls occurred could be predicted by the 3-day antecedent precipitation and freeze–thaw cycles. Some rock falls not predicted by this 3-day antecedent approach occurred during the first two weeks of spring thaw. These findings are used to propose a rock fall hazard chart, based on readily available weather data, to aid railway operators in their decision-making regarding safe operations.

Geotechnical Surveys Indicate Potential Offshore Port Facilities off Subarnarekha Outflow Sector, Orissa, India

Deficiency in major port facilities off Orissa prompted the State Government to promote development of a port facility in the Subarnarekha river outflow sector utilizing the inland water network of Orissa coast canal and Contai canal. Marine and Coastal Surveys Division of Geological Survey of India carried out geotechnical feasibility surveys to explore possibilities of setting up a port facility in this sector. Bathymetry reveals smooth, parallel isobaths signifying gentle slopes with varying gradients. The East-West profile delineates a natural channel that could be dredged into a navigational channel. Sediments are dominantly sandy silt marginally varying either into silty sand or clayey silt. Geotechnical characteristics suggest a stable substratum ideal for developing the offshore port facility. Side-scan sonar surveys reveal a seafloor bereft of any hazardous rocks or reefs. The surveys espouse immense potential for developing this sector into an offshore port facility.

Pseudo 3‐D P wave refraction seismic monitoring of permafrost in steep unstable bedrock

AbstractDegrading permafrost in steep rock walls can cause hazardous rock creep and rock slope failure. Spatial and temporal patterns of permafrost degradation that operate at the scale of instability are complex and poorly understood. For the first time, we used P wave seismic refraction tomography (SRT) to monitor the degradation of permafrost in steep rock walls. A 2.5‐D survey with five 80 m long parallel transects was installed across an unstable steep NE‐SW facing crestline in the Matter Valley, Switzerland. P wave velocity was calibrated in the laboratory for water‐saturated low‐porosity paragneiss samples between 20°C and −5°C and increases significantly along and perpendicular to the cleavage by 0.55–0.66 km/s (10–13%) and 2.4–2.7 km/s (>100%), respectively, when freezing. Seismic refraction is, thus, technically feasible to detect permafrost in low‐porosity rocks that constitute steep rock walls. Ray densities up to 100 and more delimit the boundary between unfrozen and frozen bedrock and facilitate accurate active layer positioning. SRT shows monthly (August and September 2006) and annual active layer dynamics (August 2006 and 2007) and reveals a contiguous permafrost body below the NE face with annual changes of active layer depth from 2 to 10 m. Large ice‐filled fractures, lateral onfreezing of glacierets, and a persistent snow cornice cause previously unreported permafrost patterns close to the surface and along the crestline which correspond to active seasonal rock displacements up to several mm/a. SRT provides a geometrically highly resolved subsurface monitoring of active layer dynamics in steep permafrost rocks at the scale of instability.

Computer simulation-based evaluation of rock fall roll-out distances for catchment ditch design in Ohio, USA

Catchment ditches along highways are designed to contain hazardous rock falls from cut slopes. RocFall, a rock fall simulation software, was used to evaluate the maximum roll-out distances of rock falls in order to determine rock fall catchment ditch dimensions for Ohio's cut slopes. Based on stratigraphy, cut slopes in Ohio were classified into five types. The parameters required for simulation process included friction angle between rock fall and slope face, coefficient of normal and tangential restitution, slope roughness and average weight of rock falls. A total of 400 simulations were performed for various slope heights, slope angles and catchment ditch slopes. The results are useful in designing catchment ditch for Ohio and neighbouring states where the stratigraphy consists of sub-horizontal, inter-layered hard and soft rock units. The widely used guidelines developed by the Oregon Department of Transportation do not work well for Ohio's stratigraphy.

3-D geomechanical rock mass characterization for the evaluation of rockslide susceptibility scenarios

An integrated methodology based on traditional field and remote surveys such as terrestrial laser scanning and terrestrial infrared thermography is proposed, with the aim of defining susceptibility scenarios connected to rock slopes affected by instability processes. The proposed methodology was applied to a rock slope threatening a coastal panoramic roadway located in western Elba Island (Livorno district, central Italy). The final aim of the methodology was to obtain an accurate three-dimensional rock mass characterization in order to detect the potentially more hazardous rock mass portions, calculate their volume, and collect all the required geomechanical and geometrical parameters to perform a detailed stability analysis. The proposed approach proved to be an effective tool in the field of engineering geology and emergency management, when it is often urgently necessary to minimize survey time when operating in dangerous environments and gather all the required information as fast as possible.

Size‐frequency distributions of rocks on the northern plains of Mars with special reference to Phoenix landing surfaces

The size‐frequency distributions of rocks >1.5 m diameter fully resolvable in High Resolution Imaging Science Experiment (HiRISE) images of the northern plains follow exponential models developed from lander measurements of smaller rocks and are continuous with rock distributions measured at the landing sites. Dark pixels at the resolution limit of Mars Orbiter Camera thought to be boulders are shown to be mostly dark shadows of clustered smaller rocks in HiRISE images. An automated rock detector algorithm that fits ellipses to shadows and cylinders to the rocks, accurately measured (within 1–2 pixels) rock diameter and height (by comparison to spacecraft of known size) of ∼10 million rocks over >1500 km2 of the northern plains. Rock distributions in these counts parallel models for cumulative fractional area covered by 30–90% rocks in dense rock fields around craters, 10–30% rock coverage in less dense rock fields, and 0–10% rock coverage in background terrain away from craters. Above ∼1.5 m diameter, HiRISE resolves the same population of rocks seen in lander images, and thus size‐frequency distributions can be extrapolated along model curves to estimate the number of rocks at smaller diameters. Extrapolating sparse rock distributions in the Phoenix landing ellipse indicate <1% chance of encountering a potentially hazardous rock during landing or that could impede the opening of the solar arrays. Extrapolations further suggest rocks large enough to depress the ground ice table and small enough to be picked up or pushed by the robotic arm should be present within reach for study after landing.

Musculoskeletal Stress on Miners Performing Roof Screening Operations

Roof screen is often bolted to the mine ceiling to help control hazardous rock falls in coal mines. While the screen prevents rock fall injuries, its installation may expose the miner to musculoskeletal stress. The purpose of this study was to evaluate methods of handling roof screen. Subjects performed installation tasks under a normal and intervention condition while trunk kinematics and muscle activity data were collected. Trunk kinematics were not affected by the intervention but were significantly higher in the morning than in the afternoon. Muscle activity did not differ significantly with seam height but was significantly reduced by the intervention. Overall, this study showed that musculoskeletal stressors during screen installation were reduced by the proposed intervention.

Geohazards and their control in the resettlement sites of the Three Gorges Project, Yangtze River, China

The population to be resettled from the Three Gorges Reservoir of the Yangtze River is about 1.2 million. During the first period of the Project from 1993 to 1997, about 82 thousand people were resettled; whereas about 550 thousand will be resettled during the second period of the Project from 1997 to 2003, and over 600 thousand will be resettled during the third period of the Project by 2009. Resettlement is a great challenge, since in the vicinity of the reservoir, there is not much land suitable for constructing buildings and the area is subject to various geological hazards. The paper discusses the engineering geology of the area, especially the geological hazards and their control for resettlement. The control measures for major geological hazards that have a possibility of disrupting the navigation through the Yangtze River (such as the Lianziya hazardous rock mass, the Huanglashi Landslide. and Jiguanling Rockfall) are discussed in this paper. The geological hazard prevention projects undertaken for the resettlement in the new sites (such as Waxian, Wushan, and Badong) is also described.

Assessment of Mars Pathfinder landing site predictions

Remote sensing data at scales of kilometers and an Earth analog were used to accurately predict the characteristics of the Mars Pathfinder landing site at a scale of meters. The surface surrounding the Mars Pathfinder lander in Ares Vallis appears consistent with orbital interpretations, namely, that it would be a rocky plain composed of materials deposited by catastrophic floods. The surface and observed maximum clast size appears similar to predictions based on an analogous surface of the Ephrata Fan in the Channeled Scabland of Washington state. The elevation of the site measured by relatively small footprint delay‐Doppler radar is within 100 m of that determined by two‐way ranging and Doppler tracking of the spacecraft. The nearly equal elevations of the Mars Pathfinder and Viking Lander 1 sites allowed a prediction of the atmospheric conditions with altitude (pressure, temperature, and winds) that were well within the entry, descent, and landing design margins. High‐resolution (∼38 m/pixel) Viking Orbiter 1 images showed a sparsely cratered surface with small knobs with relatively low slopes, consistent with observations of these features from the lander. Measured rock abundance is within 10% of that expected from Viking orbiter thermal observations and models. The fractional area covered by large, potentially hazardous rocks observed is similar to that estimated from model rock distributions based on data from the Viking landing sites, Earth analog sites, and total rock abundance. The bulk and fine‐component thermal inertias measured from orbit are similar to those calculated from the observed rock size‐frequency distribution. A simple radar echo model based on the reflectivity of the soil (estimated from its bulk density), and the measured fraction of area covered by rocks was used to approximate the quasi‐specular and diffuse components of the Earth‐based radar echos. Color and albedo orbiter data were used to predict the relatively dust free or unweathered surface around the Pathfinder lander compared to the Viking landing sites. Comparisons with the experiences of selecting the Viking landing sites demonstrate the enormous benefit the Viking data and its analyses and models had on the successful predictions of the Pathfinder site. The Pathfinder experience demonstrates that, in certain locations, geologic processes observed in orbiter data can be used to infer surface characteristics where those processes dominate over other processes affecting the Martian surface layer.

Rock slope hazard assessment: a new approach

Abstract Uncontrolled bulk blasting and the application of ‘standard’ designs have left a legacy of many unstable highway rock slopes, some of which are potentially hazardous. Effective management of these slopes requires knowledge of their location and the risk posed to the road user. Existing rock slope stability assessment and risk evaluation systems use various approaches to data collection, and different scales and nomenclature for results. In addition, these assessments are usually undertaken on a reactive basis, prompted by rockfalls. As a consequence road users may be exposed to risk before problems are addressed, comparison of results is very difficult, budgetary problems arise as incidents are largely unforeseen, and prioritization of funds is impossible. As a result of a research programme undertaken for the Scottish Office Industry Department (SOID) National Roads Directorate, a new, proactive approach to identifying and classifying rock slope hazards has been developed. Application of this new approach is likely to improve risk management of hazardous rock slopes. The first stage of this approach derives a rock slope hazard index from rapid, standardized field data collection. This is used to classify rock slopes into four categories depending on the requirement for future action. The second stage derives a rock slope hazard rating from detailed field surveys. The rating is a measure of the risk of a vehicle incident being caused by rockfall. The results of a field trial of the rock slope hazard index, carried out on a section of trunk road in the Scottish Highlands, are described.

146-Ft Long Precast Prestressed Bridge Girders in Washington State

T longest precast prestressed concrete bridge girders (Fig. 1) ever used for a Washington State Department of Transportation highway project are being incorporated into the Coweman River Bridges near Longview, in southwest Washington. Currently being constructed, the four bridges are part of a realignment of Interstate 5 that will shift the highway away from a slide-prone area which has created traffic hazards over the years. In order to bypass the hazardous rock bluffs of the slide area, the new section of highway crosses the Coweman River on parallel bridges in two places. Four bridge spans of 140 to 146 ft (42.7 to 44.5 m) were required to cross the river within the newly allotted section of highway right-of-way. Although prestressed concrete has long been recognized as a preferred construction material in the State of Washington, the bridge designers were concerned about the cost of such unusually long-span girders. Therefore, the designers prepared detailed cost estimates for precast prestressed concrete girders with a field-cast deck versus a cast-in-place concrete box girder structure. After comparing these estimates, superstructures using the Washington State Department of Transportation standard I-girders (Fig. 2) were chosen.