Combined Field and Structure from Motion Survey to Identify Rock Discontinuity Sets of Aa Shallow Rockslide

The present work shows the results of a combined field and Structure from Motion (SfM) survey performed on the detachment surface of a shallow rockslide that occurred in the Rosandra Valley (Trieste, NE Italy), which was aimed at testing the use of 3D models obtained from Remote Sensing (RS) techniques to identify joint sets affecting unstable rock masses. According to discontinuity orientation data acquired from the field (N = 223), the investigated rock mass is affected by at least nine joint sets characterised by a notable variability. The extraction of joint sets from the 3D point cloud representing the surveyed rock outcrop was strongly sensitive to the point cloud density and the values of the controlling parameters of the density function embedded within the discontinuity extractor. This work demonstrates that, in order to properly identify rock joint sets, the exclusive application of a RS approach cannot fully substitute the traditional field survey, and the estimation of discontinuity sets should be integrated with joint orientation data acquired using a geological compass. To maximise its capabilities, the semi-automatic discontinuity set extraction from 3D point clouds should always be supported by a significant statistical sample of joint orientation measurements that are preliminarily collected from the field.

A New Method for Automatic Extraction and Analysis of Discontinuities Based on TIN on Rock Mass Surfaces

Light detection and ranging (LiDAR) can quickly and accurately obtain 3D point clouds on the surface of rock masses, and on the basis of this, discontinuity information can be extracted automatically. This paper proposes a new method to automatically extract discontinuity information from 3D point clouds on the surface of rock masses. This method first applies the improved K-means algorithm based on the clustering algorithm by fast search and find of density peaks (DPCA) and the silhouette coefficient in the cluster validity index to identify the discontinuity sets of rock masses, and then uses the hierarchical density-based spatial clustering of applications with noise (HDBSCAN) algorithm to segment the discontinuity sets and to extract each discontinuity from a discontinuity set. Finally, the random sampling consistency (RANSAC) method is used to fit the discontinuities and to calculate their parameters. The 3D point clouds of the typical rock slope in the Rockbench repository is used to extract the discontinuity orientations using the new method, and these are compared with the results obtained from the classical approach and the previous automatic methods. The results show that, compared to the results obtained by Riquelme et al. in 2014, the average deviation of the dip direction and dip angle is reduced by 26% and 8%, respectively; compared to the results obtained by Chen et al. in 2016, the average deviation of the dip direction and dip angle is reduced by 39% and 40%, respectively. The method is also applied to an artificial quarry slope, and the average deviation of the dip direction and dip angle is 5.3° and 4.8°, respectively, as compared to the manual method. Furthermore, the related parameters are analyzed. The study shows that the new method is reliable, has a higher precision when identifying rock mass discontinuities, and can be applied to practical engineering.

2D quantitative analysis of fractures from high-resolution photos for the geomechanical characterization of rock masses

<p>The identification of discontinuity sets and their properties is among the key factors for the geomechanical characterization of rock masses, which is fundamental for performing stability analyses, and for planning prevention and mitigation measures as well.<br>In practice, discontinuity data are collected throughout difficult and time-consuming field surveys, especially when dealing with areas of wide extension, difficult accessibility, covered by dense vegetation, or with adverse weather conditions. Consequently, even experienced operators may introduce sampling errors or misinterpretations, leading to biased geomechanical models for the investigated rock mass.<br>In the last decades, new remote techniques such as photogrammetry,<em> Light Detection and Ranging</em> (LiDAR), <em>Unmanned Aerial Vehicle</em> (UAV) and <em>InfraRed Thermography </em>(IRT) have been introduced to overcome the limits of conventional surveys. We propose here a new tool for extracting information on the fracture pattern in rock masses, based on <em>remote sensing </em>methods, with particular reference to the analysis of high-resolution georeferenced photos. The first step consists in applying the <em>Structure from Motion</em> (SfM) technique on photos acquired by means of digital cameras and UAV techniques. Once aligned and georeferenced, the orthophotos are exported in a GIS software, to draw the fracture traces at an appropriate scale. We developed a MATLAB routine to extract information on the geostructural setting of rock masses by performing a quantitative 2D analysis of the fracture traces, based on formulas reported in the literature. The code was written by testing few experimental and simple traces and was successively validated on an orthophoto from a real case study.<br>Currently, the script plots the fracture traces as polylines and calculates their orientation (strike) and length. Subsequently, it detects the main discontinuity sets by fitting an experimental composite Gaussian curve on histograms showing the number of discontinuities according to their orientation, and splitting the curve in simpler Gaussian curves, with peaks corresponding to the main discontinuity sets.<br>Then, for each set, a linear scanline intersecting the highest number of traces is plotted, and the apparent and real spacing are calculated. In a second step, a grid of circular scanlines covering the whole area where the traces are located is plotted, and the mean trace intensity, trace density and trace length estimators are calculated.<br>It is expected to test the presented tools on other case studies, in order to optimize them and calculate additional metrics, such as persistence and block sizes, useful to the geomechanical characterization of rock masses.<br>As a future perspective, a similar approach could be investigated for 3D analyses from point clouds.</p>

Kinematic and Rock Mass Classification Assessment of Road Cut Slopes along with Karakoram Highway in Northern, Pakistan

Karakoram highway (K.K.H.) the only road link between two countries China and Pakistan. This road network is essential for two countries due to its strategic location and socioeconomic. The highway is more vulnerable due to landslide disasters, especially in rain and snow melting seasons, and different kinds of mass movement activities have occurred along K.K.H., such as rockfall, debris flow, and snow avalanche. The slope stability problems are widespread along with Karakorum (K.K.H.) between Besham city and the Dasu area because of the high seismic zone, rainfall, snow melting, and complex geology slope geometry, week, and adverse discontinuities sets. The detailed fieldwork was done along the Karakorum highway to minimize the risk of slope stability and for planning purposes in Besham to Dasu area and selected nine road-cut slopes. However, in these nine selected roadcut slopes, three slopes were already failed, four slopes are partially stable, and two slopes were stable. Both kinematic and empirical approaches are applied on all these nine road cut slopes and their discontinuities. The kinematic result has shown that all kinds of mode failure such as Toppling, Planar, and Wedge failure mode occurred in these slopes. The RMRb result has shown that all discounters lie in between fair to good rock. Both discrete and continuous (S.M.R.) results show that all discontinuity sets lie between the unstable, partially stable, and stable conditions.

APPLICABILITY OF THE GEOLOGICAL STRENGTH INDEX (GSI) CLASSIFICATION FOR THE TRUSMADI FORMATION AT SABAH, MALAYSIA

During the feasibility and preliminary design stages of a project, when very little detailed information on the rock mass and its geomechanic characteristics is not available, the use of a Rock Mass Classification Scheme (RMCS) can be of considerable benefit. Various parameters were used in order to identify the RMCS. The parameter comprised of Rock Quality Designation (RQD), Rock Mass Rating (RMR), Rock Structure Rating (RSR), Geological Strength Index (GSI), Slope Mass Rating (SMR), etc. In this paper, we present the results of the applicability of the Geological Strength Index (GSI) classification for the Trusmadi Formation in Sabah, Malaysia. The GSI classification system is based on the assumption that the rock mass contains a sufficient number of “randomly” oriented discontinuities such that it behaves as a homogeneous isotropic mass. In this study, the GSI relates the properties of the intact rock elements/blocks to those of the overall rock mass. It is based on an assessment of the lithology, structure and condition of discontinuity surfaces in the rock mass and is estimated from visual examination of the rock mass exposed in outcrops or surface excavations. A total of ten (10) locations were selected on the basis of exposures of the lithology and slope condition of the Trusmadi Formation. The Trusmadi Formation regionally experienced of two major structural orientations NW-SE and NE-SW. It consists mostly of dark grey shale with thin bedded sandstones, typical of a turbidite deposit. This unit has been subjected to low grade of metamorphism, producing slates, phyllites and meta-sediments and intense tectonic deformation producing disrupted or brecciated beds. Quartz vein are quite widespread within the joints on sandstone beds. The shale is dark grey when fresh but changes light grey to brownish when weathered. The results are classified as “Poor Rock” to “Fair Rock” in term of GSI. The poor categories (TR2 and TR7) represent slickensided, highly weathered surfaces with compact coatings or fillings or angular fragments. It is also characterized as blocky/ disturbed/seamy, which folded with angular blocks formed by many intersecting discontinuity sets. The fair categories can be divided into two (2) types; type 1 (TR1, TR6 and TR8) which represent as smooth, moderately weathered and have altered surfaces. It is also characterised as very blocky rock, which indicates interlocked, partially disturbed ass with multi-faceted angular blocks formed by 4 or more joint sets. Type 2 (TR3, TR4, TR5, TR9 and TR10) which represent as smooth, moderately weathered and have altered surfaces but characterized as blocky/disturbed/seamy, which folded with angular blocks formed by many intersecting discontinuity sets. It also has persistence of bedding planes or schistosity.