Comparative application of photogrammetry, handmapping and android smartphone for geotechnical mapping and slope stability analysis

Sztubecki J., Bujarkiewicz A., Derejczyk K., Przytuła M.

Abstract Modern measuring technologies give the means to perform tasks previously impossible with conventional methods. Their main advantages include reduced time consumption and higher measurement precision. Contemporary displacement and deformation studies of engineering structures often involve application of laser technologies, which are characterised by high precision of measurements. This article presents an analysis of results obtained from measurements of changes in the geometry of an engineering structure in which two complementary measuring technologies were used, i.e. tachymetric measurement with a Leica TDRA6000 laser station and laser scanning with a 3D FARO Focus S150 scanner. The utilised laser station enabled determination of 3D displacements in the local control point network installed on the studied structure as well as transfer of point clouds obtained from laser scans into a uniform coordinate system. The hybrid technology employed and the measurement method used ensured that the accuracy of the determined displacements and deformations of the structural components of the structure was high. The described measurement and result processing technology makes it possible to comprehensively analyse the geometric performance of structures, which consequently leads to the development of more complete conclusions concerning prevention of adverse effects of displacements and deformations in engineering structures.

Can R., Kocaman S., Gokceoglu C.

Several scientific processes benefit from Citizen Science (CitSci) and VGI (Volunteered Geographical Information) with the help of mobile and geospatial technologies. Studies on landslides can also take advantage of these approaches to a great extent. However, the quality of the collected data by both approaches is often questionable, and automated procedures to check the quality are needed for this purpose. In the present study, a convolutional neural network (CNN) architecture is proposed to validate landslide photos collected by citizens or nonexperts and integrated into a mobile- and web-based GIS environment designed specifically for a landslide CitSci project. The VGG16 has been used as the base model since it allows finetuning, and high performance could be achieved by selecting the best hyper-parameters. Although the training dataset was small, the proposed CNN architecture was found to be effective as it could identify the landslide photos with 94% precision. The accuracy of the results is sufficient for purpose and could even be improved further using a larger amount of training data, which is expected to be obtained with the help of volunteers.

Ozturk H.S., Kocaman S., Gokceoglu C.

Assessment of discontinuity controlled failure phenomena over large areas is extremely hard or even impossible due to the difficulties encountered at the data collection stage. Conventionally, the data collection has been made by engineering geologists via field surveys using compass and measurement tapes. The present study proposes a new low-cost and practical approach by using mobile phones and photogrammetric methods, which allows the measurement of orientation (strike and dip) of discontinuity in a computerized environment. The images acquired using a smartphone camera provide the means for highly representative surface modeling via dense image matching. Such dense measurements reduce the errors caused by sparse sampling of discontinuity surfaces. The kinematic analysis based on the orientation data obtained from the proposed methodology shows the discontinuity controlled failure susceptibility. The methodology proposed here has been applied to a part of Ihlara Valley in Cappadocia Region (Central Turkey), which has columnar structures that are extremely difficult to survey with conventional field works. The application of the proposed methodology yields successful and promising results for large and inaccessible terrain types. Although a major improvement to the proposed methodology would be using the geolocation and rotation of the images obtained from the sensors of the phone directly (thus eliminating the need for external control points with known ground coordinates), the procedure described in this study is low-cost and do not require extensive knowledge on photogrammetry for engineering geologists.

Kocaman S., Gokceoglu C.

Depending on the increase in the world population and climate changes, the number of disasters have increased gradually. To cope with natural hazards, comprehensive disaster management strategies must be developed and implemented. Among the natural hazards, landslides are one of the most harmful and they cause serious economic losses and human deaths throughout the world. To reduce these losses, comprehensive regional landslide susceptibility and hazard assessments must be performed and the mechanism of landslides must be understood clearly. If a landslide inventory database is inaccurate and incomplete both spatially and temporally, assessment of regional landslide susceptibility and hazard includes more or less uncertainties. Consequently, new approaches are needed to reduce or even to eliminate the uncertainties. For this reason, the purposes of the present study are to describe the potential role of Citizen Science (CitSci) in landslide researches and to present a simple and user-friendly mobile app for the collection of the essential data from landslides. It is expected that the use of CitSci in landslide researches would increase and help greatly for the provision of comprehensive data. In addition, the spatial distribution of the data to be collected may be correlated with the human population and the settlement density.

Thoeni K., Giacomini A., Murtagh R., Kniest E.

Abstract. This work presents a comparative study between multi-view 3D reconstruction using various digital cameras and a terrestrial laser scanner (TLS). Five different digital cameras were used in order to estimate the limits related to the camera type and to establish the minimum camera requirements to obtain comparable results to the ones of the TLS. The cameras used for this study range from commercial grade to professional grade and included a GoPro Hero 1080 (5 Mp), iPhone 4S (8 Mp), Panasonic Lumix LX5 (9.5 Mp), Panasonic Lumix ZS20 (14.1 Mp) and Canon EOS 7D (18 Mp). The TLS used for this work was a FARO Focus 3D laser scanner with a range accuracy of ±2 mm. The study area is a small rock wall of about 6 m height and 20 m length. The wall is partly smooth with some evident geological features, such as non-persistent joints and sharp edges. Eight control points were placed on the wall and their coordinates were measured by using a total station. These coordinates were then used to georeference all models. A similar number of images was acquired from a distance of between approximately 5 to 10 m, depending on field of view of each camera. The commercial software package PhotoScan was used to process the images, georeference and scale the models, and to generate the dense point clouds. Finally, the open-source package CloudCompare was used to assess the accuracy of the multi-view results. Each point cloud obtained from a specific camera was compared to the point cloud obtained with the TLS. The latter is taken as ground truth. The result is a coloured point cloud for each camera showing the deviation in relation to the TLS data. The main goal of this study is to quantify the quality of the multi-view 3D reconstruction results obtained with various cameras as objectively as possible and to evaluate its applicability to geotechnical problems.

Djuric U.

Westoby M.J., Brasington J., Glasser N.F., Hambrey M.J., Reynolds J.M.

High-resolution topographic surveying is traditionally associated with high capital and logistical costs, so that data acquisition is often passed on to specialist third party organisations. The high costs of data collection are, for many applications in the earth sciences, exacerbated by the remoteness and inaccessibility of many field sites, rendering cheaper, more portable surveying platforms (i.e. terrestrial laser scanning or GPS) impractical. This paper outlines a revolutionary, low-cost, user-friendly photogrammetric technique for obtaining high-resolution datasets at a range of scales, termed ‘Structure-from-Motion’ (SfM). Traditional softcopy photogrammetric methods require the 3-D location and pose of the camera(s), or the 3-D location of ground control points to be known to facilitate scene triangulation and reconstruction. In contrast, the SfM method solves the camera pose and scene geometry simultaneously and automatically, using a highly redundant bundle adjustment based on matching features in multiple overlapping, offset images. A comprehensive introduction to the technique is presented, followed by an outline of the methods used to create high-resolution digital elevation models (DEMs) from extensive photosets obtained using a consumer-grade digital camera. As an initial appraisal of the technique, an SfM-derived DEM is compared directly with a similar model obtained using terrestrial laser scanning. This intercomparison reveals that decimetre-scale vertical accuracy can be achieved using SfM even for sites with complex topography and a range of land-covers. Example applications of SfM are presented for three contrasting landforms across a range of scales including; an exposed rocky coastal cliff; a breached moraine-dam complex; and a glacially-sculpted bedrock ridge. The SfM technique represents a major advancement in the field of photogrammetry for geoscience applications. Our results and experiences indicate SfM is an inexpensive, effective, and flexible approach to capturing complex topography.

Sturzenegger M., Stead D.

This paper reviews the application of close-range terrestrial digital photogrammetry and terrestrial laser scanning for discontinuity characterization on rock cuts. Terrestrial remote sensing techniques are being increasingly used as a complement to traditional scanline and window mapping methods. They provide more comprehensive information on rock cuts, allow surveying of inaccessible outcrops, and increase user safety. Selected case studies are used to estimate the accuracy of several 3D model registration approaches and the most time-, effort- and cost-effective methods are highlighted. It is shown that simple registration networks are able to provide adequate measurement of discontinuity orientation for engineering purposes. The case studies presented also illustrate the effects of sampling bias and limitations related to discontinuity characterization using remote sensing techniques. Vertical orientation bias and occlusion can be of particular concern when persistent discontinuities dip at the same angle as the camera/scanner line-of-sight. Major advantages of the techniques are presented illustrating how terrestrial remote sensing techniques provide rapid spatial measurements of discontinuity location, orientation and curvature and are well suited to the quantification of persistence magnitudes greater than 3 m.

Martin C., Tannant D., Lan H.

Priest S.D.

The paper outlines a new method for estimating the distribution form, and mean size, of discontinuities from scanline data. By assuming that the discontinuities are circular discs it has been possible to apply existing solutions for the distributions of censored semi-trace lengths sampled by a scanline at an exposed rock face. These solutions have been implemented by numerical quadrature in a standard Excel spreadsheet, with solution optimisation achieved with Solver. Problems caused by a singularity in the integration were overcome by applying an integration offset parameter. A trigonometrical substitution for removing this singularity is also outlined. The numerical quadrature strategy was validated by comparison with the analytical solution for the uniform distribution, and by comparison with the results of an extensive geometrical simulation of the stereological process. A new distribution, here named the Wicksell distribution, has been identified. This distribution is characterised by the fact that the distribution of disc diameters and the distribution of complete traces on a cutting plane are identical. Two examples, based on real scanline data, are presented to illustrate the practical application of the new methods.

Fisher R.

Zhang Y.

Mei X., Wu J., Wang T., Wang T., Liang X., Wang Y., Li B., Su T., Xu L.

Abstract In the rockfall prevention and control project, the reinforced concrete (RC) slab and sand (gravel soil) soil cushion layer are commonly used to form the protection structure, thereby resisting the rockfall impact. Considering that the oversized deformation of the cushion layer under impact load using the finite element simulation cannot converge, this article establishes a numerical calculation model using smoothed particle hydrodynamics–finite-element method coupling (SPH–FEM). First, the standard Lagrange finite-element mesh is established for the whole model using ABAQUS, and then the finite-element mesh of the soil cushion layer is converted to SPH particle at the initial moment of the calculation, and finally the calculation results are solved and outputted. The results indicate that, compared with the results of the outdoor rockfall impact test, the relative errors of the rockfall impact force and the displacement of the RC slab are within 10%, which proves the rationality of the coupling algorithm; moreover, in terms of the numerical simulation, the SPH–FEM coupling algorithm is more practical than the finite element for reproducing the mobility of the rockfall impacting the sand and soil particles. In addition, at an impact speed of less than 12 m·s−1, the cushion layer is able to absorb more than 85% of the impact energy, which effectively ensures that the RC slab is in an elastic working state under small impact energy and does not undergo destructive damage under large impact energy; the peak impact force of the rockfall is approximately linear with the velocity, and the simulated value of the peak impact force is basically the same as that of the theoretical value of Hertz theory; the numerical simulation is good for reproducing the damage process of the RC slab in accordance with the actual situation. The SPH–FEM coupling algorithm is more justified than the FEM in simulating the large deformation problem, and it can provide a new calculation method for the design and calculation of the rockfall protection structure.

Lee S., Bae J.Y., Sharafat A., Seo J.

Recently, there has been a recognized need to use waste lime landfills for land reclamation projects. Waste lime earthwork is more challenging than general earthwork operations due to potential health and safety hazards and significant changes in earthwork volume. There has been substantial research undertaken on the role of advanced construction technologies in general earthwork; however, their potential in hazardous waste lime environments for earthwork management is yet to be explored. This research proposes a methodology that integrates drone and BIM construction technology for effective and efficient hazardous waste lime earthwork management for construction projects. Drones are used for surveying, providing as-built information, and BIM to model, process, and evaluate the progress of waste lime earthwork. Volume change analyses are conducted using BIM to calculate dehydration time due to the ripple effect of waste lime for cost-efficient earthwork haulage. The case study provides evidence that the proposed method using advanced construction technologies improves productivity, safety, cost control, and better project management for earthwork related to hazardous waste materials.

Hao J., Zhang X., Wang C., Wang H., Wang H.

For the stability analysis of rock slope, it is very critical to obtain the spatial geometric characteristics of the structural surfaces of the rock mass accurately and effectively. As for a high-steep rock slope of an iron ore mine, in order to solve the problems of inefficiency and high risk of traditional manual geological survey, the geological survey and stability evaluation of the slope was carried out by adopting unmanned aerial vehicle digital photogrammetry (UAV-DP) technology. Firstly, a large number of high-resolution images of the slope were obtained by UAV-DP. Then, the structure from motion (SFM) method was used to construct the fine 3D point cloud model of the slope, which was subjected to coplanarity detection and K-means clustering for identifying the structural surfaces. Finally, the stability and failure model of the slope cut by the structural surfaces are analyzed by using the stereo-projection and discrete element methods. The research results show that the error between UAV-DP and manual measurement is within the acceptable range, which demonstrates the reliability of UAV-DP used in the geological investigation. Furthermore, the stability state and failure model of the slope is also consistent well with the field observation.

Matsimbe J., Mdolo W., Kapachika C., Musonda I., Dinka M.

Despite drones being successfully utilized for monitoring and detecting hazards in mines, there is limited research on their application for open-pit stockpile volumetric computation compared to traditional methods. Furthermore, time, cost, and safety have challenged the use of the traditional approach. Present study aims to fill the gaps by conducting a comparative analysis of stockpile volumetric computation utilizing a drone and traditional approach. A mapping framework is proposed to guide mine personnel on how to conduct open-pit stockpile volumetric computations. The methodology comprises using a drone and traditional survey approach to measure the volume of a known quarry stockpile. Drone-captured images are processed in Pix4D mapper software and geometric techniques are applied to the traditional survey approach. Findings show that the smaller the error of the checkpoints the more accurate the generated model making the measurements reliable. The generated Pix4D quality report showed a root mean square error of 0.019. The drone percentage error to the actual volume is 2.6% while the traditional approach is 1.3%. Both estimations are less than the maximum allowable percentage error of ± 3%. Therefore, compared to the traditional approach drone technology provides an accurate, cost-effective, fast, and safe working distance suitable for stockpile volumetric computations in open pit quarries.

Ismail A., Ahmad Safuan A.R., Sa'ari R., Wahid Rasib A., Mustaffar M., Asnida Abdullah R., Kassim A., Mohd Yusof N., Abd Rahaman N., Kalatehjari R.

• The conventional geological mapping in determining rock slope stability is risky and costly. • The laser scanning and drone photogrammetric techniques allow it to overcome these issues by remotely collecting highly detailed point cloud data of a rock slope. • This research compares the integration of Unmanned Aerial Vehicle (UAV) and TLS photogrammetry with traditional direct methods. • The results show that both techniques provide accurate measurement and analysis compared to the traditional direct method. Recent advancements in remote sensing techniques have made it possible to overcome the risky issues using conventional methods and have opened up new opportunities for collecting data on discontinuity characteristics. This research compares the application of a Terrestrial Laser Scanner (TLS) and Unmanned Aerial Vehicle (UAV) in rock slope stability analysis. Two case studies, Ulu Choh Quarry and Jelapang Rock Slope are analysed using Kinematic Analysis and Slope Mass Rating (SMR) to depict rock through the 3D point cloud. The techniques are compared with the hand mapping method concerning the accuracy of the data acquisition in assessing the rock slope. The standard deviation for the dip and dip direction between digital capture and hand mapping is 2.97° and 2.86°, which falls under the acceptable tolerance limit. The integration of UAV and TLS also generates excellent clear point cloud data from the top to the toe of the slope.