Rapid and robust slope failure appraisal using aerial photogrammetry and 3D slope stability models

Slope failures are an inevitable aspect of economic pit slope designs in the mining industry. Large open pit guidelines and industry standards accept up to 30% of benches in open pits to collapse provided that they are controlled and that no personnel are at risk. Rigorous ground control measures including real time monitoring systems at TARP(trigger-action-response-plan) protocols are widely utilized to prevent personnel from being exposed to slope failure risks. Technology and computing capability are rapidly evolving. Aerial photogrammetry techniques using UAV(unmanned aerial vehicle) enable geotechnical engineers and engineering geologists to work faster and more safely by removing themselves from potential line-of-fire near unstable slopes. Slope stability modelling software using limit equilibrium(LE) and finite element(FE) methods in three dimensions(3D) is also becoming more accessible, user-friendly and faster to operate. These key components enable geotechnical engineers to undertake site investigations,develop geotechnical models and assess slope stability faster and in more detail with less exposure to fall of ground hazards in the field. This paper describes the rapid and robust process utilized at BHP Limited for appraising a slope failure at an iron ore mine site in the Pilbara region of Western Australia using a combination of UAV photogrammetry and 3D slope stability models in less than a shift(i.e. less than 12 h).     

Image analysis for 3D micro-features: A new hybrid measurement method

Measuring 3D micro-features is a challenging task that is usually performed using high-cost systems generally based on technologies with narrow working ranges and very accurate control of the sensor positions. Well-known image analysis methods, such as Photogrammetry, would likely lower the costs of 3D inspection of micro-features and add texture information to the 3D models; however, the behaviour of Photogrammetry is strongly affected by the scaling method because it retrieves a model that must be scaled after its computation. In this paper, an experimental study of the validity of a hybrid 3D image processing method for measuring micro-features is presented. This method exploits the Depth-from-Focus method to retrieve the correct scale for a photogrammetric model. The measurement of properly-designed and manufactured specimens was performed by following and adapting the German guideline VDI/VDE 2634, Part 3 to validate the method using calibrated specimens. The proposed system has been demonstrated to be very promising can achieve an error of less than 10 μm.     

Use of low-cost UAV photogrammetry to analyze the accuracy of a digital elevation model in a case study

For the geodetic survey of the terrain surface, the use of conventional surveying methods and instruments is common. New technologies, such as e.g. UAVs and their combination with a digital camera, bring new opportunities also in the documentation of Earth’s surface. This combination of technologies allows for the use of low-cost digital photogrammetry to document the Earth’s surface in relation to mining activities. The aim of the research presented in this paper is to analyze the accuracy of the digital elevation model (DEM) obtained using low-cost UAV photogrammetry. The surface mine Jastrabá (Slovakia) was chosen as the test area. The mine has morphologically dissected surface and is thus suitable for verifying the use of UAV photogrammetry to capture fairly intricate details on the surface. The research, which has been carried out, showed that the model created from photogrammetric data from the UAV achieves the accuracy required by current national legislation. From the selection of the test consisting of 237 points, only 3 points failed the conditions for the accuracy of the detailed points. These results indicate that the combination of low-cost UAV and a digital camera may be used as a viable alternative for the collection of data with the goal to document surface structures and to form 3D models formed from this data. The use of UAV in a photogrammetric survey of the mine brings new opportunities for the creation of documentation, because with this technology we can measure the entire surface in detail, create orthophoto maps of the entire area and document inaccessible parts of the area such as sludge dumps, and steep slopes.     

Acquiring sectional profile of metro tunnels using charge-coupled device cameras

Timely acquiring deformation of sectional profile is a proactive maintenance activity for ensuring the safety of tunnels. Metro tunnels, especially constructed by shield tunnelling method, are long span infrastructures need to inspect their deformations at many different positions. This is a vast amount of work if carried by traditional approaches manually. Some advanced technologies, such as terrestrial laser scanning, are also unable to carry out the work quickly and economically. However, only severe deformations that may lead to emergency action are required to be detected timely. Thus, the urgent demands for acquiring sectional profile of metro tunnel should be of fast in operation, accuracy under tolerable acceptance and competitive with cost efficient. This paper focuses on the method of acquiring sectional profile of metro tunnels by a cart equipped with charge-coupled device cameras. The geometric features of sectional profile are extracted from images by a series of algorithms based on photogrammetry. Using this method, the speed of acquisition is improved no less than 5 km/h with acceptable accuracy. An on-site application validates that this method is sufficient for screening out severe deformations in metro tunnel.     

Large field-of-view deformation measurement for transmission tower based on close-range photogrammetry

The loading capacity of transmission towers cannot be calculated accurately only by finite element analysis (FEA) method. Traditional displacement sensors and strain gauges are not suit due to larger measuring range. In this paper, a novel system based on close-range photogrammetry technology (CPT) is proposed for tracking the 3D deformation of transmission tower during loading test. Artificial markers are pasted on the deformation area before loading. The 3D coordinates of these markers are reconstructed by using CPT methods at each stage, and the coordinate systems of different stages are registered together by means of global transformation points. The whole field 3D deformation under different load level is then obtained by tracking the homonymous markers among different stages. It is helpful for further analysis of the failure mechanism and mechanical properties of steel structures. The effectiveness of the proposed system is demonstrated by retrieving a full-scaled transmission tower deformation during loading test. A feasible solution for improving the load carrying capacity of the tested transmission tower is discussed. Evaluation experiment results indicate that the proposed method could achieve accuracy of 0.1 mm/m.     

基于寻找最佳起始点的编码标志点解码研究

目前在数字近景工业摄影测量中,针对环形编码标志点的解码方法,通常采取在编码带上选取任意一点作为解码的起始点,按一定方向读取编码带,完成环形编码标志点身份信息的读取。理论上讲,该方法是可行的。但是由于图像噪声等因素的影响,任意选取解码起始点的方法存在较大误差,这种误差有时对于最终的测量结果是不允许的。针对上述问题,提出了一套基于寻找最佳起始点的环形编码标志点解码方法。该方法在编码标志点位置已确定的基础上,通过构造解码椭圆、坐标逆变换、寻找最佳起始点、读取并输出编码带信息等步骤,较精确地实现标志点的解码。提出的解码理论在实验室环境下通过采用Matlab2010对不同类型的拍摄图片进行验证,结果表明具有较好的鲁棒性,可以满足实际测量的要求。     

Three-Dimensional Structural Translation and Rotation Measurement Using Monocular Videogrammetry

Measuring displacement for large-scale structures has always been an important yet challenging task. In most applications, it is not feasible to provide a stationary platform at the location where its displacements need to be measured. Recently, image-based technique for three-dimensional (3D) displacement measurement has been developed and proven to be applicable to civil engineering structures. Most of these developments, however, use two or more cameras and require sophisticated calibration using a total station. In this paper, we present a single-camera approach that can simultaneously measure both 3D translation and rotation of a planar target attached on a structure. The intrinsic parameters of the camera are first obtained using a planar calibration board arbitrarily positioned around the target location. The obtained intrinsic parameters establish the relationship between the 3D camera coordinates and the two-dimensional image coordinates. These parameters can then be used to extract the rotation and translation of the planar target using recorded image sequence. The proposed technique is illustrated using two laboratory tests and one field test. Results show that the proposed monocular videogrammetric technique is a simple and effective alternative method to measure 3D translation and rotation for civil engineering structures. It should be noted that the proposed technique cannot measure translation along the direction perpendicular to the image plane. Hence, proper caution should be taken when placing target and camera.     

Feasibility of monitoring large wind turbines using photogrammetry

Photogrammetry, which is a proven measurement technique based on determination of the 3D coordinates of the points on an object by using two or more images taken from different positions, is proposed to be a promising and cost efficient alternative for monitoring the dynamic behavior of wind turbines. The pros and cons of utilizing this measurement technique for several applications such as dynamic testing or health monitoring of large wind turbines are discussed by presenting the results of the infield tests performed on a 2.5 MW - 80 m diameter - wind turbine.     

Use of Digital Terrestrial Photogrammetry in rocky slope stability analysis by Distinct Elements Numerical Methods

Current approaches to rocky slope stability analysis require knowledge of the geometrical–structural setting, as well as the physical–mechanical properties of the intact material and its discontinuities. The physical–mechanical properties are derived from in situ and laboratory tests, whereas the geometrical characteristics come from field attitude measurements. Frequently, the inaccessibility of walls does not allow direct measurement of discontinuity surfaces by traditional geological methods. In such cases, data can only be obtained by statistical methods. Although this approach is significant and provides spatial meaning, it is ineffective for deterministic analysis.This paper provides a solution to this problem by applying digital terrestrial photogrammetric techniques employing a reamed bar, an aerostatic balloon and a helicopter. Results demonstrate that the accuracy and the quantity of geometrical and engineering–geological data coming from the photogrammetric survey, allow for numerical simulation of the relationship between rock elements as a function of their physical–mechanical properties and load conditions. The 3DEC code was chosen among the different methods available to model the discontinuous media through distinct elements.The proposed methodology was applied to a quarry located in the Carrara Marble District (the Apuan Alps, Italy), the largest and most exploited mining region in Europe. The economic value of the area required a detailed study of the presence of instability phenomena so that marble extraction could continue in safe conditions.