| Discontinuities control the deformation and mechanical properties of rock masses,therefore accurate and efficient acquisition of discontinuity information is a crucial link in various types of rock engineering.For complex and high-steep rock slopes,traditional investigation methods are no longer suitable for engineering environments.Although some progress has been made in engineering geological surveys based on UAV photogrammetry,there are still some key issues that need further research and improvement,such as insufficient adaptability of photography methods to complex terrains,texture distortion,shadow occlusion,and low resolution in 3D rock slope models that affect rock structure recognition.In view of the above shortcomings and difficulties,a new method of UAV photography that can better adapt to complex terrain of high-steep rock slopes and quickly obtain fine parameters of rock structure is proposed,which is of great significance for engineering construction and operation.This study takes a railway under construction in southeastern Tibet as the engineering background,and takes the high-steep rock slope of Xiali construction site as the study area.Based on UAV photogrammetry technology,combined with relevant algorithms and mathematical models,the quality analysis of the 3D real scene model based on UAV images in the study area is deeply studied.The structural development characteristics and rock mass quality characteristics of the rock slope are also quantitatively analyzed.A comprehensive and complete technical process has been constructed for key geometric parameter collection,block identification and stability evaluation,rock structure development and quality feature analysis based on high-precision 3D real scene models of high-steep rock slopes.The main research content and achievements are as follows:1.Research on the quantitative relationship between the quality of 3D real scene models of high-steep rock slopes and the interpretability of rock mass structures.Based on the 3D real scene model established by conventional oblique photography,evaluation units are divided according to slope aspect and slope,and various photogrammetric indicators and other basic geometric parameters corresponding to each unit are collected.An in-depth analysis was conducted on the relationship between various indicators in complex geological environments and their actual impact on the interpretability of 3D models.For the first time,a multi parameter evaluation method was proposed to evaluate the quality level of 3D real scene models of high-steep rock slopes based on UAV images.The results indicate that the quality evaluation method for the 3D real scene model proposed in this study is reliable;The minimum aperture of identifiable discontinuities is about 1-2 times the theoretical resolution of the image,and it is positively correlated with the photography distance,negatively correlated with the angle between the photography optical axis and the discontinuity,and quadratic correlated with the model brightness.2.Research on improving UAV photography technology for obtaining high-resolution and high-quality slope surface images of high-steep rock slopes in complex terrain environments.Guided by the quantitative relationship between various photogrammetric indicators and the quality evaluation results of 3D models,the UAV multi-angle nap-of-the-object photogrammetry technology is proposed.On the basis of on-site investigation,a low resolution 3D model of the study area was quickly established using simulated oblique photography.The overall terrain development characteristics of the slope and the geometric characteristics of the slope surface discontinuities were fully investigated.Based on this,the main photography direction was perpendicular to each set of discontinuities,supplemented by multi-angle supplementary photography,and a multi-angle nap-of-the-object photography strategy was designed.In addition,the image effect enhancement processing further improves the interpretability of the image.Research has shown that this technology can achieve millimeter level resolution and high-quality construction of 3D real scene models of high-steep rock slopes,fundamentally improving the accuracy of structural disaster research.3.Research on rock mass structure identification and fine interpretation of key parameters of discontinuities based on 3D real scene models of high-steep rock slopes.A semi-automatic,comprehensive,and batch solution technology system was established based on the millimeter level resolution 3D real scene model of high-steep rock slopes,which includes key parameters such as orientation,trace length,spacing,aperture,and roughness measured manually by discontinuity feature points.Based on this,a total of 2217 discontinuity information were collected on the study slope.Compared with the results of on-site manual measurement,the average difference of dip direction and dip angle is 2°,and the average difference of trace length and aperture interpretation results are 1.3 cm and 9 mm,respectively.The overall accuracy is accurate and reliable.4.Research on the structural characteristics and quality characteristics of high-steep rock slopes in the study area.Based on the obtained information on the discontinuities of high-steep rock slopes in the study area,relevant qualitative and quantitative studies were conducted.The results showed that there were four sets of discontinuities developed on the slopes in the study area.Among them,the first set was a gently inclined slope,the third set was a steeply inclined slope,and the other two sets were both steeply inclined and intersected with the slope surface at a large angle.The average trace length of each set is between 3-4 m,and the overall continuity is poor,all following a lognormal distribution.The average spacing between each set is between1.6 and 3 m.Except for the third set,which follows a normal distribution,all other three sets follow a logarithmic normal distribution.The aperture has significant interval and scale effects,and the interpretation results are more ideal when the sampling length is0.5-1 m and the measurement line spacing is 1%of the sampling length.Its distribution forms are mainly normal distribution,logarithmic normal distribution,and gamma distribution.Moreover,there is a certain positive correlation between the aperture and the height and trace length of the slope.The JRC exhibits significant interval,size,and anisotropy effects.The JRC obtained at a sampling length of 1.2 m and a sampling spacing of 2 cm can better characterize the roughness of the discontinuity.Based on the above indicators and other qualitative indicators,this study proposes a new method for rock mass quality grading suitable for high-steep rock slopes-RSQ method.Combining traditional RQD method,BQ system,and SMR system comprehensive evaluation,the overall rock mass quality grade of the study area slope is ultimately determined to be Grade III.5.Identification and stability study of potential dangerous rock blocks on high-steep rock slopes in the study area.Based on the interpreted discontinuity information,a slope surface in-situ block identification method considering the true terrain characteristics of high-steep rock slopes and the 3D distribution morphology of block interfaces was proposed,and the identified blocks and their geometric information were quantitatively analyzed.The results showed that a total of 226 blocks were identified on high-steep rock slopes in the study area,including 90 independent blocks exposed on the slope surface and 136 blocks embedded inside the slope surface.Under natural conditions,there are 70 potentially unstable blocks and 27 key blocks.Under seismic conditions,the safety factor of blocks generally decreases,with 17 blocks transitioning from potentially unstable to key blocks.Research has found that the first set of gently inclined discontinuities plays a controlling role and is prone to sliding instability or falling when combined with the third and fourth sets of discontinuities.The key blocks are mainly tetrahedral,with about 76%of the block volume less than 10 m~3,mainly distributed between 170-510 m above the tunnel entrance where the bedrock is more exposed. |
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