There are three main factors controlling the formation of debris flow; of these, the ability to evaluate the volume of source materials in a catchment is the most significant. Source materials come ...from channel bed sediment, nearby landslides and rilling and surface erosion of slopes. The objective of this study was to develop a multi-source method–including field surveys, optical remote sensing interpretation, and interferometric synthetic aperture radar (InSAR) technology–to estimate the volume of source materials in the debris flow in the Xulong Gully (XLG), China. The qualitative degree of stability of the source materials was estimated with volume of approximately 91.9 × 104 m3. Considering sediment connectivity, landslides debris were interpreted using optical remote sensing, and their volume was calculated, using an empirical formula, to be about 191.01 × 104 m3. Continuous monitoring using InSAR could help to obtain the large-scope precise process of ground surface deformation. Estimated erosion rate ranges from 1633 m3/(km2·year) to 4552 m3/(km2·year) and annual volume of erosion was 9.08 × 104 m3/year–25.31 × 104 m3/year. Higher elevation with good vegetation coverage showed the sedimentation process, while lower elevation area with little vegetation showed erosion process. The highest degree of erosion occurred in the summer, followed by spring, autumn, and winter. The trend of the degree of erosion was consistent with that of the monthly rainfall in the XLG in 2018. Verification results demonstrated that the proposed approach could improve the efficiency and accuracy of the estimates of source material volume in debris flows and assess hazards.
•A quantitative approach estimating debris flow source material is established.•Proposing an improved volume statistical formula considering connectivity.•InSAR is introduced to estimate annual changing volume of erosion.•Analyzing slope erosion and sedimentation process in dry-hot valley area
Preexisting discontinuities, such as joints and beddings, are widely distributed in unconventional reservoirs. During fluid injection, hydraulic fractures strongly interact with preexisting ...discontinuities, leading to great uncertainty in prediction of fracture geometry. To investigate how preexisting discontinuities affect fracture complexity, numerical simulations are carried out using the distinct element method. A discrete fracture network (DFN) model for a shale reservoir in the southeastern Ordos basin, China is built. Four cubic models, including the (1) rock matrix model, (2) bedding model, (3) joint model and (4) bedding and joint model, are extracted from the DFN model and then are used for numerical simulations. The results indicate that preexisting discontinuities strongly influence fracture complexity: they impose a barrier for fracture growth in most cases, and thus result in a smaller fracture area and a higher fluid pressure for fracture extension. However, the roles that joints and beddings play in fracture complexity differ. Compared with the bedding model, the joint model causes a less complex fracture geometry under the same injection condition, suggesting that the joints play a more significant role in reducing fracture complexity.
•A 3D DFN model coupling different kinds of preexisting discontinuities is built.•Interaction between hydraulic fractures and preexisting discontinuities is modeled.•Influence of preexisting discontinuities on fracturing complexity is discussed.•Results show that joints play a significant role in reducing fracture complexity.
The Suwalong section of the upper Jinsha River is located on the southeastern margin of the Tibetan Plateau. Affected by the rapid uplift of the Tibetan Plateau, steep slopes have been formed by the ...rapid downcutting of rivers in this section. Tectonically, the Suwalong section is located in the Jinshajiang suture zone and features intense tectonic activity, making this section prone to geological disasters such as landslides. Through field investigation, four old accumulation bodies were found in the Suwalong section, and lacustrine sediments were observed upstream of these bodies. By analysing the surrounding landforms, appearance features, and internal rocks of the old accumulation bodies, we conclude that these four old accumulation bodies represent the remains of dams that blocked the river. These dams formed through the deposition of rockslides, rock avalanches, or debris flows that occurred on the slopes on both sides of the river. By comparing the top elevation information and the chemical and mineral compositions of the lacustrine sediments around these residual dams, the order of the demise of two dammed lakes was obtained, and the order was confirmed by optically stimulated luminescence (OSL) dating. The method in this paper has great applicability for identifying river-blocking events in other regions.
•Ancient events that blocked the Jinsha River in the Suwalong section were identified.•Mechanisms for the formation of the landslide dams were analysed.•The chemical and mineral compositions of lacustrine sediments were analysed.•The order of demise of two dammed lakes was determined.
Tertiary soft-rock strata exposed on the eastern side of Changbai Mountain are landslide-prone strata. In recent years, shallow landslides have frequently occurred along the highway in this region, ...leading to great challenges in highway construction and safe operations. National Highway 302, which is under construction, crosses an old landslide group close to the village of Xinyan. A shallow landslide that recently occurred in this section, the Xinyan landslide, which occurred in a road embankment composed of soft-rock materials, is studied herein as a case study. The field survey identifies the geological characteristics and current conditions of the landslide area and confirms an inheritance relationship between the Xinyan landslide and previous landslides. Through a laboratory geotechnical test, mineral composition analysis and microstructure analysis of landslide soils, it is found that the examined soft-rock materials exhibit both dispersion and expansion. The coupling effect of soil expansion and dispersion contribute to the formation of seepage channels and to the degradation of soil properties. Under the combined effects of these factors, local shear failure first occurs at the weakest toe of the embankment. Then, unloading effects and strain softening lead to the progressive propagation and expansion of the sliding surface. Finally, the failure of the Xinyan landslide enters a progressive failure mode from the slope toe to the interior area. Therefore, this study reveals that expansibility, dispersivity, extremely low shear strength levels, softening behavior and preferential flows are the main causes of the repeated failure of the gentle soft-rock slopes in this region. These results may serve as a good reference for the prevention and treatment of similar soft-rock landslides occurring in the Yanbian region or worldwide.
•A progressive slope failure in a road embankment composed of soft-rock materials is presented.•The soft-rock materials have the characteristics of expansibility and dispersivity.•The Xinyan landslide is an inheritance and development of the previous old landslides.•Unloading effect and strain softening leads to the progressive propagation of sliding surfaces.•Some suggestions on the prevention and treatment of similar soft-rock landslides are given.
The rapid and accurate acquisition of discontinuity parameters of rock masses is of paramount significance for the stability assessment of rock slopes. However, the complex and hazardous terrain of ...high-steep rock slopes poses challenges to conventional survey methods. Given this, this study proposes the unmanned aerial vehicle (UAV) multi-angle nap-of-the-object photogrammetry technology. This method can comprehensively consider the terrain development characteristics of high-steep rock slopes and the orientation characteristics of dominant discontinuity sets. With trained pilots, high-quality image acquisition with millimeter resolution can be achieved. This method effectively overcomes issues like texture distortion, shadow obstruction, and low resolution commonly found in conventional UAV 3D models. Subsequently, a novel non-contact method is presented for obtaining discontinuity parameters, including orientation, trace length, spacing, aperture, and roughness, based on the 3D real-scene model of the slope. The feasibility and reliability of this method are verified by collecting 1728 discontinuities along the 1300-m length of a rock slope at a construction site on a railway in southeastern Tibet. A comparison with manually measured results indicates average differences of 2° for dip and dip direction; 1.3 cm and 9 mm for trace length and aperture, respectively; and 1.89 for JRC. The study also reveals that the effective resolution of the 3D model is approximately 1 to 2 times the theoretical resolution of a UAV image, providing crucial guidance for obtaining high-quality images on high-steep rock slopes. The method proposed in this study holds significant practical value in the stability assessment and disaster prevention of rock slopes.
The Sichuan-Tibet railway, which spans many alpine canyon regions, is being built in southwestern China. Investigating the characteristics of rock discontinuity sets is the basis for identifying ...dangerous rock masses above the tunnel portals. The traditional methods of identifying discontinuity sets usually consider orientations and ignore other parameters, which results in incorrect guidance for rock engineering. To this end, the affinity propagation (AP) algorithm based on modified isometric mapping (Isomap) is proposed for partitioning discontinuity sets based on orientation, trace length, and aperture. The new unsupervised algorithm (ISOAP) uses manifold learning to complete the transformation process for orientations from spherical vectors to scalars and avoids selecting the initial clustering center to achieve global optimization. The Silhouette Index is used to intelligently scan the optimal clustering results. The proposed algorithm is tested on a complex artificial data set and on Shanley and Mahtab's data set. Since accurately obtaining discontinuity information is impossible by traditional means (i.e., using geological compasses and measurement tapes) due to the existence of a mass of high and steep slopes, the ISOAP algorithm is combined with semiautomatic technology based on unmanned aerial vehicle (UAV) photogrammetry and applied to a rock slope located along the railway. The introduction of manifold learning is beneficial for quickly applying abundant unmodified clustering algorithms to rock engineering and searching the optimal algorithm suitable for analyzing the structural characteristics of a specific fractured rock mass. The proposed method can simplify rock engineering analyses and provide more reasonable results.
•Manifold learning is applied to rock engineering.•Characterization of multiple properties of rock discontinuities.•A new unsupervised algorithm based on manifold learning.•Using a 3D model, multi-property discontinuity sets are identified by an unsupervised algorithm.
With the development of the economy, land reclamation, as a result of dredged soil, has become an effective measure to alleviate land scarcity in many coastal cities around the world. Chongming East ...Shoal (CES), a typical reclamation area in Shanghai that is formed by multi-phase reclamation projects, was selected as the study area. The small baseline subset–interferometry synthetic aperture radar (SBAS-InSAR) method was applied to derive the map of velocity distribution and accumulated deformation with 70 Sentinel-1 synthetic aperture radar (SAR) images collected from 22 March 2015 to 2 December 2019. In addition, 25 undisturbed soil samples, including dredger fill and underlying soil layers, were collected from five boreholes (maximum depth 55 m) through a field investigation. Laboratory tests were then performed on all soil samples in order to facilitate an understanding of geological features, including the measurement of basic physical properties, cation exchange capacity, compressibility, microscale structure, and pores. The present results show that the whole CES was undergoing differential ground deformation, with a velocity ranging from −47.5 to 34.6 mm/y. Fast (−3.4 mm/y) to slow (−0.3 mm/y) mean subsidence velocities were detected in multi-phase reclamation areas from inland areas to the coastline, and were controlled by building load and geological features of soil layers. Urbanization is the main factor that triggers accelerated subsidence and should receive special attention for reclamation areas that have been finished for a long time (over 20 years in this study). The geological features indicated that poor drainage conditions in offshore soil layers resulted in slow subsidence. The field investigation and laboratory test can be powerful explanatory tools to monitor the results from a mechanical perspective.
This paper presents a study on an ancient river-damming landslide in the SE Tibet Plateau, China, with a focus on time-dependent gravitational creep leading to slope failure associated with ...progressive fragmentation during motion. Field investigation shows that the landslide, with an estimated volume of 4.9 × 10
7
m
3
, is a translational toe buckling slide. Outcrops of landslide deposits, buckling, toe shear, residual landslide dam, and lacustrine sediments are distributed at the slope base. The landslide deposits formed a landslide dam over 60 m high and at one time blocked the Jinsha River. Optically stimulated luminescence dating for the lacustrine sediments indicates that the landslide occurred at least 2,600 years ago. To investigate the progressive evolution and failure behavior of the landslide, numerical simulations using the distinct element method are conducted. The results show that the evolution of the landslide could be divided into three stages: a time-dependent gravitational creep process, rapid failure, and granular flow deposition. It probably began as a long-term gravitationally induced buckling of amphibolite rock slabs along a weak interlayer composed of mica schist which was followed by progressive fragmentation during flow-like motion, evolving into a flow-like movement, which deposited sediments in the river valley. According to numerical modeling results, the rapid failure stage lasted 35 s from the onset of sudden failure to final deposition, with an estimated maximum movement rate of 26.8 m/s. The simulated topography is close to the post-landslide topography. Based on field investigation and numerical simulation, it can be found that the mica schist interlayer and bedding planes are responsible for the slope instability, while strong toe erosion caused by the Jinsha River caused the layered rock mass to buckle intensively. Rainfall or an earthquake cannot be ruled out as a potential trigger of the landslide, considering the climate condition and the seismic activity on centennial to millennial timescales in the study area.
Frequent rockfall events pose a major threat to the safe operation of the Taihang Grand Canyon Scenic Area (GCSA) in China. The traditional techniques for identifying potential rockfall sources and ...hazard assessment methods are often challenged in the alpine canyon landform. This study aims to establish an early identification framework for regional potential rockfall sources applicable to the canyon region and to assess rockfall hazards in potentially hazardous areas using unmanned aerial vehicle (UAV) photogrammetry. Specifically, by incorporating high-precision topographic information and geotechnical properties, the slope angle distribution method was used for static identification of potential rockfall sources. Moreover, SBAS-InSAR technology was used to describe the activity of potential rockfall sources. Finally, taking the key potentially hazardous area of the Sky City scenic spot as an example, the Rockfall Analyst tool was used to analyze the rockfall frequency, bounce height and energy characteristics based on the high-precision UAV 3D real scene model, and the analytic hierarchy process was introduced to achieve quantitative rockfall hazard assessment. The results show that the potential rockfall source areas in the Taihang GCSA is 33.47 km2 (21.47%), mainly distributed in strips on the cliffs on both sides of the canyon, of which the active rockfall source area is 2.96 km2 (8.84%). Taking the scenic spot of Sky City as example, the proposed UAV-based real scene modeling technology was proven to be able to quickly and accurately construct a 3D high-precision model of the canyon area. Moreover, the 3D rockfall simulation showed that the high-energy rockfall area was mainly distributed at the foot of the steep cliff, which mainly threatens the tourist distribution center below. The early identification and quantitative evaluation scheme of rockfall events proposed in this study can provide technical reference for the prevention and control of rockfall hazards in similar alpine valley areas.
•Proposed a multidimensional 3D model quality assessment system.•Proposed a five-level evaluation criterion based on 3D model quality index.•Established an UAV multi-angle nap-of-the-object image ...acquisition (MNIA) framework.•The MNIA framework mitigates 3D model texture distortion and low resolution issues.•Photographing perpendicular to discontinuities enhances 3D model interpretability.
The 3D real scene model of high-steep rock slope established based on UAV image provides convenience for non-contact identification and interpretation of rock mass structures. The quality of 3D models directly influences the interpretability of rock mass structures. However, quantitative studies on the relationship between these two aspects are scarce. Therefore, this study investigates the influence of indicators such as photography distance (D), model brightness (l), angle between photography optical axis and the discontinuity to be interpreted (θd), and texture distortion area ratio (tdp), among others, on the interpretability of the 3D models. Furthermore, it delves into the relationships among these indicators and their practical application effects in complex high-steep rock slopes. On this foundation, a novel multi-indicator quality evaluation method for 3D models constructed using UAV photogrammetry is introduced for the first time. This method, based on a composite index model and incorporating empirical approaches, classifies the quality of 3D models into five levels. Guided by the quality evaluation results and taking into account the terrain development and geometric characteristics of discontinuities, a technical framework supporting the acquisition of high-quality 3D models is proposed, known as multi-angle nap-of-the-object image acquisition (MNIA). The research indicates that the 3D models established based on MNIA exhibit significantly reduced texture distortion, leading to a substantial improvement in recognizability, with a goodness rate of 79.98%, far surpassing that of oblique photogrammetry (41.18%). This study provides crucial guidance for obtaining high-quality UAV image in complex terrain environments and holds significant engineering application value in the fine identification and interpretation of rock mass structures on high-steep rock slopes.
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