Accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation. In this study, ...physical flume tests on the breaching of landslide dams were conducted. A wide grain size distribution with unconsolidated dam material was used. Dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume. This allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream. The effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated. Experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge. A new longitudinal evolution model is proposed. This model captures the initial increase of the soil erosion rate (of landslide dam) and its subsequent decrease along the longitudinal direction. In addition, a linear relationship between the soil erosion rate and shear stress (of water flow) was observed and this is similar to that observed in large-scale natural landslide dams. Furthermore, soil erosion resistances (of landslide dam) against water flow above are observed to increase with the concentration of entrained sediments along the flow direction.
•Overtopping failure of landslide dam can be divided into three distinct stages.•A spindle-like longitudinal evolution model of landslide dam failure is proposed.•A linear relationship is found between the erosion rate and the shear stress.•Apparent soil erosion resistance against outburst flow increases along the flow direction.
Display omitted
•An inventory of 14,544 loess landslide cases was established.•Tectonics is the primary factor causing clustering of loess landslides on the Loess Plateau of China.•Loess landslides ...are classified into six genetic types.
In this study, 14,544 loess landslides collected from the Loess Plateau of China are used to reveal their distribution and origins. Main factors considered include landslide density, regional tectonics, soil properties, geomorphic structure, rainfall distribution, seismic activity, and human activity. Based on these factors, the Loess Plateau is divided into eight zones with high possibilities of landslides that are classified into six genetic types. The first genetic type of clustering distribution of loess landslides is related to several main regional active faults. The second type is related to broken pieces of loess geomorphic structures. The third type is considered to be due to unloading of the geomorphic peripheral slope that can cause the internal structural plane to open and thus controls the prototype and scale of the loess landslide. Change of hydrogeological conditions in the slope softens the loess pedestal and the slippery layer, forming a softening zone and thus controlling the shear crack and slip model of the fourth type of loess landslides. The fifth type is due to seismic activities that can generate additional stress to the Earth's surface and landform slopes, causing the opening of joints and seismic liquefaction. The last type of landslides is caused by human activities by changing the geological structure, hydrogeological conditions, and the inner stress balance of slopes.
The failure of a landslide dam is a sudden geo-hazard, which can significantly threatens the lives and property of local residents. In this study, 11 experiments were designed to reproduce the ...failure process of landslide dams with different grain size distributions and hydrodynamic conditions. In order to fully consider the influence of seepage on the stability of landslide dams with different textural properties, the inflow discharge was small in these tests. By analyzing the experimental data, we found that the textural properties plays a key role in the failure modes and process of landslide dams. The eleven tests produced five different results: the landslide dam in experiment 1 and 8 remained stable; the landslide dam in experiment 2 partially failed; in experiments 3–6, the dams failed due to overtopping and erosion, while in experiment 7, the dam failed due to overtopping and soil collapse; in experiment 9–11, the dams failed due to piping, overtopping and erosion. In addition, the evolution of the outflow discharge and density also varied for the different textural properties of the dam materials. Based on the experimental results, the landslide dam materials were classified as coarse-matrix controlled, medium particle controlled, fine-matrix controlled, and balanced composition. The failure modes and process as well as the evolution characteristics of the outflow discharge and flow density were all summarized, providing a scientific reference for disaster prevention and mitigation research of landslide dams.
•Eeven experiments were designed to reproduce the failure process of landslide dams.•The landslide dams were with different grain size distributions and hydrodynamic conditions.•The eleven model tests produced five different results.•The dam materials were classified as 4 types.•The failure modes and process of landslide dams were determined by textural properties of dam materials.
Internal erosion is a complex phenomenon that is one of the main risk factors to soil destruction. Its occurrence is mainly due to water infiltration and can cause slope instability. “Karst soil” is ...a type of loess with special soil and water sensitivity that makes it prone to landsliding. The processes of internal erosion include transport erosion and chemical dissolution, which strongly effect loess structure and strength. To reveal the internal processes and effects of the loess due to water infiltration, field investigations and indoor tests, including infiltration tests, undrained triaxial tests, particle analysis, chemical analysis, and scanning electron microscopy (SEM), were conducted. The results show that (1) the fine particles (clay and silt) and chemicals can move within the matrix of the macro-pores under seepage flow. The physical internal erosion is mainly due to fine particle migration out of the water and clay and silt particles, and the sample column settlement was 3.3 cm with a settlement ratio of 16.5%, which results in changes to the soil skeleton, increasing the porosity and infiltration rate of loess. (2) Chemical dissolution is also an important internal erosion process in loess, especially cations of Na, Mg, Ca, and K and anions of Cl, SO
4
, and CO
3
, which are mainly lost due to dissolution and flow out of with water and clay particles, resulting in altered physical characteristics of the soil. (3) Soil particles’ mitigation and chemical dissolution change the loess structure, leading to skeletal destruction and decreased peak strength and residual strength of the infiltrated sample to 7.75% and 8.13%, respectively. During internal erosion, physical fine particle migration and chemical dissolution are important for loess stability and loess slope susceptible to failure during water infiltration.
In this paper, the effect of sputtering distance between target and substrate (DTS) on the structural, morphological and optical properties of TiO2 films were investigated. X-ray diffraction (XRD) ...and scanning electron microscopy (SEM) revealed that crystallite size and surface morphology were strongly dependent on DTS. The X-ray photoelectron spectroscopy (XPS) results showed that obvious three peaks including C1S, Ti2p and O1s could be clearly observed and the binding energy was 285, 458 and 531 eV, respectively. For each sample, four peaks near 386, 462, 527 and 595 nm in photoluminescence (PL) spectra were observed and originated from intrinsic recombination, F center, F+ center and electrons transferred from 3d Ti3+ states to the deep levels OH−, respectively. Finally, the photoresponse properties of UV detectors based on TiO2 films were analyzed and the TiO2 UV detector prepared at a DTS of 80 mm showed high responsivity of 2.02 × 10−4 A/W and excellent photosensitivity of 32.25, also, exhibited a fast response with a rise time (τr) of 0.98 s and fall time (τf) of 3.14 s.
•TiO2 films was successfully prepared by magnetron sputtering technology.•Properties of TiO2 films UV detector were mainly decided by oxygen vacancy.•Device showed a fast response with rise time of 0.98 s and fall time of 3.14 s.•Device showed a high photosensitivity of 32.25.
Loess landslides exhibit strong interactions with the terrace sediments of the Jing River on the South Jingyang Platform, Jingyang, Xi'an, China. Analysis of past landslide events revealed that the ...sand layer of this terrace was thrust up to the surface, accompanied by other terrace sediments of carrying. This led to the formation of a thrust nappe structure over a long distance. We performed ring shear tests to examine the shear behavior of this sand layer, with the finding that saturated sand was highly susceptible to liquefaction-induced failure. The groundwater level of the study area is high, resulting in near-saturation of the sand layer. Therefore, topographic interferences contributed additional variables and increased interaction complexities. Simulations indicated that the liquefied sand layer was compressed and forced. Due to the absence of constraints, the sand layer near the bottom of the slope was sheared out over a relatively short distance. On the other hand, particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground. Finally, an initiation-movement model of loess flowslides is proposed. It describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides. Collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands. The landslide experienced four stages as they moved: scraping collisions, floating scrapes, folded thrusts, and nappe accumulation.
•Terrace sediments was thrust up to the surface on the South Jingyang Platform.•Strong interactions led to the liquefaction of the terrace sand layer.•Landslides experienced four stages: scraping collisions, floating scrapes, folded thrusts, and nappe accumulation.•The initiation-movement model was proposed to describe whole process of the landslide.
Mn-doped ZnO (MZO) films were prepared on glass substrates using sol-gel dip-coating technology. The microstructural, morphological, optical and photoelectric properties of MZO films were ...investigated at different withdrawal speeds (WS: 20, 40, 60 and 80 mm s
−1
). The X-ray diffraction (XRD) patterns showed that all the films obtained were polycrystalline with a hexagonal structure, and the highest crystallinity of MZO films was observed as films were deposited at 40 mm s
−1
. The UV-Vis spectra revealed that the average optical transmittance of all samples was over 60% and the energy band gap of films decreased from 3.616 to 3.254 eV with the increase in withdrawal speed. The formed Au/MZO/Au photodetectors (PDs) indicate that a device prepared at 40 mm s
−1
shows superior properties both in response speed and detection capability, and the rise time is 1.871 s and fall time is 3.309 s at 365 nm for 3 V bias and the detectivity (
D
*) reaches ∼1.7 × 10
10
Jones. Moreover, the responsivity of PDs is also affected by the distance between Au electrodes and external bias. This research provides a simple way to fabricate the UV PDs based on MZO films with faster response and higher detectivity.
Mn-doped ZnO (MZO) films were prepared on glass substrates using sol-gel dip-coating technology.
In this paper, we report the successful fabrication of ultrathin PbI2 single crystal by mechanical exfoliation method after the realization of graphene. The properties of samples were investigated by ...X-ray diffraction, atomic force microscopy and Raman scattering. The XRD spectrum indicates that PbI2 crystal has hexagonal crystalline pattern with 2H type crystal structure. The thickness around 10nm about 15 layers of PbI2 single crystal verified by AFM was obtained. Five Raman bands with peaks at 73, 95, 111, 167, and 214cm−1 are observed with 532nm laser, while there are only four bands can be observed for laser 676.4nm and 514.5nm respectively. The results of ultrathin PbI2 single crystal will stimulate further theoretical calculations and experimental investigation of their fundamental properties and potential applications.
•The PbI2 single crystals were firstly prepared by mechanical exfoliation method.•The PbI2 single crystal as thin as 10nm verified by AFM was obtained.•The XRD demonstrates that PbI2 has hexagonal crystalline pattern with a 2H type.•Five Raman bands are observed in the 50–400cm−1 region with the 532nm laser.
Display omitted
•The ratio of elements favoring alloying/intermetallic compounds is studied.•The presence of multi-component precipitates is inevitable in HEAs.•The type and number of chemical bonds ...affect the brittleness-ductility transition.
Multicomponent L12-type material has been shown to be one of the important precipitates used to enhance the properties of high entropy alloys. Its controllability is elusive due to the complexity of the content, which has led to slow progress in the study of their electronic structure. Here, we investigated the deformation mechanism of (Co, Fe, Ni)3Ti-type multicomponent intermetallics using first principles. Thermodynamic parameters, energy and electronic structure suggest that Fe favors a lower γSPF while Ni favors a higher γSPF, which is caused by the difference in the chemical bonding they contribute. The stable outermost electron orbital achieved by Ni-Ti contributes to the good mechanical properties, while the excess lone pair electrons provided by Fe would make the contribution of metallic bonding more significant. Adjustment of the intermetallics-favoring/alloys-favoring element ratio is an effective method to overcome the strength-ductility trade-off. This work provides electronic-level understanding and practical insights to better design and utilize the multicomponent intermetallics enhanced high entropy alloys.
PDF
