Most slow-moving landslides in the Three Gorges Reservoir (TGR) region of China are characterized by pre-existing shear surfaces. The large deformation within the shear zones usually gives rise to ...clastic soil formation. The creep properties have large influence on the kinematic feature of landslides. In this paper, we report an in-situ direct shear creep test carried out in the shear zone of a reactivated slow-moving landslide in the TGR region. Correspondingly, some laboratory ring shear creep tests are carried out to interpret the movement pattern of this landslide. The shear zone soil exhibits similar non-attenuating creep responses in both the in-situ direct shear and laboratory ring shear creep tests. At the same stress level, however, the in-situ direct shear creep test yields a larger rate of creep displacement due to shearing along the landslide direction. In the ring shear creep tests, at the prepeak stage, the critical creep stress that triggers creep failure is slightly lower than the peak shear strength but much larger than the residual strength; at the postfailure stage, the critical creep stress of the shear-zone soil is equal to the residual shear strength. The rate-dependent residual shear strength may account for the stepwise movement pattern of the landslide.
•We give insight intos the time-dependent behavior of clastic soil in a slow-moving landslide in TGR region, China.•The landslide exhibits stepwise movement pattern according to recent monitoring data.•In-situ direct shear creep test and laboratory ring shear creep test were carried out to interpret the movement mechanism of the landslide.•The stepwise movement of the landslide was explained on the basis of the strain rate effect.
Continuous river incisions, heavy precipitation events, reservoir water-level fluctuations, and changes in groundwater flow are the main driving factors of extensive landslide activities in the Three ...Gorges area of the Yangtze River in China. Although the triggers for these major landslide events can be technically detected, predicting and mitigating them remains challenging. This is especially the case where ancient, deep-seated, multi-stage landslides have created complex geological structures that make it difficult to uncover their evolutionary processes and to determine slip surfaces. This study, based on elaborate investigation of the Outang landslide in the Three Gorges Reservoir area, proposes a general framework for analyzing the spatial and temporal evolution of a multi-stage riverbank landslide. The framework applies three-dimensional geological modeling to integrate large amounts of data from earth surface investigations, subsurface explorations, in-situ monitoring and geological dating. The results indicate that the Outang landslide has a total volume of 8.3 × 107 m3 and a maximum thickness of 114 m. It consists of four individual sliding bodies that have been formed consecutively since 130 ka BP. Furthermore, the original slip surfaces of the sliding bodies are found to be interconnected, forming one large active landslide continually creeping towards the Yangtze River. While the entire landslide is in motion, the western, eastern and up-slope portions of the sliding mass are moving at a faster velocity of up to 12.6 cm per year. Our analysis of the Outang landslide reveals that its evolution can be subdivided into three sliding modes. These modes could serve as a reference for analyzing the spatial and temporal evolution of similar multi-stage landslides along riverbanks.
•Integrative workflow for identifying ancient and active slip surfaces.•Framework to study the spatial-temporal evolution of multi-stage landslide.•Three basic modes of successive slide events.•3-dimensional evolution model for a representative multi-stage landslide.
We study the creep properties of clastic soil in residual state. The intact samples are taken from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Firstly, the ...patterns of the landslide movement are analysed based on recent monitoring data, which indicate that the soil within the shear zone is undergoing two deformation processes: a creep phase, characterised by different creep rates, and a dormant phase. We then study the creep behaviour of the soil samples through a series of ring shear creep tests under various shear stress conditions. The creep response depends strongly on the ratio of the shear stress to the residual strength, and the normal effective stress, whereas the creep rate decreases due to strength regain. The long-term strength of the clastic soil is close to the residual strength. Therefore, the residual strength obtained from conventional shear test, which is less time consuming than creep test, can be used in long-term stability analyses of creeping landslides.
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•H2O2 was synthesized by pulsed electrocatalysis.•The key parameters of square wave pulse were determined by theoretical analysis and electrochemical testing.•The effects of pulsed ...period, duty ratio and waveform on the electrosynthesis performance of H2O2 were investigated.•The mechanism of pulsed electrocatalysis on enhanced H2O2 electrosynthesis was revealed.
Pulsed electrocatalysis is emerging as a promising strategy for the improvement of electrocatalytic performance. Herein, the 2-electron oxygen reduction reaction (2eORR) for H2O2 synthesis was taken as a model reaction to explore the effects of pulsed parameters on electrocatalysis. Firstly, the key parameters of a square wave pulse were determined by theoretical analysis and electrochemical testing. Secondly, we found that the pulsed period of the square wave pulse should be neither too short nor too long due to the opposing effects of non-Faradaic and diffusion processes. The lower duty ratio was more favorable for 2eORR. Finally, the effects of the pulsed waveform were explored. We found that the enhanced effects on 2eORR under the rapid sweep potential of a triangular or sine wave were similar to those for a square wave with a short period. Under a sine wave pulse with a frequency of 0.2 Hz, the H2O2 production rate and Faradaic efficiency of 2eORR were increased by 1.4 times and 3.62 times, respectively, compared with the results obtained under constant potential, and the energy consumption was reduced by 75 %. The enhanced effects described above could be attributed to the diffusion layer becoming thinner while the pulsed potential was applied. The reaction rate was increased by the diffusion of reactants (i.e., O2, H+) to the electrode surface and the intrinsic selectivity of 2eORR was increased by the oxygen-rich environment. In addition, the ineffective electroreduction of H2O2 was also reduced by the diffusion of H2O2 toward the bulk solution. This work provides new insights into the determination of parameters, waveform effects and the mechanism of pulsed electrocatalysis.
The Three Gorge Reservoir, one of the largest civil engineering projects in human history, dams the Yangtze River to form a 660-km-long and 1.13-km-wide reservoir. Today, although the project has ...been completed and is in normal operation, the on-going landslide initiation and movement in response to the reservoir operating is one of the main geologic hazards. The Huangtupo (meaning “yellow soil slope” in Chinese) Slope typifies such on-going landslides along the reservoir. Observations from a multi-year monitoring program conducted on this slope indicate that there are multiple slides on the reservoir banks that move episodically into the reservoir and their movements appear to be highly correlated with the initial and seasonal changes in the reservoir pool level. A hydro-mechanical numerical model is constructed to investigate the quantitative links among the episodic movements and the variations in pore water pressure, suction stress, hydrostatic reservoir water loading, and slope self-weight induced by the fluctuating water levels. Modeling results identify regions within the variably saturated slope where significant changes in stress occur during the periods of the initial impoundment that raised water levels from 68 to 135 m and that occur in response to seasonal fluctuations of the reservoir pool level between 145 and 175 m. We find that the rise or decline of reservoir pool level can either increase or decrease the stability of landslide. In general, hydrostatic reservoir water loading has positive correlation with the stability; pore water pressure and suction stress have negative correlation with the stability; and the effects of slope self-weight depend on the dip angle and mechanical properties of sliding surface.
This paper presents a model for estimating the moisture of loess from an image grayscale value. A series of well-controlled air-dry tests were performed on saturated Malan loess, and the moisture ...content of the loess sample during the desiccation process was automatically recorded while the soil images were continually captured using a photogrammetric device equipped with a CMOS image sensor. By converting the red, green, and blue (RGB) image into a grayscale one, the relationship between the water content and grayscale value, referred to as the water content–gray value characteristic curve (WGCC), was obtained; the impacts of dry density, particle size distribution, and illuminance on WGCC were investigated. It is shown that the grayscale value increases as the water content decreases; based on the rate of increase of grayscale value, the WGCC can be segmented into three stages: slow-rise, rapid-rise, and asymptotically stable stages. The influences that dry density and particle size distribution have on WGCC are dependent on light reflection and transmission, and this dependence is closely related to soil water types and their relative proportion. Besides, the WGCC for a given soil sample is unique if normalized with illuminance. The mechanism behind the three stages of WGCC is discussed in terms of visible light reflection. A mathematical model was proposed to describe WGCC, and the physical meaning of the model parameters was interpreted. The proposed model is validated independently using another six different types of loess samples and is shown to match well the experimental data. The results of this study can provide a reference for the development of non-contact soil moisture monitoring methods as well as relevant sensors and instruments.
Hybridization is a core element in modern rice breeding as beneficial combinations of two parental genomes often result in the expression of heterosis. On the contrary, genetic incompatibility ...between parents can manifest as hybrid necrosis, which leads to tissue necrosis accompanied by compromised growth and/or reduced reproductive success. Genetic and molecular studies of hybrid necrosis in numerous plant species revealed that such self-destructing symptoms in most cases are attributed to autoimmunity: plant immune responses are inadvertently activated in the absence of pathogenic invasion. Autoimmunity in hybrids predominantly occurs due to a conflict involving a member of the major plant immune receptor family, the nucleotide-binding domain and leucine-rich repeat containing protein (NLR; formerly known as NBS-LRR). NLR genes are associated with disease resistance traits, and recent population datasets reveal tremendous diversity in this class of immune receptors. Cases of hybrid necrosis involving highly polymorphic NLRs as major causes suggest that diversified
gene repertoires found in different lineages would require a compatible immune match for hybridization, which is a prerequisite to ensure increased fitness in the resulting hybrids. In this review, we overview recent genetic and molecular findings on hybrid necrosis in multiple plant species to provide an insight on how the trade-off between growth and immunity is equilibrated to affect hybrid performances. We also revisit the cases of hybrid weakness in which immune system components are found or implicated to play a causative role. Based on our understanding on the trade-off, we propose that the immune system incompatibility in plants might play an opposite force to restrict the expression of heterosis in hybrids. The antagonism is illustrated under the plant fitness equilibrium, in which the two extremes lead to either hybrid necrosis or heterosis. Practical proposition from the equilibrium model is that breeding efforts for combining enhanced disease resistance and high yield shall be achieved by balancing the two forces. Reverse breeding toward utilizing genomic data centered on immune components is proposed as a strategy to generate elite hybrids with balanced immunity and growth.
Landslide-induced tsunamis may cause fatalities, damages and financial losses. In the Three Gorges Reservoir Area of China, several large landslides are still unstable and persistently creeping ...toward the Yangtze River. In this paper, we investigate the impacts of landslide-induced tsunamis in the Three Gorges Reservoir by using a hybrid numerical approach. One of the largest unstable mass in this area, the Huangtupo landslide, is chosen as the study object. First, the landslide deformation and initiating velocities are obtained by using the finite-discrete element method. The landslide-induced tsunamis and their impacts on shipping on the Yangtze River are then investigated through smooth particle hydrodynamics modelling. Our results reveal that an approximately 80% reduction in shear strength of the tip in the landslide will lead to catastrophic failure of the landslide, with sliding velocities of up to 8 m/s. Subsequently, such a collapse may initiate a river tsunami, propagating up to 9 m on the nearby reservoir banks within 3 km. The impacts on surrounding floating objects, such as surges and sways, heaves and rolls, are up to 110 m, 8 m and 6°, respectively. The simulations indicate that although the likelihood of a catastrophic failure of the whole landslide is low, the partial sliding still poses severe threat to the nearby reservoir banks and shipping on the Yangtze River. Thus, we recommend continuous monitoring as well as landslide early warning systems at this and also other hazardous sites in this area.
In recent years, hundreds of Earth observation satellites have been launched to collect massive amounts of remote sensing images. However, the considerable cost and time to process the significant ...amount of data have become the greatest obstacle between data and knowledge. In order to accelerate the transformation from remote sensing images to urban thematic maps, a strategy to map the bare land automatically from Landsat imagery was developed and assessed in this study. First, a normalized difference bare land index (NBLI) was presented to maximally differentiate bare land from other land types in Wuhan City, China. Then, an unsupervised classifier was employed to extract the bare land from the NBLI image without training samples or self-assigned thresholds. Experimental results showed good performance on overall accuracy (92%), kappa coefficient (0.84), area ratio (1.1321), and match rate (83.96%), respectively. Results in multiple years disclosed that bare lands in the study site gradually moved from inner loops to the outer loops since 2007, in two main directions. This study demonstrated that the proposed method was an accurate and reliable option to extract the bare land, which led to a promising approach to mapping urban land use/land cover (LULC) automatically with simple indices.
Although slice methods are simple and effective slope stability analysis approaches, they are statically indeterminate. Several modifications of the slice method, such as the Spencer, ...Morgenstern-Price, and Chen-Morgenstern methods, are statically determinate and solvable as they assume the inter-slice force inclination angle; however, there is a small gap between the assumptions and actual landslide stability analysis. Through reasonable theoretical analysis, the Su slice method provides a reliable approach for determining the inter-slice force inclination angle that can be used in slice analysis to accurately analyse, calculate, and evaluate the stability of landslides. However, the Su slice method requires further research and analysis, especially in terms of the parameter values sin
λ
bi
and
ρ
. In this study, we investigated more accurate methods for calculating the parameters sin
λ
bi
and
ρ
. In addition, an adjustment coefficient (
μ
) was introduced to improve the solution method for the inter-slice force inclination angle. The inter-slice force inclination and safety factors of three landslides with arc-shaped slip surfaces and one landslide with a polyline-shaped slip surface were analysed and compared using the different slice methods. The improved inter-slice force inclination not only satisfies the calculation of static force equilibrium condition but also satisfies the calculation of both the force and moment equilibrium conditions. The improved method for calculating inter-slice force inclination presented the best correlation. The safety factors calculated using the improved Su slice method were close to those obtained using numerical simulations and the Morgenstern-Price method. Despite negligible differences among the safety factors calculated using the Su slice, improved Su slice, and M-P methods, the accuracy of the improved Su slice method was better than the M-P method in terms of inter-slice force inclination angles which can be useful to improve protection engineering design.
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