Increasing Slope Angle Research Articles

Hybrid Plasmonic Slot Waveguides With Sidewall Slope

We investigate the effect of sidewall slope in hybrid plasmonic slot waveguides on the characteristics of its guided sub- wavelength hybrid modes at the telecommunication wavelength of 1.55 μ.m. The rectangular cross-section of the waveguide turns to a trapezoidal-shape with the increase of the sidewall slope angle and mode attenuation increases gradually. We showed strong mode attenuation for a waveguide with a triangular cross-section. The guided mode properties are improved by increasing the width of low refractive index dielectric slots. These investigations are in a good agreement with the experimental results drawn from a previous study and can be exploited for elucidating the characteristics of the complementary metal oxide semiconductor- compatible hybrid plasmonic slot waveguides.

Dynamics of Cross-Isobath Dense Water Transport Induced by Slope Topography

Abstract Dynamics of cross-isobath downslope transport of a dense water mass induced by small-scale topographic variation is investigated based on a high-resolution numerical experiment with realistic settings, a simplified analytical model for water particle advection, and idealized sensitivity experiments. The existence of a submarine ridge induces two different processes for cross-isobath downslope transport of dense water: a strong but narrow and thin downslope current at the east side of the ridge and cyclonic eddies with dense water cores to the west of the ridge. The former downslope current is produced in response to the rapid increase of slope angle near the ridge. The latter eddies are formed by stretching of the dense water layer near the crest, where isobath curvature is so high that offshore centrifugal force overcomes the coastward Coriolis force. From a simple analysis on the equation of motion for a fluid particle placed on a slope with curved isobaths, a general criterion that describes whether a density current follows or crosses isobaths is derived, which is supported by idealized sensitivity experiments. The location where cross-isobath transport of dense water takes place is determined by relative magnitude between spatial derivatives of isobath curvature, planetary vorticity, and slope angle. Based on these arguments, a parameterization is proposed to represent the effect of unresolved small-scale topography in coarse-resolution models.

English

The objective of this study was to investigate the effects of physiographic features such as slope, altitude, aspect and soil on landslides dimensions and distribution in Pahnehkola forest, north of Iran. 30 landslides were selected for detailed observation, with their occurrences recorded by global positioning system (GPS) along the surveyed forest road. Then, landslides were mapped in Arc view and subsequently digitized into a geographic information system (GIS). Results indicate that the landslide area at a distance of 80 to 100 m from road edge was significantly more than that of other distances. The landslide dimensions increased with increasing slope angle. The mean of landslide area and mean of landslide volume on the Northwest aspect was significantly more than that on other aspects (P<0.01). The mean of landslide dimensions in altitude class of 400 to 650 m was significantly less than that in altitude class of 150 to 400 m (P<0.01). The mean of landslide dimensions increased significantly with increasing soil liquid and plastic limit. The logistic regression modeling indicate that independent variables including aspect, liquid limit, plastic limit and soil moisture, significantly influence the landslides area. The majority of landslides were situated along roads and on faults, and shallow landslides were more frequent along roads compared to those on faults.   Key words: Landslide, forest road, physiographic features, GPS, Pahnehkola forest.

Application of geogrids in waste dump stability: a numerical modeling approach

Geosynthetic is widely used to reinforce the weak rock mass, mine waste dump, soil slopes road cut slopes, etc. The present paper discusses the effect of geogrids on the stability of mine waste dump. The stability of mine waste dump has been done by Fast Langrage Analysis of Continua (FLAC) slope software, which is based on finite difference method. Reinforcement by geogrids mainly depends on the tensile strength, aperture size of geogrids, and particle size distribution of dump rock mass. Different permutations and combinations of spacing between two geogrid sheets have been taken into consideration to study the stability of mine waste dump. The factor of safety is calculated to quantify the effect of geogrids on waste dump slope. It has been observed from numerical modeling that the maximum slope angle is 45° at a height of 10 m. The scope of increasing slope angle from 45 to 60° is evaluated using geogrids. It has been found from the study that the factor of safety increases as the spacing between geogrids decreases. Maximum strain is also plotted of each case to identify the slip circle. The positions of geogrids modify the probable slip circle or failure plane of mine waste dump. Using ten geogrids at a spacing of 1 m, the slope angle can be increased up to 60° with factor of safety of 1.4.

Grip and detachment of locusts on inverted sandpaper substrates

Locusts (Locusta migratoria manilensis) are characterized by their strong flying and grasping ability. Research on the grasping mechanism and behaviour of locusts on sloping substrates plays an important role in elucidating the mechanics of hexapod locomotion. Data on the maximum angles of slope at which locusts can grasp stably (critical angles of detachment) were obtained from high-speed video recordings at 215 fps. The grasping forces were collected by using two sensors, in situations where all left legs were standing on one and the right legs on the other sensor plate. These data were used to illustrate the grasping ability of locusts on slopes with varying levels of roughness. The grasping morphologies of locusts' bodies and tarsi were observed, and the surface roughness as well as diameters of their claw tips was measured under a microscope to account for the grasping mechanism of these insects on the sloping substrate. The results showed that the claw tips and part of the pads were in contact with the inverted substrate when the mean particle diameter was in the range of 15.3–40.5 µm. The interaction between pads and substrates may improve the stability of contact, and claw tips may play a key role in keeping the attachment reliable. A model was developed to explain the significant effects of the relative size of claw tips and mean particle diameter on grasping ability as well as the observed increase in lateral force (2.09–4.05 times greater than the normal force during detachment) with increasing slope angle, which indicates that the lateral force may be extremely important in keeping the contact reliable. This research lays the groundwork for the probable design and development of biomimetic robotics.

Mechanism and modelling of shallow soil slope stability during high intensity and short duration rainfall

Shallow landslides in nearly saturated uncohesive to slightly cohesive soils are triggered by high intensity, short duration rainfall which infiltrates into soil and changes intergranular friction and effective stresses. For this, the especially developed Soil–Water Interaction Modelling System (SWIMS) was used with CL-ML type soils. For simplicity, rainfall intensity and duration were kept constant. Results showed that (1) All 35° slopes were failed by translational failure. For the other (15°,25°) slopes, no failures were observed; (2) For all slopes, FOS increased with increasing compaction degree and decreased with increasing slope angle; (3) Other parameters, such as soil density, porosity, saturation degree, water contents, and water permeability may also affect shear strength/slope stability, especially for low degrees of saturation (S<95%), compared to high degrees of saturation (S=,>95%). (4) A correlation of SWIMS tests observed that average wetting band depths (hobser), with the calculated wetting band depths from the Lump Equation (hLE), were poor, as hobser values were much higher than hLE values. Differences increased for very low degrees of saturation (S), compared to S>95%. This meant that the Lump equation underestimated wetting band depths. Further, if the Lump equation is still considered valid, this would imply either water-permeability increases, porosity decreases or both occur towards full saturation; a process where the last possibility is the most probable occurrence.

Research the Excavation Angle Affect on Seismic Dynamic Response of Slope

Based on the concentrated deformation and destruction characteristics of excavation damage slopes in Wenchuan earthquake，as granite the media of excavation damage slope for the finite element model. In 45° slope as the natural slope，the excavation damage effect and seismic dynamic response of different excavation angle have been studied under the excavation high is certain condition, it’s include natural slopes, excavation angle 56°, 72° and 90°. Analysis shows that excavation damage not only themselves destroyed the stress balance of slopes, but also impact on the seismic dynamic response of slopes, and the seismic dynamic stress, displacement and acceleration increased with the increase of slope angle. It’s not conducive to the stability of slope and the results coincides with the investigation conclusion that Wenchuan earthquake mountain disaster outbreak in the terrain mutation site. And the analysis also shows that slow excavation angle is an important measure to improve the seismic performance of the slope.

Finite Element Analysis for Bearing Capacity of Rectangular Footing Resting Near Sloped Cohesive Soil

Finite element method is used to investigate the ultimate bearing capacity of rectangular footing resting on cohesive soil near slope. The effect of footing aspect ratio (L/B), distance ratio (b/B), and slope angle (β) on the bearing capacity are calculated. A new reduction factor (Rs) is proposed to compute the ultimate bearing capacity for rectangular footing adjacent to slope of cohesive soil from ultimate bearing capacity for similar rectangular footing resting on ground level of cohesive soils. This study shows that the ultimate bearing capacity for rectangular footing adjacent to slope of cohesive soils decreases when slope angle (β) and aspect ratio (L/B) increases. Also the ultimate bearing capacity increases when the distance ratio (b/B) increases. Finally, the effect of slope diminishes as the distance ratio (b/B) equal, or exceeds 0.75

Influence of tensile force of agave and tea plants roots on experimental prototype slopes

The study is aimed to determine the influence of tensile force of roots of agave (Angustifolio marginata) and tea (Acalypha siamensis) plants on landslide in prototype slopes. The plants of agave and tea were planted in different prototype slopes and the corresponding tensile forces were measured with the installed strain gauge in-situ. The study found that the tensile force of tea plants increase with increased root diameter inside the prototype slopes with angle which ranged from 30 to 40°. But, the tensile force of agave roots decreased slightly with increased slope angle. Again, the tensile force increased significantly with increased width-height ratios of agave leaves. The plant agave and tea showed significant results to protect the experimental prototype slopes. Regression relationship between tensile force and root’s diameter of tea and agave plants has been established. Further research can bring positive impact in using such plants in actual natural slopes in order to prevent the landslides. Key words: Tensile force, agave and tea plants, roots, slope, landslides.

The spatial dimension of pastoral herding: A case study from the northern Negev

Sustainable management of heterogeneous grazing systems requires better understanding of the spatial dimension of grazing ecology. We deployed animal-borne GPS devices to map the daily foraging excursions of a shepherded flock of 200 goats under traditional Bedouin management, on a study site in the semiarid region of the northern Negev, Israel. A total of 88 daily foraging excursions were mapped during the herbaceous growing seasons of 2002 and 2003, and the spatial dimension was analyzed with GIS tools. A typical foraging excursion lasted 5.5 h, during which the flock moved across the landscape at an average speed of 0.3 m/s (1.1 km/h) and traveled 5.4 km. The foraging route was highly elongated in shape and reached a distance of 1.5 km from the night corral. Flock movement speed was affected significantly by distance from the night corral, being greatest at shortest and longest distances. Speed decreased with increasing slope angle and differed between aspects. The frequency of flock presence across the study site deviated significantly from random with respect to aspect but not to slope angle and distance from the corral. The effect of aspect changed slightly between the study years. The product of daily distance traveled and flock path width yielded a rate of area coverage of 0.122 km2per day. The average amount of herbage dry matter removed on any one pass of the flock is therefore in the order of just a few grams per square meter. The use of the area available to the flock was highly non-uniform, which suggests that better planning of grazing management could mitigate negative effects of grazing.

FEM Analysis on Tensile Forces of Liner System with a Change of Slope Angle

As there is a few area or topographic factors for landfill site, the slope angle becomes steeper because it makes much disposal capacity. Tensile force in the geotextile is caused by compaction work of disposed waste, and the tensile force is transferred into the liner system by friction, but the tensile force of liner system will change with a change of slope angle, so it is very important to determine the amount of tensile forces creating at the fixed ends of liner system for avoiding the tearing failure of liner system and designing the anchorage. In this paper, FEM analyses, in which the joint element was used to model the interface between the liner system, were conducted to estimate the tensile forces creating at the fixed ends of liner system with a change of slope angle from 1:2.5 to 1:0.2. The analysis results show that the tensile forces creating at the fixed end of liner decrease as the slope angle increases.

Disaster chains initiated by the Wenchuan earthquake

The Wenchuan earthquake caused numerous landslides and avalanches, which initiated causal chains of geological and ecological disasters. Field investigations and field experiments were performed in the earthquake area in 2008 and 2009 to study the disaster chains. Four types of disaster chains have been identified and seven cases have been studied. In the disaster chains, each episode was caused by the previous episode, or the causal episode. In the first chain, landslide created a quake lake, which was followed by landslide dam failure flood and very intensive fluvial process. The last episode of the chain was loss of habitats and destruction of aquatic biocommunities. The Tangjiashan and Huoshigou landslides initiated such a type of disaster chain. The second chain consisted of landslide, drainage system burying, debris flows, and development of new drainage system and intensive fluvial process. The Wenjiagou landslide initiated such a type of disaster chain. The third chain consisted of avalanches, grain erosion (unusual erosion of bare rocks due to insolation and temperature change), slope debris flows, and flying stones. Many such disaster chain events occurred on the mountains by the Minjiang River section from Yingxiu to Wenchuan. The fourth chain has only two episodes: avalanches during the earthquake occurring on elevation between 100 and 800 m from the riverbed, and rock falls or new avalanches due to increased slope angle of high mountains (400–1,500 m from the riverbed). The Chediguan bridge was broken by such avalanches in July 2009, in which six were killed and more than 20 were injured. For all the disaster chains, the volume of mass movement in each episode was much less than the causal episode (previous episode). In other words, there was an attenuation along the causal chains. The attenuation factor is defined as the ratio of the volume of mass movement or affected area in one episode of a chain to the volume or affected area in the causal episode. The study concluded that the attenuation factor ranges from 0.02 to 0.3. Macroinvertebrates were used as indicator species to evaluate the ecological effect of the disaster chains. The number of species was greatly reduced by the causal chains, although the river section was not directly affected by landslides.

The effects of slope and fuel bed width on laboratory fire behaviour

A set of 109 laboratory fires in Pinus halepensis fuel beds (1 kg m–2) was used to test the effects of slope (0°, 10°, 20°, 30°) and fuel bed width (1, 2, 3 m) on fire behaviour variables such as rate of spread, fuel consumption, flame residence time, temperatures and flame geometry. The qualitative behaviour of the fires is also reported. The 20° and 30° upslope fires are pointed in shape and fire whirls moving along the fire flanks in the direction of the fire head are systematically observed in 30° upslope fires. Flame residence time increases with increasing slope angle, and both slope angle and fuel bed width affect rate of spread. The slope effects observed in 10° and 20° slope angles and in the narrowest fuel beds (1 and 2 m) are similar to those predicted by operational models. However, the observed slope effect at the 30° slope angle is underestimated by these models, in particular in 3 m-wide fuel beds. Flame temperatures correlate closely with dimensionless height and flame lengths correlate closely with fire line intensity. Mechanisms that could explain the different effects observed are suggested and discussed.

Catchment‐wide denudation rates at the margin of NE Tibet from in situ‐produced cosmogenic 10Be

Terra Nova, 23, 42–48, 2011AbstractWe present denudation rates for catchments in the Qilian Shan and two mountain ranges in its foreland, which differ markedly in elevation and catchment morphology. Catchments with mean slope angles below ∼25° yield 10Be‐derived denudation rates &lt;∼200 mm ka−1 and have narrow and symmetric slope–frequency distributions, which become broader as the mean slope angle increases. Denudation rates for catchments with mean hillslope angles steeper than ∼25° range from ∼100 to ∼800 mm ka−1. Field observations suggest that these higher and more variable rates are the result of erosion by bedrock landslides, which contribute to mass transport on the hillslopes. Six catchments aligned along the mountain front of the central Qilian Shan have reached threshold values of slope and relief. These basins also show remarkably similar slope–frequency distributions with negative skewness and a pronounced peak at a slope angle of 30°–35°. We hypothesize that these catchments have attained an erosional steady state.

Failure of a layer of buried surface hoar

In order to study the formation of the initial failure leading to dry‐snow slab avalanche release, we performed loading experiments in a cold laboratory with natural samples including a layer of buried surface hoar. The experimental setup was such that the layered snow samples were loaded continuously for various tilt (slope) angles; loading rates varied between 1 and 20 Pa s−1. The stress at fracture decreased with increasing loading rate and increasing slope angle, i.e., increasing shear component of the load. The latter result means that the layer was stronger in compression than in shear which is attributed to the particularly anisotropic nature of layers of buried surface hoar. Particle image velocimetry revealed that almost 90% of the sample's global deformation was concentrated in the weak layer. For avalanche release our results imply that the shear component of deformation is of particular importance for failure initiation.

Effect of ecological engineering design on biological motility and habitat environment of Hynobius arisanensis at high altitude areas in Taiwan

Because of thriving tourism in recent years, concrete constructions have been installed by creeks in order to protect the safety of tourists, but the effect of concrete structures on the habitats and the mobility of certain species is still unknown. This study evaluates the different effects of various water bank substrates in terms of the influence on Hynobius arisanensis's (Maki) motility in Alishan National Park. Comparing the concrete area with two other areas where primitive streams flow by, it was observed that concrete structures lead to increased flow velocities, shallower water depths and poorer water quality. In the biological motility assessment, moss, rock, wood, clay and concrete as distinct water bank substrates were used to test the climbing ability of H. arisanensis. Based on the seasonal humidity changes in winter and summer of Alishan area, H. arisanensis's climbing ability was tested in two conditions, high humidity/high temperature and high humidity/low temperature. It was determined that climbing ability dropped rapidly with increasing slope angles. It was observed that the climbing ability of H. arisanensis is slightly decreased in low temperature. Regarding the upper limit of design slope suitable for H. arisanensis are: wood and concrete are ≤45°, moss surface ≤60° and clay surface ≤30°. The results here can provide insights for future engineering projects on creek banks to benefit H. arisanensis conservation.

Variations of horizontal and vertical velocities over two-dimensional transverse dunes: A wind tunnel simulation of the effect of windward slope

The changes in wind velocity induced by dune topography have an important significance in dune dynamics. In this paper, the horizontal and vertical velocities over six transverse dune models were measured non-intrusively by means of Particle Image Velocimetry in a wind tunnel. The windward slope angle and the free-stream wind velocity both affected the horizontal and vertical velocity components. On the windward side, the acceleration of horizontal velocity depended mainly on the windward slope angle and the height above the dune surface, but was also affected by the free-stream wind velocity. The speed-up ratio increased with increasing slope angle but decreased with increasing height. The ascending vertical velocities also increased with increasing slope angle and free-stream wind velocity. The maximum values moved upper along the dune when the windward angle became steeper. In the leeward sides, the horizontal velocity decreased and reversed because of airflow separation; the maximum reverse velocity in the separation cell was about 17% of the free-stream wind velocity. Behind the dune crest, the airflow moves downwards, and its maximum downward velocity is found near the flow reattachment point. Finally, we discussed the significance of these velocity variations for sediment transport and dune dynamics.

Retrogression characteristics of landslides in fine-grained permafrost soils, Mackenzie Valley, Canada

Thirteen landslides (retrogressive thaw flows) were investigated to study the behavior of thaw retrogression in permafrost in the Mackenzie Valley, Northwest Territories (NWT), Canada. Those landslides are all in fine-grained ice-rich permafrost soils. Such landslides usually start from small-scale slope failures followed by retrogressive thaw flows when ice-rich permafrost soils are exposed to the atmosphere. The landslides were marked with survey stakes to measure their retreat rates for the thawing season of 2007. Two correlations are presented: one is between scarp wall height and retreat rate; another is between overall slope angle and retreat rate. It was found that thaw flow retrogression rate increases with increase in scarp wall height and slope angle up to a certain limit. It was also confirmed that thaw flow retrogression is not influenced by slope orientation.

The influence of topographic and lithologic features on horizontal deformations

SUMMARY A number of studies have been carried out in order to determine the magnitude of effects originating from the surroundings of an observation site which influence seismometer records or deformation observations with tilt- or strainmeters. The investigations generally comprise thermal, atmospheric, topographic, and cavity effects, as well as ocean loading. Recently, these studies have been continued and extended using Finite Element (FE) modeling. The effects are investigated exemplarily using air pressure variations as loading signal. The observatory sites differ in their local surroundings. Based on this the influence on topographic and lithologic features is investigated with respect to air pressure changes. The models developed reflect different topographies around stations: wide and narrow valleys, hill flanks, and flat areas. At the foot of the hill flank, galleries are integrated into the models. The topographic and the gallery geometry influence are systematically investigated with regard to e.g. rock coverage above an observation site, changes in the hill slope, width of a valley, and lithology. The deformations are only caused by air pressure changes and not associated with gravity changes due to an advancing pressure front. For loading different air pressure scenarios are simulated with an uniform load and a pressure front which moves over the model in different directions. As an elastic rheology is considered, the effects can be scaled to actual occurring air pressure variations. Initial studies focus on the cavity effect to estimate the order of magnitude to separate the pure cavity effect from other influences. Studies of topographic effects, e.g. an increasing slope angle, yield a non-linear increase in the strain component with amplitudes up to 2 nstrain and tilt changes up to 2 nrad for a uniform air pressure load of 1 hPa for PREM parameterized models. Different lithologies can result in five times larger deformations. For moving high pressure areas, changes emerge in strain of up to 2 nstrain and in tilt of up to 4.2 nrad. The results obtained improve the interpretation of deformations observed with regard to fundamental geodynamic processes, and contribute to the selection of future observation sites.

Incipient Motion of Riverbank Sediments with Outflow Seepage

Based on a force analysis, an expression is derived to describe the critical Shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters, outflow seepage, and physical and mechanical properties of sediments. Parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage, slope angle, and flow direction on the critical Shields number. The results show that the critical Shields number decreases with an increase in the hydraulic gradient. Where bank collapse is concerned, the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface. At a certain value of hydraulic gradient, the critical Shields number decreases with increasing slope angle. Open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward.