Initial Slope Angle Research Articles

Development of the morphodynamics on Little Ice Age lateral moraines in 10 glacier forefields of the Eastern Alps since the 1950s

Abstract. Since the end of the Little Ice Age (LIA) in the middle of the 19th century, Alpine glaciers have been subject to severe recession that is enhanced by the recent global warming. The melting glaciers expose large areas with loose sediments in the form of lateral moraines, amongst other forms. Due to their instability and high slope angle, the lateral moraines are reworked by geomorphological processes such as debris flows, slides, or fluvial erosion. In this study, the development of the morphodynamics and changes in geomorphological processes on lateral moraines were observed over decades, based on a selection of 10 glacier forefields in the Eastern Alps. To identify geomorphological changes over time, several datasets of archival aerial images reaching back to the 1950s were utilized in order to generate digital elevation models (DEMs) and DEMs of difference. The aerial images were complemented by recent drone images for selected moraine sections, enabling a high-resolution analysis of the processes currently occurring. The results concerning the development of morphodynamics on lateral moraine sections are diverse: some slopes display a stagnation of the erosion rates, whereas the rates of one section increase significantly; however, the majority of the slopes show a decline in morphodynamics over decades but stay on a high level in many cases. In particular, moraine sections with high morphodynamics at the beginning of the observation period mostly show high erosion rates up until present-day measurements, with values up to 11 cm yr−1. These moraine sections also feature heavy gullying on their upper slopes. A correlation between the development of morphodynamics and the time since deglaciation could scarcely be established. In fact, the results instead indicate that characteristics of the lateral moraines such as the initial slope angle at the time of deglaciation have a significant influence on the later morphodynamics. These observations raise concerns as to whether the until now often conducted analyses based on the comparison of lateral moraine sections with different distances to the glacier terminus, assumed to represent varying time spans since deglaciation, can provide sound evidence concerning the process of stabilization.

Stability prediction and optimal angle of high slope in open-pit mine based on two-dimension limit equilibrium method and three-dimension numerical simulation

The optimization design of the open pit slope can ensure safety in production at the same time bring considerable economic benefits, so it is necessary to evaluate the stability of the initial excavation scheme of the high slope in an open-pit mine and optimize the initial slope angle according to the evaluation results. In this paper, an exhaustive study of Anyi open-pit mine in mouding County Yunnan province China has been made, and the following results have been achieved: (1)Confirmed the geological factors which affected the slope stability of open-pit mine; (2)Quantified the stability of the open-pit mine slope; (3) Under the premise of safety, the angle of the open pit high slope has been optimized on the base of the calculations of the open-pit mine high slope stability so as to ensure the maximum economic benefit. In this paper, the study area was divided into six zones. Firstly, qualitative analysis of slope stability was made by analogy method of engineering geology and stereographic projection method according to the orebody location, the properties of rock and soil in slope, the height of slope, and so on. The analysis shows that the preliminary design of slope angle is so large to ensure safety. Secondly, the stability of different slopes of a high slope is the quantitative analysis of different zones in high slope was made by two-dimensional limit equilibrium method and the finite difference method. In this paper, the mechanical parameters of rock are obtained by a laboratory test, and the stability of the high slope is quantitatively analyzed by two-dimensional limit equilibrium and three-dimensional numerical simulation.

Runout Number: A New Metric for Landslide Runout Characterization

ABSTRACT Landslide runout has traditionally been quantified by the height-to-length ratio, H/L, which, in many cases, is strongly influenced by the slope of the runout path. In this study, we propose an alternative mobility measure, the unitless Runout Number, measured as the landslide length divided by the square root of the landslide area, which characterizes landslide shape in terms of elongation. We used a database of 158 landslides of varying runout distances from locations in northern California, Oregon, and Washington state to compare the two runout measurement methods and explore their predictability using parameters that can be measured or estimated using geographic information systems. The Runout Number better describes the overall runout for several landslide and slope geometries. The two mobility measures show very little correlation to each other, indicating that the two parameters describe different landslide mobility mechanisms. When compared to predictive parameters shown by prior research to relate to landslide runout, the two runout measurement methods show different correlations. H/L correlates more strongly to initial slope angle, upslope contributing area, landslide area, and grain size distribution (percent clay, silt, total fines, and sand). The Runout Number correlates more strongly to planimetric curvature, upslope contributing area normalized by landslide area, and percent sand. Although these correlations are not necessarily strong enough for prediction, they indicate the validity of both runout measurement methods and the benefit of including both numbers when characterizing landslide mobility.

Effect of Dry-Wet Cycle on Stability of Granite Residual Soil Slope

The dry-wet cycle has a significant effect on the shear strength of the granite residual soil, which will affect the stability of the slope. A numerical model of the road cutting slope considering the strength change of the granite residual soil under conditions of dry-wet cycle was established. The numerical model was compared with the previous research results to obtain a good agreement, indicating the validity of the model established. Then several influence factors such as the number of cycles, initial cohesion, friction angle, initial slope angle, excavation slope angle and other factors are considered, and the parameter analysis of the stability development of the road cutting slope with the strength changes of the granite residual soil under dry and wet cycling conditions is considered. The research results show that the dry-wet cycle has a great impact on the stability of the road cutting slope of granite residual soil, which reduces the slope stability by about 10-30%. The conclusions of this paper provide a certain theoretical guidance for the design and application of the roadside slope engineering of granite residual soil.

Analytical modeling of oil production rate during the entire steam-assisted gravity drainage process in heavy oil reservoirs

The steam-assisted gravity drainage (SAGD) process is a widely used thermal recovery technique for heavy oil reservoirs worldwide. In addition to numerical simulation methods, analytical models are alternative tools for the prediction and evaluation of heavy oil recovery by SAGD. In this study, a new analytical oil production rate prediction model for the entire SAGD process, including the rising, transition, expanding and depletion stages, is derived based on the movement rules of the steam chamber interface. The main improvements compared with existing analytical models in this work involve the introducing of a transition stage which is between the rising and the expansion stages, the modification of the depletion stage, the consideration of homogeneity with anisotropy, and the modification of the initial slope angle and shape factors which vary with reservoir parameters and steam injection parameters. Furthermore, the new analytical model is validated against with a relatively complete analytical model and numerical simulation models under field conditions. The results show that the new analytical model can predict the oil rate during the entire SAGD process more accurately than other available analytical models and with high agreement with numerical simulation results and field data. The results also show that the continuity of oil rate is improved by introducing the transition stage. The anisotropy of the permeability cannot be ignored, because it affects the peak oil rate and plateau time of the SAGD process. Moreover, the new model can quickly diagnose the phase of the steam chamber development, which provides guidance for the follow-up adjustment in heavy oil field application.

An experimental investigation on slope stability under drawdown conditions using transparent soils

This paper presents an experimental investigation into slope failure during water-level drawdown using transparent soil. The internal characteristics of slope failure are not well-known due to the limitations of the techniques used in the experiments conducted to date. In this study, transparent soil is used to visualize the process of slope failure. We developed a water-level control system to implement simulation of the drawdown of the water level at various speeds and used a charge-coupled device camera to capture images during the entire slope failure process. Particle image velocimetry was used to measure the displacement of the sand particles and identify the sliding zones. The flow paths of the fluid inside the slope were illuminated using an organic dye. The results show that the slope failure process can be divided into two stages: surface and overall sliding. The overall sliding of the slope is caused by the gradual development of partial instability, and the failure mode is a cyclic failure. The slope angle is different above and below the water level during the process of sliding. In our experiments, the slope angle is about 20° above the water level, which is the same as the final stable slope angle, and about 35° below the water level, which is the same as the initial slope angle. This means that the drawdown influences the angle above the water level but has little influence on the angle below the water level. The results of this paper provide a better understanding of the physical behavior and failure mode of soil slopes caused by drawdowns near the coast.

The relationship between the slope angle and the landslide size derived from limit equilibrium simulations

Katz et al. (2014) carried out a study of controls on the size and geometry of landslides using two-dimensional discrete element numerical simulations. One of their conclusions is that in addition to the peak strength of the slope material, the initial slope angle is another factor that controls the amount of material available for landslides, thus the size, of the resultant landslide. It means that in steeper slopes, more material disintegrates for a given material strength, and consequently the produced landslide is larger. However, in our studies based on limit equilibrium simulations, the sliding mass volume decreases with the increasing slope angle for a given material strength, just contrary to the result of Katz et al. One possible explanation is that when the slope angle in our model increases, the geometry of the potential critical slip surface changes, leading to a decrease of the amount of material available for potential sliding that compensates the increasing gravity effect owing to the enlargement of the slope angle. It suggests that there exist different controls of the slope angle on the landslide size for given material strength.

Controls on the size and geometry of landslides: Insights from discrete element numerical simulations

We use numerical two-dimensional discrete element method (DEM) to study the controls on the size and geometry of an individual landslide. This method allows us to analyze the temporal and spatial evolution of slope failure and landsliding from the intact, pre-failure slope to the restabilized, post-failure slope.The size of our simulated landslides reflects the amount of disintegrated material available for sliding, which is controlled by the peak strength of the slope material and to a lesser degree by the pre-failure slope angle. The observed size of natural landslides, therefore, reflects mainly the local natural material strengths. We hypothesize that the observed global characteristic landslide size is a result of the limited thickness (generally up to a few meters) of disintegrated and weathered material that exists on hillslopes, poised and ready for sliding. The primary controls on the landslide geometry, quantified as the ratio of their thickness to length t/l, prove to be the residual friction angle of the slope material and the original slope angle. The t/l is observed to be unchanged for a given initial slope angle and independent of the slope material peak strength or the slope height. We suggest that the narrow range of observed natural t/l is a result of narrow ranges of mechanical properties and initial slope geometries involved in natural slope failure.

Evaluating selected factors affecting the depth of undercutting in rocks subject to differential weathering

One of the most important considerations in designing cut slopes in sub-horizontal, inter-layered, sedimentary rocks subject to differential weathering is predicting the total depth of undercutting. Undercutting-induced rockfalls are a major problem for many roadways in Ohio. The total depth of undercutting was measured for 59 profiles from 18 cut slope sites in Ohio with references to cut faces of hard rock units containing pre-split blast-hole traces. The presence of blast hole traces ensured that the rock face represented the slope surface that was cut during construction. Additionally, initial design plans were used for reference. Step-wise regression was used to determine the geological, geotechnical, and geometrical factors that have the highest influence on the total depth of undercutting. Selected independent factors used in the regression analysis included the vertical distance of the undercut unit from the slope crest, the relative position of the undercut unit from the slope crest, the total thickness of the undercut unit, the spacing of orthogonal joints within the undercut unit, the slake durability index value of the undercutting unit, the initial slope angle, and the age of the road cut. Factors that showed the most significant correlation with the total depth of undercutting were found to be the vertical distance of the undercut unit from the slope crest, the relative position of the undercut unit from the slope crest, the total thickness of the undercut unit, joint spacing within the undercut unit, and the slake durability index of the undercutting unit. The regression analysis resulted in an R 2 value of 0.61, with the depth of undercutting correlating most strongly with a closer relative position of the undercut unit to the slope crest above it and to a closer spacing of orthogonal joints within the undercut unit. These results can be attributed to the fact that more porous and fractured rock units closer to the slope crest intercept and transport greater amounts of infiltrating groundwater, producing greater depths of undercutting. Also, closely jointed rock units are more permeable, allowing more groundwater seepage, which also leads to greater undercutting.

Travel Distance Prediction of Landslides Triggered by the M8.0 Wenchuan Earthquake

Volume and slope are two important factors affecting the runout distance of landslides. Field investigation on 46 landslides triggered by the Wenchuan earthquake show that there are positive linear correlations between the logarithmic values of landslide volume and travel distance. And there is also a positive linear relationship between the equivalent friction coefficient and tangent value of initial slope angle for the landslides. On the basis, we obtained an empirical-statistic equation between the horizontal and vertical travel distance, the volume and initial slope angle. This can provide a basis for prediction of earthquake-induced landslides.

3-D vibration analysis of circular rings with sectorial cross-sections

The free vibration characteristics of circular rings with sectorial cross-section are studied based on the three-dimensional (3-D), small strain, linear elasticity theory. The complete vibration spectrum has been obtained by using the Ritz method. A set of three-dimensional orthogonal coordinates composing of the polar coordinates (r,θ) at the origin of the sectorial cross-section and circumferential coordinate ϕ around the ring is developed to describe the variables in the analysis. Each of the displacement components is taken as a triplicate series: two Chebyshev polynomial series, respectively, about the r and θ coordinates, and a trigonometric series about the ϕ coordinate. Frequency parameters and vibration mode shapes are computed by means of the displacement-based extremum energy principle. Upper bound convergence of the first eight frequency parameters accurate to at least five significant figures is presented. The effect of radius ratio, subtended angle, and initial slope angle on frequency parameters is investigated in detail. All major modes such as flexural modes, thickness-shear modes, stretching modes, and torsional modes, etc. are presented in the paper. The present results may serve as a benchmark reference to validate the accuracy of various approximate theories and other computational techniques for the vibration of circular rings.