scholarly journals Refinements to the stability index for skier-triggered dry-slab avalanches

1998 ◽  
Vol 26 ◽  
pp. 296-302 ◽  
Author(s):  
J.B. Jamieson ◽  
C.D. Johnston
Keyword(s):  
Shear Strength ◽  
Normal Load ◽  
Stability Index ◽  
Weak Layer ◽  
Induced Stress ◽  
Using Data ◽  
The Stability ◽  
Shear Frame ◽  
Stability Indices

Stability indices for skier-triggering of slab avalanches are discussed in terms of an adjustment to the skier-induced stress to allow for ski penetration and an adjustment to shear strength (measured with a shear frame) to allow for normal load due to the slab overlying the weak layer. The proposed adjustment to shear strength depends on the microstructure of the weak layer. These adjustments are incorporated into a refinement of the previously established Swiss stability index for skier-triggering. The percentage of correct predictions for the Swiss and refined indices are evaluated using data from 115 weak layers on skier-tested avalanche slopes, 83 of which were classified as persistent weak layers of surface hoar, faceted crystals or depth hoar and 32 as non-persistent weak layers. The refined index reduces the number of incorrectly predicted slab avalanches for the persistent weak layers.

scholarly journals Refinements to the stability index for skier-triggered dry-slab avalanches

1998 ◽  
Vol 26 ◽  
pp. 296-302 ◽  
Author(s):  
J.B. Jamieson ◽  
C.D. Johnston
Keyword(s):  
Shear Strength ◽  
Normal Load ◽  
Stability Index ◽  
Weak Layer ◽  
Induced Stress ◽  
Using Data ◽  
The Stability ◽  
Shear Frame ◽  
Stability Indices

Stability indices for skier-triggering of slab avalanches are discussed in terms of an adjustment to the skier-induced stress to allow for ski penetration and an adjustment to shear strength (measured with a shear frame) to allow for normal load due to the slab overlying the weak layer. The proposed adjustment to shear strength depends on the microstructure of the weak layer. These adjustments are incorporated into a refinement of the previously established Swiss stability index for skier-triggering. The percentage of correct predictions for the Swiss and refined indices are evaluated using data from 115 weak layers on skier-tested avalanche slopes, 83 of which were classified as persistent weak layers of surface hoar, faceted crystals or depth hoar and 32 as non-persistent weak layers. The refined index reduces the number of incorrectly predicted slab avalanches for the persistent weak layers.

scholarly journals Shear frame stability parameters for large-scale avalanche forecasting

1993 ◽  
Vol 18 ◽  
pp. 268-273 ◽  
Author(s):  
J.B. Jamieson ◽  
C.D. Johnston
Keyword(s):  
Shear Strength ◽  
Large Scale ◽  
Normal Load ◽  
Meteorological Data ◽  
Stability Index ◽  
Stability Parameter ◽  
Stability Parameters ◽  
Avalanche Forecasting ◽  
Study Plot ◽  
Shear Frame

During the winters of 1990, 1991 and 1992, a field study of stability parameters for forecasting slab avalanches was conducted in the Cariboo and Monashee mountains of western Canada. In a level study plot at 1900 m and on nearby slopes, the shear strength of the weak snowpack layer judged most likely to cause slab avalanches was measured with a 0.025 m2 shear frame and a force gauge. Based on the ratio of shear strength to stress due to the snow load overlying the weak layer, a simple stability parameter and a more theoretically based stability index which corrects the strength for normal load were calculated. These stability parameters are compared with avalanche activity reported for the same day within approximately 30 km of the study plot. Each stability parameter is assessed on the basis of the number of days that it successfully predicted one or more potentially harmful avalanches and the number of days that it successfully predicted no potentially harmful avalanches. Both parameters predicted correctly on at least 75% of the 70 days they were evaluated. The simpler empirical stability parameter worked as well as the one that corrects strength for normal load. For large-scale forecasting of dry-snow slab avalanches, shear frame stability parameters appear to be a useful addition to meteorological data, snowpack observations and slope tests.

scholarly journals Shear frame stability parameters for large-scale avalanche forecasting

1993 ◽  
Vol 18 ◽  
pp. 268-273 ◽  
Author(s):  
J.B. Jamieson ◽  
C.D. Johnston
Keyword(s):  
Shear Strength ◽  
Large Scale ◽  
Normal Load ◽  
Meteorological Data ◽  
Stability Index ◽  
Stability Parameter ◽  
Stability Parameters ◽  
Avalanche Forecasting ◽  
Study Plot ◽  
Shear Frame

During the winters of 1990, 1991 and 1992, a field study of stability parameters for forecasting slab avalanches was conducted in the Cariboo and Monashee mountains of western Canada. In a level study plot at 1900 m and on nearby slopes, the shear strength of the weak snowpack layer judged most likely to cause slab avalanches was measured with a 0.025 m2 shear frame and a force gauge. Based on the ratio of shear strength to stress due to the snow load overlying the weak layer, a simple stability parameter and a more theoretically based stability index which corrects the strength for normal load were calculated. These stability parameters are compared with avalanche activity reported for the same day within approximately 30 km of the study plot. Each stability parameter is assessed on the basis of the number of days that it successfully predicted one or more potentially harmful avalanches and the number of days that it successfully predicted no potentially harmful avalanches. Both parameters predicted correctly on at least 75% of the 70 days they were evaluated. The simpler empirical stability parameter worked as well as the one that corrects strength for normal load. For large-scale forecasting of dry-snow slab avalanches, shear frame stability parameters appear to be a useful addition to meteorological data, snowpack observations and slope tests.

scholarly journals Snow instability evaluation: calculating the skier-induced stress in a multi-layered snowpack

2016 ◽  
Vol 16 (3) ◽  
pp. 775-788 ◽  
Author(s):  
Fabiano Monti ◽  
Johan Gaume ◽  
Alec van Herwijnen ◽  
Jürg Schweizer
Keyword(s):  
Crack Propagation ◽  
Snow Cover ◽  
Stability Index ◽  
Elastic Half Space ◽  
Average Density ◽  
Additional Stress ◽  
New Approach ◽  
Weak Layer ◽  
Failure Initiation ◽  
Induced Stress

Abstract. The process of dry-snow slab avalanche formation can be divided into two phases: failure initiation and crack propagation. Several approaches tried to quantify slab avalanche release probability in terms of failure initiation based on shear stress and strength. Though it is known that both the properties of the weak layer and the slab play a major role in avalanche release, most previous approaches only considered slab properties in terms of slab depth, average density and skier penetration. For example, for the skier stability index, the additional stress (e.g. due to a skier) at the depth of the weak layer is calculated by assuming that the snow cover can be considered a semi-infinite, elastic, half-space. We suggest a new approach based on a simplification of the multi-layered elasticity theory in order to easily compute the additional stress due to a skier at the depth of the weak layer, taking into account the layering of the snow slab and the substratum. We first tested the proposed approach on simplified snow profiles, then on manually observed snow profiles including a stability test and, finally, on simulated snow profiles. Our simple approach reproduced the additional stress obtained by finite element simulations for the simplified profiles well – except that the sequence of layering in the slab cannot be replicated. Once implemented into the classical skier stability index and applied to manually observed snow profiles classified into different stability classes, the classification accuracy improved with the new approach. Finally, we implemented the refined skier stability index into the 1–D snow cover model SNOWPACK. The two study cases presented in this paper showed promising results even though further verification is still needed. In the future, we intend to implement the proposed approach for describing skier-induced stress within a multi-layered snowpack into more complex models which take into account not only failure initiation but also crack propagation.

scholarly journals A Recommendation for the Application of the Roch Index for Slab Avalanche Release

1979 ◽  
Vol 22 (88) ◽  
pp. 547-549 ◽  
Author(s):  
R. A. Sommerfeld ◽  
R. M. King
Keyword(s):  
Shear Strength ◽  
Stability Index ◽  
Slope Instability ◽  
Weak Layer ◽  
Statistical Correction

AbstractDetailed measurements on several avalanches verify that a Daniels’ (1945) type statistical correction to Roch’s (1966) stability index would accurately predict snow-slope instability. It is recommended that one-half the median of at least 50 shear-strength measurements be used as a measure of the strength of a weak layer.

scholarly journals Voltage Collapse Prediction of IEEE 30-Bus system

2021 ◽  
Vol 28 (1) ◽  
pp. 98-112
Author(s):  
Mohammed Ibrahim ◽  
Abdulsattar Jasim
Keyword(s):  
Power System ◽  
Modal Analysis ◽  
Voltage Stability ◽  
Stability Index ◽  
Maximum Load ◽  
Voltage Collapse ◽  
Analysis Method ◽  
The Stability ◽  
Stability Indices ◽  
Participation Factor

Voltage collapse in the power system occurs as a result of voltage instability, thus which lead to a blackout, and this is a constant concern for network workers and customers alike. In this paper, voltage collapse is studied using two approved methods: the modal analysis method and voltage stability indices. In the modal analysis method, the eigenvalues were calculated for all the load buses, through which it is possible to know the stability of the power system, The participation factor was also calculated for the load buses, which enables us to know the weakest buses in the system. As for the Voltage stability Indices method, two important indices were calculated, which are: Fast Voltage Stability Index (FVSI) and Line stability index (Lmn). These two indices give a good visualization of the stability of the system and the knowledge of the weakest buses, as well as the Maximum load-ability of the load buses. The above mentioned two methods were applied using software code using MATLAB \ R2018a program to the IEEE 30-Bus test system. In the modal analysis, the buses which have the maximum participation factor are 26, 29, and 30 this indicates that they are the weakest in the system. as well as in the voltage stability indices. These buses have the lowest maximum load ability which demonstrates the possibility of using both methods or one of them to study the voltage collapse.

scholarly journals Evaluation of the shear frame test for weak snowpack layers

2001 ◽  
Vol 32 ◽  
pp. 59-69 ◽  
Author(s):  
Bruce Jamieson ◽  
Colin D. Johnston
Keyword(s):  
Shear Strength ◽  
Stress Concentrations ◽  
Weak Layer ◽  
Fracture Surfaces ◽  
Strength Change ◽  
Coefficients Of Variation ◽  
Significant Difference ◽  
Metal Frame ◽  
The Mean ◽  
Shear Frame

AbstractThe shear frame allows testing of thin weak snowpack layers that are often critical for slab avalanche release. A shear metal frame with an area of 0.01–0.05 m2 is used to grip the snow a few mm above a buried weak snowpack layer. Using a force gauge, the frame is pulled until a fracture occurs in the weak layer within 1 s. The strength is calculated from the maximum force divided by the area of the frame. Finite-element studies show that the shear stress in the weak layer is concentrated below the cross-members that subdivide the frame and where the weak layer is notched at the front and back of the frame. Placing the bottom of the frame in the weak layer increases the stress concentrations, and results in significantly lower strength measurements than placing the bottom of the frame a few mm above the weak layer. Based on over 800 sets of 7–12 tests in western Canada, coefficients of variation average 14% and 18% from level study plots and avalanche start zones, respectively. Consequently,sets of 12 tests typically yield a precision of the mean of 10% with 95% confidence, which is sufficient for monitoring of strength change of weak layers over time in study plots. With consistent technique, there is no significant difference in mean strength measurements obtained by different experienced shear frame operators using the same approximate loading rate and technique for placing the frame. Although fracture surfaces are usually planar, only one of eleven shapes of non-planar fracture surfaces showed significantly different strength compared to planar fracture surfaces. For weak layers thick enough for density measurements, the shear strength is plotted against density and grain form. From these data, empirical equations are determined to estimate the shear strength of weak snowpack layers.

scholarly journals A Recommendation for the Application of the Roch Index for Slab Avalanche Release

1979 ◽  
Vol 22 (88) ◽  
pp. 547-549 ◽  
Author(s):  
R. A. Sommerfeld ◽  
R. M. King
Keyword(s):  
Shear Strength ◽  
Stability Index ◽  
Slope Instability ◽  
Weak Layer ◽  
Statistical Correction

AbstractDetailed measurements on several avalanches verify that a Daniels’ (1945) type statistical correction to Roch’s (1966) stability index would accurately predict snow-slope instability. It is recommended that one-half the median of at least 50 shear-strength measurements be used as a measure of the strength of a weak layer.

scholarly journals Snow instability evaluation: calculating the skier-induced stress in a multi-layered snowpack

2015 ◽  
Vol 3 (8) ◽  
pp. 4833-4869
Author(s):  
F. Monti ◽  
J. Gaume ◽  
A. van Herwijnen ◽  
J. Schweizer
Keyword(s):  
Crack Propagation ◽  
Snow Cover ◽  
Stability Index ◽  
Elastic Half Space ◽  
Average Density ◽  
Additional Stress ◽  
New Approach ◽  
Weak Layer ◽  
Failure Initiation ◽  
Induced Stress

Abstract. The process of dry-snow slab avalanche formation can be divided into two phases: failure initiation and crack propagation. Several approaches tried to quantify slab avalanche release probability in terms of failure initiation based on shear stress and strength. Though it is known that both the properties of the weak layer and the slab play a major role in avalanche release, most previous approaches only considered slab properties in terms of slab depth, average density and skier penetration. For example, for the skier stability index, the additional stress (e.g. due to a skier) at the depth of the weak layer is calculated by assuming that the snow cover can be considered a semi-infinite, elastic half-space. We suggest a new approach based on a simplification of the multi-layered elasticity theory in order to easily compute the additional stress due to a skier at the depth of the weak layer taking into account the layering of the snow slab and the substratum. We first tested the proposed approach on simplified snow profiles, then on manually observed snow profiles including a stability test and, finally, on simulated snow profiles. Our simple approach well reproduced the additional stress obtained by finite element simulations for the simplified profiles – except that the sequence of layering in the slab cannot be replicated. Once implemented into the classical skier stability index and applied to manually observed snow profiles classified into different stability classes, the classification accuracy improved with the new approach. Finally, we implemented the refined skier stability index into the 1-D snow cover model SNOWPACK. For the two study cases presented in this paper, this approach showed promising results even though further verification is still needed. In the future, we intend to implement the proposed approach for describing skier-induced stress within a multi-layered snowpack into more complex models which take into account not only failure initiation but also crack propagation.

scholarly journals The influences of temperature and normal load on the shear strength of snow consisting of precipitation particles

2012 ◽  
Vol 53 (61) ◽  
pp. 31-38 ◽  
Author(s):  
Hiroki Matsushita ◽  
Masaru Matsuzawa ◽  
Osamu Abe
Keyword(s):  
Shear Strength ◽  
Normal Load ◽  
Temporal Variations ◽  
Dendritic Morphology ◽  
Rate Of Increase ◽  
Different Depths ◽  
Snow Crystals ◽  
Coulomb Failure Criterion ◽  
Shear Frame ◽  
Over Time

AbstractAn experiment using artificial snow was conducted to clarify the influences of temperature and normal load on temporal variations in the shear strength of snow. Artificial snow consisting of dendritic crystals was allowed to accumulate to ∼60 cm depth for the experiment. The shear strength, temperature and weight of the overlying snow were measured at three different depths in the accumulated snow. For the measurement of shear strength, the shear frame index (SFI) was found using a shear frame by placing weights with different masses on the snow contained within the frame. The measured SFI values were treated with the Mohr–Coulomb failure criterion to find the snow cohesion factor C and the internal friction factor tanϕ. The results highlighted similar trends for SFI and C values by which their rate of increase over time was greater with higher snow temperatures and normal load caused by overlying snow. This indicates that C contributes significantly to increased SFI values. tanϕ decreased over time with higher snow temperatures and increased with lower snow temperatures. In low-temperature conditions, in particular, it is likely that snow crystals are compacted but maintain their dendritic morphology.

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