Analysis of a Failed Slope

1971 ◽  
Vol 8 (4) ◽  
pp. 596-599 ◽  
Author(s):  
S. Thomson
Keyword(s):  
Upper Cretaceous ◽  
Slip Surface ◽  
Failure Surface ◽  
Friction Angle ◽  
Western Canada ◽  
Residual Value ◽  
Clay Shales ◽  
Cohesion Parameter

In September 1963, a landslide occurred in Upper Cretaceous clay shales of Western Canada. An analysis indicated that peak strengths were being mobilized on the steeply dipping portion of the slip surface and that strengths less than peak but greater than residual were acting along the lower part of the failure surface.In March 1971, a stadia profile of the failed slope was obtained and analyzed. In the 7.5-year interval, movement increased the scarp height from 22 to 34 ft (7–10 m). The results of the analysis indicate that the cohesion parameter has tended to zero and that the friction angle has decreased toward a residual value, at least along a part of the failure surface.

scholarly journals Calculation of Active Earth Pressure for Narrow Backfill with a Curved Slip Surface

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Zhihui Wang ◽  
Aixiang Wu ◽  
Yiming Wang
Keyword(s):  
Equilibrium Equation ◽  
Slip Surface ◽  
Limit Equilibrium ◽  
Retaining Wall ◽  
Earth Pressure ◽  
Failure Surface ◽  
Friction Angle ◽  
Force Balance ◽  
Vertical Force ◽  
The Earth

A method was proposed to calculate the earth pressure from a cohesionless backfill with a high aspect ratio (ratio of height to width of retaining wall). An exponential equation of slip surface was proposed first. The proposed nonlinear slip surface equation can be obtained once the width and height of the backfill as well as the internal friction angle of the backfill were given. The failure surface from the proposed formula agreed well with the experimental slip surface. Then, the earth pressure was calculated using a simplified equilibrium equation based on the proposed slip surface. It is assumed that the minor principal stress of the backfill near the wall and at its corresponding slip surface where the depth is the same is the same. Thus, based on the vertical force balance of the horizontal backfill strip, assuming the wall-soil interface and the slip surface is in the limit equilibrium state, defined by the Mohr–Coulomb criterion, the differential equilibrium equation was obtained and numerically solved. The calculated results agreed well with the test data from the published literature.

The Edgerton Landslide

1978 ◽  
Vol 15 (4) ◽  
pp. 510-521 ◽  
Author(s):  
S. Thomson ◽  
R. W. Tweedie
Keyword(s):  
Slip Surface ◽  
Failure Surface ◽  
Strength Loss ◽  
Soil Parameters ◽  
The North ◽  
Slide Mass ◽  
Clay Shales ◽  
Field Evidence ◽  
Shearing Resistance ◽  
Gradual Loss

In September 1974 a large landslide occurred about 48 km northeast of Wainwright, Alberta. This failure presented features of interest but preslide conditions could not be reliably determined. Immediately south of this landslide a scarp some 150 m long and 0.6 m high had formed, probably contemporaneously with the failure. Field inspection suggested that this incipient failure was a sufficiently independent feature to merit detailed investigation. The major failure was termed the North Slide and the incipient failure was termed the South Slide. Collectively these slides make up the Edgerton Landslide.The failure occurred largely in flat lying, poorly indurated interbedded sandstones, siltstones, and clay shales of late Upper Cretaceous age which are overlain in the upland areas by a thin veneer of till of Wisconsin age. In the vicinity of the landslides there are many old slump areas much subdued by erosion. Field evidence indicated that the lower part of the recent failure surface had reactivated an old failure surface, whereas the scarp area represents a first time slide.The South Slide was investigated by boreholes and test pits. Samples were obtained for laboratory testing and piezometers and tiltmeters were installed in selected boreholes.The scarp increased in height and by May 1976 it was 2.3 m high. There was no sign of a toe cropping out down the slope; however, the tiltmeters became closed off successively in a downhill direction. There is strong evidence to suggest that failure is progressing from scarp to toe.Analyses of the failure indicate residual angles of shearing resistance were being mobilized along the outer pre-sheared part of the failure surface due to old landslides. The recent slip surface comprises an inward extension of this old surface and an upward portion rising at an angle of about 55° to meet with the known scarp. Along this latter portion of the recent failure surface the soil parameters yielding the most reasonable factor of safety are a peak angle of shearing resistance and a cohesion very much less than that determined from laboratory testing.It is postulated that the failure occurred due to a gradual loss of soil strength, manifested by a virtual disappearance of cohesion, with the final triggering mechanism being a springtime rise in the pore pressure within the slide mass. Factors involved in the strength loss are suggested as including deep weathering during the Tertiary, valley rebound, and old landslide activity.

Meaning, Measurement, and Field Application of Fully Softened Shear Strength of Stiff Clays and Clay Shales

2021 ◽  
Author(s):  
Gholamreza Mesri ◽  
Cai Wang ◽  
Thierno Kane
Keyword(s):  
Shear Strength ◽  
Slip Surface ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Field Application ◽  
Slope Failures ◽  
Stiff Clays ◽  
Clay Shales ◽  
First Time ◽  
Fully Softened Shear Strength

Fully softened shear strength mobilized in first-time slope failures, introduced by Skempton in 1970, corresponds to a random edge-face arrangement and interaction of clay particles in an entirely destructured fabric of stiff clays and clay shales. A series of triaxial compression tests was conducted on reconstituted normally consolidated specimens of 15 stiff clay and clay shale compositions. Based on the laboratory results an empirical correlation for secant fully softened friction angle, ϕ'fssσ'n, was developed for clay compositions with plasticity index in the range of 10 to 250%, in effective normal stress range of 10 to 700 kPa. The laboratory measurements confirm an empirical equation for fully softened shear strength in terms of parameters ϕ'fss100 and mfs. The field application of secant fully softened friction angle was examined by stability analyses of 63 first-time slope failures in 38 geologic materials. These include 45 slope failures with a segment of observed slip surface at residual condition and the back-scarp mobilizing fully softened shear strength, and 18 slope failures with entire observed slip surface at fully softened condition. The back-calculated fully softened secant friction angles for first-time slope failures are in good agreement with ϕ'fssσ'n correlation based on laboratory tests.

Convergence aspect of limit equilibrium methods for slopes

1990 ◽  
Vol 27 (1) ◽  
pp. 145-151 ◽  
Author(s):  
R. N. Chowdhury ◽  
S. Zhang
Keyword(s):  
Factor Of Safety ◽  
Slip Surface ◽  
Limit Equilibrium ◽  
Solution Process ◽  
Iterative Solution ◽  
Friction Angle ◽  
Equilibrium Analysis ◽  
Negative Slope ◽  
Slip Surfaces ◽  
Geological Discontinuity

This note is concerned with the multiplicity of solutions for the factor of safety that may be obtained on the basis of the method of slices. Discontinuities in the function for the factor of safety are discussed and the reasons for false convergence in any iterative solution process are explored, with particular reference to the well-known Bishop simplified method (circular slip surfaces) and Janbu simplified or generalized method (slip surfaces of arbitrary shape). The note emphasizes that both the solution method and the method of searching for the critical slip surface must be considered in assessing the potential for numerical difficulties and false convergence. Direct search methods for optimization (e.g., the simplex reflection method) appear to be superior to the grid search or repeated trial methods in this respect. To avoid false convergence, the initially assumed value of factor of safety F0 should be greater than β1(=−tan α1 tan [Formula: see text]) where α1 and [Formula: see text] are respectively the base inclination and internal friction angle of the first slice near the toe of a slope, the slice with the largest negative reverse inclination. A value of F0 = 1 + β1, is recommended on the basis of experience. If there is no slice with a negative slope for any of the slip surfaces generated in the automatic, search process, then any positive value of F0 will lead to true convergence for F. It is necessary to emphasize that no slip surface needs to be rejected for computational reasons except for Sarma's methods and similarly no artificial changes need to be made to the value of [Formula: see text] except for Sarma's methods. Key words: slope stability, convergence, limit equilibrium, analysis, optimization, slip surfaces, geological discontinuity, simplex reflection technique.

Seismic uplift capacity of inclined strip anchors

2005 ◽  
Vol 42 (1) ◽  
pp. 263-271 ◽  
Author(s):  
Deepankar Choudhury ◽  
K S Subba Rao
Keyword(s):  
Limit Equilibrium ◽  
Ground Surface ◽  
Failure Surface ◽  
Friction Angle ◽  
Uplift Capacity ◽  
Principle Of Superposition ◽  
Seismic Acceleration ◽  
Acceleration Coefficient ◽  
Angle Of Internal Friction ◽  
Seismic Forces

Uplift capacities of inclined strip anchors in soil with a horizontal ground surface are obtained under seismic conditions. Limit equilibrium approaches with a logarithm-spiral failure surface and pseudostatic seismic forces are adopted in the analysis. The results are presented in the form of seismic uplift capacity factors as functions of anchor inclination, embedment ratio, angle of internal friction of the soil, and horizontal and vertical seismic acceleration coefficients. The uplift capacity factors are worked out separately for cohesion, surcharge, and density components. Use of the principle of superposition for calculating anchor uplift capacity is validated. The vertical seismic acceleration coefficient always reduces the uplift capacity, whereas the horizontal seismic acceleration coefficient reduces the uplift capacity in most cases. The roles of anchor embedment ratio, soil friction angle, and anchor inclination in determination of the seismic uplift capacity are also discussed. Comparisons of the proposed method with available theories in the seismic case are also presented. The present study gives the minimum seismic uplift capacity factors compared with the existing theory.Key words: seismic uplift capacity factors, inclined strip anchors, limit equilibrium, pseudostatic, c–ϕ soil.

Ichnology and Sedimentology of a Mud-Dominated Deltaic Coast: Upper Cretaceous Alderson Member (Lea Park Fm), Western Canada

2008 ◽  
Vol 78 (12) ◽  
pp. 803-824 ◽  
Author(s):  
J. Hovikoski ◽  
R. Lemiski ◽  
M. Gingras ◽  
G. Pemberton ◽  
J. A. MacEachern
Keyword(s):  
Upper Cretaceous ◽  
Western Canada

Pseudo-Static Analysis of Slope Considering Circular Rupture Surface

2014 ◽  
Vol 5 (2) ◽  
pp. 37-43 ◽  
Author(s):  
Sima Ghosh
Keyword(s):  
Factor Of Safety ◽  
Limit Equilibrium ◽  
Slope Angle ◽  
Failure Surface ◽  
Friction Angle ◽  
Equilibrium Analysis ◽  
Seismic Slope Stability ◽  
Slide Mass ◽  
Critical Circle ◽  
Seismic Forces

In this present paper, a circular failure surface passing through the toe is assumed for a homogeneous soil, and the Fellenius line is used to locate the centre of the most critical circle. Using limit equilibrium analysis under the influence of static forces such as weight of potential slide mass and surcharge along with the pseudo-static seismic forces are considered to obtain the factor of safety of the slopes. Factor of safety is found through the application of force equilibrium. The effects of variation of different parameters like slope angle (i), soil friction angle (F) and seismic acceleration coefficients both in the horizontal and vertical directions (kh and kv respectively) on the factor of safety are presented. Finally, the present results are compared to the existing solutions available in literature and found to give minimum values of factor of safety using the present approach for seismic slope stability analysis.

An Early Cretaceous (Berriasian) fossil-bearing locality from the Rocky Mountains of Alberta, yielding the oldest dinosaur skeletal remains from western Canada

2020 ◽  
Vol 57 (4) ◽  
pp. 542-552 ◽  
Author(s):  
Ramon S. Nagesan ◽  
James A. Campbell ◽  
Jason D. Pardo ◽  
Kendra I. Lennie ◽  
Matthew J. Vavrek ◽  
...  
Keyword(s):  
North America ◽  
Early Cretaceous ◽  
Depositional Environment ◽  
Upper Cretaceous ◽  
Upper Jurassic ◽  
High Energy ◽  
Western Canada ◽  
Western North America ◽  
Terrestrial Vertebrate ◽  
Overlying Strata

Western North America preserves iconic dinosaur faunas from the Upper Jurassic and Upper Cretaceous, but this record is interrupted by an approximately 20 Myr gap with essentially no terrestrial vertebrate fossil localities. This poorly sampled interval is nonetheless important because it is thought to include a possible mass extinction, the origin of orogenic controls on dinosaur spatial distribution, and the origin of important Upper Cretaceous dinosaur taxa. Therefore, dinosaur-bearing rocks from this interval are of particular interest to vertebrate palaeontologists. In this study, we report on one such locality from Highwood Pass, Alberta. This locality has yielded a multitaxic assemblage, with the most diagnostic material identified so far including ankylosaurian osteoderms and a turtle plastron element. The fossil horizon lies within the upper part of the Pocaterra Creek Member of the Cadomin Formation (Blairmore Group). The fossils are assigned as Berriasian (earliest Cretaceous) in age, based on previous palynomorph analyses of the Pocaterra Creek Member and underlying and overlying strata. The fossils lie within numerous cross-bedded sandstone beds separated by pebble lenses. These sediments are indicative of a relatively high-energy depositional environment, and the distribution of these fossils over multiple beds indicates that they accumulated over multiple events, possibly flash floods. The fossils exhibit a range of surface weathering, having intact to heavily weathered cortices. The presence of definitive dinosaur material from near the Jurassic–Cretaceous boundary of Alberta establishes the oldest record of dinosaur body fossils in western Canada and provides a unique opportunity to study the Early Cretaceous dinosaur faunas of western North America.

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