The shear strength of clay-filled bedding planes in limestones ? back-analysis of a slope failure in a phosphate mine, Israel

1997 ◽  
Vol 15 (4) ◽  
pp. 263-282 ◽  
Author(s):  
Y. H. Hatzor ◽  
M. Levin
2001 ◽  
Vol 38 (4) ◽  
pp. 828-849 ◽  
Author(s):  
Ergün Tuncay ◽  
Resat Ulusay

This paper describes the investigation of a large and progressive slope failure in the south sidewall of the Himmetoglu coal mine in northwest Turkey. A number of slope instabilities leading to interruptions in mining have been experienced at the mine. Geotechnical investigations consisted of structural mapping, observations of instabilities, review of detailed groundwater information, long-term monitoring of slope movement, and back-analysis of the various failure modes. Deterministic and probabilistic approaches based on the limiting-equilibrium method were employed to examine various slope profiles and excavation sequences for achieving better stability conditions. Analysis of the movement monitoring records and geotechnical information indicated that the failure of the south sidewall slope developed by a combination of sliding along the bedding planes in the hanging wall and faults in the mode of multiplanar sliding. The movement history and the results from the back-analysis of the failures revealed that the stability of the slope was highly sensitive to changes in the length of the lower part of the sliding surface, and the shear strength reduced to residual values along the discontinuity surfaces 8-10 m above the coal seam at the time of failure. The results of the analysis both from deterministic and probabilistic approaches suggest that an excavation sequence consisting of a number of stripping stages from the uppermost benches and advancing to the toe of the slope may provide the resistance to stabilize the overall slope. Simple and preliminary economic assessments based on the overburden costs in conjunction with the deterministic and probabilistic approaches are briefly discussed.Key words: back-analysis, deterministic approach, Himmetoglu coalfield, monitoring, multiplanar failure, probabilistic approach, shear strength, slope stability.


1989 ◽  
Vol 26 (2) ◽  
pp. 227-234 ◽  
Author(s):  
D. M. Cruden ◽  
S. Thomson ◽  
P. C. Tsui

This first detailed report of the geotechnical characteristics of ice-thrust soft rock examines Upper Cretaceous, once heavily overconsolidated mudstones in the Highvale coal mine, Alberta. The fissured and brecciated sample from an ice-thrust shear zone in the mine behaves as a lightly overconsolidated sediment in laboratory tests and shows a non-brittle mode of shear deformation with a maximum shear strength close to residual. This behaviour is due to weathering and glaciotectonic deformation, which have jointed, sheared, and remoulded the mudstone, thus eliminating the fabric formed by overconsolidation.In the ice-thrust mudstone, platy clay minerals dominate and have been grouped into aggregations or shear-remoulded matrices. The strength of the brecciated portion of the mudstone ranges from peak to residual. The strength along principal displacement shears is at or close to residual, as back analysis of a slope failure shows. Key words: ice-thrust shear zone, glaciotectonic deformation, consolidation, nonbrittle deformation, principal displacement shears, shear strength.


Author(s):  
Andrew Lees ◽  
Michael Dobie

Polymer geogrid reinforced soil retaining walls have become commonplace, with routine design generally carried out by limiting equilibrium methods. Finite element analysis (FEA) is becoming more widely used to assess the likely deformation behavior of these structures, although in many cases such analyses over-predict deformation compared with monitored structures. Back-analysis of unit tests and instrumented walls improves the techniques and models used in FEA to represent the soil fill, reinforcement and composite behavior caused by the stabilization effect of the geogrid apertures on the soil particles. This composite behavior is most representatively modeled as enhanced soil shear strength. The back-analysis of two test cases provides valuable insight into the benefits of this approach. In the first case, a unit cell was set up such that one side could yield thereby reaching the active earth pressure state. Using FEA a test without geogrid was modeled to help establish appropriate soil parameters. These parameters were then used to back-analyze a test with geogrid present. Simply using the tensile properties of the geogrid over-predicted the yield pressure but using an enhanced soil shear strength gave a satisfactory comparison with the measured result. In the second case a trial retaining wall was back-analyzed to investigate both deformation and failure, the failure induced by cutting the geogrid after construction using heated wires. The closest fit to the actual deformation and failure behavior was provided by using enhanced fill shear strength.


2021 ◽  
Vol 13 (23) ◽  
pp. 13452
Author(s):  
Kuo-Shih Shao ◽  
An-Jui Li ◽  
Chee-Nan Chen ◽  
Chen-Hsien Chung ◽  
Ching-Fang Lee ◽  
...  

This study presents the case of a landslide triggered by a high groundwater level caused by several days of continuous rainfall in the northeastern region of Taiwan. The slope where this landslide occurred consists of closely jointed and weathered bedrock. By means of finite element limit analysis and the Hoek–Brown failure criterion, this study performed a slope failure simulation similar to the actual landslide and deduced the reasonable value range for the combination of key Hoek–Brown failure criterion parameters through back analyses. The results indicate that the key parameters affecting the bedrock’s slope stability were the geological strength index (GSI) and the disturbance factor (D), whereas the effects of the unconfined compressive strength (σci) were less significant. The results of the back analysis reveal that the suitable D-value range and GSI of closely jointed and weathered sandstone in the northeastern region of Taiwan are 0.8 to 0.9 and 20 to 30, respectively. These back-analyzed value ranges can serve as a reference for broader applications in the preliminary stability analysis of similar rock slopes where it is difficult to perform in situ investigation.


1992 ◽  
Vol 29 (1) ◽  
pp. 94-102 ◽  
Author(s):  
R. N. Chowdhury

Understanding of progressive failure of slopes is of immense interest to geotechnical engineers and others concerned with the occurrence of landslides. One important aspect of research is the development of relevant analytical and numerical techniques. Both deterministic and probabilistic approaches can be used to study the development of progressive failure, provided valid geomechanics models form the basis of such studies. In this paper the risk of failure is simulated within a probabilistic framework. Of particular interest is the increase in the probability of failure, as overstress (and consequent localized failure) is considered to have actually occurred over an increasing proportion of a slip surface within the slope. The perception or interpretation of local failure is often based on observational data from surface measurements and subsurface instrumentation. Knowledge of spatial progression of failure may similarly be based on indirect and direct evidence. In the proposed simulation process the peak and residual shear strength of the slope material are regarded as one-dimensional random fields, and therefore spatial variability of each parameter is taken into consideration. Key words : analysis, clays, failure, shear strength, slopes, stability, landslides, probabilistic analysis, reliability analysis, progressive failure, slip surfaces, risk simulation, statistical analysis.


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