R. Ulusay et V. Doyuran, CHARACTERISTICS OF A MULTIPLE RETROGRESSIVE FAILURE IN A COAL-MINE INSOUTHWEST TURKEY, Engineering geology, 36(1-2), 1993, pp. 79-89
This paper describes the geotechnical investigations and the stability
analysis of a multiple retrogressive circular failure developed throu
gh a few benches cut in deposits of a weak transition zone at a strip
coal mining area, southwest Turkey. The instability was analyzed to un
derstand the possible causes of failure and to determine mobilized she
ar strength at the time of failure through the use of back analysis. G
eotechnical investigations comprised geological mapping, review of dri
ll core and groundwater data, sampling and laboratory testing, and bac
k analysis of the failure. The failed material is essentially composed
of poorly consolidated claystone, which is a clay in engineering term
s, and minor amounts of clayey silts. To evaluate the shear strength p
arameters mobilized during failure, drained soil shear tests were carr
ied out on specimens taken from potential failure surface materials. B
ased on the results of the back analysis performed for various conditi
ons and using the held observations, actual failure surfaces were defi
ned by successive slip surfaces developing from the toe and advancing
to the crest of the slope. The analysis also indicated that the instab
ility was initiated by the construction of steep and high benches in t
he transition zone deposits. It was further noted that there is a good
agreement between the laboratory-derived residual shear strength para
meters and the results of back analysis. The results of the stability
analyses performed to determine safe side slopes in the transition zon
e are also presented.