ENGINEERING GEOLOGICAL CHARACTERIZATION OF COAL-MINE WASTE MATERIAL AND AN EVALUATION IN THE CONTEXT OF BACK-ANALYSIS OF SPOIL PILE INSTABILITIES IN A STRIP MINE, SW TURKEY
R. Ulusay et al., ENGINEERING GEOLOGICAL CHARACTERIZATION OF COAL-MINE WASTE MATERIAL AND AN EVALUATION IN THE CONTEXT OF BACK-ANALYSIS OF SPOIL PILE INSTABILITIES IN A STRIP MINE, SW TURKEY, Engineering geology, 40(1-2), 1995, pp. 77-101
Coal mine waste material, which usually consists of a mixture of coars
e-grained particles to rock fragments grading to fine-grained particle
s, causes geotechnical and environmental problems on disposal. A study
of the geotechnical aspects of the problem is, therefore, important i
n rational planning for the disposal, reclamation, treatment and use o
f such material. Spoil pile instability has been a continuing problem
in the Eskihisar strip coal mine of southwestern Turkey. Particularly
shallow-seated circular failures appearing along the haul road and ins
tabilities covering large agricultural areas outside the dumping yard
increase the importance of spoil pile stability. The fact that the hei
ght of spoil piles dumped by trucks on both sides of the haul road wil
l increase much more in the future has focused the attention of the mi
ners to this problem. This study outlines the geotechnical characteris
tics of waste material from the Tertiary coal-bearing rocks derived fr
om field and laboratory investigations, and describes the causes and m
echanism of spoil instabilities which threaten the safety of the haul
road and the agricultural areas in the vicinity of the pit. Gradation
results suggest that fines and coarser material were approximately equ
ally represented in the spoil. The percentage of fines is indicative o
f material degradation as evidenced by slaking tests. Site observation
s and numerous back analysis of investigated failures reveal that the
failures do not penetrate the foundation material and only occur along
circular surfaces through the spoil material. It is also noted that s
urface water infiltration, reducing the effective shear strength of th
e spoil material, contributes to failures. Shear test results indicate
that the spoil is a nearly cohesionless material with a residual inte
rnal friction angle of about 33 degrees, which confirms the values der
ived from standard penetration tests. It is also noted from back analy
ses that the spoil material exhibits a shear strength at or approachin
g the residual value at the time of failure. The use of shear strength
parameters defined by the linear Mohr-Coulomb envelope yields results
that are comparable with those obtained when the non-linear failure e
nvelope is used, provided that such strength parameters were de fined
at the operating normal stress levels on the failure surfaces.