Summary

The physical and mechanical properties of 100 mm samples extracted from two boreholes through a spoil heap at Yorkshire Main Colliery are considered in order to determine whether or not degradation is taking place within the body of the heap. There is evidence that the aerial ropeway tip evolved in three phases and that the small variations in material properties are more readily attributable to these stages of development, rather than being a consequence of systematic degradation with the age of the spoil. Statistical treatment of consolidated-drained triaxial data and comparison with ‘fabricated’ samples (made up in the laboratory) of unweathered parental rock-types from underground imply that the shear strength of the tip samples is not changing with time. The zone of instability within which superficial movements can occur is considered to be of the same order as the depth of the erosional run-off channels, namely 3 m. Permeability tests, together with the chemistry of the groundwater show that there is restricted water movement through the body of the tip. The detailed nature of the investigations has facilitated certain preliminary conclusions to be drawn about the representability of samples.

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