Soil development on colliery waste tips in relation to age. I. Introduction and physical factors. II. Chemical factors.
Chronological changes in the physical composition of colliery waste were studied on nine tips of ages 0-178 years, in the Somerset Coalfield.Surface instability persisted over 178 years and always exceeded that found on a natural soil slope, but gully erosion was eliminated after 45 years.Spoil particle sizes decreased rapidly at the surface, but only to a small extent at 20-cm depths.Coal-like material initially comprised 53.62% of the total waste, but decreased to 2.45% at the surface after 55 years.A pronounced vertical stratification of the colliery waste developed within 21 years. The chemical composition of the parent rock was similar on all tips.Calcium and magnesium concentration increased with time, but pH decreased from 9.02 to 2.99 within five years, then rose gradually to pH 6.73 by 178 years.Sulphate content closely followed the changes in pH. Phosphate content followed a trend which was the reverse of sulphate. Organic matter increased from 0.79 to 6.25% within 98 years.It is suggested that coal may be an initial source of nitrogen in the spoil.