The ever increasing demand on land use has led to large areas of land
being considered for development, which because of past mining
activities are covered by substantial depths of fill materials. This paper
examines the problem faced with the development of land infilled with
open cast mining backfill, in predicting the behaviour of the fill upon
development. To be able to design foundations suitable to withstand the
movements that occur within open cast backfills or design a backfilling
operation that produces land suitable for a proposed after development, a
means of predicting backfill settlement is required. Factors critical to this
prediction are the timing of backfilling operations, the compactive state of
the backfill and the inundation of the backfill. The analysis of a considerable quantity of data collected from the
monitoring of backfilling operations and backfill movement at a range of
open cast coal sites located within the UK has given the authors a better
understanding of how open cast backfills behave in terms of long-term
creep settlement, collapse settlement and how these are effected by
backfill scheduling. This knowledge has been encoded into a program
running under Microsoft Windows that enables a user to make settlement
predictions for a point, a given section or area or for the whole site.
Differential settlements, critical to any development design, can also be
determined between any two points taking into consideration the
heterogeneous nature of open cast backfills. The program was tested with data from an open cast coal site in the
UK. Compaction monitoring during the placement of the backfill material
enabled a model of the backfill to be constructed taking into account
backfill properties and scheduling. This model, taken as input into the
program, enabled future backfill settlement predictions to be made. A
comparison is given between these results and actual settlements obtained
from a short-term settlement monitoring scheme.