SOIL-STRUCTURE INTERFACE BEHAVIOR OF CEMENTED- PASTE BACKFILL MATERIAL MIXED WITH MINING WASTE

Abstract

The use of mining wastes as a component of cemented paste backfill provides an
environmentally acceptable method of waste disposal at a lesser cost as the method does not require tailing
dams for storing the large volume of wastes. This study determines the applicability of cemented-paste
backfill materials mixed with aggregate quarry wastes as ground support to concrete structures. Aggregate
quarry waste with varying fine contents was used as a substitute for sand in cemented-paste backfill and the
mixture was referred to as cemented-paste tailing backfill (CPTB). Its micro fabric structure was determined
through SEM-EDX tests. Test results showed that CPTB with 20% and 40% fine contents has acceptable
values of strength properties in terms of its unconfined compressive strength and interface friction angle.
The unconfined compressive strength in relation to its curing period is in the range of 120 kPa to 150 kPa
which can be described as having stiff consistency. The stress-strain interface behavior between CPTB and
concrete structure was evaluated through a direct shear test using strain rates that simulate the rapid and slow
rates of loading. In both conditions, the stress-strain behavior exhibits strain softening. The average interface
friction angle is 38o which can be associated with its dense condition. The modified hyperbolic model was
applied to evaluate the soil-structure interface behavior of CPTB. Hyperbolic parameters were formulated to
predict the interface shear stress - shear strain behavior of the CPTB when in contact with concretes structure
at any value of shear strain and normal effective stress.