Effect of Reinforcement on Multi-tiered Fly Ash Wall

Fly ash is a by-product formed by the burning of coal in thermal power plants. In India, the generation of fly ash in the year 2014 to 2015 was 184.14 million tons. However, only 55.69% of the total fly ash was utilized. The disposal of fly ash is a major environmental concern. The present study aims at utilizing fly ash as backfill for the wall in a tiered configuration. A multi-tiered wall is a soil wall constructed in tiered configuration by providing offset at different elevations of the wall. The behaviour of multi-tiered wall is essentially affected by the critical offset distance which can be defined as the length of the offset beyond which the tiers of the multi-tiered fly ash wall start behaving as individual walls and there is limited interaction between the two tiers. There are very few studies on multi-tiered walls investigated by using laboratory model tests. Also, the studies of the behaviour of tiered walls utilizing industrial waste such as fly ash are limited. In the present study, laboratory model tests were conducted utilizing fly ash as backfill material and jute geotextile as reinforcement under strip loading. The two-tiered wall was modelled and the offset distance was varied as 0, 0.2L, 0.4L and 0.6L, where L is defined as the height of lower tier. The length of reinforcement was taken as 0.7H where H is the total height of the wall. Unreinforced and reinforced models were tested to determine critical offset distance, the effect of offset distance and reinforcement on different parameters governing the design of the tiered wall. From the observed failure pattern of model tests, it was found that inclusion of reinforcement increases the critical offset distance. The critical offset distance was found to be 0.4 times the height of lower tier for the unreinforced model and 0.6 times the height of lower tier for the reinforced model. The inclusion of reinforcement also reduces the horizontal wall facia displacement. Decrease in wall facia displacement was also observed with increase in the offset distance.