A composite backfill is described in this study

which is composed of waste foundry sand

fly ash

expanded polystyrene（EPS） bead

cement and water in designated proportions

and takes the advantage of low thermal conductivity

frost resistance and light weight.Based on the thermal resistance law and the law of ratio effective thermal conductivity

a simplified model was established

which treats the composite matrix as numerous heat transfer cubic elements which are physically contacted to transfer heat.A spherical EPS bead is centered in an element

which is surrounded by cemented earth material.Finite element（FE） analysis was conducted to simulate the heat transfer taken place through the element

and to estimate the thermal conductivity of the backfill by using ANSYS software package.It is indicated that the thermal conductivity of the backfill decreases with the increase of EPS content.The test results were well simulated by the FE results.