Natural convection from a buried pipe with a layer of backfill is numerically examined in this study. The objective of the present study is to investigate how a step change in the permeability of the backfill would affect the flow patterns and heat transfer results. Numerical calculations have covered a wide range of the governing parameters (i.e., $10⩽Ra1⩽500$ and $0.1⩽K1∕K2⩽10$) for various backfill thicknesses $(0.5⩽t∕ri⩽2)$. The results suggest that a more permeable backfill can minimize the heat loss and confine the flow to a region close to the pipe.

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