EVALUATION OF POPLAR-WOOD CHIPS AFTER 19 YEARS OF BURIAL AS SWAMP ROADWAY FILL

Wood chip fill material from a highway shoulder-widening in northern M innesota was evaluated by a variety of physical tests after 19 years o f burial. Chips discolored when excavated (typical tannate oxidation r eaction) and remained gray on air-drying. Chips from the shallow layer burial sites were essentially sound if collected just beneath the cla y cap and approximated sound chips in moisture level, bulk density, an d specific gravity, but were slightly less acidic than fresh aspen/bal sam poplar, Those chips collected near the sphagnum peat base (50 cm d own from clay) were somewhat soft on the surface and broke easily on b ending. These chips had notably higher moisture contents at collection and lower specific gravities than those from the clay cap zone. Micro scopic examination of chips noted extensive pitting and erosion of woo d fiber walls and destruction of wood parenchyma (storage) cells consi stent with attack by bacteria known to develop in waterlogged wood wit h limited oxygen available. Chips from a thicker fill layer design fol lowed this pattern for one collection site, (i.e., sound chips at uppe r level under clay cap; degraded chips near peat, 150 cm from clay), b ut chips at upper and lower levels were basically sound at the second collection location. Though chips did have different moisture-holding capacities, their overall bulk density was essentially the same for lo cations within each site. Absence of fungal degradation is attributed to lack of oxygen rather than limitations of pH, water, or nutrients. These data support use of wood chips for lightweight fill of roadways in swamps.