Performance of Fill that Contains Organic Matter

The paper describes a case history of severe damage to a house due to the settlement of fill containing organic matter. As the organic matter in the fill decomposed, the house settled, causing 10 cm. (4 in.) of foundation differential movement. The fill settled so much that open voids developed beneath the footings and the rear yard flatwork. One‐dimensional compression tests were performed on soil samples with different percentages of organic matter, where the organic matter was allowed to decompose, and the corresponding settlement was measured. The laboratory tests indicate an empirical relationship in which percent organics equals percent settlement, for a condition of complete decomposition. The amount of settlement was similar for organic matter distributed throughout the sample or placed as one layer at the center. The detrimental effects of organics in fill include a reduction in soil density, increased compressibility during loading, and time dependent settlement as the nonhumic substances decompose and compress.