Construction over organic soils in an urban environment: four case histories

Abstract

Four case histories relating to construction over organic soils in an urban environment are reported. Three of the cases can be classified as failures; buildings were unwittingly constructed over organic soils and the subsequent performance of the buildings was unsatisfactory. The presence of peat was recognized in the fourth case, but the design was carried out to accommodate the resulting settlements. Case history 1 deals with a small industrial mall that was founded in fill and was partially located over a peat-filled pocket. The building experienced large differential settlements, and extensive repairs consisting of piled foundations in the affected area were required. Case histories 2 and 3 concern single-family houses that were founded in fill overlying organic soils. Differential settlement caused severe damage to the houses. Repairs were required and consisted of levelling the structures on the original foundations and reducing the loads to minimize future settlements. In addition, a unique method of foundation wall reinforcement was employed in case history 2. Case history 4 documents the performance of a municipal roadway and sanitary sewer constructed over a deposit of organic materials. This sewer was designed with a flexible pipe to float within the fill over the compressible material, with provision being made for future settlement. Settlements of the road surface have been monitored. The information presented should assist the design engineer in mitigating the effects of having compressible, organic subsoils beneath structures.Key words: organic soils, peat, case histories, settlement.