Case study and back analysis of a residential building damaged by expansive soils

This paper presents a case study of a residential house damaged by expansive soils. The field investigation revealed that the damage was most likely caused by excessive lawn watering and leaks of sewer pipe and/or stormwater pipe, which resulted in non-uniform soil moisture conditions. Three-dimensional back analysis of this distressed structure indicated that stresses were most critical at a re-entrant corner and that steel reinforcing bars in the beam in this area had yielded. The results of the back analysis also indicated that a stronger footing was required to limit differential deflection to an acceptable level and reduce stress in the footing. The case study has clearly shown that a leaking underground water pipe and/or excessive watering of a garden could cause more severe distortion to a single storey masonry veneer house than could be expected from seasonal moisture change and the deeper moisture re-distribution caused by the imposition of the house on seasonally dry reactive soil. Moreover it has been demonstrated that it would be extremely costly to design a footing for extreme, or abnormal, moisture changes.