Case Study of Movement and Damage to a Residential Building Founded on Expansive Clays
This paper presents a case study of a residential house damaged by expansive soils. The field investigation revealed that the damage was caused by a combination of sewer pipe leak and stormwater leak. A back-analysis procedure using finite-element analysi
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CASE STUDY OF MOVEMENT AND DAMAGE TO A RESIDENTIAL BUILDING FOUNDED ON EXPANSIVE CLAYS Jie Li School ofCivil, Environmental and Chemical Engineering, RMIT University Melbourne, Victoria, 3001, Australia This paper presents a case study of a residential house damaged by expansive soils. The field investigation revealed that the damage was caused by a combination of sewer pipe leak and stormwater leak. A back-analysis procedure using finite-element analysis is presented that is based the measured slab surface levels. The results of the back-analysis indicated that a stronger footing was required to limit differential deflection and stress level in footing to an acceptable level, INTRODUCTION Damage to lightly loaded structure s founded on expansive soils has been widely reported throughout the world. Expansive soil is predominantly clay soil, which undergoes apprec iable volume change following change in moisture content. This volume change occurs as shrinkage upon drying, and swelling upon wetting . Buildings constructed on expansive soils may be subj ected to severe movement arising from non-uniform soil moisture changes. Consequently the distortion may be manifested as cracking of walls and possibly loss of function of doors and window s. Over the last 40 years or so, a great effort has been devoted to method s of analysing and designing structural footing systems on expansive soils. However, there are a number of cases where residential structures have experienced significant cracking despite engineering design that conforms to the Australia Standard for residential footing design. Therefore, more research is needed to get a better understanding of the problem and to improve the current design approach. In this study, the field investigation and back analysis of a cracked residential building were carried out. The back-analysis procedure was based on the three-dimensional finite element method and floor slab levels obtained from a level survey of the deformed structure. The purposes of this case study are to determine the causes of deformation and cracking and to find out how failure could have been prevented . This paper presents the results of the case study . Site Investigation The case study described herein refers to a single storey articulated masonry veneer dwelling built on a highly expansive soil foundation . The house was constructed in March 1986 in a
northern suburb of Adelaide. Three boreholes were drilled at the site before construction to evaluate the soil reactivity. The site classification for reactivity following the Australian Standard for Residential Slab and Footings (AS2870, 1996) was Class E (i.e., extremely reactive). The footing layout is shown in Figure 1. The external beams were 300 mm wide by 950 mm deep reinforced with 8N16 rods, 4 at the top and 4 at the bottom. The internal beams were 250 mm wide by 950 mm deep reinforced with 6N 16 rods, 3 top and 3 bottom. The slab was 100 mm thick and was reinforced with F62 mesh placed 25 mm from the top surface of the slab. 0 0
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