ULTIMATE STRENGTH OF RAMMED EARTH WALLS WITH OPENINGS

Rammed earth (pise) produced from naturally occurring and readily accessible lateritic soil is used in some developing countries to provide walls in low-cost housing and similar developments, mostly of one or two storeys. Such structures can readily be produced by manual compaction of moistened laterite between vertical formwork, using simple tools. Current interest lies in understanding the properties of rammed earth and improving its strength and durability when used to form load-bearing walls. Experimental tests have been undertaken to investigate the behaviour and ultimate strength of rammed earth, For these tests, 5 t of each of four different types of lateritic soil were transported from Ghana for testing at Newcastle. The ultimate strength of cubes of rammed earth were determined at different ages, using a controlled method of construction and testing, This strength increased within the first 7 days to about 2 N/mm(2), although in some cases this reduced to about 1 . 8 N/mm(2) after 28 days. The ultimate strength of rammed earth walls with substantial openings (as might be provided for windows and doors) suggested that a safety factor ranging between 8 and 40 would exist under conditions of normal domestic use. Although no clear failure mechanism could be identified in walls with curved or pointed arched openings, these were generally stronger than walls with rectangular openings, which generally failed in a consistent manner, Steel bars used as Engineering, reinforcement within walls with rectangular openings of lar openings did not appear to increase the ultimate strength, although they served to localize damage under failure conditions. Lightweight material falling from the soffit of an opening in a rammed earth wall gave a visual indication of imminent collapse. Tests have shown that deformations within rammed earth under substantial maintained load are likely to continue for at least seven weeks from the time of application, although about 80% of the final deformation is likely to occur within two weeks.