Characterization of coarse soils derived from igneous rocks for rammed earth

• Published in: Engineering geology Vol. 228; pp. 137 - 145
• Main Authors: Lin, Hongjie, Zheng, Shuang, Lourenço, Sérgio D.N., Jaquin, Paul
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 13.10.2017
• Subjects: Coarse soils; Hong Kong; Particle-scale studies; Rammed earth; Particle-scale studies; Hong Kong; Rammed earth; Coarse soils
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2017.08.003

Rammed earth refers to a conventional construction method as well as a material comprising gravel, sand and fine soil. There has been an increasing interest due to it being a sustainable and environmentally friendly material. The strength of rammed earth depends on the material and environment (e.g. temperature and relative humidity). While rammed earth is an established and accepted construction material in some countries (e.g. Australia and New Zealand), its use in South China is mostly related to historical structures of which the UNESCO Tulou buildings in Fujian Province is an example. In addition, South China has a sub-tropical climate with a distinctive rainy, humid and hot season followed by a dry and cool season, and soils are granular due to the underlying igneous geology. With a coarse fraction (sand and gravel) in excess of 80%, their appropriateness as earthen materials is, at first sight, debatable. This paper aims to assess the pertinence of three representative soils from Hong Kong (residual soil, alluvium and completely decomposed granite) for unstabilised rammed earth. Unconfined compressive strength tests and shrinkage measurements at different relative humidity, as well as the organics content are determined. To aid the interpretation of the strength and shrinkage data, a fundamental characterization is conducted, namely of the wettability and particle attributes (size and shape). By comparing the results to established guidelines for earthen construction, the three soils are shown to achieve strengths in the range 0.2–1.4MPa and shrinkage after equilibration for one week up to 4%, with the residual soil outperforming the others. Moreover, it was found the strength of the soils was influenced by the relative humidity and was strongly dependent on changes of dry density. The wettability results confirmed the higher organics for the alluvium while the more rounded particle shape and greater content of potassium feldspar of the completely decomposed granite corroborated with its lower strength. The results highlight the importance of conducting a fundamental characterization of natural soils for rammed earth via the particle attributes, wettability and mineralogy. •The strength of selected coarse soils for rammed earth is very sensitive to changes of dry density.•High organic content of alluvium was validated by wettability measurements.•Reduced strength of completely decomposed granite possibly due to rounded particle nature and high feldspar content.