The residual shear strength of tropical soils

Abstract

Abstract:The paper discusses the residual shear strength of tropical soils. Ring shear tests have been performed with tropical soils from southern Brazil using the Bromhead apparatus. The data from the study are compared with data obtained in a comprehensive literature review of the subject. The residual friction angle of tropical residual soils from sedimentary formations decreases with increasing plasticity index following a general trend presented in the literature. Most of the residual soils described herein have also shown this trend. However, some of these residual soils, particularly basalt saprolitic soils, have shown quite low residual friction angles despite having low plasticity index and clay fraction values. It has been confirmed that the residual shear strength of tropical soils depends chiefly on mineralogy, particle size distribution, effective stress, parent rock, weathering degree, pedogenetic evolution and -when partly weathered minerals are present -degradation upon shearing. The substantial range of new data shown in the paper has allowed the definition of general boundaries of different soil behaviour in a chart of residual friction angle versus plasticity index. Each region has been associated with a different type of tropical soil.Key words: tropical soils, residual soils, residual shear strength, laboratory tests.Résumé : Cet article discute de la résistance au cisaillement résiduelle des sols tropicaux. La résistance au cisaillement des sols tropicaux du Sud du Brésil a été mesurée au moyen de l'appareil circulaire par torsion (appareil de Bromhead). Les données de l'étude sont comparées avec celles obtenues au cours d'une revue de littérature sur le sujet. L'angle de frottement résiduel des sols résiduels formés par l'altération des formations sédimentaires décroît avec l'augmentation de l'indice de plasticité selon une tendance générale présentée dans la littérature. La plupart des sols ré-siduels décrits ici ont également montré cette tendance. Cependant, certains de ces sols résiduels -particulièrement les sols de basalt saprolitique -ont montré des angles de frottement résiduels très faibles en dépit de leurs faibles valeurs d'indice de plasticité et de fraction argileuse. Il a été confirmé que la résistance au cisaillement résiduelle dépend principalement de la minéralogie, de la granulométrie, de la contrainte effective, de la roche-mère, du degré d'altération, de la pédogenèse, et -lorsque des minéraux partiellement altérés sont présents -de la dégradation au cours du cisaillement. La plage substantielle des nouvelles données montrées dans l'article a permis de définir des limites générales du comportement de différents sols dans un graphique de l'angle de frottement résiduel en fonction de l'indice de plasticité. Chaque région a été associée à un type différent de sol tropical.Mots clés : sols tropicaux, sols résiduels, résistance au cisaillement résiduelle, essais de laboratoire.[Traduit par la Rédaction] Rigo et al. 447

Geotechnical Aspects and Stability of Road Cuts in the Blue Nile Basin, Ethiopia

“…Soil layers developed in sedimentary terrain normally contain platy clay minerals and unweathered coarse particles (Skempton 1985). Hence, the residual strength, on top of other factors, depends on particle size and interlocking (Mesri and Cepeda-Diaz 1986;Wesley 2003;Rigo et al 2006;Frydman et al 2007). For reasons probably related to this, the values of the residual strength in the study areas showed high variability with a friction angle in the range between 8°and 21°.…”

Residual shear strength of a weathered graphitic-quartz-mica schist in humid tropical Peninsular Malaysia

“…This residual friction angle of 26.5 o ; is definitely very close to the residual friction angle of 25.5 o determined for the total 3. y = 0.3808x 0-400 kPa 0.0 20.9 0.9381 Table 3: Results of consolidated drained shear box tests on weathered graphitic-quartz-mica schist (Raj, 1988). Rigo et al (2006) sample (Sample C), as well as the overall residual friction angle of 25.2 o for normal effective stresses less than 150 kPa. There is also limited published data from other tropical areas with which the present results can be compared; a limitation pointed out by Rigo et al (2006).…”

“…Rigo et al (2006) sample (Sample C), as well as the overall residual friction angle of 25.2 o for normal effective stresses less than 150 kPa. There is also limited published data from other tropical areas with which the present results can be compared; a limitation pointed out by Rigo et al (2006). Bucher & Kyulue (1980) for instance, have from ring shear tests, determined residual friction angles of 29.2 o , 22.2 o , and 29.5 o , for a micaceous soil from Ghana, a weathered mudstone from Tanzania, and a lateritic soil from Tanzania, respectively (Table 4).…”

“…In a comprehensive literature review, Rigo et al (2006) have stated that the residual strength of transported soils and soils resulting from weathering of sedimentary rocks is extensively described in the geotechnical literature with well-known examples being the over-consolidated clays, clays and clay shales of northern Europe and North America. Rigo et al (2006) furthermore, noted that there is significantly less published data on the residual strength of soils in tropical areas.…”

“…In a comprehensive literature review, Rigo et al (2006) have stated that the residual strength of transported soils and soils resulting from weathering of sedimentary rocks is extensively described in the geotechnical literature with well-known examples being the over-consolidated clays, clays and clay shales of northern Europe and North America. Rigo et al (2006) furthermore, noted that there is significantly less published data on the residual strength of soils in tropical areas. The soils of tropical areas also often indistinctly to distinctly preserve the minerals, textures and structures of the original bedrock, giving rise to anisotropic weathered materials, especially when developed over inherently anisotropic bedrock as metamorphic rocks (Deere & Patton, 1971).…”