The behaviour of semi arid residual soils derived from the weathering of Johannesburg quartzite are difficult to predict because of their heterogeneous particle constitution and weakly bonded structure. The collapse behaviour of undisturbed and remoulded weathered Johannesburg quartzite was investigated; and the reliability of the collapse settlement data was also evaluated. The results showed that a combination of low initial saturation of 13% and consolidation stress of 200 kPa result in the greatest collapse and that in order to avoid collapse, at any stress range, the soil must be compacted at a degree of saturation higher than 26%. The effect of desiccation on the magnitude of collapse settlement is dependent on the fines content and clay minerals. The collapse settlement of the undisturbed and remoulded quartzite was more sensitive to changes in dry density than changes in moisture content. Statistical analysis of collapse settlement test data of 15 undisturbed and remolded samples inundated at consolidation stress of 200 kPa revealed a mean, covariance and 95.5% reliability of 4.75%, 13.65±1.477% for undisturbed samples and 6.82%, 7.57±1.17% for remolded samples. The implications are that the higher values of collapse settlement associated with remolded samples should be recommended for geotechnical design.
Key words: Collapse settlement, desiccation, weathered quartzite, soil structure.
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