Piezocone Investigation of Paleo River Channels at Changane River, Mozambique, for a Railway Embankment

摘要

Development of a heavy minerals mine al Chibulo, Mozambique, required the construction of a railway embankment across the Changane River, a tributary of the l.impopo. The embankment will be about 5.5 kms long and between 4m and 6m high. The investigation, at the bankable feasibility stage, comprised boreholes at three bridge crossings and piezocone testing across the flood plain. These revealed four distinct paleo channels with depth of up to 30m infilled with recent alluvial deposits. Analysis of the piezocone data, from which compressibility and consolidation parameters were derived, showed that an average embankment settlement of about 1.5m will take place with a maximum of 3m. lime for consolidation will vary from a couple of years up to many decades. The proposed solution is a combination of preloading, surcharging and in the worst cases and at bridges, the addition of vertical sand drains. These together will reduce the post-construction settlements to less than 250mm over a decade; differential settlements over short distances will be negligible hence the situation will be manageable despite the extremely poor subsoil conditions.