Unsaturated Soils Mechanics for Engineering Practice (UnsatPractice)

This partnership programme involves collaboration between Durham University UK and five universities in South Africa (the University of Pretoria, the Central University of Technology, Free State, the University of Kwazulu Natal, the University of Cape Town and Stellenbosch University) on a project entitled "Unsaturated Soils Mechanics for Engineering Practice (UnsatPractice)". The unsaturated characteristics of soils give rise to many geotechnical problems in the UK and in South Africa including collapse of foundations due to inadequate bearing capacity, structural damage due to excessive ground heave, sinkhole formation, slope instability both in terms of natural slopes and man-made embankments, as well as road and railway formation failure. The network comprises 13 academic staff and will train 20 PhD students. The research activities within the network are divided into three strands: laboratory and in-situ testing of unsaturated soils, development of numerical models and applications to engineering problems. The network partners will generate significant follow-on projects by seeking new research funding from national and international research councils and agencies and will establishing formal long-term sandwich PhD programmes before the end the award period.

Expansive and collapsible soils are particularly sensitive to soil moisture changes. As the water content of an expansive soil increases during the wet season, the soil swells causing surface heave. During the dry season, shrinkage occurs producing settlements. Collapsible soils are characterised by large inter-particle voids, supported either by suctions in the pore-water, by cemented bonds between particles or by clay "bridges" between particles (that are themselves supported by suctions). If the soil is wetted, the suctions reduce and/or the cementing is dissolved or removed and the soil "collapses" causing a sudden reduction in volume resulting in surface settlements. This seasonal shrink/swell cycle can cause significant damage to buildings directly founded on these soils. This seasonal shrink/swell cycle can cause significant damage to buildings directly founded on these soils. The costs of damage due to shrink/swell movements on clay soils have resulted in economic losses estimated at over £1.6 billion in the UK during drought years in the 1990s. Similar figures are evident from France where losses have been as high as £2.7 billion in a single year. In China, losses due to land subsidence in Shanghai are estimated to be about £10 billion over a decade with £0.3 billion a year in losses in three other cities. Of relevance to this proposal is the fact that collapsible soils cover 67% of the total area of South Africa and their presence has an impact on most infrastructure development.

The network will enhance the ability of the partners to respond to the needs of both the domestic and international construction industry to evaluate optimal foundation and pavement designs in unsaturated soils. Therefore, the combined research will reduce potential damage to properties and infrastructures. The network will enhance significantly the mobility and international visibility of each of the partners involved. It will also provide a legacy of well-trained UK and South African experts equipped to solve the engineering challenges of infrastructures in unsaturated soils.