Geotextile solves hospital drainage problem

Midstream MediClinic where various in-situ soil types posed a challenge for effective drainageThe vast Midrand Estates, in Gauteng, comprises Midstream, Midfield, Midlands and Midstream Hill Estates. Adding to these facilities a new hospital has been constructed on Midstream Hill by main contractor Basil Read, with Jodan Construction undertaking the earthworks, including the installation of the sub-soil drainage systems.

The site for this new Mediclinic Hospital has undergone extreme excavation operations to accommodate basement parking. As a result the natural flow of ground water has been altered, resulting in a high water table being exposed in the cuttings, making it imperative to install an effective drainage system.

The difficulty in this area is the vast amount of different in-situ soils, ranging from sandy material to black clay and, of most concern at the hospital site, the presence of residual granites and ferricretes.

These sub-soil conditions could result in clogging of drains by means of ferric oxide build-up on conventional woven and nonwoven continuous filament geotextiles, thus a drainage product with larger openings was a necessity. Endecon Ubuntu (Pty) Ltd. Consulting Engineers proposed that Kaytech Geomesh would be the most suitable product.

Kaytech’s Geomesh, is a dimensioned, PVC-coated, multi-filament woven polyester, designed for soil reinforcement and as a high modulus separator in composite drains.

The conventional method of drainage would be to utilise washed river sand dimensioned as backfill over slotted pipes. However this sand may also potentially clog over time and the engineers proposed that a select, suitable geotextile would be the most practical solution for the problem since its installation is similar to that of a conventional sub-soil drain which is more familiar to the site labour.

Other factors in this decision were the cost implications of importing washed river sand and that the structure of Geomesh is very similar to the retention characteristics of a medium to coarse-grained river sand. The final product consisted of the installation of a conventional shaped drain: 300mm x 300mm with a 110mm slotted pipe and 19mm stone all of which was wrapped with 2500m2 of Geomesh.

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