The application of recycled gypsum has been successfully shown to benefit slope stabilisation.

The results of these UK trials indicate that the application of recycled gypsum at between 2 and 4 kg/m2 aids the stability of soils on slopes – both on clay and sandy textured material. At the highest rate tested (10 kg/m2), there was no significant increase in the ability to reduce soil surface erosion or slippage. The preliminary erosion trial in 2006 indicated that an application rate of 4 kg/m2 ( 40 tonne/Ha) was more effective than lower rates at reducing erosion and this is the recommended application rate.

The main aim of the UK trial was to investigate the effect of the incorporation of recycled gypsum on surface soil erosion from slopes. However, the results have highlighted other properties of gypsum application that may, in fact, be more important for the longer term stabilisation of soil slopes.

The principal conclusions from the results are as follows.

  • At the higher slope gradients (25 Deg and 32 Deg), there was evidence of reduced surface erosion following the application of recycled gypsum on the sand textured soil.
  • The recycled gypsum needs to be well incorporated into the soil otherwise the material itself will be washed off the surface.
  • A recycled gypsum application rate of 4 kg/m2 was optimum for reducing erosion and for ease of soil incorporation.
  • Surface application of gypsum reduced down-slope soil movement on clay soil to a depth of 120 mm compared with 215 mm for untreated soil. The mechanism is uncertain, but may be due to changes to water penetration in the soil. This requires further investigation.
  • Gypsum application has no deleterious effect on the establishment of a recommended grass and clover seed mixture for highway use. 
  • Gypsum application reduces weed invasion.

REGYP can supply recycled gypsum for civil projects and Pacific Fertiliser can supply natural gypsum if and when needed for the civil projects.

Source: recycled gypsum in Slope stabilisation report Nov 2007