Civil Engineering April 2021 | Vol 29 No 3

Civil Engineering April 2021 45 aggressive environments but comes at a significantly increased cost. Care should be taken to prevent galvanic corrosion or in environments with high chlorides. Corrugated sheeting (DCP): Due to the method of installation of SDAs, it is not possible to achieve DCP. The Federation of Piling Specialists states that DCP cannot be achieved on tensioned SDA bars and that they should therefore not be used in permanent stressed grouted anchor applications. This is in agreement with EN1537 and the current SAICE Lateral Support in Surface Excavations Code of Practice. Using SDAs/HBSN as permanent soil nails in coastal environments and when assuming sacrificial thickness allowances poses a significant risk to a project due to atmospheric corrosion and corrosion that could occur inside coupler connections. If SDAs are used in permanent applications, it is advised that the engineer install sacrificial test nails that can be extracted and inspected during monitoring activi- ties. A monitoring plan must be provided to the client, implemented at time periods as detailed, and corrosion assessed during these assessments. In addition, the use of a staggered altering coupler layout could be considered. The use of fibre-reinforced plastic (FRP) or temporary cased drilling with strands or solid threadbar fully sheathed should instead be considered in permanent applications. However, cased drilling will come at a significant increase in cost compared to uncased drilling or SDAs installation due to the efficiency that can be achieved. Drilling equipment that uses interconnecting casing is however available internation- ally. Hopefully, these will be available in South Africa soon. SEISMIC LOADING The following question was asked to respondents: Do you design walls for earthquake induced loading? This question was asked as the authors are of the opinion that seismic loading is considered too lightly by geotechnical Figure 10 Seismic hazard map of South Africa (Council of Geoscience, year unknown) SEISMIC HAZARD MAP OF SOUTH AFRICA INCLUDING THE KINGDOMS OF LESOTHO AND SWAZILAND Peak ground acceleration (g) with a 10 % probability of being exceeded in a 50 year period NAMIBIA BOTSWANA Limpopo Province MOZAMBIQUE Northern Cape NorthWest Western Cape Eastern Cape Free State LESOTHO Mpumalanga Gauteng KwaZulu- Natal Pretoria eSWATINI 0.24 0.20 0.16 0.12 0.08 0.04 g