Civil Engineering April 2021 | Vol 29 No 3

Civil Engineering April 2021 37 grouted anchors replaced with R51N SDA IBO grouted anchors assuming the same bond capacity. It is however known from empirical bond resistance graphs, such as Ostermayer (1974), that the fixed length of an SDA would need to be increased as an IRS (Injection Répétitive et Sélective) post-grouted anchors solution utilises post injection pressures, which aren’t applied to SDAs. Recommended bond strengths provided by suppliers of SDA corresponds to the “without post-grouting” curves of Ostermayer (1974). The capacity of SDAs is however highly dependent on the installation methodology employed by the contractor as discussed in Bayesteh & Sabermahani (2018). The results of the adjusted analyses are provided in Table 1. From the table it can be seen that sim- ilar or slightly lower displacements can be achieved when replacing strand grouted anchors with SDA grouted anchors when assuming the same bond capacity. This is due to the elastic displacement of the free length that will be lower. Strands and SDAs have the same elastic modulus but different ultimate strength for the same cross sectional area. Therefore, the same load attracted to SDAs with smaller ultimate capacity should result in smaller elastic load-deformation due to the larger axial stiffness (EA). This analysis however also assumes similar grout-soil-load-displacement (bond-stiffness) behaviour (compared to those assumed in the analyses of IRS post-grouted anchors in Part 2 of this Figure 4 Excavation supported with temporary prestressed SDA grouted anchors and steel walers in Cape Town’s foreshore area (Design by Keller Africa, consisting of CFA piles and jet grouted infill columns) Table 1 Results from finite element analysis using prestressed R51 SDA grouted anchors (SLS calculations) Solution 2.5 m c/c with SDAs prestressed to 80% FHWA 2.5 m c/c with SDAs prestressed to 80% FHWA Analysis Type Hardening Soil – RS2 Hardening Soil with Small Strain Stiffness – RS2 A1 (kN) 452 442 A2 (kN) 368 350 A3 (kN) 384 365 BM per pile (kN.m) 227.5 182.5 Dz (mm) maximum all stages 36 18 Dz for strand anchors (from Table 2 in Part 2) 36 20