Remediation of Johannesburg M1 And Oxford Road Bridge by Jet and Compaction Grouting-Paper

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The M1/Oxford Road Bridge approach in Johannesburg experienced more than 400 mm of settlement and outward rotation in sections of its retaining wall, with movement continuing since the early 1970s. Geotechnical investigations linked the damage to deep, fault-related zones of weak, weathered silts and clays, compounded by wetting from leaking stormwater pipes and altered groundwater conditions.<br /><br />The remedial design aimed to improve ground stiffness and limit both vertical settlement and lateral wall movement, without relying on highly loaded elements that the existing foundations might not safely support. The solution combined three techniques: jet-grouted columns beneath the retaining-wall foundations to provide support; compaction-grouted columns beneath the wall toes to resist outward rotation; and reinforced rigid inclusions behind the wall and beneath the roadway to strengthen the retained fill and reduce lateral pressure. A reinforced load-transfer layer was incorporated beneath the reinstated road.<br /><br />Construction was carried out from the motorway, without access to neighbouring properties, while traffic remained open on the opposite carriageway. Grout returns were captured and controlled at the drilling locations. In total, 32 jet-grouted columns were installed, with the deepest extending to 28 m; approximately 193 m³ of grout was used for compaction grouting.<br /><br />The work was completed without reconstructing the existing walls or embankment. Monitoring after construction showed movements within acceptable limits, with no further significant settlement reported. The case demonstrates how targeted ground improvement can stabilize distressed infrastructure under constrained access and traffic-management conditions.

Keywords

Johannesburg

M1/Oxford Road Bridge

retaining wall settlement

ground improvement

jet grouting

compaction grouting

rigid inclusions

fault-related weak soils

stormwater leakage

infrastructure stabilization