Construction World January 2023

ROADS & BRIDGES

THE SLOPE STABILISATION AT SIR LOWRY’S PASS

This civil engineering construction project involved the stabilisation of cut slopes on the eastbound side of the N2, Section 2, between km 12,06 and km 12,31, at Sir Lowry’s Pass, near Somerset West in the Western Cape.

T he design was undertaken by Zutari’s Cape Town geotechnical and highway teams and Naidu Consulting were appointed to oversee the project management and construction monitoring aspects. Civils 2000 of Cape Town partnered with GeoCiv (formerly Mega Pile Inland) to form the C2KMPI Joint Venture. These teams brought more than 50 years of combined experience to the project. The scope of works included the stabilisation of 250 m of road cutting on Sir Lowry’s Pass. The 13 m high cuttings were unstable and there had been many instances of rock falls endangering the passing traffic. The existing road accommodates two lanes in each direction and was reduced to one lane in each direction to provide working space during the soil nail drilling operations. The work zone was further protected by concrete NJ barriers with access into the work zone strictly controlled by the dedicated traffic management subcontractor. The initial activities involved the clearance of alien and loose vegetation and debris from the work faces and the barring down of loose boulders and rocks from the cut faces. The drilling and installation of soil nails and small diameter drain pipes followed and was completed by Civils 2000’s JV partner, GeoCiv.

Once the soil nailing had been completed GeoCiv moved offsite and Civils 2000 continued with the construction of 100 m of 2 m high gabion in Zone A along the toe of the slopes, 90m of gabion buttresses ranging in height from 11 m to 13 m. GeoCiv installed and grouted 84 15m long soil nails and 488 10m soil nails. The work was completed by the construction of a stone pitched open drain along the top of the slope to intercept runoff, the installation of drainage chutes, channels, and drainage structures and the revegetation of areas damaged by the works. This project presented several unique challenges in that the existing road width had to be reduced to achieve the drilling and yet traffic flows were to be maintained during the works. In addition, the nature of the work required thinking ‘out of the box’ to solve the problems of access to high steep slopes and working on the slopes in dangerous elevated positions while eliminating risks to those below, including traffic. These challenges were met and the project completed very successfully. Construction Innovation Technology The removal of loose boulders from the upper reaches of the slopes presented a challenge because access and the safety

26 CONSTRUCTION WORLD JANUARY 2023