KWADABEKA VALLEY FOR THE MR577 PROJECT – GEOTECHNICAL CHALLENGES

Dulce Simoes Lateral Support

Franki Africa was appointed by main contractor Group Five to carry out the lateral support works for the Kwadabeka Valley for the MR577 Project.  In order to construct the new road, a major cut-and-fill operation was required up the valley from the Umgeni River.  Franki’s scope included temporary rock fall protection works and permanent lateral support with cuts of up to 52m high in parts.  The original scope of work was for close to 20 000m of rock bolts, 7 000m² of shotcrete and 300m of temporary rock fall catch fences.

The most difficult aspect of the project was the access to the work areas. The natural slopes varied between 30 o and 45o and stretched over 100 m from the valley to crest. Franki utilised tracked drilling rigs, an excavator mounted drilling boom and two shotcrete teams on site. With lateral support works starting approximately half way up the slope, access for plant, material and personnel proved challenging.  Initial works included barring down loose rocks from the slope above the work area and erecting a temporary catch fence for protection during subsequent works below. Apart from the steep slope and risk of falling rocks, scorching temperatures of over 45oC and snakes on-site made tasks all the more challenging.

The first two or three rows of rock bolts were installed through a gabion interceptor wall. Franki installed the bolts and then coupled extensions onto these as the gabions were constructed. With access along a single 3m to 4 m wide bench, the coordination of material deliveries and construction works proved difficult and resulted in frequent delays. Ongoing design changes as unexpected fractures, tension cracks and rock strata were uncovered also contributed to extending the contract period.

Soil conditions varied from topsoil to loose talus to fractured sandstone of varying strengths and the engineers found it difficult to keep up with continually changing design requirements. The scope of works increased considerably because of this, and the eventual value of the works was three times the tendered value, it included extensive rock anchoring and over 3 000m² of drape mesh and took over three years to complete. Franki employed up to 50 people from the local community during this period.

The difficult working conditions and continual changes lead to extreme challenges but the final result is an impressive lateral support structure that has enabled the P577 to pass safely through the Kwadabeka Valley.

Article published in the Imiesa Magazine – January 2018