Mafika Lisiu Pass Lesotho

The Institute of Civil Engineers presented its National Award for the Most Outstanding Civil Engineering Achievement of 1990 to the Northern Access Route (Km 0 – Km 56) to Katse Dam in Lesotho. The road includes the 3 000 m high Mafika Lisiu Pass over the Malutis, one of the highest mountain ranges in Southern Africa.

In order to facilitate easier passage of heavy vehicles through the 15 m radius bend a 50 m approach section was reduced from an average road gradient of 14% to 5%, with a grade of 2.5% through the bend. The total road width of 8 m was increased to 14 m.

In order to accomplish this geometry a 130 m long Reinforced Earth retaining wall was designed. The maximum height is 18 m. The tight 22m radius of the facing elements and the height of the wall required that it be tiered to ensure the necessary flexibility of the facing elements. The reinforcing strips are HA steel. The weather in the Malutis can change in minutes to rain, hail or mist. The local weathered basalt backfill from just above the structure originally to be used was too wet and due to daily showers could not be compacted at optimal moisture content. Consequently, a free-draining crushed doleritic basalt backfill was borrowed from a pit at the foot of the pass.

The road to the Pelaneng Adit crosses a high embankment with a large ARMCO culvert. A tiered Terratrel-faced Reinforced Earth structure provided cost savings by reducing the culvert length.

The approach embankment to the Malibamatso  Bridge has slopes that would be submerged by the Katse dam. These had to be battered back from 1.5:1 to 2.5:1 and then picked up vertically with a  6 m high TerraTrel faced Reinforced Earth structure to attain the original grade of the road.

Project details:

Contractor: LTA Construction Lesotho

Consulting Engineers: Van Wyk & Louw (SMEC)

Supervising Engineers: O’Dwyer, Jeffares & Green