Project Overview

Dawnus was appointed to design, construct and provide the monitoring regime for two tailings storage facility dams for the iron ore process plant waste product. The first of these dams was a zoned (clay/sand) earth fill tailings dam with filter beds. The dam was constructed as a layered earth structure with an integral filter medium.

Dawnus were responsible for the full package of works from ground investigation, design through to construction. We have also set up a monitoring system for this structure. The dam uses 500,000m3 of material and the earthmoving was completed in 3 months. 

To supplement the original storage facility, African Minerals commissioned Dawnus to design, construct and provide the monitoring regime for a further tailings storage facility for the iron ore process plant waste product. The design capacity requirement of the storage was 3,500,000m3; this was increased to 4,000,000m3 by excavating dam wall material from within the impounded area. 

Site and Geotechnical Investigation commenced in November 2012, with borrow pit exploration commencing in January 2013. Construction of the zone fill dam commenced following completion of design on 1st February 2013. The total construction volume of fill materials is 3,000,000m³. The length of the dam is 1450m, with a maximum height of 45m and maximum width of 200m. The overall works consisted of: 

  • Clay zone 140,000m³
  • Filter layers 120,000 tonnes (80,000m³)
  • Supporting rock toe 20,000 tonnes (10,000m³)
  • Laterite capping 150,000m³
  • Top soil erosion protection 20,000m³
  • General fill 2,600,000m³
  • Laboratory and site engineering to support
  • Filter media and rock toe produced by Dawnus Wendugu Quarry
  • Quarry at Tonkolili Spillway construction approximately 200m³ concrete 

On all our projects in West Africa we have employed local people and provided training and development in a range of construction disciplines, to European standards.

Project Gallery


African Minerals


Sierra Leone

Project Value


Contract Period

62 weeks