12.13 Centerline Method
Centerline construction is similar to both the upstream and downstream construction methods in that the embankment begins with a starter dam and tailings are spigotted off the crest of the dam to form a beach. The centerline of the embankment is maintained as fill and progressive raises are placed on both the beach and the downstream face (Figure 12). The tailings placed on the downstream slope should become compact to prevent shear failure. The centerline method of construction provides some of the advantages over the other two methods while mitigating some of the disadvantages. As in the downstream method, drainage zones can be incorporated into the construction. A wide beach is not mandatory and this method is amenable for use with tailings that contain a relatively low percentage of sand. Since less sand is required, the dam raises may be added faster than that in the upstream or downstream methods. Coarse gradation of the tailings is necessary if rapid drainage is required to provide support for construction equipment. Although this embankment type is not amenable to permanent storage of large volumes of water, short term storage of water due to heavy precipitation events or mill shutdown does not adversely affect the dam stability.
Figure 11: Example of tailing embankment
If the embankment has been properly compacted and good internal drainage is provided, this embankment is resistant to seismic activity as well. Even if the slimes placed against the upstream slope liquefy, central and downstream portions of the dam may remain stable due to their good compaction and drainage characteristics.