Construction World December 2021

CONSULTING ENGINEERS

over to the Starter Pond, f rom where the dredge would commence mining operat ions in the new ore body. The const ruct i on o f thi s f l oat-over channe l i nvo l ved the remova l o f a 65 000 m³ mi xture o f c l ay and peat . Four ponds were const ructed for re l ocat i on , stag i ng , f l oat-o f f and star t i ng . Two r i ver c ros s i ngs were a l so t raver sed a l ong the re l ocat i on route , whi ch i nc l uded up to 2 m Ø cor rugated stormwater p i pes . Rel ocat i on pond The re l ocat i on pond covered an area o f 11 ha wi th 6m hi gh conta i nment berms const ructed f rom l oca l cohes i onl es s compacted sand . I n ant i c i pat i on o f the pond eventua l l y be i ng f l ooded to accommodate the f l oat i ng WC p l ant and dredge onto the 1 , 5 m hi gh conc rete p l i nths , and shor t l y therea f ter to be dra i ned ent i re l y, spec i a l at tent i on had to be g i ven to the pond f l oor underneath the p l i nths and 23 mm thi ck mas s conc rete s l ab. Cogni sance a l so had to be taken o f the potent i a l o f r i s i ng groundwater whi l e cons i der i ng the pond f l oor des i gn . Af ter drawi ng the hi gh groundwater down v i a a ser i es o f subso i l dra i ns wi thi n the pond , a 150 mm thi ck l ayer o f sand f i l l ed geoce l l s were p l aced on 600 mm thi ck compacted i ns i tu mater i a l . Thi s was fo l l owed by a l ayer o f 180 mm thi ck granu l ar mater i a l and stab i l i zed wi th 6% cement and compacted , fo l l owed by a 170 mm thi ck l ayer o f the same stab i l i sed mater i a l , and compacted .

54 20 th Best Project Awards 2021