| The buttresses rise from caisson caps, each covering six concrete caissons. |
| In 1996 the log shafts had been replaced by concrete caissons, but the mine was essentially dormant. |
| The housing consists of prefabricated concrete caissons which are inset in the lagoon floor and contain service tunnels and machinery. |
| The caissons, with concrete compressive strengths of 5000 to 6000 psi, were in good condition and are being reused. |
| The caissons were huge hollow reinforced concrete blocks that were floated across the channel and then sunk when in position. |
| The caissons themselves are socketed into rock located 1.2 or 2.4 m below ground, depending on the location. |
