One such method is to inject cement into mud at the bottom of the sea, creating columns strong enough to build on. Another, used in building the new bridge, involves dropping giant steel cells filled with debris onto the seabed to anchor seawalls supporting an artificial island. That method came into question during the bridge’s construction when the structures started drifting from their positions, causing additional costs for repairs and to reinforce the adjoining seawalls.

Source: Los Angeles Times April 03, 2019 09:56 UTC