The pier foundations were no longer taken down to bedrock ; instead they were constructed by sinking brick-lined wrought-iron caissons onto the riverbed , removing sand until the caissons rested upon the consolidated gravel layer which had been misreported as rock , and then filling the caissons with concrete .
The pier foundations were no longer taken down to bedrock ; instead they were constructed by sinking brick-lined wrought-iron caissons onto the riverbed , The company which had the contract for building the bridge went bankrupt while Bouch was redesigning the bridge .