It was not intended to operate this way when it was built. Maybe there was a plan to fill holes with concrete but never on that scale as was decided later. Note

It was not intended to operate this way when it was built. Maybe there was a plan to fill holes with concrete but never on that scale as was decided later. Note decided later - unclear whether ever enough grouting was done to fill the need. The stoppage of grouting was just another straw on the camel's back.