Plan B

The manhole rings were delivered this morning, so the contractors returned to prepare for dropping them into the hole. However digging out the results of a few overnight mudslides soon showed that the optimism from a couple of days ago was unfounded. We have not hit the rock at the bottom of the old quarry, and the ground is not firm enough to take a pile. He dug another 4 or 5 feet and still did not find anything solid.

In his opinion, using manhole rings and a concrete pile is no longer cost effective - too much of all of it would be needed. He made a call to the Structural Engineer and they agreed to abandon the idea of the centre pile under the chimney and attempt to go for just the one in the North West corner, with a beefed up re-inforced beam to stretch the whole width.

Unfortunately, later in the afternoon, the dig in this corner has yielded similar results - 5m deep from the basement floor level and still nothing solid found. Both holes have now been filled in and the Structural Engineer is now considering a "raft" foundation instead. I have not done the research yet, but I believe that this is where a thick reinforced concrete slab is layed across the whole site (the raft) and the walls built on top of it. The idea is that the load of the structure is spread across the entire raft (not just a "trench" foundation) thus reducing the Ground Bearing Pressure to a figure that is comfortably lower than the Bearing Capacity of the ground.

This has not been a good day. We now have to wait for a raft design to be done, followed by a costing in order that we can decide what to do next. Bahhhh.