Building Settlement Mitigation with Perimeter Piles?

This morning when I was buying Bangka noodles (one of Indonesian delicacies) for breakfast, in one of my civil engineering WhatsApp groups I saw the picture above. A drawing showing addition of pile foundations around the building to prevent further settlement.  The added piles shall have continuous cap which in turn shall be connected to the existing mat foundation. As a geotechnical engineer with 36 years of teaching and practicing experiences, my immediate comment was: "At the first glance (haven't read) the solution doesn't seem right".

Then, while enjoying breakfast with Bangka noodles, I read the article in the ENR news about the settlement of this Millennium Tower in San Francisco which had settled by about 450mm. Here is the link of the ENR news:

After reading the article, I was more and more doubtful whether the solution according to the picture can work.

My doubts were answered when watching another news about the building in youtube:

Wow.... It said the retrofitting work was stopped. It was stopped when during the piling activities, the rate of settlement was even greater than before the retrofitting work was carried out.

A few things that cause my doubts are:

  1. Can piles on the perimeter resist the on-going settlement? Will the joint between the new mat casted as the piles’ cap and the existing mat foundation be strong enough to withstand the load? Note that when the building settle further, a large stress at the mat joint can take place and there will be moment generated in the joint area and also on the new piles.
  • Looking at the existing pile foundation arrangement, the settlement was due to soil pressure under the building, and not only on the perimeter of the building.
  • When new piles are constructed, a full casing bored piling method must be executed in a very careful manner. If bored piling is drilled without a casing, the soil which has already suffered large stresses will seek stress relief through the drill hole and this will cause the building to settle further.
  • To prevent or to reduce further settlement, the soil underneath the existing foundation must be stiffened. In my opinion, the possible way to do this is to do under-pining under the existing mat, or a carefully controlled jet grouting technique.


Whatever is the solution provided. The implementation of the repair work will be very expensive (the proposed perimeter piles cost US$100 million). Apart from that, it is a high-risk operation that must be monitored with instruments and closely monitored.


Repairs are always risky and cost much more than carrying out a proper soil investigation. An experienced geotechnical expert is necessary for the design and construction process. Strict supervision is also required.

*Don't treat the soil as a stepdaughter, because the revenge of the stepdaughter will be tremendous”.

Happy weekend.

GTL, 210904