Demolition and site preparation continues throughout the site. One of the most fascinating parts of recent work has been the extraction of old wooden piles that were installed in support the original transit center when it was constructed 70 years ago.
Having watched pile drivers in operation in years past, I never imagined that piles could be pulled back out of the ground. How is that possible, when thinking of the (sometimes) hours of pounding necessary to drive them deep into the ground ? Well, it indeed is possible, and is quite a fascinating think to see.
A steel pipe with a greater diameter than the original pile is driven into the ground encasing the pile. Filled with water, its sits awhile, and then is grabbed by a hydraulic machine that shakes the surrounding pipe, creating sort of “mini-earthquake” that liquifies the soil. The end of the pile is then grabbed by the hydraulic machine with pulls it from the ground. Wow ! Usually for us here in San Francisco, liquified soil is a bad thing, but in this case it enables the removal of an old tree trunk that has been deep in the soil for 70 years !
And I learned another amazing thing while watching this process. While it was assumed the piles would be coated in creosote to improve their longevity, and cost was built into the demolition project to make sure they were disposed of in the appropriate manner, when pulled from the earth they were completely clean ! There was no creosote or other material used when the piles were originally placed. Another fascinating thing — there is virtually no rot or decay visible on these piles, despite their long service in the ground. I was told this is due to the fact that, while they were continuously in a wet environment, with little oxygen present in the soil at their depth, decay is an extremely slow process, occurring over thousands and thousands of years.
One Friday, as I was taking photographs at the the site, I met a father and son team, owners of a sawmill near Santa Rosa. They were loading a large flatbed truck with a load of these old piles. They are planning to dry these logs, plane them a bit, and prepare them for use in building log homes in the Sierra Nevada area. I have also heard rumors that a few logs are being used by someone who is building a boat !
Here are a few views of these amazing old logs, now freed from their long years of loyal service supporting the old Transbay Terminal. Well done !