The excavation is complete for this phase and it’s time to move on to pin piles. Since the soil under our house is not considered to be load bearing, a series of 2″ and 3″ steel pipes must be driven into the ground to support the foundation. The steel reinforced foundation spans the pipes and acts as a beam, transferring the downward forces to the steel pipes. The concrete footing portion of the foundation is often referred to as a “Grade Beam” when it is pile supported. Most of the new footings for this project are grade beams.
So I started off by laying out where all of the pin piles go by driving a wooden stake into the ground for each location. This involved laying out the entire perimeter of the house with string line. Once again we break out the trusty laser, that not only provides level, but also right angles. It took a week given the complexity of our property but I managed to get all the strings up that marked the exterior / interior grade beams and various footings.
If you look carefully in the image below you’ll see rows of wooden stakes that indicate where a pile will go. Each of the 82 stakes were painstakingly located using a 4′ level and the string line.
The layout was completed on a Sunday, just in time for the folks from Pile King to start early on a Monday morning. As usual it started with the offloading of a large piece of equipment from a trailer. From there the workers backed up a large flatbed truck filled with bundles of 3″ diameter pipe at 21′ long. The machine gingerly jerked the bundles of pipe off the back of the truck and we were off to the races.
The machine is a modified trackhoe with a 1000 pound jackhammer that moves up and down on a long steel beam. The pipes are pulled up to the top of the steel beam and pounded into the ground with the jackhammer. It was quite a dance for the large machine to move through all of my carefully placed stakes. Admittedly many of them didn’t fair well but I watched the dance like a hawk and put the stakes back in place as they were toppled.
The soil at the site consists of mostly glacial till, which is extremely hard. This made for very uneven depths on the piles, with some going 25 feet deep and others only 3. Because our project is in an ECA we have what’s known as Special Inspections. One of the requirements is to “Load Test” a few of the piles to make sure that the pile will hold the correct amount of weight without moving. The test involved moving the excavator above the pipe and placing a hydraulic jack between the pipe and the machine. A small micrometer is used to show any movement as the excavator is jacked up. Luckily we passed with flying colors and all is well.
After 4 long days on the job we had 82 new piles in the ground and were ready to have the excavator come in and dig the trenches around the piles so concrete could be poured.