We had our foundation piers drilled and filled today.  This was a fascinating process that was well executed given the number of factors at play. Foundation piers are 12″ diameter columns that are drilled 9′ below grade and bellbottomed 36″ to support the beams and slab that rests on top of them.  They are internally braced with rebar that also ties into the beams and serve to stabilize the ground under the slab and limit grade dependencies in the case of a structural foundation like ours.

The process of laying out piers begins with a survey that pinpoints the boundary lines of the slab with corner markers.  The number varies but we had six corners staked. Once the corners are staked according to the survey, the foundation contractor, Larry Langan & the team at Foundation Builders, placed batter boards at each corner and ran string lines to mark the edges of the slab according to the pier diagrams. Once the slab perimeter was marked, they began to place individual stakes at every beam to mark the drilling locations. This took a day to accomplish but attention to detail is very important as the beams must rest on and be supported fully by the piers. This means you have a very small margin of error for these pier drilling targets down to a couple of inches before they will be out of alignment with the beams and therefore be less effective in their role.  Being particularly sensitive to the importance of having a good foundation, I double and tripled checked the stakes myself by running string lines over all the planned beams to ensure they were dead on.  A good step to take since it did indicate some variances of 1-3″ in a few stake locations. This was subsequently confirmed and corrected the next day by Foundation Builders.

And now the fun part begins, drilling and filling piers.  There was a crew of no less than 10 men involved at all times including 2 supervisors. They ran 3 Bobcat Skid-steer loaders with two running augers and one with a belling bit.

The Bobcat operators drilled piers at the staked locations to a depth of 7′ with two running simultaneously with crews moving the excavated earth away from the hole and measuring to depth.  A few of the holes would start to fill at the bottom with groundwater and the decision was made to postpone drilling the last 2′ and belling the bottom until the concrete pump and mixer trucks arrived.  Once they were on site, they would complete the remaining bore depth, bell the bottom, and fill immediately with concrete so as to avoid any collapsed holes.

In fact, for this reason piers are dug and filled on the same day as a standard practice to ensure that no bores collapse in any fashion due to weather, groundwater, earth movements, etc.

While the holes were being drilled, the crew made the rebar forms on-site for each pier.

When the pump truck was pumping concrete via its boom over the bored holes, the foundation team would place and set the rebar structure in the pier.  While this was going on, other team members were marking heights and setting nails in the bores to ensure the right height of fill.  This was all happening in parallel and with multiple crews working all at once.

Incredible orchestration from an experienced crew finished all 104 piers in a single day with time to spare.  Thank you Larry and Foundation Builders!