TML> Pearl's Retaining Wall goes Vertical

Notes from Windward: #68


Pearl's Retaining Wall goes Vertical

Opalyn starts on the next step

  September 25:

     Been off working on other projects such as the GEK, but now that summer's heat is past, it's time to get back to work on the Pearl's retaining wall. While there's more excavation to be done on the water-line trench and the west-corner pad, we completed excavation and got ready to pour our first section of footing this past week.

Sarah shows off her water line trench

     Sarah and Kerst have been working hard to uncover enough of the water line to allow us to reroute the line. We are exploring the options of sinking the line deeper underneath the Pearl or routing it around the Pearl and reconnecting it at the downhill manifold. Andrew continues excavation for the west corner pier while I've been completing excavation on one of the footing sections. The goal here is to preserve as much of the soil undisturbed to maximize the underlying soil's carrying capacity, so we excavate only the space that we'll be filling with rock and concrete.

a 6' section of footing fully excavated

     With the footing excavation complete, it was time to start preparing to pour concrete. First we cut out the forms used on the pads. This involved using a saws-all and pry-bar to cut through and remove the 2x6" form boards. Next, I headed down to the shop to cut some rebar.

cutting 20' "sticks" of rebar to the desired length

     With the rebar cut to length, several pieces were ready to be tied in place while others needed to be bent at 90° to create the L-shaped members that will join the retaining wall to its footing.


     With the rebar tied in place, we're ready to pour concrete.

  September 27:

     With the crew assembled and the supplies standing by it was time to start up the mixer. As the first mix of Portland cement, sand, and gravel went into the mixer, the rest of the crew clears a path for the wheelbarrow.

Sarah and Oana bring in the first mix

     The wheelbarrow is carefully maneuvered into place to deliver the cement into the earth form

Opalyn helps guide the cement into place

     While waiting for the next mix, the cement is tamped into place


     Rocks about the size of an orange are added to the concrete to increase the volume, add strength and prevent the need for a partial mix.

almost done

     With lots of hands pitching in, we successfully placed six mixes--approximately 6.5 cubic feet of concrete--and had the tools cleaned up in under an hour. Yeh, team!

the first of the footing sections is in place

  September 29:

The Pearl Goes Vertical

     With the concrete footing in place, I collected tools and supplies to create the form for the vertical wall, even breaking out the shop-vac to clean up some dirt that had fallen onto the footing.

[Walt this work is the tightest bit of "in situ" pouring that we've done, a technique that involves minimizing the amount of dirt moved either by hand or by machine. One of the challenges that comes with that involves the lack of any where for run-off to go, so it's important to keep at least the part of the footing that would connect with the vertical retaining wall clean in order to get a good bond. Next section we pour, we'll set up the forms so that at least six inches of the vertical wall is poured a half-hour after the footing, thereby insuring a better bond.]

     Two one-foot wide strips of plywood were placed vertically. One piece of plywood was placed between the piers and the soil using shims to secure it in place. The other was cut to length and placed between the adjacent piers. Using spacing blocks to keep the forms six inches apart, the plywood was tied to the rebar creating a trough.

forming the base of the retaining wall

     Katie, Oana, Andrew, and Walt pitched in to help the wall climb vertically. Andrew and Walt worked at the mixer; Oana brought each wheelbarrow over, I transferred concrete into the form, and Katie used a piece of rebar to pack the concrete into place.

Katie works the cement into place

     The two mixes we placed produced six inches of vertical wall nearly 7-feet long.

Oana and Andrew lend a hand

     We returned to the site the next morning with another piece of plywood to protect the new pour from soil falling off the ledge. With this piece in place we cranked up the mixer again and placed two more mixes. Then Andrew and I broke out the concrete vibrator and vibed the concrete into place. The vibrator makes the concrete temporarily more fluid and we choose not to use it yesterday because we did not want to risk blowing out the forms. Today, with six inches already hardening we put the vibrator to good use.

the wall continues to climb and is approximately one-foot tall

     The next morning I removed the form and took a look at our short wall. You can see the effects of the vibe and how there are more air holes in the lower half of the wall.


  November 5:

Completing the Third Pier

     As the first section of the retaining wall continues to rise, we have been working on completing the adjacent piers. The northeast center pier is at finished height but needs more concrete to finish it off. The northwest center pier needs a boost. One more layer of cinder blocks will not produce the height required and two layers put it over the top. We decided to mount a collar to allow a pad to be poured similar to what we did on the northeast corner pier.


As I transfer cement from the wheelbarrow into the collar, Kerst is tamping the cement into place while keeping an eye on the elevation of the pad.


     With the cement pad at the appropriate height we transferred the rest of the cement into the vertical wall.

     Last week we used the cement vibe three times, once for each wheelbarrow full. We also almost blew out the forms so today we decided to put two wheelbarrows full of cement into the form then use the vibe. It worked well and did not risk the forms.

     After we cleaned up all the concrete tools it was time to return to the northwest center pier and set in two cinder blocks. This is a challenging task for two reasons. First, we had to release the forms slightly to allow the cinders to slide down into the cement. Then we had to wiggle the blocks so they sat level and in-line with the rest of the pier. The next day we removed the collar form and secured the rest of the rebar for the vertical wall.


     With these tasks complete, on our next pour we filled the northwest and northeast center piers along with raising the wall.


     We now have three of the six piers complete and one wall is nearing the halfway point.


Notes From Windward - Index - Vol. 68