Wednesday, June 15, 2011

Fill and The Wall

The past week has been pretty exciting in terms of seeing changes on the ground, and feeling like we're moving forward at a fast pace. We imported fill material (mostly from the neighboring property where we had been storing our excavation material from March), and built the first phase of the 5.5-meter tall retaining wall that will run along the front (north) side of the property holding up the future street.

Fill and Ground Beams
The nearly 600 cubic meters of  fill material were brought in using trucks and a bulldozer, then compacted with a ride-on roller (120 centimeters wide) to achieve an acceptable density for the material that will go under the building slab. After getting off to a slow start due to a couple of holes in the tires of the bulldozer/backhoe, the subcontractor finally got rolling:

(first layer of fill mostly in place)
(bulldozer spreading the fill)
(new loads coming in)
(truck being loaded for the next run)
The driving skills demonstrated by the machine operators were pretty impressive, since these guys had to not only back up into the site each time they had a load to drop off, they did that on dirt ramps that they were building for themselves as they went along in order to get the material all the way to the back of the site.

(truck backing up into the site)
(bulldozer waiting to spread the new load)
(contractor eyeing the progress)
I'm used to hearing about fill material being compacted in lifts of 6 inches, with compaction approvals from geotechnical engineers. However, I consider myself lucky to have gotten two compaction rolls (at an average of 60-70 centimeters or 25 inches each) after we insisted, while the contractor or I sprayed water with a regular hose along the surface!

(second layer of fill being rolled)
After the compaction, the backhoe helped start the trenches (in lieu of timber forms) that will hold the reinforcement for the Ground Beams connecting all the columns, and the crew did the rest of the work by hand.

(crew digging trenches after backhoe was done)
The crew dug trenches, constructed forms on the outside of edge of the future slab pour, tied the steel bars together and built stacked rock walls along the trenches to hold the concrete in place when it comes time to pour the slab on grade. You can see a picture below of what the end result looked like for one of the Ground Beams along the east side:

(Ground Beam reinforcement and trench along east side)
 The Ground Beams will fall directly under the slab, and will be poured at the same time. Below is what the site looked like at the end of the day today, with about 85% of the pads ready for the plastic tarp and steel grid mat that will act as the moisture barrier and reinforcement for the slab respectively. However, we still need the plumbing contractor and the electrical contractor to lay their conduits and sleeves in the ground prior to covering the pads up with the steel grid mats, so tomorrow should be an interesting day for coordinating all that work.

Retaining Wall
There is a 5.5 meter (18-foot) tall, 30-meter (99-foot) long, and 40 centimeter (1.3-foot) wide reinforced concrete retaining wall designed at the front of our site, and over the past couple of weeks we've completed the work on the footing, the forms and the first phase of its construction. The base of the wall falls on two rock benches that are not at the same elevation, so we had to split the forming of the wall into two parts as well. 

The first phase is approximately 3 meters tall for an approximately 25-meter run,  the second phase will be the remaining 5-meter run for that same height, while the third and final phase will be taking the entire 30-meter run from 3 meters tall to 5.5 meters tall. The photos below show the progress of the wall construction:

(foreman eyeing the footing and starter bars for the first section that's about to be formed)

(hammering the planks that will support the forms)
(forms being erected)

(forming complete on one side, and steel being tied inside)
(steel completed, and scaffolding being built)  

(view of scaffolding from the bottom)
(starting the forms for the footing of the higher / west section)
(supports for the forms, to hold the weight of the concrete)
(the side of the footing closest to the street, formed using rocks and dirt)
(ready for the pour)
The concrete pour was slower than post foundation pours because of the restricted space for operations, plus the need to pour the 3-meter height in several lifts to ensure that the concrete is uniform, that the vibrator gets to all areas within the forms and that the weight of the concrete doesn't cause the forms to burst apart. We poured ours in 4 lifts, and poured the footing for the second (west) section of the wall at the same time.

(crews operating the vibrator following the concrete pump hose along scaffolding)
(same operation from opposite perspective)
(close up of the slow pour)
(footing being poured)
(phase one of the wall complete)
We plan to have the second phase of the wall poured at the same time the slab and Ground Beams are poured. The wall will use up about 90 cubic meters of concrete for the first two phases (including footings), while the slab and Ground Beams will use up around 50 cubic meters. The next couple of days should include the slab pour, and I hope my next post will show the floor of the second basement level completed.

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