Digging a Big Hole Part 1

Things are moving quickly but it's the hurry up and wait phase of the build.  Basically the way to make a gunite pool is to dig a hole about the wall thickness greater than what you want for the pool, 12 inches in this case, install metal rebar and water circulation ports, wait for metal inspection, then shoot the gunite at the metal and smooth the inside.  The wait part is the roughly 28 days it takes to cure before you can apply the finishing materials.  So here we are, at the start of the hole digging phase, but it really gives you a good idea what the pool will look like when finished.

  There hasn't been an excavator this big on the property since the initial house foundation laying so it was exciting to see one again.  We've had smaller ones for some of the landscaping installation in the back yard, but nothing this large.  I was a bit worried about the path it needed to take to get to the back yard as the rear corner of the house barely had the width to accommodate the large machine but the skill of the driver allowed passage with no permanent damage. 

   The reason why we've held off on landscaping development around the side of the house should be apparent now.  Excavators leave a wake of ground destruction behind them when they pass.  We might have lost a few smaller plantings near the front yard and much of the hill leading up to the back yard is compressed and torn up at the same time.  I've written off most of the grass in my back yard for this year and will look forward to rehabilitating it with fresh dirt and seed.  There were some dry spots in the lawn after the first hydroseed application and I wasn't really ever satisfied with the soil amendment so now I'll get the chance to correct those issues.

The first day of digging was mostly occupied with carefully measuring out the perimeter of the pool, adjusting the staking, and painting where the dig will take place.  As mentioned above, the actual dug out area will add about a foot for the thickness of the walls, but the pool decking area that will surround the pool and the retaining wall on the back were taken into account.  Since the pool shape is curvy and organic, the large circles that constitute the pool were determined and center points were staked.  The circles could then be painted in and joined together free hand with additional curves. The excavated dirt was bermed on the back side of the yard to make it all level, since there's a pretty significant drop off that needs to be compensated for.

   The deep end of the pool was dug first  They used a laser level at the designated high spot of the yard as the primary point of reference in combination with the engineering drawings.  The drawings have the pool edge coping stone set a little bit above the level of the rest of the pool, with the pool decking sloping towards the grass.  The orange string line was placed at the top of the pool coping level and pulled level across the pool to the low side so they could roughly see how much excavated dirt to place back there.  As discovered when we built the house, there's a thin layer of top soil followed by all sand.  I'm not sure if the staining seen in the sand layers is from the excavator disturbing the soil as it plunged down to dig or if the nutrients from the soil were working their way down, enriching the sand, but it is interesting to see.  The pool will go from about 3'9" in the shallow to 6' in the deep.  We discussed keeping the pool around four and a half to five feet in the deep end and it's been the trend to have "adult pools" like this.  It allows you to walk around the entirety of the pool without having to tread water, but we specifically wanted a deep part to swim down in.

   Here's the excavated sand approximately at the required height to create a level surface on the back side of the pool.  This specific area will actually be lower in elevation to the pool for a little fire sitting area, but that construction will come in the second half when we build out the pool decking.  I do think that some special attention needs to be paid to the back side of the pool shell in this area since it will be faced with rock, so I'll have to discuss it with Eli.  The berm height is pretty significant and while the engineering drawing shows about a 3 foot drop from the retaining wall, it feels like it will be a little bit more.  The area of the berm near the excavator will actually be a planting bed with no walkway so good soil amendment will be needed here.  There are a two sprinkler heads in the area of the pool that will need to be addressed.  One was intended to be a landscape sprayer and the other was a grass sprayer.  I think all the planting areas can be either fed off of the existing bed sprayer circuit, or tied into the lawn sprayer, but I would probably prefer the former.

   Here's another shot of the soil stratification.  I guess we're lucky to be on sand since we don't have to worry about water drainage issues.  You can see the thing, 2" layer of topsoil laid down when the yard was leveled.  While it might be good enough for grass to grow, it doesn't create a deep root zone to make the grass more drought tolerant.  Since most of the undisturbed yard is like this, I'll have to keep applying top dressing amendments to try to grow that fertile zone deeper.

   That's all the update for now, but more will be coming soon.  There will a 1 day pause in digging for personal reasons, but should resume, and possibly be completed, by the end of the week.  As mentioned earlier in this post, after the digging is completed, drains and some returns are placed.  We currently have the drain, two skimmer boxes, and sun shelf bubbler on site, but I haven't seen any return nozzles, so I'm not sure how that works.  They might just lay a bit of pipe for the concrete wall penetration and later finish it with a surface mounted outlet or something.  A steel rebar cage is installed in the perimeter of the pool, which is formally inspected.  Then the gunite (or shotcrete) is sprayed into the rebar caging and smoothed.