Excavation

Prerequisites for Excavation:

• Layout completed.  Otherwise they don't know how/where to dig the hole in the ground
• Notice / Confirmation # from Bluestake.  They want to make sure you had them come out (or intend to have them come out) to identify the utility lines before any digging commences.
• If you are planning for a rock waterfall, determine if you would like a "submerged boulder" look in the pool.  The excavators will need to know this upfront so that they excavate the area for the waterfall pad properly.

The Excavators basically dig the hole in your ground for the pool.  They use the markings painted in by the Layout sub as a guide to dig from.  Most excavators will use a backhoe to do the dig, but if they can't bring it into the area where they do the dig, they use smaller bobcat tractor instead.  Usually, this means more time which translates into costing more $$$.  If they can get a backhoe into your back, they usually try to pull up the dump truck that will carry the fill right into the backyard as well.  That way the backhoe doesn't have to travel far to dump its load.  In my case, since my access way to the back was only 10ft wide, they had to leave the dump truck outside.  The excavation sub estimated that my job would take about a day and a half, but ended up taking two days due to the distance they had to drive to the landfill to dump the dirt.

The excavators that I subcontracted were extremely knowledgeable about pool excavation.  They do work for about 20 pool companies in the Metro Phoenix area and have dug thousands of pools.  I found that there were a lot of smaller companies that do pool excavation, but none that I spoke to had the experience level that they did.  Its interesting too, that they had an extremely competitive bid.  It came in at a figure that was better than some of the smaller companies.  They have about 10 crews during this time of year (summer) to handle the demand.

Thursday, August 15, 2002 8:03am
The excavators actually showed up earlier than their dispatcher said they would.  Fortunately, I had cleared out the side of the house that the bobcat would be coming through just a few minutes earlier.  It was filled with weeds, and all kinds of extra junk that would have impeded their path.  I woke up at 5am in the morning to get a head start and cleared everything by 7:45am.  The excavation crew consisted of three guys.  The crew chief was the one who ended up working the bobcat and doing the skill work.  The other two guys were the assistants who did the support work (e.g. put up the forms, check elevation, mark form lines, do measurements, trimming, take down gate, etc.).  The crew chief told me later that he had been with the company for about 2 years and dug about 3-4 pools a week.  That put him at between 300 - 400 pools dug.  That was pretty impressive.

The first order of business was dismantling the front gate that led to the back.  I made the mistake of getting a 4 ft gate when we bought the house rather than an 8ft RV gate, which is not wide enough for a bobcat to get through.  Interestingly, they didn't charge me anything for taking down the gate.  People have told me that it would be about $100 to have someone come to dismantle it.  I guess it was included as a part of the job.  They weren't very nice to it.  A couple of whacks with a sledge hammer was all that was needed.  He wasn't a guy you wanted to get mad.

The First Crisis
Before they actually started digging, the crew chief asked me what the elevation of the pool needed to be.  I thought to myself, "Hmmm, I have no idea what he's talking about."  When I asked him what he meant, he tried to explain, but it was kind of hard to understand.  He was Hispanic and his English wasn't very good.  He paused for awhile then said that he was going to call the office to find out.  I suddenly felt very foolish.  Here I was the General Contractor, and I couldn't tell my sub what he needed to know in order to do his job.  I started to get concerned.  The excavation is the foundation for a quality pool.  If the excavation is not done properly, it leads to problems for the shotcrete, steel, and decking subs later.  For example, if they over dig it or dig it imprecisely it leads to overbreak conditions which leads to the necessity for extra shotcrete.  The gal in my office who along with her husband GC'ed  their pool said that they ended up having to order more shotcrete than originally estimated and it ended up costing them an extra $700.  Anyways, as all these thoughts started shooting through my mind, a mild panic started to overtake me.  Then I remembered Mike, my layout sub, who offered to be my GC, which I respectfully declined.  I swallowed my pride and called him up.  It sounded like I woke him up when I called.

"The excavator guy is asking me about pool elevations.  What should I tell him?"  Mike proceeded to chide me for not going with an experienced GC and told me that this is what $400 would have bought you - peace of mind.  After he finished his diatribe, he graciously offered to talk to him.  Whew.  I handed the phone to the excavation guy and noticed him nodding as Mike spoke to him.  When he was done, I got him back on the phone and asked him what that was all about.  He laughed and said that essentially, he wanted to know what the elevation was going to be for the pool.  Its to allow for proper drainage.  He said that typically you want to allow a 1/4" per foot slope for your decking so that water drains away from the pool.  But you want to do it in a way so that the deck that runs toward your patio slab meets up with the slab.  Knowing the elevation will help you to figure that out.  He said essentially, the elevation is the height of the bond beam minus 2.  Uh, sure, Ok.  I felt so useless.  I wasn't about to risk the quality of the pool, so I swallowed my pride again and asked him if he could come out for a separate inspection for $40 after excavation was done.  He agreed to be back late on Friday when the excavators were wrapping up.  I asked him later on how big of an issue that would have been had that got messed up.  He said that it would have been huge. I took it in stride and carried on like nothing had happened.  That was what I would consider my first crisis as a GC.  I know there will be more, but as I thought about this, I realized how much of a blessing it was to have him act as a stand-by consultant if I needed him.  I asked him if it was Ok to ask for consultation on a per sub basis (basically call him out for a visit only if I needed it).  He agreed.  Since I paid for the visit already, I was determined to get all the details.

Here is what I found out (this is really information that goes into the decking/shotcrete section, but I'm putting it here to explain the elevation question that the excavation guy asked me):

I drew a little (exaggerated) diagram so that it would be easier to understand.  Basically all that is happening is making sure that the water that falls onto the deck (e.g. from rain or splashing) drains away from the pool, but doing it in a way that the deck slab meets up with the patio slab at the same point of elevation.  Its a drainage issue with aesthetics in mind.  What the excavation sub was asking was where should the top of the bond beam be?  The bond beam is the 12" thick section of the pool shell on the top that forms the "lip" around the entire pool.  Its there to reinforce the integrity of the pool's structure.  The back side of the bond beam goes down 6"-7" vertically from the top of the bond beam where it then cuts in at a 45" angle towards the inside of the pool.  It then straightens out to run parallel with the inner surface of the shell and forms a uniform 6" shell vertically all the way down until it starts to curve or radius of the pool.  This curved area near the bottom of the pool is often referred to as the cove and is made 8" thick instead of 6" because this is where the weight of the pool bears down.  The coves could be thicker than 8" depending on pool depth (the deeper the pool, the thicker the cove) and possibly other surcharge forces acting on the pool.

One other note of interest.  Notice at the top of the picture above, I show the various lines that have significance to the pool.  The original pool shape line is the perimeter line of the pool from my pool design drawing.  Six (6) inches outward from that is where the Layout sub spray-painted his layout line.  Eight (8) inches outward from the layout line is where the excavators will put up the forms (I'll explain the forms later).  That means that the pool is now 14" further out than where the pool perimeter line is drawn in my pool picture.  If you notice where the bond beam starts in the back and where the cantilever edge on the Kooldeck overhangs (by 1-1/2")  the bond beam, you should be able to see now why its necessary to put the forms out 14" from the original pool line (bond beam + cantilever overhang = 12" + 1.5" = 13.5").  The extra 1/2" is for margin of safety.  That way, no one can accuse anyone of their pool being too short.  

In the vertical direction, there is a similar situation as shown in the diagram (also not-to-scale) below:

Once the 6" forms have been set at the proper elevation and have been established to be level, the excavators will dig until they reach a depth that measures the exact depth of the pool (as specified from the drawing) plus 9".  This distance is measured from the top of the form to the dirt at the bottom of the pool  The extra 9" is for the 6" pool shell plus the minus 3" water level (water will be 3" below top of bond beam).  Theoretically, you should also take into account the thickness of the interior (pebble-tec), but I found out from the interior sub that the coating is only 1/4" to 1/2" thick at the most.  That's pretty much in the noise.  The forms are all not set at the same height.  For the raised bond beam at the back of the pool, they raise the form by 3 inches.  For the raised spa, they raise the form by 12 inches.  I have some pictures later on this page that show that.

On our way
It was so exciting to see them take the first scoop of dirt (the picture to the right shows the first scoop)!!  The layout was cool, but now, my pool was OFFICIALLY underway!  They first asked me if I wanted to keep any extra dirt for landscaping needs.  They would take the first scoops and set it aside for me.  That was nice of them to ask me that.  I would have forgotten to ask.  However, I wished they could have given me scoops deeper down where the soil is a lot softer (the first few feet is almost rock hard due to compaction and grading from the home builder.  Obviously, that would not have been possible since the hole will have become too big to get around (I needed it beyond the pool).    Oh well.  I ended up taking the initial 6 scoops over to the other side of the house (for a large planter I want to build later) and a few scoops around the waterfall area.  I told them upfront that I also needed to have them dig me a backwash pit.  Its important to tell the excavators about any extra pits or dirt you need upfront, because once they start digging, it may quickly become impossible to get beyond the hole they're digging to access the other side of your property.  My Home Owners Association's (HOA) by-laws state that I cannot backwash my filter into the street.  I have to retain the water on my property.  Backwash pits are common in AZ where this is the case.  Basically all it is, is a trench about 4' x 10' that's anywhere from 6" deep to a 36" deep.  People usually fill it with river rock or some other filler after its dug.  When you backwash, the water fills up this pit and is retained on your yard, where it gets absorbed into the ground or evaporates.  I called up the City of Chandler and they told me they don't have any kinds of restrictions as to where you put in in your yard or how you create it.  On we go!

While the crew chief started excavating, the assistants started pounding the metal stakes in the ground all around the pool.  These stakes will be used to hold up the forms (using thin strips of 6" flexible pegboard material) that will surround the perimeter of the pool.  They drove the stakes into the ground 8" away from the layout line (see picture to left), which was 6" larger than the original pool line.  The picture to the right shows the stakes near the pool entry first step.  The only place they didn't place it 8" away was where the waterfall pad was located.  You can see that in the picture to the lower right - they placed the stakes right on the layout lines.  This was because there would be no 6" shell in the area where the waterfall was located.  The shotcrete guys are just going to lay down a 6" flat pad to lower the rocks onto.  

The assistants also started marking certain stakes with their orange spray-paint and started to measure the distance from them to the original layout lines that were drawn inside the perimeter of the pool.  They then spray-painted the measurements right on the dirt like shown in the pictures to the left and right.  They did this because these lines typically get destroyed pretty quickly once excavation starts.  This would include lines that marked the benches, pool lights, water fall edges, and any other lines drawn inside the pool.  These measurements are used later to help them remember how to reconstruct these lines so that no information is lost.

Here's what the pool looked like after about 2 hours of digging (picture below to the left).  It doesn't seem like much progress has been made, but in actuality, the first couple of feet of surface soil is the hardest.  The home builder is required to compact the top soil and grade it per code, so its tough stuff.  Once the excavators get below this surface layer, it will be like cutting through butter.  In the mean time, the assistants used surveying equipment to make sure the top of the forms were all perfectly even and level in elevation (middle picture below).  You want a perfectly flat and level pool.  Also, you can start seeing the forms start to go up around the waterfall pad area (picture to right below).  Also notice in the same picture how they have reconstructed the original layout line that was destroyed by the bobcat.  They used those numbers they spray-painted on the soil to figure out how to redraw the lines inside the pool.

Here's a picture of the first entry step into the pool (picture to left below).  Finally, after the first day of excavation has completed, here's what the pool looks like (picture to right below).

Just before they left for the day, I asked them to give me an ETA for completing the job.  They said that it would probably take another full day.  It turned out that the landfill that they took the dirt to was in another city and they didn't anticipate having to drive that far.  After the excavators left, I got on the phone with the Layout sub again and asked him to come by to do an inspection just before the excavators were planning to leave on Friday.  So far so good.  The excavation had gone extremely well as planned except for that semi-humorous fiasco about the elevation earlier in the day.  I didn't think things would have gone as well as they had so far.  End of the first day of excavation.  They said they would be back on the job the next morning at around 8:30am.  It was about 4:10pm when they left.

Friday, August 16, 2002, 2:00pm
I had to go in to work in the morning to install some software on my laptop.  After lunch, I was able to load up everything I needed to work from home in the PM, and arrived back home around 2pm.  The picture to the right  is what I saw when I first walked into the back.  Wow - I couldn't believe it.  This was really starting to look like a pool.  It almost looked done.  Man, I gotta say that I was impressed.  I couldn't believe how accurate and precise everything looked and how fast they got to this point.  Then again, I've never built a pool before, so I really can't say how fast it really was.  It was fast to me.  I expected the second day to be much more productive.  After getting through the first few feet of compacted soil, I knew working with soft loose soil underneath was going to speed things up.

Here are some other noteworthy shots.  The first one on the left below shows the shape of the waterfall pad and the bench just below it firming up.  The waterfall pad is kind of interesting.  Here's a schematic that shows how a pad for a waterfall should look like if you want submerged boulders near the front of the waterfall (for the rocks-in-the-water effect) as opposed to a pad for one in which you don't.  The difference is a 9" drop in the front of the waterfall for the "submerged" look, which then takes a step up.  This difference would later turn into a mini crisis near the end of the day.  But I digress.  The excavator was skillful enough to come within 2 inches of the desired shape using the bobcat.  Talk about precision!  He then let one of his assistants (also shown in that picture) finish it off by doing the trimming with a hand shovel.  The middle picture shows the back bench firming up nicely.  To show how precise these guys are, the excavator measured the bottom of the pit near the 4ft depth end of the pool and took into account the 9" they need to leave for the shell and took the tape measure up to the string which coincides with the top of the form.  It was exactly 48" - wow!  If you don't believe me, click on the image to the right to see an enlarged version of it.

Here are some pictures of the various heights of the forms.  Its important to note that the top of the form is where the top of the bond beam will be.  Then on top of that will sit the 4" thick Kooldeck slab when the decking subs come through.  All the forms should be at the same elevation except for the spa (raised 12" higher) and the rolled bond-beam on the back side of the pool (raised 3" higher).  Notice that the one on the left below shows the raised bond beam 3" higher than the forms on either side of it.  The picture on the right shows the raised spa 12" higher than the pool form (each strip is 6" high).

Here are some additional shots.  Here's one that shows the nice dirt ramp that the excavator made coming in and out of the pool (below to left).  Once the inside of the pool is done, the bobcat will come out one last time and they crew will finish up the last part (spa) by hand.  The middle picture shows how nice and vertical all the walls are.  The walls were supposed to come down more or less vertical until you get close to the bottom, at which point, a small curved radius is dug to turn into the floor of the pool.  The deeper the depth of the pool, the bigger the radius needs to be.  The excavator said that at 3ft depths, no radius is necessary.  At 4ft depths, about a 6" radius is created.  At 5ft, a 12" radius is needed.  The assistants took the time to make sure all the walls were all nicely trimmed with the hand shovels.   The last image to the bottom right shows them wrapping up with the spa area.  At this point, the bobcat couldn't do much more.  It can't be used to finish the spa or it won't be able to get out.  The spa was finished by hand by the whole crew.  Much of it had been dug already, so it was a matter of just shaping it with the hand tools.

 One other interesting note - the side of the pool which had the access for the bobcat will be filled with dirt in sandbags rather than with loose dirt.  The reason for this is so that the dirt, being extremely loose, doesn't fall back into the pool.  Had it been a full pool wall, the crew would have created a wall of filled bags, maybe stacking them a dozen high.  The higher that last wall, the more sandbags needed.  Fortunately for the crew, the wall they were working on was the dam wall between the spa and pool, and not much is really needed there.  You can see in the pictures below the crew filling the sandbags, putting on the last few forms, and doing some final shaping and trimming of the spa.

Second Mini-Crisis
Just as the guys were starting to wrap up, the Layout sub walked in and started looking at the work.  He took out his tape measure and started silently checking depths, measurements, etc.  When he got to the waterfall, he said, "Uh-oh.  Ben, didn't you say you wanted submerged boulders for your waterfall to give it the "in-the-water" look?"  I said, "Yes."  He replied, "Then this is not deep enough.  You have the 9" you need for the submerged rock pocket, but the waterfall pad itself is 6" deep.  They need to dig an additional 6" to account for the slab."  The excavator looked stunned.  He said that this is how they did all their waterfalls.  I told him that when I FAX'ed in my bid, I specifically asked for submerged boulders for the waterfall.   I noticed a pained grimace came over his face.  I could hear him cursing under his breath.  It was 4pm on a Friday afternoon, and the last thing he wanted to do was  to spend another hour breaking through rock hard soil for an additional 6 inches.  He said that the first 12" - 24" of soil really need to be dug with the bobcat because its so hard.  He said that it would be difficult now that the bobcat can't be used.  After talking it over some more, they were able to locate a small jack-hammer type of tool they kept handy in their truck.  With that, all three went to work and were able to dig an additional 6" across the entire plane of the waterfall pad within an hour.  The picture on the left below shows the excavator using the hammer tool to break through another 6" and his assistants help by carrying off the loose dirt.  The picture on the right below shows the new waterfall level that is 15" instead of 9" deep.  Another mini-crisis averted!

The last thing they needed to do before they were done for the day was the backwash pit.  I asked them to just make it 4ft wide (which was the width of the bobcat bucket) by 12ft long by 1 ft deep.  The picture to the left shows where I put it.  I chose to put it in the same side of the house that the equipment will be located.  That way the backwash tubing wouldn't need to pulled all the way across the pool to the other side of the house.  After the pool is put in, I plan on filling up the pit with river rock.  I don't know what the capacity of pit is (few hundred gallons?), but I'm guessing that its going to hold more then enough water to do a backwash for a sand filter.  I just hope I'm right.  The excavators charged an extra $100 for backwash pits.  And that was it!

Ta da ....  At the end of the 2nd day, excavation was done.  Here are two views of the completed job, looking at the hole from both sides of the backyard:

I couldn't believe I was done with excavation!!  Next up was the plumber.  I didn't know if I could schedule him to come in as early as Monday, but I was planning to call him to see what his schedule was like for next week.  Just before the excavators left, I wrote them out a check and bade them farewell.  They ended up leaving behind the rubble from the gate they smashed down.  They said that the clean-up crew could take all that stuff away when they clean the rest of the junk up from the pool after the decking/tile/fencing people finish their work.

Some measurements that as a GC I needed to check to make sure pool was properly excavated:

• Measuring from the top of the forms to the bottom of the pool, all depths should be: depth + 9" (+/- an inch or two tolerance)
  • 3'6" depth point should be 42" + 9" = 51" => measured 53" 
  • 4'0" depth point should be 48" + 9" = 57" => measured 58"
  • 5'0" depth point should be 60" + 9" = 69" => measured 70"
• First entry step should be 9" + 6" = 15" => measured 15"
• Spa measurements:
  • First entry step should be 9" + 6" = 15" => measured 15"
  • Spa seat should be 12" below first entry step 15" + 12" = 27" => measured 28"
  • Spa floor should be 12" below spa seat 27" + 12" + 9"  = 48" => measured 46"
• Waterfall pad (for submerged boulders) should be 9" below form + 6" for shell = 15" => measured 15"
• Bench seats are placed 27" down from top of pool => measured 28" for both waterfall and back bench
• Pool lights are cut out 18"W x 18"W x 36"D 
• Skimmer is cut out 24"W x 24"L x 27"-29"D
• Pool widths from form to form should also be measured (across the pool) and checked against the drawing to make sure widths and lengths are all adequate.  This should be done as soon as forms go up so that something can be done about it should something go terribly awry.
• Only first entry step is excavated/shaped.  The second and third steps are minor steps and don't require custom trimming.  They can be completely formed by the shotcrete.  The excavator just leaves a 45" slope in their place to aid that process.  See pictures below:

Problems with the Excavation Phase / Things I would have done differently:

• Didn't know what the elevation of the pool was supposed to be.  The Layout sub bailed me out.  Actually, the excavator should have been able to figure it out.  All he needed to know was to calculate how are away the deck edge was to the patio edge and slope down a quarter inch per foot of deck run toward the patio.  Then take into account the thickness of the deck.
• Excavators messed up on the waterfall pad.  The Layout sub bailed me out again.  I should have caught that.  I should have known that 9" is what was needed for the step down, but that I needed an extra 6" more for the pad itself (Duh!).  I'm guessing it would have been like pulling teeth to get them to come out another day to dig an extra 6" on the waterfall pad.  The fact that the Layout sub caught it before those guys left was HUGE!  The $40 I paid the Layout sub to come inspect the excavation work was well worth the money.  Looking back at it, I should have been more upfront and gone over all the details of the pool with the subs just to make sure we were all on the same page and nothing was missed.
• Actually, there was another problem with their "fix" to the waterfall pad.  To better understand it, look at the waterfall pad schematic first.  Only the first 12" or so of the waterfall pad should have been 9" below zero bond beam.  That way, only the front boulders are submerged.  The boulders behind them should be dry and at +0".  So from the 12" line all the way to the back of the pad, it should have been at +0".  There should have been a step up from -9" to 0" elevation, but they took out an additional 6" all the way across the pad.  This is not a major problem, though.  It just means that I will have to spend more money to fill that area with concrete rather than having that area filled with compacted earth.  One note - I was tempted to backfill that back waterfall pad area with loose dirt to save on concrete, but both the rockworks guy and shotcrete guy screamed for me not to do it.  If the dirt is not compacted, it will most likely shift and settle after the concrete is poured and could compromise the integrity of the pad.  Better to pay an extra $100 or so for an extra yard of concrete and have peace of mind than to nickel and dime only to have major structural damage later.  I'm glad the subs are looking out for me.