Continuing our series of blog posts covering the small steps of how to build an inground pool, today's topic is one of the big ones. Pool excavation is the technical term, or you could just call it the Big Dig. Whatever you call it, and whether or not you will actually do the digging yourself and operating the backhoe or bucket loader, or just work alongside a contractor - there are some important things you should know.
At this point, you’ve already checked with the city or county commission that handles pool permits, and filled out all of the necessary forms and requirements. You also have the dig sheet that came with your inground pool kit.
One other important prep step is to call your local Dig Safe or Miss Utility. Most areas have a free service that will come out and mark all underground lines. To avoid any problems, make sure that you contact them to schedule a visit to your dig site, in advance of digging your pool.
Step 1: Mark the Overall Area
If our pool is 18’ x 36’ and we have a walk-in step at the end of the pool, we actually have 18’ x 40’. The area needed just for the pool construction is dug out 5’ longer and 5’ wider to allow for spacing for your bracing. So, we need a hole that measures 23’ and 45’.
Going one step further with this, let’s say you are looking to build a concrete pool deck around your pool, 4 ft on the long sides and the deep end wall and 10 ft behind your shallow end, walk-in steps. Adding up your width, we have 23’ for pool and bracing + 8 ft of decking for a total width 31 ft. For length, we have 45’ + 14 ft of decking. 59 ft total
Mark out the overall 31’ x 59’ area with lime or paint or 4 stakes and string lines. This area includes any planned decking.
Step 2: Remove the Grass
Next, remove all the grass and topsoil from this area. You can use a skid loader, or use flat shovels and scrapers. Some rental shops have a sod cutter machine that you could use to replant your grass in another area. Any removed topsoil can be put in an out of the way location, and will come in handy after the pool is built.
Step 3: Mark the Pool Area
Including spacing for bracing; our pool area is 23’ x 45’. Mark out the pool dig area with lime or paint and/or 4 stakes and strings.
Step 4: Measure for Depth
The top of your pool wall will stick up about 6” above the surrounding ground, to account for the sloping pool deck. When installing your patio you want to pitch away from the pool ¼” slope for every foot of decking. Our 4 foot deck in this example will pitch a total of 1 inch, from front to back. Our 4 inch thick deck, plus 1 inch of gravel, plus 1 inch of slope, equals our 6 inches. The finished wall height for our example is 6" higher than the surrounding ground.
For a standard inground pool kit, the walls are 42” tall and we have to add our pool coping that sits on top of that also. If you use concrete receptor coping you would add 2 ½” - for a total of 44 ½” height. Now if we want that to be 6” above the ground (to meet the pool deck) that means our walls will only go 38 ½” deep into the ground. Note that your pool's finished elevation should be 3-4" above surrounding yard areas to prevent run-off onto the pool deck and even worse, into the pool. If it cannot be avoided, install small retaining walls to direct run-off around your pool.
This top wall measurement will be important to establish, so that you dig from a common reference point. Use a transit to shoot accurate measurements around the pool if you can. This will save work shimming the walls to be level later. Good measurements at this stage will help the excavator to not overdig or underdig the pool.
Step 5: Dig the pool to the shallow end depth
What you want to do now is dig the area down to that depth all throughout the pool area. You will also need to make this area level, so it may be different depths around the pool if the yard has a slope.
You can dig this part of the pool using a front loader, or a small Bobcat type of skid steer loader. A skilled operator will have an easier time than one who is not, however, if there is room to move around, even amateurs can successfully dig a pool.
Of course you’ll need to place the material removed out of the way, until it is needed again for backfilling against the braced up walls, over top of the concrete collar that is poured. Keep in mind that you may need two scheduled appearances of some earth moving equipment, the first to dig the pool, and then again to backfill the pool walls.
Step 6: Mark the Deep End Hopper Bottom
After you have the area dug flat to your correct shallow end wall level all over, you can string out your actual pool wall line (inside dimensions). What we are looking for now is our 18’ x 36’ pool area. Stakes and strings from all 4 corners, making your rectangle. Place the stakes low to the ground, with the string marking where the foot of the wall will be resting. After staking out the pool shape, measure from opposite corners - corner to corner, and make sure they are square, or that the cross measurement is identical in both directions.
Shallow End: On an 18 x 36 pool, the shallow area is 12 ft long before the floor “breaks”, and begins sloping to the deep end. From the shallow end corner, measure 12 ft down the string line and place another stake and do the same on the opposite side of the pool. Run a string line from one stake to the other across the pool to mark the end of the shallow area.
Slope: Your slope from shallow to deep is 14 ft long so measure from your shallow end stake down the string line 14 ft on each side. Place a stake on each side of the pool, marking the end of the slope and the beginning of the deep end floor. Run a string from stake to stake, across the pool.
Deep End: From the 14 ft stake point, measure 6 ft more . Place another stake on each side of the pool at this point and run a string across. This marks your deep end bottom and what you have left is 4 feet until the wall, which is the slope going up the deep end wall.
From side to side, across the deep end, measure-in 4 ft from each corner and those will be your side slopes. Place stakes and string at this point. That will give you a 10ft wide bottom floor. You should now have the bottom floor "boxed-out" with stakes & strings. Measure across the box, at a diagonal, to make sure the floor is a perfectly square rectangle.
You can now is dig down 4'-10" ft deep from that string line which will give you your 8’2” deep. We dig a bit deeper to account for floor material that will raise the floor to an 8ft depth in the deep end.
Angled Sides: Traditional deep end "Hopper bottoms" have a very angular shape. To get the angle right for the walls, place a pin in the center of the corner of the wall and a pin at the bottom of the 8’2” corner and put in a string line to the right depth of 8’ and that will be your 2 deep end corner angles. Now come back 6 ft from that point towards shallow and run a string line across the width of the deep end. This will be the other 2 corners of the deep end, dig that down to the 8’2” depth and you have your deep end pad done. Next you will take a string line from those 2 pins back up to the end of the shallow which will be the 2 pins at 14ft and dig that area out and that is your shallow to deep end slope.
Step 7: Dig the Deep End
Usually we want to start digging from the deep end wall back towards the shallow end. Dig the hopper out first, then dig away the back wall, following the strings marking the angles from deep end wall corner to deep end hopper bottom. As you back up out of the deep end, you can shape the side walls, following the string from end of shallow floor to beginning of hopper bottom. Alternatively, you can dig the deep end angled walls from up above the pool, with the long arm of the excavator. Work slowly on the hopper bottom, using all of your expertise to dig the deep end according the dig spec sheet that we provide.
You have now successfully dug your pool and the string lines will be at the finished depth of your pool. Using stakes & strings are your guide to a perfect pool bottom. If you have any questions along the way, that's what we're here for. Our customers can call their personal expert pool consultant, any day of the week at 855-863-4301.
SPP Pool Expert