1. Mark The Underground Utilities
The first thing you want to do before any digging an inground pool in your yard is make a call to Dig Safe. In some areas it may be called something different like Call Before You Dig or some other name, but this is a law. If this is not done, not only is it not safe but if you hit some utilities underground you will be fined and be responsible for the repair cost.
There is now a national Call Before You Dig line, just call 811 to reach this free service. Usually within 48 hours, they will have a county official come to your property and mark all of the underground utilities. They use a different colored paint for gas, electric, water and cable.
2. Other Underground Stuff
Sprinklers. Before you dig your pool, check for things such as underground sprinkler lines that possibly can be either removed from the area or at least remove the sprinkler heads, as they are the most expensive parts. You may want to mark on a plot plan where each of the heads you removed goes, to make it easier to find when construction is done.
Septic Fields. Leach fields for a septic tank may have been shown in a different area on the plot plan at your city or town but were actually installed right where your proposed pool is going. This happens occasionally when the contractor changed the location and never changed it with the town. In older communities, you may encounter long forgotten leach fields, built before city water and sewer was brought to your area.
Tree Roots. Things such as trees should not be near the pool area for a few reasons. Eventually the root system may work its way towards the pool and undermine the pool liner. Also, leaves or pine needles falling from the tree into the water can be a headache. Shade from trees will keep your water cooler, which can raise heating costs.
Boulders. You may encounter boulders the size of bowling balls, no problem. But if you find very large boulders, a skilled excavator can maneuver them out of the ground in most cases. If it is too big for the bucket size, large boulders can be strap lifted out of the pool. They can then become part of your post pool construction landscape.
Water. When you dig a pool, hitting water is fairly common. Depending on where you hit water and how it is coming in, there are different solutions to handle the water.
If you dig a pool to 8 ft deep and you hit water at the 7 ft mark, what you would do is over-dig the bottom floor. Dig into the side slopes 1 ft more and 1 ft deeper in the bottom depth, making your 8 ft deep end - 9 ft deep. Have a few yards of gravel delivered, enough to bring the level back to your 8 ft depth. Sometimes this will be enough to fix the problem and allow the pool construction to continue. You may have to put a sump pump in the bottom to keep out the water if the stone alone does not work.
In more extreme water problems a french drain may need to be installed. This is an 3 or 4 inch under ground drainage pipe, buried in the stone at the deepest point. The drain pipe runs out of the pool (under walls), and connects to a self priming pump outside the pool. If you have to do this you would keep the pump running until the pool is built and full of water and only at that point can you shut the pump off.
3. Dig the Shoebox
Before you start the dig process you want to stake out your pool to know exactly what and where to dig. First, mark the over dig area - this is generally 5 ft longer and 5 ft wider than your actual pool size - with paint or flour, something you can see. For example, if you have a 16 x 32 pool your over dig would be 21 x 37.
Strip the top soil off and put it in a separate pile for use during the backfilling process. Once you have stripped the top soil you can start digging down to a flat, shoebox shape, 42” deep ( the wall height of the pool ). You will end up with a large hole 5 ft longer and wider than your pool size, and a flat and even 42" depth overall.
4. Stakes & Strings
Once you have the shoebox dug, it's time to stake out your pool. Measure in 2 ½ ft in from the over dig all the way around. Using our 16x32 pool size example, square up the 16 x 32 pool area within the 21 x 37 over dig area. Place a pin or stake in each of the 4 corners and a string line all around to make up your pool.
Locate the Break. From the shallow end on our 16 x 32 we measure down the 32 ft side - 8 ft, (from points 5 to 4 and 6 to 7). This is the end of our shallow area, known as the "break" from the shallow section to the sloped section. Run a string line across the pool, from point 4 to 7, now we have our shallow end located.
Locate the Hopper. The slope length is 14 ft, so we measure at the base of the wall from point 4 to point 3, and then the opposite side, from pt 7 to pt 8. Put a pin on each side, just below the wall (indicated by the red dots). This is where our slope ends and the hopper pad or the flat bottom begins. Run a string line across the pool, from point 3 to point 8.
Now we measure 6 ft along the base of the wall, from point 3 to 2, and from point 8 to 9. This lays out the other side of the flat, 8 ft deep bottom. What you should have left is 4 ft to the end of the pool., or from point 2 to 1 and 9 to 10.
Now we move to the width or the ends of the pool. Measure 4 ft from the deep end corner pins on the pool and place a pin at points A, B, C and D. Run a string line from shallow end pins to deep end pins, or from A to B and C to D.
Now you will have a 6 x 8 rectangle made by the intersection of the string lines towards the deep end of the pool. This is your deep end flat hopper pad.
5. Dig the Deep End
Now you are ready to continue digging your pool. Remove your inside string lines and replace them with bright paint to help the excavator locate the hopper bottom. Start digging out the square hopper, digging down 4 ft-8 in more (from the 42" depth) to make it 8 ft deep at the pool bottom.
Once you reach that depth in the flat, start from the corners of the hopper bottom and dig up to the back wall of your deep end and that will be your back slope. Now go from either side of the deep up to the side walls to get your side slopes. Finally, work on the slope from points 4 and 7, to the near corners of the hopper bottom. You now have the pool rough-dug.
Replace the string lines used to locate the hopper bottom, and use a plumb bob to double check the location, and to measure the depth of your hopper bottom. At the correct depth for your pool bottom should be 2” deeper than your finished depth This 2" depth will be filled with your finishing floor material.
It's likely that you'll need some flat shovels and trowels to perfect the angles of the walls, or the joint where the deep end wall sections come together. It won't need to be perfect, because you'll be adding 1-2" of floor material, but it should be pretty close to the original spec shape before beginning the floor work.
For more information on Digging an Inground Pool, see these other fine blogs written by Yours Truly:
Of course, you can always talk with us before and during your pool dig, if you run into something you are unsure about. When you purchase your inground pool kit from SPP - we're with you every step of the way, from layout to landscaping!
SPP Pool Expert