DIG DAY - few soil/dig issues - any expert thoughts out there welcomed

[Riddler0520]

Hi everyone

well, 2 day dig and a few issues but things I believe got resolved - just looking for some confirmation from the experts on the site

our lot (backyard) has always had a wet spot and we are dealing with a 5.5 ft elevation change - our lot sits downstream to lots at higher elevations so water drains down and catches in our low spot of our back yard

NC Clay
3.5’-6’ depths
Dig down and start to see some soil (grey in color and wet’ish) different from the orange clay - more exists where the low spot in yard was and deeper depth and has always been wet - always have curious what it looked like beneath the ground (the cause)

PB wanted to ensure a strong base so he dug down to over 9 feet (actually hit some rock at that depth) and brought in 3 trucks of gravel (forget how many tons) and compacted it down to build a solid foundation + he said he would act as a filter for water to run through more easily

He has 3 feet to play with to install gravel, rebar and concrete

This is not my area of expertise and hope we have some members with thoughts on what we ran into and what we did

Color of clay ?
Solution with thick gravel base ?

Anything else I should ask them about ?

thanks all for your help - this site is a savior

 

[Riddler0520]

Vertical Image

 

[ncpoolguy]

Excavators just finished our dig and we had that same gray soil, didn’t know what it was! It was rock hard. We too have a lot that several houses slowly drain to—we put a French drain to solve that problem and figured the gray soil was further making water pool at the bottom.

 

[Riddler0520]

Excavators just finished our dig and we had that same gray soil, didn’t know what it was! It was rock hard. We too have a lot that several houses slowly drain to—we put a French drain to solve that problem and figured the gray soil was further making water pool at the bottom.
View attachment 157277

Thank you
Fellow North Carolinian

Good luck on your pool build

Did your PB have any concern with the grey soil and water penetration ? Is he putting down gravel as a base ?

We too will do a few catch basins and drain along the perimeter to redirect runoff water from higher elevated lots

 

[HermanTX]

Congratulations on becoming a pool owner and welcome to TFP forum. Post some pictures of your proposed pool graphics if you have any. Your PB did a good job to think through a solution while he had the heavy dirt moving equipment on site. The only thing I can think of is to ensure that water coming from land "upstream" of you has a way to go around your pool (such as the french drain noted by @ncpoolguy) and not through your pool - i.e.. flowing across your deck and into the pool. This happened to someone (another post) and they were trying to clean up the mud in their pool from a neighbor's yard. Will you have an auto overflow on your pool? Where will that flow to? Your yard looks bigger and not that close to your neighbors so you may have some room to ensure any drain off goes elsewhere.

Please put your pool information in your signature line - go to settings in your profile. This will help others in the forum to assist with any further questions that may arise.

 

[Riddler0520]

Congratulations on becoming a pool owner and welcome to TFP forum. Post some pictures of your proposed pool graphics if you have any. Your PB did a good job to think through a solution while he had the heavy dirt moving equipment on site. The only thing I can think of is to ensure that water coming from land "upstream" of you has a way to go around your pool (such as the french drain noted by @ncpoolguy) and not through your pool - i.e.. flowing across your deck and into the pool. This happened to someone (another post) and they were trying to clean up the mud in their pool from a neighbor's yard. Will you have an auto overflow on your pool? Where will that flow to? Your yard looks bigger and not that close to your neighbors so you may have some room to ensure any drain off goes elsewhere.

Please put your pool information in your signature line - go to settings in your profile. This will help others in the forum to assist with any further questions that may arise.

Thank you for your reply

Tried to taking elevation and surrounding issues into consideration as slope of yard and future water has been top of mind (not as much thinking of what’s under the ground)

The entire pool will be elevated with the front lip about 18” which will match an existing wall and fire pit and the raised spa at the highest point of the yard - the back pool wall will be raised about 6”-8” so we can have stone vaneering but most importantly act as a small retaining wall to redirect any water off of the surface

French drains and basins will loop around the full perimeter and final grade will try and redirect rain ground away

I think we are doing a good job above ground thinking through things and now need to make sure under the ground has been done right - think it has as the explanation and all of the extra time they put into digging to 9 ft+ and 3 dump trucks of gravel - he seemed confident would more than support.

 

[Rich D]

Do you have any pics of the wet area before the excavation?
Did the PB determine where the ground water level was when he was excavating? The first few feet were most likely wet from perched trapped surface water then I would have expected a dry clay for several feet then you should have seen ground water seeping in from side walls. That would be the current summer water table.

Do you have a current drainage system for your gutter downspouts and if so where does it go to?

The obvious place you will have surface water issues is where the existing retaining wall meets the pool. (where the excavator bucket is in one of the first post pics) I would not trust a French drain in that area. I would create a low spot and install a mini catch basin with a frame and grate to grade. As well as have some surface French drains going into the catch basin as well. The out fall from that should a solid pipe out to daylight.

Are you rebuilding that existing retain wall? Does it have a existing drain behind it?

 

[Riddler0520]

Do you have any pics of the wet area before the excavation?
Did the PB determine where the ground water level was when he was excavating? The first few feet were most likely wet from perched trapped surface water then I would have expected a dry clay for several feet then you should have seen ground water seeping in from side walls. That would be the current summer water table.

Do you have a current drainage system for your gutter downspouts and if so where does it go to?

The obvious place you will have surface water issues is where the existing retaining wall meets the pool. (where the excavator bucket is in one of the first post pics) I would not trust a French drain in that area. I would create a low spot and install a mini catch basin with a frame and grate to grade. As well as have some surface French drains going into the catch basin as well. The out fall from that should a solid pipe out to daylight.

Are you rebuilding that existing retain wall? Does it have a existing drain behind it?

Thank you for your reply

Image below is prior to dig and the water/low point of yard it the area behind the existing wall/fit pit beyond the plant beds

The existing wall will stay and had a few weep holes and we will replace the down spout drains and tie those in the new drains as well

Second pic is the hole this morning - we put all the gravel in the hole yesterday and don’t believe it rained but still have water seeping in (>9ft deep) - is this normal ? Guess they will need to keep it pumped out during rest of build

In our main yard we will install a number of wide catch basins in addition to piping along the pools perimeter

In addition there are a few places where the old/new wall will meet where we will install a catch basin and drainage

Is it OK to construct the pool shell with ground water seeping in ? After the Gunite is hit, there is no way for water to seep through the walls/bottom ?

I don’t know enough about this stuff but imagine since they build pools in Fl at almost zero elevation this has to be OK

 

[ncpoolguy]

Thank you
Fellow North Carolinian

Good luck on your pool build

Did your PB have any concern with the grey soil and water penetration ? Is he putting down gravel as a base ?

We too will do a few catch basins and drain along the perimeter to redirect runoff water from higher elevated lots

No concern with the gray clay soil from our excavator. There wasn’t any water seeping up from our dig, but before we put the pool in, we would always have seeping water coming up from the soil at the bottom of the hill. (Which is why we had a French drain put in before we planned on a pool.)

 

[kimkats]

I LOVE your design! I

I am going to call in a couple of people who may have some input on the ground water issues. @bdavis466 @jimmythegreek

 

[Rich D]

- we put all the gravel in the hole yesterday and don’t believe it rained but still have water seeping in (>9ft deep) - is this normal ? Guess they will need to keep it pumped out during rest of build

Yes, if it does not rain then where it stops rising is your current water table.

In addition there are a few places where the old/new wall will meet where we will install a catch basin and drainage

Where is all this drainage going to outfall? How much lower than the pool deck is the lowest point on the property where you can daylight a drain line? Where do the roof drains currently outfall?

Is it OK to construct the pool shell with ground water seeping in ? After the Gunite is hit, there is no way for water to seep through the walls/bottom ?

Yes, it is done all the time. How much higher is the current water level than the proposed bottom of the pool? They will let the ground water come in the main drain opening and pump it out for the build. Then they will install a hydrostatic valve in the main drain bucket that will keep the ground water out as long as you have water in the pool but will let it in when you drain the pool and the pressure gets greater on the other side of the valve. This will prevent your pool from floating when you need to drain it for maintenance.

Relying on just the hydrostatic valve can be problematic. When ground water goes through the valve it can carry debris that can cause the valve to stick open. They can also get clogged and not work correctly.

I would install a sump pit beside the pool at least 1 ' below the lowest point of the pool. This does not need to go at the very edge of the pool. You can dig a trench and install a 6" perferated pipe encased in stone and filter fabric below the bottom of pool to get the sump away from the edge of the pool.

This will allow you be able to monitor the ground water level (this can be very helpful in many ways) and pump it down when you need to drain the pool. That would prevent water going through the hydrostatic valve and make any maintenance much easier to preform.

 

[Riddler0520]

Yes, if it does not rain then where it stops rising is your current water table.



Where is all this drainage going to outfall? How much lower than the pool deck is the lowest point on the property where you can daylight a drain line? Where do the roof drains currently outfall?



Yes, it is done all the time. How much higher is the current water level than the proposed bottom of the pool? They will let the ground water come in the main drain opening and pump it out for the build. Then they will install a hydrostatic valve in the main drain bucket that will keep the ground water out as long as you have water in the pool but will let it in when you drain the pool and the pressure gets greater on the other side of the valve. This will prevent your pool from floating when you need to drain it for maintenance.

Relying on just the hydrostatic valve can be problematic. When ground water goes through the valve it can carry debris that can cause the valve to stick open. They can also get clogged and not work correctly.

I would install a sump pit beside the pool at least 1 ' below the lowest point of the pool. This does not need to go at the very edge of the pool. You can dig a trench and install a 6" perferated pipe encased in stone and filter fabric below the bottom of pool to get the sump away from the edge of the pool.

This will allow you be able to monitor the ground water level (this can be very helpful in many ways) and pump it down when you need to drain the pool. That would prevent water going through the hydrostatic valve and make any maintenance much easier to preform.

Rich, thanks so much for taking the time with such a detailed response.

PB and crew coming by tomorrow to continue to frame out the walls

The deep end is only 6 feet and they dug just over 9 feet - they brought in 2 dump trucks of gravel (can’t recall how many inches) but he said it was significantly more than a normal install.

So that leaves them with 3 ft for gravel, rebar and Gunite to achieve depth level - they over dug for this issue specifically he said

He mentioned the hydrostatic valve as well but not sump pump option ?

Even with all of the drains we are putting around the perimeter and yard the reality is our yard is the low point on our street and the 4 lots to the right are all at higher elevations so we can all the runoff. He also said final grade they would swale the water away from pool but that is surface water right, not all the water under the ground

All gutters have always tied into French drains as everything runs to an adjacent dry creek and dumps out

Attached a pic of where the old and new rear retaining walls will meet - definitely need to have a large catch basin and good drainage to move the water that will just catch in this corner - any thoughts on what I should suggest or listen for from PB ?

Also inc arial view so you can see what we did was leverage the pool wall as a retaining wall with the bottom right, having a small wall and then the higher one above that runs ultimately into the SPA

They should be doing rebar this week if weather holds up - knowing we have water and soil issues being addressed is there anything they should be doing more of with Rebar to ensure added skeletal reinforcement ?? This site is amazing and reading up as much as I can

 

[Rich D]

Second pic is the hole this morning - we put all the gravel in the hole yesterday and don’t believe it rained but still have water seeping in (>9ft deep) - is this normal ?

How far down is that standing water in the pic from the top of that form board?

All gutters have always tied into French drains as everything runs to an adjacent dry creek and dumps out

Can you tell approximately how much lower is that creek bed than the top of there forms for the pool beam? Is the place we're it dumps out on your property?

He mentioned the hydrostatic valve as well but not sump pump option ?

The sump would be a additional structure that is not required but it is just what I would do in this situation because you are already dug that deep and to install it now is relatively short money for the benefit it will supply. To be clear when I say "sump" this is a 10" ads pipe set in the ground vertically that goes down to 1' below bottom of pool and comes to the surface. You do not need to install "pump" unless the ground water gets very high or you want to pump the water out of the pool. Mention this to the PB and get his thoughts on it. The decision to install a sump would weigh heavily on the current ground water level so please answer the first question above ..

knowing we have water and soil issues being addressed is there anything they should be doing more of with Rebar to ensure added skeletal reinforcement ??

It sounds like the PB removed any questionable material and replaced it with clean stone on top of ledge. That is a good solid base. I would not think additional rebar would be necessary but that would be a question for a structural engineer. Ask the PB if there is a structural engineer overseeing these details.

 

[Riddler0520]

How far down is that standing water in the pic from the top of that form board?



Can you tell approximately how much lower is that creek bed than the top of there forms for the pool beam? Is the place we're it dumps out on your property?



The sump would be a additional structure that is not required but it is just what I would do in this situation because you are already dug that deep and to install it now is relatively short money for the benefit it will supply. To be clear when I say "sump" this is a 10" ads pipe set in the ground vertically that goes down to 1' below bottom of pool and comes to the surface. You do not need to install "pump" unless the ground water gets very high or you want to pump the water out of the pool. Mention this to the PB and get his thoughts on it. The decision to install a sump would weigh heavily on the current ground water level so please answer the first question above ..



It sounds like the PB removed any questionable material and replaced it with clean stone on top of ledge. That is a good solid base. I would not think additional rebar would be necessary but that would be a question for a structural engineer. Ask the PB if there is a structural engineer overseeing these details.

Standing water I would say is at the 7ft depth but that’s a rough guess looking after we pumped water out of deep end - assume that’s the water table or the path the drainage takes downhill

The adjacent creek is much lower than the top of the frame boards - if I had to guess I would say 6ft lower - and yes, existing French drains and future drainage will open up at creek

Attaching a picture of the creek running between our property and neighbors - it is technically common space and the water eventually goes under the street into a pond that connects with the city - side yard is torn up but expected that

The walls that have caved/or had chunks of soil fall with rain is the area of the grey soil which PB said is “bad soil” or just saturated as has never dried out

They are going to finish forming out the pool shape and he said he plans to put plywood behind to act as a wall for I guess the Gunite to hit against - he said they are considering putting more gravel behind the Gunite wall/sides when they backfill in - does this sound like a good approach ?

How important if any does the earth/soil walls really matter ? I’ve seen pools constructed literally in the air with no actual land/soil so I might be over reacting to the grey soil issue and it’s importance behind the Gunite walls

Thank you

 

[jimmythegreek]

PB should install some piping that he perforates in the gravel under deep end for future pump out if needed. Easy amd cheap to do, run it to an adjacent sumo pit as rich described and insist this pit be installed. Not gonna cost much now amd may be a lifesaver later on, at the least you can monitor ground water. If it was me I'd have it setup with electric amd discharge and a float pump from the get go. Being you are near a creek and low I foresee hurricanes amd heavy rains giving you issues one day

 

[Rich D]

Standing water I would say is at the 7ft depth but that’s a rough guess looking after we pumped water out of deep end - assume that’s the water table

Certainly sounds like that would be your current water table. This will most likely get higher during the wet seasons.

The adjacent creek is much lower than the top of the frame boards - if I had to guess I would say 6ft lower - and yes, existing French drains and future drainage will open up at creek

I would recommend getting a laser level or a optical builders level to shoot some grades (your PB must have one) and determine if the creek bed is at or below the bottom of the proposed pool. If the creek it is the same or lower than the bottom of the pool then your best bet is to simply install a gravity drain from below the pool floor to the creek bed. If there is some pitch to the creek bed that is great However a 6" sdr pipe can be laid level in theses types of situations and will work just fine. You will want to perferated the first 10' of the pipe as well as perferate the end cap to get the water into it, then the rest can be solid. It is very important to encase the entire run of pipe in stone and the stone should be completely wrapped in a good quality filter fabric. Do not run any other drainage into this pipe. You should lay a second pipe that has pitch on it to accept any other drainage you install for storm water. If the creek is higher that the bottom of the pool then you should install the sump as described earlier and put a 6" outfall pipe from the sump to the creek at the elevation of the creek. This pipe can be installed flat as well and should be encased in stone and fabric . That will keep your ground water level at the same elevation as the creek at all times of the year and you will still be able to pump it down below the bottom of pool for maintenance.

How important if any does the earth/soil walls really matter ?

As far as shooting the gunnite on the plywood that is standard. I would recommend a granular backfill for good drainage so the water will easily get down to the drain and not collect under the deck.

 

[Riddler0520]

Certainly sounds like that would be your current water table. This will most likely get higher during the wet seasons.



I would recommend getting a laser level or a optical builders level to shoot some grades (your PB must have one) and determine if the creek bed is at or below the bottom of the proposed pool. If the creek it is the same or lower than the bottom of the pool then your best bet is to simply install a gravity drain from below the pool floor to the creek bed. If there is some pitch to the creek bed that is great However a 6" sdr pipe can be laid level in theses types of situations and will work just fine. You will want to perferated the first 10' of the pipe as well as perferate the end cap to get the water into it, then the rest can be solid. It is very important to encase the entire run of pipe in stone and the stone should be completely wrapped in a good quality filter fabric. Do not run any other drainage into this pipe. You should lay a second pipe that has pitch on it to accept any other drainage you install for storm water. If the creek is higher that the bottom of the pool then you should install the sump as described earlier and put a 6" outfall pipe from the sump to the creek at the elevation of the creek. This pipe can be installed flat as well and should be encased in stone and fabric . That will keep your ground water level at the same elevation as the creek at all times of the year and you will still be able to pump it down below the bottom of pool for maintenance.



As far as shooting the gunnite on the plywood that is standard. I would recommend a granular backfill for good drainage so the water will easily get down to the drain and not collect under the deck.

Thank you - they have a laser level as they are using it to shoot the retaining wall and steps etc...

I will ask them about the gravity drain as that make sense and keeps water from collecting below and around the deck

They excavating more of the grey/wet clay today and got all of the loose stuff away - they have finished forming the walls and plan to put gravel and sure soil behind the walls to aid in water filtering - that is reassuring you are mentioning the same.

Below is progress as of end of day today - they have plumbed some drain in the deep end, think that helps pump the deep end but only noticed it after they left for the day.

I’ll share an update on the creek and drain after speaking with PB. He is pretty patient with me trying to explain things where I can understand.

Q: if you don’t install the drain as suggested, what are the issues that could result ?

He doesn’t seem that worried about things and seems to be taking the appropriate steps.

I guess next up is some of the roughed in plumbing and rebar.

Another silly question - if I want to measure to make sure everything is to speck - what should I allow for edge to edge - thickness of wall for width, height of walls/deck (to coping) etc ...

They’ve made some adjustments especially to retaining wall and steps onsite vs drawings as their explanations for the changes all made sense.

Thank you

 

[Rich D]

Q: if you don’t install the drain as suggested, what are the issues that could result

Think of all that stone and granular backfill material surrounded by a clay barrier. It is basically a underground bath tub that will now attract and hold water. This can saturate the surrounding clay and that mysterious white soil and cause it to settle or swell which could give you soggy areas under your deck and in the lawn. The way that white material is caving in and the fact is was saturated and had to be removed is a good indication it was previously disturbed of was placed there as fill. You really want to remove as much water from that area as possible. The wick drain I described will dry out the entire area and keep the ground water away from the pool shell. The fact the area was always wet before is a huge indication that a wick drain is required to dry up this area.

 

[Rich D]

Be sure to have a conversation with the PB about proper compaction of all the backfill material. That site material can not be properly compacted to put your deck on. You now have some very deep fills which most gunnite pool installs do not have. You will need a good granular material compacted in lifts or clean stone (which does not require compaction) as he used below the pool. Driving over the material or letting it settle over time are not acceptable compaction methods an will lead to settling material.

 

[Riddler0520]

Be sure to have a conversation with the PB about proper compaction of all the backfill material. That site material can not be properly compacted to put your deck on. You now have some very deep fills which most gunnite pool installs do not have. You will need a good granular material compacted in lifts or clean stone (which does not require compaction) as he used below the pool. Driving over the material or letting it settle over time are not acceptable compaction methods an will lead to settling material.

Thank you again - you are extremely helpful and giving me things to review with PB.

When you say fills - I presume you mean the open space behind the walls where they excavated some extra soul away and needs fill ? What would be your preferred method of compaction ?

Did they need to do the same for the floor ?

Crew came today to do rebar and rough plumb - I’ll attach a pic if you would be so kind and zoom and give thoughts
Is there anything I need to ask them about what they did with rebar - not sure given the site, if a certain approach needed to be taken.

This can be an intimating and overwhelming process but this site and your help really is appreciated.

We’ve got some time now to discuss the gravity drain and options as the city inspection I believe is next before it’s shot.

THANK YOU