Should Wet Well be doweled to Pavement or Not 3

[oengineer]

I am working on a Wet Well Design that will have pumps sitting on top of it. The Wet Well will NOT have a concrete top covering it. Instead, a pump skid will rest on top of the Wet well to cover the hole. The interior diameter of the wet well is 8'-0".

I have attached a link with 2 types of options for constructing the Wet Well:

https://files.engineering.com/getfi...3-95cf-fa4c131232da&file=WET_WELL_OPTIONS.pdf

For option 1: A 1'-0" thick pavement is doweled into the Wet Well. Then the pump skid is placed on top of the wet well to cover the 8'-0" dia hole. Then the anchor bolts for the pump skid would be installed into the pavement.

For option 2: A 1'-0" thick pavement is adjacent to the Wet Well, but separated by expansion joints. The pump skid anchor bolts will be installed into the walls of the wet well. The Wet Well would be independent of the 1'-0" thick pavement, based on the expansion joint.

The PIP CVC01015 Civil Design Criteria, regarding pavement and foundations, states " Expansion joints are not required except at foundations and for other items penetrating through the paving. Note that a pair of #3 bars (10 mm bars) shall be embedded mid-slab at 6 and 12 inches (150 mm and 300 mm) in from a re-entrant corner."

I would imagine this is applicable for this situation.

Would it be better to have the Wet Well act separate from the pavement (option 2) or have the pavement & wet well act as one (option 1)?

Does doweling the pavement to the wet well add any structural strength/capacity to the wet well? Would it be a better way to anchor the pump skid?

Is it a better design to keep them independent via expansion joint?

Are there any technical documents that address this kind of situation?

Comments/suggestions are appreciated.

 

[oengineer]

If anyone is aware of the advantages vs disadvantages of both option 1 & 2, please feel free to comment.

 

[r13]

I prefer option 2, more clean and simple.

 

[STrctPono]

I never dowel 2 separate pours of concrete together unless I am able to waterproof the joint or use a corrosion proof bar like GFRP. I don't know if the inside of this wet well will be coated with a waterproofing like bitumastic or some sort of lining? Maybe not, maybe it will be left as is concrete.

Option 1 requires the wet well to be constructed first and then the pavement poured on top. I wouldn't think this would be an issue as this would seem like the natural progression of things anyway. This also adds the benefit of eliminating the annular joint around the wet well. Your pavement slab is 12" thick with double layer mat of reinforcing. That's pretty thick. What is driving on this pavement? If there are some heavy loads then perhaps it would be best not to transfer the load down through the walls of the wet well.

Option 2 offers the benefit of isolating any load transfer from the pavement to the wet well walls. But it introduces an annular joint around the perimeter of the wet well that could prove problematic if there is alot of water that could find its way through the joint and down to saturate the soil beneath.

If this is exterior, you don't have any heavy vehicles driving near this wet well, and pump vibration isn't a concern then I'm inclined to go with option 1 but to use prebent GFRP dowels instead of steel. If the wet well is inside, you have heavy vehicles driving nearby, or pump vibration is a concern, then I would be more inclined to go with option 2.

 

[oengineer]

I never dowel 2 separate pours of concrete together unless I am able to waterproof the joint or use a corrosion proof bar like GFRP. I don't know if the inside of this wet well will be coated with a waterproofing like bitumastic or some sort of lining? Maybe not, maybe it will be left as is concrete.

Option 1 requires the wet well to be constructed first and then the pavement poured on top. I wouldn't think this would be an issue as this would seem like the natural progression of things anyway. This also adds the benefit of eliminating the annular joint around the wet well. Your pavement slab is 12" thick with double layer mat of reinforcing. That's pretty thick. What is driving on this pavement? If there are some heavy loads then perhaps it would be best not to transfer the load down through the walls of the wet well.

Option 2 offers the benefit of isolating any load transfer from the pavement to the wet well walls. But it introduces an annular joint around the perimeter of the wet well that could prove problematic if there is alot of water that could find its way through the joint and down to saturate the soil beneath.

If this is exterior, you don't have any heavy vehicles driving near this wet well, and pump vibration isn't a concern then I'm inclined to go with option 1 but to use prebent GFRP dowels instead of steel. If the wet well is inside, you have heavy vehicles driving nearby, or pump vibration is a concern, then I would be more inclined to go with option 2.

Could you please clarify what you mean by "annular joint"? What potential issue would this cause around the perimeter of the wet well? Could a water proof/tight expansion joint resolve this issue?

This wet well will be outside. I am not sure about heavy vehicles driving near the wet well, but it is located near a road.

The following is the information on the pumps resting on the skid above the wet well:

Their are 3 pumps resting on top of the Wet Well top slab.

Each pump weighs 1,583 lbs. Each pump has a power rating of 1800 RPM. Each pump has an operating speed of 40 HP.

The total pump weight is then 4,749 lbs for all 3 pumps. The total power rating for all 3 pumps 5400 RPM. The total operating speed for all 3 pumps is 120 HP.

With the weight of the pumps, motors, control panel, pipes, & valves the total weight of the skid on top the Wet Well is 5,500 lbs.

 

[STrctPono]

With those size pumps I would be inclined to isolate the 2 systems. Keep the wet well structure, pump skid and pumps isolated from the surrounding pavement. Go with Option 2.

When I mentioned annular joint I was referring to the expansion joint gap that would occur between the pavement and the wet well walls. It's probably not that big of a deal since it's unlikely the site will be graded such that all the water collects at this location. You can always use a pour-in-place silicone like Dow Corning 902 silicone to seal the joint but that will only last about 5-10 years.

Don't forget to add trim bars with diagonals in the pavement around the wet well opening.

 

[oengineer]

With those size pumps I would be inclined to isolate the 2 systems. Keep the wet well structure, pump skid and pumps isolated from the surrounding pavement. Go with Option 2.

When I mentioned annular joint I was referring to the expansion joint gap that would occur between the pavement and the wet well walls. It's probably not that big of a deal since it's unlikely the site will be graded such that all the water collects at this location. You can always use a pour-in-place silicone like Dow Corning 902 silicone to seal the joint but that will only last about 5-10 years.

Don't forget to add trim bars with diagonals in the pavement around the wet well opening.

Well, it seems like you are saying water entering the joint location could be a critical problem. This project is located in a city prone to flooding, so this is beginning to be a concern to me.

I can talk to the lead civil engineer on the project about the drainage in this area, but I am concerned about water infiltrating the joint.

What do you mean by "Don't forget to add trim bars with diagonals in the pavement around the wet well opening"? Do you mean ACI's requirement for openings in concrete (i.e. like walls)?

 

[STrctPono]

Well, it seems like you are saying water entering the joint location could be a critical problem.

I don't believe it to be a critical problem, but a detail that I try to take care of nonetheless. I try to avoid saturating the subgrade soils around structures if I can help it. More of a service level concern than an extreme event type concern. If this area floods, that joint is the least of your worries.

What do you mean by "Don't forget to add trim bars with diagonals in the pavement around the wet well opening"? Do you mean ACI's requirement for openings in concrete (i.e. like walls)?

Yes.

 

[oengineer]

Based on the pump skid arrangement, I have 2 Types to be considered for the wall thickness of the Wet Well. I believe this information should impact which of the two Options about the pavement should be used.

In the images below, the 3 squares in the inner circle represent the 3 pumps. The rectangle on the left is the Control Panel. All of these rest on top of the pump skid, which is 108" x 99.25".

Type 1: This is using a 24" thick wall for the Wet Well, while maintaining the inner diameter of 8'-0". In this case, out of the 4 anchor bolts located at the 4 corners of the pump skid, 2 anchor bolts will be located on the adjacent 1'-0" thick pavement. The total outer diameter for the Wet Well would be 12'-0" diameter (Please see image below).

Type 2: This is using a 15" thick wall for the Wet Well, while maintaining the inner diameter of 8'-0". In this case, out of the 4 anchor bolts located at the 4 corners of the pump skid, possibly all of the anchor bolts will be located on the adjacent 1'-0" thick pavement. The total outer diameter for the Wet Well would be 10'-6" diameter (Please see image below).

I present these cases because I believe option 2 goes really well with Type 1. The pavement would still receive load from the skid due to the 2 anchors on the pavement, but the remaining load would be transfer to the wall of the Wet Well (the Wet Well wall may possibly receive more load due to how close the pumps are to the wall).

For Type 2, the option 1 may work well (having the Wet Well doweled into the pavement). I was trying to keep the Wet Well independent from the paving, but based on potential the annular joint issue, I think it may play into which way to go. The issues would be the minimum edge distance of the anchor bolts. The skid barely extends pass the Wet Well when using a 15" thick wall.

[ADD] - The anchor bolts for the pump skid are post-installed bolts. Just FYI.

 

[cvg]

suggest precast reinforced concrete pipe for the sump, wall thickness is only 9.5 inches
anchor the pumps into a concrete collar poured around the top of the pipe. that collar could be square. than your pavement is outside of that and not doweled.

 

[oengineer]

suggest precast reinforced concrete pipe for the sump, wall thickness is only 9.5 inches
anchor the pumps into a concrete collar poured around the top of the pipe. that collar could be square. than your pavement is outside of that and not doweled.

A cast-in-place wet well is provided on our drawing but we do have a note mentioning that an alternative precast design is acceptable (contractor would have to provide it along with sealed calculations)

 

[oengineer]

When I mentioned annular joint I was referring to the expansion joint gap that would occur between the pavement and the wet well walls. It's probably not that big of a deal since it's unlikely the site will be graded such that all the water collects at this location. You can always use a pour-in-place silicone like Dow Corning 902 silicone to seal the joint but that will only last about 5-10 years.

It appears that if I provide the expansion joint detail and notes in the image below, it should resolve any issues with water infiltration at the expansion joint:

I would think that the joint sealant & the backer rod would prevent infiltration of water to the soil below.

Please provide comments if I am missing something regarding the issue of the angular joint.

 

[oengineer]

I prefer option 2, more clean and simple.

I prefer Option 2, as well. But my issue is that it is a change from what was previously done (Option 1 was done before), so i want to have a strong justification for altering it by going with option 2.

 

[dhengr]

Oengineer:
I would watch out for several different things which I’m not sure your details contemplate in detail. You should probably not attach that pump skid to both the slab and the well wall, due to potential of differential movement. Ask the skid builder to relocate two of the A.B. holes so all four A.B’s. fix into the well wall, and then, just allow that a few feet of the skid cantilever out over the slab, allowing some clearance and carry the control box and work platform.

I wouldn’t attach the slab to the well wall because of the potential of differential vert. movement of the two, or concentrated loading on the slab from a truck or some such going through a few dowels. Slope the slab away from the wet well, for 10’ or so. Furthermore, due to flooding potential, do you want to be pumping the world dry, through that well? Or, should the top of the well wall be 3-4’ above grade (or some such) so that minor flooding is held back, with some control?

 

[r13]

Originally you were relied on the slab to support the pumps due to dynamic concerns. Subsequently you found the pumps came with skid and the dynamic concerns were eliminated by the vibration isolators, thus it become possible to anchor the skid directly on the wet well wall instead of fastening the skid on the more costly slab. Option 2, IMO, is cheaper to construct, and cleaner around the well. Cost reduction is the key point here. But now you need to come up a good skid-wall connection design then.

 

[oengineer]

Ask the skid builder to relocate two of the A.B. holes so all four A.B’s. fix into the well wall, and then, just allow that a few feet of the skid cantilever out over the slab, allowing some clearance and carry the control box and work platform.

This is what I am thinking about doing. That is the reason I went back and mentioned the anchors are post-installed in my post above.

I wouldn’t attach the slab to the well wall because of the potential of differential vert. movement of the two, or concentrated loading on the slab from a truck or some such going through a few dowels.

I appreciate the confirmation on my suggested revision to the Wet Well design that I am proposing. I know others in this thread have preferred option 2 as well (i.e. retired13, STrctPono).

Slope the slab away from the wet well, for 10’ or so. Furthermore, due to flooding potential, do you want to be pumping the world dry, through that well? Or, should the top of the well wall be 3-4’ above grade (or some such) so that minor flooding is held back, with some control?

A paving & drainage plan has been created. They are still revising it, but based on their red lines the water is sloping away from the Wet Well. I will discuss this with the Lead Civil Engineer. Thank you.

 

[oengineer]

Originally you were relied on the slab to support the pumps due to dynamic concerns.

Originally, I thought that there was going to be a top slab for this Wet Well, but later I was informed by the Lead Civil Engineer that that is not the case. It will be an open hole so that it is easier for the contractor who installs the pumps to suspend them in the Wet Well.

Subsequently you found the pumps came with skid and the dynamic concerns were eliminated by the vibration isolators, thus it become possible to anchor the skid directly on the wet well wall instead of fastening the skid on the more costly slab.

After discussing with the Lead Civil Engineer, I was asked to anchor the skid directly on the wet well wall instead of fastening the skid on the slab (since there is no longer going to be a top slab on the Wet Well).

Option 2, IMO, is cheaper to construct, and cleaner around the well. Cost reduction is the key point here.

Thank you.

But now you need to come up a good skid-wall connection design then.

I would imagine that the skid-wall connection would basically be the contractor anchoring some post installed anchors (like Hilti bolts) to the wall. The contractor mentioned that they typically use 3/4" diameter post-installed bolts, so I would think as long as a minimum edge distance of 5" is maintained from the edge of both sides of the wall it will suffice.



Should the expansion joint detail & note I show in a previous post prevent water infiltration around the joint?

 

[r13]

1) Make sure the wall thickness can accept the anchor comfortably, with leveled surface, as field installation is sometimes more difficult than direct embedment. Also, there is always chances to drill into rebars, and/or splitting the concrete.
2) Yes, when CIP concrete cast against hardened surface, it require flexible joint to minimize separation due to drying shrinkage, and prevent water penetration.

 

[oengineer]

@retired13, STrctPono, dhengr

Thank you for your help!

@Everyone

Thank you all for all of your input & help!