Can we provide a settlement joint under the water? 3

[sea2003]

Hi All,

I am designing a two-story parking structure under the groundwater level with dimensions 600 feet x 600feet, the whole building is submerged under the water moreover, we want to connect the parking building to an existing tunnel.

I have three questions:

1- Can we provide expansion joints in the slab every 150 feet but we will not extend to the retaining wall due to the high water level?
or you recommend casting the whole slab and wall without any expansion joint only construction joint?

2- I believe we need a settlement joint between the existing tunnel and the new building, did you know how can we construct such a settlement joint under groundwater level? and do you recommend an alternative solution to avoid any water leakage at the connection between the existing tunnel and the building?

 

[JedClampett]

If a settlement joint is an expansion joint(?):
Question 1: No: The joints need to extend into the wall. and No: 600 feet is too long without an expansion joint.
Question 2: I'm not sure if you mean during construction or for long term. During construction, dewatering is required to build below the groundwater level. And the solution to any leakage is to provide waterstopped joints. And for any construction joints, too.
Question 3 (that you didn't ask): Is buoyancy an issue. Absolutely!

If you've never done this before, you need to walk down the hall and ask someone who has. You're spinning your wheels.

 

[sea2003]

Thank you @JedClampett.
Regarding to your response of Q1 , if we extend the expansion joint into the wall , this joint can not resist the water pressure ( 22 feet under the water) and cause water leakage at the end , so I was thinking if I cancel this joint at the wall only .

For Q2 , my concern is the differential settlement for long term , the vertical water stop is not enough to resist the water pressure .

For Q 3, the building foundation to be raft on tension pile to resist the uplift force .

I have tried to find a qualified person for discussion but I can not find , I believe the group here would help .

 

[JedClampett]

if we extend the expansion joint into the wall , this joint can not resist the water pressure ( 22 feet under the water) and cause water leakage at the end , so I was thinking if I cancel this joint at the wall only

If you waterstop the joint, it will resist 22 feet of head. I don't know where you're getting your waterstop information, but if you go the Sika/Greenstreak website, they'll give pressure ratings for their waterstops. Most are in the hundreds of feet.
If you stop the joint at the wall, mother nature will create a joint with disastrous results. You'd have a discontinuity where the EJ stops and a large crack will form.

 

[HTURKAK]

I am not sure that i understand the full picture.. Will you please provide a sketch showing the existing tunnel connection, section showing the grade, GWL, storey hts, foundation and piling..
Questions,
-If you provide tension piles , that means the parking structure is floating with self weight so effective stress will be zero. What kind of settlement is foreseen ? and what is the amount of predicted settlement ?

- What is the cover depth ?

- What is your connection detail of tension piles to mat foundation? It seems that, it is not a good idea to perforate the waterproofing ..

In general i agree with JedClampett .. and if i were the designer ,
- Provide EJ for walls and slabs with doubling the beams and columns at EJ's . The EJ distances would be based on temperature and shrinkage calculation . The underground temperature does not fluctuate too much. IMO, 200 ft distance between the EJ could be enough.
- I will not provide EJ for mat foundation but CJ should be planned to minimize the shrinkage .

- If the own weight of structure together with overburden soil does not provide a reasonable F.S. against floating, , i would prefer to increase the wt of mat with ballast fill rather than tension piles...

 

[sea2003]

I am not sure that i understand the full picture.. Will you please provide a sketch showing the existing tunnel connection, section showing the grade, GWL, storey hts, foundation and piling..

Hi HTURKAK,
please refer to the attached sketch all units in millimetres

Questions,
-If you provide tension piles, that means the parking structure is floating with self-weight so effective stress will be zero. What kind of settlement is foreseen? and what is the amount of predicted settlement?

you are right but the new structure will be on the pile foundation while the existing tunnel is on the raft foundation. so any movement between the two structure will cause water leakage.

- What is your connection detail of tension piles to mat foundation? It seems that, it is not a good idea to perforate the waterproofing ..

well the waterproofing is not a big deal, moreover, we take into consideration the crack width

 

[HTURKAK]

Hi SEA2003 ,

I looked to the sketch ..

Pls find below my opinion,

-still deletion of tension piles is an option.. The uplift force 80 kN/m2 and the dead weight of the structure should be in the range of = (1.7+0.6)*25+ 0.55* 18=67 kN/m2 . Just extra excavation 1.2 m and addition of balast layer+ 0.15 m sog over the balast will satisfy F.S. against flotation.

- You may provide corbel under the existing tunnel to avoid the differential settlement.Just extent the 1 st basement floor slab under the tunnel.

- The waterproofing of the joint is an issue.The use of waterstop EJ type dumbell -center bulb may be considered.

Good luck..