If your project is a high-rise building, the water level will probably be higher than the bottom of the foundation. Mostly, high-rise buildings have three basements or more. This is especially true if, the project is near the seashore. If so, you should be thinking about applying some important techniques to avoid water leakage.
One time we had a high-rise building project where the water table was below the foundations. That project had three basements, meaning it was nine meters below ground level because each basement was three meters in height.
I was really amazed when I came to the site (I was newly hired back then) and I was roaming around, expecting to see a dewatering machine running but I was blown away that there was no machine for dewatering. I think the project was at 20 percent of its completion at that time.
I asked the construction manager, and his reply was, “ We proposed to the engineer that we shut off the dewatering at 20 percent of completion, due to the reason that there was no water.”
You are so lucky if your project was just like what I had. You will feel comfortable because you might be free from any potential water leakage.
But what if your project has the water table just one meter below the ground? It sounds stressful, right?
Like my friend who messaged me asking, “What is the solution to solve the leakage on our basement wall? It ‘s coming from the tiny cracks on the wall.” If you were a quality manager or a project manager on his site, you would probably acquire high- blood pressure from the stress of the problem.
Now, in order to avoid the potential leakage of water on underground concrete structures such as the basement, water tanks below ground, here are Seven Steps to Avoid Water Leakage to your Underground Structures.
1. Provide a Block Wall Before the Retaining Wall
It is important to include, in the design of your basement retaining wall, the block wall where the waterproofing will be laid. A method statement of your blockwork should be made for a proper work sequence and to ensure the safety of the work. Don’t proceed with your project if this is not incorporated in the detail drawings – otherwise, you will have completely messed up later on.
You will experience a lot of problems with leakages of water like my friend experienced.
2. Use Blinding Concrete on the Bottom of the Foundation
If your foundation is mat or raft, it could mean that your project is consists of common foundations, which what we did in Al Mamzar, Dubai, at The Square project. The purpose of blinding is to receive the waterproofing to be laid upon it. The blinding could have a thickness ranging between 50mm to 100mm depending on the design.
3. Water Proofing Membrane
Membrane is the best waterproofing to use on huge foundations, such as mat or raft and other foundations, that are below the water table. Ensure that the membrane has a torch- applied feature and is bent to the primer underneath. You may ask, why you need a torch applied, this is to ensure a binding with the side and end laps. It should have a great binding ability and cohesiveness after torching.
I suggest reading the method statement for waterproofing membrane and you will learn the process for how the membrane is applied on the blinding and block wall.
4. Use Water Bars
You should use water bars as a seal between the old and the new concrete. The purpose of water bars is to avoid leakage of water between the joints. It will swell once it gets wet, and then will serve as a sealant. It is important to use a water bar product or material which is swellable.
When you construct a retaining wall, make sure before you cast the next wall, that you ensure the water bar is placed on the horizontal and vertical face of the old concrete. A civil or a quality inspector should see to it that this is in place before closing the forms.
5. Provide PCC on the Waterproofing
PCC should be used to protect the membrane from any type of potential damage. The PCC should have a concrete grade of C25/20. After the PCC is laid, then the steel reinforcement rebars should be laid on, – if there is no PCC then the steel reinforcement rebars would definitely create damage to the membrane. That’s why it is important to protect the membrane with PCC. Unlike a wall, it doesn’t receive much pressure as, like the floor, a 1-meter thick mat slab would be laid onto it.
6. Provide Protection Boards on a Vertical Surface
Protect the waterproofing membrane on the wall by providing protection boards. Sometimes the supplier of the membrane provides that package when you procure them to supply your project. A 6mm protection board is enough to support the membrane.
Remember, that there should be lapping, but not like in the waterproofing membrane. It is recommended that you check the lapping length with your applicator or supplier, but in our project, we used 10mm lapping on both sides.
7. Always Raise Inspections for the Completed Waterproofing Works
It is suggested by qualityengineersguide.com to strictly check the waterproofing works. There are plenty of reasons why you need to carefully check the supervision of this work. Reason one is the carpenter, – he/she will damage the waterproofing membrane by drilling a hole through the PCC down to the membrane. Crazy, right? The truth is a carpenter doesn’t know the idea or purpose of having a membrane underneath the PCC. He or she doesn’t know that it is for the purpose of avoiding water leakage.
In one of my projects, the carpenter was planning for the wooden support to be connected to the vertical shutter of the mat to make it strong enough, because we had planned to cast the mat foundation by panel or stage-by-stage. The mat area had over 30,000 square meters so it was cast part-by-part.
Reason two is the lapping of the membrane. It is strongly advised that the lapping must be followed as per the manufacturer’s recommendation. There would be a side lap and end lap.
In the construction of a building, especially a high-rise, you should be strict when it comes to the detail drawings of the waterproofing membrane, so you will know what you need to do and which actions will be taken. Having an advanced study of where the waterproofing should be applied is an advantage because you will have a lot of time to check beforehand. That way, you will not just stare at the waterproofing activity, and then get rattled because of the time constraints.
Quality Engineer Tips:
1. I recommend reading the method statement for the application of waterproofing membrane. This is to ensure you have an understanding of the methodology.
2. Make sure you require the subcontractor to submit an Inspection and Test Plan, to ensure various inspection stages.
3. Conduct random site surveillance, to ensure materials for waterproofing that have been delivered to site are as per approved material submittal.