Deep foundation Recomendation 1

[deemtocomply]

I'm currently designing foundations for a three-storey apartment building located near the coast. The geotechnical report indicates sandy soil conditions with a high water table (approximately 1.5 meters below ground level). I'm considering the use of concrete piles, but I’m unsure whether this is still a suitable option under these conditions.


If concrete piles are viable, what additional factors should I take into account? One concern is the potential for reinforcement corrosion due to the aggressive environment. To mitigate this, I'm planning to increase the concrete cover and possibly control the crack widths in the piles. Would these measures be sufficient, or should I consider an alternative foundation system?

 

[HTURKAK]

I'm considering the use of concrete piles, but I’m unsure whether this is still a suitable option under these conditions.

IMO, suitable but if precast driven pile since the compactness and quality control better than bored piles.
You may consider steel driven piles with choosing thickness with suitable corrosion allowance together with corrosion coating and CP .

 

[jhnblgr]

What does the geotechnical report say and what were the characteristics and depth of the borings?

Did you get any at grade bearing capacity?

Research galvanized or epoxy coatings, also maybe call up a supplier to see what they typically run into.

 

[phamENG]

Lean on the geotech for pile recommendations. They'll know if you need them for bearing/settlement considerations, and they should know if you need them for scour if you're that close to the coast - but you may need to nudge them in that direction if there's a regulatory reason that goes beyond site specific engineering.

 

[deemtocomply]

Thanks, everyone. That was very helpful.

I've just reached out to the geotechnical engineer for recommendations. Based on the borelogs, the bearing capacity is quite low: around 200–250 kPa end bearing at a depth of 3.5 meters, with no data available beyond that.

Would it be appropriate to design the piles as marine piles, such as steel tubes filled with concrete? Or would that be overengineered for a project of this scale?

 

[deemtocomply]

IMO, suitable but if precast driven pile since the compactness and quality control better than bored piles.
You may consider steel driven piles with choosing thickness with suitable corrosion allowance together with corrosion coating and CP .

The corrosion allowance applies to steel piles, but what about the reinforcement in bored or driven concrete piles? I can increase the concrete cover, but controlling crack widths could be challenging, especially since I need to account for moments caused by lateral loads.

 

[HTURKAK]

he corrosion allowance applies to steel piles, but what about the reinforcement in bored or driven concrete piles?

I suggested two options ,
- Precast driven pile , ( size could be 300X300 mm)
- Steel pile with protective coating and increased wall thickness with added CA. ( size could be Pipe DN 300)

I did not suggest bored piles however , if this is the only alternative , you may consider epoxy coated reinf.

 

[LittleWheels]

We ban epoxy-coated rebar on our designs. Too much opportunity for corrosion initiating at coating defects or coating damage, which is then localised and intense. Most of our work is marine or coastal.

 

[deemtocomply]

We ban epoxy-coated rebar on our designs. Too much opportunity for corrosion initiating at coating defects or coating damage, which is then localised and intense. Most of our work is marine or coastal.

what do you use then? stainless reinforcement or just control the crack width?

 

[drlt5]

I would be more worried about the settlement than the corrosion of the bars etc. As long as you consider the sufficient clearance for the reinforcement based on the environmental condition plus the concrete class, type and grade for this specific environmental condition, what else is there to be worried about other than the capacity of the piles, punching on your foundation and the settlement. I would consult with a pile contractor and a geotech eng.

 

[LittleWheels]

what do you use then? stainless reinforcement or just control the crack width?

Increased cover and crack width limitations. Stainless is too expensive for most of our clients.

 

[soheyla_sa]

In marine environments, concrete must have a specific strength, and the water-to-cementitious material ratio needs to be limited to control sulfate attacks. There are also limits on chloride ion content to prevent corrosion. Simply increasing the concrete cover thickness is not enough to ensure durability. These limitations are described in the ACI Manual of Practice. Although I don’t have that manual, similar requirements are presented in the ACI 350-06: Code Requirements for Environmental Engineering Concrete Structures and Commentary, especially in Chapter 3.
Additionally, in my country, when it’s necessary to bore deeply to reach suitable soil, we sometimes use micropiles and deep soil mixing methods instead of traditional piles. These techniques help improve soil conditions without extensive boring.
I hope this is helpful to you.

 

[HTURKAK]

Simply increasing the concrete cover thickness is not enough to ensure durability.

That is the point. In case of bored , cast in situ piles , altough the use of rich concrete could seems to be an option , it is almost impossible to get well compacted concrete to form an impermeable mass . That is why i suggested precast driven pile or coated steel pipe pile.

 

[soheyla_sa]

I am agree with you. and I think the cost and the equipment available in the site is the important part. I had a project which the best selection for me was bored piles