Soldier pile wall next to existing structure 3

[milkshakelake]

I'm designing a 14' deep basement wall next to a 3 story brick building. The adjacent building is 4' away and its footing is 5' deep so there is a surcharge. The peak of the surcharge would be about 8' to 9' below grade in my estimation.

Normally, I use a tangent or secant pile wall when there's a building surcharge. However, is it acceptable to use a soldier pile wall with wood lagging? If there is backpack or grout between wood lagging, maybe there won't be soil loss through the gaps. The soil is about 6' of fill and then silty sand with traces of rock. A weird idea I was thinking was to use steel plates instead of wood lagging up to the peak surcharge point to minimize the number of gaps.

The reason I'm considering soldier pile wall is because the next door building is relatively small and this project is too small to justify a tangent pile wall (5 stories, 40'x100' lot).

 

[EireChch]

I think your deflections would be too high with a king post wall. The magnitude of deflections of these types of walls is highly dependent on the workmanship, can you guarantee that!

In any case you would want to do pre, during, and post construction survey of the brick building. Any slight cracking etc and youre setting yourself up for a loss.

 

[milkshakelake]

I can use walers and rakers to control the deflection.

Thanks, I'll definitely do a pre/during/post construction survey.

 

[msquared48]

I would definitely use rakers here...

Mike McCann, PE, SE (WA, HI)

 

[EireChch]

I think you could design a wall that is stiff with shorter spaced soldier piles and concrete planks but the settlement will likely be from the movement of the soil towards the wall. Hence why I was saying the workmanship needs to be perfect. A 3m brick story building could apply a surcharge of 50kPa against your wall? Not an insignificant surcharge

 

[milkshakelake]

@EireChch I'm not super worried about the stiffness and deflection, as that can be taken care of by the rakers. The main concern is the soil loss, which wouldn't be helped by shorter spaced soldier piles. And there's no way to guarantee the workmanship. I'm definitely leaning to not doing it.

 

[r13]

I'm not super worried about the stiffness and deflection, ...

You should, as deflection will cause settlement of the neighboring building. I don't know how much movement will cause structural damages, shouldn't be much though. Soil loss is valid concern, why not use sheeting in lieu of lagging? Also, wouldn't vibration from pile driving a concern too?

 

[jayrod12]

I think you should be looking at tangent pile or secant pile wall in a case like this. Driving sheet piling would potentially cause issues in the existing building. Soldier pile and lagging has constructability concerns. Tangent/secant walls are fairly stiff, provide minimal disturbance the the adjacent property, and if designed correctly could be used as the foundation wall for the new building.

 

[milkshakelake]

@jayrod12 Agreed, that's what I usually do but this project is so small that it's not worth it. I think I'll recommend a stepped footing and lose some cellar space.

@r13 Not using sheeting because it's vibrated into place and could cause the brick to crack. I'd specify a drilled-in pile, not vibrated. But based on the comments, it sounds like a bad idea.

 

[r13]

The sheeting is a form of lagging, not the typical sheet piling. Cut the sheet to size that fit in between drill-in piles. Add stiffer wood laggings sparsely as required to support the sheet. Overlap the sheet to prevent soil loss. Labor intense proposition though.

 

[EireChch]

Sheetpiling way be a good option. There are many good silent “hammers” which press the sheet pile into the ground without vibrations

 

[milkshakelake]

@r13 I never heard of that, but it could work. You're saying put metal sheeting (say 2" Vulcraft 19 gage) between the soldier piles and add some wood lagging at like 3' on center? Or did I completely misunderstand you?

@EireChch You mean a variable moment vibration hammer?

 

[PEinc]

Generally, an adjacent building this close to the excavation should be underpinned. Soldier beam wall and sheet pile walls are generally defined as flexible structures. Flexibility means movement. Movement mean damages. Depending on the soil and building conditions, the underpinning may need to be laterally tiedback or braced temporarily until the new building is built and backfilled or permanently if necessary. If you cannot get permission to underpin the building, you could install secant or tangent piles, braced or tiedback as required. This could be expensive. You may be able to support the existing building with conservatively designed, closely spaced, extra stiff, drilled-in soldier beams with wood lagging and tiebacks or braces as required. I would not drive either soldier beams or steel sheet piling for reasons mentioned above. If the wood lagging is installed properly, there should not be soil lost through the lagging. In fact, there should be louver spaces, about 1.5" wide, installed between the lagging boards. The purpose of the louvers is to assure that the boards are in full contact with the soil and to allow a small gap to add replacement soil if necessary as the excavation progresses toward subgrade. The soil does not run out through the louver spaces. The louvers also allow a space to install filter fabric or hay if needed to retain the soil if and when there may be some water seepage through the sheeting wall. Drill holes for soldier beams should be entirely filled with lean mix, low strength (about f'c = 100 psi) concrete or flowable fill. Do not fill the drill holes with drill spoils, sand, gravel, or strong concrete. The drill spoils, sand, or gravel will be loose and will run out when you excavate in successive lifts for the lagging. This lost backfill will cause voids and will allow the soldier beams and retained soils to move. Strong concrete will be a problem if it extends up where the lagging needs to be placed and it is very expensive and slow to chip out. Sometimes, strong concrete is specified for filling the drill hole below subgrade, below the lowest lagging boards.

If someone cannot or does not want to install expensive underpinning, secant piles, or tangent piles; then that person (who is saving money) also needs to accept the increased risk of building movement and probably/hopefully only minor damages.

http://www.PeirceEngineering.com

 

[r13]

Milk,

You read my message right. This method is best for sandy soil. The sheeting should be placed horizontally for stiffness.

 

[PEinc]

I believe that you are getting some bad advice, milkshakelake.

http://www.PeirceEngineering.com

 

[milkshakelake]

I believe that you are getting some bad advice, milkshakelake.

Thank you for the heads up. I really appreciate it. It's hard for me to judge what is good advice or not.

Underpinning is out of the question; the adjacent building owner is not having it. Tiebacks are also not allowed for this reason. I'm processing what you and others have said.

 

[r13]

A suggestion for ease of install laggings. (Note: Leave the backside lean concrete in place for bearing)

 

[Retrograde]

If I did a solider pile wall I would use shotcrete, not timber lagging. Should still be cheaper than a secant pile wall.

 

[EireChch]

I think silent piling with a GIKEN press in method would be a very good solution for you. They are essentially vibrationless.

You can have soil loss from construction of secant pile walls, you wont get anywhere near the same level of soil loss with installation of a sheet pile as you are not removing soil.

PEinc is right that there are flexibility issues. However, you could prop your wall from top down. I doubt you'll get permission to anchor beneath your neighbors land if they wont let you underpin their building. A temporary prop/strut replaced with the first floor slab etc could be an option.


Some links below.

https://aarsleff.co.uk/company-news...r-eco-700s-silent-vibrationless-sheet-piling/

https://www.youtube.com/watch?v=M5FqzeV_bC0

 

[PEinc]

Underpinning is out of the question; the adjacent building owner is not having it. Tiebacks are also not allowed for this reason. I'm processing what you and others have said.

Check your local building code. Some local building codes require neighbors to protect their own properties if they refuse to let the contractor do it. Your neighbor may therefore be responsible if you are not allowed to use tiebacks or underpinning.

http://www.PeirceEngineering.com