How would you do shoring & construction sequencing in this case?

[hotmailbox]

Please see sketches below to understand the situation. I know this is pretty common but I don't have much experience in how shoring contractor works and what their capabilities are so I am not so sure how to install soldier piles in this particular area to build the new concrete wall.
Does it make sense to brace the existing CMU wall then saw cut 24" or more wide vertical strip including existing foundation (if we can't core through it) at the soldier pile locations for drilling then install I beam as normal? What else can you do in this case?

 

[EireChch]

A few questions:

Why are you removing the existing concrete wall? Can you not underpin it?

what is the retained material?

What is the surface of the neighbors parking? Asphalt, concrete, stone?

 

[hotmailbox]

1. Because this is a new development and the existing CMU wall is unknown and not in a good shape for new construction. Also the new wall is needed to run perfectly parallel to the property line to meet some clearance requirements.
2. Asphalt concrete over soils behind the retaining wall.

 

[EireChch]

Whats the soil ? Is it granular or cohesive? i.e. sand or clay?

You will need to cut strips to install the solider piles, install the solider piles (what spacing? 2m?), remove the concrete wall section between the piles, accept that there will be some loss of material behind the wall and cracking to the asphalt, install the lagging, and then move to the next section. Then reinstate your neighbors asphalt. Hopefully your neighbour accepts all this...

I dont think you would want to core through a 9ft high conc wall. Of course its possible but not practical.

If you want to reduce the amount of loss of material behind the wall you will need to reduce you solider pile spacing, but then it becomes expensive with additional piles and time.

If the existing walls foundation is as you have shown, could you not install a sheet pile wall on the boundary wall? You may need to steal piece of your neighbours land over a short section but if you discuss this with them and explain that it will be a hell of a lot cleaner and shouldnt damage their carpark!

 

[PEinc]

In my opinion, it would be easier to do the following:
1. Demo the existing wall that projects above the neighbor's paved lot.
2. Design cantilevered, temporary sheeting and get permission from the neighbor to install it as close as you can to the property line and on the neighbor's property.
3. You don't show elevations so I do not know how high the sheeting wall needs to be but it looks like it could be cantilevered - even though you might ask if you can slope a little of the neighbor's property in order to reduce the height of the sheeting wall.
4. Build up in front of your existing wall if necessary to drive or drill-in soldier beams as close as you can to the back side (property line side) of the existing wall.
5. Demos the existing wall below the top of the soldier beams in sections of about 3 to 5 feet while installing wood lagging between the soldier beams.
6. Continue demo and lagging until you reach the subgrade of the proposed new wall footing.
7. Build the new wall tight against the sheeting wall.
8. The temporary sheeting can then be cut off and removed to about 2 feet below finished grade in the neighbor's lot.
9. If you got permission to slope some (maybe about a foot or two) of the neighbor's property, then the tops of the soldier beams would already be a few feet below finished grade and would not need to be cut off and removed.

http://www.PeirceEngineering.com

 

[hotmailbox]

Thanks PEinc & EireChch for your valuable time and suggestions.

EireChch,
The soils behind the existing wall is expected to be Silty SAND (Alluvium) because the 10feet of soils in project site at the same elevation elsewhere was reported as such. Soldier piles are expected to be 8'-0" o.c.

PEinc,

I got a bit confused. Let me know if I understand correctly.

So if the neighbor is ok (very unlikely), we install soldier beams on the neighbor side as close as possible to the property line. Where is the cantilevered sheething? and why do we need that? I am not so sure I get the picture. Do you think the sketch below is correct?

Any other options if neighbor refuses this?
Satellite view of the situation.

 

[EireChch]

As I in interpret PEincs proposal, the purpose of the temp sheeting is to allow you to install the Solider Piles and lagging while not losing material. I am assuming the temp sheeting is essentially trench sheeting as I would call it, very thin sheet piles essentially. Like a U shaped sheet pile that is 100mm in depth.

This is installed as tight to the boundary as possible, however it it looks like you will need to steal some space from your neighbour. That is the benifit of the temp sheeting as it isnt as beefy as permanent sheet piles.

Your piles are installed at the back of your existing wall and then up to your boundary line. It is only your temp sheeting that may encroach into your neighbours property.

 

[PEinc]

After removing the upper portion of the existing wall that projects above the neighbor's original grade at the wall, the temporary soldier beams would be installed on the neighbor's property, as close to your existing wall as possible. As you start demolishing the remainder of the existing wall in sections about 3 to 5 feet high, you will install wood lagging between the soldier beams to support the neighbor's property. When the entire existing wall has been removed and the lagging has been installed down to the proposed subgrade of the proposed, new retaining wall, the soldier beams will be cantilevering without needing any other bracing or tieback anchors. Generally, cantilevered soldier beam walls are ABOUT 12 to 14 feet maximum height. For soldier beams spaced at 8' c.c. with a total lagged excavation of about 12 feet, I ESTIMATE that the soldier beams may be ABOUT HP12x53's or HP14x73's about 25 feet long. This is just an educated guess - NOT A DESIGN. You must prepare your own design using all site specific earth and surcharge loads.

If the total depth of your excavation below the neighbor's property is higher than that, you may want to ask him if you can temporarily slope and excavate a few feet deep in on his property and within about 5 feet of the soldier beam wall. After your new wall is built and the soldier beams are cut off a few feet below finished grade, you backfill behind the wall on your neighbor's property and return his property to original or better condition.

(EDIT) WARNING: The new wall may be (will be) subject to crash loads from cars on the neighbor's property.

http://www.PeirceEngineering.com

 

[PEinc]

If the neighbor is unwilling to let you encroach on the parking lot, you may need to offer to rent the affected spaces until the new wall is built.

http://www.PeirceEngineering.com

 

[hotmailbox]

Thanks, all.

I know what to do if the neighbor is cooperating. Cantilevered soldier beams are only 13 feet max so not a big deal if we can drill on the neighbor's side. Just like typical shoring work.

The purpose of my post was to seek for ideas of how to do this in case the neighbor goes against us. I talked to the owner to deal with the neighbor as soon as possible.

 

[PEinc]

If the neighbor does not let you install temporary sheeting on his property, you may need to brace the existing wall at two levels (wales and braces), underpin the existing wall, and then build a new wall in front of and against the existing wall. You will lose some space in your lot because your new wall will be built in front of the existing wall. Once your existing wall is braced, you should be able to trim back the existing wall footing before or after you underpin the wall.

Another choice is to install soldier beams in front of the existing wall footing and let them project up to about 2 feet below the elevation of the neighbor's property. Then stack lagging boards between the soldier beams and backfill between the lagged soldier beams and the front of the existing wall. Then, build a new wall in front of the temporary sheeting and leave the original wall in place. With this method, you will also lose some space in your lot. Other possible ways to do this would involve getting permission to install tieback anchors or soil nails across the property line or would require moving the proposed wall much farther away from the existing wall and more into your lot.

http://www.PeirceEngineering.com

 

[hotmailbox]

Thanks, PEinc

The design is so tight now and architect and owner are fighting over an inch because of the code clearance requirements. I don't think they can afford losing space. I hope we can rely on the fact that the neighbor parking is encroaching into our lot and using our wall as fence wall (and they have to build their own fence wall) and offer them the solution to re-build things more nicely. Hope the neighbor takes the bait.

Do you still think that it's not wise to brace the existing wall then saw cut the existing wall & footing (in 2ft wide strip @ 8'-0" o.c.) to make space for soldier pile shaft drilling? It sounds like labor intensive and costly but it's still technically feasible, don't you think?

 

[PEinc]

It depends on the capabilities of the contractor and his equipment. Will you be leaving in the remaining portions of the wall or removing them in lifts as you place lagging? How close to the existing wall can you drill? Drilling equipment might not be able to get close enough to install the soldier beams back where you want them. What retains the original wall backfill (under the parking spaces) when you cut the slots in the wall? You may need lagging in each soldier beam slot. Then, this lagging will be in the way of drilling for the soldier beams.

Your problem started with the architect not knowing enough about excavation support methods.

http://www.PeirceEngineering.com

 

[hotmailbox]

This may clarify my idea.

I hope arching effect can hold the soils in the open strips and hope we can ask the neighbor not to park cars near the cut.

 

[PEinc]

Clarify? Nope. Just brings up more questions and problems. Good luck with that one.

http://www.PeirceEngineering.com