Installing foundation next to deteriorating rubble wall without underpinning

[vasilios31]

We are proposing to install a footing/foundation next to a two story brick building with a deteriorating loose rubble wall foundation installed on fill. The depth of the existing footing is 4'. Adequate bearing material is at 10'. We do not want to underpin the existing building because there are already signs of settlement (vertical cracks in wall) and we are afraid of causing additionl damage during the process. The neighbor is a big problem and we do not want to touch her building. We propose to excavate down 4' to match the adjacent footing and install helical piles to the bearing stratum. We then step the foundation wall away from the existing building and excavate 6' more to the desired depth of cellar level.

Is there an easier, more cost effective way, of installing this foundation?

 

[oldestguy]

If you would provide a test boring description of conditions, that would help. Also a cross section sketch. Have you done a stability analysis?

 

[Ron]

Since you have already indicated that the building owner is difficult, you might want to approach this anticipating that the owner will claim you have damaged her building during your construction. You will need to do several things. First, you must get permission to enter onto the property and do a detailed present condition survey of the building. Document any and all deficiencies that are observable using written notes, photos and video. Make sure that if there are current cracks that you mark the crack terminations and place a crack monitoring device across the cracks to check for movement. Do this with enough time ahead that you can document crack moment that results from thermal influence and from wetting/drying influence. This will help you discern whether there is crack movement associated with the construction activities.

If the owner is unwilling to give you access, then have your attorney put the owner and the building department on notice that you have attempted to do this in an effort to mitigate potential issues with construction activities and to protect yourself from subsequent claims.

If the owner is unwilling to repair their foundation, again have your attorney put them on notice that their failure to stabilize a deficient foundation may cause damage to the foundation during your construction. Further, if the foundation is truly unstable to the point of potential collapse or significant movement, you do not want to place your team in danger during construction and that they might be liable for any damage to your construction or personnel for their failure to mitigate a hazardous condition.

Enlist your local building department to help you with this. They usually have a bit more power than they're willing to exercise....push their limit on this.

Monitor vibrations and protect your excavations during construction. Set triggers on the vibration monitoring that will alert you to potentially damaging vibrations.

Treat this seriously. It is a common source of construction litigation.

 

[oldestguy]

While Ron's advice is great, more is needed. Check the laws dealing with responsibilities there. In our area the neighboring owner is responsible for holding his building in-place if the excavation is less that 8 feet, called standard depth. However anything deeper than that number is your responsibility. This may vary depending on distance from property line.

 

[thaidavid40]

Did you guys consider drilling and pouring a secant wall first, then excavating for the basement?
Dave

Thaidavid

 

[PEinc]

Oldestguy and Ron have provided good advice. Remember, just excavating down to the bottom of the existing foundation wall can cause the building to settle more than it has already. Bearing capacity is a function of the overburden pressure. Excavating this overburden and cause the building to settle before you start underpinning or installing the helical piers that you mentioned.
You also did not mention how far away from the building you would step the new deeper footings. The farther, the better. The closer, the more chance of dropping the building.
I recommend underpinning the building.

http://www.PeirceEngineering.com

 

[vasilios31]

Thank you all for the responses. We are in the process of obtaining permission to perform a pre-construction survey of the existing building. We will also monitor during excavation and construction.

In our area it is the responsibility of the owner excavating to support the adjacent building.

We have provided a 1 to 1.5 slope from existing foundation to proposed. We will also install foundation in sections.

A secant pile wall would be very expensive comparably to our solution.

I have attached a sketch of our proposed solution.

 

[PEinc]

Please let us know how this works out for you.

http://www.PeirceEngineering.com