Building Movement: cause and fix

[efsinc]

The client says his 2 story, wood framed, raised foundation, Northridge CA area apartment building is moving.

Upon first site visit, indeed there is an apparent 'bulge' at the first floor sill level, about 3 feet above grade. No measurements were taken yet, and i could not be sure visually whether the cripple wall from grade to 1st floor sill was tilted outward and the wall from 1st floor sill to roof plumb, or whether the cripple wall is vertical and the upper story walls leaning inward. There is obvious stucco damage along the 1st floor sill plate line for 100 + feet of a 200 foot long wall confirming movement.

Owner says the movement began 1-2 years ago and has been accelerating in the last 3-6 months.

The ground was moist, but the owner claims it was from recent rain and is not 'permanent'.

Building dates from the 1960s and received significant cosmetic damage and subsequent repairs in the 1994 earthquake. No plans are available. I don't know if a professional inspection was performed at the time of the EQ.

Q1. What might be the cause of this movement and how might that cause be conformed?
Q2. What would be the method of remediation?

 

[Ron]

Post a couple of photos and/or sketch of the damage/building lines.

 

[Ltwine]

I suspect the subgrade has started to move again along weak spots created during the previous quake. The shifting could be three dimensional, and detected by a survey tied to some bench marks. A geotech guy may be brought in later.

 

[dik]

Additional information is needed. What is the soil type? Clay, Granular, or something else. What are the soil characteristics? high moisture can reduce the bearing strength with many soils. Has there been a change in the use of the building? to cause higher loading? You would be well served to have a good geotechnical engineer take a gander. or a good structural engineer.

Dik