foundation wall
foundation wall
(OP)
Hi,
Can Somebody give me an idea to fix an exisitng 6-foot tall foundation wall? The foundation walls were constructed with 4 inch brick and 4 inch CMU block bonded with ties. The walls are neither reinforced nor grouted. The air gap between two courses is approximately 1-inch. Both brick and CMU block are supporting the superstructre load (roof and load bearing walls. In order to bring the pour garage slab at the planned elevation, the ingterior of the garage was filled with 5 feet of unontrolled fill. The maximum foundation wall height in this area is approximately 7 feet. Because of the imbalanced condition, the contractor placed 3-foot tall soil berm againt the exterior of the garage walls. The problem is the right and rear walls of the garage are in the crawl space. The placed berm obstructing the vents and crawl space door. It also created an unbalanced condition. I am planning to recommned the client to construct a retaining wall approximately 5 feet fromt foundation walls.
As an alternative, I am planning to recommend to attach 6-inch thick solid grouted CMU block to the existing wall on the exterior of the foundation walls. If they attach the new block with Portland cement paste, the final wall product will act as a compiste wall. Per building code an unreinforced and un grouted wall can support 5 feet of backfill. I don not know if my recommendation is technically correct or not? Do you think that there will be any cons with this solution? Can somebody suggest me any other solutions. The construction of the house is in the middle.
Can Somebody give me an idea to fix an exisitng 6-foot tall foundation wall? The foundation walls were constructed with 4 inch brick and 4 inch CMU block bonded with ties. The walls are neither reinforced nor grouted. The air gap between two courses is approximately 1-inch. Both brick and CMU block are supporting the superstructre load (roof and load bearing walls. In order to bring the pour garage slab at the planned elevation, the ingterior of the garage was filled with 5 feet of unontrolled fill. The maximum foundation wall height in this area is approximately 7 feet. Because of the imbalanced condition, the contractor placed 3-foot tall soil berm againt the exterior of the garage walls. The problem is the right and rear walls of the garage are in the crawl space. The placed berm obstructing the vents and crawl space door. It also created an unbalanced condition. I am planning to recommned the client to construct a retaining wall approximately 5 feet fromt foundation walls.
As an alternative, I am planning to recommend to attach 6-inch thick solid grouted CMU block to the existing wall on the exterior of the foundation walls. If they attach the new block with Portland cement paste, the final wall product will act as a compiste wall. Per building code an unreinforced and un grouted wall can support 5 feet of backfill. I don not know if my recommendation is technically correct or not? Do you think that there will be any cons with this solution? Can somebody suggest me any other solutions. The construction of the house is in the middle.






RE: foundation wall
RE: foundation wall
Thanks
Kumar
RE: foundation wall
RE: foundation wall
RE: foundation wall
I would also be concerned with water penetration and freeze/thaw action on the CMU isf left ungrouted and unsealed.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: foundation wall
I really appreciate your suggestions. I attached an hand sketch here for clarity. Finished product may look ugly. Comments please.
RE: foundation wall
RE: foundation wall
As it I now see (with a sketch) and understand that the slab is a floating slab inside the brick and the brick is not on the exterior as I had earlier supposed.
The first thing to do is determine the loads on the load bearing portion of the wall and recognize the dead loads in an analysis of the wall with an unbalanced soil load. You may find out that the wall carrying the dead loads may be enough for the low effective distance used for the unbalanced lateral soil load.
Is there any type of common tie, such as a solid CMU or bond beam at the top of the masonry wall to make the brick and block to carry the load jointly. If not the wythes will carry the load separately (uncoupled)and be weaker than a coupled or bonded masonry wall. Filling the 1" gout space is not really an option since there is no way to know if the 1" void is really clear or the mortar excess can cut off grout spacing. Placing grout in such a narrow space (not meeting any code requirements for minimum grout dimensions) is very questionable. Even the lowly ACI 530 specifications for "Empirical Design" specify a minimum wall thickness, but other ACI 530 methods allow 6" walls that are very common around the world.
Unfortunately, the option of adding a 6" partially grouted wall (which can be engineered easily), but the wall would end up being on the wrong side (compression) of the surcharge, so the effects of the steel are not very beneficial. Also tying the footings adequately to involve the rest of the structure would be problematic.
It is not necessary to solidly grout all of the cores of CMUs below grade according to any major code I am aware of (there may be local codes and traditions)and never came up when the ACI 530 was written over a 2 year period. Grouting is only necessary in the cores or cells where there is reinforcement, although in the older shapes of block, slop and grout migration into other cells was common, causing problems with other uses later. All too often, full grouting makes people feel good because it seems "stronger".
Since the unbalanced load due to the elevation difference even with slopes and possible slab surcharges, the wall may still work. If the dead load is sufficient to reduce the tension in the wall.
I suspect this is an addition on a previously designed residential structure that was built with a non-typical detail to avoid a brick ledge for the veneer.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: foundation wall
A cantilever retaining wall of that height needs a footing approximately three feet wide.
Another solution, if the slab has not been poured, is to tie the top of the new wall to the slab by means of dowels drilled through the existing wall and spaced at, say four foot centers.
BA
RE: foundation wall
I don't think there is a bond beam at the top. This is a new construction and half of the work was completed by the time we got the work. It looks like the load is on both existing brick and CMU block. As you said, filling 1 inch void with grout is not possible now.
BA,
Your suggestion is also good. I was thinking about connecting both old and new walls with dowels. I did not think about connecting the new wall with slab. Anyhow, the slab was not poured yet.
thanks
Fargo Farmer
RE: foundation wall
concretemasonry says:
I seem to be interpreting your sketch differently. I believe the left side of your sketch is the exterior. Top of slab adjacent to the 4" CMU is 5' above top of footing. Exterior grade is not shown.
Please clarify.
BA
RE: foundation wall
I agree in general. I took the left side as the exterior since I noted the right side was the "dirt" placed to support the floating slab, which is not unusual in some residential work for a garage slab.
The additional "fix" of adding additional fill on the external side was probably not noted or included on the drawings, but just seemed a logical "fix" to me in an attempt to reduce the effects and unbalanced load on the minimal wall. I could be in error. Unfortunately, an uncontrolled fill sloping away does not give much relief.
The information provided is really not very complete for a definite suggestion to "sign off" on.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: foundation wall
BA
RE: foundation wall
Sorry for the confusion. But you are right, the left side of the sketch is the exterior. Approximately 1 foot of fill will be placed on the exterior side. Do you guys think it will not work. unfortunately two more houses were built in similar fashion.
Thanks
RE: foundation wall
Whether or not it will produce satisfactory results in the long term depends on several variables which we cannot assess from afar, namely:
- Location of project...freeze/thaw conditions
- Quality of uncontrolled fill under slab
- Compaction of fill under slab
- Adequacy of attachment of new footing to existing
- Adequacy of ties between existing brick and block
A local engineer would be better able to review the work and provide an opinion.BA