Repair of Pushed-in Basement Foundation Wall in New $400,000 House GENERAL INFORMATION Date of Site Inspections: May 22, 1999 Location: 4080 Rockhill Drive, Charlotte, NC Prepared for: Mr. Robin H. George Source(s) of Information Interview with Robin George. Photos taken by George. George letter to Corporate Homes, Inc. dated May 3, 1999. Dilworth Engineering report and sketches dated April 29, 1999. Darnell Woods letters dated May 3 and May 19, 1999. Corporate Homes New Homes Purchase Agreement and attachments. Purpose of the Investigation Observe the damaged basement and garage foundation walls. Determine the cause and nature of the damage. Determine if the damaged foundation walls are still functional. If repairs are necessary, determine one or more repair options. Orientation Unless otherwise stated, all directions (left, right, rear, etc.) are in relation to an observer standing in the garage and facing the damaged wall. | Top | Table of Contents | BACKGROUND Corporate Homes, Inc. began construction of a 5800 sq. ft. home for the Georges this spring. The house was designed to have a full basement. The concrete foundation was poured on April 21 and backfilled on April 23 with a front-end loader. When the garage was backfilled, the 9' high by 22' long foundation wall between the garage and basement was overstressed. The wall bowed outward and cracked in several places. | Top | Table of Contents | DESCRIPTION The building foundation is stepped to accommodate the sloping site. The wall heights vary from 9' to 1.5', depending on the outside ground elevation. The thickness of the walls varies from 10"" to 5½"". The damaged wall section is 10"" thick. The wall sits on a 24"" wide by 10"" thick continuous footing. According to Mr. George, the walls and footings contain steel reinforcement. Mr. George thinks that the reinforcement in the walls consists of ½"" diameter steel rods spaced at 36"" on center, vertically and horizontally. The reinforcement is in the center of the wall. According to Mr. George, the wall reinforcement was tied to vertical rods embedded in the footings. Mr. George said that the walls were poured in one continuous operation. He said that the concrete was supposed to achieve a compressive strength of 3000 pounds per sq. inch at 28 days. | Top | Table of Contents | METHOD OF INVESTIGATION Mr. George provided me with letters, photos, and other documents that I reviewed before visiting the site. I also interviewed Mr. George concerning how the damage occurred and the Builder’s recommendation for correcting the problem. During the site visit, I inspected the foundation and photographed the damage. With the assistance of Mr. George, I measured the bow in the wall. In addition, I measured the damaged foundation wall and adjacent walls. I consulted with a company that specializes in sawing concrete walls to determine how the damaged wall section would be cut out, if this repair option were chosen. | Top | Table of Contents | OBSERVATIONS The wall between the garage and basement is bowed and cracked in several places. There are three diagonal cracks in the face of the wall (Photos 2 - 5). The cracks extend several feet down the wall. The longest crack extends from the top of the wall to the footing, and it is about 1/32"" wide (Photos 4 & 5). There are also cracks in the foundation walls that turn back on the left and right sides (Photos 6 & 7). The cracks go through the wall (Photos 8 - 11). The crack on the left side is about 1/8"" wide. The cracks on the sidewalls were caused by vertical rotation of the top of the 22' long wall. The wall is also bowed horizontally. With the assistance of Mr. George, I pulled a nylon string across the top of the wall from corner to corner and measured a æ"" bow at the center of the wall. The bow continues down the wall, decreasing in severity as it gets closer to the footing (Photo 7). The combination of vertical rotation and horizontal bowing has created a noticeable belly in the wall. The wall was backfilled with 8.5' of sandy-silty fill on the garage side (Photo 1). According to Mr. George, the backfilling was done with a large front-end loader. Apparently, the front-end loader was used to compact the fill as well. Evidence suggests that the wall is continuing to move outward. I observed a 1/8"" space between the wall and backfill. In addition, Mr. George said that the crack in the top of wall on the left side had increased in width since he last inspected the damaged wall (Photo 8). The stub wall to the left of the garage entrance is cracked and loose. It was probably hit by the front-end loader. | Top | Table of Contents | FINDINGS AND CONCLUSIONS The damaged wall was severely overstressed during the backfilling operation. The wall was apparently hit by the front-end loader or forced out by the fill as it was being pushed against the wall and compacted. The wall was backfilled after the concrete had cured only 48 hours. It is not considered good practice to backfill concrete foundation walls until they reach ? their design strength. Usually that takes about 7 days. The wall was backfilled without any lateral bracing in place. It is not considered good practice to backfill foundation walls until the first floor deck is in place or temporary braces have been installed. The severity of the cracks and bulge in the wall are indications that the wall has failed due to being grossly overstressed in bending. It is difficult to accurately assess the present strength of the wall without extensive testing and performing a structural analysis. In my opinion, the wall has lost 75-90% of its ability to resist lateral loads and 40-60% of its ability to support vertical loads. The strength of the wall cannot be restored because permanent damage was done to the concrete and reinforcing in the wall. As the newly poured wall bent outward, the concrete on the compressive side of the wall was crushed and the reinforcing on the tension side was pulled loose. As noted earlier, the wall is 10"" thick. The wall was designed with extra thickness so it would be strong enough to resist several tons of lateral force exerted by 9' of fill plus the weight of the garage floor slab and two cars. It also has to support about 1500 lbs. per lineal foot of vertical load imposed by the superstructure. The wall has to be strong enough to simultaneously handle these lateral and vertical loads. Because the combined loads are high, it is the most critical part of the foundation. In addition to the requirements to support vertical and lateral loads, the wall has a third function. It must also keep out subsurface water so the basement remains dry. There is a greater risk of water getting into the basement because the wall is cracked. | Top | Table of Contents | RECOMMENDATIONS Replace the entire foundation. The advantages of this option are: (1) the house is constructed on a completely new foundation, (2) there is no risk that the value of the house will be diminished, (3) problems that may develop in attempting repairs that are somewhat uncommon are avoided, (4) full liability for design and construction remains with the Builder, and (5) good will. The disadvantage is the high cost to the Builder and the delays that would result. Cut out the damaged wall section and replace it with a new wall section. The new wall would have to be designed as a retaining wall to give it sufficient strength to resist lateral loads without depending upon connections to the existing foundation walls. The advantage is that the foundation would be restored to almost new condition. The disadvantages are the high cost to the Builder, the requirement for above average quality controls during the repair process, and the delays that would result. Leave the damaged wall in place and construct a new wall behind it on the garage side. The new wall would have to be designed as a retaining wall for the reasons given above. The advantages are: (1) lower costs to the Builder, (2) simplicity of construction, (3) the existing foundation is not disturbed, and (3) minimum time delay. The disadvantage is that the damaged foundation wall must be partly depended upon to support the vertical loads. In addition, it is not a ""clean"" solution to the problem in that a defective structural component is left in place. | Top | Table of Contents | LIMITATIONS The observations described in the report are valid on the date of the investigation and have been made under the conditions noted in the report. We prepared the report for the exclusive use of Robin George and his successors and assignees. Criterium-Stanton Engineers does not intend any other individual or party to rely upon the report without our express written consent. If another individual or party relies on the report, they shall indemnify and hold Criterium-Stanton Engineers harmless for any damages, losses, or expenses they may incur as a result of its use. The report is limited to the visual observations we made during our inspection and information provided by Robin George. We did not undertake any digging or excavation, or perform any destructive or invasive testing. Accordingly, we cannot comment on the condition of components that we could not see. In addition, we are not responsible for conditions that were not within the scope of our services at the time of inspection. We did not assess the stability of the foundation wall and/or underlying soil. We did not perform any computations or engineering analysis as part of this evaluation. This report should not be considered a warranty of condition, and no warranty is implied. | Top | Table of Contents | William A. Stanton, P.E. | Top | Table of Contents | | Structural Inspections | Residential & Commercial Services |