Case of the Month: Why the Wall Cracks?

Apr 1, 2016 by

The residential concrete block wall was damaged, reportedly during recent heavy storms. GEI was assigned to inspect and photograph the site to identify the predominant cause and approximate age of the damage and to provide a general scope of work to repair it.

Our expert visited the property, in the presence of the tenant. The property was a single-family residence, constructed circa 1962. The expert took a series of photographs of the site and damaged wall.

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While near the general vicinity, the residence was not located in the Alquist-Priolo fault zone, nor was it located in an earthquake-induced liquefaction area. These factors allowed the property to be resistant to smaller earthquakes (<3.5 magnitude). Inspection of the rear wall showed that one section, towards the center of the whole rear boundary, had a loss of the top course of hollow concrete blocks.

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Close inspection of the tree trunk surfaces on the adjacent property, near the top of the wall location, showed abrasion marks left by their continuing contact with the top of the wall.

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Trees of this size will move readily with wind and, if the wall was of faulty construction, will result in failure of the wall. Such faulty construction of the wall was clear in the east end of the wall, where the growth of an adjacent large tree had caused movement and cracking of the wall and its foundation. Inspection of the interstices of the fallen wall top showed that the fallen section included no required rebar and grout fill to resist cracking, as was required by the local building code for construction of masonry walls six feet or less.

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The existing remaining wall did not meet these criteria. Based on the foregoing, the expert’s opinion was that the predominant cause of the damage observed was faulty construction. A properly constructed wall would normally withstand a base wind speed of 80 mph. The subject wall cracked and failed prematurely. The approximate age of the cause of those damages was consistent with the date of construction of the wall and not less than twelve months prior to the date of inspection.

So what needed to be done to correct these deficiencies? Perform the following:

1. Obtain a building permit for the project and provide training and protection for workers as determined by Cal/OSHA.

2. Demolish the required length of the existing defective wall and remove the concrete blocks and foundation.

3. Excavate to the required depth and width for a new foundation and pier pads, including cutting away any tree roots adjacent and still living.

4. Insert tree root barriers as needed and in accordance with best practices, to prevent further root intrusion.

5. Construct a new hollow concrete masonry block wall 6-inches thick, in accordance with city building codes, including grout fill, rebar and offset foundation strip, and masonry piers of 18 inch square plan sections at 15 feet on centers with expanded bases, and having capping pieces to match the existing style, with cast surface patterned blocks to match.

6. Remove all debris, including hauling debris to, and paying for, dump fees, and leave the whole site in good or better condition on completion.

7. Provide a signed permit with authorized inspector signatures to homeowner within one month of completion.

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