Foundation walls for the basements have developed cracks. For the conditions described, indicate the probable cause of the wall crack condition. (a) Walls are concrete block construction; cracks exist along several horizontal mortar joints; wall deflects (bulges) inward near mid-height. (b) Walls are concrete block construction; diagonal cracking, or step-cracking, exists where two walls meet and form a corner. (c) Walls are poured concrete construction; diagonal cracks exist, all starting at the corners of various window openings.

(a)

The possible causes of horizontal mortar joint cracks and inward bulging of the wall at mid-height are as follows:

• Heavy moving loads generally imposed due to heavy vehicles passing near the wall.
• Heavy earth loading due to damaged backfill or wet soil.

(b)

The possible causes of diagonal or step cracks present where two walls meet and form a corner are as follows:

• Point loads whose value is greater than the compressive strength of the concrete used.
• The uneven settlement caused by volumetric changes in the underlying soil or increased load on one side of the foundation.