Johann F. Szautner, PE, P.L.S. ::::
Case Synopsis: An elderly lady tripped over a three inch raised-up portion of two adjoining sidewalk slabs, while walking in the neighborhood she lived in. As a result of her fall, she sustained a broken wrist and lacerations to her face.
Expert Analysis: Uneven sidewalk slabs are not un-common occurrences. These defects, and associated hazards, are easily eliminated by proper design, construction and maintenance. The design must provide for sufficient concrete strength, placement on an adequate sub-base of aggregate, and placement of contraction, expansion and isolation joints. Additionally, the walking surface must be provided with a slip resistant finish.
The underlying soil has to be compacted. Aggregate placement is important to break-up the capillary action of the underlying soil and thus avoid frost heave. Adequate slab joint placements are important to eliminate slab movements, which will result in break-up and buckling of the concrete walking surface.
Engineering investigation included inspection of the sidewalk, taking sidewalk core samples, measurements and photographs. The analysis established that the sidewalk buckling was caused by inadequate control of thermal movement of the concrete slabs. Although analysis of core samples revealed sub-standard concrete strength, and inadequate thickness of the aggregate base, these deficiencies had no impact on the thermal movement, the root cause for the buckling.
While expansion joints were not specified in the contract documents, their placement is standard industry practice for concrete contractors.
Result: Case settled.