Did a Cracked Pipe Cause a Landslide?

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A landslide that released fly ash materials into a drainage stream causing environmental concern was attributed to a failed municipal water pipe. The section of pipe that was removed had been examined by others and specimens had been cut from it during the previous examinations. Once we were afforded access to these specimens, we performed acompositional analysis on the pipe wall. Our examination noted that the observed graphitization corrosion was consistent with the age and service life of the pipe and that the crack originated in the graphitized zone. Using a scanning electron microscope (SEM), we generated high magnification images and elemental compositional information from fracture surfaces and corrosion products of the pipe sections and fragments. An analysis was also performed on the concrete lining of the pipe to determine its integrity.

The results of this investigation determined that the failure was stress governed and was caused by externally induced mechanical stresses that initiated a transverse crack in a graphitized area of the cast iron portion of the pipe wall. The sudden loss of many tons of cover material caused an upward heave in the surrounding soil allowing the crack to propagate through the wall and fracture the concrete liner, giving rise to the leak. We concluded that the failure was a victim of the landslide and not the cause.