The Structural Capacity of Repaired Manholes
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Five manhole models, three composed of brick and two composed of concrete, were created in the laboratory with the goal of simulating existing manholes in the field that have been deteriorated by stress and corrosion. The samples were rehabilitated using three different liners: a plastic polyurea spray-on liner applied to a brick manhole, an HDPE slip liner (grouted in place) applied to a brick and concrete specimen, and a calcium aluminate grout applied to a brick and concrete specimen. Each sample was tested under axisymmetric pressure in the hoop compression cell, simulating horizontal effective stresses that act on a manhole in a radially symmetric manner. At 500 kPa, minimal radial deflections were observed with no notable damage to any specimen. Each specimen was then tested in a diametrically opposed 2-point loading setup to test the manhole in bending which may be induced to on a structure in the field by surface activity or adjacent excavation. The sample rehabilitated with the plastic spray-on liner behaved in a ductile manner, yielding at the lowest strength. The samples rehabilitated with the calcium aluminate grout exhibited high peak strengths, but yielded in catastrophic failure at small deformations. The samples repaired with the HDPE slip liner also produced high peak strengths with the grout component yielding in brittle failure, but residual strengths mobilized in the HDPE liner prevented total collapse of the samples. Although all of the liners tested present viable rehabilitation solutions within the prescribed deformation limits, the HDPE slip liner is the preferred method of treatment solely based on considerations of strength and ductility; practical considerations of cost and constructability also need consideration.