Smeared and Discrete Crack Evaluations of a Lock Exhibiting Earth Pressure-Induced Cracking

摘要

This report discusses the results of an evaluation of crack initiation and propagation at Snell Lock, one of the locks constructed on the St. Lawrence Seaway during 1956 and 1957. The rock-founded, unreinforced concrete gravity lock walls of Snell Lock experienced cracking as a result of earth loading in excess of those anticipated during structural design. The objective of this study is to appraise two analytical procedures used to evaluate the potential for and/or the extent of cracking within massive concrete structures. The two analytical procedures available for analyzing hydraulic structures that may exhibit cracking during loading are based on either the smeared crack theory or the discrete crack theory. The smeared crack theory uses a strength-of-materials approach to evaluate crack initiation potential and/or crack propagation in a material. A linear elastic fracture mechanics (LEFM) discrete crack analysis is used to assess if a discrete crack will propagation or arrest for a given increment of loading. Generally, LEFM relate the stress magnitude and distribution at the crack tip to the nominal stress applied to the structure; to the size, shape, and orientation of the crack or discontinuity; and to the material properties. The demand due to loading(s) applied to the retaining structure and specifically to the region of cracking is represented by stress intensity factors. The capacity of the material is characterized by the fracture toughness.