The principal parameter applied in the linear elastic fracture mechanics crack propagation models is the fracture toughness, K1c, of concrete. No definite relationship is readily available in the literature of dam concrete to determine the fracture toughness from standard material parameters such as strength, elastic modulus, and aggregate size. And only a handful of experimentally
determined results has been reported so far. Saouma et al. (1989) found a Kic value of 1.1 MPa-m1/2. Linsbauer (1990) reported K1c, values in the range of 2.0 — 3.5 MPa-m1/2. The following guideline has been proposed by Saouma et al. (1990) to select K1c: a zero value as a first approximation; should the response be unacceptable, a value of K1c = 1.0 MPa - m 1/2 is used; and if this value still results in unacceptable crack lengths, laboratory experiments could be performed on recovered core specimens. Due to multiaxial confining stresses in the field conditions, the in situ values for fracture toughness, K1c, were determined as three times the unconfined laboratory test values (Saouma et al. 1989, 1991b). The fracture toughness can also be estimated from the following well-known relationship (Irwin 1957):
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