DWR_3391241 - Laserfiche WebLink

as medium dense to dense based on standard penetration test results. The standard penetration tests performed In the alluvium identified two loose or soft areas, one near the left abutment and one in the vicinity of Boring 18 (Lincoln-Devore 1974). The loose zone in Boring 18, however, did not appear in Boring D-2 (D'Appolonia, 1981b) located nearby (see Figure 4). Direct shear test results (Dames and Moore, 1975) on the alluvial soils gave a range of strength between 30 to 36 degrees for the friction angle and a cohesion of 200 pounds per square inch or less. The lower end of this range was selected because of the 1 potential for soft materials in the foundation. The selected values are considered conservative. The Creede Formation bedrock was modeled as two separate zones including (a) a fractured zone, and (b) an intact zone as discussed in Section 3.2. The fractured zone was modeled as an anisotropic material with the 7 following effective strength parameters: - Angle of Internal Friction (Between +10° to -10° from horizontal) = 29' - Angle of Internal Friction (Outside the limits) - 38` - Cohesion = 0 Observations of the rock core indicated that joints were either along the bedding plane, oriented within approximately ten degrees of hori- zontal, or random high angle fractures. Along the bedding plane, the rock strength is controlled by the shear strength of the joints. Joint shear strength was evaluated by estimating compressive strength of the rock from visual observations of core, stress level under the dam load, and observed joint roughness. For shear plane orientations not parallel to the bedding, the fractured tock will exhibit a higher strength, more comparable to a dense, coarse granular material. The intact rock zone of the Creede Formation sandstone was assigned strength values repre- senative for medium hard, sound sandstone. 10