June 2022 G-01483.84-017-R-Rev0 Because the 23 Table 6: Design properties of materials. Material Unit weight (kN/m3) Drained Shear Strength Cohesion (kPa) Friction Angle (°) Firm clay 17 0 26 Very stiff to hard clay 18 0 28 WRS 20 0 40 MS andesite 20 Modified Hoek-Brown (refer Table 7) Table 7: Rock Mass characteristics. Rock Strength Structure Surface condition σc (MPa) Mb S a Andesite MS Very blocky Fair 35 4.19 0.003 0.5 6.4 Groundwater During construction of the WRS, the potential exists for pore pressures to be induced in the foundations from the weight of the WRS. The amount of induced pore pressure is dependent on the rate of increase in height of the WRS and the permeability and compressibility of the foundation soils. Based on these factors we consider that there will be a potential for increase in pore pressures in the foundation soils. The material to be placed in the WRS is expected to be gravel and cobble to boulder sized material. The mass permeability is anticipated to be reasonably high and the waste dump material is expected to be generally well drained. The groundwater conditions adopted for the stability analyses are summarized in Table 8. The pore pressure for the soils and the WRS is described by the pore-pressure parameter Ru. This parameter reflects the potential for construction induced pore pressures or restricted drainage in the WRS. The pore pressures in the shallow soils are dependent on the weight of the overlying soil and material in the WRS. The pore pressure for the underlying andesite rock is assumed to be equal to the existing groundwater level. This groundwater configuration is anticipated to be conservative for slope instability because the Willows Access Tunnel will act to lower the groundwater pressures below the WRS. Two groundwater conditions (refer to Table 8) for the foundation soils have been adopted in the stability analyses to account for the uncertainty in the potential pore pressure increase during construction. Table 8: Groundwater conditions adopted for analyses. Materials Groundwater Condition Groundwater Condition 1 Groundwater Condition 2 Firm clay (weathered volcanic ash) Ru = 0 Ru = 0.1 Very stiff to hard clay (highly weathered andesite) Ru = 0 Ru = 0.1 WRS fill mainly comprising tunnel spoil Ru = 0 Moderately strong andesite rock Original groundwater level
RkJQdWJsaXNoZXIy MjE2NDg3