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Memo to Kate Pickford 3 January 13, 2006 Gravel Pit Access Road Stability File No. M-2005-045 that is only slightly higher than the shear strength assigned to the soil. The shear strength fox bedrock input to the model is an internal friction angle of 25 degrees and cohesion of 400 psf. Pore water pressure within soil and bedrock has a profound affect on the materials ability to resist shearing stress. Of the three test borings advanced by Trautner, only boring no. 2, located at the top of the slope, encountered saturated soil. The Trautner Report shows that the water table at the location of boring no. 2 is 14 feet below the ground surface and two feet above the soil bedrock contact. Trautner hypothesizes that this is infiltrating irrigation water that accumulates and migrates along the contact, which is an effect commonly observed in irrigated areas. The DMG's model conservatively uses a water table that is two feet above the soil bedrock contact through the entire slope cross-section under consideration. As discussed below, DMG has modeled the ground water both as the likely case of perched water flowing along and above the bedrock contact causing a two foot thick zone of saturation, and as being caused by piezometric pressure in the bedrock, resulting in a highly conservative analysis of slope stability. Discussion of Results Enclosed with this memo are printed results of the DMG's slope stability analyses. Analysis no. 1 is for the case where infiltrating irrigation water is flowing along the bedrock contact. For this analysis, pore water pressure in the bedrock was set at zero. The Galena software was used to analyze approximately 20,000 potential slope failure surfaces, and was set to seek the failure surface with the lowest factor of safety, i.e., that failure surface that is most likely to landslide. With no bedrock pore pressure, and since the bedrock is more resistant to shearing that the soil mantle, the lowest safety factor potential failure surface for the entire slope is a circular surface that occurs entirely in the soil mantle as illustrated in the enclosed cross section diagram for analysis no. 1. The calculated safety factor for this analysis is 1.84, indicating the slope is very stable. Analysis no. Z incorporates the conservative assumption that the ground water observed in Trautner test hole No. 2 is a result of piezometric pressure in the bedrock. In this case the bedrock unit is modeled as being saturated, with the ground water being confined by the overlying clay soil creating a slight piezometric pressure. Galena was again used to search for the lowest safety factor potential failure surface. In this case, pore pressure in the higher shear strength bedrock results in the lowest safety factor failure surface intersecting the bedrock unit to a depth of more than 30 feet below the ground surface. However, the calculated safety factor for this surface is 1.60, again indicating that the slope is very stable, even under the assumed worst case pore pressure conditions modeled by analysis no. 2. Analysis no. 3 models the affect of the proposed access road cut at the location on the slope where the road will pass beneath the Williamson residence. The location of the road cut at this location on the slope was scaled from the revised Exhibit C Map cited above. The lowest safety factor potential failure in this analysis daylights into the road cut as illustrated in the enclosed cross section diagram for analysis no. 3. The lowest calculated safety factor for analysis no. 3 is 1.81, which demonstrates that the construction of the road cut, if done correctly, will not destabilize the slope. Stipulations far the Approval of the Permit Application • The fill section of the access road will be constructed as a mechanically reinforced embankment as shown in the preliminary access road designs dated August 31, 2005.