Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 16 should be placed in lifts no thicker than 18 inches consolidated in place with vibratory equipment. Each lift of fill and all subgrade should be firm and unyielding under construction equipment loading in addition to meeting the compaction requirements to be approved. 6.9 PERMANENT CUT AND FILL SLOPES On a preliminary basis, all permanent cut slopes in bedrock should have a maximum inclination of 2:1 (horizontal:vertical); however, all cut slopes will need to be observed by our engineering geologist during site grading to confirm that cuts expose relatively competent, favorably bedded rock.. All permanent fill slopes derived from on-site soil or bedrock materials should have a maximum inclination of 2:1 (horizontal:vertical). Fill slopes should be overbuilt and trimmed back, exposing engineered fill when complete. If adverse bedding conditions are encountered during site grading, some slopes may need to be over-excavated and re-constructed as a buttress fill slope. Preliminary guidelines for over-excavation and engineered fill buttress construction are discussed in the following sections. Final slope grading and engineered buttress fill design criteria should be developed during the design-level geotechnical investigation. 6.9.1 Engineered Fill Buttress As discussed, the proposed 20- to 30-foot-high cut slopes to be located along the western end of the site will expose interbedded sandstone, siltstone and shale. Although the bedding of these materials appears to be generally favorable, portions of the exposed bedrock materials may be relatively weak and may be susceptible to shallow sloughing. To reduce impacts due to cut slope instability, on a preliminary basis, we recommend that south-facing cut slopes greater than 10 feet high be over-excavated and reconstructed as an engineered fill buttress. This buttress should extend at least 10 to 20 vertical feet above the proposed residential pads. If required, the top of the buttress should include a debris catchment bench and a drainage ditch to collect and control surface water runoff. Appropriate keyways, benches and subsurface drainage will be required for slope buttresses, as discussed below. 6.9.2 Keyways and Benches In general, fill placed on existing ground inclined at 6:1 or greater, or new cut slope buttress fills, should be benched into the existing slope and a keyway constructed at the toe of the fill. Benches should be angled slightly into the slope be spaced vertically at no greater than 5 feet between benches and extend at least 3 to 5 feet into competent material. Depending on the thickness of any colluvial/residual soil layer that blankets the bedrock, the benches may need to be widened beyond the minimum width to extend into competent bedrock. Keyways should extend at least 5 feet below grade or into competent bedrock, be at least 20 to 25 feet wide, and be angled slightly into the slope (minimum 2 percent inclination). A typical keyway and benched fill detail is shown in Figure 6; final buttress fill configuration should be determined during the design-level geotechnical investigation. Ii! CORNERSTONE EARTH GROUP