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Grand Island Resources, LLC Page 4 <br />Idaho Tunnel Portal – Slope Stability Analysis <br />Applied GeoLogic LLC 5/7/2020 <br />Mix Design Information (per cubic yard): <br />Cement: 622 lbs <br />Water 323 lbs <br />Cellular Foam: 18.7 cf <br />Air Content: 69% <br />Unit Weight: 35.0 pcf <br />water/cement ratio: 0.52 <br />Permeability (ASTM D2434): 8.7 x 10-2 cm/sec <br />Compressive Strength <br />7-Day:100 psi <br />28-day:214 psi <br />Placing the cellular concrete backfill was originally scheduled for April 1, 2020 but was postponed due to <br />the Corona virus and social distancing concerns. At this time, it is not known when the work will resume. <br />Following placement, the cellular concrete backfill will harden rapidly and allow rehabilitation of the <br />tunnel to resume within several days following receipt of the appropriate approvals <br />This Technical Memorandum presents the results of an engineering evaluation of the geotechnical <br />stability of the overall slopes above and adjacent to the portal slopes, and provides this information to <br />DRMS. <br />1.2 Geology <br />1.2.1. Regional <br />The Caribou area, which is part of the Front Range Mineral Belt, is underlain by igneous and <br />metamorphic rocks of pre-cambrian age. These rocks are and, with the exception of locally covered by <br />unconsolidated quaternary glacial and stream deposits. . is devoid of sedimentary rocks., The pre- <br />Cambrian rocks in the Caribou area and in the adjoining areas to the north and south are intruded by <br />Tertiary igneous rocks which form several small stocks. The three principal rock formations in the <br />Caribou area are the Idaho Springs formation and the Boulder Creek granite of pre-Cambrian age, and <br />the Tertiary monzonite of the Caribou stock. The Caribou stock also contains comprises small bodies <br />of diorite, diabase, gabbro, and ultra-basic rocks. Minor units The Idaho Springs formation consists of <br />include pre-Cambrian amphibolite, mica schist, biotite gneiss, quartz monzonite gneiss and pegmatite. <br />1.2.2. Roadside Geology <br />The Caribou Road (County Road 126) above the Idaho tunnel is located entirely in mixed soil and rock <br />colluvium and regolith materials. Fresh gneiss of the Idaho Springs formation is present a short distance <br />above the road and to the south of the tunnel portal.