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Grand Island Resources,LLC Page 4 <br /> Idaho Tunnel Portal—Slope Stability Analysis <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 metamorphic <br /> rocks of pre-Cambrian age. These rocks are and,with the exception of locally covered by unconsolidated <br /> Quaternary glacial and stream deposits. . is devoid of sedimentary rocks.,The pre-Cambrian rocks in the <br /> Caribou area and in the adjoining areas to the north and south are intruded by Tertiary igneous rocks <br /> which form several small stocks. The three principal rock formations in the Caribou area are the Idaho <br /> Springs formation and the Boulder Creek granite of pre-Cambrian age,and the Tertiary monzonite of the <br /> Caribou stock. The Caribou stock also contains comprises small bodies of diorite, diabase, gabbro, and <br /> ultra-basic rocks. Minor units The Idaho Springs formation consists of include pre-Cambrian amphibolite, <br /> 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. <br /> Applied GeoLog;c SLC 5/7/2020 <br />