2020-05-13_PERMIT FILE - M2020022

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AUSTIN & BETSY CLENNIN Page 1 BECKER PIT Permit # M-2020-022 GEOTECHNICAL STABILITY EXHIBIT - Dry slopes This information is presented to address the plan to mine within 200 feet of the dirt road owned by the Colorado State Land Board listed in Exhibit L. The road is located in the southeast corner of the permit area. The mine depth in this area will be approximately 30 feet deep and the road at the fence crossing will be 35 feet from the top of the mining slope . It is impor- tant here to mention that the slope along the road will be mine at rate flatter then 3h to lv to keep it open as the mine devel- ops . As mining moves along the west line away from the road mining will revert to a near vertical face with cut/fill sloping to leave the final 3 : 1 slope . I added the location of two cross- sections on the Mining Plan Map - Exhibit E-2 used to do the geotechnical analysis for these conditions . In this area the setback from the permit/affected lands line to the mining dig line (TOS) is 10 feet and from the property line/road is a total of 35 feet . Cross-section A shows how the slopes will be reclaimed and lists the angles needed to do the analysis . Cross-section B is done on a different angle to take in the working face line to determine if Mining to within 50 feet of the Top of Slope and then using a cut/fill method to do final grading was enough to protect the road and have a factor of safety of at least 1 . 5 : 1 . The attached sketches are cross sec- tions showing the setbacks and slopes we described. The colors noted in the text correspond with the slope lines shown on the sketch. The table used to calculate the Safety Factors is also included. The following information is the analysis data used to calculate the safety factor for the different conditions or proposed setback distance discussed in the following text . From previous studies it has been determined that an appropriate friction angle for Dry rocky sand and gravel is 35 ' and is adequate when non-site-specific information is available . This number falls into the parameters listed in Rock Slopes: Design, Excavation and Stabilization, Publication No. FEWA-TS-89-045, Table 1 - Typical Soil and Rock Properties for Sand and Gravel, uniform grain size like what is found on the mine (copy attached) . The mate- rial in the mine is in-place sand and gravel, is assumed to be cohesionless and having an friction angle (D of 35' (green line) The formula used for the factor of safety (FS) calculation is FS = Tan(D _ Tan6, where (D is the friction angle of the material or the angle of the working face and 6 is the slope angle from the