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Mr. Mark Johnson <br /> March 17, 2017 <br /> Page 4 <br /> clay minerals parallel to the shear plane. Under these conditions a claystone exhibits its lowest strength known as <br /> residual strength. Residual strength bedrock occurs in discrete zones, parallel with the sheared surface or zone, <br /> whereas fully softened strength occurs over a broader area (not used in this modeling). Based on data from other <br /> recent jobs and engineering judgment, the residual strength claystone was modeled in a four-foot thick layer <br /> (conservative)overlying the peak strength bedrock as follows: <br /> Dry Unit Weight Moist Unit Weight Saturated Unit Friction Angle V° <br /> (pco (pco Weight(pco Cohesion C'psf <br /> 116 Peak= 126 Peak= 135 Peak= 100 Peak=25 <br /> Residual= 110 Residual= 133 Residual=0 Residual=15 <br /> STABILITY ANALYSES RESULTS <br /> Stability analysis included one conditions: <br /> 1. Proposed dry mining slopes(dewatered). <br /> Setbacks listed in Table 1 indicate the minimal setback from the structure to the mining limits. The setback <br /> distance can be increased as needed to address other restrictions <br /> The factor of safety shown below is the minimum factor of safety of the three conditions listed above. <br /> TABLE 1 -SLOPE STABILITY RESULTS AND SETBACKS <br /> Section Location Critical Structure Modeled Surcharge sf Factor of Safety <br /> AN Western Boundary WCR 13/N County Road 1 400 4.265 <br /> BB' Western Boundary WCR 13/N.County Road 1 400 1 749 <br /> CC' Northern Boundary Hwy 392/WCR 68 400 1.749 <br /> DD' Eastern Boundary Overhead Power Line J 200 1 408 <br /> The mining setback will be 15-feet minimum from the high wall to the property line/easement or structure. <br /> CONCLUSIONS <br /> The minimum distances proposed in this report will protect the subject structures, however, the actual setbacks <br /> may be increased for constructability and maintenance considerations. <br /> LIMITATIONS <br /> Our review is based on regional geologic mapping, present mining plans, public well construction data, and stability <br /> analyses using typical strength parameters for the various strata in the critical sections. Should the mining plans <br /> change or subsurface conditions vary from those portrayed in this letter, we should be contacted in order to re- <br /> evaluate the potential effects on permanent man-made structures. Stability analyses were run at the structure in <br /> question and were not run on failure surfaces closer to the highwall. Note also that surcharge loads due to <br /> temporary material stockpiles and overburden berms were not considered in the analysis. <br />