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May 29, 2009 <br />1.0 INTRODUCTION <br />Page 1 <br />As per the proposal by Agapito Associates Inc. (AAI), dated June 26, 2008, submitted to <br />Trapper Mining Inc. (TMI), AAI has completed Task 2 of the six (6) geotechnical tasks (AAI <br />2008). This task involved conducting a detailed stability analysis of the Horse Gulch fill as well <br />as the reclaimed K-Pit and an associated buttress. The purpose of this analysis was to assess the <br />long-term stability of the planned backfill in Horse Gulch and the K-Pit Buttress. The results of <br />this analysis are intended to provide TMI engineered designs for its use in providing the <br />Colorado Division of Reclamation Mining and Safety (CDRMS) options regarding the K-Pit fill. <br />2.0 SLOPE STABILITY ANALYSIS <br />Due to the complex topography of the Horse Gulch fill, the modeling was performed with <br />the FLAC3DTM computer program (Itasca Consulting Group 2005). The program is a well- <br />known three-dimensional (3D) time-explicit, finite-difference program for engineering <br />mechanics computation. FLAC31) is an industry accepted tool for solving 3D geomechanics <br />problems in geotechnical engineering. The program is capable of simulating inelastic behavior <br />of 3D soil or rock structures (or of other materials) that undergo plastic flow when elastic yield <br />limits are reached. Materials are represented by polyhedral elements within a 3D grid that is <br />adjusted by the user to fit the shape of the object to be modeled. Each element behaves <br />according to a prescribed linear or nonlinear stress/strain law in response to applied forces or <br />boundary restraints. The material can yield and flow, and the grid can deform by moving with <br />the material. <br />The time-explicit, Lagrangian calculation scheme and the mixed-discretization zoning <br />technique used in the program ensure that plastic collapse and flow are accurately computed. <br />Because no matrices are formed, large 3D calculations can be made without excessive computer <br />memory requirements. The limitation of the time-explicit formulation is that small time <br />increments and damping are required for quasi-static analyses, but these are overcome by <br />automatic inertia scaling and damping that does not influence failure modes. <br />The original ground surface and the final fill contours are based on digital topographic <br />maps provided by TMI. Drilling information was used to define the layers of soil and rock. The <br />determination of material properties is discussed later in this report. <br />2.1 Horse Gulch Model Geometry <br />' The simulated region covers an area 3,863 feet (ft) west to east by 3,582 ft south to north. <br />Model coordinates are consistent with the Colorado State Plane Coordinates referenced to <br />1,430,000E and 400,000N in feet. The boundaries of the model extend from 2,843 to 6,706 ft in <br />the east-west direction (X-coordinates) and 811 to 4,393 ft in the north-south direction <br />(Y-coordinates) as shown in Figure 1. The model depth goes from the irregular ground surface <br />down to an elevation of 7,150 ft mean sea level (MSL); this represents a maximum model <br />' thickness of 535 vertical feet. <br />Agapito Associates, Inc.