PERMFILE136178 - Laserfiche WebLink

Home Browse Search

• 1.0 INTRODUCTION 1.1 PURPOSE The purpose of this stability analysis is to calculate the factor of safety (FOS) under static conditions for the Sedimentation Pond 016 embankment in order to document design compliance with applicable regulatory standards under Rule 4.05.6(1 1)(j) or (k). 1.2 METHODOLOGY The static FOS for Sedimentation Pond 016 was calculated using a basic, two-dimensional equilibrium analysis program called SLOPE/W (Version 3). The calculated FOS is the ratio of those resisting forces that would prevent embankment movement or failure to the cortesponding driving forces. Resisting forces include the internal svength parameters for both the soil materials used in the consvuction of [he embankment and the underlying base materials on which the facility will be consvucted. Potential driving forces include gravitational forces on the embankment and (oundation materials and the gravitational and lateral forces associated with the water volume that could be impounded behind the embankment. For this analysis, a circular failure mode was assumed, and the FOS was calculated using the Bishop method. 1.3 PROCEDURE The embankment cross-section shown on Exhibit 13-SA of the Seneca II W Petmit (Leidich, 1999) was used to evaluate embankment stability. A water surface elevation behind the embankment of 7,463 fee[ above mean sea level (amsl) was used (or the analysis. This water surface elevation is equivalent to the elevation of the invert to the principal spillway. The embankment is designed with slopes of 3H:1 V. The design width of the embankment crest is ] 5 feet. • Total height from the bottom of the pond to the top of the embankment is 23 feet. The emergency spillway invert is 3 feel below the embankment crest. As designed, the base of the embankment slopes from the upsveam embankment toe to the downsveam embankment toe at approximately 6'90. The potential phreatic surface for the stability analysis is based on a water surface elevation of 7,463 (t- amsl corresponding to the invert elevation of the principal spillway. The phreatic surface through the embankment was estimated based on Darcy's law and observation of similar homogenous pond embankments at the mine site. At these locations seepage does not occur above the embankment toe. The resulting surface is shown on the SLOPEJW computer printouts contained in Appendix B. An undisturbed sample was collected from the foundation area of the proposed Pond 16. The foundation soil sample was obtained from a Shelby tube sample taken from a test pit at the location of the proposed embankment. Triaxial, (with pour pressure), grain size and Atterberg limits were run on the sample and the results can be found in Appendix A, and are summarized on Table 1. The properties for the embankment fill were obtained from tests on a sample from Pond 010. The Pond 10 embankment svength results were selected to represent the svength properties o(the Pond 16 embankment fill due to the similarity in index properties between the sample from the Pond 16 foundation azea and the Pond 10 embankment. The Pond l0 embankment shear svength test was performed on a remolded sample at 95% o(the maximum dry density from the standard Proctor test (ASTM D698). The results can be found in Appendix A, and are summarized on Table 1. •