Laserfiche WebLink
A( OM AECOM 303-694 2770 tel <br /> 6200 S Quebec St. 303 694 3946 fax <br /> Greenwood Village,Colorado <br /> 80111 <br /> www.aecom.com <br /> March 23, 2017 <br /> Mr. Dillon Benbow <br /> Climax Molybdenum Company <br /> Henderson Mill <br /> 19302 County Road 3 <br /> Parshall, Colorado 80468 <br /> Subject: Original 3 Dam Regrade Design Information, Henderson Mill Tailings Dam, near Parshall, <br /> Colorado <br /> Dear Dillon, <br /> AECOM Technical Services, Inc. (AECOM) prepared this letter report, which presents the design and <br /> construction drawing for the regrade of the original 3 Dam. Presented below is a brief background, <br /> summary of our design, and construction drawings. <br /> INTRODUCTION <br /> AECOM was contracted by Climax Molybdenum Company (Henderson) to prepare construction <br /> drawings to depict the slope regrade of the original 3 Dam to 4H:1V(Horizontal:Vertical). The <br /> purpose of the slope regrade is to mitigate undrained stability concerns recently identified on the <br /> original 3 Dam slope. <br /> BACKGROUND <br /> In 2016, a field investigation was conducted on 3 Dam, including the original dam and stepback, <br /> which included advancing 4 Cone Penetration Testing (CPTs) and drilling 17 boreholes, as shown on <br /> Figure 1. This field program was to complement previous field work that had been conducted at 3 <br /> Dam. The previous field investigation locations are also noted on Figure 1. <br /> A subsequent laboratory program followed the field program and included a suite of strength and <br /> index tests on disturbed and undisturbed samples to supplement the existing material <br /> characterization understanding. Findings from the 2016 field and laboratory investigations include: <br /> • Updated section geometry including updating the tailings zonation and further classifying the <br /> foundation material into an upper and lower foundation material. <br /> • Tailings are less than 100% hydrostatic in portions of 3 Dam. <br /> • Updated material properties used in slope stability analyses. <br /> Figure 2 reflects the updated internal geometry for Study Section 2 based on CPT and borehole <br /> information included on the figure. The location of Study Section 2 is shown on Figure 1. <br /> Stability Analyses <br /> The limit equilibrium computer program UTEXAS4 (Wright, 1999) and Spencer's method of slices <br /> were used for the stability analyses. Spencer's method satisfies all conditions of static equilibrium, <br /> including horizontal and vertical force imbalance and moment imbalance. Search routines available <br />