Laserfiche WebLink
DEERE & AU LT <br /> July 13, 2018 <br /> Mr. Joe Lamanna <br /> Boral Aggregates <br /> 11778 Highway 52 <br /> Fort Lupton, Colorado 80621 <br /> Re: Stage 6 Berm Stability Analysis; D&A Job No. CG-0473.006.00 <br /> Dear Mr. Lamanna: <br /> This letter presents Deere & Ault Consultants' (D&A) berm stability analysis at the Fort Lupton <br /> Mine Stage 6 Pit. This analysis addresses the existing berm which was constructed earlier this <br /> year. The berm is located approximately 400 feet south of the north end of the pit. This berm was <br /> constructed to impound groundwater in the northern portion of the mined-out pit. This water <br /> storage is needed to mitigate impacts to the hydrologic balance north of the pit. The berm is <br /> considered to be a temporary structure which is needed until a soil-bentonite slurry wall is <br /> constructed around the Stage 6 cell. Our engineering services included a geotechnical <br /> investigation and slope stability analyses. The goal of the investigation and analysis was <br /> required by State Division of Reclamation and Mine Safety (DBMS). The following report <br /> provides details from the geotechnical drilling that was performed, and the slope stability <br /> analysis. <br /> OVERVIEW <br /> The berm was constructed in March 2018, and extends east-west across the pit. The berm spans <br /> approximately 500 feet, while the width of the berm varies from 80 to 100 feet (Figure 1 and 2). <br /> The northern face of the dam is generally a 2:1 (horizontal to vertical) slope, while the southern <br /> face is around a 1.5:1 slope (Figure 2). The berm consists of a sandy clay with gravel fill. <br /> There are two spillway pipes located on each end of the berm with rip rap placed on the southern <br /> face (Figure 1). These pipes were placed to help regulate the water level in the north end of the <br /> pit. The current water level in the north end is at approximately 4,878 feet. <br /> GEOTECHNICAL DRILLING AND LABORATORY TESTING <br /> Three exploratory borings were drilled across the berm on May 23, 2018 (Figure 1). Summary <br /> logs are provided in Figure 3 including the results of laboratory. Table 1 presents a summary of <br /> the laboratory test results. A standard proctor test was performed on the berm fill by combining <br /> samples from all of the boreholes. Standard proctor testing indicates an optimum moisture <br /> i content of 13.0 percent of dry weight, and a maximum dry density of 114.6 pcf. The laboratory <br /> results for the testing are presented in Appendix A. The dry density varies from 111.9 to 126.6 <br /> pcf with an average of 117.0 pcf. The moisture content varies from 6.3 to 17.2 percent and has an <br /> 600 S.Airport Road,Building A,Suite 205 <br /> Lon-mont,CO 30503 <br /> Phone: 303-651-1463 9 fax: 303-651-1469 <br />