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Timm Comer Mill Platform Machine Vibration Effects Project 74201125E ame September, 20, 2012 The compatibility of a liner to the material in contact with it is commonly investigated in the laboratory with a puncture resistance test. The puncture resistance test places a 12" diameter sample of the liner between material representative of the overliner and underliner soils used in the field and subjects the system to normal stresses greater than or equal to the maximum normal stress expected from the overburden. A puncture resistance test was conducted on a sample of 80 mil high density polyethylene (HDPE) liner with an overliner material having a similar gradation to the material in contact with the liner under the mill platform foundations. Additionally, 10 to 12 rocks were hand placed directly on the liner to simulate worst -case conditions. A vertical stress of 122,400 psf was applied to the test specimen for 28 hours. Visual inspection and vacuum testing of the liner at the end of the test indicated that the liner did not have any defects (Golder, 2005). The maximum repeated vertical stress on the liner resulting from the model was 3,300 psf, which is about 3% of the load applied during the puncture tests indicating that stress induced puncture will not occur. The liner used for the puncture resistance test was an 80 mil HDPE liner while the liner proposed for the design is an 80 mil linear low density polyethylene ( LLDPE) liner. LLDPE liners have a lower elastic modulus and a larger allowable maximum strain making LLDPE liner more ductile compared to HDPE liners. The higher ductility of the LLDPE liner proposed will further enhance the compatibility with the soil in contact with the liner by deforming around the particles reducing the susceptibility of puncture. The maximum repeated vertical and horizontal strains occurring on the liner was estimated from the model to be approximately 0.033% and - 0.0065 %, respectively. Negative strain values indicate elongation while positive strain values indicate compression. At strains this small, it can be assumed that the material would not be sliding along the liner causing wearing to occur, but rather be straining with the liner. This can be assumed because the stiffness (modulus) of the soil under the confining pressure associated with 15 feet of overburden combined with the additional vertical stress from the foundation is much greater than the stiffness (modulus) of the LLDPE geomembrane liner. The softer geomembrane liner would deform with the straining soil and the movement of soil particles relative to the liner would be zero. Slope Stability Response to Machine Vibration Slope stability in regards to the machine vibrations from the dynamic loads was evaluated qualitatively. The machine vibrations, while large, are typically smaller than the design earthquake of 0.14 times the force of gravity (g). Pseudostatic slope stability analyses were conducted as part of the design of the mill platform and resulted in acceptable factors of safety of 1.0 or greater. The acceleration imparted on the foundation soil from the machine vibrations was evaluated from the vertical displacements beneath the foundation estimated from the model (Figure 5). The vertical acceleration of the soil directly beneath the machine foundations was calculated as 0.003g. The pseudostatic evaluation subjects the slopes to a horizontal acceleration of 0.14g, several orders of magnitude greater than the ground acceleration produced from the mill vibrations, indicating that the machine vibrations will not affect slope stability. The propagation of surface waves along the mill platform could cause shallow surface failures, or sloughing, to occur in the top 2 feet on the slopes surround the mill platform. Sloughing occurs because the dynamic forces from the machine vibration could be larger than the low confining stresses at shallow depths. Slope maintenance of the cosmetic sloughing failures may be required from time to time during SAprojects \1125g squaw gulch valley leach facililty design \h2 - design \mill platform machine vibration letters sept 2012 \mill platform machine vibrations (3).doc 7