Laserfiche WebLink
Timm Comer <br />Mill Platform Machine Vibration Effects <br />Project 74201125G <br />September, 20, 2012 <br />ameO <br />cannot predict permanent plastic deformations (i.e. settlement due to densification). The results are the <br />elastic response due to the dynamic foundation load. Non - linear models capture large strains and <br />permanent displacements, but the parameters that describe such models are not as well established as <br />those of the equivalent - linear elastic model. A substantial field and laboratory testing program to obtain <br />model parameters is required for non - linear models. <br />To simplify the analysis, only structural fill was evaluated for dynamic response. The other materials <br />beneath the mill platform include bedrock, drain cover fill and low volume solution collection fill and are <br />not of concern due to either thickness or density. The structural fill is of concern due to depth of the fill, <br />over 100 feet of fill in some areas, and because it makes up the majority of the foundation soils. The <br />structural fill consisting of minus 24" well graded gravel placed beneath the liner system and the select <br />structural fill consisting of minus 3" well graded gravel placed between the liner system and the low <br />volume solution collection fill were model as homogeneous soil. The dynamic properties were <br />conservatively selected for a sandy gravel with medium density. This is a conservative assumption <br />because the structural fill and select structural fill have larger grain size and higher density compared to <br />the modeled fill. Larger grain size and increased density generally result in higher shear moduli and <br />stiffer dynamic properties in cohesionless fills as indicated by studies conducted by Seed and Idriss <br />(1984). <br />The structural fill is approximately 75 feet thick beneath the center of the mill foundation so a block of <br />material 100 feet thick was conservatively modeled. A thicker layer is considered conservative as there is <br />more compressible material to contribute to the elastic strains. The structural fill was modeled with a unit <br />weight of 130 pounds per cubic foot (pcf), and a Possion's Ratio of 0.35. The shear modulus was defined <br />as a function of vertical effective stress based on correlations by Seed and Idris (1970). The shear <br />modulus is shown graphically in Figure 1. Equivalent - linear elastic modeling estimates strain softening by <br />a shear modulus reduction function which relates shear modulus to cyclic shear strain. For this analysis <br />the shear modulus reduction function was estimated from the confining stress and plastic limit of the soil <br />based on methods developed by Ishibashi and Zhang (1993) and is shown graphically in Figure 2. The <br />damping ratio is also described as a function of cyclic shear strain and can be estimated similarly to the <br />shear modulus reduction function using the confining stress and plastic limit of the soil by the methods <br />developed by Ishibashi and Zhang (1993). These functions compare well with the dynamic functions <br />suggested by the research of Seed et. al. (1984) for rock fill material. The damping ratio function is <br />shown graphically in Figure 3. <br />S:\projects\1125g squaw gulch valley leach facililty design\h2 - design \mill platform machine vibration letters sept 2012 \mill platform machine vibrations (3).doc 2 <br />