Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />within the reservoir area. There appears to be a sufficient quantity of borrow material to construct <br />the dam within the reservoir boundaries. However, the quantity of clay borrow from the reservoir <br />area is not sufficient to construct the whole dam of clay soil. There does appear to be an adequate <br />quantity of sandy clay with a PI of approximately 15 to construct a clay core with the exterior <br />shells constructed of the low to nonplastic materials. <br /> <br />4. Groundwater. Groundwater was not encountered in any of the borings advanced at the <br />site during our investigation. <br /> <br />Seismological Consideration. <br /> <br />1. General. A general review of published literature was conducted to provide a basis for <br />determining the seismicity of the proposed reservoir site. <br /> <br />2. Published Seismic Risk Maps. The seismic risk zones published by the Uniform Building <br />Code indicates Colorado is in the Zone 1 category which indicates minor seismic risk <br />corresponding to Modified Mercalli Intensities V to VI. <br /> <br />3. Ground Motion. Based on the Intensity VI and considering the attenuation to the site, a <br />MM Ihtensity V would be felt at the dam site. <br /> <br />Geotechnical Evaluation <br /> <br />1. Stability, The dam stability was analyzed utilizing the slope stability program Slope- W <br />by the Geoslope Corporation. The Total Stress shear strength parameters used in the analysis are: <br /><I> = 180 c = 350 psf Y = 125 pcf <br /> <br />For the Effective Stress shear strength parameters, the following were used in the analyses: <br /> <br /><I> = 260 <br /> <br />c = 100 psf Y = 125 pcf <br /> <br />Based on the slope stability analyses conducted for End-of-Construction, Steady State Seepage, <br />and Steady State Seepage with earthquake, 3 horizontal to 1 vertical were determined to be <br />adequate for the dam embankment configuration. <br /> <br />2. Seepage. An evaluation of the seepage characteristics of the soil that will be used to <br />constructed the dam, have lead us to propose the following seepage measures be incorporated into <br />the dam. <br />· Cutoff trench - required to be excavated to rock to cut off seepage under the dam. <br />· Drainage Blanket and Chimney Drain - required for internal drainage in the dam <br />to intercept seepage. <br />· Internal Core - the interior of the dam will require a core constructed of material <br />with a Plastic Index of at least 12. <br />· Foundation Grouting - the rock found in the dam foundation is expected to be <br />fractured and susceptible to seepage losses. The foundation is expected to require <br />some grouting to reduce seepage and protect the foundation from piping. Coring <br />and pressure testing the rock prior to design will be required to determine the <br />scope and extent of grouting required. <br />· Reservoir Liner - required to reduce the loss of water from reservoir storage due <br />to seepage. <br /> <br />3. Foundation Conditions. The foundation of the dam, based on our geotechnical <br />investigation, consists of sandy clay, clayey sand, and sandy silt overlying sandstone <br />bedrock. The overburden soils are stable bearing material but are susceptible to piping <br />due to seepage. The sandstone formation has high bearing values but is highly fractured, <br />thinly bedded, and may be susceptible to piping due to solutioning and erosion. Both the <br /> <br />Stone Canyon Dam Feasibility <br /> <br />Page 9 <br />