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<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 />project site and the low average temperature. The mean yearly temperature Is <br />43. and the highest average monthly temperate for Is 67., The aggregate may be <br />produced at cooler temperatures than used In the analysis as the contract may <br />require It be produced In the fall prior to the year the RCC Is placed. This <br />would reduce the crack potential slgnlrtcantly from that In the analysle. <br /> <br />Uelng the elte temperatures as Indicated above and assuming an adiabatic <br />temperature rise for the RCC of 26. to 36., the potential for cracking was <br />analyzed. For an adiabatic rise of 25. the maximum crack width potential was <br />determined to be 0.10 Inches with no cracking about 28 feet above the dam base. <br />For an adiabatic rise of 35. the maximum crack potential was determined to be <br />0.26 Inches with no cracking 34 to 42 feet above the base. Theee analysis are <br />summarized In the appendix and FIgures I and 2 Included herein are graphs of <br />the crack potential at different heights and locations In the dam. <br /> <br />The 0.26 Inch crack Is not expected for a dam of this length with only 200 <br />pounds of cement per cubic yard of concrete. The publiShed data on RCC mixes <br />would Indicate an adiabatic rise of 26. would be expected but may be as high as <br />36.. We do not believe crack control measures are required In this dam. Dams <br />much larger than this dam and much longer have been built without slgnlrtcant <br />cracking. Also the loss of water through any crack that may form Is aesthetic In <br />nature more than a structural problem. <br /> <br />In the final design of the dam we have Included two expansion Joints with <br />waterstops. These were not Included due to the expected crack potential but <br />were Included due to the sharp break In the rock elevation which may create a <br />stress crack In the dam at these two locations. The two JoInts were Included at <br />this time but may be eliminated If the change In rock elevations proves to be <br />more gradual than Indicated by the seismic survey. The construction contracts <br />will be bid such that the control Joints are a separate bid Item and can be <br />eliminated from the contract easily. The City of Greeley may opt to grout the <br />cracks later If they do form, especially If the cost to Install the joints Is <br />excessive. <br /> <br />e, Seismic Considerations. The Peterson Lake Dam site Is In an area that <br />has a low seismic potential. Bulletin 46 by the Colorado Geologic Survey, <br />COLORADO EARTHQUAKE DATA AND INTERPRETATIONS 1867 TO 1984, Indicates <br />potentially active faults 16 miles and 18 miles fram the site. Bulletin 46 and <br />Bulletin 43, EARTHQUAKE POTENTIAL In COLORADO, by Kirkham and Rogers <br />Indicates one Intensity VII and one Magnitude 2.6 earthquake within 20 miles <br />from the site. At a distance of 50 miles from the site the large number of <br />earthquakes In the Denver area come Into play with several hundred being <br />recorded up to a magnitude 5.3. The bulk of these are thought to be Induced by <br />Injection at the Rocky Mountain Arsenal and are not truly representative of the <br />area, <br /> <br />Kirkham and Rogers recommend all of Colorado be designed for a minimum as a <br />Zone 2 region and that the Eastern Mountain Province be designed for a <br />magnitude 6 to 6,75 earthquake. Based on work by Seed and Idrlss, "Character- <br />Istics of Rock Motions During Earthquakes", ASCE SM 5, September 11169, this <br />would produce a maximum rock acceleration level of 0.08g to 0.125g. Algermls- <br /> <br />PAGE 6 <br />Peterson Lake Dam Design Report <br />