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- 7- <br />n <br />U <br />Based on the results of this test as well as our previous experience, <br />we believe that the modified procedure should be used in control of <br />compaction to achieve high structural strength fills for the haul roads. <br />The tests were conducted using samples with 100 percent passing a 3/4- <br />inch sieve. The field conditions indicate a high percentage of plus <br />3-inch rock which should increase the performance characteristics of the <br />fill. <br />In our report of investigation of proposed spoil disposal areas, we <br />presented results of tests to evaluate the physical properties of the <br />spoil material. We anticipate spoil will be used to construct most of <br />the fills for the haul roads. The spoil will function as a granular ma- <br />terial with a clay binder while being compacted. The spoil grades gen- <br />• erally from 12 inches down to the No. 200 sieve size and it is very likely <br />that the material will break down significantly when subject to handling <br />and compaction. We estimate the compacted dry density will range from <br />110 to 120 pcf, depending on the source of the spoil. Optimum moisture <br />content should range from about 10 percent to 15 percent of the dry <br />weight. The actual density and optimum moisture content can only be <br />determined in the field as the construction progresses and must be based <br />on samples of the material being placed in the fill. It is likely that <br />the compaction process will break down the clay materials sufficiently <br />and there will be bonding to develop cohesive strength in the fill. How- <br />ever, for purposes of stability analysis, we recommend designing the fill <br />for an angle of internal frction ¢ of 37 degrees and neglecting any co- <br />• hesive strength. The 37 degree friction angle is based on observation <br />