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i. ~ • 2. Gradation Characteristics • Several typical spoils lifts were photographed. Enlargements of these photographs were utilized to estimate grain size distributions of the cobble to boulder sized rock present in the lower portion of the lifts. A sample of relatively unsorted, well graded spoil was obtained from the test section. The particles 6 inches and above were hand separated ~ and measured in the field. A laboratory gradation was performed of the remaining fraction. The results of the laboratory and photographic generated grain size distributions are shown on Figure 5. The particle size distribution of the sorted spoil was determined at a height of 8 to 13 feet above the base of a lift and is shown as Curve 2 on Figure 5. This material was very ~ uniform with a median particle diameter (D 50) of approximately 10 inches. The shape of the curve would be expected to remain similar with the median particle size decreasing as you progress up the slope. In effect, the particle size distribution curve shifts to the left and flattens as the less sorted spoil is encountered. ~ A sample of the less sorted spoil was obtained from the test section. The particle size distribution of this material is shown as Curve 1 on Figure 5. The test drain section constructed by Colowyo Coal Company is shown on Photos 5 and 6. The test section included an 8 x 24 foot drain section consisting of light grey sandstone. Spoil was end dumped over the edge with a lift thickness of approximately ~ 30 feet. Placement procedures were consistent with typical spoil placement procedures. The effects of gravity sorting are evident in the photographs. A layer of sorted rock is visible over the drain section and at the base of the lift. After completion of the test section the spoil and drain were cut back to observe a cross-section through the buried drain as shown on Photos 7 and 8. The cuts were ~ performed with a D-9 bulldozer and some disturbance was expected. Fracturing of individual rocks, displacement, and sloughing of fines did occur as a result of dozer disturbance as evident on Photo 7. The fine spoil on the face of the drain sloughed down during excavation but was not spoil which infiltrated during construction. ~ Observation of the interior void spaces of the drain showed no signrficant contamination by spoil. The perimeter of the drain showed good separation of spoil and drain rock even considering the disturbance during excavation. Photo 8 shows a typical interface of the spoil and drain rock (note scale to side of photo). The effects of particle sorting were consistently visible around the drain perimeter. This sorted layer was somewhat disturbed by excavation of the cross section but appeared to be continuous ~ over the drain. The test section confirmed that a layer of gravity sorted material formed at the base of the lift and over the drain section using standard Colowyo spoil placement procedures. This layer was disturbed by excavation but still evident during our observations. As ~ discussed in the previous section a higher lift thickness will produce a thicker sorted layer; we recommend an initial lift thickness of at least 50 feet. 3 •