1991-01-22_REVISION - C1981035 - Laserfiche WebLink

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M r Memo to Harry Ranney Nat King Coal PR-02 page 2 Further, the Terzaghi and Rankine methods analyze the bulk stability of the refuse structure. They were intended to determine whether the overall mass would remain in a selected location. They do not address the important consideration of the facial slope stability of the structure. The more sophisticated and contemporaneous techniques do accommodate analysis of the surficial stability of the structure. An analysis will have to be completed using one of the more comprehensive methods capable of evaluating the surficial zone stability of the proposed refuse structure. In order to complete such an analysis it will be necessary for Mr. Johnson to determine appropriate values for the angle of internal friction and cohesion of the refuse material . This will entail the collection of appropriate samples and the completion of laboratory mechanical tests of the refuse shear strength. Rule 4.10.4(4) limits the facial gradient of a coal refuse structure to no steeper than 2 (horizontal ) : 1 (vertical ). The cross sections contained within Mr. Johnson 's analysis indicate the following proposed slope gradients for the proposed structure: Station Cross-Section Slope Gradient 0 + 27 ' 1 .53 (h) : 1 (v) 0 + 40' 1 .39 (h) : 1 (v) 0 + 60' 1 .57 (h) : 1 (v) 0 + 80 ' 1 .76 (h) : 1 (v ) 1 + 00' 1 .81 (h) : 1 (v) 1 + 40' 1 .85 (h) : 1 (v) Rule 4.10.4(4) allows no variance from this facial gradient limitation. The design will have to be amended to conform with the regulatory limitation. In summary, I recommend the permit revision application PR-02 be denied until the applicant has completed a more comprehensive stability analysis of the proposed refuse structure, including determinations of surficial stability and appropriate material properties for the refuse material . cc: Jim Stevens JP/JP