Laserfiche WebLink
11 <br />JOHN F. ABEL, JR. <br />MINING ENBINEEK <br />Mr. George A. Holcomb <br />Dreco Mines <br />1144 Miracle Mile <br />Tucson, Arizona 85705 <br />Dear George: <br />April 18, 1985 <br />TO LOOKOUT VIEW GOUKT <br />OOLDE+'r N" C�— O�EOSOti <br />`�aii reel <br />RECEIVED <br />AUG 16 S5 <br />MINED LAND <br />RECLAMATION DIV#MN <br />I have throe major recommendations for action with respect to ultimate <br />pit slope design at the Crystal Hill Mining Co. pit: <br />(1) Three detail line joint samples consisting of approximately 100 joints <br />each should be taken in the pit. One each in the quartz latite, the <br />sedimentary ash -fall tuff and the agglomerate. This can be accomplished <br />by LaRon Taylor, geologist at the site. <br />(2) Each of the rock units should be physically tested to determine the angles <br />of surface and internal friction and to determine rack -on -sock and intact <br />rock cohesion. 1 rec._ 04 that two uniaxial and six triaxial specimens <br />be tested for each rock unit, and that three sets of specimens be tested <br />in direct shear. A price list is conveniently attached. <br />(3) The existing pit and haul road bench faces should be described by direction, <br />slope angle, hiesht and rock unit involved. These bench faces are in <br />effect test benches, against Which the ultimate pit wall can be compared. <br />Dan King, the mining engineer at the sits, can probably develop this <br />data. This is in effect bectstrapping, we will use the existing stability <br />to demonstrate future stability. <br />I have reached several tentative conclusions as the result of my visit. <br />First, the already existing 60 -ft high bench in the quartz latite indicates <br />considerable stability. The face of this bench is iron stained along the <br />two joints which control the approximately 720 bench face angle. The iron <br />staining should decrease with depth. There is, however, no visual evidence <br />as yet foi such a decrease in weathering with depth, and, thereby, an increase <br />in stability. The planned 10 -fk wide bench vidth/40 -ft bench height should <br />provide.a stable overall pit wall angle of 600 on the northeast side of the <br />pit. There was not sufficient exposure of northwest and southeast pit wall <br />benches to do more than determine that the potentially adverse W480E striking, <br />440 SE dipping joint set detected by R. D. Call is present in the agglomerate. <br />The potentially adverse M48OR striking, 630M dipping joint set was not observed. <br />