Laserfiche WebLink
April 1, 2003 <br />To: Erica Crosby <br />From: James Dillie <br />Re: Geotechnical Stability Exhibit, Fetcher/Vale Pit, M-2002-119 <br />Per Mr. Posey's request, I reviewed the geotechnical stability exhibit that Greg Lewicki, <br />consultant for Elam Construction, submitted to the DMG regarding the applicant's response to a <br />recent adequacy letter. <br />I understand that the permit applicant wishes to mine the pit highwalls at a O.SH:1V gradient. <br />The pit depth is estimated at 50 feet. In addition, the applicant proposes to stockpile the salvaged <br />topsoil around the edges of the pit and proposes to situate the toe of the topsoil stockpile <br />approximately 20 feet back from the top of the highwall cut. <br />Normally, unless a structure is neazby, highwall slopes are not a problem during mining <br />operations and would not need to be engineered, but they are supposed to remain stable after <br />mining ceases. In this instance, since topsoil stockpiles are proposed to be located within 200 <br />feet of the cut slope, the applicant needs to demonstrate that the slopes aze stable. The applicant <br />should be reminded of Rule 3.1.9(3) which states that the topsoil shall be stored in places and <br />configurations to minimize erosion and located in azeas where disturbances by ongoing mining <br />operations will be minimized. Irr addition, pursuant Rule 3.1.9(4), relocation of topsoil stockpiles <br />on the affected land require Boazd or Office approval..A major failure of the highwall would not <br />only relocate the topsoil stockpile (without $oazd or Office approval) but could cause the topsoil <br />to mix with other materials reducing its effectiveness as a growth medium. Either or both events <br />could result in the issuance of a possible notice of violation. <br />In order to demonstrate to the DMG that the slopes should remain stable during mining <br />operations azound the edges of the affected land azea, the applicant is required to provide a <br />geotechnical evaluation of all geologic hazazds that have the potential to affect any proposed <br />slope or highwall within the affected area (see Rule 6.5(1)}. Or, the applicant may also be <br />required to provide engineering stability analyses for certain slope configurations as they will <br />occur during operations (Rule 6.5(2)). <br />Instead of submitting an engineering stability analysis, the applicant's consultant provided a brief <br />geologic overview of the proposed mined deposits. During Mr. Lewicki's onsite inspection <br />(2002) he found that the deposit is well cemented and stated that the material " cannot be <br />sampled and sent to a laboratory for triaxial testing since the action of breaking the material out <br />will destroy the chemical and physical bonds..." If the deposit is well cemented and competent <br />its stability may depend solely on the existence of natural fractures and their orientations rather <br />than slope gradient. ff the rock is classified at R2 or higher it probably will not fail through the <br />intact rock. It would appeaz then that the major concern for this type of deposit would be the <br />natural fractures and their orientations. Rock that is classified at Rl or SS or below, most <br />definitely would need further testing to determine sheaz strength, cohesion, etc. because this type <br />of deposit has a high probability that a failure will occur through the soil slope instead of a <br />fracture. <br />