2014-08-20_REPORT - C1996083 (2)

Home Browse Search

Bowie No. 2 #01349 -0001 HUddlcsflon - ➢cm 08/15/14 r s.r:,.,:I uI We can run dozens of Proctors and simply match compaction tests to the Proctor which `tits'. However, more important than any individual Proctor value, our responsibility is to ensure that the gob is being placed in a well compacted manner. As a result, the testing is completed by highly experienced personnel. Darren Phipps and Miriam Sanchez both have over 25 years of construction materials testing experience. As a result, they have the skill to select an appropriate Proctor value. However, they also have the skills, knowledge, and expertise to identity that proper compaction has been achieved, even without a Proctor value. While HBET has absolute confidence in our technicians, we understand the desire of DRrb1S to have numbers. As a result, going forward, at a minimum, HBET will conduct one -point Proctor tests on a sample collected each day of on -site compaction testing to ensure that the value falls on or very close to one of the existing curves. Where there is a significant material change, a full Proctor test will be run. Comment: Depending upon the rational provided for using an extremely loti , jVIDD (79.5 pefi as a reference, it may be appropriate to utilize a different Proctor- Curve for those four test locutions. Response: The four tests in question were completed on Gob Pile 4, in an area being prepared to receive additional new gob. Based upon information provided to HBET, this area had been exposed for approximately two years during which time the coal had weathered significantly. This is the reason for the extremely low Proctor value on a sample collected from that area. With regard to compactions in excess of 1OO %, Mr. Phipps indicated that he observed compaction effort in this area far in excess of what is typically done in other areas of the site. It is possible that the additional compactive effort broke down the material and may have slightly changed the Proctor value. However, as stated above, our responsibility is to ensure that the gob is placed in a well compacted manner and Mr. Phipps is confident that this is the case. As a result, another Proctor was not run on this material. Instrumentation Monitoring Comment: The pore pressure at VTVP -06 has began to rise shadily (cis shou,n on Buekhorn's July 1, 2014 Figure 2) since the previous reading in 11ay 2014. What pressure fir this installation tii,oidd be a cause for concern fir the stability of CPVDA #2?. Response: Based upon our analyses of the firll buildout of Gob Pile #2, a pore pressure of 36 psi at VWP -06 would reduce the faetor -of- safety to below 1.5. This is still well in excess of the most recent (July 2014) value of 16.8 psi. ;{:\2003 ALL PROJECTS'.00-439 -JE Stover Associates Ine1004394003 Bowie Mine\200- Ged,Gob 2'.00439 -0003 L0S1-414.doc 2