WorldWide Drilling Resource

30 MARCH 2015 WorldWide Drilling Resource ® values, even with proper maintenance and circuit power. Almost always what happens is, you will write a “1” to the bit and read back a “0” because of current leakage within the cell. The bit voltage “leaks down” from a 1 to a 0 due to a defect within the cell. Recently, we had a customer call with a problem. He set his water pump control unit to turn off at 27 psi, but he would come back a little later and find the setting was 24 psi. This was caus- ing his water pump control unit to turn off prematurely because he needed to have it turn off at 27 psi, not 24 psi. Checking the binary values used here, we noted that 27 decimal is 0001 1011b and decimal 24 is 0001 1000b. Do you notice something about the two right-most digits (LSBs)? They were writ- ten as a “logic 1”, but didn’t stay that way. The two right-most digits changed to 0s, representing the wrong value. This is very unusual, but it happens. If this was the only problem found, we could still use the unit and repro- gram it to do something else as long as it did not access the defective bits of memory. However, it required consid- erable time to make the changes and do the testing, so the easiest solution was to send the customer another water pump control unit. Digital technology is incredible tech- nology and is not going away anytime soon. Even though it is quite reliable, it can be defective in rare cases. While the problem may be “worked around”, often the most practical solution is to replace the unit and use the defective one somewhere else where the “prob- lem memory” will not be a problem. Britt Britt Storkson may be contacted via e-mail at michele@ worldwidedrillingresource.com Storkson cont’d from page 29. Open-Cut Project at Pinkerton Tunnel Part 1 Adapted from an Article by Dale L. Ramsey which Appeared in The Journal of Explosive Engineers The Pinkerton Tunnel open-cut proj- ect in Somerset County, Pennsylvania, was par t of the Nat ional Gateway Clearance Initiative designed to achieve a minimum of 21 feet of vertical clearance along CSX transportation rail corridors, enabling double-stacked intermodal railcars to be transported between Mid- Atlantic states and their ports to Midwest markets in the U.S. The project involved drilling and blasting 1 million bank cubic yards of rock in two years, and involved many challenges. Maintaining active rail traf- fic throughout the project was impera- tive. Two passenger, and 38 freight trains ran under the project daily. The original tunnel was placed into service in 1877, so tunnel integrity and construction standards also posed a challenge for the new project. Planners explored a var iety of methods to achieve their clearance goals. Due to geologic conditions, the tunnel was not a candidate for channel relining, and the open-cut method was chosen. During the planning phase, huge voids were found between the tunnel liner and rock strata. This created con- cerns of potential rock falling into the voids, hitting and damaging the tunnel liner during blasting operations. After initial clearing and grubbing of the proj- ect, top soils and subsoils were removed, and a series of 6.75-inch holes were drilled up to 150 feet in the void spaces, and 150 psi flowable fill was gravity fed into the voids to provide a cushion for the liner to prevent damage from falling debris. The project was in close proximity to the Great Allegheny Passage Trail and the Casselman River, making recre- ational bicycle and foot traffic a primary concern during blasting operations. Stringent vibration standards were placed on the project, along with drilling and blasting restrictions. Personnel were placed on the trail to secure the blast area perimeter and to observe boat traffic on the Casselman River. Since trains were also running during the project, blasting window curfews were coordinated with the CSX Employee- in-Charge and two flaggers communi- cated with rail traffic. Cut depths were limited to 20 feet, and hole diameters were limited to a 3- inch maximum diameter. Drilling pat- terns were l imited to a 5- by 6-foot ratio, and a maximum 8-foot dimension. Due to the rugged terrain and rock type, top hammer track-style drills were chosen to drill 3-inch-diameter holes on a burden of 7 feet, and a spacing of 8 feet, to a maximum depth of 20 feet. A self-imposed limit of 200 holes per blast was permitted based on daily production requirements and vibration concerns. Don’t miss Part 2 next month! Aerial photo of construction on the Pinkerton Tunnel open-cut project. Train exiting the Pinkerton Tunnel before the open-cut project began. Groundwater Awareness Week March 8-14, 2015 Don’t Forget...