Railway Track & Structures - August 2008 - (Page 32)

Technical report needed and then what the rate of change degradation was from the stoneblower,” said Zarembski. In general terms, the data showed that under the lighter-axle-load British system, the stoneblowing cycle was two to three (plus) times as long as a tamping cycle on the same track. On Queensland Rail, because the network carries heavier axle loads, the stoneblowing cycle was of the order of two times as long as the tamping cycle. “The beneﬁt wasn’t quite as great as Network Rail, because of the axle loads, but it was still signiﬁcant,” said Zarembski. Zarembski explains his results: “With tamping, you come along, add some stone and squeeze the stone under the ties; there is ballast memory and there is degradation associated with trafﬁc. In addition, the act of tamping disturbs the compacted ballast beneath the tie which tends to settle under trafﬁc. With stoneblowing, you’re placing stone accurately and securely on top of the undisturbed ballast which reduces settlement due to compaction. In addition, you’re also using a more homogeneous stone. With tamping, you’re using regular ballast with closed gradation, which means there are particles of various sizes. In stoneblowing, there is more uniform support in terms of the placement of the ballast and quality of ballast under each tie and, since this is an ‘open gradation’, it allows good drainage.” Zarembski notes that stoneblowing is a more-expensive approach because a stoneblower is more expensive than a tamper. However, he also notes, stoneblowing has several classes of beneﬁts. “The ﬁrst beneﬁt is the increased cycle, you don’t have to come back and tamp as often, you’re coming back half as often, so there’s clearly a cost savings. Secondly, tamping squeezes the ballast and, if you squeeze the ballast often enough, you’re going to crush it and you are going to get ﬁnes. Eventually the ballast will need to be cleaned because it becomes fouled. Stoneblowing doesn’t squeeze the ballast. As a result, there isn’t the degradation of ballast that contributes to fouling and the rate of fouling is much slower, which means deferred ballast cleaning. The British Rail approach is to defer up to double the ballast-cleaning cycle,” said Zarembski. Economics over cost For your consideration Dr. Allan Zarembski suggests the following list of factors to consider when weighing the merits of tamping and stoneblowing: • Density of track • Relative cost of maintenance activities • Operational cost (such as train delay, work window, fuel, modest derailment savings) • Extension of tamping cycle 32 Railway Track & Structures August 2008 www.rtands.com http://www.rtands.com

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Railway Track & Structures - August 2008 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Wish List: What Chief Engineers Really Want in M/W Machinery Keeping Ballast in Shape Amtrak Turns to Sophisticated System to Manage NEC Assets Supplier Profiles Products and Literature People Calendar Sales Representatives Website Directory Advertisers Index Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - August 2008

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