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Title: Investigation of construction techniques for tactical bridge approach roads across soft ground
Authors: Webster, Steve L.
Watkins, James E.
Keywords: Accelerated traffic tests
Base courses
Bridge approaches
Soft soils
Military bridges
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The objective of this study was to investigate and test the feasibility of various new techniques for constructing bridge approach roads across soft ground. A test section containing seven test items was constructed on a soft clay subgrade which had an average strength of 0.9 CBR. Accelerated traffic tests were conducted using various loads on a 5-ton military dump truck. Traffic was recorded in terms of coverages of equivalent 18-kip single-axle, dual-wheel load operations. Item 5 was a control item consisting of 14 in. of crushed stone placed directly on the soil subgrade. It had developed an 11-in. rut after 200 coverages of traffic. ltem 1 consisted of an M8A1 mat road that was placed on and tack welded to parallel mat runners placed along the truck wheel paths. The runners were very effective in strengthening and anchoring the mat road over the soft subgrade. This item withstood 54,000 coverages with no damage. Item 2 contained standard 1-ft-thick commercial wire gabions, filled with 3- to 7-in. rock, and surfaced with 2 in. of crushed stone. The performance of this item was extremely good. After 54,000 coverages, the average rut depth was only 7 in. A major finding of this investigation was the potential use of sand-confinement systems for base courses over soft subgrades. Both a large-volume confinement system (item 3) and a small-volume system (item 4) outperformed the crushed stone control item by a substantial margin. This investigation also showed that the placement of a fabric or membrane between a soft clay subgrade and crushed stone base can offer substantial savings in the design thickness of a road. Item 6 was identical with the control item except that a pervious polyester fabric was placed between the base and subgrade. This item withstood 2500 coverages before developing ah 11-in. rut. This represented a savings in design thickness of approximately 27 percent. Item 7 was also identical with the control item except that an impervious coated nylon membrane (T-16) was placed between the base and subgrade. This item sustained 37,000 coverages before developing an 11-in. rut. This represented a design thickness savings of 48 percent. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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