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1.Introduction
This test procedure covers the determination of the rebound deflection of a pavement under a standard wheel load and tire pressure. The Benkelman (portable) Beam apparatus is a convenient, cost effective and accurate device used for measuring the deflection of flexible pavements under moving wheel loads. The beam is commonly used as a tool for evaluating compaction and moisture content in new construction projects.
The Benkelman Beam measuring process commences between the wheels of a stationary truck and records the latter half of the deflection bowl as the truck moves away. The full rebound of the pavement can be assessed from continuously reading the dial gauge after the truck has moved.
2.Field Review
Evertek Engineering Ltd. (Evertek) has prepared this road assessment report of the Dormick Avenue East Bound Lane (EBL) & Meadows Street South Bound Lanes (SBL) the roadways immediately to the north and east, respectively of the residential development located at 32166 Dormick Avenue in Abbotsford, BC. Based on the project information, it is our understanding that half road rehabilitation of the existing roadways is required as part of the residential development project on the property. The purposes of Evertek’s field review were to observe the current surface conditions of the roadways and to provide geotechnical recommendations for re-paving. The combined subject section of the roads is approximately 70 metres (30 metres along Dormick Avenue and 40 metres along Meadows Street). It is understood that Dormick Avenue and Meadows Street are classified as “Urban Local”.
Our observations are summarized below:
To evaluate roadway subgrade conditions, a total of 7 individual rebound readings were obtained on Dormick Avenue. The corrected individual readings (with seasonal and temperature correction factors applied) ranged between 0.31 mm to 0.61 mm. The Maximum Probable Spring Rebound (MPSR) calculated by statistical analysis of the individual readings is 0.79 mm. According to the City of Abbotsford Bylaws, the maximum design deflection for an Urban Local Road is 1.50 mm.
3.Results
A total of 9 individual rebound readings were obtained on the Meadows Street SBL alignment. The corrected individual readings (with seasonal and temperature correction factors on applied) ranged between 0.35 mm to 1.03 mm.
The Maximum Probable Spring Rebound (MPSR) calculated by statistical analysis of the individual readings is 1.16 mm. According to the City of Abbotsford Bylaws, the maximum design deflection for an Urban Local Road is 1.50 mm.
Based on the results of Benkelman beam testing and our site observations, the MPSR at both road sections is considered adequate with respect to deflection. Thus, in our opinion both road segments would need minor rehabilitation. With regards to the rehabilitation works, Evertek recommends the following:
1.Given the current asphalt surface conditions, milling of the existing asphalt upper course and re-paving may be considered to be a suitable rehabilitation. The base and subbase materials may remain.
2.The asphalt should be laid in two separate lifts (76 mm thickness total). The asphalt should be compacted to at least 97 percent of the Marshall mix design bulk density.
Refs:
[1]https://roads-waterways.transport.nsw.gov.au/business-industry/partners-suppliers/documents/test-methods/deflection-testing-of-earthworks-and-pavement-layers.pdf