Agenda - Public Works Committee - 05/15/2007

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CASE #2 CONSIDER SHOULDERING MATERIAL TO BE USED IN 2007 STREET MAINTENANCE PROGRAM By: Steven Jankowski, City Engineer Background: As a part of the process of overlaying streets in rural areas (no curb) it becomes necessary to transition the new raised grade ofthe pavement to the adjacent grade. Ideally, this transition would be the one and one half inch height of the overlay tapered over a distance of two feet. In practice the actual width of this shoulder. varies with the slope to the ditch and the actual fall to the grade next to the pavement. At intersections there is often a depression of several inches even before the overlay from traffic cutting short the comer. The material that has been used for shouldering through the 2003 program had been topsoil dressed with seed and mulch. While this eventually would provide an aesthetic appearance of having a maintained lawn ending at the edge of the bituminous, using topsoil for shouldering has a number of shortcomings including: . It is easily washed" away by heavy rain events and would need to be replaced by the Public Works department. . It settles and does not provide the original transition after a period of time. . The material is not very dense and provides little lateral support for the edge of the pavement which is the weakest part of the road. . In 2004 there was only a small portion of overlay that needed to be shouldered in that years program and a Class 2 shouldering material was used as an alternative to topsoil on a short segment of Bowers Drive. Class 2 is a dense well graded mixture of aggregate sizes which is similar to Class 5 except that the largest particle is % inches in diameter versus 1 inch for Class 5. This Class 2 shouldering aggregate eliminates the negatives outlined above with topsoil used as a shoulder material. 'However, Class 2 generates. complaints which include the aesthetic appearance of the aggregate material being less than that oflawn grass, and the presence ofloose rock migrating into the lawn and thus being a mowing hazard. In the subsequent 2005 year program Class 2 shouldering was used on 7 miles of overlaid roadway adjacent to 253 property owners, and in the 2006 program 8.15 miles of street was overlaid adjacent to 274 property owners. In 2005 the City received 5 complaints, and in 2006 received several complaints by residents regarding the use of the Class 2 shouldering material. The City responded to these complaints by picking up excessive rock through raking and other hand work. Staff will have photos of areas illustrating the use of both these shouldering materials within the past several programs. 3