15 Dec, 2013
The gravel road design & maintenance data, as well as the technical data contained in this document are based on studies/information provided by the Minnesota Department of Transportation, The Federal Highway Administration, and the Center for Transportation Studies at the University of Minnesota.
Specific road conditions described within Star Lake Township are based on observations from the Town Supervisors, Town Employees, local contractors, and Otter Tail County employees.
BACKGROUND: Star Lake Township currently maintains approximately 32 miles of township roads. All township roads are gravel surfaced, and all Otter Tail County roads are hard surfaced. Approximately 53% of all roads in the U.S. are gravel. The number of gravel roads and the need for continued upkeep mean that designing and maintaining gravel roads is critical to our transportation system, and to the public’s safety, comfort, and convenience. The good news is that we have a lot knowledge and resources available to help us develop and maintain GOOD gravel roads.
It’s important to understand that most gravel roads today were built in a different era, e.g. the agrarian period of the late 1800’s and early 1900’s. This is certainly true of the roads in Star Lake Township. In essence these roads were built for horse drawn wagons, and were constructed with whatever materials were available locally, and at the lowest cost. A common technique for building a roadbed in the soft sand or often swampy portions in this area was to use timber laid out in a crisscrossing fashion. This technique is referred to as “corduroy”, and for the most part has served us well. It is still in place in many portions of our township roads today. Unfortunately, it often shows itself in the spring, and becomes quite problematic for our motor grader operator.
The point to the short history lesson above is that our township roads were not designed to support the volume of traffic, or the weight/size of the vehicles and equipment that are using them today. The 18 wheeled milk tankers of today could likely not be imagined by the dairy farmer of 1903. The same said for the 56 passenger school buses, or the Case IH Quad-Track and its assorted loads. A lot has changed in the past 125 years or so, but for the most part our roads have not.
Many of the century old timbers in the “corduroy” have rotted or moved leaving soft spots, or a generally unstable roadbed. It is a road problem that we deal with in a remedial fashion, i.e. we fix it as we need to, and to the degree that our budget, equipment, and available technology will permit. Unfortunately, this often equates to throwing money in a hole!
A proper repair of these failing roadbeds would require excavation of the existing roadbed, and replacing it with new substrate and a new road surface. To do this broadly would be beyond the financial means of Star Lake Township, and to propose such would be irresponsible.
However, where we have clearly identified these reoccurring problem areas, it would seem to be financially prudent to develop a plan to repair them properly. Fix it right and fix it once! These projects will need to be evaluated, costed, prioritized, and incorporated into our larger road maintenance plan.
A common theme in the research studied for this analysis is that a gravel road doesn’t have to equate to a bad road. The rest of this document is going to discuss how we can have Good Gravel Roads, or at least the BEST gravels roads we can afford.
MAINTENANCE: Generally, gravel roads are maintained by performing routine blading to maintain a four degree positive crown, with a smooth driving surface, and a well sloped shoulder. Surface gravel is added as needed either by “spot graveling”, or by applying new gravel to entire sections of roadway. Weather and traffic volume has a huge effect on gravel road conditions, and consequently on frequency of maintenance.
There are two basic principles of good gravel maintenance.
1. Proper Use of the Motor Grader,
a. To properly shape the roadway & maintain that shape,
b. Achieve & maintain a four degree crown,
c. Well sloped shoulders,
i. Reducing the development of secondary shoulders,
ii. Utilization of “shouldering disk” (reclaimer) also an important factor,
d. Maintain positive drainage of roadway,
e. Repair of potholes, ruts, corrugation, etc.,
f. Prevent incursion of vegetation on roadway,
i. Utilization of “shouldering disk” also an important factor,
g. Having a cost efficient and reliable motor grader to accomplish all of the above,
i. Star Lake Twp’s. current motor grader is rapidly becoming obsolete, and increasingly expensive to operate,
ii. To own, to rent/lease, or to contract may be a conversation forced upon us sooner than we would like,
2. Use of good gravel; in our case, Class I Gravel or at a minimum Class IV Modified,
a. Common misunderstanding – washboarding (i.e. Corrugation) is caused by grader operator or traffic speed, when the problem is most often caused by poor gravel (i.e. low binder content),
b. Long-term, quality gravel reduces gravel costs and maintenance costs,
c. Best to choose highest quality gravel that budget can afford,
d. A higher binder (clay) content will:
i. Permit water to drain off the roadway vs. soaking in,
ii. Will have greater compaction thereby minimizing shoulder collapse due to heavy loads/high volume of traffic,
iii. Will hold the aggregate together longer vs. losing it to the ditches,
e. Dust Control. In addition to being a mess and an inconvenience – dust is the binder content in the gravel blowing away. The binder holds the gravel together; decreasing binder content = loose, disappearing aggregate. Road stabilization agents (magnesium/calcium chloride) enhance the compaction of the binder material, as well providing a secondary benefit of greatly reducing road dust.
f. NOTE: According to the Environmental Protection Agency – a single vehicle traveling on a gravel road once a day for a year can produce one ton of dust per mile. Ten vehicles a day = 10 tons of dust/year; that’s a lot of gravel disappearing.
g. Ideally, all new gravel in Star Lake Township should be Class I, or Class IV Modified; with Magnesium Chloride applied.
DESIGN/SHAPE: The three most important things regarding gravel road design, shape, and long-term serviceability are:
a. get the water OFF the roadway – proper slope=positive drainage,
a. keep water OUT of the roadbed soils – good quality gravel, ditch depth, smooth/clean bottom,
a. keep the water AWAY from the road – working culverts/clean ditches,
Water is not only a problem on top of the roadway – subsurface moisture kills gravel roads by causing frost heaves/boils, and soft spots. Consider standing water on roadway or ditch as a “red flag” for a needed road fix.
1. Complete road audit to identify:
a. High volume roads,
b. Location of standing water on roadway locations,
c. Locate & mark all culvert locations,
d. Needed tree trimming locations,
e. Signage needs,
2. Develop Dust Control Suggestions,
3. Review gravel specs with Egge (15-18% binder), pit run vs. crushed??
4. Locate soft spots & frost heave locations & develop repair plan,
5. Develop culvert maintenance plan,
6. Develop list of road repair projects to include projected cost & priority,