Over the past few decades, there have been significant changes in both farm size and farm equipment. Combined with a regulatory emphasis that has encouraged farmers to store manure as a liquid and apply it in a short time frame, the farm equipment industry has responded by producing larger and larger manure hauling and application equipment.
The shift to larger and heavier equipment has occurred at a faster rate than both pavement design technology and the state regulatory approach to larger farm equipment. Innovations such as steer able axles, flotation tires, and tire design changes are not reflected in state DOT regulations. In the minds of some manure applicators and farmers, this has forced the adoption of equipment and practices that, while complying with the letter of the law, actually create more pavement damage.
The Iowa Department of Transportation conducted a study in 1999 to address pavement damage caused by heavy farm equipment. Based on the results from this study Iowa passed legislation that was found acceptable to both the DOT and industry. South Dakota also performed a similar study in 2001. In their study field test sections were constructed and instrumented to measure pavement responses such as strain, pressure, and deflection caused by some agricultural equipment. Theoretical modeling was also conducted to investigate pavement damage. The study resulted in recommendations on changing regulations concerning certain types of farm equipment.
In 2001 the Minnesota Department of Transportation conducted a scoping study on the impact of agricultural equipment (animal husbandry vehicles, grain carts, etc.) on Minnesota low volume roads. The main purpose of the study was to determine if agricultural equipment caused excess pavement damage in Minnesota. The study reviewed several county roads that were claimed to have been destroyed by farm equipment. However, the study found that other heavy vehicles, such as trucks hauling gravel or rock from quarries, might also have contributed to the damage on the roads. This study concluded, "it is difficult to link specific pavement damage to agriculture equipment and quantitatively estimate the reduction in pavement life with current available information." One of the recommendations from the study was to conduct a field study at the MnROAD test facility to specifically address pavement damage due to agricultural equipment.
The regional aspect of this project is a major selling point. Many states in the Upper Midwest have the same concerns about heavy farm equipment, and the pooled fund study framework allows for these states to pool their resources and research some common issues. As noted earlier in this proposal, farm equipment is constantly changing weights, configurations, tire pressures, etc. This project would study the current version of a number of vehicles. Finally, it is envisioned that MnROAD could become a national center for testing overweight vehicles from farming and a number of other industries. The proposed new test sections could be used for other types of equipment long after this project is complete. The basic framework for this research might be of interest to other industries such as tire manufacturers, logging trucks, mining vehicles, forage harvesting equipment, and other heavy farm equipment.
The objectives of this study are to determine the pavement response under various types of agricultural equipment (including the impacts of different tires and additional axles) and to compare this response to that under a typical 5-axle semi tractor-trailer. This may be accomplished by constructing new instrumented test sections at MnROAD and/or to retrofit instrumentation into the existing test sections. The final scope and work plan for the study will be developed by the participating agencies.
This pooled fund study, with contributions from Mn/DOT and other participating organizations, will fund both the possible construction of pavement test sections and the research on heavy farm equipment. This research will allow policy and design decisions to be driven by direct experimental results rather than by models that may not have been calibrated for the types of loadings and tire configurations of current and evolving agricultural equipment.
Scope of Work
(Image is available at http://www.pooledfund.org/documents/solicitations/1040/1040.jpg)
Once the pooled fund study is funded, the scope of work will be determined by the participating organizations. In general, the following tasks will be considered:
Task 1: Selection of Typical Pavement Structures
A survey will be distributed to local engineers to collect typical pavement test sections. From the collected information, determine at least two test section structures to be constructed at MnROAD.
Task 2: Instrumentation Design
Meet with participating states and experts to design instrumentation for the test sections. Strain gauges, LVDTs, and thermal couples should be included in the instrumentation.
Task 3: Construction of MnROAD Test Sections
The test sections selected from Task 1 will be constructed and instrumentation will be installed in each section as designed in Task 2. The east loop on the low volume road (see link to the picture below) could be modified to develop multiple accelerated tests to determine if damage is caused by heavy farm equipment. The loop itself is constructed of 12 inches of concrete, so it could withstand the heavy farm loads without being damaged. A bypass would be built across the median so as to leave intact the existing test cells on the tangent sections.
Task 4: Pavement Responses Monitoring
Various types of agricultural equipment will travel over the test sections at different speeds. The pavement responses in terms of strain and deflection will be measured using the MnROAD data acquisition system. Also, the pavement responses under a standard 5-axle truck will be measured to compare with those under the agricultural equipment. Typical field monitoring activities, such as FWD, distress surveys, faulting measurements, and rutting measurements, will be performed in conjunction with the traffic loadings.
Task 5: Computer Modeling
The pavement response under farm vehicles and semi trucks will be modeled to predict the performance under heavy traffic.
Task 6: Pooled Fund Travel
Funds will be available for the participating states to travel and discuss the progress of the study.
Task 7: Final Report
Interim and final reports will document the findings of this study.
Mn/DOT (as the lead state) and other participating organizations are asked to contribute $35,000 per year for 3 years for the construction and research proposed in this pooled fund study.