Gravel Surfacing Guidelines for South Dakota

A high proportion of local roads in South Dakota are gravel surfaced. Maintenance costs on these roads derive predominantly from blade maintenance and resurfacing. Local agencies have historically used a wide variety of aggregates--pit run, screened, and crushed--for surfacing gravel. In some cases, state gravel surfacing specifications were used, but in others base course specifications, local specifications, or no specifications at all were employed. Under light traffic and limited truck traffic, these materials have performed acceptably if not optimally. However, under increasing levels of general, commercial, and agricultural traffic many surfaces fail prematurely at considerable cost, due primarily to gravel loss. Inadequate subgrades likewise contribute to failures as surfacing and subgrade materials intermix and no longer provide adequate support. Safety and environmental impacts are also associated with gravel surfacing performance. Unbound surfacing can create heavy dusting under traffic and replacing short-lived surfacing consumes limited aggregate resources. In extreme cases, thin or loose gravel surfaces can pose safety risks to traffic. Faced with budget shortfalls, transportation agencies struggle to maintain gravel surfaces. Some agencies have attempted to extend life through the use of materials that meet state gravel surfacing specifications addressing aggregate gradation, soundness, fractured faces, and plasticity index. A few have specified materials with higher plasticity index to achieve a more strongly bound surface, and some have used chemical stabilizers for high traffic areas, Other agencies have chosen the opposite approach, using sub-specification materials with low initial cost and forgoing compaction during construction. The relative performance and economy of these approaches are debated among local road managers and elected officials. Although several good gravel surfacing guidance documents exist, many are dated and underemphasize gravel loss as a key performance indicator. Much of the information is generic in content and geared to a highly technical audience. Few documents focus on conditions unique to the semi-arid Upper Great Plains environment--extreme freeze-thaw cycles, radical swings in moisture levels and air temperatures, and highly variable soils, often poorly drained or with significant expansive clay content. Research is needed to develop comprehensive but practical guidance for cost-effective design, construction, and maintenance of gravel surfacing for local roads in South Dakota. The objectives of this research project are to: (1) identify and describe current and best practices for design, construction, maintenance, rehabilitation, and stabilization of gravel surfacing among Upper Great Plains states; (2) assess the performance and costs of new, unstabilized gravel surfacing test sections constructed with: commonly used materials and construction methods that do not meet state specifications; materials and methods that comply with state specifications; and materials and methods that exceed state specifications; (3) develop guidelines for cost-effective design, construction, stabilization, maintenance, and rehabilitation of gravel surfacing for local agencies in South Dakota; and (4) develop training materials to assist local road managers and elected officials with cost-effective gravel surfacing design, construction, maintenance, rehabilitation, and stabilization of gravel-surfaced roads. Research tasks of the project are as follows: (1 )Meet with the project technical panel to review project scope and work plan. (2) Review and summarize existing literature pertaining to prevailing and best practices in gravel surfacing design, construction, rehabilitation, maintenance, and stabilization relevant to conditions encountered in the Upper Great Plains region. (3) Interview at least fifteen South Dakota Department of Transportation (SDDOT), county, town, township and tribal officials to identify prevailing and best practices employed within South Dakota, to identify local concerns related to gravel surfacing, and to solicit information about instructive case studies. (4) Prepare for review and approval of the a project's technical panel a technical memorandum that summarizes the findings of tasks 2 and 3 and defines a comprehensive plan for construction, inspection, testing, and evaluation of unstabilized gravel test sections in three regions of the state employing: commonly used material that does not meet state specifications (with and without compaction); material that meets state specifications (with and without compaction); and materials that exceed state specifications (with compaction only). (5) Meet with the project's technical panel to review the technical memorandum and refine plans for construction and evaluation of the gravel surfacing test sections. (6) At construction and at least three times thereafter (fall of 2010 prior to onset of winter, spring 2011 following winter, and fall of 2011 prior to onset of winter), perform tests and inspections to determine gravel surfacing retention and condition of each gravel surfacing test section. (7) Analyze and compare the construction and maintenances costs and the performance of the gravel surfacing test sections, with emphasis on aggregate retention, projected surfacing life, and estimated life cycle costs of the construction alternatives employed. (8) On the basis of the literature review, interviews of state and local officials, and evaluation of the gravel surfacing test sections, develop concise but comprehensive guidelines for design, construction, rehabilitation, maintenance, and stabilization of gravel surfaces in South Dakota. (9 )Prepare for review and approval of the project's technical panel a technical memorandum summarizing the results of tasks 6-8. (10) Upon approval of the technical panel, develop training materials that are suitable for presentation to local road managers and elected officials by the South Dakota Local Transportation Assistance Program. (11) Prepare a final report and executive summary of the research methodology, findings, conclusions, and recommendations. (12) Make an executive presentation to the SDDOT Research Review Board.