Welcome to the Unpaved Road Material Design Tool


Ride quality affected by washboarding

There are millions of kilometers of unpaved roads around the world managed by numerous authorities, land owners, and public and private organizations. Common to all of these roads are unacceptable levels of dust, poor riding quality (caused by erosion, washboarding, and/or raveling), and/or impassability in wet weather, and expensive maintenance and gravel replacement activities. Along with good construction practices, these problems can often be mitigated through better gravel selection, or by blending two or more materials to meet a performance-based specification.

With the growing interest in converting severely distressed low-volume paved roads to engineered unpaved roads, understanding expected performance in terms of the material
Distressed Low-volumne Paved Road

Distressed low-volume paved road

properties after the conversion, which typically involves pulverizing the existing surface and blending it with the underlying layers, is increasingly important to ensure that the unpaved road is “better” than the paved road was. Mechanical stabilization of unpaved roads through blending of two materials is not new. However, determining appropriate blending ratios to meet performance-based specifications tends to be done on a trial
Engineered Unpaved Road

Engineered unpaved road

and error basis until a satisfactory blend is achieved. This tool aims to eliminate the trial and error nature of material blending by providing a more accurate starting blend that can then be refined to provide optimal performance for a given application.

An overview of performance-based specifications for unpaved road materials can be downloaded here. Use of this tool is fully described in the UCPRC guidelines entitled Guidance on the Conversion of Severely Distressed Paved Roads to Engineered Unpaved Roads and Guidance on Performance-Based Material Selection and Blending for Unpaved Roads.

This Unpaved Road Material Design Tool has been developed to guide selection and/or blending of materials to meet a performance-based specification. Using the tool requires input of laboratory test results for the actual materials that will be used. Skipping the laboratory testing and guessing input values, or using default values from other projects, will lead to inaccurate output values. Output from the tool provides a starting point for a blend, which will need to be tested to confirm that it meets the required specification. In no event shall the University of California be liable to any party for direct, indirect, special, incidental, or consequential damages, including lost profits, arising out of the use of this system, even if the University of California has been advised of the possibility of such damage. The University of California specifically disclaims any warranties, including, but not limited to, the implied warranties of merchantability, fitness for a particular purpose and noninfringement.