RD18 - Use of Soil Stabilizers on Highway Shoulders: Installation Report


Executive Summary:
Introduction

An amendment to House Bill HB5001, Item 487B, calls for the Virginia Transportation Research Council (VTRC) to “study the use of soil stabilizers in highway shoulders with the objective of finding a method of substantially reducing the occurrence of pavement/shoulder drop-off at a reasonable cost.” The complete amendment is provided in the Appendix.

Current research involving soil stabilizers on unpaved roads suggests that these products may be used to stabilize unpaved shoulders and reduce the incidence of low shoulders along the pavement edge. To facilitate an objective performance evaluation, a trial installation was constructed in which representative stabilizer additives were thoroughly mixed into the shoulders of a primary road in Powhatan County, Virginia.

Objective

The purpose of this project is to evaluate the use of soil additives as stabilizers for aggregate and topsoil shoulders. The objectives of the study are to determine (1) the effect soil stabilizers have on the incidence of pavement-shoulder drop-off, and (2) the costs and benefits of using stabilizers versus paving the shoulder or maintaining the shoulder as originally composed.

Methodology

VTRC has an ongoing study of the use of stabilization techniques on unpaved roads. The study is evaluating a number of soil stabilization additives along a single secondary system gravel road using a test and control process. The installation report for the project indicates to be most effective, all the additives tested should be deeply mixed with the aggregate and compacted. This process is known as full-depth reclamation (FDR). Details of the installation may be found in VTRC Report No. 04-R18 entitled "Stabilization Techniques for Unpaved Roads."

The unpaved road study tested a number of acrylic, soybean/soy lecithin, and chloride salt products. The experimental plan for the current study called for testing one of each type of product based upon preliminary performance data from the unpaved road study. The additives commercially known as Centrophase AD, Soiltac, and magnesium chloride were to be tested.

FDR was to be used in the current study as the basis for the initial testing of the performance of soil additives when used on shoulders. A 0.3-mile-long segment of Route 522 in Powhatan County was chosen as the study site. The Centophase AD and Soiltac test sections were constructed on September 14, 2004. The FDR process could not be satisfactorily completed because the equipment was too large to work effectively in the shoulder area. In addition, achieving the same elevation of the shoulder and the hard surface pavement was difficult. When the process could not be modified without compromising the stabilizer mix design, the installation of the magnesium chloride was cancelled.

Performance Evaluation

After two test sections were installed, the problems of equipment size and weight and the need to comply with requirements regarding mixing and necessary elevation could not be resolved. Rather than continue with the construction of test sections that could not comply with the study specifications, the work was stopped and the placement of the additional test sections was cancelled.

Ongoing Work

Although the work to date has not verified the ability of soil stabilizers to work effectively on unpaved shoulders, it has established that alternate methods for applying stabilizers need to be investigated. The shoulder stabilization process requires equipment that can work in areas from 1 to 6 feet wide yet can scarify and mix the material to a 4- to 6-inch depth. Equipment will be sought that complies with these requirements, and additional test sections will be installed in the spring of 2005. The results, conclusions, and recommendations of this additional study will be reported in late summer 2005.