Effective and Safe Berming for Pavement Shoulder Maintenance in Cold Regions

Abstract

Berming is a common nationwide practice in the United States for pavement shoulder maintenance, especially for states located in cold regions. Competent berming helps to improve the load support capacity of the pavement shoulder and prevent vehicle drop-off accidents. The durability of berm materials is compromised by snow plowing operations during the winter season. A nationwide survey of state departments of transportation shows that it is highly desirable to improve the effectiveness and safety during berming operations; compaction of berms is widely believed to improve their resistance to snow plowing, which will also lead to longer lasting berms. To evaluate the performance of alternative berm materials and compaction procedures, experimental studies were conducted on four common types of berm materials to evaluate the effects of compaction method (i.e., Proctor and vibratory compaction) and compaction energy. The experimental results indicate that vibratory compaction is effective for crushed limestone, but less effective for recycled asphalt pavement (RAP) material. Natural soil berm material is not well compacted by vibratory compaction. Heat treatment of RAP up to 60°C did not increase its interparticle adhesion. Sixteen trial sections that include combination of four types of berm compaction equipment and four types of berm materials were placed along two interstate highways routes. The berm compaction equipment studied include the berm monster, two-wheel vibratory roller, side-mounted roller, and pull-behind roller. Observations show that a side-mounted roller provides better compaction for both vertical edge and safety edge pavements. RAPs show a similar behavior under compaction as crushed limestone in the field. Tack coating significantly improves the stiffness of the berm and retains berm materials from erosion. Recommendations are provided to ensure effective and safe berm compaction, which will lead to longer-lasting berms to mitigate cold region pavement maintenance efforts.