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89 EDGE-OF-ROAD BERMS An edge-of-road berm is a mound of earth, usually constructed of mine waste, placed along the outer edge of an ele- vated roadway to prevent a runaway vehi- cle from leaving the roadway. Model tests, field tests, and computer analyses were used to determine how such berms should be constructed. Berms are currently constructed of a wide range of overburden material. A rear-dump truck hacks perpendicular to Lhe road edge and dumps successive mounds of spoil along the road edge. The over- burden material can consist of rock 12 to 18 in. in size mixed with soil. There are no special soil grading (sizing) pro- cedures used to select berm material. The final shaping of the berm can be per- formed by a small front-end loader. If necessary, the bucket of the loader is used to tamp the berm material. Erosion of berms is a problem in areas with fre- quent or heavy rainfall. In these areas, .:.:... q) ~ Deems ~. ~... I i ' + ; r r i '~ , Berm oe.erra~~en "..:. ~ :..: f /, .: ~ ~: : Pate 01 r . ' i ins ea O~n 0 ~. APO~oe[e re~octly •oProecn enau IOi ... .. ... ... ...... .. Tne s~nkaQe Berm wne ei i~me ~ -- ~r~:. ... .. ... .... _ Bmm sio oe (B1- FIGURE 1. • Configuration of edge-of-road berm. some berms are seeded to minimize erosion damage. All earthen berms deform during impact by a vehicle. Analyses show that failure occurs when [he berm is too small or too weak. A large runaway haulage vehicle can easily plow through or over such a berm. There is the possibility of a slope failure of the road edge when a haulage truck penetrates too far into the berm. Therefore, to prevent a haul- age vehicle from coring too close to the road edge during collision with a berm, the berm is said to have failed when a vehicle's leading tire penetrates more than halfway through it. In this in- stance, the vehicle has "vaulted" the berm (fig. 1). To prevent the vehicle from vaulting the berm, berms must be constructed to a height-versus-strength relationship that will assure vehicle restraint by redirection, penetration, berm climb, or rollover. Redirection occurs when a vehicle in- teracts with a berm or barrier, usually at a shallow angle, and climbs it, only to slide down again to the roadway be- cause of insufficient frictional contact. Penetration occurs when a vehicle con- tacts a weak berm and is stopped by the soil resistance forces created by the vehicle tires and body plowing through the berm. Climb occurs when a berm has sufficient strength to allow a vehicle to ride up the berm. The change in the ele- vation during climbing will cause the vehicle to stop. Collision with a deformable berm is usually a combination of penetration and climb; as the leading vehicle tire pene- trates the berm, the tare sinks, increas- ing rolling resistance, while climbing the berm. To prevent a vehicle from leaving an elevated roadway, a properly designed berm must be constructed with its onboard face at an angle that will cause a vehicle to roll over onto the roadway if the vehicle exceeds the