Rip Rap is medium to large sized angular pieces of stone placed as a permanent, erosion resistant ground cover. The material is usually classified as either graded or uniform. Graded rip rap is a mixture of stone varying in size, uniform rip rap is all of similar size. Rip Rap protects channels, stream banks, slopes, or areas exposed to wave action. It also protects the underlying soil from erosion as a result of concentrated runoff. It stabilizes slopes that are unstable due to ‘seepage’ and also slows the velocity of runoff which helps infiltration. Rip Rap can also be found at culvert inlets/outlets, bridges, and slope drains. Rip Rap can also improve the drainage water quality by decreasing velocity and catching/settling sediment.
Some disadvantages of rip rap are:
- lesser habitat enhancement properties
- less economical than vegetative slopes.
A common crew required for installing Rip Rap stone is a laborer and an operator. The equipment required will be a an excavator with a 3-6 ton lifting capacity as being productive with Rip Rap material will require a machine and bucket that can handle sizable scoops of material for placement. Some hand work is typically required. If the engineer or inspector is present, some things he will likely be looking for are good quality stones, correct stone size, and proper thickness. Also, it is typical that a bed of stabilization/separation fabric or smaller aggregate is placed under the rip rap to keep the soil underneath from ‘pumping’ up through the rip rap.
A keyway is typically excavated at the toe for reinforcement. The depth of the keyway is typically at least 1.5 times the thickness of rip rap specified. The inspector will typically want the rip rap installed as soon as possible after the grade is correct below to reduce the amount of time the soil is exposed to erosion. Graded Rip Rap is typically the most common type installed. Filter fabric if used should be heavy duty. The common thickness of the rip rap specified should be at least 1.5 time the maximum stone diameter.