08-15-1983 Planning Packet - Laserfiche WebLink

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coefficient under /ada, New Mexi- Duisiana highway ;n using plant mix years because of :ts. > airport runways 1967 at Farnbor* the British Royal European airfields \ir Force. Since nia Highway De> i graded base nverltional surfac* apid drainage in nstitute Research ler ERA sponsor- porous bases and [ in conjunction lications of plant s experiment was potential of deliv- e subbase rather to a stormwater . Also evaluated conventional and materials. The les were tested to physical and eco- as porous pave- Of those tested, asphalt concrete the most suitable >erior characteris- ability to be laid >aving. pavement types concrete lattice gs the Franklin Insti- cost of concrete orm sewers to be :ost of an equiva- ?halt installation ver relief. Howev- ill have to consid- >ome storm sewer e field data on ir j '5, wk 4'-‘ •> r'*t L c>.. V iI I u mm porous pavements Is available. The economics of porous pavements are very “site specific” as they are governed by design difference, the cost and proximity to the supply of stones and gravel and the perme ability of the adjacent soil. Each user will be required to do an eco nomic evaluation when considering the installation. Initial porous pavement installa tions in Delaware and Pennsylva nia proved successful on a structur al and drainage basis. Subsequent installations in Woodlands, Texas, and Rochester, New York, were instrumented and monitored to provide greater information on the benefits and drawbacks. Pavement Design ^ Each porous pavement design is unique and is evaluated and ap proved by regulatory agencies only after a long analysis and review. In a cooperative agreement with the city of Austin, Texas, the EPA hopes to standardize design ap proaches for parking areas and residential streets to allow design ers latitude for creativity. For corn- plex conditions a thorough analysis is essential. The need to evaluate the runoff changes and water quality constitu ent changes from urbanizing activ ities is paramount in the design of porous pavement systems. Unfor tunately, most engineering prac tices hold the view that all pave ments have to be ev?’'.iated solely from a runoff quality {" ow rate and volume) viewpoint. Only recently has water quality degradation be come a concern for most practition ers and public officials. To develop the design of a po rous pavement, the design storm, contributing area and soil perme ability will determine the storage volume required for the reservoir base. Characteristics of the drain age basin including permeability of the soil, topography and climate will impact the volume and rate of runoff and flow through the porous pavement and existing subsurface soil. Storage capacity, however, can be limited by physical and eco nomic limitations. If so, relief mea sures should be incorporated to prevent negative impacts that could develop—flooding, freezing, septic conditions, etc. The considerations discussed here will result in a design for porous pavements. This design The pavements provided good load- bearing and rapid drainage. the reservoir base course and to stabilize the surface, a two In. layer of 0.5 in. crushed stone aggregate is recommended. Based on previ ous experience, this stabilizer course is necessary because vehi cles hauling asphalt hot mix across the reservoir course would create ruts that require constant grading to finished grade prior to hot mix application. Open Graded Asphalt Concrete Surface Course: Porous asphalt consists of a wearing course of open-graded asphalt concrete over a base course of uruform sized aggregate. It differs from conven tional asphalt concrete in that it contains very little dust or sand; Its void volume typically is around 16 percent as compared with the two to three percent void volume of conventional asphalt concrete. which was adapted from Thelen and Howe is as follows: The Subbase: All soils under roads may become wet but they must drain to maintain bearing strength. Because soils under po rous pavement gel wet, they must be water permeable and they must not “heave” from freezing or thaw ing, and must not swell or lose their strength when wet. Most soils can meet these requirements if proper drainage is available. The Reservoir Base Course: !n porous pavement, the base con sists of large-sized and graded stones, lightly rolled into an open, interlocking structure that not only transmits mechanical loads, but also stores runoff the soil cannot immediately absorb. This water is held in the reservoir formed by voids in the rock matrix until it can percolate into the soil. These voids can be as high as 40 percent of the total volume. The aim of having a reservoir is to store runoff for sev eral hours to allow it to percolate into the soil. The Reservoir Top Stabilizing Course: To assist in final grading of m Porous Pavement Research Projects In Rochester, New York, two parking lots were selected to dem onstrate the effectiveness of po rous pavements to reduce the rate of stormwater runoff and to investi gate the long-term structural integ rity of such pavements under se vere environmental conditions. One of these sites was selected to evaluate the structural integrity and permeability for the porous pavement under conditions of heavy truck traffic. Results of the study indicated: (1) Peak runoff rates were reduced by as much 83 percent. (2) The pavement, subjected to 100 freeze/thaw cycles, showed no ob servable structural degradation. Water drained through the pave ment without problems during the winter. (3) Through observations and flow monitoring, the structural integrity of porous pavement (in stalled where heavy vehicles were parked) was not impaired. (4) Clog ging did result from runoff carrying a heavy sediment load and was relieved through cleaning. (5) Cost of constructing a porous pavement parking lot using impermeable membrane and underdrains was slightly higher than a conventional ly-paved lot with stormwater inlets RURAL AND URBAN R0A06/JULY. 1983 49 'U 4 4 !?U iF 'f !>■ '‘ v \ ■ and subsurface piping In Austin, Texas, tl jective for this rese demonstrate, evaluat Figure 1. Concrete p Figure 2. Typical se 50 RURAL Arc LR6->