Installation
First , the site should expose and prepare the subgrade soil layer found naturally on site . The soil subgrade must have vertical saturated hydraulic conductivity of at least 2 inches per hour when aggregate is installed . In order to achieve maximum infiltration rates , use light equipment to prevent over-compacting the subgrade soil when excavating . If required by approved plans for enhanced load bearing or infiltration capacity , application of additional subgrade soils will occur following excavation . After the subgrade soil layer is graded to specifications , it should be scarified with light equipment to a minimum depth of 6 inches .
Second , an open-graded reservoir layer ( or subbase ) is applied on top of the subgrade soil layer . This layer generally consists of open-graded ASTM No . 2 or No . 3 stone ( 1 to 2.5 in ) ( ASTM 2017 ). Optionally , geotextile fabric can be installed above the subgrade soil before installing the stones . For pavement subbases constructed on grade , geotextile layers should be incorporated at equal elevations for every 6 to 12 inches of grade change . This should be repeated until the designed thickness of the reservoir base course layer is reached . The density of the subbase shall be determined using the Sand-Cone method ( AASHTO T 191 ), Drive Cylinder Method ( AASHTO T 204 ), Nuclear Methods ( AASHTO T 238 ), or other methods approved by the supervising engineer or County Public Works Director . Following the completion of the subbase layer , an inspection needs to be conducted before proceeding with the subsequent phases of installation . An engineer or other certified inspector should perform this inspection . Following inspection and approval , side slope geotextiles shall be added . Geotextiles should have a minimum 16-inch overlap and be secured 4 feet outside the excavation site to prevent conveyance of runoff or sediment .
PERVIOUS PAVEMENT SYSTEMS
Third , a layer of choker course ( or filter course ) is applied evenly over the top of the reservoir layer , sufficiently to allow the placement of pavement surfaces . The thickness of the layer should be a minimum of 2 inches . Recommended material for the choker course is a washed ASTM No . 57 size stone ( 3 / 16in-1in ). The porous concrete and porous asphalt applications are installed directly on top of the choker course ( ASTM 2017 ; UF IFAS ; Bean et al ., 2019 ). The infiltration of the compacted subbase following the installation of choker course shall be determined using ASTM D3385 ( e . g ., double-ring infiltrometer test ) or alternative approved by the supervising engineer or public works director .
Depending on the pavement chosen and permitting standards with the County , bedding course material is added on top of the choker course . This additional layer applies to installations of pervious interlocking concrete pavers , concrete grid pavers , and plastic reinforcing grids with turf options ( Bean et al ., 2019 ). Bedding course should be ‘ washed ’ stone or pea gravel ( ASTM No . 8 or 89 stone course ( 3 / 64 to 3 / 8 inches )) ( ASTM , 2017 ). The recommended depth of this layer is approximately 1 inch ( WEF-Stormwater Report ; UF-IFAS ; Bean 2019 ).
Following a successful ASTM D3385 test of the subbase aggregate , the geotextiles should be folded back along all bed edges , a 4-foot edge strip should be installed , and additional measures deployed to prevent movement of sediment into the site . Following stabilization of the subbase , the temporary sediment devices can be removed .
Finally , the pervious pavement surface material can be installed . The recommended surface material thickness for each of the materials varies ; pervious interlocking concrete ( PICP ) 3 to 3.5 inches in depth ; porous asphalt between 3 to 6 inches in depth ( 2 inch minimum ); porous concrete ( PC ) between 4 to 8 inches in depth ; and plastic reinforcing grids ( PRG ) with turf between 2 to 4 inches in depth ( WEF-Stormwater Report ; UF-IFAS ; Bean 2019 ). This thickness will vary however , depending on the available material ’ s properties and the amount of expected traffic on-site . PICP and PRG systems have larger voids within the pavers , which are typically filled with a stone aggregate or coarse sand to allow water to infiltrate through the paver surface porous pavements ( PA and PC ) have voids by omitting finer particles that are generally included in their conventional , impervious counterparts .
FALL 2022
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