Landscape and Irrigation is read by decision makers throughout the landscape and irrigation markets — including contractors, landscape architects, professional grounds managers, and irrigation and water mgmt companies and reaches the entire spetrum.
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Landscape Design and Construction PICP Construction Tips Keys to installing permeable interlocking concrete pavement Figure 1. ICPI recently launched a PICP certificate course for contractors. Besides meeting training needs within the industry, the ICPI is encouraging PICP course certificate holders as a requirement in federal, provincial, state and municipal construction specifications, as well as private sector projects. P ermeable interlocking concrete pavement (PICP) is gaining in- creased use in residential and commercial projects thanks to the need by U.S. and Canadian municipal governments to curb stormwa- ter runoff. Many PICP designs take advantage of the soil infiltration to reduce stormwater runoff even in clay soils. Unlike interlocking concrete pavement (ICP), PICP is generally built on native, undisturbed, non-compacted soils in order to promote infiltration. Com- paction greatly reduces a soil's infiltration capacity. If the soil subgrade is compacted, the amount of water infiltration decreases 50 to 90 percent with the higher percentage applying to clay soils. Therefore, the Inter- locking Concrete Pavement Institute (ICPI) recommends not compacting soils under 20 Landscape and Irrigation March 2012 PICP in many designs beyond grading and trimming for drainage. PICP design and construction uses na- ture's compacted soils. The natural (undis- turbed) in-place density of native soils increases with excavation depth, and infil- tration rates generally decrease with depth due to increasing density. While native soil densities are not as high as those resulting from deliberate compaction (as with a vi- bratory roller compactor), the native densi- ties provide some support to the PICP base/subbase and loads placed on them. Excavation and grading equipment passing over the soil subgrade surface re- sults in some compaction, and increased density results in decreased soil infiltration. Compaction incidental to construction equipment passing over soil is generally not to the same depth from deliberate soil compaction with equipment typical to parking lot or road construction. Nonethe- less, such incidental compaction helps de- feat the infiltration benefits of soil in PICP. Designers need to consider this condition and provide reduced soil infiltration in their base and drainage designs. Better still, designers and contractors can specify ways to preserve or restore soil infiltration dur- ing construction and some ways to accom- plish this are presented here. If a contractor inadvertently compacts the soil subgrade with construction equip- ment, the soil can be raked with the teeth of a bucket to loosen the compacted soil layer. An interesting research project by en- gineer and University of Tennessee Profes- sor John S. Tyner examined the potential for restoring infiltration rates in clay Ten- nessee soil prior to installing pervious con- www.landscapeirrigation.com All photos courtesy of the Interlocking Concrete Pavement Institute