SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: https://read.dmtmag.com/i/64785
ification of +/- ¼ inch over the plane of the field is achievable by a qualified laser grader (be sure to check the quality of the laser sys- tem). The laser source should be accurate to at least 10 arc seconds at 3,000 feet; it should have been calibrated within the past 6 months. Wording of the specification is impor- tant: within ¼ inch over the plane of the field is really + or – 1/8 inch from absolute; +/- 1/4" from absolute is a total tolerance (deviation) of ½ inch—a significant differ- ence that most designers are unaware of (see diagram). The issue is significantly magni- fied if a designer still uses a horizontal dis- tance of 10 feet. Make sure the specification includes proof rolling of both the sub grade and the top surface. Note that 95% com- paction on stone means that the stone has been crushed and hydraulic conductivity has been compromised. The designer must be very specific concerning the number of passes with a given weight roller. PRIMARY GOALS pre-qualifying contractors is essential. Drainage and compaction are conflicting interests. On the one hand, you want water to flow efficiently through the base mate- rial, which means open pores and spaces in the rock. But compaction will decrease the www.stma.org The primary goals of a proper base are: Stability. The sub-base must be properly compacted to greater than 95% standard proctor in order to support the relevant loads on the field, which are the athletes themselves, and the occasional maintenance equipment. You are not building a parking lot designed to support huge static loads, nor are you building a road. But the base does need to be stable enough for moderate vehicles for short durations. Ensure that proof rolling is part of the specification for both the sub-grade AND the stone layers. This will also avoid the finger-pointing after a base is approved, and subsequently dis- turbed when the turf is laid. If the base is compacted properly, then it should not shift during turf installation. Some more rigid underlayment systems also help protect the base during turf installation, since tire loads are not directly on stone. Drainage. This is a tricky one and where surface. The sub-base and surface should be pore space and thereby decrease drainage. And overworking the stone can lead to "choker layers" forming, which cause pond- ing. So how do you get a base that is both compacted AND drains well? That is the art of building a stone base, and not everyone can do it. Planarity. This is the trueness of the on grade to specified tolerances as described above. This can be simply checked using simple devices. Having a laser on a machine does not guarantee quality. Owner confir- mation of the specifications of both surfaces is most important. Specifications should be no greater than +/- ¼ inch when measured vertically over the plane of the field and must also state that the vertical distance is SportsTurf 27