Oak Hills Multi-Sport Athletic Complex Construction

What goes under synthetic turf

A synthetic field gets sold as a carpet. It is a drainage structure that happens to have a carpet on top, and nearly everything that decides how it plays in year eight is buried before the turf shows up on a truck.

The sequence in this scope says so plainly. Existing dirt and spoils are removed to make room for the underground system. The subgrade is graded and compacted to the site plan — compaction being the step that gets rushed on a schedule and the one that produces the low spots that read as standing water three seasons later. HDPE perforated pipe is laid to collect what comes through the carpet. A permeable geotextile liner goes over it so the stone above keeps its voids instead of silting shut. Then #304 and #57 gravel is laid and compacted: the open-graded stone to hold water and move it, the dense-graded base to hold the shape and the grade. A reinforced concrete curb is poured around the whole perimeter to contain the system. Only then does the turf go down.

The civil design leaned on that stone for more than drainage, and this is the part worth repeating to a treasurer. The scope was written on the assumption that Hamilton County would accept using the underdrain gravel itself as the stormwater detention, with a county-required separate detention system priced as an addition. That single assumption decides whether a field project also needs a basin somewhere on the site, and it is answered by the civil engineer months before anyone orders a carpet.

The four light pole footers and bases are poured in the same operation, for the same reason. They are the only other elements that have to reach down through the drainage layer, and cutting them in afterward means cutting into the system that keeps the field playable.

None of this is visible in a photograph of a finished field. All of it is what a district is actually buying.

Engineering, architecture and construction under one agreement

The distinguishing fact about this project is not on the field. Oak Hills bought civil engineering, architecture, structural engineering and construction on one agreement, and all three engineering disciplines were carried in house by the builder.

What that buys is interfaces. A turf field, a pole barn, a press box, four high-mast light poles and a scoreboard are five design problems that meet in exactly three places: the ground, the permit, and the power. The light pole bases sit inside the field's drainage system, so the structural design of the poles and the civil design of the underdrain are one decision, not two. The barn and press box need elevations, a code review and a risk analysis; the poles need general structural notes and stamps; Hamilton County reviews all of it as one permit package, so a delay in any single piece is a delay in all of them. Electrical is one bored run from the school's existing electrical room to the transformer and then out to the barn, the press box, the scoreboard and the four poles — whoever fixes those locations is writing the boring plan.

Under separate contracts each of those seams is a place where one party's drawing stops and another's begins, and where a question gets asked twice and answered once. Under one agreement they are internal. The practical version for a district is that the conditional use submittal, the stormwater pollution prevention plan, the detention as-built and easement plat, the construction staking, the permit documents and the crew building from them all answer to one schedule and one party.

It also concentrates responsibility, which is the reason the defined edges of the agreement deserve a careful read. One architect design revision to the barn and press box is included. Geotechnical engineering is not, and the county retained the right to require it at added cost. Zoning approval for the lighting requires photometric data and may impose restrictions on light levels and pole locations. Those are the three places where a single-source agreement stops absorbing risk, and they are the three a facilities director should ask about first.