SportsTurf

32 SportsTurf | April 2016 www.sportsturfonline.com FIELD SCIENCE INSTALLING BASE MATERIAL Base material here is defi ned as sand or pitrun placed over the drain lines and the graded sub-base. This material should drain rapidly to facilitate faster movement of water to all drain lines. If ample quantities of low cost sand are available, the entire profi le could be made up of sand to the grass surface. Base materials can include pitrun with a maximum of 2-3% total silt and clay. Other materials may include pea gravel, coarse sand, with particles ranging from No. 8 to No. 3/8 screen. Never permit abrupt profi le changes, especially fi ne sands or soil over coarse gravel. Saturated zones will occur at these interfaces. Try to maintain textural uniformity in the profi le. The depth of base material can vary from 4 to 12 inches. Carefully deposit base material over the fi eld to avoid disruption of the base grades and to prevent damage to the drainage lines. During installation never run wheeled equipment across drainage lines. The base material can be brought to grade with light tack type equipment or light grading equipment. Under no circumstances should efforts be made to heavily compact the base material in any manner other than normal grading operations to bring the fi eld to grade. SUBSURFACE DRAINAGE Installation of drainage lines is necessary when water tables are too close to the surface and must be lowered. Drainage should also be installed when subsoils are impermeable or so slowly permeable that turfgrass rootzones remain saturated for extended periods. Subsoils that are moderately permeable (1/2 inch per hour or greater) do not require extensive drainage installation. A standard percolation test conducted at about 30 inches deep will help determine the need for drainage lines. When drainage is necessary, adhere closely to the following procedures. Install drain lines on 15-foot centers ranged longitudinally on the football fi eld. This spacing interval of drain lines will allow free movement of vehicles during the construction process and will facilitate rapid water movement into the drain lines. Install drain lines 16 to 24 inches below the grassed surface at a 1 to 2% minimum grade. Drainage trenches should be 6 to 8 inches wide and should be dug with laser-controlled machines. This will insure the proper grade and depth of drain lines. Drainage trenches should be dug with a wheel ditcher with a cleaning shoe that leaves a "V" shaped, clean, and graded trench bottom. If other types of trenchers are used, the contractor should cut a level (fl at) bottom and excavate 2 inches deeper than the required invert elevations and place (1/8 inch minus to 5/16 inch minus) pea gravel 2 inches deep, leveled to grade for placement of the drain lines. Drain lines can be placed longitudinally from end to end on naturally sloping terrain or crowned fi elds, but this is not practical on fl at terrain. The herringbone method is a typical alternative to longitudinally oriented drain lines. Typically, the fi eld should be divided from the center and trenched in each direction, reducing the length of run in half. Since a perimeter drain should be installed around the football fi eld to facilitate drainage of both the fi eld and the running track, these longitudinal drain lines can be coupled with the perimeter drain and discharged into storm sewers or other suitable sites. Some drainage lines are manufactured with slits 360° around the tubing and some are drilled with holes only on one side at 45° angles. In the latter case always place the holes downward. During installation, attempt to keep soil off the drain lines and trenches. Carefully cap blind ends and properly connect and tape all joints to prevent entrance of soil material or animals. Drainage lines spaced on 15 feet centers should be installed with 3- or 4-inch semi-rigid drainage tubes with slits or drilled holes to facilitate infl ow of water. After the drain lines are in place, backfi ll trenches with pea gravel (1/8 to 5/16 inch) or coarse sand to a depth of 2 to 4 inches over the top of the drain tubing to avoid migration of fi ne sand particles into the drain line causing clogging of the drains (Figure 2). Manufactured fi lter devices either wrapped around the tile or placed over the tile to prevent migration of the fi ne particles are not recommended. Cases have been reported where these fi lter materials have become clogged with fi ne particles and sealed the drain lines. Extend drainage lines through the end zones to tie in with the perimeter drains near the running track. The drainage line surrounding the running track will intercept Sand-based field with a 4-inch base material layer Sand-based field with a 4-inch base material layer Sand-based field with a 4-inch base material layer Sand-based field without a base material layer Figure 2: Cross sectional view of drainage profile with (top) and without (bottom) a 4-inch base material layer.

• Cover