Previously in this blog, I documented the assembly of a small run of trench drain that was to be used in a garage that was being built. This current article will address the installation of trench drain in an existing driveway. Most homeowners that purchase trench drain are looking to resolve an existing drainage problem. From my observation, driveway drainage problems are the most common. The problem can vary from being merely a low spot in the drive that causes the pooling of water to the unfortunate deluge of water that enters the garage each time there is a heavy rain.
In this situation, the homeowner was getting water into his garage with every hard rain. Further investigation suggested that water was running through a seam at the asphalt-garage floor interface and filtering to the foundation which caused dampness at the base of his basement walls and an over active sump pump. In addition to having a driveway that gently sloped toward the house, his house was at the low end of the street, which made his site more prone to collecting street run-off. To make matters worse, he had downspouts from the roof on either side of the garage door that supplied more water to the affected area.
To remedy his problem, it was decided that a trench drain be installed abutting his garage floor to accept the water from his downspouts. The water was to be discharged toward his back yard, which sloped to a creek. The home owner selected a pre-sloped 4″ wide polymer concrete trench drain (Polycast 600) with cast iron grates and steel channel protectors. The drain channels of this system were pre-sloped (not neutral) so water would flow the moment it entered the drain.
Prior to any work, a sheet of plastic was hung to protect the garage door and siding from slurry and concrete splashes. A cut line was made in the asphalt 20 inches in front of the garage door using a concrete saw. The diamond blade on this saw had a 6″ cutting depth which made it able to cut through the 4 inches of asphalt and another 2 inches of the gravel below. This asphalt strip was then cut into smaller squares for easy handling during removal.
The sectioned asphalt and underlying gravel was removed manually. In this case, gravel and asphalt was put into the back of a pick-up truck and taken to a land fill for disposal. During this time, the downspouts were fitted with the 4″ PVC fittings necessary to divert the roof water into the trench and drainage pipe.
To assemble the channels, placement began at the lowest point (invert out) and progressed to the shallowest end. A level line was established just below the surface of the asphalt and 14″ from the edge of the garage floor. Installation hardware was attached to the first polymer channel section (4 foot length). The channel was then set in place, suspended 4 inches above the excavated surface, with the use of #4 rebar.
The top edge of the channel was adjusted to meet the level line. Vertical adjustments were done by sliding the installation chair on the rebar. Horizontal alignments were made with the adjusting bolts on the installation chair. Installation hardware was added to the end of the second channel and attached in an “end to end” manner with the first channel. Again, the second channel was suspended 4″ above the excavated surface and adjusted laterally and horizontally on the rebar supports to match the level line. This technique was repeated until the last channel section was put in place.
Once the channel was assembled, end caps (with knockouts) were installed, down spouts and piping was attached and grates were put in place. The grates were wrapped in plastic sheeting to protect them from concrete, as well as to help keep concrete out of the trench. Some people place a strip of plywood in the grate recess during concrete pouring. This is a good idea. It allows you to keep the grates clean and the trench free from concrete and not deal with the plastic sheet.
Concrete placement was done next. For this installation, the drain was centered in a 20″ wide excavated trench that was approximately 12″ deep. A minimum 4″ space was below the channel and 6″ on either side of the channel for concrete to fill. No reinforcing was used in the concrete (4000 psi mix). The concrete truck discharged the mix directly into the trench. Two men placed the concrete in the trench using hand tools. It would have been useful to have a pencil vibrator during the placement. Never-the-less, concrete pouring only took about one half hour.
Once the concrete was placed and the truck had left, the grates (with plastic sheeting) were removed and concrete finishing began. After removal of the trench cover, some clean-up of the channels was required using a wet rag. Trowels and edging tools were used in the finishing. Once the concrete began to set and finishing was complete, the grates were put in place and the lock bolts were tightened.
On the following day, some house-keeping was required to complete installation. Concrete forms were removed, dirt was placed in areas affected by the excavation, mulch was replaced, flower planters were put back construction rubbish was picked up and the asphalt driveway was power washed.