How to install a trench drain
Trench drain systems collect water from surfaces such as driveways, garages, walkways and yards, keeping them clear from accumulated water or liquid. Trench drain systems are also used in streets, footpaths, airports, highways, chemical factories, wineries, historical & tourist sites, and for hazard spillage. Trench drain systems are essentially paths for the water or liquid to drain from a particular area, protecting the surface, while also enhancing aesthetics.
Trench drain systems come in different shapes and sizes, and are made of different types of materials, allowing selection based on site specific needs. Some materials used are high density polyethylene (HDPE), fiber reinforced concrete (FRC) and polymer concrete. Let us take a look at the installation of trench drain systems for the above mentioned materials.
Slip joints make channel connections a lot easier.
Excavation depth based on load class
|Class||Min Width Each Side||Min Depth Below|
|A – 15 kN||4”||4”|
|B – 125 kN||4”||4”|
|C – 250 kN||6”||6”|
|D – 400 kN||6”||8”|
|E – 600 kN||8”||8”|
|F - >600 kN||12”||12”|
Channel recess for pedestrian traffic – 1/8”
Channel recess for vehicular traffic – 1/4”
Installation of trench drain systems made with HDPE
- Gather required tools and materials such as HDPE trench drain, sealant, caulking gun, level, vibrator, shovel etc. Arrows should be marked on the channels to indicate direction of flow.
- Dig the trench based on the load class i.e. the estimated load the trench drain system is expected to withstand.
- Arrange the trench drain channels alongside the trench beginning at the drain outlet, where the channel will be the deepest.
- Locate and install expansion joints parallel and perpendicular to channel as specified in the plan.
- Assemble a catch basin or end outlet at the deepest end of the trench drain system.
- On either side of the channel, set out a string line at level with the final elevation at which the trench drain system will set. If frame used is of ductile iron it needs to be accommodated by setting the string line 1” below finished grade.
- Assemble the channels starting at the deepest end by snapping the channel sections together in pairs of two.
- Align the channel with blank grate inserts and fasten with screws, ensuring flush ends.
- Align the assembled channel into the excavated trench.
- Fix rebar into the provided slot in each channel section and drive it half to one foot into the ground until it remains fixed.
- Align and check for straightness using string line.
- Continue process till all channel sections are in place and aligned.
- First pour concrete on rebar base on either side and under the channel between the rebar.
- Repeat concrete on rebar.
- Start pouring concrete in equal amounts on either side of the channel and use vibrator to prevent voids.
- Allow concrete to set for 24 hours and remove the blank grate inserts.
- Install the grates for the finished trench drain system and allow concrete to completely cure and set prior to commissioning.
Installation of trench drain systems made with fiber reinforced concrete (FRC) and polymer concrete
Unlike HDPE trench drains, fiber reinforced concrete (FRC) and polymer concrete trench drains are breakable and should be handled with care. The installation technique of both these materials is similar. Protective gear should be used while grinding, cutting or drilling the concrete products as the dust can get into the eyes and nose. All operations should be conducted in a safe space away from flammable areas.
- Gather required tools and materials such as FRC or polymer concrete trench drain channels, cement, shovel, trowel, cutters, adhesive, sealant, etc. Pay attention to the arrows marked on the channels to indicate direction of flow.
- Excavate trench based on the load class along the center line of the proposed trench drain system. Ensure correct slope is maintained while excavating.
- Compact the trench bottom properly and run a string line for the entire length at finish level.
- There will be some fabrication to be done on site requiring cutting such as for miters, tee junctions and odd lengths. Masonry or diamond disc saw can be used for concrete channels and band saw can be used for cutting the iron grates.
- Cut open required pipe size such as for catch basin outlet, and attach using appropriate sealant depending on the liquid the drain will transport. For corrosive liquids, the sealant should be chemically resistant.
- Start setting out at the outlet end, minding the channel height based on gradient, and taking note of flow direction, indicated by arrows. Make sure string line or laser is set at correct level.
- The channels can be positioned using 3 methods
- Patty Method
- Hanging Method
- Installation Device
- Once positioned, place plywood pieces of ¾” in the grate rebate of the channel. This will prevent the channel wall and joints from moving or dislocating due to the weight of concrete.
- Cover open areas of the channel with plywood to prevent concrete from filling into the channel.
- Use concrete with compressive strength of 4000 psi.
- After hardening of first lift, concrete can be poured evenly and carefully on both sides of the channel. Use vibrator to prevent voids from forming in the concrete.
- Concrete should be flattened using a trowel, tapering down to channel edge, ensuring that the top of adjacent pavement is approx. 1/8” above grate level allowing proper drainage.
- After concrete has set, hardened and cured for at least 24 hours, the protective ply can be removed and grates can be installed.
- To prevent channels from cracking, transverse joints and expansion joints should be provided at correct locations. If spacing is not easily possible, cuts can be made at appropriate locations and sealed with flexible sealant.
- Finish pavement with asphalt or brick pavers as required in contract.
Let the concrete settle and dry.
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