Trench drain

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A trench drain (also channel drain, line drain, or strip drain) is a specific type of floor drain containing a dominant trough- or channel-shaped body. It is used for the rapid evacuation of surface water or for the containment of utility lines or chemical spills. Employing a solid cover or grating that is flush with the adjoining surface, this drain is commonly made of concrete in-situ and may utilize polymer- or metal-based liners or a channel former to aid in channel crafting and slope formation. Characterized by its long length and narrow width, the cross-section of the drain is a function of the maximum flow volume anticipated from the surrounding surface. Channels can range from 1 inch to 2 feet in width, with depths that can reach 4 feet.

Trench drains are commonly confused with french drains, which consist of a perforated pipe that is buried in a gravel bed, and which are used to evacuate ground water. A slot drain, also wrongly associated with a trench drain, and consists of a drainage pipe with a thin neck (or slot) that opens at the ground surface with sufficient opening to drain stormwater.

Contents 1 Types 1.1 Cast in place 1.2 Former systems 1.3 Pre-cast concrete 1.4 Liner systems

[edit] Types

There are four common types of trench drains which are based on forming or installation method. These are cast-in-place, pre-cast concrete, liner systems and former systems.

[edit] Cast in place

This is the original standard for trench drain systems. Here, a concrete trench is formed in the ground using wood forms, reinforcing bar and manual labor. It involves several steps:

1. Building a wooden mold that will ultimately form the channel for the trench drain;
2. Attaching a set of metal frames to the top edge of the form (which will hold the trench grating);
3. Suspending the form inside the trough (and flush with the surface elevation), such that there is space (6" or more) below and to each side of the form;
4. Attaching the drainage pipes to the suspended form;
5. Filling the trench with concrete (surrounding the form base and sides) and finishing the concrete flush with the metal frame;
6. And after drying, removing the wooden form, cleaning the pipe inverts and placing the grates in the frame.

This installation method is by far the most labor-intensive. In addition, material costs is a function of the width of the grate used in the trench.

[edit] Former systems

This installation method is the logical successor to the cast-in-place method. The former system gives a cast-in-place product without the hassle of making the form. Rather than wood, the forms are made of lightweight expanded polystyrene (EPS) or cardboard. The forms attach to a prefabricated frame and grate system that can then be easily set in the trough and aligned for the pouring of concrete. And, like the cast-in-place method, the form is removed after the concrete has dried. The real savings with the former method is in time required for making and setting the form. The efficiency of the former system helps speed up the installation thus reducing labor costs.

[edit] Pre-cast concrete

Trench drains are made in a factory that specializes in making concrete shapes. The channel pieces are large and heavy, requiring cranes and heavy equipment to move them. The channels are formed in a large metal forms that (usually) have a pre-determined channel width and depth. Like in the cast-in-place method, a metal frame is attached to the form and concrete is poured and finished in a factory atmosphere. The advantage to the pre-cast trench drain is again time savings—big time savings at the job site. Once a trough is dug and the base of gravel is laid to the proper elevation, the pre-cast trench sections can be installed and quickly be put into service. There is no waiting for concrete to set and no stripping of forms. Pre-cast trench can be installed in a matter of hours and ready for immediate use.

There are several detractors to this system type, however. First of all, pre-cast trench drains do not generally come in narrow widths. A 10-inch channel is generally the smallest; sixteen to twenty inches is typical. And, having a product so large and massive requires big equipment to install, such as backhoes. This may already be on the jobsite if there is a lot of digging. Needless to say, a home owner should not consider pre-cast trench for a landscaping project. Also, there is a manufacturing process that needs to be addressed, which includes scheduling. A person generally can not go to a pre-caster and buy 50 feet of trench drain out of the yard; it probably has to be manufactured. And lastly, the cost of pre-cast trench can be high.

[edit] Liner systems

The popular trend in trench drains are liner systems. Made from materials such as polymer concrete, fiberglass, structural plastic and steel, liner systems are the channel and grate components that are assembled in the trench and around which concrete is poured to form a drain system. By themselves, these liner systems do not have the strength and integrity to hold up under the physical requirements needed for the drain. A concrete (or asphalt) drain body is required to encase the channel to give the channel compressive strength and rigidity to ensure the drain will be able to withstand the traffic load it was designed to handle.