What Are Graveless Sewer Lines?

Systems

• Sewer systems requiring a leach field traditionally need a large trench to be dug, into which a perforated sewer line is sunk and covered with gravel. The use of gravel is required to allow liquid to drain from the perforated pipe; the perforations in the pipe are larger than in other sewer systems to prevent clogging. A septic system using either gravel-filled or graveless trenches consists of home plumbing, a sewer line, a septic tank and a sewer line leading to a sewer or leach field.

Gravel

• The graveless system of installing sewer lines consists of a corrugated pipe properly sized to the demands of the sewer wrapped in a geotextile. Before installing a graveless sewer line, a smaller trench should be dug than is required for a gravel-filled trench. When the sewer line is installed the native soil is returned to the trench around the pipe. A graveless system is suitable for use in soil conditions where the percolation rate of water is less than 60 minutes per inch and can be used with percolation rates of between 61 and 90 mpi, North Dakota State University reports.

Pipes

• Graveless sewer systems require plastic pipes that are corrugated on both the inside and outside; the manufacturing material is commonly high-density polyethylene. Corrugated pipes can be moved and curved to fit any property shape, according to the Plastic Pipe Institute. Graveless pipes can be installed using an 8-inch pipe to replace a 2-foot-wide gravel-filled trench, or a 10-inch corrugated pipe can replace a 3-foot-wide gravel-filled trench.

Advantages

• Amongst the advantages are the reduced costs of installing a graveless sewer system. Costs are reduced because of the smaller number of workers needed to install the pipes. Other cost reductions include the reduction in materials costs, no gravel must be bought or heavy equipment required to complete installation. The lack of heavy equipment also causes less compaction of soil around the sewer system that can lead to problems with sewer drainage, North Dakota State University reports. Corrugated sewer systems are acceptable under most state and local government building codes in the U.S.