Installing Of French Or Sub-soil Drains
Fig. 45.—Sub-soil drain.
When a building is erected on a site that is wet or springy, some means of carrying off the surplus water in the ground must be provided for, or the basement of the building will be flooded with water. For the thorough understanding of the methods employed in laying a drain of this kind, I will go over it carefully and the beginner can read it and then study it, and understand just how it is done. A site may appear to be dry on the surface of the ground and yet be very wet under the surface. If no information can be had regarding the site, it is always well to drain the site if it is on a slope or near a body of water and on the water shed of a river or lake. If a building is a large one and the foundation goes down very deep, the site should always be drained. The drain is laid under the basement floor and around the outside of the foundation wall on a level with or lower than the basement floor. The value of draining a building site when the building is first started is very often overlooked. The cost of the drain will be saved in a few years as the basement will be free from all excessive dampness. The expense of installing a sub-soil after the building is up and in use is great as well as inconvenient. The drain is called "sub-soil drain" on account of its location under the ground and on account of its duty of taking off all surplus water that is underground. With the surface water taken off by the surface drains and the sub-soil drained by the sub-soil drains, a wet building site can be made practically dry (see Fig. 45).
Materials Used in Sub-soil Construction.—The object of the drain is to collect water and carry it away from the building by means of pipes. Terra-cotta pipes, with or without hubs, are used. Perforated tile pipe is sometimes used. This pipe is unglazed terra-cotta pipe with 1-inch holes in the sides about 3 or 4 inches from the center. These holes allow the surplus water to enter the bore of the pipe and thus be carried off beyond the building site.
When the sub-soil of a small building needs draining, the trenches made for the house drain and its branches are used as a drain in the following manner: The trenches are dug deeper than is required for the house drain. The trenches are then filled to the correct level with broken stones. There is space between these stones for the water to find passage to a point away from the building. When this method is employed, some provision must be made to prevent the house drain from settling. When locating the drain, we must consider approximately the amount of water that is likely to be in the soil and required to be carried off. If there is considerable water, the pipes should extend all around the outside of the building foundation wall, also a main pipe running under the cellar bottom with six branches, three branches on each side.
If there is not a great deal of surplus water in the soil, the drain around the outside of the foundation wall should be put in and one drain line running through the basement will be sufficient.
Laying the Pipe.—The drain pipe should be handled with care, for it is easily broken. The trench should be laid out and dug, then the pipe can be laid in it with a grade toward the outlet or discharge. If pipes with a hub on one end are used, the hub should not be cemented. A little oakum is packed in the hub to steady the pipe and keep sand out, the bottom of joint is cemented, a piece of tar paper can be laid over the top of the joint to keep the sand out. With joints made this way, the water can find its way to the bore of the pipe and yet the sand will be kept out of the pipe. As soon as the water gets into the bore of the pipe it has a clear passageway to some discharge point away from the building. If tile pipes without any hubs are used, some covering should be put around the joint to keep out the sand and still allow the water to find its way into the pipes.
Discharge of Sub-soil Drain.—The water that accumulates in a sub-soil drain must be carried off to some point away from the building. As the pipes are generally under the cellar bottom and under the house drain, it is very evident that this drain cannot discharge into the house drain sewer, directly. If the building site is on a hill, the drain can be carried out and discharged on the surface at a point that is somewhat lower than the level of the pipe under the building. Where this cannot be done, it will be necessary to have the different lines of pipes discharge into a pit. The water is accumulated in this pit until it is filled, then it will automatically empty itself as later explained.
Pit Construction.—The pit for the sub-soil water is constructed of cement. A pit 2 feet square or 2 feet in diameter and 3 feet deep will answer all requirements. A pit of this depth will allow a pitch for all lines of pipe, and is large enough for ordinary installations. The pit is built up to the surface of the cemented floor of the basement and covered with a removable iron cover.
Cellar Drainer or Pump.—A cellar drainer is employed to empty the above-mentioned pit. The cellar drainer works automatically. When the pit is filled with water, the drainer operates and empties the pit and discharges the water into a sink or open sewer connection. When the pit is emptied, the drainer shuts off. The cellar drainer is operated by water pressure. When the valve is opened, a small jet of water is discharged into a larger pipe. The velocity of this small jet of water creates a suction and carries along with it some of the water in the pit. This suction continues until the tank is empty. There should always be a strainer on the suction pipe, also on the supply pipe, to prevent any particles of dirt getting into the valve. The pipes leading to and from the drainer should empty into an open sink where it can be seen. There is a possibility of the drainer valve leaking and then the water pressure will leak through it, causing a waste of water. If this leakage can be seen where it discharges, then the trouble can be rectified. The cellar drainer is connected directly with the water pressure and should have a valve close to the connection to control the supply.
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