French Drainage System

WHAT IS A FRENCH DRAIN?
French drains are trenches that contain a perforated drain pipe enveloped in gravel. Either the entire trench is lined with filter fabric, or the pipe is wrapped in filter fabric.

Generally, the trench is covered with grass.

WHEN DOES FCS RECOMMEND USING A FRENCH DRAIN?
French drains are designed to remove water that accumulates below the surface. French drains are very good at collecting water accumulating in marshy or boggy areas that have been created by over-watering or poor drainage.

HOW LONG DO FRENCH DRAINS LAST?
If the trench for a French drain is lined with filter cloth, the drain will last for many years. If only the pipe is wrapped in filter cloth, soil will wash into the gravel in just a few years.

HOW DOES FCS INSTALLED THEM?
We start with digging a trench and grade it so the bottom is flat and evenly sloped. Next, we line the trench with filter fabric. After the fabric is installed, 1 to 2 inches of gravel is placed in the bottom of the trench. A perforated pipe is then laid on the gravel. The trench is then filled 4 to 6 inches below the surface and the edges of the filter fabric are laid over the top of the gravel. Finally, the top of the trench is filled with soil.

The French drains can either work with gravity, if enough of a slope is available, or connected to sump pumps depending on your need.

Holes are dug at intervals along the affected areas of the foundation. If a pier is necessary in an area that is covered by concrete then a hole must be cut through the concrete.

After the holes are dug, a hydraulic press is used to force the concrete segments into previous using the entire weight of the foundation to force the lower segments deeper.

Many concrete piers are manufactured with a 5/8 inch hole running the length of the pier so that it can be threaded on re-bar, cable, or other material that is rigid enough to prevent lateral shifting. In areas where there is no lateral shifting solid concrete segments work just as well with the added benefit of being stronger.

This process continues until the piers reach bedrock or until the friction between the soil and the surface of the concrete segments becomes so great that the weight of the foundation is no longer sufficient to press them deeper. This is commonly referred to as the “Point of Absolute Refusal.”

After all piers are pressed to the point of absolute refusal, hydraulic jacks are used to raise the foundation in multiple locations and a concrete cap and steel shims are placed between the top of the pier and the foundation. The jacks are then slowly released allowing the weight of the foundation to rest on multiple piers at the same time, insuring that the weight that each pier supports is only a fraction of the weight
that was used to press it into place.

Use of pressed concrete piers is the most popular method of foundation repair and probably accounts for more home foundation repair installations than all other methods combined. It is effective in most scenarios and is the only solution in areas where there is no bedrock or soil dense enough for other methods. It also usually costs less than other repair methods.

Pros
1. It is quick, usually 1 to 4 days depending on the number of piers
2. If installed correctly, it is extremely reliable
3. It is installed directly beneath the foundation
4. It is very cost effective

Cons
1. Installation can be messy because a large amount of soil must be removed in  order to provide working room beneath the foundation. Most contractors provide sheets of plywood or other materials to hold the soil until it needs to be replaced. Any excess can be used in low areas or hauled away.
2. Plants may need to be removed, but most companies will carefully remove them and replace them upon completion.