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Railroad Drainage Design Assistance

Since it is well documented that excess water in the railroad structure is responsible for significant degradation in load carrying capacity (with resultant structural damage) it is apparent that an effective drainage system will reduce required maintenance and extend structure life.

The following discussion then will center on what are best practices to achieve the above utilizing Multi-Flow drainage systems in a variety of situations.

I. Standard rail line

A. New construction
Although the grading and compaction of the base material is the first defense against water absorption, it is also apparent that if adequate rainfall or other sources of water are available, the base material can become saturated over time. The ballast begins to push down or "bowl" into the base material resulting in a loss of both longitudinal profile and cross level.

It is therefore essential to collect and remove water, which percolates through the ballast and accumulates in the subballast and at the intersection of the subgrade.

This can be achieved by installing 6-inch Multi-Flow longitudinally, under each rail in the roadbed using a minimum 8 inch deep trench with a minimum width of 4 inches. After placing the drains in the center of the trench it should be backfilled with a select granular material (between a #10 and #30 US standard sieve) to the top. Vibratory compaction or water jetting can achieve consolidation. Outlets to daylight should be installed transversely at intervals not to exceed 200 feet. Subballast can then be placed and compacted followed by the tie/ballasting operation.

B. Grade sections
Special consideration should be given to areas of track with significant grades, as the water may tend to move longitudinally down the bed without encountering a drain line. Therefore the following remedy is suggested.

A "chevron" pattern of drain lines, which extend across the roadbed in a "V" configuration will allow the water to be intercepted quickly and brought to the edge for outlet. It is critical that the 45-degree lines, which emanate from the center of the bed, then are placed so that the drain lines outlet down-grade (downhill) from the apex in the center. A minimum 1% slope in the trenching is advisable for best performance. (The slope of the rail bed itself may provide some of the 1%).

The trench depth at the center of the bed would again be approximately 8 inches deep. While centering the 6-inch Multi-Flow in the trench the select granular material would be added to fill the trench. Again, consolidation could be by vibratory method or water jetting.

Outlets would consist of Multi-Flow end outlets with a short section of PVC pipe and a screen type rodent guard.

The subballast could be placed and compacted followed by the tie/ballasting operation.

C. Cuts
Because of the potential for runoff as well as ground water accumulation in the area where a cut exists, it is advisable to not only drain the rail bed section at that location but also to install drain sections outside of the bed structure itself. These "barrier drains" then would prevent accumulations of water and transverse movement of water in the shallow subsurface of the cut.

Ideally, the Multi-Flow would be installed parallel to the track in the lowest part of the cut.

The 18-inch Multi-Flow would be installed in a trench approximately 26 inches deep at it's shallowest and 4 to 6 inches wide. A 1% slope is advisable for best performance. After the Multi-Flow has been centered in the trench it should be backfilled with a select granular material as previously discussed. Because there is no anticipated loading over the drain system in this location, consolidation of the backfill material may not be necessary. It may be prudent however, to over fill the trench slightly to allow for some settling to occur initially.

Outlets to the drain should be PVC pipe with the rodent screens , and should occur every 500' unless the slope is over 1%, in which the length can be extended.

II. Rail yards
Another application where Multi-Flow can be most beneficial is in the railroad yard where the lack of grade can create problems with ponding water and attendant structural problems between the track sets.

Installation can be very straight forward, as most of these yards already have some type of storm sewer or culvert conduits installed which service surface inlets throughout the yard.
These can serve as outlets for the Multi-Flow collection system.

A typical installation would be to create a 4 inch wide trench approximately 24 inches deep midway between the track sets (but probably not more than 20 feet in any case). The 18-inch Multi-Flow would be centered in the trench and then backfilled with the select granular material mentioned previously, and consolidated. It may be advisable to allow 4 to 6 inches in the top of the trench to backfill with a class #5 gravel to allow better compaction for surface traffic.

Again, it is advisable to maintain 1% slope in the drain lines towards the point of outlet. Further, best performance is achieved with total run length of 400 feet or less between outlets.

If the outlet is into a culvert or drain already located in the yard as mentioned above, an inspection port adapter provided by Multi-Flow will allow the water to exit the Multi-Flow system and drop down using an ABS/PVC pipe to enter the deeper drain pipe system from the top. This is very easy to achieve and takes advantage of the high capacity outlet system already installed.

Should there be no exiting system to attach to, it may be necessary to bring the drain to a central location point and install a deeper transport pipe (PVC) to bring the collected water to a suitable outlet or city storm drain.

III. Refurbishment of existing rail beds
Because of substantial variations in existing problems, structures and materials that may be present in refurbishing situations two different scenarios are noted for addressing the problem. It is obvious that the more thorough method has a much greater chance of a satisfactory outcome.

A. Reconstruction
After removal of the rails and ties, all ballast and subballast is bladed off. The subgrade is then inspected for integrity, and any problem areas (such as bowls created by ballast encroachment) excavated, filled with accepted material and compacted.

6-inch Multi-Flow is then installed by trenching in the center of the roadbed using a minimum 8 inch deep trench with a minimum width of 4 inches. After placing the drain in the center of the trench it should be backfilled with a select granular material(between a #10 and #30 US standard sieve) to the top. Consolidation can be achieved by vibratory compaction or water jetting. Outlets to daylight should be installed transversely at intervals 200' to 400' depending on available slope.


B. Local repairs
Local Repairs refers to the installation of Multi-Flow drainage systems on existing track sections as a temporary measure to keep the track usable until a permanent fix is completed, and must be kept operational throughout the drainage installation.

This will require that the drainage system be placed at the extreme sides of the ballast section.

While this method will drain significant amounts of water from the structure, it will probably not be as successful as installing drainage in a new or completely reconstructed rail bed. The reasons for this are many and varied but include the fact that it is extremely difficult to properly define and drain the "bowls" that have developed due to poor subgrade conditions. Further it precludes identifying and repairing any serious deficiencies in the subgrade. The risk of contaminating the granular backfill is also a concern.

In this situation, the placement of the 6-inch Multi-Flow will be adjacent to, but not over 2 feet from the end of the ties, running parallel to the rail.

The depth of the trench will be deep enough so that it is at least as deep as the "bowl" of the ballast section.

Select granular backfill material would be installed around the Multi-Flow until it is deep enough to intersect the clean ballast section.

It should be noted that using some device (chute or boot) would be necessary to stabilize the ballast during trenching, placement of the Multi-Flow, and backfilling in order to prevent it from caving into the trench.

Again, lateral outlets should be used to empty the drain system with spacing not exceeding 200 to 400 feet would be preferential, depending on available space.

Any "bowls" that are encountered that are deeper than the Multi-Flow system should be addressed separately by installing a 6-inch Multi-Flow drain laterally at or below the deepest level of said bowl. These laterals should use the standard granular backfilling material.

Rail mounted equipment does exist to do this type of installation, however it would not be cost effective on relatively short jobs. Track mounted machines which can straddle the rail and run on the ties are available and would be suitable for smaller problem areas.

Although the Multi-Flow system offers significant strength and performance advantages, like any construction project, the outcome is entirely dependant upon quality installation methods and procedure.

How Artificial Drainage Works