Prototype Information
The most important feature of economic maintenance is the proper drainage of the track and the entire roadway. The worst enemy of the roadbed is water, and the farther it can be kept away, or the sooner it can be diverted from the roadbed, the better the track will be protected.
To be serviceable under all conditions ditches, drains and culverts must be sized to handle the water expectations, and be secure in foundation and end construction against washing out.
Types of roadway drainage
Drainage of the roadway is effected by providing (1) ditches, (2) drains, and (3) culverts.
Ditches. A ditch is a
waterway along side a road or railroad that conveys water away from the
roadbed. A ditch design is standard for roadbeds and is found on the
roadbed engineering diagram.
There are two types of ditches: side ditches paralleling the right of way and intercepting ditches located along berms and embankments.
Drains. A drain is a waterway that conveys ditch water away from the roadbed or to permits the escape of rain water, melted snow or springs draining toward an embankment. There are three types of drains, box drains, surface drains and french drains. Box and surface drains are used to collect surface water and focus its discharge off the roadway. French Drains collect subterranean as well as surface water.
Box drains. Box drains made of plank of durable lumber, like cedar, are admisible for small cross drains where the depth under the track is not sufficient for masonry or pipe culverts.
Surface drains. A Surface Drain (area drain) only collects surface water.
French drains. French Drain collects subterranean as well as surface water.
Culverts. A culvert is an opening
through the roadbed wth a depth of roadbed over it. Although it can
resemble a bridge in some cases, the difference is that a bridge
replaces an entire section of roadbed. There are four basic types of culverts, Open, Pipe, Box and Arch.
Open culverts (also called beam culverts). Where the track crosses small rapid streams which wash down large quantities of drift, and the track ia close to the bed of the stream, it is sometimes necessary to construct an open culvert, in order that the opening may be accessible for cleaning out when it becomes filled or obstructed.
Formerly it was much the practice to construct such culverts by merely laying two stringers across walls of masonry or heavy sills, to carry the rails. Such openings in the track are not to be advised, as a derailed car or truck running into the culvert can wreck the train. Where an open culvert is unavoidable a standard bridge floor should be built over the opening.
Pipe Culverts. For small culverts vitrified clay pipe and cast iron pipe are in extensive service. In shallow embankments, where there is not sufficient height to build a masonry culvert, pipe is commonly used, while on some roads, vitrified pipe is used under banks of considerable height and cast iron pipe under banks of almost any height. The chief considerations in the use of these materials are cheapness and the rapidity with which they can be laid. In filling open culverts the use of pipe affords a convenient means of maintaining an opening, and iron pipe is extensively used inside old wooden culverts that are about to fail. Vitrified clay culvert pipe is used in sizes up to 36 ins. (and even 48 inch.) diameter, although many roads limit the maximum size to 24 inch diameter and some roads have established 18 inch diameter as the largest size.
The quality used in railroad culverts is
known as "extra thick" or "double strength" pipe, being 25 to 33 per
cent thicker than the clay pipe commonly used in residential sewers. The standard
thickness of shell for railroad culvert pipe is one twelfth of the
inside diameter of the pipe, while for sewer pipe the standard
thickness is one fifteenth or one sixteenth of the inside diameter.
Box Culverts.
- Timber Culverts. In districts where timber has been plentiful it has been used in culverts a great deal, especially where difficulties have stood in the way of delivering permanent materials at the site of the culvert in time for the graders. In timber countries such culverts ran be quickly and cheaply built, and under certain circumstances such construction is undoubtedly economical. As most kinds of wood placed in the ground will rot out in 8 or 10 years the larger number of timber culverts have been built only with the idea of temporary construction.
- Masonary Culverts. Masonry
culverts of suitable weathering brick, stone or concrete,
The WWSL
See 4.1.8 Ditches, Drains and Culverts for more information and construction details.
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