4.1.1.2 Embankment

In 4.1.0 Right of Way I discussed how a railroad company got the land that it operates on. In 4.1.1 Roadway Roadway is planned and constructed based on the roadway engineering plan. The plan identifies all the issues involving construction, to include:

1) Geography: that is the roadbed, embankment, cuts and fills, drainage,  and

2) Track structure: Ballast, Ties, Rails, Turnouts, Track crossings (Special works), and other associated materials.

In this page we will discuss the geographic issues in roadbed engineering and construction, specifically roadbed.

In this page we will discuss roadway engineering and construction of embankments.

Prototype Information

An embankment is

an artificial mound or bank of earth or stone built to carry a road or railroad over an area of low ground. Railroad engineers see it as a low cost solution for the roadbed in preference to bridging. 

Formation of Embankments. 

Embankments are made of local materials and built in layers. Generally, stone and heavy material should form the slopes and finer material be placed in the center of the embankment. The more solid and compact the roadbed is made, the more impervious it will be and the better it will drain water and support the loads brought upon it by traffic.

Width of embankment at top

The roadbed on top of an embankment is not the standard roadbed width. Because of the possibility of shrinkage of the embankment due to poor construction material or erosion due to improper drainage, the width of the roadway is wider than the usual roadway width. Width can also be based on the height of the embankment. Without discussing the details of the formula, here are the common standard widths of embankments for the railroads in the WWSLs operational area.

On the Great Northern Railway all single track roadbed was 14 foot wide on tangents and 16 foot wide on curves. 

On the Northern Pacific Railway all single track roadbed was 16 foot wide.

On the Milwaukee Road all single track roadbed was 18 feet wide.  

On the Union Pacific the width is differentiated based on main or branch line and the standard changed over the years. In 1906 - all roadbed on embankments were 16 foot wide. In 1927 the  main line was 18 foot wide, a branch line was 17 foot wide -  with a caveat that when embankments greater than 10 foot in height the roadbed would be 24 foot width. In 1967 the main line was 28 foot wide, the branch line was 20 foot wide.

 UP double track branch line

Slope of embankment

The slope of railway embankments varies from 1   (horizontal) to 1(vertical) for rock fills to 11 to 1 for ordinary earth, and easier slopes for soft material like clay soil, when such must be used. By building up a rough dry wall on the exterior of a rock fill it may be made to stand at a slope somewhat steeper than 1 to 1. Ordinary earth will stand for a time at a slope steeper than that, but under the action of the rains, the winds and frost it will gradually wear down to about 11 to 1.

The WWSL

There is one true embankment on the WWSL. It is located in the Chehelis River floodplain just south of the Demaine Yard. (Section 4 - Chehelis River Section). 

The Satsop River Bridge South Abutment has embankment engineering in its design. 

Although not a true embankment, Polson Canyon has embankment slope engineering along the meandering Satsop River.

Project Process

Chehelis River Embankment

Engineering

The Chehelis River right of way is to be double tracked - one track for the 2nd Division main line and the second  track to be a DCC programming track (the DCC control center being located directly below this section). As such, the roadway will conform gernerally to the right of way indicated below. 

Due to right of way constraints, the outside (aisle side) portion of the embankment will be to engineering specification, ending at the fascia. The inside curve of the embankment will be sloped 1 to 1, indicating that there has been some shrinkage of the embankment over time and the relaxed engineering standards of the WWSL.

Construction  

The basic structure of the embankment is 2 layers of  2 in. extruded styrofoam xx inches wide at the base. (The embankment height is approximately 4 inches high). 

The roadbed template is laid out on the extruded styrofoam with the outermost track tie line at the 4 inch mark and the main line track at the 6 inch mark. The remainder of the right of way profile is layed out ready for cutting.

I clamped the foam panel to the section, and temporarily secured the fascia. I used a wire saw from my Boy Scout camping days to cut the profile on the outside (aisle) edge. One hand followed the roadbed line, the other hand followed the vertical line of the fascia board. 

The inner embankment was cut with a hot foam cutter to WWSL Common Standards .

The resulting embankment is glued to the base panel in preparation for laying track and scenic development.

Reference

UP Double Track Common Standard 

UP Rip Rap Protection Common Standard