This week, TME Looks Back: Vietnam examines “Culvert Expedient in Vietnam” from the July-August 1965 issue of TME. Published under Military Engineering Field Notes, a section of the magazine dedicated to short, technical briefs from military engineers in the field, author Capt. Charles Ogren of the Corps of Engineers details the solution to improving drainage so that a key road was able to remain open.
The article appears below in mobile-friendly form.
In the summer of 2016, SAME will publish a special issue of The Military Engineer commemorating the service and contributions of military engineers in the Vietnam War. As part of the run-up to the publication, we will be featuring on Bricks & Clicks a special series entitled TME Looks Back: Vietnam featuring past articles, photos, advertisements, covers, and other material that first appeared in the magazine during the 1960s and early 1970s. [The TME editorial staff welcomes input as we develop the Vietnam Commemorative Issue. Contact Stephen Karl at email@example.com for more information or click here to contribute editorial content. Contact Stephanie Satterfield at firstname.lastname@example.org for sponsorship/advertising inquiries.]
Culvert Expedient in Vietnam
By Capt. Charles T. Ogren, USA
Because of a drainage deficiency, runoff from the first rains of the winter monsoon threatened the only road to an outpost of the Vietnamese 25th Infantry Division. The 25th Engineer Battalion of the division solved the problem by constructing an unusual expedient culvert.
The road, which was adequate during the dry season, consisted of a stable subgrade, a strong base course, and a rolled lateritic surface. On both sides of the road, at different elevations, lay rice paddies which were kept flooded most of the year. The elevation of the road above the irrigation water in the higher paddy was about 30 inches.
When the heavy rains came, water from the paddy on the uphill side spilled over the road, damaging the surface and base course. The installation of culverts was necessary.
Corrugated metal pipe was available, but only in half sections of 36-inch diameter. Building culverts of this material posed some problems. The installation of a conventional 36-inch culvert with the required 18 inches of cover, without raising the original road grade, would place the invert 24 inches below the normal water level of the higher paddy. The water in the higher paddy would then drain to the lower paddy on the other side of the road, leaving the higher paddy without irrigation water. Also, the excavation which would have to be done under wet conditions to place the culvert would be difficult.
Installing the culvert with the invert 3 inches above the normal level of the higher paddy water would require a large amount of fill for cover, and would create an undesirable hump in the road. Obviously a culvert different from the conventional 36-inch diameter pipe was needed.
An expedient culvert was fabricated using the 36-inch corrugated metal half sections, M-6 steel plank, and barbed wire. A crew of four engineers bolted the pipe half sections together end-to-end to the length required to cross the road. This was like the top half of a conventional metal pipe culvert. Two men then tied barbed wire across the diameter of the pipe at approximately 1-meter intervals.
Corrugated metal pipe was available, but only in half sections of 36-inch diameter. Building culverts of this material posed some problems. The installation of a conventional 36-inch culvert with the required 18 inches of cover, without raising the original road grade, would place the invert 24 inches below the normal water level of the higher paddy.
While this was being done another four-man crew prepared the culvert bed. This was a flat surface wide enough for three M-6 steel planks placed side by side. These were the length of the culvert and sloped longitudinally to drain. The plank formed the invert of the culvert, providing a scour-resistant surface and distributing the live and dead loads transferred to it by the upper pipe section. The prepared pipe was placed on the plank, curved side up. It was then covered with 12 inches of fill and the road surface. Figure 5 shows the completed culvert.
In the construction of this culvert available material was used, earthwork was minimized, and the existing road elevation was closely maintained. The structure allowed flood water to pass without road damage, and preserved irrigation water levels. Frequent inspection of three culverts of this type was made during and after the wet season. It was found that the expedient culvert fulfilled drainage requirements. Each one remained aligned. There was no silt deposit on the invert, and excessive scour did not occur beneath the plank or in its open spaces. With this improved drainage the road remained open to vehicular traffic.
[reprinted from TME / July-August 1965]