The corner of 18th & Monroe at the time this photo was taken in 1928 was the site of a gas station (see the NoNox sign) which employed my father in the late 30's when it was Hite's Shell operated by Romuald T. Hite. In the 60's Mr. Hite retired and sold the business to James A. Fitzpatrick. Both my brother and I worked for Fitz in the late 60's. Of note, in addition to the food chain stores in view, there was a District Grocery Store on the NW corner of the intersection. In the 50's and 60's it was a vibrant little business area.

Collapsible forms are a quick way to create tunnels or sewer piping. Dig a trench of the desired depth and proper width. Pour a concrete footing before or after, plop the forms in place and snug them end to end. Pour concrete, wait. Collapse the forms, and pour the floor. You now have a sewer or raceway to run water, gas, electric, telephone or even liquid fuel lines. I think the floors would be poured after as the arc of the form collapsing would need more height to have clearance. Either that or the floor would be cast with 'curbs' to set the forms on and have clearance to collapse them at the bottom.
In Chicago there was a complete delivery 'small gauge railroad' underground allowing business to be supplied without surface traffic interference. The archways appeared similar.

The wooden forms look to be centering for the arch of a brick culvert or sewer tunnel. They seem to be hinged in the centre, to allow them to be removed after the arch is built over them. But no sign that anything so extensive is being built.

Could almost see them used for sub-surface work when road needs to be kept open, but their shape would require tons of extra work.

According to the volume "The Gas Age" from 1920, which I found on Google, S.W. Barrow was a contractor in D.C., installing gas lines, water heaters and the like. I take it that the photo depicts one of his projects.

The location is 18th Street N.E., just south of Monroe Street N.E.

An interesting puzzle, as I have no idea what "S.W. Barrow" refers to. I searched the LOC site for S.W. Barrow, and found one other image. In that image, a street lamp with "18th ST N.E." is visible under high magnification, as well as a brick corner building with "3500". With that information, I was able to find the still-extant corner building at 3500 18th St N.E. Amazingly, the old A&P building(s) are still there, although the "Piggly Wiggly" down the street is long gone.