![]() An arched bridge channels the weight from above to the foundations below. A newer method today supports the spans using cables anchored to the ground on either side of the bridge.Īrched Bridges are one of the oldest forms of bridges. The frame is removed after the stones are in position. This allows the stones to be put in position. Before an arch can be built a wooden frame is built. For years, engineers used a technique called centering, in which a wooden form supported both spans until they locked together at the top. The stone is built up on top of the form until the arch is complete, after when the form is knocked out or, sometimes, burnt awayīuilding an arch bridge isn't easy, since the structure is completely unstable until the two spans meet in the middle. How arch bridges are built The wooden form, or template (in brown). The resistance to slipping between stones was provided by the compression force and the friction between the stone. The surfaces of the stones used in the semicircular arches constructed by the Romans were cut, or "dressed,'' to make a very tight joint it is interesting to note that mortar was usually not used in these joints. If the foundation of the arch should move, the compressive forces between the wedge-shaped stones may decrease to the extent that the arch collapses. It is common to use very heavy walls (buttresses) on either side of the arch to provide the horizontal stability. (That is, the stones are forced to squeeze against each other.) This results in horizontal outward forces at the springing of the arch (where it starts curving), which must be supported by the foundation (abutments) on the stone wall on the sides of the arch. The stability of this true (or voussoir) arch depends on the compression between its wedge-shaped stones. Ruts in the path prevent the use of strollers, however.The semicircular arch developed by the Romans was a great technological achievement in architectural design. The rails and ties have been removed providing a wide walking path. It is constructed on an abandoned railroad line, the "Red Line," on which trains traveled from Acton to Nashua. From there the walk to the bridge is level and only about a half-mile long. ![]() LocationYou can park near the sign on Cold Spring Road, which is just north of the intersection with Forge Village Road. The Stone Arch Bridge area is administered by the Westford Conservation Commission. If you are continuing from the Tom Paul Trail at Pine Ridge Road, proceed through the Spalding Town Forest to the Stone Arch Bridge trail head. You can actually walk all the way to the Stone Arch Bridge from Westford town center on the 2.5-mile Tom Paul Trail (see also full-length map). You might want to bring along binoculars and a birding guide. Shortly before the trail end ends at an active railroad crossing, another kiosk was built in 2021 by Scout Jack Sielian. In late fall, the brook hosts many species of migrating ducks. This is a short, hilly loop trail which affords nice views of the brook’s north side. A little further along the main trail, on the right, the Stone Arch Bridge trail is marked. Notice the beaver dam built right next to the bridge. To fully appreciate its beauty, you need to continue on and take a trail to the right which angles backwards to the bottom of the bridge. The bridge was built by the railroad in 1872, and was constructed entirely of huge granite blocks, without mortar. ![]() The main trail crosses over the top of the Stone Arch Bridge. Along the bird sanctuary trail, there are nesting boxes and benches erected by Eagle Scouts. This is a good place to spy wood ducks, red-winged blackbirds, kingfishers and a beaver lodge. This short, hilly trail loops around a peninsula which juts out into Stony Brook. On your left, a trail to the Russell Bird Sanctuary is marked. Also look for red fox hunting mice on the hill.Īs you continue on the walk, you will pass a vernal pool on your right, which in early spring, may be full of “quacking” wood frogs and singing spring peepers. The birds have taken up residence and one can now observe vibrant bluebird pairs perching on the hill’s grass and weed stems. Trashmore,” but at which a resident has erected a sign naming it “Bluebird Hill.” This caring individual has erected bluebird nesting boxes on the dump’s vent pipes and also around the edge of the hill. On your right, you will pass the old, capped dump, which residents used to call “Mt. The primary access is on Cold Spring Road, next to a large kiosk.
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