When excavation became mechanized in the late 1800s, nearly all excavation was done by the venerable steam shovel. Starting out as part-swing railroad shovels, they evolved into fully revolving types and, by the 1920s, became popular with the general contractor. These versatile machines could be adapted for clamshell, shovel, dragline and crane work. There were early efforts of so-called trench diggers, but their complicated designs failed at the first sign of hard digging. Reliable cable backhoes were still a decade away, so contractors had to resort to the tried-and-tested cable shovel—but fitted with long sticks for trench work.
Historical pictures depict heavy steam shovels perched on timbers across trenches with workmen laying pipe below—a situation that would trigger a lot of safety violations today.
But the practicality of digging trenches with a shovel was all wrong. The weight of the shovel would aggravate any instability in the trench, not to mention vibration that would cause loose rocks to fall onto the men working below. Shovels would sometimes fall into the trench when they slipped off the timbers. And think of the labor required to move and place all that heavy lumber. To reduce labor, some manufacturers offered trench shovels with extremely wide undercarriages to straddle the trench without using timbers. But these machines were difficult to steer and involved a major strip-down when it came time to move to the next job.
The geometry was all wrong, too. With such a long stick dangling in the bottom of a deep trench, hoisting the dipper by ropes from the short regular-length boom seriously reduced breakout force at the dipper teeth. Operators had to learn special techniques such as letting out enough hoist rope to allow the stick to be crowded out to its fullest extent. And they had to maneuver the dipper when out of the trench so that the back end of the stick would not strike the cab. It was an inefficient and awkward method to dig trenches. Thank goodness for the introduction of hydraulics and the modern simple backhoe.
You can read more about the evolution of construction equipment in Keith Haddock's illustrated book "The Earthmover Encyclopedia," available in book stores. Also, consider a membership in the Historical Construction Equipment Association, www.hcea.net.