Good morning to everyone A technique I've seen used to go under a road or surface obstruction is to dig work-pit holes on opposite sides and use a hydraulic-jack laying on its side with its base pressing against a steel-plate or block of wood positioned against the back-side of the access pit. The jack's extending-post then presses against the end of a 'penetration pipe' whose length is increased by adding additional sections.
If the soil is basically rock-free you could use a garden hose with one of those axially-thin adjustable spray nozzles set to generate a thin jet of water and feed it under the object. This technique might require a nozzle fitted on the end of a two-foot long guide-pipe to keep the path pretty straight. The eroded dirt flows back out of the hole along the hose/pipe into your work pit. As a kid I lost about 20-feet of hose digging a 'hole' straight into the ground after turning off the water and the slurry settled in around the hose... 73 Dick/w7wkr/CN98pi _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
