flexible , elongated , tubular ducts or conduits are assembled above ground on transverse supports into a duct bank of an array of layers held by a plastic grid of transverse spacers . an underground trench can be excavated having substantially straight sidewalls , while excavated soil from the trench is placed on the side away from the assembled duct bank . two or more pieces of equipment , spaced apart , sequentially lift and laterally move the assembled duct bank to the trench . transverse support members spanning the trench are removed , and the assembled duct bank is lifted and lowered sequentially into the trench using a small angle of displacement from the horizontal while lowering the assembled duct bank onto transverse support members positioned in the bottom of the trench , to provide an underground duct bank . round , freely rotatable , plastic spacers in groups of four facilitate lowering the assembled duct bank into the trench . in one aspect , the ducts or conduits are connected to a concrete manhole at a sidewall through a bell - end , adjustable in length , having threads in the outer surface of the bell - end for receiving an adapter threaded on one end and adapted to receive the duct or conduit into the adapter &# 39 ; s other end .