Might try a net search on "propagate bamboo".
If it were me, I would try for a more mature root stock, one with bigger taller stalks. To make it easy first cutt off the 4-5 m stalks then dig up as much of the
roots as possible. This spring the root ball will send up new shoots. Next year to establish a larger area faster, start bending mature stalks to the ground and bury as many nodes as it takes to keep the stalk down. The next spring you'll have new shoots at each node that was touching soil.
Also, instead of saying "cutt off a mature stalk and lay it in a trench" I should have said, cut a section out of a mature stalk (at least 1" diameter) that contains 3 or 4 nodes. You wouldn't need the whole 4-5 m stalk, although the more nodes the more potential for roots and sprouts.
Anyway you go you'll most likely be successful, Bamboo is not known for stubborn propagation.
hope this is helpful,
Paul