This is an interesting alternative to the typical tiered worm farm. . .
I have been experimenting with this concept for about six months now and so far it is working perfectly. I first saw the idea after watching the Olomana Permaculture and Aquaponics DVD, which is available through BYAP.
The basic concept of the system revolves around a large PVC pipe. The pipe is drilled with numerous large holes, about 10 mm in diametre, or slits, and is buried into the ground. I have been using 100mm PVC as it is about 4mm thick, (nice and strong), anything larger was too expensive.
Food is added to the chamber where the worms eat through it, turning it into vermicastings. They then tunnel through the surrounding soil, along with the help of earth worms, to distribute the castings throughout the surrounding soil. This creates viens of vermicastings throughout the soil, similar to the veins of gold in rocks. The worms then continue feeding, continuously repeating the cycle over and over again.
I've placed one tube near a few of my plants and they are all looking very healthy. I have modified and expanded the concept quite a lot and will post of variations later on.
Looking down the tube.
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Worm tube next to apricot.
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I rotate the tube usually once a fortnight or so to sever any roots etc. 
).