Field stabilized earthworks consist of sand or dirt trapped inside a force bubble. The dirt stops incoming attacks in a manner similar to sandbag fortifications. The force bubble plays the role of the bag, holding the dirt in place.
The main advantage of field stabilized earthworks is that it permits a relatively weak force bubble to provide good protection over a large area. More powerful force bubbles, such as force shields, are expensive to produce, and thus it is manifestly impractical to cover a large structure such as a castle or city wall with them. On the other hand, a weak force bubble sufficient to support the weight of sand can cover such an area easily.
Field stabilized earthworks also have a second key advantage: they lack any of the limitations of force shields. Energy attacks may pass through the force bubble without interference, but are stopped by the dirt behind it. Dispelling weapons can temporarily disable the force bubble, but the sudden loss of dirt generally dislodges the weapon, restoring the barrier to full strength.
A third key advantage of field stabilized earthworks is realized when the type of dirt used is sand, particularly shifting sand. In this case, the barrier gains the ability to "heal" damage, as the sand simply flows to fill in any gaps created by attacks. This can be particularly disconcerting during siege warfare, as a wall made of field stabilized earthworks is seemingly indestructible.
Walls of this type have a particularly striking appearance, as they can be over a hundred feet tall yet lack any visible structural support. The wall looks like ground, but with a sheer vertical surface that seems to defy gravity.