When used to dig earth, sand, and similar things, the Shovel of the Earthmover will dig a 3x3 horizontal or vertical area of that material instead of just one block.
If you right-click on the side of a block, it will attempt to place a 3x3 horizontal or vertical section of the same block (as long as you have sufficient material in your inventory). Note this only works with earth, sand, and similar materials.
While shift-clicking, it functions like an normal shovel.
Here is a video that explains how the shovel of the earthmover works:
"Combining a wand of excavation with a thaumium shovel, you have created a peerless digging implement.
When used to dig earth, sand and similar materials, it will dig a 3x3 area instead of just one block.
The shovel can also be used for construction. If you right click on the side of a block, it will attempt to place a 3x3 horizontal section of the same material in the world as long as you have sufficient blocks in your inventory.
If shift is held while using this tool, all its special properties are suspended and it functions like a normal shovel."
You need the research Wand of Excavation first.