I have a tendency to take on huge digging projects. Not mining projects; digging projects.
For surface digs, these are usually there to add flair to the map; such as a 20m x 20m sinkhole completely finished with stone, and with access minecart tracks to subterranean mines and such; and sometimes they are loooong minecart tunnels (a recent project saw me digging a 3m x 3m x 2800[sic]m tunnel).
The problem with a lot of these projects is that as this is on an SMP server, my access to TNT is somewhat stunted; digging takes forever.
For tunnels there's not a lot to be done for this; but for pits I'm intensely curious as to wether or not I'm using an efficient method of digging:
Usually I'll use a mix of horizontal and vertical digging; digging first down to however deep I need the pit, expanding to cover the entire projected area, and then using the original shaft to create a staircase to go back up to the surface, and digging straight down in 4×4 squares until done.
I've also tried taking off one level of dirt/stone at a time, but the problem with both these methods are that they are intensely monotonous.
Are there any other, less soul-crushingly repetitive methods that can be employed?
(Might be tangentially related to Movement and digging/mining speed.)
Best Answer
When I dug a pit to bedrock, this is the technique I used after I ran out of TNT.
Overall plan
Dig a vertical shaft down to the bottom level (use safe techniques to avoid dropping into a cave) and place ladders to climb up.
Dig horizontally to make a 2-block-high space covering all of the horizontal area you're planning to dig out. This tells you when to stop digging later, and also checks for deep caves filled with lava. (Note that lava lakes, which can occur at any height, are still a hazard.
From the top, dig down around the edges (vertically) of the area (techniques covered below). This checks for caves intersecting the region you are digging.
Having made these cuts, you now have a better idea of what hazards the remainder contains that you might encounter while digging out.
If you are not entertained by being the proud owner of a slightly floating landmass, proceed with digging out the middle.
Vertical digging techniques
Caution: These techniques are optimized for simplicity, not safety. You should get a brief glimpse of any caves but you might not react fast enough.
While standing on top stand just on the edge of one block while facing another block, and aim so that your line of sight intersects both. You want to be positioned such that both blocks are supporting you, so that when you click to mine, you remove both blocks before you actually fall.
Then hold down the mouse button. You will repeatedly mine two blocks and fall one block. When you reach bottom, you will fall 3 blocks into your previously cleared space (taking no fall damage since it's less than 4).
If you have an L-shaped set of 3 columns, you can position yourself to do the same all-at-once digging trick, but there's no way to do it with a 2×2 (since your aim can't pass through all four).