concrete-blockretaining-wall
Some retaining walls from the home improvement store stated that Maximum Wall Height is 2 feet. For example, Tranquil Olde Manor Concrete Retaining Wall Block from Lowes. My question is that why there is such limitation and if I can do some "workaround" to get it to stand up for 3 feet instead? I mean if I glue them and have proper crushed rock / drainage, I don't feel like 3 feet would cause any issue.
Can you give me some suggestion on why or why not? Thanks
The blocks you linked to are more for decorative purposes; one or two courses around flowerbeds or trees. What you're going to need for 3'-4' of retaining wall is something like this:
This is engineered block from http://www.anchorwall.com (I'm not affiliated; it was the first thing that came up when I Googled "Retaining wall blocks"). As you can see, they (and most other providers) can put that "hand-chiseled" look on just about any type of manufactured stone, and color it to your liking, so you should be able to get pretty close.
Understand that a wall like the one in the picture will probably run you between 15 and 20 grand, installed. On top of the blocks and the labor, there is a LOT of prep work that goes into building a wall like this. You have to consider grade on both sides of the finished wall, water drainage (water will sink into the soil and collect behind the wall), as well as build a proper foundation beneath grade (this particular wall represents maybe about 20 TONS of stone, so it needs a very solid base of compacted crushed gravel to prevent shifting and sinking). And yes, you need all of this, because if this wall moves, the soil behind it moves, and then whatever that soil is supporting (like your house) will move.
When it comes to cutting block, you don't need to cut it (but cutting a score can be helpful). Using a rock hammer (and perhaps a chisel) to break the rock is the way it's done.
The method for shaping rocks is kind of simple, but a video is a better way to describe it... so here's a few youtube videos about shaping rocks.
Rock hammer (more like what you're working with)
Otherwise (if you are adamantly opposed to breaking or shaping stone), you could build a form and pour a concrete joint (like in the shape of a Y). If that's the plan, I would probably start with this, then lay the rock.
Also, a suggestion to make it look a little better might be to make an exposed aggregate joint. There are several ways to accomplish that, but it's not really relevant here.
Best Answer
This is about load bearing and claims. The pressure associated with 2 ft of dirt is probably well within the load bearing specification of the blocks in question. 3 feet may not cause any issue, but you cannot hold the manufacturer liable if it collapses and/or if someone gets hurt.
If you exceed the manufacturers specifications an inspector might have a problem with it too. I would recommend adding weep holes, french drains, and possibly a deadman. And since much of the weight comes from moisture, the backfill could be gravel, to improve drainage. In fact there are lots of ways to shore-up a retaining wall, but the onus would be on the "engineer" if something were to fail.
Here's a good picture of some retaining wall features. Source: http://www.fairfaxcounty.gov/nvswcd/youyourland/soil.htm
Edit- A tie back is used on block walls. Screw types and anchor plates are common, but there are probably many ways to accomplish the act of tying or holding the wall in a similar fashion.