Bricks, Masonry, Asphalt and Concrete - estimating retaining wall

I am trying to build retaining wall/walls around my backyard. Came across a few big blocks from Keyastone, I think they are 75lbs but it’s going to be enough just for the first row of my wall. Next I found about 400 of the 4” or 25lbs ones. I doubt that they will look any good on top of the 8” inches, should I get enough of the 6” blocks to make another row to be placed on top of the first row? I have a hard time estimating how much of DG will I need. I live in SO California, so no frost line concerns, but how deep do I need to go with DG? I have about 125ft leangth and assuming I’d need at least 6” extending beyond the widest or the bottom block that’s 12” deep so 18” wide DG pad?
Thanks!

Each retaining wall manufacturer has their own "special" way they have the blocks interlock from row to row. Don't mix different brands or sizes just because you saved a few bucks and was able to get some blocks.

You are just asking for problems when the soil they are supposed to be retaining starts to push on the wall and it gives way because the blocks are not properly locked together.

Find a brand/style you like and go online and they have estimator links to tell you how deep in the ground you have to go, how many blocks per linear feet of wall etc.

As sgtgerryf says, you cannot mix sizes or systems.

The interlock is necessary for wall stability and strength.

I do not know which Keystone unit you are looking at, but almost all of the interlocking units/systems with the "lip" for shear resistance cannot be interchanged if you want strength and a good appearance.

There are a few systems with pins that may possibly be used with decreasing thicknesses, but they are rare and usually not cost-justifyable.

Decreasing the wall thickness does not make sense for a gravity wall since there is less weight on the bottom units, which is the critical part of the wall.

What is DG? - I hope it is not some abbreviation for a footing. Segmental retaining walls units are never placed on a concrete footing!!!! - This applies to all walls - even those that are 40' to 50' high and several miles long.

Judging from your small quantities, it appears your wall is less than 4' high. Just to be safe, you should verify that a permit is not required. If one is required, you could be forced to tear it out and you would not have any insurance coverage in the case of flooding, mudslides, etc. Southern California has soil and weather conditions that have attracted attention to all grading and construction of walls.

Dick

Thanks a lot for your help! lots of things to take into consideration.