How to build a retaining wall levelling pad?

[sach78]

Need help in levelling the foundation of retaining wall. I am using keystone standard units to build the retaining walls but I am struggling to level the first course of the blocks. For foundation, I have used roadbase compacted to 75mm and I have used crushed stone on top of the compacted road base for better drainage. Can anyone advise if I should be using the sand and cement  mix to make a levelled pad?

[MitchellMc]

Hi @sach78,

How far off level are you? If you're not using anything to assist you with levelling, then I would encourage you to get two garden stakes, a string line and a line level. Once you know what you're shooting for, you can add sand to finish off the surface. Place a stake at either end of the trench and then tie your line between the two stakes slightly above your current gravel. Make sure the line is taught. Place the level in the middle of the line and adjust the line up and down until the level reads flat. Fill below the line with sand until you reach the line and compact it. It doesn't need to be perfect, but the line will assist you in getting very close.

Please let me know if you have further questions.

Mitchell

[sach78]

Hi Mitchell,

Thanks for your reply.

I have only placed two blocks on the pad and I am off by about 10mm and given that aggregates have an uneven surface I am concerned that by that time I finish laying all base block, I will be off by quite a bit. Do you think laying aggregates on roadbase was a good choice to build a level pad? Or, as you suggest finishing it with sand a cement a better choice to achieve a levelled pad? Thanks again

Sachin

[MitchellMc]

Hi @sach78,

If you're off by 10mm over two blocks, then I'd agree that by the time you reach the end of the wall, it will be very unlevel. I'd suggest that you need a significant amount more aggregate spread over the lower areas to raise them. Start your string line at the highest point and then fill the lower end to meet it.

I think laying aggregate on road base was a good choice, but since the soil was so even to begin with you simply haven't added enough of it to form a flat surface. It is best to create a level surface before you consider bedding the blocks in sand and cement.

Mitchell

[sach78]

Thanks for your valuable advice @MitchellMc. So one last question if I may ask, do you recommend having the sand and cement bedding on top of the aggregate or can I just lay the blocks straight on top and let gravity do its magic? 

[MitchellMc]

You can lay the blocks directly onto the aggregate @sach78. However, please be advised that if this is a larger wall that required engineering, then the plans will stipulate what base the blocks must be on.

Once you have the aggregate level, it can be helpful to bed the blocks onto sand, sand and cement, or a mortar base. This allows you to make fine adjustments to the block and get it perfectly in line with the previous one. Once you get this first layer right, the next course will be a breeze.

Mitchell