The walkway from the driveway at basement level comes up to the first floor entry in a series of broad steps along the front of the house. It was constructed using 6x6 pressure treated timbers making a frame holding brick pavers. It came with the house when I bought it 15 years ago. The pavers are constantly sinking. I've redone the walkway 3 times bringing the pavers flush with the timbers. Three years ago I excavated all the crushed stone and sand all the way down to the clay soil underneath, compacted that with a hand tamper, then tamped down layers of crushed stone and asphalt leaving only 1/2" of sand to screed for the pavers. In the past three years the pavers have sunk 1 to 2". It's time to do something again, and I'd like to have this be the last time.
Any suggestions one what to do? I don't see signs of material washing out. And the timbers don't seem to have sunk visibly.

hire someone to pour concrete. Expensive, but the only way to really fix it for good.

This all depends on the size of your area.
The wood should NOT be holding your pavers in, it should merely be a border decoration.

You need to remove wood, excavate all down to soil, then remove three inches of soil,compact with power compacter, fill with crushed rock, compact with power compacter until they are at the desired height to add 1/2 inch sand on top of the crushed rock, they pavers are 3/8 of an inch above border, then power compact pavers till they have settled the 3/8s of an inch.

Replace wood.
Sweep dry coarse sand into the cracks between pavers.

This is at best an abstract of how to do it so it last for years, but you need some way to be able to screed rock in and not just go by guess and by gosh.
We redid a lot of paver sidewalks but with rare exceptions the base was set on sold soil so we mearly added fresh base and sand.
The fact yours is sinking means the sub-base was never compacted or has a soil that is still composting.
If the above is true, you will have to remove soil till you are down to a non-composting level which could be as much as a foot.

yeah you could also have old tree roots in the area breaking down? If so that can cause the sinking. Does this spot get along of water flowing or pooling around it, that might be causing it too.

Thanks for all your answers.
The walkway came with the house so I don't know the construction. I'm thinking I need to excavate a section and find out what support the timber frames have, if any. I suspect that the 6x6 frames are supported somehow because they don't seem to have moved relative to the house in the 15 years I've been in the house yet the pavers and fill keep going down around 1/2" per year, approx. From the last time I fixed it, I dug down to soil which seemed to be clay. I tamped the crap out if that with a hand tamper. It sounds like I may need to excavate some of the clay as well. I'll definitely rent a jumping jack tamper this time.
There is also a sink hole in another part of the front yard that continues to drop over time. I filled that with fill dirt 10-12 years ago but it's now as bad as it was. I'm suspecting there may be some underground water action, except that the house and adjacent areas show no signs of settling.

giametti, welcome! Do you live in a city or county, which ever it is you can go to their website or into their offices and ask to see what your property was from the time
it was built and any improvements. GIS information should be on their sites. They
should be able to help with the soil type also. It just depends if they have permits for the said walkway or not. A site plan should be on file of your property. Hope this will help.

Water, where I live, water runs underground, things sink into the soil and just keep sinking, the water keeps it from ever compacting - watershed type soil. The lighter your walkway, the slower the soil will sink, I believe

giametti said: Thanks for all your answers.
The walkway came with the house so I don't know the construction. I'm thinking I need to excavate a section and find out what support the timber frames have, if any. I suspect that the 6x6 frames are supported somehow because they don't seem to have moved relative to the house in the 15 years I've been in the house yet the pavers and fill keep going down around 1/2" per year, approx. From the last time I fixed it, I dug down to soil which seemed to be clay. I tamped the crap out if that with a hand tamper. It sounds like I may need to excavate some of the clay as well. I'll definitely rent a jumping jack tamper this time.
There is also a sink hole in another part of the front yard that continues to drop over time. I filled that with fill dirt 10-12 years ago but it's now as bad as it was. I'm suspecting there may be some underground water action, except that the house and adjacent areas show no signs of settling.

Continual sinking hole, most likely, means a large tree root, or, as I found where I am now, still not sure which, a large old outhouse pit, or a dry well.
I went out one morning and part of my garden had become part of an over six foot deep and wide circular hole.

So did any of your pavers actualyl fall into a bit of hole?
You could have, many inches to over a foot under the clay, some thing that is buried under fill and is not composting/rotting.
I put in paver stone patio/walk fifteen or so years ago; I put in six to sixteen inches of crushed rock base (deeper where it was on the edge of a hill, and suddenly , about five years or so ago, in one area the pavers started tipping and falling. (it was an area that had once been a gravel car park).

I pulled the pavers up and there was under the pavers a canyon that was from two to six inches deep, and wide, that started where fancy brick formed a fern garden and ran/stopped under a side-walk put in before I put the pavers in (not by me).
I fixed that, and few years later brick on the other side of the side-walk did the same thing plus the ones I had redone were bulging up slightly, so I ended up pulling brick on both sides of the side-walk, filling in another canyon and chopping up and removing some cement (powder when put in) from the other repair. (I filled the area with polymeric sand.)

I have no idea what is down there (I assume as dangerous as that is, it is a rotting root) but now I watch those pavers carefully.

If I were you I would pull the top section, a middle section and the bottom section and see if there is a channel under there that just disappears into the soil at one point. (where my cavern ended I poked hard with a rod but hit solid dirt, not a hole like I had expected.)
Your timbers look like rail-road ties, probably laid fresh when new.
Have you ever pulled one up before?
Whom ever did it may have put some form of dead-man under them so they would not move.

After you pull the pavers dig down, as far as you can with a shovel in each area, that will give you an idea of what is down there. (When I put my pavers in , I found a garbage dump from construction when the over one hundred year old house modified decades ago.)