I had a similar issue with the front path in my last house. The path was made up those slate tiles with mortar in between. I rented a jack hammer and split the whole thing up but to my dismay there was another layer of concrete underneath. I just laid a couple inches of sand on top of the underlying concrete, smoothed it and levelled it then embedded the new cobblestones into the sand. Grouted with ..well grout..and the whole thing worked out really well. I was worried about the drainage so I made sure the path had a slight incline so that any water build up would run off. All in all it worked out perfectly. Hope this answers your question.

Part of my training and experience as a landscape designer is horticultural construction--sidewalks, etc. I hope I can help.

Let me see if I understand you correctly--you've got to bust up a section so that you can run a pipe. Another part of the sidewalk has sunk down so low that the lawn has taken over. Do I assume that there are still sidewalk sections in place at ground level that would need to be incorporated? Why is the sunken part of the sidewalk sunken? Did a tree root or trunk die and leave a hole? Is it possible that the ground is unstable at that spot?

I took a look at your profile, and I see that you do live in an area where the ground freezes and thaws. How deeply do you think the old section is sunken? It would be great if you have some digital pictures you could post with your comments. It is possible that you could work dry-laid cobbles or pavers over crushed aggregate, or sand, as stephenm has done if you have a depth of 6-10" to work with over the old surface. Deeper would be better in your zone--we could do it here with only 6", but you would have freezing and thawing to deal with.

The bad news is that this is going to be a heavy job whether you break up the old sidewalk or just work over it with sand and aggregate. I am a die-hard do-it-yourselfer myself, but there are some projects well worth hiring help for... Pictures and other info would be really helpful!

Vicki Womack--The Landscape Doctor

You can go over the old if you add at least 2 inches of sand and a border to keep it all from spreading out. With the current cost of ready mix cement bags and the work involved.,,you might consider flag stone ready made stone.

Wow, you've all been so helpful. I don't know of any reason for the sidewalk sinking. I've been here 15 years and it just seems to be slowly disappearing. Its only dropped a few inches... just enough for dirt and mud to leave a thick layer on it. I'm trying to be a do it yourselfer now that I'm on my own and working 7 days a week...... but jackhammer? aggregate? I think that ready made flagstone, sand and grout is starting to look like a reeeeal good idea. Frankly I got excited as all get-out because I successfully installed anti-sag hardware in my gates LOL. Thanks everyone sooo much. I don't feel so alone with all this advice. Bless you all.

It is sinking because you allow water to sit on it and undermine it...It will not stop until you change the water flow.Either raise the sidwalk or divert the water.

"It will not stop until you change the water flow" i was thinking something similar. try to figure out exactly why the soil is sinking. dont put new money over bad foundation. get that figured out, then next step is conc/sand bed/tiles/bricks...whatever you decide looks best with the rest of your yard/house. it's a chance to make it look good too and enhance the overall appearance. be patient doing it. Rome wasnt built in a day! best of - mark