How to fix sunk pavers and discolouration?

[antrix_bansal]

sunk inHi 

i just had a paver sunk in as i was walking over it. I did not trip so i am safe. But that made me look around and i saw some pavers have moved quite a bit attached photos. Also i tool some photos from below and looks like sand soil has just eroded but no sure where did it go as there was soil in all 4 directions. 

2) secondly , i have these brick pavers adjacent to these pavers , which when pressure cleaned and sealed were all looking good but in 4 weeks they all have become discoloured and gone dark and i am not liking the look of it. Could this be from a leakage  of water somewhere ? 

Is there a bigger problem here ? 

[EricL]

Hello @antrix_bansal 

In the interest of health and safety I suggest not walking on your pavers for the meantime as parts of it may be compromised.

It appears that water has entered the sand base of your pavers and is slowly washing it away. This is why one of the pavers has sunk, the sand base was gone and only the paving sand at the sides was holding it up. In order to repair it properly, all the pavers must be removed and the source of the water leak must be addressed. Once the water leak is repaired the sand base can then be re-laid and the pavers can be put back in. 

In regards to your discoloured pavers, it's possible that water has affected it as well. If water is present underneath the pavers mould could possibly infest the pavers. Thereby producing that dark stain on the surface. I suggest investigating and lifting a few pavers as well to see if the sand base is waterlogged. If it is, the source of the water again must be addressed.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

[antrix_bansal]

Thanks again Eric. Is there a moisture meter or any scanner that can help me to identify water leakages? As this may not be from supply line. Is there a possibility that it may be damaging the slab and foundation? 
also could this be coming from my neighbour property as i have noticed their water meter always keeps on ticking always? 

[EricL]

Hi @antrix_bansal 

The only way to find out is to track the pattern of the drain on your sand foundation. I suggest engaging the services of a leak detection specialist that offers thermal scanning. You will see the cooler parts of your paved walkway which will indicate where water is settling or passing through.

Eric

[Dave-1]

Good morning @antrix_bansal 

Going through your photos a few times there definnetly seems to be a very shallow dip at the darkest of the mould, it is also inline with the paver that has collapsed (The exit from the catio towards the pool photo) I also cant see any drains across the area other then the airvents for your house.

Id say the excess water has found the easiest path and slowly eaten away the sand until collapse, And like @EricL I would suggest to lift the pavers to see where and how far the errosian extends. It may head back to a cracked storm waterpipe that has been filled with leaves, excess water with no drainage over the pavers but you wont know until the pavers get lifted. If you dont lift all of them and only stick the the ones heading away from the hole then you may find there is a similar situation elsewhere down the tarck. You could tap them with a broom handle but im not sure how confidant I would be with the sound effects.

Because the darkest mould is in a long straight run is why I am thinking the water has taken the easiest path, where the sand is going to is another question. Just had a look at your pool, do you have to constantly top it up by any chance?  Its all in that straight line from back door towards the pool.

Dave