Retaining wall became damp

[Florida]

I have recently moved to a new build were the neighbours garage wall is in my garden.
There is a retaining wall along the garage that goes down in steps.
We had our garden landscaped by a professional landscaper who kept the Astro turf about 2 inches away from the retaining wall but filled the gap with shingles which went above the lowest point of the retaining wall, but only slightly. My neighbours have complained to the builders as they have water ingress in there garage & the builders are implying that it is our garden work that has caused it.
Can anyone advice that the shingles that are above the retaining wall would cause this? They are still below the highest point retaining wall but go over the slightly over at the lowest point of the retaining wall.
The landscapers we used are a reputable company that have been around over 20 years so I find it hard to believe they would do something that would cause damage to some one less property.
Any advice would be greatly appreciated

 

[Swwils]

Photo or drawing please

 

[Florida]

Have added pics

 

[BathDIY]

I am by no means an expert but I cannot see the DPC, is it under the level of the grass?

Either way, if you build up soil against a wall (especially if it's single skin) then water could well make its way through to the other side (above or below the DPC).

I owned a house where my DPD was at (slightly below) ground level and I had to dig a trench and fill with Pea gravel to prevent water from getting in. The trench was deep though not a few CM like yours.

DPC normally (as I understand it) should be at least 2 brick courses above ground level, someone will correct me if I am wrong here.

This may help you find a solution, which may be a trench as I have described above. https://www.pavingexpert.com/dpc01

 

[Florida]

We presume the dpc is behind the retaining wall as we could not see the dmc either.The retaining walk is part of our garden which runs all down the side of the garage & half way across the back

 

[BathDIY]

Have you raised the level of the ground on your side above where it was previously? If you have then it's the kind of change that might cause an issue as far as I can see.

In any case, I would call the landscapers and see what they have to say about all this.

 

[Florida]

Yes the level of the ground has been raised, but by wood not soil as the grass we had out down is astro turf. So I dont know if that changes things. The retaining wall is ours & the garage is directly behind the retaining wall, so not sure if that would protect the damp proof course. we have had the garden done nearly a year ago & the problem has just started last month. So again am confused if it would take that long for the garage to leak if our garden was at fault. Its all very stressful, Yes I think I will give the landscaper a call tomorrow & see what they say. Thanks for your advice.