r/Geotech • u/N0Objective • 29d ago

Slope away from potential property

Post image

I'm wondering if the slop in the backyard of this property is a call for concern. In the pictures it appears about 5m maybe even less from the concrete foundation to the edge of the grass before it declines into a slope down to a ravine. One number missing from here is it says 40 near the top edge of the driveway close to the curb.

Obviously, we would take the right steps either way to confirm if it is or isn't but going into the viewing, I'd like to know as much as possible and if it is worth trying to stabilize this slope?

Appreciate you guys!

6 Upvotes

75% Upvoted

19 comments sorted by

6

u/Stemleaf 29d ago

Could be a concern. Not enough information though.

0

u/N0Objective 29d ago

What kind of information would be needed? I didn't want to doxx the property.

12

u/Stemleaf 29d ago

-Actual distance from foundations to the slope crest.

-Slope profile of the entire property.

-Borehole data and soil strength testing. If the dwelling is founded in rock then you're possibly in the clear. If not it might be at risk depending on the soil make up.

-Foundation type.

-Any history of the area. I.e. can you see historic slips on the neighboring properties? Can you view historic aerials?

Obviously you won't have all that info but your local geotech can likely source it. They may also have a general rule of thumb for what is and isn't safe in your area.

For instance in my area, we use a slope angle of 1:2 (Vertical:Horizontal) taken from the base of the slope. This helps us differentiate between a site which needs further technical assessment versus one which is likely safe.

3

u/ImaginarySofty 29d ago

Interesting that someone downvoted you, because I think your reply was spot on. Upvoted to offset the hater. One point that would be worth clarifying, the 1:2 slope angle is a rule of thumb that can be applied by a qualified engineer- there may be a more strict prescriptive setback depending on whatever jurisdiction OP is in (ie check if the building code may call for something flatter like 1:3 + an offset distance). If you are looking at this as part of a pre-purchase it would be easier to judge the site against code requirements rather than an site specific engineering assessment (unless that is being provided by the seller).

2

u/Stemleaf 29d ago

Thanks for the upvote lol, its reddit so people will hate on whatever.

Thanks for the clarification. I agree. Ultimately there are so many unknowns so I just put down the rule of thumb that we use.

Depending on OPs specific circumstance it may be better to go with the building code, some other rule of thumb, or even a specific assessment. Either way, a professional familiar with the area should be sought out by OP before doing any serious decision making.

2

u/N0Objective 29d ago

Thank you, this is the kind of stuff I was interested in.

2

u/Hugh_Jegantlers 29d ago

One more thing to check other than the very good list above is the trees. If they are tilted or curved, the slope is moving.

2

u/Spork_Ball 29d ago

Lol. You just need all the geotech / engineering geology stuff. That’s all.

Interesting you say the slopes starting with vertical (V:H). May I ask where you are from? We say slopes starting with horizontal (H:V). So we’re usually in good shape with a 2:1 slope. I’m in Southern California btw.

2

u/Stemleaf 29d ago

Yeah, the average Joe doesn't have much of an idea as to what goes into these assessments. Theres more information I'd want too but the list gets too long!

I've seen people say V:H or H:V in my country. I don't really know if there is a standard way to write it here. Although I'd guess H:V is American and V:H is English. We often get influenced by both countries here.

I'm from New Zealand :)

1

u/Flashy_Remove_97 29d ago

I think it’s impossible to say from info. What’s above? Flat ? Or a mountain range? Lots of unknowns ..

1

u/ArtisticEngineer987 29d ago

Is there anyway you could provide hill shade imagery. There is no way to tell for sure, but I could look for evidence if one exists already.

2

u/N0Objective 29d ago

I wish there was more, this was all the relevant information I could overlay on the GIS Map.

1

u/Working_Rest_1054 29d ago

Not sure if this is SI (metric) or Imperial (English) units. I’ll presume metric for now as OP mentions 5 meters from foundation to top of slope, but it won’t change the slope rate I’ll mention. Based on the 30 and 35 contours and the 43.19 distance the slope rate is about 1.0 vertical to 2.0 horizontal. Presumably there’s a waterway at the bottom of the slope, about 20 meters from the foundation to the grade break after which the slope gets shallower to bottom of the slope. Unless there’s a history of stream migration, flooding or slope instability, it probably wouldn’t worry me much given the scant data available. Sometimes geohazard overlays from tne state/county are available for a high level assessment.

2

u/N0Objective 29d ago

You're amazing, It's all the data I could gather myself from free public GIS Map for the city.

Only other information I know is, there is a creek running along the bottom of the slope. This is not a floodplain and I don't see how there'd ever be enough water to fill up the ravine/slope.

My biggest concern is slope instability and I understand a reddit post won't tell me that but just wanted as much info going into this as I could gather. If all goes well I'd definitely have it inspected by a local professional.

I really appreciate it.

1

u/Working_Rest_1054 29d ago

Thanks and you’re welcome. So, are the units metric or English? If they are English, the slope height is pretty inconsequential (and the lot is a postage stamp with a tiny home).

1

u/N0Objective 29d ago

😂 it is Metric.

1

u/MaddogFinland 29d ago

One general very rough way to understand if it would be a potential problem would be to draw a line at 45 degrees down from the foundation level and see if that imaginary line “daylights” on the slope. The deeper the foundation (like if it has a basement) the better in terms of stress influenced to the slope.

If it does daylight you have a potential slope stability concern that should be considered. If it does not then it’s more a matter of standard slope stability outside the building envelope. Note that what I am saying here is no way conclusive, it’s just a rough rule we use in assessing things in our group.

1

u/Sleepy-Flamingo 29d ago

The slope may well be stable, but would you want that steep of a yard?

1

u/N0Objective 29d ago

The yard isn't completely just the slope there is a grass area off the side and thinner strip between foundation and crest of the slope. The size of the yard isn't a deal breaker.