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Speaker 1: You're listening to a podcast from News Talks be follow

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Speaker 1: this and our wide range of podcasts now on iHeartRadio.

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Speaker 2: We have been talking broadly about landslides and landslips. How

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Speaker 2: do you assess the danger? We're keeping it away specifically

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Speaker 2: from the landslip in Mount Morganui because we don't have

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Speaker 2: the details and obviously that recovery and rescue operation is underway.

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Speaker 2: But to chat further broadly about landslides and landslips, we

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Speaker 2: are joined by Andrew Stalt. He is a geo mechanical

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Speaker 2: engineer at Auckland University. Andrew, very good afternoon to you,

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Speaker 2: and thank you very much for your time.

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Speaker 3: Hi Taylor, thank you for having me Andrew.

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Speaker 4: It's Matt here as well. How are you today? Now?

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Speaker 4: How do you spot a bank or a cliff that

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Speaker 4: might be about to slip.

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Speaker 3: There's a few things, so to give it away. The

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Speaker 3: first is, well, if you look at the slope itself,

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Speaker 3: if it's step thirty five degrees, pretty hard to hike up,

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Speaker 3: that might be a slope that could business suceptible. And

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Speaker 3: it's usually soil slopes at that and you might see

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Speaker 3: a few things. You can look up at the slope

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Speaker 3: and what we call a scarp. So at the top,

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Speaker 3: if a slip is starting to happen, you might see

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Speaker 3: evidence of cracks forming at the top of the slope,

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Speaker 3: indicating that mass is going to come down and move

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Speaker 3: at you closer to the ground, closer to you know,

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Speaker 3: and where we might have houses, more flat ground, you'll

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Speaker 3: start to see the soil slumping. You might see if

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Speaker 3: you have a retaining wall it's starting to tilt more

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Speaker 3: towards well down slope. You might see cracks forming in

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Speaker 3: the ground at the toe or in your pavement, in

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Speaker 3: your your your concrete backyard. Yeah.

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Speaker 4: What role do trees play in slip Prevenchin We've been

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Speaker 4: talking about this a bit today and what are the

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Speaker 4: best trees to stop slops?

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Speaker 3: In New Zealand, you kind of have different two different

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Speaker 3: types of slope failures that you're kind of worried about.

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Speaker 3: You have the very near surfaced ones where the soil

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Speaker 3: is being eroded away or carried by water as you know,

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Speaker 3: slips along the surface, and so trees and vegetation are

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Speaker 3: actually great at helping to hold those slopes together, preventing

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Speaker 3: those what I would call a shallow failure. And so

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Speaker 3: I don't I don't know what specific trees would be

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Speaker 3: the most beneficial, but you want things with really sturdy,

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Speaker 3: strong roots. The trees will be a little bit more,

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Speaker 3: they won't be as helpful. And the more deep sleated landslides,

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Speaker 3: the ones that sometimes you see, the really deep curving

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Speaker 3: surfaces that you might see, you know, on the roadslips

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Speaker 3: when you're driving by, the roots aren't deep enough to

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Speaker 3: really interact or to help stabilize that those deep seated failures.

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Speaker 4: Yeah, and what role does a geotechnical engineer have and

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Speaker 4: this whole business across the country in terms of adentifying

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Speaker 4: slips and installing slip prevention.

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Speaker 3: Yeah, so you're geotechnical, Well, they'll look for a few things.

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Speaker 3: They'll try to figure out how strong the earth is.

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Speaker 3: So if it's soil, they'll look at its friction, its strength,

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Speaker 3: ability to hold together. They'll look at the geometry of

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Speaker 3: the failure. So if the slope is really steep, that's

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Speaker 3: just something that at least when I'm even just driving

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Speaker 3: by on the side of the road, I'll look and say, yeah,

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Speaker 3: that's a little steep, little suss And so that's when, yeah,

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Speaker 3: your geotechnical engineer will look at those issues. The other

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Speaker 3: thing they might help do is if you're looking at

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Speaker 3: retaining a slope or if you're planning on cutting a

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Speaker 3: slope on your property, talking to a geotechnical engineer will

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Speaker 3: help assess that water is a big thing that really

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Speaker 3: drives these failures. As we all know, we have these

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Speaker 3: rainfall events and then we suddenly have slips all over

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Speaker 3: the country.

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Speaker 1: Right.

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Speaker 3: Yeah, and so the water does two things. It's increasing

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Speaker 3: the load on the slope, so basically the soil weighs more.

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Speaker 3: The other aspect is that the soil partially gets the

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Speaker 3: strength from friction, and when you add more water into

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Speaker 3: the slope, it's temporarily kind of pushing those grains a

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Speaker 3: little bit apart. And so geotechnical engineers, if you look

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Speaker 3: at the side of roads, when you're driving along the

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Speaker 3: motorway and you see retaining walls, there's almost always drains

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Speaker 3: installed at the bottom of the slope or a retaining

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Speaker 3: walls just to help or leave that excess water pressure.

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Speaker 2: Makes a lot of sense. Yeah, absolutely, Andrew, We've only

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Speaker 2: got about thirty seconds left. But are there some good

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Speaker 2: places people can go if they want to find some resources,

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Speaker 2: get some more information.

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Speaker 3: Yeah, so there's an ongoing research projects where we're trying

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Speaker 3: to identify these landslide hazards. Hore Tiri Retue Penoa Sliding

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Speaker 3: Lands program also for this general so we're looking at

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Speaker 3: where these landslipes are likely to happen in the face

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Speaker 3: of climate change. Also, I recommend looking at Tokatoake. The

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Speaker 3: Natural Hazards Commission has great advice on what to look

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Speaker 3: for and then after a slope stability issue happens, what

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Speaker 3: you can maybe do to help help solve your issues.

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Speaker 2: That's brilliant. Andrew, thank you very much for your time.

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Speaker 2: Really appreciate it. That is Andrew Stok, GEO mechanics engineer

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Speaker 2: at Auckland University.

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