[TheForge] opinions please, 2 Qs

Wed Apr 10 03:37:57 EDT 2013

Good analysis Jerry!
What i fear here is water percolating down through fractured rock
to a slanted clay layer below.
The vulnerable slope's toe is completely gone on 2 of the 4 sides of us, though we are solider than talus...i think.

On Apr 9, 2013, at 5:51 PM, Jerry Frost wrote:

That's a valid consideration Bruce. Not enough folk pay attention to the subsoil conditions, not even engineers, we have plenty of examples of highway engineers ignoring some really basic rules of thumb. Slide Mountain about 50 miles north of here is a prime example of what happens when you disturb the toe of a "stable" talus slope. This is a B-A-D thing. Well called Bruce.

The soils on and below Whidbey Island are largely fines, alluvial and in some cases glacial. the "slides" are rotational shear motions. What happens is the soils above the tidal zone are resting on saturated silts and clays below the tidal zone. This is fine except for a couple problems: first, they're saturated with water and being silts and clays they're above they're plastic limit and it only takes minor changes to drive them above theyre liquid limit.

Once they're liquid limit is exceeded the soils will flow in the direction of least resistence. Normally the bluffs are directing their weight straight down and keeping the saturated soils below their liquid limit and in a hydrostatic state. What can happen and apparently ( all I have is the view of the TV coverage) did is something caused a layer below the bluff to exceed it's liquid limit so the weight of the bluff is now on a liquid bearing with no other direction to go but outwards. It'll slips on it's liquid bearing and as it flows outwards the bluff behind shears loose in a circular motion. The back of the failure moves almost directly downwards while the main body can't so it moves outwards. The bottom of the bluff at the former face is the least competent area so it not only moves outwards but is lifted upwards by the hydraulic action of the mass on the liquid lense.

Seen in cross section this forms a circular motion from the inward failure line to the former foot of the bluff in a shear. Hence the "name" Rotational shear failure.

Okay, that's just what it LOOKS like to me but without actual data it's just opinion based on years of test drilling the ground failures and reading reports. A large portion of Anchorage, downdown 3rd. Ave. and out to Earthquake park slid in rotatinal shears into Cook Inlet in the 64 quake so we had lots of data to look at.

Again, that's just what it looks like to me, call it an educated supposition.

Pete's place is a little different. They're not resting on a saturated nearly liquid lense of silt/clay. They're on incompetent bedrock overlain by clayey soils. It isn't a stable face but it's not the same situation. Sure, Pete needs to take care, especially in the monsoon season but the soils can be stabilized or are competent enough for careful abuse. Ries's advice about mounting the Anyang will distribute the impact energies enough to mitigate liquifaction. Provided Pete isn't beating long rounds dring monsoon season. Failures there are likely to be plate shear failures where a section x' deep and however wide cut loose and slide off down the face like a lawn on a slip and slide. Think plate avalance for a visual. These are often gradual events, not sudden calamities but can be fast badnesses.

Jer
----- Original Message ----- From: "Bruce ." <freemab222 at gmail.com>
To: "Blacksmithing List Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Monday, April 08, 2013 1:11 PM
Subject: Re: [TheForge] opinions please, 2 Qs

> I dunno.  After the problems they've been having in the Puget Sound
> area, I'd be reluctant to have a power hammer on a Big Sur cliff!
> 
> http://www.washingtontimes.com/news/2013/mar/28/dozens-residents-flee-puget-sound-landslide/
> 
> On Mon, Apr 8, 2013 at 4:34 PM, Jerry Frost <akfrosty at mtaonline.net> wrote:
>> Good news about selling all your facey nobes and such. Just goes to show
>> blacksmiths do have an eye for quality.
>> 
>> The Big Blue would probably fit what you do like a glove, even if it needs
>> some work, provided the price is right.
>> 
>> I'm afraid I don't have a clue about the Anyang's current value. I'd love to
>> have it but couldn't even afford shipping. <sigh> A foundation for it, even
>> on your cliff side wouldn't be a terrible problem, forget massive, you need
>> a competent foundation. That means one right for the job. I'd either drill,
>> drive and grout or drive piles and pour a cap. It wouldn't go anywhere and
>> this type  foundation would help stabilize that part of the hill.
>> 
>> Jer

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