[TheForge] opinions please, 2 Qs

[Jerry Frost]

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