Index Home About Blog
From: (Andy Dingley)
Subject: Re: RAV4 invoice vs MSRP vs Jeep Cherokeei
Date: Thu, 13 Jun 1996 18:45:32 GMT

The moving finger of and Dawn) having

>>I sometimes drive on mud that's reckoned to be about 30' deep. 
>isnt that called quicksand??....(GRIN) 

Quicksand isn't really ground, it's standing water with a lot of mud
in it  8-)   You only get quicksand when the water table is almost at
the surface. There's enough mud in it to be marginally cohesive when
left alone, but any disturbance breaks this down and it starts
behaving as water again. If your vehicle floats, you're OK, otherwise
you're going to sink as surely as if you'd driven into a lake. They're
rare because they have no stability against erosion - unless they're
formed in the bottom of a hollow or something, the first rain will
just wash them away.

Quicksand depends on what weight you're putting on the surface (NB -
weight, not pressure). Most quicksands only do their real horrid sucky
thing if you put too much weight on them, people are OK, cattle might
or might not be, but vehicles are usually enough to start it. It's
related to the weight over an area of approximately a vehicle -
although wider tyres will reduce ground pressure over the immediate
surface, the pressure a few inches down is independent of tyre size,
unless you've got full tracks fitted.

This is quicksand for a few hours a day, when it's wet enough. It's
actually a river outlet into the sea, at an extremely flat coastline.
Although the tide difference is only a few feet,  it goes out for
miles. When the tide is in, this inlet is under water. When the tide
is right out, there's a small river to ford. When the tide is part way
in, the sea level is just below the surface of the mud and it's fluid
enough to be quicksand. 

It's noticably worse when the tide is on the way in. Although the
water isn't moving fast, there seems to be a lag effect of the water
permeating the mud. Dig a hole on a falling tide and it's dry, dig it
on the rising tide at nominally the same tide level and as soon as you
disturb the surface, there's a noticable increase in water flow. I
presume that the quite sticky sandy mud around here is much less
permeable (like mud) until disturbed, then behaves more like a porous

The 30' figure is from the length of some nearby piling. It may be
anything from 20 to 40'.

Index Home About Blog