PERMFILE108040

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Sections 10 - 16
• Section_Exhibit Name: Exhibit 12 Experimental Part 3
• Media Type: D
• Archive: No

- c-
zone generally has a cohesion as well as an angle of internal friction. •
These piles ~•;ere quite old and did not have a topsoil cover and a:ere nc~.
graded. given piles •which svere 2C to ~!C years old were stable at the angle
or' repose. In our cpinion, there will be a zone of weathering which ccuid
extend uo to o ; eel over the long ier~, hoer?~,er, the :.:ass of .the pi e :vii 1
remain essential':y granular in nature.
':!hen evaiuatiny angle of repose as a measure of the angie of internal fric-
lion, there are certain additional aspects which should be considered. Cne
particular aspect e; some importance is the effect of cohesion. In nature
there are seldom truly cohesionless materials. Even very granular materials,
such as sands are likely to exhibit some small amount of apparen*. cohesion.
In the case of a sand, a slight cohesion may make the grains capable of
standing at a somewhat steeper angie or' repose- The apparent cohesion is
an efr"ect of the negative pore pressures (capillary attraction) or cementa-
tion and are only ohservad in fine-grained materials. In the case of spoil,
it is doubtful that there is any cohesion between the individual grains.
Thus a lower anyie of re?ose is obtained. The fine material bet~.veen the
coarse grains of file spoil will tend to act as a lubricating anent and, thus,
further icwer the ar;gle of repose. The second aspect to consider is inter-
locking of the grains. Blasting tends to create a sharp-edged material
where interiockina is r=lativeiy high. Interlocking does not appreciably
afr"ect the angle of re?ose (14}, but increases the angle of internal friction
of the mass as a whole. Accounting for these two factors, it is reasonable
to conclude *_hat the use of the angle of repose for granular material, such •
as spoil, to estimate she angie of internal friction may be crude, but con-
servative. P.ecently, Blight and Steffen (2) and Blight (3) reported the
angle of repose fora given ~dasie material varied from 37 to 40 degrees, but
the angle of "shearing" resistance :~ithin the body of the r"ill teas between
~l degrees and-'.~ decress.
The commenter mentioned "If the character of the spoil material was co-
hesionless, the research performed tc date, suggest 'that at the depth of
the fill (loading) increases the ample of internal friction of progressively
deeper materials will decrease". Research presented by Warachi> et al. {11}
suygests that this may be true for cases of relatively high confining pres-
sures. This is predominantly an effect of contact stresses breaking do~,vn
the intact material. Examining the data presented by P-larachi (11) we find
that the angle of internal friction is decreased on the order of 4 degrees
fora confining pressure of 250 osi. or a stress of approximately BO psi
the charge is or• the order c. i decree. To determine this effect on the
analysis of the Colo•,vvo slope, we nave calculates file stresses for the
critical circles ~:rithin the fill and'ir.d that the maximum stress is on i:he
order of ig0 osi. The average stress is on the order of BO psi. Using
i~larachi's data, we find that the angle of internal frction will decrease
on the average of 1 decree and a maximum or approximately 4 degrees.
In our opinion, this reduction in shear strength is compensated for by
other effect;. 0f pri~~~ary concern in this cast, is the effect of plane
•