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

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Paragraph 3 discussed the effect of topsoil on the stability of the fil'i..
'dhile we have found 'no proof to indicate ;.hat the topsoil was removed, .;here •
is adequate supporting data to indicate that there is no topsoil beneath the
fill. At the time of construction, reculat~ons ::ere in effect which re,uired
tfre removal of topsoil from spoil storage areas. In addition, the drill
log data and discussions contained in the Golder report (20) .do not indicate
the presence er° topsoil or oroanic matter within the area of the proposz.i
fill. it should be noted that these borings firer? taken after some portions
Of the fill hdd been Cons t'r UC ted. ARO tllc r' faCtCY' or cOnsidera L-O^ ~.: :..3t
the arid climate of the •,ves*_ern slope is not conducive Lo ti7e deveioome r of
extensive organic topsoil layers. For these reasons, :re believe the analyses
conducted svitirout the topsoil layer are adequate to rrlode7 the condition of
the fill.
As stated in paragraph 4, the use of a standard penetration test is a Trough
measure of the in-situ density and support characteristics of the granular
material. However, the method is a commonly accepted practice which has been
in constant use since it was introduced by Mohr in 1927 (8). Virtually every
textbook on aeotechnicai engineering contains relationships bet•,veen the
angle of internal friction (d) and the penetration resistance (4, 16, 17 ).
Using ;:n ang!° of .nLeYnal trlCt70n (;j) Uf 26 degrc55 fGr the COIIU`17Um
is conservative. i•7ost texts indicate a 2 angle of 28 degrees or more for
very loose sands •,vith a blow count or" 4, or less (12). The data presented
in the Golder Associates' report (2C) shows an average 61ow count .of 13 'for
the colluvium,~.,hich indicates a p angle of approximately 31 degrees (12).
l•lhile it may be true that densification through load will not increase the
pl angle to 40 degrees, there is a eenerai agreement among geotechnical •
engineers that an increase in the relative density will increase the angle of
internal friction. Terzaghi (15) discussed the relationship o-rith density
and indicated there may be as much as a 15 degree increase in ~ for granular
soils when going from the loosest tc the densest state. Regardless of
the validity of the internal friction assumptien,ihe purpose `.vas to illus- i
trace the effect of the parameter and not to suggest it is valid. In fact,
the original purpose of using such a trieh a angle in the colluvium ~das to
force the failure surface into the spoil by creating a harder foundation.
As can be observed, the opposite effect ~:ras noted, ie., the failure was
forced deeper into the bedrock. But, in the process, the much higher factors
of safety obtained were relevant to the overall analysis. These higher
factors of safety also indicate the spoil is quite stable notwithstanding the
foundation spits.
The letter also references the work by Leps and i•larachi (10, 11) where it
mas demonstrated that for a cohesionless reckfiil there is a decreas? i^
anyle of internal friction with confinrng pressure. lJhere the granular
rockfill consists of large particles with a high void ratio, the contact
stresses are extremely high and the reduction in r"riction angle •.vith higher
confining pressures may be appropriate. Uesic, et al(i8), has shown that: for
sands and granular soils a similar effect is noted. The reduction in angle
•