PERMFILE64444

• Permit No: M1998058
• IBM Index Class Name: Permit File
• Doc Date: 9/15/1998
• Doc Name: MEMO-STABILITY OF HIGH PRESSURE GAS PIPELINE TELLIER GRAVEL PIT JOHNSON EXCAVATION INC FN M-98-058
• From: ALLEN SORENSON
• To: ERICA CROSBY
• Media Type: D
• Archive: No

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Landslide stabilizing options

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Landslide
laLlvallpn

Gmund surtace w
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landslitle slip Mane

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_ - Assumed ground water
_
belDre Oralninq
Eagle fliver b 50 I00 200
sal., n
'all ariaryses assume b ~ 2(I'. CPbafion = 0 as me slrengm al Ibe sli0e malarial. OGs

Slabiliry analyses'
G;r Cnnaai0ns FlGar 01 salery
I Present con0ilions no mnigalion. gmuna walar u i 00
SIIOwn
Z Fully aidinea. gmuna wales b01pw ;tact! ;IiP Plana 1 la
7 Fa 6uumss conmm~ea. grouna wale) as in Lase 14
a rnP al lanaslia! emvalaa, gmuna waiN as in I i6
Case I
The authors...
' r
Miller Bu4ovans4y
Bruce MJler is employed by Western
Gas Supply Co as the operations supervisor
.n the central Roc4y Mountain drslria of
Colorado. He has IS years' experence in
pipeline consirumm~. Held operation,
measuremem. comrol technology and
Transmission supervision He Ido4 his
undergraduate work in zooloRY and chem~
islry al Southern Ilhnors Unrversity and
graduate vudy at the University of IlLnois
and Colorado Sute UmversnY
M¢hal Bukovans4y, prinopal of
Golder Associates, has more than 30 years
experience in Reotechnical engnaeeanR
related m oval and mmmg engineering
protects in vanuus pans of the world. He
is a graduate a irchnical University of
Prague, Qechnslovakia, wish a diploma
in civil enRineomR and has a PhD in
engmecnng genlogv. alw uom Czecho-
slovakia
strain gauges was not removed from
the old, detached line that was left
below ground. As can be expected,
nu development of slgn(icant strains
has been noted by monitoring per-
formed between the time of excava-
tion to the end of 1966.
Other measures. Other mitigatng
measures were considered poor to the
aboveground installation. It is grate
possible that in the suture, West Gas
may choose to apply ~eume of them.
Continuous development of the
landslide could finally lead West Gas
to consider some of the following
alternatives.
• Installation of the line below the
landslide slip plane. The underground
installation would have to be per-
formed by directional drilling, rather
than by installation in an open cut.
Unfortunately, the cost of such an
installation would be relatively high.
• Stabilization of the landslide. This
is technically feasible because the
landslide yardage is fairly limited.
Stabilization could be performed by
dewatering of Che landslide, an exca-
vation of the landslide's upper por-
tion, or construction of a tae buttress.
These alternatives were studied and
analyzed as shown on Fig. 6.
The stability analyses are based on
the assumption [hat [he present factor
of safety of the landslide is equal to I .
As the accurate course of the landslide
slip plane and groundwater conditions
are not known, these assumptions are
only very approximate.
Increases of (actors of safety with
individual stabilizing measures are
shown on Fig. 6. II appears that the
most effective method of landslide
stabilization is dewatering.
At present, West Gas is not utilizing
any of these mitigating measures. The
area in the vicinity of Landslide 7 will
be closely monitored in the future and
potential mitigating measures imple-
mented only after long-term evalua-
tion oithe area's behavior.
Relerenc<s
I Bu4ovans4y, M , GrcenwiauA, I H ,and Malur.
G . "MainWininR A Nmural Gas Pipeline in
Active Landslides." Proceedings ul the Interna-
Imwl Conference Advances in Underground
Pipeline Engmcerinq, PL Div., ASCE, Unversitv
of w'isconsin. Madison, Aug. 2r-29, 1985.
Greenwood, LH , Bukovansky. M , anJ Maior,
G.. "Lme~MOnnurinR mslrumen6 prove ehes~
live for western U 5 areas subsea to land
slides," OGI. Feb. 1I, 1986. pp. bB '3.