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APPENDIX E
EXCAVATION STABILITY M&T CHICO RANCH DINE RECLAMATION
WEST OF DAYTON, CALIFORNIA
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D(CAVATION STABILITY
M&T CHI -GO RAUCH MINE RECLAMAT O!N
MT Of DAYTON, CALIFORNIA
Submitted To:
Knife River Coal Mining Company
1.915 -North Kavaney Drive
Bismarck. North Dakota 68501.1698
Submitted By:
AGRA Earth & Environmental, Inc:
3232 West Virginia Avenue
Phoenix, Arizonas 85009-160:2
August 22,1897
AEE Job No. 7-117.000294
p I X81
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53
Q'\AGFIA
Earth & Env/ronlrientn't
QAGRA
Earth & Environmental
August 22, 1997
AEE Job No. 7-117-000254
Knife River Coal Mining Company
1915 North Kavaney Drive
Bismarck, North Dakota 68SM - f 898
Atteotiom Mr. Michael W. Pole
Manner - Engineering & Environment
Gentlemen:
RE: EXCAVATION STABILITY
M&T CHICO RANCH MINE RECLAMATION
WEST OF DAYTON, CALIFORNIA
AGRA Earth &
Environmental, Inc,
3232 West Virginia Avenuo
Phoonix, Arizona (k5oo9-15()2
Tel (602) 272-6849
Fox (B02) 272-7239
At the request of Mr. Michael W. Volo, Engineering & Environment Manager, of Knife River
Coal Mining Company (KRCI, presented herein is our letter report concerning the stability of
excavation slopes proposed for reclamation of the M&T . Chico Ranch Mine. A project
description, analysis results and reoortimendations are presented In the following sections.
1.0 PROJE T DESCRIPTION
Details of the proJect were provided by Mr. Pole to Dennis Bryan, P.E. of AGRA Earth &
Environmental, Inc. (AEE). It is understood that an aggregate pit appro)dmaitehy 1.6 miles long
and 0.2 mile wide at the M&T Chico Ranch Mine property will be dredged to a depth of about
70 feet. It was requested by KRC that slope stability analyses be performed and that a safe
slope for the. final dredging be provided.
The property consists of mostly flat, low-lying river ffoodplains with- occasional standing water.
' Chico Creek flows through the property and the water table depth is very shallow, -probably
within 2 to 3 feet ot'the ground surface in most looetions.
' 2.0 GEOTECHNICAL PROFILE
Based on boring logs for the project (AEE Job No.. 6-417-8481, dated 5 April 1996) the native
soils at the project site can be described as three -layer system as follows:
54
Engineering & Envlronmenl.-! Services
Excavation Stability AEE Job No_ 7-117-000254
M&T Chico Ranch Mine Reclamation Augkist 22, 1997
West of Dayton, California Page 2
A. To depths of 10 to 30 feet, but typically 12 to 16 feet, brown sandy clay was
encountered in the borings.
a, Beneath Stratum A and extending to about 60 to 65 feet are sandy gravel and gravelly
sand with occasional cobbles.
C. Oone.ath. Stratum 8 is low plesticlty sandy clay, .
.Based on the boring logs and the results of sieve analyses, estimated soil strength parameters
are listed in Table 1.
TABLE 1 =Estimated Soil Strength Parameters
3.0 SLOPE STABILITY ANALYSIS
The design level.earthc(uake is defined as the event that has an. exceedance probability of 10
percent in 50 years. The ground motion map produced by Frankel et al, (100)" for the
National Earthquake Hazards Reduction Ptograrn INEHRPI indicates the M&T Chico Mine site
has a peak acceleration of 0.128, as shown in Figure 2, for rock site conditions, For the soil
conditions at the site, and depending on the depth to bedrock, the peak horizontal acceleration
may vary from 0,089 to 0.129.
Typical Out alopee of 2:1 (horizontal to vertical), 3:1 and 4:1 for excavation to a depth of 65
feet wars analyzed. The typical section developed for the analysis -is in the area of N9800 and
E4200. Static, pseudo static and sudden drawdown cases were evaluated.
The computer program STABL5 (Achilleos, 1988), developed by Purdue University, was
utilized for slope stability analyses. More specifically, the J..anbu method was chosen for the
analyses. Pstimated feetora of safety are summarized in Table 2. Safety factor as a #unction
of pseudo static acceleration is presented in Figure 1. Selected details, of analyses are
"References are listed at the end of this report. 55
E-3 �. *AGRA , .
Earth A. Envlronrrtenta!
! : Excavation Stability 4 AEE Job No: 7-117-000254 n `+
M&T Chico Ranch aline Reclamation r r August 22, 1997
West of Dayton, California Page 3 '
A presented in the graphic form in Appendix A.: r The figures show the. ton most critical �he$r
surfaces for each case analyzed: -
• Y ' -0 c - L - r t
a�st4a w A'r • ` _ - _ .Ed h 6 f.,yjL�y i -d'
•'+. t 4- sa Qr y >.�. z3` .rr . {l iy ja�'42.Y}•c�'
- {' `'L' .''- 1 c,- +`` : y' . aji �F - ,*-'4_•' Yt Sr gig" _
0.06
1.00_ ' 0:69. 0.80 i 1.04 . hiAhi _ ..
1.41 123 108 .1.58 1.27
4.1 2;82 123— 1:47 -. 1.20 - .2.14 • .1.7-5
Note:.' (1) It assumed that rapid drawdown and earthquake will nvt occur at the same
time. .. _ •
(2) Did not evaluate.
t' 4.0 RECOMMENDATIONS _ Y
' Generally, minimum safety factors of 1.5,-1.1 and 1.1 for static, pseudo static and drawdown
'Based.on the analyses presented in Section 3.0, it is our.
are required for a perrii�lnsnt slope, ,
recommendation that a minimum 3:1 slope should be maintained for the MV Chico Ranch .>
' Mine project..
'
Should you have any questions regarding this letter report, please +do not ha
`
the undersigned at 16021 772=6848Ict-
.•
- R6spectfully submitted , _ ,' ,, 4 r , , �. ti � � 'x. , • ' J'�, ° `
r rt , to
u No. G 2AP�
`+
.j
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AGRA Earth & Envi �SBJ�gReviewi3d
t - - ,kQ - '� '. r * ,C • r„ Qui 1r
w No. 4652 s of��
I: Suang S. Ch h 4�. _ Lawrence A. Hans
a n
id
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Senior Vice Prset ,
r' Senior Enginae ' EXP . �.
ON
c: Addressee (3► �lF 0 IV1`\�o��
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Excavation Stability AEE Job Mo. 7-117-000254
M&T ,Chico Ranch Mine Reclamation August 22, 1997
West of Dayton, California Page 4
REFERENCES
Achilleos, 5-.,1988, User Guide for PC STABL 5M, Purdue University and Indiana Department
of Highways, Joint Highway Research Project, Report JHRP-88119, December.
Frankel, A., Mueller, C,, Rarnhsrd, 7., Perkins, 0,, Leyendeoker, E.V., Mokman, N., Hanson,
S., and Hopper, M., 1996, National Seismio Hazard Maps, June 1988, Documentation:
Denver', .Colorado; U.S. Geological Survey Open File ROPOTt 96-862;
Acceleration
:ig ure 1 ® Factor of Safety vs.. Maximum
T Chico Ranch Mine, Regan -a on
• Slope
•
2.5
• -X- 4:1i
61
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O_ . r . . • . . . . . . . . . . _•
RRcd ,
1.0
W M i
0.51
a:oo ox.2 0.04o.as 0.08 0-.1-0 0.12
L1ent—a-1 :rafiun:,n (n)
APPENDIX A
SELECTED DETAILS OF ANALYSIS
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CHICO MINE CASE 1B — SLQP:E 2:1 DEEP FAILURE
SAFETY FACTOR = L.6,33 150 RANDOM TRIAL SURFACES
Stratum A
Stratum B
Stratum. C
. 5
EMM & En-vftn.MIgntal ., !nc
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125 15.0 175 ZUU 225 ZAD 275
300 321
200
MINFs CASE 2D — SLOPE 3:1 40percent DF.A}aT.
CF3iCC
175SAF
ETY FACTOR = 1.275 FRdM 150 RANDOM TRIAL SURFACES
150
125
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S'tratum. A
100
Stat= B
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Stratum C
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