Appendix B (G-B) - Abridged RSF Calculation Package

SIRI
srk consulting 999 Suitonsulting(U.S.),Inc.
999 17th Street,Suite 400
Denver,CO 80202
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RSF Calculation Package [e-mail]
www.srk.com
ABRIDGED Calculation Package taken from Appendix A (Pre-feasibility Engineering Design
Report for Rock Storage Facilities A and X, Kings Mountain Mining Project Rev03) of Appendix
H (Design Reports) with Plate 1 included. Other deleted Plates and Appendices from this RSF
Calculation Package memo may be made available upon request.
To: Claudio Andrade, Keith Viles Date: April 19, 2024
Company: Albemarle Corporation From: Diego Cobos
Copy to: Breese Burnley Reviewed by: Tarik Hadj-Hamou
Colleen Crystal
Subject: Slope Stability Calculations for Preliminary Project#: USPR000576
Design of Rock Storage Facilities RSF-A and
RSF-X
Albemarle Revision #: 02
Document Number:
1. Purpose and Scope
The objectives of this calculation package are to:
• Evaluate the stability of the proposed preliminary design configurations of Rock Storage
Facilities RSF-A and RSF-X under static and seismic loading conditions.
• Support the development of mitigating design elements and recommendations to address the
potential presence of unsuitable soils in some foundation areas.
• Using sensitivity analyses, evaluate the currently available site characterization data and
develop recommendations for further characterization in later design phases.
2. Documents Reviewed
SRK reviewed the following information for the purposes of this calculation package:
• DRAFT Rock Storage Facilities RSF-A and RSF-X, Select Phase Site Characterization
Report, Kings Mountain Mining Project(SRK, 2024a).
• DRAFT Technical Report, Select Phase Rock Storage Facilities A and X, Preliminary
Engineering Design Report, Kings Mountain Mining Project (SRK, 2024b).
• DRAFT Drawing Set - Preliminary Rock Storage Facility Design, Kings Mountain Mining
Project.
• Available literature regarding regional geological and geotechnical conditions and legacy
reports provided by Albemarle, including: Report of Investigation of Tailings Dam for Foote
Mineral Company (Golder Associates, 1975) and Foote Mineral Reservoir Dam Removal
Design Report(Schnabel, 2011).
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3. Project Description
Proposed rock storage facilities RSF-A and RSF-X will be located within the Kings Mountain Mining
Project (KMMP or Project)just north of Interstate 85 (1-85), as shown in Figure 1.
RSF-A is a permanent non-acid generating (NAG) RSF constructed in the west-to-southwest area of
South Creek and to the east-to-northeast of Tin Mine Road. RSF-A will mostly be comprised of coarse
rock sourced from the open pit. SRK understands that Albemarle also plans to use the facility to store
finer-grained materials comprising dense media separation (DMS) rejects, excavated sand from the
existing legacy tailings storage facility (Old TSF; Golder, 1975), waste rock from the existing tailings
storage facility (TSF) embankment, and minimal quantities of optional off-site fine material. Both the
legacy tailings and waste rock are to be removed to make way for the construction of RSF-X, but all
materials destined for RSF-A will need to be comingled at a mix ratio that does not negatively affect
the strength governed by the coarse waste rock component.
RSF-X is a temporary geomembrane-lined PAG RSF constructed over the footprint of the existing old
TSF (Golder, 1975)and adjacent to South Creek reservoir. Prior to construction of RSF-X, the existing
tailings will be removed from the existing impoundment. The RSF will then be initially constructed with
an engineered foundation subgrade constructed with coarse materials contained within the existing
embankments. RSF-X is proposed to be constructed in two phases, with the first phase including the
contact water management pond and the southwestern half and the second phase completing the
footprint to the northeast. The RSF is considered temporary because the PAG waste rock will be
relocated to the bottom of the pit as part of site closure.
Preliminary designs for RSF-A show a total height of approximately 280 ft high with 2.5H:1V
(horizontal:vertical)sideslopes founded atop in-situ saprolite and partially weathered rock. Preliminary
designs for RSF-X indicate a total height of approximately 200 ft with 2.5H:1 V sideslopes, also founded
on saprolite and partially weathered rock.
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4. Design Acceptance Criteria
A semi-qualitative Waste Dump and Stockpile Stability Rating and Hazard Classification (WSRHC)
was completed for RSF-X and RSF-A using the Guidelines for Mine Waste Dump and Stockpile Design
(Hawley and Cunning, 2017).The WSRHC evaluates 22 key factors that affect the stability of the RSFs
and assigns a relative hazard rating. These factors are assigned a numerical rating and compared to
the maximum possible WSR of 100; higher ratings indicate a more stable configuration. The WSRHC
and associated WSR are utilized to establish appropriate stockpile operation and monitoring guidelines
for the RSFs at the KM project.
The results indicate that RSF-A and RSF-X are considered Waste Sump and Stockpile Hazard Class
(WHC) III with an instability hazard of Moderate. The selected DAC are based on the expected failure
consequence on impact to adjacent infrastructure and environmental features and are discussed in
further detail in Section 4.0 of the preliminary RSF-A and RSF-X design report (SRK, 2024b).
SRK developed the design acceptance criteria (DAC) summarized in Table 1 based upon
internationally accepted practice as well as upon acceptance criteria guidance presented in Hawley
and Cunning (2017). Although the RSF's are not regulated dams, SRK has also considered slope
stability requirements from the North Carolina Dam Safety regulations under Title 15A of the North
Carolina Administrative Code (NCAC) Chapter 02K.
The selected DAC are based on the expected failure consequence on impact to adjacent infrastructure
and environmental features.
Table 1: Kings Mountain RSF Slope Design Acceptability Criteria
RSF Slope Consequence l Minimum Fos Minimum s Allowable
Static Pseudo-Static Deformation(4)
RSF-A(north and Moderate Greater than (>) 1.3 >1.1 <24 to 36 inches
west slope) Consequence
RSF-X(all slopes) High
RSF-A(east slope Consequence >1.5 >1.15 <12 to 24 inches
and south
per 15A NCAC 02K.0208
2 Static is 1.5 for all per 15A NCAC 02K.0208
3 Pseudo-static Fos min>/=1 or> 1.2(if liquefiable soils in the foundation)under seismic loading event with 2%probability of
exceedance in 50 years(-2500 year ARP)based on the USGS Seismic Hazard Maps for seismic events with this return period
for the region where the facility is located per 15A NCAC 02K.0208.
^SRK is proposing to use a deformation-based approach comparing yield to seismic loading for both the 2475-year and 10,000-
year ARP events.
5. Ground Motion Parameters
Development of site-specific seismic hazard parameters are discussed in detail in Section 2.3 of the
Site Characterization Report (SRK, 2024a), and summarized in Table 2 below. For the stability
analyses described herein, SRK has determined the yield acceleration (ky)for each cross-section and
compared that value to the postulated shaking levels USGS 208 NSHM mapped. Peak ground
accelerations in Table 2 facilitate calculation of estimated displacements under earthquake loading
scenarios for the 2,475-year and 10,000-year average return period (ARP) events. Note that the
1:10,000-year ARP is derived from the Global Industry Standard on Tailings Management (GISTM)
(ICMM,2020)and while not strictly applicable to rock storage facilities, has been adopted herein based
on the foundation conditions.
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Table 2: Seismic Accelerations from LCI (2023) and USGS (2018)
Average Return Period Lettis PGA(LCI,2023)' USGS 2018 NSHM Remarks
Hard Rock Soil/Ground
(3,000 Surface Mean
meters per (Site Specific for Hard Rock Soil
second Vs30—500 m/s
(m/s)) RSFA and Vs30—
2,000 m/s RSFX)
475-year 0.0329 0.068g RSFA 0.056g 0.058g
0.045g RSFA
2475-year 0.088g PGA 0.172g RSFX 0.150g 0.153g Design Basis
0.1445 RSFA Earthquake DBE
Maximum Credible
0.2 g Earthquake,
—10,000-year (0.25g, 84th 0.313g 0.310g Deterministic
percentile) Maximum or PSHA
"equivalent" 10,000
year ARP event
6. Geotechnical and Stability Sections
SRK prepared five geological/geotechnical cross-sections in evaluating subsurface conditions at RSF-
A and RSF-X. The locations of the cross-sections are shown in Plate 1 at the end of the text with the
locations of relevant borings and Cone Penetration Test (CPT) probes. The five cross-sections are
included at the end of the text as Plates 2 through 6. The stability of the proposed facilities was
evaluated at three representative geological/analytical cross-sections labeled RSF-A BX-BX', RSF-X
-I' and RSF-X C-C'. The stability cross-section locations were selected based on the preliminary
design geometry of each facility,the underlying original ground grades,and knowledge of the subgrade
conditions derived from available borings and CPT probes. A detailed description of site subsurface
conditions can be found in SRK, 2024a.
The logs of the borings and the televiewer records were reviewed to assign the thickness and extent
of the geological units under each section, as further described in Section 4.4 and shown in Section
5.
6.1 Material Properties
Site and material characterization properties are described in detail in the report Rock Storage
Facilities RSF-A and RSF-X, Select Phase Site Characterization Report, Kings Mountain Mining
Project(SRK, 2024a).
• As discussed in the above referenced report, the general underlying conditions at the site
consist of four units, which from top to bottom are:
• A layer of vegetative soil and fill (natural or man-made) and or residual soils ranging from silty
clay (CL) to fat clay (CH) in the upper 5 feet. This layer is referred to as overburden in the
borehole logs. The overburdened transitions to soil-like decomposed,weathered rock referred
to as a saprolite.
• The classification of the soils in the saprolite range are predominantly low-plasticity micaceous
silt(ML)to silty sand according to Unified Soil Classification System. At the site, the saprolite
with measured SPT blow counts (Nm) of between 10 and 17 blows/ft are observed (in
televiewer logs) as having some, but minimal, relict structure.
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• A layer of partially weathered rock (PWR). The saprolites at the sites are distinguished from
the underlying PWR primarily on the basis of blow counts,with PWR being logged once refusal
(Nm>50 blows/2 inches) is recorded. The PWR is also characterized by more prominent relict
structures from the parent bedrock.
• Underlying bedrock, which varies in nature across the site, as shown of the geology map in
SRK (2024a).
The thickness of each of these units varies across the site as the rate of decomposition from bedrock
to the saprolite is variable due to the nature of the parent bedrock and hydrological or hydrogeological
regimes. The transition between units is not always clear, however, with a USCS classification of SM-
ML and generally lower blow counts (higher void ratios), the saprolites are distinguished from the
overlying residual clayey soils(CL to CH)soils. MH/OH classifications in the saprolites can vary based
on mica content.
The residual soils and saprolites in the region are the products of the chemical decomposition of the
various complex aluminum silicate minerals in the original rock (Sowers and Richardson, 1983). The
products are clay minerals, hydrous micas, iron oxides and semi-soluble carbonates and bi-
carbonates.
6.1.1 Overburden and Residual Soil
At the site, the overburden and residual soils consist predominantly of 5 to 10 feet of medium stiff
sandy to clayey silts with some localized zones of medium stiff to stiff lean-to-fat clays (CL-CH) with
measured blow counts ranging from 4 to 16 (in both current and prior 1975 borings). The design
stability analyses presented herein assume that all the residual/overburden soils will be removed, as
they are not suitable for foundation support for the proposed structures.
6.1.2 Saprolite
Saprolites retain the structure of the parent rock, but with only a trace of the original bond strength
(Lambe, 2019). At low confining pressures, if unsaturated or partially saturated and/or when bonds
and true cohesion are still intact, the matrix may stand vertically in exposed cuts. However, the initial
relict structure and weak bonds (true cohesion) may be easily broken at low confining pressures, with
significant initial compressibility, i.e. initially a contractive response. An undrained response is also
possible in the saprolite, and as such they may not be suitable for foundation support for the proposed
RSF-X/RSF-A structures at the geometries and heights currently proposed (250 to 300 feet).
The design section stability analyses presented herein assume that the majority of the saprolite in the
upper 10-20 feet below existing (or pre-existing) native grades will be removed based on the lower
blow counts (10<Nm<20) and the potential for contractive, undrained behavior under low confining
stresses.
Saprolites at the site typically classify as micaceous sandy silts and silty sands with some low-plasticity
clay minerals.The clays are typically kaolins and gibbsite and typically have very low plasticity(Sowers
and Richardson, 1983), but because of the mica content, often feel plastic when squeezed. In addition,
the liquid limit is often indeterminate (the soil slides in the cup rather than flows) and the thread in the
plastic limit test is spongey and breaks at diameters of 5 or 6 mm because of the micas, thus the
plasticity indices are often erratic.At the site, they are identified primarily on the boring logs as distinct
from the overlying residual (overburden)soils on the basis that at the sites,the saprolites are classified
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as predominantly sandy silt to high-plasticity silt(ML-MH),while the overlying residual soils range from
SM-ML to CL-CH. The saprolites at the sites are distinguished from the underlying PWR primarily on
the basis of blow counts, with PWR being logged once refusal (Nm> 50 blows/2 inches)are recorded.
The saprolitic(residual soils)and underlying partially weathered rock(PWR)zones at the site inherited
the discontinuities of the parent rock, along with the inherited anisotropic behavior from the fabric of
the parent rock. The initial relict structure and weak bonds may be easily broken with a contractive
response at low confining pressures, with significant initial compressibility. However, at higher
confining pressures, the saprolites tend to dilate and more closely follow the behavior for native low-
plasticity fine-grained silts (ML-MH) as noted by Wijewickreme et. al (2018), with the exception that
the stress-strain response is more a function of effective confining stress, initial static shear bias,
density, and degree of weathering than on over-consolidation ratios, which are not necessarily
applicable in weathered soils with relict structure.
The saprolites do show potential for a contractive, yet generally ductile, response under static and
seismic loading. A brittleness index of 20% <IB< 40% is assumed, in part based on literature review
of observed potential for strength reduction (peak to residual)of 35%to 55% (Lambe and Riad, 1990)
at<2.5%strain depending on test type (and sample discontinuities/relict structure present in sample).
An initial reduction of 12 to 22% interpreted at 10% strain was reported by Sorensen et. al (2023)for
saprolite materials with generally higher fines clay content, for which it was noted that at small shear
strains (<5%), some degradation in stiffness was evident, however, a subsequent dilative response of
the material at higher shear strains (10-15%)was also observed.
A potential for immediate breaking of weak bonds and potentially contractive and undrained behavior
was also noted in CPT soundings conducted at the site (SRK, 2024a). Preliminary laboratory triaxial
testing (to date)indicated predominantly dilative behavior over the range of confining pressures tested
in the relatively undisturbed samples. The saprolite matrix may therefore be assumed to be potentially
contractive under initial static loading (due to fills) but thereafter (at higher confining stresses and
strains) as well as cyclic loading, the matrix may be assumed to be strain-softening, but ductile.
It is further noted that laboratory sized specimens can provide misleading shear strengths based on
sample disturbance: highly micaceous residual soils can also expand elastically when unloaded during
sampling, this expansion breaks weak bonds and decreases the laboratory measured shear strength
and stiffness at low confining pressures.The initial contractive/collapse appears to happen at relatively
low shear strains (< 1%) and at confining stresses between 2,000 and 3,500 psf. In-situ there is also
the potential for horizontal stress paths at constant q and decreasing p', corresponding to documented
historic slope failures caused by rising pore pressures (and or artesian conditions) (Lambe and Riad,
1990).This failure mode is possible in the field but may not be captured in the typical laboratory testing
stress path (i.e., typical triaxial tests fail samples along the wrong stress path and result in
unrealistically high p' values at failure).
The saprolite will also likely experience a gradual shear stiffness reduction and cyclic-mobility type
strain accumulation at higher magnitudes of cyclic loading.
For the reasons noted above, and because the saprolite matrix is initially compressible under the
relatively high confining pressures anticipated and there is potential for excess pore pressure
development (particularly along joints/seams/relict structure) which cannot be ruled out, a preliminary
and generally conservative strength envelope was developed(after Lade,2010)and is shown in Figure
2 below.
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Sensitivity analyses with lower bound undrained strengths assigned have also been included for
consideration, pending the results of recommended laboratory testing programs for development of a
better understanding of the in-situ saprolite materials stress-strain response, particularly at higher
confining stresses.
After the initial break, saprolites do have a dilative tendency at higher confining stresses. Disturbed
saprolite samples subsequently exhibit dilative behavior at higher confining stresses, i.e. once the
initial bonds are broken. Literature (Sorensen et al.)have also documented the dilative behavior of the
matrix at higher confining stresses and at higher shear strains (10-15%). However, additional
laboratory testing is required to confirm the stress-strain response of these materials at the range of
loadings proposed for the existing facilities.
6.1.3 Partially Weathered Rock to Intact Rock
The partially weathered rock (PWR) zone, where present as logged, has the potential to include
alternating seams of saprolite and less-weathered rock. But in general, as logged at the sites, was
defined based on refusal blow counts or Nm>50 and on the basis of much more evident relict structure,
primarily from televiewer logs.
In several borings across the sites,the transition zone is less distinct and the borings indicate saprolite
immediately underlain by competent, intact rock with predominant discontinuities(anisotropy)evident,
including both shallow(low angle, < 20 degrees)and more steeply dipping (40 to 70 degrees)foliation,
discrete fault and joint sets.
6.1.4 Anisotropy in Saprolite and PWR
Anisotropy is present in the saprolite and PWR and was considered in the stability analyses presented.
Because the saprolites and PWR can retain the mineral segregation, mineral alignment and structural
defects of the parent rock,the saprolite can exhibit localized surfaces of weakness that are responsible
for documented historic slope failures despite high average strengths that indicate stability (Lambe
and Riad, 1990). The temperate warm climate, abundant rain (more than 30 inches per year)and well-
established vegetation have been favorable to accumulation of weathering products. Joints (not
foliations) can be coated with a waxy black mineral, iron-manganese-organic complex, leached into
the cracks from the residual soils above (Sowers and Richardson, 1983).Additionally, SRK has noted
that the potential occurrence of graphitic layers in the saprolite and or PWR, is considered reasonable
given the geologic setting at Kings Mountain. Graphite layers could result in potentially weaker zones
along both individual low angle (< 20 degrees)foliations and discontinuities and high angle (40 to 70
degree)discontinuities across the sites in both the PWR and overlying saprolite zones.
6.1.5 Existing Embankment Fills, RSF-X
The embankment fill materials at the legacy TSF(proposed RSF-X footprint)that were sampled during
the 2022 and 2023 field investigations varied, but were predominantly classified according to the
Unified Soil Classification System (USCS) as silty sand (SM) to silt with sand (ML) with gravel and
cobbles to poorly graded gravel with silt and sand (GP-GM)to sand with gravel (SP)zones.
6.1.6 Selected Materials Properties for Stability Analyses
The shear strength parameters for the materials relevant to the analyses presented herein are reported
in Table 3.
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Table 3: Material Parameters
Dry Unit Undrained
Material Weight Cohesion Friction Angle Su Su S,.
(pcf) (Pcf) (0)
Proposed
Embankment 146.4 0 35 -and Buttress
Existing
Embankment 141 0 32 -and Filter
Existing and
Proposed 100 0 26 0.22 0.12
Tailings
Shear/Normal Function(')
h
Saprolite 110 S = Q.Pa. Gaa) Capped at Su =2,000 psf
250 22 to 26 -
Partially
weathered rock 160 250 26 >/=3,000 psf - -
PWR
Overburden/Fill 110 0 24 - -
Bedrock 170 500 40 -
'After Lade,2010—See Figure 2
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Literature Best Fit Curve Lines-Extended DRAFT ___Lower Bound/ResiduaL Fit
12
———FuL y-Softened-Selected Design VaLues Best Fit
11 ———Upper Bound/Peak Fit
O B563@81',30 to 150A strain
10
———0,26 Steady State after Lambe and Riad,1990(far reference line
only)
9 ■ B563@ 81',21n 50A strain(Sandy MH,Native Sapproble per
Boring Log,IN.=67)
❑ B570@101@30 to 15%Strain
8 ♦ B570@101@2-5%Strain(ML,possibly fill,Sapprolite interpreted
post-drilling based on photos),N.=42)
4 Selected Design Envelope,Su 7
y O Boone Landslide,CIU(peak)
6 / O Balsam Gap 11 Landslide ClU(peak)
m / �
n '
+ Ogunro,In-Situ 85T(peak)
5 /
0,21 deg.Residual Ring Shear Lambe&Riad,For reference line,
4 ' 2 only
/
/ • Lambe DS and Ring Shear,Residual
3IN
,
Su (fully-softened)capped at 2,000to2,800psf
forSaprolite pending additionaltesting
z +m' .
b'
0
0 5 10 15 20 25 30 35 40
Average normalstress(ksl)
Figure 2:Shear/Normal Shear Strength Function for Saprolite
7. Geological and Analytical Sections
The following sections provide a summary of the slope configuration and material characterization for
cross-sections RSF-A BX-BX', RSF-X 14 and RSF-X C-C'. Cross-section locations are shown on
Plate 1 at the end of the text.
7.1 RSF-A Critical Section BX-BX'
RSF-A Section BX-BX (Plate 4) is a SE-NW trending section through RSF-A. The foundation of the
proposed embankment is at an elevation of 840 feet amsl and the proposed facility reaches an
approximate elevation of 1,220 feet amsl.
Underlying conditions at critical section BX-BX are shown on section at borings RSF-9, TSF-7, TSF-
2, and TSF-11, representing some of the deeper horizons of saprolite(at the southern perimeter of the
facility).
The analyses for this section consider a proposed excavation depth of approximately 20 to 30 ft below
the toe of the proposed facility (Figure 4), and a set of runs considering no removal of the saprolite
material (Figure 3).
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Cola Name Ul1R Td111 SOang01 EWedNe Eiective Pkzwnetrk
Weight Cohesion Function Cohesion Fricdml Surface
W, guq tpsry Angle(')
Bedrock 140 5W 40 1
E.P.R. 110 sep cep
2000
W.M."d 160 3,000
rock
WRF 136 0 35 1
Figure 3: Analytical Section RSF-A BX-BX (without excavation)
Cob, None line Strength Effective Enec- Pier tn.
Weight Funcfon Cohesion Friction Sur-
(PO) IPsfl Angle
13 tl—k 140 5W 40 1
■ Saprolte 110 sip rap
20m
■ Wm[ red 160 25D 26 1
rock
WAF 135 0 35 1
-------------
Figure 4: Analytical Section RSF-A BX-BX (with excavation)
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7.2 RSF-X Critical Section 1-1
Section RSF-X 1-1 (refer to Plate 1 and Plate 6 at end of text) is located perpendicular to the southern
flank of the proposed facility, adjacent to South Creek Reservoir. This critical section also includes a
portion of the existing embankment and 1975 reinforcing buttress, as shown in Figure 5 and Figure 6.
Underlying conditions are represented by borings TSFM-14, TSFM-12, TSFM-3 and TSFM-6.
The proposed facility has toe and crest elevations of approximately 850 ft amsl and 1,100 amsl,
respectively.
The analyses presented consider a partial removal of the existing facility and excavation of the
saprolite material with replacement of a non-acid generating material. A second set of analysis was
included with no removal of the saprolite.
:-- - __.....-,.._........ ` S7 R ATI4Q4P A`
a Q
SELTOAI B 4R0405E0
EMS
Figure 5: Cross-section RSF-X 1-1 (Golder, 1975 section B-B')
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CNer Name UM — 3tr.Gd, Eftcft E1lec_ Pier_ RE, Add
MOM C.N.W. FunElm CW�1eston F,,tl, SURan Weighl
Z, DO IPA An01e r)
6e k 14d 500 40 1 0 Y
ErgrROGkRI 105 0 37 1 0 Yes
..b.. 110 0 20 1 0 Yes
u _mi IM 0 37 1 n Yes
ad 135 0 32 1 0 Y.
-b anq.1
I
. S .M. 110 p®p 0.3 NO
2000
M.1h ed 160 3.QW 0.3 No
rock
VMF 135 0 35 1 0 Y
in
675
1 650
n25 1.099805050 66
S3
TSF6
975
9 SF
075 TSF 14 FP 825 ..................... ................... .......... .............. ....................
eo6
� 7l5
750 Rork ROCK R�_k
y 7 5 ROCK
W 700
675
656
825
600
575
,W
525
500
4I5
456
25
4
W
Distance
Figure 6: Analytical Section RSF-X 1-1, with Excavation of A Portion of The Saprolite and
Replacement with NAG Waste Rock
7.3 RSF-X Critical Section C-C
Section C (refer to Plate 1 and Plate 5 at end of text) is located parallel to Section 1-1 across the
southern slope of the proposed RSF-X. Section C-C' differs from Section I-1' in that it also includes a
zone of high-plasticity clay (CH) residual soils, as encountered on boring TSFM-11 approximately
between elevations 840 and 830 ft amsl, beneath the historical fill extents (as shown in Plate 5). It is
possible that this fat clay layer is native and was not stripped prior to construction of the existing
embankments. The analyses presented consider a partial removal of the existing facility and
excavation of the saprolite material with replacement of a non-acid generating material (Figure 8). A
second set of analysis was included with partial removal of the saprolite (Figure 7).
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Colon Name Unit Strength Total Effect- E6ecfive Piezometric
Weight FunCim Cohesion Cohesion Friction Surface
IPM 13 s0 (Pef) Angle PI
❑ B.,J 1, 140 500 40 1
❑ NAG mabrial 120 0 37 1
Old 135 0 32 1
embanlanent
1
■ Resitlual CH 120 1,500
■ Se mne 110 saP raP
20M
■ WRF 135 0 35 1
1,100
075
1050
1 025
1 000
975
9W
925 Resitlual CH TSF 11
9DD
875 TSF 15
825
C 800
� T/5
> 750
N 725 ROCK Rock
w 700
675
650
625
6Do
575
550
525
5D0
475
450
425
400
100 200 300 400 500 800 700 80D D00 1,000 1,100 1,200 1,300 1,400 1,500
Distance
Figure 7: Profile View of Cross-section RSF-X C-C, with Partial Excavation of Saprolite and
Replacement With NAG Waste Rock
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Cilu home U.1 st.gth Td Ege Emd- P--t-
Weghl Function CdiE=ti Cd_M F— Sum-
I'M iP� An CI)
Bedod 140 500 40 1
NAGm1 1 120 0 37 1
Old 135 0 2z 1
embanmeml
Re d,J J CH 12o 1.50o
""'I" 110 s9Pep
2000
WRF 1Cs 0 0
1 i PP
tme
1.OE0
02F
1.000
ws
95P
925 R-d,,d CH TSF11
9pp
]` TSF15
g,p Fill
825 —
SAP
C EOP
O
� 150
m ]2` ROCK Rods
W 700
6:0
s2E-
bpp
s]=.
55p
c2=.
.pp
4.p
925
90P
100 200 300 400 S00 600 100 800 900 1d9P 1,1W 1200 1,300 1,=00 1500
Distance
Figure 8: Profile View of Cross-section RSF-X C-C, with Excavation of Saprolite and
Replacement With NAG Waste Rock
7.3.1 Phreatic Surface
The phreatic surfaces within and on the downstream side of the embankments measured during the
field investigations in RSF-A and RSF-X areas in 2022 and 2023 are reported on both the analytical
and geologic sections. For the sections on RSF-X, the phreatic surface is controlled by the elevation
of South Creek Reservoir.
7.3.2 Stability Analyses
The stability evaluations presented herein were performed using SLOPE/W software (by Geostudio),
a two-dimensional 2D slope stability program using limit equilibrium analyses method. SLOPE/W uses
an automatic search routine to generate circular and non-circular (block/wedge) slip surfaces. The
block/wedge routine was used to analyze slip surfaces along the interfaces of the foundation, through
the saprolite layer. The Spencer (1967) method was utilized for all model runs. The model of each
section was developed using the geometry based on the proposed grading plan and the geo-
mechanical properties of the materials, as summarized in Table 3.
The stability of the embankments at RSF-X and RSF-A were evaluated for the following:
• Static conditions
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Pseudo-static conditions to estimate yield coefficients (ky)
7.4 Cross-section RSF-A BX-BX'
Limit equilibrium stability analyses were performed for static factors of safety using circular and non-
circular failure surfaces. A summary of the results of the analysis are included in Table 4, with all
stability runs for cross-section RSF-A BX-BX included in Attachment 1.
For the analysis case with no excavation, the shear strength of the saprolite required to achieve a
minimum factor of safety of 1.5 and a facility slope of 2.5H:1 V would have to be approximately
6,000 psf.
Table 4: Summary Slope Stability Results, RSFA Section BX-BX'
Static FoS
Section Scenario Non- ky Attachment
Circular Circular
Design Case:Undrained Strength Function on Saprolite
Fully-Softened Tau(Lade, 2010)FN, Su=2,000 psf capped+Anisotropic- With excavation and shear key
to--max. 30 ft dee .
RSF-A BX-BX 2.5:1 (H:V)with saprolite excavated to PWR 1.49 1.59 0.17 1
RSF-A BX-BX 3:1 (H:V)with saprolite excavated to PWR 1.59 1.72 0.18 1
RSF-A BX-BX 3.5:1 (H:V)with saprolite excavated to PWR 1.88 1.97 0.2 1
RSF-A BX-BX 4:1 (H:V)with saprolite excavated to PWR 2.01 2.7 0.22 1
Sensitivity, Undrained Strength Function on Saprolite
Full -Softened Tau Lade, 2010 FN, Su=2,000 psf capped+ Anisotro is- With no excavation.
RSF-A BX-BX 3.0:1 (H:V)Overall <1.0 <1.0 - 1
RSF-A BX-BX 3.5:1 (H:V)Overall 1.03 <1.0 - 1
RSF-A BX-BX 4:1 (H:V)Overall 1.13 1.0 - 1
Sensitivity, Drained Strengths on Saprolite
c=250,phi=26 de rees.
RSF-A BX-BX 2.5:1 (H:V)Overall 1.66 1.83 0.21 1
RSF-A BX-BX 3:1 (H:V)Overall 1.92 1.83 0.24 1
RSF-A BX-BX 3.5:1 (H:V)overall >2.0 >2.0 0.3 1
As shown in Table 4, the design case for full-softened strength envelope achieves the required
minimum static FoS for a 2.5H:1 V slope, only with excavation of saprolite (Figure 10).
Kyield (computed for a FoS = 1.0 with residual strength envelope) on this section is 0.17. As
summarized in Table 7 and Table 8, negligible deformations under 2,475-year postulated shaking
(PGA - 0.15 g) and < 12 inches under the 10,000 year ARP postulated shaking (PGA - 0.31 g),
respectively.
Sensitivity runs are included varying the overall slope inclination between 2.5H:1V to 3.5H:1V, for
which the factors of safety for this cross-section are reported in Table 4, and shown in Attachment 1.
Without saprolite excavation (Figure 9 and Table 4), slopes only achieve the required minimum factors
of safety for drained conditions.
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Colw Name Unit Total Strength Electihe Elrecgve Pkrzometrk
Weight Cohesion Function Cohesion Faun SV1ace
aPan (Pan 41091, Angle(*)
Badnock 140 S00 40 1
sagolee 110 eap cap
2000
Weathered 160 3.000
rack
WFF 135 0 35 1
0.65
•
---- --- - - - -- - --
----_ _____
m
Figure 9:RSF-A Critical Analytical Section (SLOPE/W Results) BX-BX' Without Excavation, at
2.5:1 Slopes
Color Nave Una Strength Ette cave Ettedve Piaometr.
Weight Fun don Cohesion Fndon sum.
IPctl (PM Angie l°I
Bedrock 140 500 40 1
■ Sep I. 110
"e0m
■ W thered 160 290 26 1
mek
WRF 135 0 35 1
1.59
iamb
,.- ab o��nee ,sue 2- �.� 2- �. �.� 2-
Figure 10: RSF-A Critical Analytical Section (SLOPEM Results) BX-BX' With Excavation at
2.5:1 Slopes
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7.5 Cross-section RSF-X I-I'
Limit equilibrium stability analyses were performed for static factors of safety using circular and non-
circular failure surfaces. A summary of the results of this analysis are included in Table 5, with all
stability runs for cross-section RSF-X 1-1 included in Attachment 2.
Table 5: Summary Slope Stability Results, RSF-X I-I'
Static FoS
Section Scenario Circular Non- kyield Attachment Filename
circular
Design Case: Undrained Strength Function Saprolite
Fully-Softened Tau(Lade, 2010) FN, Su =2,000 psf capped+Anisotropic- With full excavation of all
saprolite.
RSF-X 1-1 2.5:1 (H:V) 1.99 1.96 0.32 2 RSFX 11 014
RSF-X 1-1 3:1 (H:V) >2.0 >2.0 0.35 RSFX Il_015
Sensitivity:Su-Undrained Conditions on Saprolite and PWR
Fully-Softened Tau(Lade, 2010) FN, Su=2,000 psf capped+Anisotropic- With limited excavation of
saprolite.
RSF-X 1-1 2.5:1 (H:V) 1.43 1.0 - 2 RSFX ll_002
RSF-X 1-1 3:1 (H:V) 1.68 1.15 0.04 2 RSFX ll_003
RSF-X 1-1 3.5:1 (H:V) 1.88 1.45 0.09 2 RSFX ll_004
Sensitivity, Drained Strengths on Saprolite
c=250,phi=26 degrees- With limited excavation of saprolite.
RSF-X 1-1 2.5:1 (H:V) 1.84 1.93 0.25 2 RSFX ll_013
RSF-X 1-1 3:1 (H:V) 1.98 >2.0 0.26 2 RSFX ll_005
Sensitivity-Additional Runs
RSF-X 1-1 3:1 (H:V)Su= 3,700 required, 1.46 1.5 0.13 2 RSFX 11 011
for FoS = 1.5
RSF-X 1-1 3:1 Liner Interface, 'interface=20° - >2.0 0.28 2 RSFX ll_011
RSF-X 1-1 2:1 Liner Interface, 'interface=20° - 1.74 0.25 2 RSFX 11 012
As shown in Table 5, for RSF-X, Section 1-1' design case (for fully-softened strength envelope)
achieves the minimum required static FoS for a 2.5H:1V slope, only with full excavation of saprolite
(Figure 12) over the design shear key extents. Without saprolite excavation, the slopes only achieve
the minimum required factor of safety when using drained shear strengths.
Kyield (computed for a FoS = 1.0 with residual strength envelope) on this section is 0.17. As
summarized in Table 7 and Table 8, < than 6 to 12 inches of deformation is anticipated under the
2475-year postulated shaking (PGA- 0.15 g) and < 24inches of deformation is anticipated under the
10,000 year ARP postulated shaking (PGA- 0.31 g), respectively.
Sensitivity runs(reported in Table 5)are included varying the overall slope inclination between 2.5H:1 V
to 3.51­11:1V are included in Attachment 2.
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Cdor Name Unit Strength Effective Effective Pi—metric
Weight F—bon Cohesion Friction Surface
IPCQ IPan Angle n
❑ Bedrock 140 500 40 1
■ Engr RocUll 135 0 37 1
membrane 110 0 20 1
NAG material 120 0 37 1
Old 135 0 32 1
enhankmenl
1
Saprotte 110 sap rap
2000
■ Wealhaw 160 260 26 1
rock
■ WRF 135 0 35 1
1.00
•
1,1w
075
1,050
1,025
000 6
975
950
925 F1
900
875 TSF 14
850
O
N 750 Rock ROCK Rock
N 725 ROCK
W 700
675
650
625
600
575
550
525
500
475
450
425
400
100 200 300 400 5Iq 800 700 B00 B00 1100 1,100 1,200 1,300 1,400 1,500
Distance
Figure 11: RSF-X Critical Analytical Section (SLOPEIW Results) I-I' Without Excavation at
2.5:1 Slopes
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cd. Mena Unit Strength Effect- FJtediie Pie—
Weight Functon Ceti Frtdien Sn".
IPd} tin An91i
El Bodied, 140 500 40 1
■ Eng RoclPtll 135 0 37 1
■ embrene 110 0 21 1
NAG mat eial 120 0 37 1
Old 135 0 32 1
embarianentl
■ Saproite 110 sap cap
2000
■ Weathered rock 160 200 25
■ WRF 135 0 35 1
1.96
1,mu
1,o7s
1,0so
0zs
1,000 6
975
3so
925 1
900
S75 LTSF14
as0
azeitF
c s00 A
750 Rod; F�SK Fod<
g}i 725 ROCK
W 700
675
65P
625
600
575
55P
525
so'
475
450
42`
400
0 100 200 DO 400 SOP 60P 700 300 900 1,000 1,100 1,200 1,30P 1.4, I.`00
Distance
Figure 12: RSF-X Critical Analytical Section (SLOPE/W Results) I-I' With Excavation at 2.5:1
Slopes
7.6 Cross-section RSF-X C-C'
Limit equilibrium stability analyses were performed for static factors of safety using circular and non-
circular failure surfaces. A summary of the results of this analysis are included in Table 6, with all
stability runs for cross-section RSF-X 1-1 included in Attachment 3.
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Table 6: Summary Slope Stability Results, RSF-X C-C'
Static FoS
Section Scenario Circular Non- kyield Attachment Filename
circular
Design Case:Undrained Conditions on Saprolite
Fully-Softened Tau(Lade, 2010) FN, Su=2,000 psf capped+ Anisotropic- With full excavation
oof CH Native Residual Soil and underlying Saprolite
RSF-X C-C 2.5:1 (H:V)Overall 1 >2.0 1 >2.0 1 0.33 1 3 1 RSFX CC_007
Sensitivity. Undrained Conditions on Saprolite
Fully-Softened Tau(Lade, 2010) FN, Su=2,000 psf capped+ Anisotropic- With CH in
Foundation, below exis ing embankments and limited excavation of saprolite
RSF-X C-C 2.5:1 (H:V)Overall 1.3 0.93 - 3 RSFX CC_001
RSF-X C-C 3:1 (H:V)Overall 1.5 1.13 0.05 3 RSFX CC_002
RSF-X C-C 3.5:1 (H:V)Overall 1.67 1.3 0.07 3 RSFX CC_003
Design Case:Undrained Conditions on Saprolite
Fully-Softened Tau(Lade, 2010) FN, Su= 1,500 psf capped+ Anisotropic- With CH in
Foundation, below exis ing embankments and limited excavation of saprolite
RSF-X C-C 2.5:1 (H:V)Overall 1.22 0.82 - 3 RSFX CC_004
RSF-X C-C 3:1 (H:V)Overall 1.44 1.0 - 3 RSFX CC_005
RSF-X C-C 3.5:1 (H:V)overall 1.59 1.14 0.03 3 RSFX CC_006
Sensitivity, Drained Srengths on Saprolite
c=250, phi=26 degrees- With limited excavation of saprolite
RSF-X C-C 2.5:1 (H:V)Overall 1.62 1.82 0.21 3 RSFX CC_009
RSF-X C-C 3:1 (H:V)Overall 1.92 >2.0 0.25 3 RSFX CC_010
RSF-X C-C 3.5:1 (H:V)Overall >2.0 >2.0 0.28 3 RSFX CC 011
As shown in Table 6, for RSF-X, Section C-C' design case (for full-softened strength envelope)
achieves the minimum required static FoS for a 2.5H:1V slope, only with significant excavation of
saprolite (Figure 13 and Figure 14).
Kyield (computed for a FoS = 1.0 with residual strength envelope) on this section is 0.33. hence
negligible deformations are anticipated under both the 2,475-year postulated shaking (PGA-- 0.15 g)
10,000 year ARP postulated shaking (PGA- 0.31 g) events, respectively.
Sensitivity runs(reported in Table 5)are included varying the overall slope inclination between 2.5H:1 V
to 3.5H:1V are included in Attachment 2.
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Otlw Nnw UM BFa npUl Ta M a- EMiw P—W
W.4"t N.M. Cah"_ Cah.w. Fda- 9aILro
(PC9 pall (P-9 h Glk P)
Badwk 140 500 40 1
m9G.a I 120 0 37 1
Om 135 0 w 1
alberimeM
1
Pesiiuel CH 120 1,FAO
. 5eproM IIO sap rep
2000
NRF 135 0 35 1
I,015 •
I,o50
I A15
I,dW
M50
B25 Rasdl,el CH T,11
Moo
675 T9FI5
-- ---� — --------
� Z175
S
m 725 ROCK H��k
W 1m
'75
050
sss
575
525
500
45
4zs
�ro
IW 2W ]W 100 540 800 i40 B00 900 1,400 1,1W 1�W 1,300 1,400 1,504
Distance
Figure 13: RSF-X Critical Analytical Section (SLOPEM Results) C-C' Without Excavation of
CH Residual Soil and Limited Saprolite Excavation Depth at 2.5:1 Slopes
wpm w w� ca�� ca�o� FddAn wrta«
lodl I�fl �fl eigel%
❑ m 202
❑ mamma a
mnwnnv
■ IwacH 11.
■ sapmlrce saoc
R—A CH TSF11
iSF15
Fil I
ROCK R
W
Distance �
Figure 14: RSF-X Critical Analytical Section (SLOPEM Results) C-C' With Full Excavation of
CH Residual Soils and Saprolite Over Shear Key Extents at 2.5:1 Slopes
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8. Deformation Analysis
Several stability scenarios were selected for estimation of seismic-induced deformations.The methods
by Makdisi & Seed (1978), Bray & Travasarou (2007), and Bray and Macedo (2014) were used to
estimate a range of possible deformations for the facilities for the following:
• Peak Horizontal Ground Acceleration (Expected value), PGA = 0.13 g for the 2,475 - year
ARP event, characterized by a Moment Magnitude (Mw) 7.5
• Peak Horizontal Ground Acceleration (Expected value), PGA = 0.31 g for the 10,000 - year
ARP event, characterized by a Moment Magnitude (Mw) 7.5
The de-coupled seismic deformation analysis was conducted in two steps:
Step 1: For each representative cross-section, a search of critical potential slip surfaces is performed
and the yield acceleration ky for the slope is determined though a trial and error process. The yield
acceleration ky is defined as the acceleration applied to the slope that will leads to a pseudo-static
factor of safety of 1.0. Yield accelerations were computed for the critical analysis sections using the
program SLOPEW, as documented in the computation package presented in the attachments to this
report. The resulting yield accelerations are summarized on the tables summarizing the factors of
safety from the three analysis sections (Table 4 through Table 6).
Step 2:The permanent seismic displacements under postulated loading were estimated by procedures
based on a simplified Newmark sliding block analysis. Historically, the rigid-sliding block procedure
proposed Makdisi & Seed (1978) has been widely accepted to calculate the permanent seismic
deformations of earthen embankments and slopes.Among others, Bray&Travasarou (2007)and most
recently Bray and Macedo (2014) have proposed improvements to this historic model. The Bray and
Travasarou (2007) approach proposes to recognize the nonlinear response of a deformable
earth/waste slope (non-linear coupled stick-slip deformable sliding mass model), to incorporate
additional site characterization parameters (including site period, Ts) on the magnitude of
displacement as well as to take into account the effects of postulated ground motion parameters
(intensity, frequency, duration). The Bray and Macedo (2014) model further proposes details on type
of fault, and incorporates peak ground velocity. As requested by Dr. Bray (personal communication),
he has noted a number of issues with the prior Bray and Travasarou (2007) computation and has
requested that its use be discontinued. Therefore, only the Makidisi-Seed and Bray and Macedo
estimates are compared in Table 7 and Table 8.
Seismic displacement estimates for sections RSF-A BX, RSF-X 1-1 and RSF-X C-C were computed
using these models and selecting the design case and some of the sensitivity runs presented.
The thickness of the potential sliding mass for each analysis was estimated from the stability models,
and a shear wave velocity of 500 m/s was assumed for RSF-A and RSF-X. Published PGA's were
obtained from mapped values (Table 1). Degraded spectral accelerations were obtained from the
available Lettis (2023) report.
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Table 7: Summary of Seismic-Induced Displacements for 2,475-Year ARP
RSF Section Scenario Filename for ky PGA Mw H H Vs Ts 1.3 Sa(1.3
Stab (ft) (m) (m/s) Ts Ts)
RSF-A BX 2.5 to 1 RSFA BX_012 0.17 0.14 7.5 250 76.2 500 0.396 0.515 -
RSF-A BX 3.5 to 1 RSFA BX_011 0.22 0.14 7.5 200 60.96 500 0.317 0.412 -
RSF-X C 2.5 to 1 RSFX CC_007 0.33 0.14 7.5 75 22.86 500 0.119 0.155 -
RSF-X C 3 to 1 RSFX CC_002 0.05 0.14 7.5 200 60.96 500 0.317 0.412 0.40
RSF-X C 3.5 to 1 RSFX CC_006 0.03 0.14 7.5 200 60.96 500 0.317 0.412 4.68
RSF-X I 2.5 to 1 RSFX II_014 0.32 0.14 7.5 275 83.82 500 0.436 0.567 -
RSF-X 1 3 to 1 RSFX II 003 0.04 0.14 7.5 200 60.96 500 0.317 0.412 1.55
Table 8: Summary of Seismic-Induced Displacements for 10000-year ARP
RSF Section Scenario Filename for ky PGA Mw H H (m) Vs Ts 1.3 Ts Sa (1.3 11
Stab (ft) (m/s) Ts) (
RSF-A BX 2.5 to 1 RSFA BX_012 10.171 0.31 7.51 2501 76.21 500 10.396 I 0.5151 0.230 -
RSF-A BX 3.5 to 1 RSFA BX_011 1 0.22 1 0.31 7.51 2001 60.961 5001 0.3171 0.412 0.270 -
RSF-X C 2.5 to 1 RSFX CC_007 1 0.33 1 0.31 7.51 751 22.861 5001 0.1191 0.155 0.490 -
RSF-X C 3 to 1 RSFX CC_002 1 0.05 1 0.31 7.51 2001 60.961 5001 0.3171 0.4121 0.270 <
RSF-X C 3.5 to 1 RSFX CC_006 1 0.03 1 0.31 7.51 2001 60.961 5001 0.3171 0.4121 0.270
RSF-X 12.5 to 1 1 RSFX II_014 1 0.32 1 0.31 7.51 2751 83.821 5001 0.4361 0.5671 0.220 -
RSF-X 1 3 to 1 1 RSFX II 003 10.041 0.31 7.51 2001 60.961 5001 0.3171 0.4121 0.270 <
9. Conclusions
The design case for RSF-A and RSF-X includes removal of the weak saprolite below the toe of the
proposed facility, over the shear key extents to depths of between 10 and 20 feet (on average)and to
a maximum depths of up to 30 ft deep at RSF-A(in localized areas along the southern perimeter)and
approximately 20 to 25 ft (in localized areas along the southern perimeter and below prior existing
native grades)at RSF-X. With the proposed removal of unsuitable material, stability analyses result in
acceptable static factors of safety for facility overall slopes of 2.51HIA V, as is currently planned.
These runs consider a strength function conservatively capped at a shear value of 2,000 psf, which is
based on analysis of available literature and preliminary site-specific laboratory test data.
Sensitivity runs using reported drained strength envelopes on saprolite from literature values (c=250
psf, phi=26 degrees), were also performed and are included in this report, but these are considered
unconservative, particularly at higher confining pressures given the non-linear envelope fitted to
available data (refer to Figure 3).
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133, No. 4, April 2, 2007.
Bray, J.D., and Macedo, J. (2014).
CDA. (2013). Dam Safety Guidelines 2007 (2013 Edition).
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forces. Geotechnique, 11-26.
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