Appendix C (G-C) - Abridged WSB-1 Calculation Package

srk consulting 999 Sonsulting(U.S.),Inc.
999 17th Street,Suite 400
Denver,CO 80202
WS13-1 Calculation Package F:[phone]
ABRIDGED WSB-1 CALCULATION PACKAGE DOCUMENT taken [e-mail]
from Appendix B (Pre-feasibility WSB-1 Engineering Design Report) "� srk.com
of Appendix H (Design Reports). This abridged document includes
Plate 1 and excludes all other Plates and appendices. The deleted
plates and appendices of this report may be made available upon
request.
To: Claudio Andrade, Keith Viles Date: April 19, 2024
Company: Albemarle Corporation Calculations Salvador Beltran,
by: Diego Cobos
Approved by: Breese Burnley Reviewed by: Tarik Hadj-Hamou
Subject: Slope Stability Calculations for Pre-feasibility Project#: USPR000576
Design of Water Storage Basin 1
Albemarle Revision#: 01
Document Number:
1. Purpose and Scope
The objectives of this calculation package are to:
• Evaluate the stability of the embankment of proposed Water Storage Basin 1 (WSB-1) under
static and pseudo-static conditions
• Determine the required dimensions of a stabilizing buttress to bring the embankment into
compliance with design criteria (i.e., factors of safety)
2. Documents Reviewed
SRK reviewed the following information for the purposes of this calculation package:
• Water Storage Basin 1 (WSB-1)—Pre-feasibility Site Characterization Report(SRK Consulting
Inc., 2024)
• Laboratory testing data derived from field investigation conducted in 2022 and 2023-24
• Historical data from the site, including Report of Investigation of Tailings Dam for Foote Mineral
Company (Golder Associates, 1975) and Foote Mineral Reservoir Dam Removal Design
Report (Schnabel, 2011).
3. Project Description
The proposed WSB-1 will occupy the footprint of the former Foote Mineral Chem Tailings
Impoundment, currently known as the Executive Club Lake, as shown in Figure 1. The proposed
WSB-1 is also shown relative to Interstate 85 (1-85)and proposed rock storage facilities across 1-85 at
the Kings Mountain Mine site.
The existing embankment will be utilized and the section that was removed as part of facility closure
and reclamation in the early 1990s will be reconstructed using compacted fill and/or waste rock. The
reconstructed embankment will be reinforced with a compacted fill downstream buttress constructed
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over a blanket drain placed on the downstream face. Once completed, the crest of the WSB-1 will
reach an elevation of 850 feet (ft) above mean sea level (amsl) and have downstream and upstream
slopes at inclinations of approximately 2.5H:1V (horizontal to vertical). A spillway will be constructed
at the northern abutment with an outlet invert at 843 ft amsl. The existing concrete-lined spillway
channel will be replaced with a new concrete channel that will follow the same alignment and direct
stormflows into the channel downstream from the embankment. Hydrological analyses completed as
part of facility design indicate a maximum pool elevation of 843 ft amsl during the Probable Maximum
Precipitation (PMP) event, resulting in 5 ft of freeboard above the maximum predicted storm surge
elevation.
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4. Design Acceptance Criteria
SRK developed the design acceptance criteria (DAC) summarized in Table 1 based upon
internationally accepted practice as well as the following:
• North Carolina Administrative Code Subchapter 2K- Dam Safety
• Global Industry Standard on Tailings Management(GISTM, 2020)
• Canadian Dam Association's Dam Safety Guidelines (CDA, 2013) and Technical Bulletin:
Application of Dam Safety Guidelines to Mining Dams (CDA, 2019)
• IRMA Standard for Responsible Mining IRMA-STD-001 (IRMA, 2018; Section 4.1.3.)
For the purposes of pre-feasibility level design, WSB-1 is considered to be a "Class U dam in
accordance with Title 15A of the North Carolina Administrative Code, Section 02K.0105 based on the
potential downstream consequences. Refer to Section 4.7 below for a discussion of dam breach
analyses and a formal determination of dam classification.
Table 1: WSB-1 Slope Design Acceptability Criteria
Minimum
Loading Condition Criteria Factor of
Safety
Static Design Basis, Long Term (Steady State Seepage, 15A NCAC 02K.0208 1.5
Normal Reservoir Level)
SRK recommended for TSF:
DBE (2475-year ARP) Acceptable deformation per standard n/a
of practice, less than or equal to 24
inches
SRK recommended for TSF:
MCE(10,000 year, 84th percentile) Acceptable deformation per standard n/a
of practice= no catastrophic failure,
no significant loss of freeboard
Pseudo-static, FoS under seismic loading event with 2% 15A NCAC 02K.0224 >/= 1.0
probability of exceedance in 50 years(-2475 year ARP) 15A NCAC 02K.0224 1.2
based on the USGS Seismic Hazard Maps for seismic
events with this return period of the region where the SRK recommended for TSF: if
facility is located). coupled with appropriate deformation 1.1
analysis for DBE and MCE as noted
For WSB-1, PGA-0.15g per mapped values(USGS, above
2018)(refer to Table 2
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. For the stability analyses
described herein, SRK 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 to facilitate calculation of estimated displacements under earthquake loading scenarios for the
2,475-year and 10,000-year average return period (ARP)events.
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Table 2: Seismic Accelerations from LCI (2023) and USGS (2018)
Average USGS 2018
Return Lettis PGA(LCI,2023) NSHM Remarks
Period
Hard Rock Soil/Ground Surface
Mean (Site Specific for
(3,000 meters Hard
per second Vs30—500 m/s RSFA Rock Soil
(m/s)) and Vs30—2,000 m/s
RSFX
2475-year 0.088g PGA 0.172 g 0.150g 0.153g Design Basis Earthquake
DBE
Maximum Credible
10,000- 0.2 g Earthquake, Deterministic
year(see (0.25g, 84th 0.313g 0.310g Maximum or PSHA
Figure 15) percentile) .equivalent" 10,000 year
ARP event
6. Geotechnical and Stability Sections
SRK prepared three geological/geotechnical cross sections in evaluating subsurface conditions at
WS13-1.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 cross sections are included at the
end of the text as Plates 2 through 4. The stability of the proposed TSF was evaluated at one
representative geological/analytical cross-section labeled B-B'.The stability cross section location was
selected based on the preliminary design geometry of the facility, the underlying original ground
grades, and knowledge of the subgrade conditions derived from available borings and CPT probes.
Refer to a detailed description of site subsurface conditions in SRK (2024a).
Logs of the borings and the televiewers records were reviewed to assign the thickness and extent of
the geological units under each section described further in Section 7.
6.1 Material Properties
Site and material characterization properties are described in detail in the report Water Storage Basin
1 (WSB-1)—Pre-feasibility Site Characterization Report(SRK Consulting Inc., 2024).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). This layer is referred to as overburden
in the borehole logs.
• A layer of soil-like decomposed rock referred to as a saprolite. The classification of the soils
in the saprolite layer were described according to the Unified Soil Classification System
(USCS) and range from low plasticity clay (CL) to low plasticity site (ML) with some
lenses/seams of higher plasticity.
• Underlain by partially weathered rock(PWR).The materials in the PWR are similar in geologic
origin to those of the saprolite, but stronger as indicated by blow counts per foot from Standard
Penetration Testing (SPT). The PWR also includes more prominent relict structures from the
parent bedrock.
• Underlying bedrock, which varies in lithology across the site — refer to the sitewide geology
description in SRK (2024).
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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 ft 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. 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, though considered unlikely since the existing dam has been in place for
decades.
The design section stability analyses presented herein assume that the overburden and residual soils
within the expanded footprint of the dam will be removed, but that the saprolite will remain in place.
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
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
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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%to 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.
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.
Analysis of the televiewer data indicate that there is a potential for low angle relict structures(foliations,
joints and fault discontinuities)within the PWR at the proposed TSF location. Careful consideration of
anisotropic strengths (across matrix versus along weaker joints and foliations) must be considered for
this unit, as the reduction in strength along these weaker planes is significant.
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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 (400 to
700) discontinuities across the sites in both the PWR and overlying saprolite zones.
6.1.5 Selected Materials Properties for Stability Analyses
The shear strength parameters for the materials relevant to the analysis of the embankment of the
WSB-1 are reported in Table 3 and shown in Figure 2.
Table 3: Material Parameters
Dry Unit Effective Total
Material Weight Cohesion Friction Angle Su
(Pcf) Pc o
Proposed Embankment 146.4 0 Shear/normal
function
Existing Embankment and 141 0 30
Filter
Shear/Normal Function(')
[J b
Saprolite 110 5 = Q'pa` pa
Capped at Su =2,000 to 2,800
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 ———I- erBound/ResidualFit
12 ........................................................................................................................................................................
———FuLLy-Sattened-selected Design Values Best Fit
11 ———Upper Bound/Peak Fit
O B563@81%101o15%strain
10
———0,26 Steady State after Lambe and Mad,1990(far reference line
only)
9 III B563@81',210 5%strain(Sandy MH,Native Sapprolite per
Baring Lag,Nm=67)
3570@101 @ 10 to 15%Strain
8 ♦ B570 @101 @2.5%Strain(ML,possibly fill,Sapprolite interpreted
post-driW ng based on photos),Nm=42)
Y / —Selected Desi g�i Envelope,Su
� 7 a
y ' 13 Boone Landslide,CIU(peak)
N
`m g 0 Balsam Gap I I Landslide CIU(peak)
s
y Ogunro,In-Situ BST(peak)
5
m --- -0,21 deg.Residual Ring Shear Lambe&Riad,For reference line,
G /, 7 only
/
4 / • Lambe DS and Ring Shear,Residual
9 ——
3
'Su (fully-softened)capped at 2,000to 2,800 psf
13 forSaprolite pending a Iditionaltesting
z o1/ — '
/
i
0
0 5 10 15 20 25 30 35 40
Average normal stress(ksf)
Figure 2: Residual Shear/Normal Shear Strength Function for Saprolite
7. Critical Geologic and Analytical Sections
The stability of the proposed embankment configuration was evaluated at three critical cross-sections
labeled A, B and C, as shown on Figure 3. The details of each stability section are shown in Figure 4,
Figure 5, and Figure 6. The critical cross section locations were selected based on height of the
proposed embankment, the slope of underlying native ground, and the subsurface details recorded in
the boring logs.
The details for each slope stability section were developed based on geologic sections cut through the
site based on drill hole locations. These geologic sections are shown in plan-view on Plate 1 at the
end of the text, together with the locations of geotechnical characterization borings completed in the
vicinity. The boring logs and the televiewers records were reviewed to assign the thickness and extent
of the geological units under each section, each of which is described further below.
The following sections provide a summary of the analyzed slope and foundation configurations.
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ey
a�P
EXECUTIVE
CLUB
LAKE .
.1PILL'AAY
.WSB-1 EMBANKMENT
8 5
C
BUTTRESS
a i
0 150 300
aou FEET
Figure 3: Location of Stability Cross Sections
7.1 WSBA Critical Section A-A'
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 4, with all
stability runs for cross-section WS13-1 A-A included in Attachment 1. Runs included drained and
undrained strength envelopes for the saprolite and partially weathered rock layers.
Section A (Figure 4) is located on the northern end of the embankment where the original dam was
breached in the 1990s (refer to Figure 3). The foundation of the proposed embankment is at an
elevation of 820 ft amsl and reaches an elevation of 850 ft amsl. Underlying conditions are represented
by borings TSFC-9/SNKM23-580, TSFC-LF-2/SNKM23-566, and TSFC-3/SNKM22-410.
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PROPOSED BUTTRESS PROPOSED EMBANKMENT Flay.s3s ss Dev.ails
PROPOSED FILTER Eln e31.z6• WATER SURFACE T
w — FILL
a18198 TAILINGS
at fi163' ._
Elea-8165 I
Ekv.nl.zc 53r.6D695 PARTIALLY WEATHERED ROCK
775
al 761 3'
Elev-770 95'
F_Ir.75525'
770 Elegy]51 3
BEDROCK
iSr Cy�[IKPA2358D TSFC-LF-2,Sf:KIA2,GG TSFG3SNKM22d10
35 H AS 140 175 21-J 245 260 315 350 185 12D J55 490 525 560 595 630 665
Figure 4: Profile View of Cross-Section WS13-1 A-A'
7.2 WS13-1 Critical Section B-B'
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 4, with all
stability runs for cross-section WSB-1 B-B' included in Attachment 1. Runs included drained and
undrained strength envelopes for the saprolite and partially weathered rock layers.
Section B-B (Figure 5) is located perpendicular to the existing cobble/gravel drain rock buttress at the
low point in the downstream toe of the existing embankment (refer to Figure 3). At this point, the
embankment has a height of approximately 60 ft from the crest to the downstream toe, with the
elevation at the downstream toe at approximately elevation 790 ft amsl.
Underlying conditions are represented by borings TSFC-10/SNKM23-577, TSFC-7/SNKM23-570,
TSFC-4/SNKM22-415, TSFC-LF-1/SNKM23-573.
PROPOSED BUTTRESS EXISTING EMBANKMENT
EXISTING FILTER Elev.847.4T El..845.3 FJeea39'
WATER SURFACE
PROPOSED TOE BUTTRESS FJ---8002s
I
wTzleo7z �199a OVERBURDEN �79g TAILINGS
at 7964'
Ele;13a 2 Ele.?.a ti Elev 781 4T Elev.7aa
Flee 779.8' i
PARTIALLY WEATHERED ROCK 1 El9v,TfiY
-le.'J1 25 El.740.67 1 741.1T
6aa WEAK LAYER E1e,79z oz Elev.5ss 56
BEDROCK
G15 I TSFC 715NKM235701
TSFC-10'SNKM23-577 I TSFC-0SNKM22415 T5FC-LF-I/5NKM2a-573
11D 165 220 275 330 305 �0 495 55C 605 660 715 "0 625 UD 935 990
Figure 5: Profile View of Cross-Section WS13-1 B-B'
7.3 WS13-1 Critical Section 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 4, with all
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stability runs for cross-section WSB-1 B-B' included in Attachment 1. Runs included drained and
undrained strength envelopes for the saprolite and partially weathered rock layers.
Section C (Figure 6) is located on the southern end of the existing and proposed embankment and
corresponds to the maximum height of the embankment, as measured from the embankment crest to
the downstream toe (refer to Figure 3). The foundation of the existing embankment is at an elevation
of approximately 797 ft amsl and the proposed crest is at 850 ft amsl.
Underlying conditions are represented by borings TSFC-11/SNKM23-578 and TSFC-12/SNKM23-561
(refer to PLATES at end of text). A buttress was extended to this portion of the embankment to raise
the factor of safety to meet the stability criteria. The buttress rises to elevation of 850 ft amsl and with
an outer slope of 2.5H:1 V.
EXISTING EMBANKMENT
PROPOSED BUTTRESS
PROPOSED FILTER Elm.adslr
WATER SURFACE •
Elm.BW.94' _
w r 801 W m e13.1r
TAILINGS
Elw.ns.9d• Em.776.5r PARTIALLY WEATHERED ROCK
F1m.738 94' Elev.7d5.7r
660 BEDROCK
515
GS 130 195 260 ]2i ?00 Ji 910 97S 1040 1105 1170 1235
Figure 6: Profile View of Cross-Section WSBA C-C'
7.4 Phreatic Surface
The phreatic surfaces within and on the downstream side of the embankments were measured during
the field investigations in the WSBA area conducted in 2023 (refer to pre-feasibility site
characterization report—SRK[2024]). The stability analyses were performed assuming that WSBA is
full of water up to elevation 845 ft amsl and that the saturated levels in the embankment could rise to
near ground surface.
8. Stability Analyses
The stability analyses described herein were performed using the SLIDE 2 software,a two-dimensional
2D slope stability program using limit equilibrium analyses method (RocScience, Inc 2022). SLIDE 2
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. The SLIDE 2 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 TSF was evaluated for the following:
• Static conditions
• Pseudo-static conditions to estimate yield coefficients (ky)
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8.1 WSB-1 Critical Cross-Section A-A
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; all stability
runs for cross-section A-A are included in Attachment A-1.
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Table 4: Cross-Section A-A Factors of Safety
Static FS I Pseudo-Static FS kh=0.075 Pseudo-Static FS kh=0.15 Pseudo-Static FS kh=0.3
Section Scenario Circular I Non Circular Circular I Non Circular Circular Non Circular Circular I Non Circular k field Attachments
Design Case Su Fully-Softened Tau Lade,2010 FN,Su=2,000 psf capped+Anisotro is
A-A Proposed with 1.9 3.5 1.4 2.4 1.1 1.8 0.8 1.1 0.2 1
Buttress
Design Case Su Fully-Softened Tau Lade,2010 FN,Su=1,500 psf capped+Anisotro is
A-A Proposed with 1.3 2.7 1.0 1.8 0.8 1.3 0.6 0.8 0.075 1
Buttress
Sensitivity-Drained strength parameters on Saprolite
A-A Proposed with 1.6 3.1 1.0 1.7 1
Buttress
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As shown in Table 4, the design case for fully-softened strength envelope on the saprolite foundation
achieves the minimum static FoS for the proposed geometry. Sensitivity runs are included varying the
tailings shear strength between its expected peak and residual values, for which the factors of safety
for this cross-section are reported in Table 4, and shown in Attachment A-1.
The calculated minimum factors of safety for the existing embankment and the phreatic surface
discussed in Section 5-2 are 1.9 for a circular failure and >2 for a non-circular failure using the
undrained shear strength envelope (Lade, 2010).A residual strength envelope capped at 1,500 psf for
the saprolite results in factors of safety below the minimum criteria. Sensitivity analysis using drained
parameters for the saprolite results in acceptable values for static and pseudo-static conditions.
Method Name Min FS t hWeght Strength Cehesinn Phi Shear Normal Ve"i°a' Mlnlmam Shear water No
Material Name Color (lhs/ft3) Type (psf) (deg) Function Strength Strength ipsf) Surface type Nu Ru
Bishop simplified 1.9 146.4 shaar Normal Rage
Proposed tees(low- Water
Spencer 1.9 emnankment ■ ,anrtlen beenm sedate custom 1
GLE Morgenstern-Price 1.9 "g 10o OefLI`a' 04 s water casmm
Taving stress"atie sedate
Saprolite ® 110 Coulomb 0 24 Surface Custom 0
Bedrock 170 Coulomb 0 40 5 a�ee Custom 1
Water 62.4 No strength water Custom 0
ac
Fill ❑ 11p Mahr- 0 24 Nonee 0
oulomb
P—.1 ally Mohr-
Weathered 110 Coulomb 0 24 None 0
Rock
1.9 W
35 = o 00
0 100 200 300 400 500 HID 7
Figure 7—WSB-1 Critical Analysis Section A-A
8.2 WSBA Critical Cross-Section B-B
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 is included in Table 5; all stability
runs for cross-section B-B are included in Attachment A-2.
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Table 5: Cross-Section B-B Factors of Safety
Static FS Pseudo-Static FS kh=0.075 Pseudo-Static FS kh=0.15 Pseudo-Static FS kh=0.3
Section I Scenario Circular I Non Circular Circular I Non Circular Circular I Non Circular Circular I Non Circular k ield Attachments
Design Case Su Fully-Softened Tau Lade,2010 FN,Su=2,000 psf capped+Anisotro is
B-B Existin 1.31 1.51 1.0 1.21 0.81 1.01 0.61 0.71 1 2
B-B Proposed with Buttress 1 1.41 1.71 1.0 1.31 0.81 1.11 0.61 0.81 0.075 1 2
Design Case Su Fully-Softened Tau Lade,2010 FN,Su=1,500 psf capped+Anisotro is
B-B Existin 0.91 1.51 0.7 1.21 0.61 1.01 0.41 0.71 2
B-B Proposed with Buttress 1 1.01 1.71 0.8 1.31 0.61 1.11 0.41 0.71 0.015 1 2
Sensitivity-Drained strength parameters on Saprolite
B-B I Existing 1.31 1.5 1 1 0.9 1.0 1 2
B-B Proposed with Buttress 1 1.51 1.71 1 1 1.0 1.11 2
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The calculated minimum factors of safety for the existing embankment and the assumed phreatic
surface are 1.3 for a circular failure and 1.5 for a non-circular failure. Pseudo-static factors of safety
using circular and non-circular failure surfaces were calculated and the minimum factors of safety were
0.9 for a circular failure and 1.0 for a non-circular failure. With the addition of an approximately 20 ft
wide blanket drain and buttress along the downstream slope of the existing embankment, the static
factors of safety are calculated to be 1.5 for a circular failure and 1.7 for a non-circular failure. The
pseudo-static factors of safety are calculated to be 1.0 for a circular failure and 1.1 for a non-circular
failure. The stability criteria of the proposed WSB-1 embankment configuration meet established
stability criteria listed in Table 1.
Material Name color °nit Weight she ry� Cahm Phi Shear Normal Vertical Minimum Shear Water RP
Method Name Min FS byh3J ((MI) (deg) Fue[ , Strength Ratio Strength(p fJ Surtax
Proposed 1a0a Sheen Normal "Pi
Water
Bishop simplified 1.7 mbankme^r runetl"n hound) s°dare
Existing Mohr- Water
Spencer 1.9 Embankmem ❑ 141 Coulomb ° 0 nae
verd�al waxer
GLE/Morgenstern-Price 1.8 bag Tailings — slfe ai 04 s",race
saproRte ■ u° Co tomb ° z4 s dace
Bedrock 170 ° 40
Coulomb Sudxe
Water ❑ b2.4 No strength Water
Sudat¢
S E111ting Fllter ■ 141 Mohr- 0 30 Water
1 7 Coulomb Surface
Proposed Toe 160 Mohr- ° 35 Water
Runress 1111 Coulomb Surface
Chuburden ■ 11° Coulomb 0 24 SUHtace
Partially 110 hi­
Mohr- 0 2J Water
W¢ath¢red Rock ❑ Coulomb Sudan¢
weak layer ❑ 110 Mohr- 0 10' None 0
Coulomb
1
o ioo 20o sou aao sou sou goo sou sou i000
Figure 8—WSBA Critical Analysis Section B-B
8.3 WSBA Critical Cross-Section 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 the analysis are included in Table 6; stability runs
for cross-section C are included in Attachment A-3.
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Table 6: Cross-Section C-C Factors of Safety
Static FS Pseudo-Static FS kh=0.075 Pseudo-Static FS kh=0.15 Pseudo-Static FS kh=0.3
Section Scenario Circular I Non Circular I Circular I Non Circular I Circular I Non Circular I Circular I Non Circular I k ield I Attachments
Design Case Su Fully-Softened Tau Lade,2010 FN,Su=2,000 psf capped +Anisotro is
C-C I Existing 1.11 2.01 0.91 1.61 0.71 1.21 0.51 0.81 1 3
C-C Proposed with Buttress 1 1.81 2.91 1.31 2.01 1.11 1.51 0.71 0.81 0.181 3
Design Case Su Fully-Softened Tau Lade, 2010 FN,Su= 1,500 psf capped+Anisotropic
C-C Existing 1.0 2.01 0.81 1.61 0.71 1.21 0.51 0.81 3
C-C Proposed with Buttress 1 1.4 2.91 1.11 2.01 0.81 1.51 0.61 0.81 0.08 3
Sensitivity-Drained strength parameters on Saprolite
C-C Existing 1.1 2.0 1 1 0.7 1.3 3
C-C Proposed with Buttress 1 1.81 2.91 1 1 1.21 1.6 1
3
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As shown in Table 6, the design case for fully-softened strength envelope on the saprolite foundation
achieves the minimum static FoS for the proposed geometry.
The calculated minimum factors of safety for the existing embankment and the phreatic surface
discussed in Section 5-2 are 1.1 for a circular failure and 2.0 for a non-circular failure. Pseudo-static
factors of safety using circular and non-circular failure surfaces were calculated. The calculated
minimum factors of safety are 0.7 for a circular failure and 1.3 for a non-circular failure.
With the addition of an approximately 20 ft wide blanket drain and buttress along the downstream
slope of the existing embankment, the static factors of safety are calculated to be 1.8 for a circular
failure and 2.9 for a non-circular failure.The pseudo-static factors of safety are calculated to be 1.2 for
a circular failure and 1.6 for a non-circular failure. The stability criteria of the buttressed stabilized
embankment meet established stability criteria listed in Table 1.
uea shear ve&-I
Material 6tmeN Geheslen Phi Minimum Shear Water Type Name Geier Weight Typpe (psn (deg) Nmmal Strength Strength(psf) Surfare Type Hu
(Ibs/NS] Function Ratle
Pcopoietl 146.4 Normal User befi d Water Custom 1
Embankment ll� fuaaahl 1 Surface
Existing 0 3n Water
]41 C1--m 1
Method Name Min Emh t nt ❑ EeuMohmmbr- sarface
FS EA ng,'g er
10d verrcai o wat custom
Tailings ❑ Svess Ratio 4 S Surf iace
Bishop simplified 1.8 saprohte 1. Mohr- 0 2e Ovate` cu:mm 1
coummb sarfaee
Spencer 1.8 CMuhr- Water
Bedrock 1)9 40 6urfare Cusom 1
GLE/Morgenstern-
oulomb n
1.8 Water 62.4 Nostrength Su��Ce Custom 0
Oerburtlen ® 1. Mohr- 0 24 Water Custom 1
Coulomb Surface
P-all,
Weatheretl ❑ 1. Coulomb n 2e Surface Custom 1
Ro[
1.8 W
50
Figure 9—WSB-1 Critical Analysis Section C-C
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9. 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
The seismic displacement analysis is 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 previously. The
resulting yield accelerations are summarized on the tables summarizing the factors of safety
from the analysis section (Table 4).
• Step 2: The permanent seismic displacements under postulated loading were estimated by
procedures based on a simplified Newmark sliding block analysis. 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 Tables 7 and 8.
To evaluate the worst-case scenarios from the slope stability analyses described above, seismic
displacement estimates for the most critical of the three sections-section B-B -were computed using
these models for the and 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 300 m/s was assumed for the tailings material. Published PGA's were
obtained from mapped values (Table 2). Degraded spectral accelerations were obtained from the
available Lettis (2023) report.
From these analyses, slope displacements of 2 to 20 inches were calculated for the 1:2,450-year
event, with a maximum of more than 24 inches in the event for a 1:10,000 year event.
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Table 7: Summary of Seismic-induced Displacements for 10,000-year ARP
Section ky PGA Mw H (ft) Vs(m/s) Ts 1.3 Ts Sa(1.3 Ts) Makdisi,Seed &Choi(in) Bray&Macedo in
B-B 0.08 0.17 7.5 60 400 0.13 0.17 0.47 2 4
B-B 0.015 0.17 1 7.5 60 400 0.13 0.17 0.47 >24 20
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10. Conclusions
This calculation package was prepared in support of the pre-feasibility design of proposed WSB-1 at
the Kings Mountain Mining Project. The proposed blanket drain and buttress on the downstream face
of the existing embankment of WSB-1 will be constructed on soils and weathered bedrock following
the removal of existing unsuitable soils, unless otherwise noted in the construction documents. Shear
strength parameters for the different materials included in the stability analyses were obtained from
published data and the results of site investigations and laboratory characterization of tailings and
native soil materials as discussed in the report titled Water Storage Basin 1 (WSB-1)—Pre-feasibility
Site Characterization Report(SRK 2024). The seismic loading parameters were derived from the site-
specific seismic hazard analysis by Lettis (2023a).
The stability analyses performed confirm that the current conceptual design of the proposed WSB-1:
• Meet the criteria established for the static condition, with a FoS greater than or equal to 1.5
for each section analyzed
• Meet the criteria established for the pseudostatic condition, with a FoS greater than or equal
to 1.0
SRK recommends that the analyses described herein be reviewed and revised following the
completion of the 2023 site and material characterization and the next phase of facility design.
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11. References
Bishop, A. (1955). The use of the slip circle in the stability analysis of slopes. Geotechnique 5 (1), 7 -
17.
Bray, J.D., and Travasarou, T. (2007). Simplified Procedure for Estimating Earthquake Induced
Deviatoric Slope Displacements,Journal of Geotechnical and Geoenvironmental Engineering,Volume
133, No. 4, April 2, 2007.
Bray, J.D., and Macedo, J. (2014).
CDA. (2013). Dam Safety Guidelines 2007 (2013 Edition).
GEOVision, (2023). Seismic Investigation, Kings Mountain Mine, North Carolina.
Golder Associates, (1975). Report on Investigation of Tailings Dam for Foote Mineral Company,
unpublished report prepared for Foote Mineral Company by Golder Associates, March 1975.
GTR. (2020). Global industry Standard on Tailings Management.
Hawley, M. and Cunning,J. and CSIRO(2017). Guidelines for mine waste dump and stockpile design.
Clayton South, VIC : CSIRO Publishing.
Hynes, M., & Franklin, A. (1984). Rationalizing the Seismic Coefficient Method. Department of the
Army, Waterways Experiment Station, Corps of Engineers.
ICMM. (2021). Tailings Management: A good practice guide.
IRMA. (2019). Standard for responsible Mining - Guidance Document. Version 1.
Lambe, P. C., and Riad, A. H., 1990. Determination of Shear Strength for Design of Cut Slopes in
Partly Weathered Rock and Saprolite. Department of Civil Engineering North Carolina State University.
Lambe, 2019
Leps, T. (1970). Review of shearing strength of rockfill. Journal of the Soil Mechanics and
Foundations Division. 96 (4), 1159-1170.
Lettis Consultants International, Inc.,2023. Development of Site-Specific Ground Motions for the Kings
Mountain Mine Development, North Carolina, March.
Makdisi F. and Seed R.B. [1978], "Simplified Procedure for Estimating dam and Embankment
Earthquake Induced Deformations", Journal of Geotechnical Engineering Division, American Society
of Civil Engineers, Vol. 112, No. 1, January, pp44-59.
Morgenstern, N. R., & Price, V. E. (1965). The analysis of the stability of general slip surfaces.
Geotechnique 15 (1), 79-93.
NCEQ. (2017). North Carolina - Department of Environmental Quality. Subchapter 2K- Dam Safety.
RocScience Inc. (2022). Slide 2 Modeler, 2D Limit Equilibirum Analysis for Slopes.
Schnabel Engineering (2011). Foote Mineral Reservoir Dam Removal Design Report, prepared for
Wildlands Engineering, Inc. (on behalf of Chemetall Foote Corporation), by Schnabel Engineering
South, PC, Kings Mountain, N.C., July 6, 2011.
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Spencer, E. (1967). Method of analysis of the stability of embankments assuming parallel interslices
forces. Geotechnique, 11-26.
Sorensen et. al (2023). Undrained Cyclic Shear Behavior of Sensitive Saprolite Soil, Geocongress
2023 GSP 338.
Sowers, G., and Richardson, T., (1983). Residual Soils of Piedmont and Blue Ridge. Transportation
Research Record.
SRK (2024a). Archdale Tailings Storage Facility, Select Phase Site and Tailings Characterization
Report, Kings Mountain Mining Project, unpublished report prepared for Albemarle Corporation by
SRK Consulting (U.S.), Inc., April 2024.
SRK (2024b). Archdale Tailings Storage Facility, Select Phase Preliminary Engineering Design
Report, Kings Mountain Mining Project, unpublished report prepared for Albemarle Corporation by
SRK Consulting (U.S.), Inc., April 2024
Wijewickreme, D., Soysa, A., Verma, P. (2018). Response of natural fine-grained soils for seismic
design practice:A collection of research findings from British Columbia, Canada, in Soil Dynamics and
Earthquake Engineering 124, Elsevier, 2019.
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Plates
DC/THH KM_WSB-1_StabilityCalcPackage_Memo_USPR000576_FNL.docx April 2024

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TSFC-5 SNKM22-417
TSFC-1 TSFC 6 SNKM23-558
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1295000.00 1296000.00 1297000.00 1298000.00 1299000.00 130000.00 1301000.00 1302000.00
REVISIONS DESIGN: REVIEWED:AA PREPARED BY: DRAWING TITLE:
LEGEND REV. DESCRIPTION DATE DRAWN:LE APPROVED:AA KM WSB-1 CROSS SECTIONS
OO Boreholes 2022
0 250 500 COORDINATE SYSTEM: � Sr consulting PLAN VIEW
NADS3 NORTH CAROLINA STATE PLANES,US FOOT PROJECT:
Boreholes 2023
DATE: REVISION: DRAWING NO.
FEET KINGS MOUNTAIN MINE :
CPT Ak A L B E MA R L E 3/27/2024 0
IFTHEABOVE BAR Albemarle-Lithium
by. PLATE 1
DOES NOT MEASURE 1 INCH, AlbemarIe-L11hiUm SRK PROJECT NO.:
FILE NAME:WSB-1 Lithology Cross-Sections_versionl.dwg THE DRAWING SCALE IS ALTERED USPR0576.800
C:\Users\aalzate\OneDrive-SRK Consulting\0800_TSF\040_Drafting\Task-300_Cactus_Design\Working\BK\WSB-1 Lithology Cross-Sections_versionl Awg