closure of remote historic underground mines … of remote historic underground mines in desert...

Closure of Remote Historic Underground Mines in Desert EnvironmentsClosure of Remote Historic Underground Mines in Desert Environments

AGAPITO ASSOCIATES, INC.Consulting EngineersAGAPITO ASSOCIATES, INC.Consulting Engineers

2002 SME Annual Meeting and Exhibit2002 SME Annual Meeting and Exhibit

James A. Cremeens Agapito Associates, Inc.Michael H. Rauschkolb U.S. Borax, Inc.


• Geotechnical solutions were developed for closure of two historic underground borate mines in the deserts of California

• The Old Borate mining district located in the Mojave Desert near Barstow California

• Mined from 1890 to 1907

• The Lila C. Mine near Death Valley California

• Mined from 1907 to 1916 and 1920 to 1926

• Geotechnical solutions were developed for closure of two historic underground borate mines in the deserts of California

• The Old Borate mining district located in the Mojave Desert near Barstow California

• Mined from 1890 to 1907

• The Lila C. Mine near Death Valley California

• Mined from 1907 to 1916 and 1920 to 1926


CALIFORNIA

SanFrancisco

Lila C. Mine Site

Old Borate Mine Site

DeathValley

N

LosAngeles

SanBernardino

Location of the Old Borate and Lila C. Mine Sites

Location of the Location of the Old Borate and Old Borate and Lila C. Lila C. Mine SitesMine Sites


Big Borate CanyonBig Borate CanyonBig Borate Canyon


Big Borate Canyon post-1898

Big Borate Canyon Big Borate Canyon postpost--18981898


Haulage AditHaulage AditHaulage Adit


Decline ShaftDecline ShaftDecline Shaft


Dugout DwellingDugout DwellingDugout Dwelling


Underground at Old Borate

(Circa 1902—from Reynolds 1999)

Underground at Underground at Old Borate Old Borate

(Circa 1902(Circa 1902——from from Reynolds 1999)Reynolds 1999)


Closure CriteriaClosure CriteriaClosure Criteria•Prevent public access

•Protect wildlife

•Minimize impact to fragile desert landscape

•Assure environmental compatibility

•Optimize use of native materials

•Prevent public access

•Protect wildlife

•Minimize impact to fragile desert landscape

•Assure environmental compatibility

•Optimize use of native materials


Wildlife ProtectionWildlife ProtectionWildlife Protection• Conducted by bat and desert tortoise specialists

• Daytime internal examination and night bat surveys with night vision equipment and ultrasonic detectors

• No tortoise sign found within mines

• Bats or bat sign found in most of the mine openings

• Mine openings fenced to allow bat exit but not re-entry

• Conducted by bat and desert tortoise specialists

• Daytime internal examination and night bat surveys with night vision equipment and ultrasonic detectors


• Bats or bat sign found in most of the mine openings

• Mine openings fenced to allow bat exit but not re-entry


Pre-Construction DesignPrePre--Construction DesignConstruction Design

•ADITS•Collapse and Regrade•Polyurethane Foam

•SHAFTS and STOPES•Pre-Cast Concrete Panel Caps

•ADITS•Collapse and Regrade•Polyurethane Foam

•SHAFTS and STOPES•Pre-Cast Concrete Panel Caps


31

Original Ground

Final Grade (3H:1V)

Excavation (1.5H:1V)

Shaft Opening

Precast Concrete Panels

ExtremelyWeathered Siltstone

UnweatheredSiltstone

1.51

Prepare Smooth FoundationSurface and Shim Such ThatPanel Edges are Flush andPanels are Coplanar

Panel

Foundation

Backfill with Mine WasteRock (optional)

48"Typ.

2L

12"Typ.48"

Typ.

ShaftOpening

Armor Finished Slopewith Cobbles and Boulders

PanelAbutmentJoint

SurficialMaterialBackfillSurvey

Monument

Pre-cast Concrete Panel DesignPrePre--cast Concrete Panel Designcast Concrete Panel Design


• Strength of weak siltstone and claystone did not increase with depth

• Low bearing capacity• Foundation could be easily eroded• Ground caved and grew laterally with excavation

• Excavated mine openings were larger than surface expression• Large spans for pre-cast concrete panels• Increased number of concrete panels• Would have required steel beam support for large

spans

• Strength of weak siltstone and claystone did not increase with depth

• Low bearing capacity• Foundation could be easily eroded• Ground caved and grew laterally with excavation

• Excavated mine openings were larger than surface expression• Large spans for pre-cast concrete panels• Increased number of concrete panels• Would have required steel beam support for large

spans

Field ConditionsField ConditionsField Conditions


Final DesignFinal DesignFinal Design

•SHAFTS and STOPES•Boulder Plug

•ADITS•Collapse and Regrade with Boulder Plug•Polyurethane foam

•SHAFTS and STOPES•Boulder Plug



Components of a Typical Boulder Plug ClosureComponents of a Typical Boulder Plug ClosureComponents of a Typical Boulder Plug Closure

Original

Final Grade

Excavation

Boulder Plug

ExtremelyWeathered Siltstone

UnweatheredSiltstone

SurficialMaterialBackfill

SurveyMonument

(1H:2V)

Ground


Typical Adit Boulder Plug ClosureTypical Adit Boulder Plug ClosureTypical Adit Boulder Plug Closure

Excavation

Adit

1.51

Backfill

Regraded to Original

Monument

Original

Adit Portal

Boulder

Slope or Flatter

Ground

Survey

BackfillMaterialSurficial

(1.5H:1V)(Collapse)


Excavating a StopeExcavating a StopeExcavating a Stope


Typical Boulder Plug Placement SequenceTypical Boulder Plug Placement Sequence

Placing Initial BouldersPlacing Initial Boulders Completed Boulder PlugCompleted Boulder Plug


Typical Boulder Plug Placement SequenceTypical Boulder Plug Placement Sequence

Beginning Backfill and Regrade

Beginning Backfill and Regrade

Placing FinalSoil Cover

Placing FinalSoil Cover


Summary of Old Borate ClosureSummary of Old Borate ClosureSummary of Old Borate Closure

• 120 mine openings closed in 5-week period

• Boulder plugs satisfied design criteria

• Closure costs were significantly reduced by using native materials

• Lower unit costs = more mine openings closed

• 120 mine openings closed in 5-week period

• Boulder plugs satisfied design criteria

• Closure costs were significantly reduced by using native materials

• Lower unit costs = more mine openings closed


Lila C. Mine Site—Circa 1907


Main Haulage Level of the Lila C. Mine—Circa 1910


Stope at Lila C.Stope at Lila C.Stope at Lila C.


Decline shaft at Lila C.Decline shaft at Lila C.Decline shaft at Lila C.


Open Stope at Lila C.Open Stope at Lila C.Open Stope at Lila C.


Wildlife ProtectionWildlife ProtectionWildlife Protection• Conducted by bat and desert tortoise specialists


• Surveys revealed four species of bats in the mines

• Two bat “Species of Special Concern” found

• Bat accessible designs were included in closure

• Conducted by bat and desert tortoise specialists


• Surveys revealed four species of bats in the mines

• Two bat “Species of Special Concern” found

• Bat accessible designs were included in closure


Bat Accessible ClosuresBat Accessible ClosuresBat Accessible Closures•Bat gates and cupolas designed by specialty contractor

to protect bat access, preserve ventilation, and maintain temperature

•Underground surveys conducted to optimize bat accessible design

•Bat gates and cupolas designed by specialty contractor to protect bat access, preserve ventilation, and maintain temperature

•Underground surveys conducted to optimize bat accessible design


Closure DesignClosure DesignClosure Design

•SHAFTS and STOPES•Rock Mattress – AAI innovation


•SHAFTS and STOPES•Rock Mattress – AAI innovation



NativeGround

NativeGround

OriginalGrade

Partially Collapsedand Backfilled Stope

Pre-closure Daylighted Stope Configuration

PrePre--closure closure Daylighted Daylighted Stope Stope ConfigurationConfiguration

Limits of

Mattress

Excavation

BackfilledStope

(1H:1V)

GabionsBackfill

Final Grade

NativeGround

Rock

Rock Mattress Excavation and Construction of a

Daylighted Stope Closure

Rock Mattress Excavation Rock Mattress Excavation and Construction of a and Construction of a

Daylighted Stope ClosureDaylighted Stope Closure

Lila C. Mine—Typical Profiles


Open StopeExisting

GabionsBottom Layer

GabionsTop Layer

Gabions In PlaceBottom and Top Layer

CL

Rock Mattress Construction for a Daylighted Slope

Rock Mattress Construction for a Daylighted Slope


a) Pre-constructiona) Pre-constructionattress Construction for a Daylighted Stopeattress Construction for a Daylighted Stope

b) Grading Hanging Wallb) Grading Hanging Wall


Rock Construction for a Daylighted StopeRock Construction for a Daylighted Stopec) Wheel Roll Compactionc) Wheel Roll Compaction

d) Gabion Constructiond) Gabion Construction


Rock Construction for a Daylighted StopeRock Construction for a Daylighted Stopee) Filling Gabions withNative Rocke) Filling Gabions withNative Rock

f) Backfilling OverGabion Rock Mattress

f) Backfilling OverGabion Rock Mattress


Rock Construction for a Daylighted StopeRock Construction for a Daylighted Stopeg) Partially BackfilledRock Mattressg) Partially BackfilledRock Mattress

h) Final Grade and Armored Slope

h) Final Grade and Armored Slope


Rock Construction for a Shaft ClosureRock Construction for a Shaft Closure

a) Shaft after Surface Preparation for Rock Mattressa) Shaft after Surface Preparation for Rock Mattress

Plywood Barrier to Keep Debrisout of Shaft During Excavation

Rock Debrison Plywood Barrier

ShaftPerimeter



b) First Layer of Gabions of Shaftb) First Layer of Gabions of Shaft

ShaftPerimeter



c) First and Second Layers of Rock-filled Gabions—Completed Rock Mattress at Shaft

c) First and Second Layers of Rock-filled Gabions—Completed Rock Mattress at Shaft

First Layerof Gabions

Second Layerof Gabions



d) “Load Test” on a Rock Mattress at Shaftd) “Load Test” on a Rock Mattress at Shaft


Backfillover L26a

L26b


e) Backfill over Rock Mattresse) Backfill over Rock Mattress


Typical Foam Seal ConstructionTypical Foam Seal ConstructionTypical Foam Seal Constructiona) Preparing Backing Latticea) Preparing Backing Lattice

b) Applying Foamb) Applying Foam

c)Completed FoamApplication

without Backfill

c)Completed FoamApplication

without Backfill


Bat GateBat GateBat Gate


Construction and Final Configuration of Bat CupolaConstruction and Final Configuration of Construction and Final Configuration of Bat CupolaBat Cupola

a) Landing Ring and First Course Concrete

Pipe in Place

a) Landing Ring and First Course Concrete

Pipe in Place

b) Completed/Backfilled

Shaft ExtensionAnd Bat Cupola

b) Completed/Backfilled

Shaft ExtensionAnd Bat Cupola


Cost Comparison (USD-2000)Cost Comparison Cost Comparison (USD(USD--2000)2000)

•Gabion Rock Mattress with concrete $21,920

•Plastic Grid $21,712

•Foam Plug $20,890

•Gabion Rock Mattress $18,880

•Gabion Rock Mattress with concrete $21,920

•Plastic Grid $21,712

•Foam Plug $20,890

•Gabion Rock Mattress $18,880


Thank-YouThankThank--YouYou

closure of remote historic underground mines … of remote historic underground mines in desert...

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