STABILITY ANALYSIS FOR THE RIGHT ABUTMENT SPILLWAY ISABELLA DAM CA
AEG Annual Meeting September 2017 Main Dam
Michael Nield, Senior Engineering Geologist U.S. Army Corps of Engineers, Huntington WV LRD Dam Safety Production Center Dam Safety Modification Mandatory Center of Expertise
“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”
BUILDING STRONG® and Taking Care of People!
File Name 1 Stability Analysis for the Right Abutment Spillway – Isabella Dam, CA OUTLINE
A. PROJECT INFORMATION 1. Project Location 2. Project Description 3. Site Geology
B. SPILLWAY STABILITY 1. Founding Elevations 2. Plane Analysis 3. Wedge Analysis
C. CUT-SLOPE STABILITY 1. Stereonet Analysis 2. Construction Concerns
BUILDING STRONG® 2 and Taking Care of People! Isabella Dam – Project Location
Vicinity Map
Kern River Watershed
ISABELLA DAM
ISABELLA DAM
Bakersfield
BUILDING STRONG® 3 and Taking Care of People! Isabella Dam – Site Plan Constructed 1948-1953 Primary Purposes: Flood control (~ 74%); Irrigation (~21%); Non-Federal Hydropower (~5%) AUXILIARY DAM • 100 ft high • Homogeneous silty sand • Foundation = alluvial soils and bedrock MAIN DAM • 185 ft high • Zoned earth fill (almost homogeneous) • Foundation primarily granitic bedrock
SPILLWAY • Ungated spillway OUTLET WORKS • Ogee Weir • Hydropower
BUILDING STRONG® 4 and Taking Care of People! Primary Issues – Potential Failure Modes
Kern Canyon Fault (Previous Interp: Inactive) Erosion Through Rupture Auxiliary Dam a Crack Near the Main Dam Crest
Cross Section – Kern Caynon Fault – Auxiliary Dam
Seismic Stability of Borel Conduit and Tower Undersized spillway
Internal Erosion and Erosion Along the Hydrologic Liquefaction Potential of the Conduit Overtopping Foundation Alluvium
BUILDING STRONG® and Taking Care of People! Consequences of Dam Failure - Inundation
Vicinity Map
Kern River ISABELLA Watershed DAM
Subsequent Immediate Inundation Inundation Area Area
BUILDING STRONG® and Taking Care of People! Isabella Dam – Proposed Modifications Kern Canyon Fault
Main Dam
Auxiliary Dam
Existing Service Spillway
BUILDING STRONG® 7 and Taking Care of People! Proposed Modifications – Emergency Spillway Proposed Kern Canyon Fault Emergency Spillway
Main Dam
Auxiliary Dam Upstream Labyrinth Weir Existing Service Spillway
Emergency Spillway Physical Model
BUILDING STRONG® 8 and Taking Care of People! Proposed Modifications – Emergency Spillway Proposed Kern Canyon Fault Emergency Spillway
Main Dam
Auxiliary Dam
Existing Service Spillway
BUILDING STRONG® 9 and Taking Care of People! Proposed Modifications – Main Dam Proposed Kern Canyon Fault Emergency Spillway
Main Dam Cross Section - Main Dam
Auxiliary Dam
. Raise Top of Main Dam by 16’ . Downstream Filter & Drain
BUILDING STRONG® 10 and Taking Care of People! Proposed Modifications – Main Dam Proposed Kern Canyon Fault Emergency Spillway
Main Dam
Auxiliary Dam
. Raise Top of Main Dam by 16’ . Downstream Filter & Drain
BUILDING STRONG® 11 and Taking Care of People! Proposed Modifications – Auxiliary Dam Proposed Kern Canyon Fault Emergency Spillway
Main Dam
Auxiliary Dam Section - Auxiliary Dam Inside Fault Zone
. Raise Top of Main Dam by 16’ . Downstream Filter & Drain
. Raise Top of Auxiliary Dam by 16’ . Downstream Buttress with Filter & Drain
Section - Auxiliary Dam Outside Fault Zone BUILDING STRONG® 12 and Taking Care of People! Proposed Modifications Proposed Kern Canyon Fault Emergency Spillway
Main Dam
Auxiliary Dam
. Raise Top of Main Dam by 16’ . Downstream Filter & Drain
. Raise Top of Auxiliary Dam by 16’ . Downstream Buttress with Filter & Drain
BUILDING STRONG® 13 and Taking Care of People! Proposed Modifications – Right Abutment Spillway Main Dam
Right Abutment Spillway
State Route 155
3D ImageExisting of Proposed Service Right Spillway Abutment Spillway BUILDING STRONG® 14 and Taking Care of People! Site Geology
Mount Adelaide (early Cretaceous) Cretaceous-aged Alta Sierra Granite
Light gray, medium grained, hard
Alta Sierra (late Cretaceous) Varying degrees of weathering Right Abutment Spillway Moderate to severely fractured
Kern River Granite Dam (late Cretaceous)
Geologic Map – US Geologic Survey Mount Adelaide Existing Service Spillway (early Cretaceous)
BUILDING STRONG® 15 and Taking Care of People! Exploratory Drilling 1F-16-02
Proposed Right Abutment 1F-13-13 Spillway Core Samples 1F-13-14 1F-13-15 1F-13-16 1F-13-17 Exploratory Drilling
1F-16-04 Main Dam Raised 16’
1F-16-03 Inclined Boring Vertical Boring Boring Location Plan Down-Hole Camera BUILDING STRONG® Down-Hole16 Camera Images and Taking Care of People! Granite - Weathering
Decomposed Granite: reddish brown, soft, soil-like w/ relic bedrock structure, under 2,000 psi UCS
Highly Weathered Granite: light reddish brown, soft to mod. hard, individual grains can be easily plucked with a knife, 2,000 – 8,500 psi UCS. Predominant rock type at spillway site.
Moderately Weathered Granite: light reddish gray, moderately hard to hard, difficult to pluck individual grains with knife, 8,500 to 10,000 psi UCS. Boring F1-13-15 Showing Varying Degrees of Weathering
Slightly or Unweathered Granite: Light gray, hard, 10,000 to 25,000 psi UCS.
BUILDING STRONG® 17 and Taking Care of People! Discontinuities SR 155
Main Dam Exposure at Site - Showing Low-Angled Joints
Typical Fracture: planar shape; smooth surface; occasionally open, iron stained or clay coated; and continuous (10’ to +100’ length)
Distinct Joint Sets (A - K)
Moderate to intensely fractured
Aerial View - Showing High-Angled Joint Sets Shear Zones
BUILDING STRONG® 18 and Taking Care of People! Stability Analysis for the Right Abutment Spillway – Isabella Dam, CA OUTLINE
A. PROJECT INFORMATION 1. Project Location 2. Project Description 3. Site Geology
B. SPILLWAY STABILITY 1. Founding Elevations 2. Plane Analysis 3. Wedge Analysis
C. CUT-SLOPE STABILITY 1. Stereonet Analysis 2. Construction Concerns
BUILDING STRONG® 19 and Taking Care of People! Potential Spillway Erosion - Consequences
Isabella Dam – Right Abutment Spillway Oroville Dam - Spillway Erosion
BUILDING STRONG® 20 and Taking Care of People! Right Abutment Spillway - Design
Upstream Dam Crest Downstream
Plan View Main Dam
Profile View
BUILDING STRONG® 21 and Taking Care of People! Founding Elevation – Typical Upstream of Dam2680 Monolith
Top of Ground Soil
Boring 2660 DG Decomposed Granite F1-16-02 DRAIN Foundation Concrete Highly Weathered Granite 2 HW SOIL (SM) 1 2640 DG Spillway HW MW Moderately Weathered Temporary Granite Detour MW 2620 Slightly Weathered Road SW HW Granite Preliminary Foundation 100 0 2600 UW Unweathered Granite Approximate Base RQD WEATHERING of Near-Surface Elevations Decomposed . Foundation surface will Granite 2580 be free of all soil, Decomposed Granite and loose rock. 2560 . -100 -80 -60 -40 -20 0 20 40 60 80 100 Foundation geometry will Cross Section – Station 101+70 consist of stair-stepped series of horizontal BUILDING STRONG® and Taking Care of People! 22 surfaces. Founding Elevation – Typical Dam Crest2680 Monolith Top of Ground Soil
Boring 2660 DG Decomposed Granite Raised Dam Embankment F1-13-14
2 1 HW Highly Weathered Granite DRAIN 2640
Dam GP Moderately Weathered & Spillway MW Embankment GM Granite SP DG Preliminary Foundation Elevations HW 2620 Slightly Weathered SW Foundation Concrete Granite MW & HW 2600 UW Unweathered Granite
HW
Approximate Base of Near- . Foundation surface will Surface Decomposed Granite 2580 be free of all soil, Decomposed Granite Approximate Top of Rock and loose rock. 2560 . -100 -80 -60 -40 -20 0 20 40 60 80 100 Foundation geometry will Cross Section – Station 102+90 consist of stair-stepped series of horizontal BUILDING STRONG® and Taking Care of People! 23 surfaces. Founding Elevation – Typical Downstream2680 Monolith Top of Ground Soil
2660 DG Decomposed Granite Boring F1-16-04 HW Highly Weathered Granite 2640 DRAIN Foundation Concrete Spillway 2 MW Moderately Weathered SW 1 Granite DG 2620 Slightly Weathered Temporary Foundation Drain SW Granite Detour Road HW Preliminary Foundation Elevations
2600 UW Unweathered Granite
Approximate Base of . Foundation surface will Near-Surface Decomposed Granite 2580 be free of all soil, Decomposed Granite and loose rock. 2560 . -100 -80 -60 -40 -20 0 20 40 60 80 100 Foundation geometry will Cross Section – Station 104+20 consist of stair-stepped series of horizontal BUILDING STRONG® and Taking Care of People! 24 surfaces. Preliminary Foundation Elevations
Upstream Dam Downstream Crest Foundation Drains Joint Drains
Foundation Concrete Profile View . Final foundation elevations will be established in the field.
. Experienced on-site geologist is required.
. Localized problematic areas are expected.
. Dental concrete may be required. Core Samples from Boring 1F-16-02
BUILDING STRONG® 25 and Taking Care of People! Spillway Structure - Design Details
Dowel Bars
Waterstop Foundation Drain
Section - Downstream - Foundation Drain Expansion Joint Detail
Joint Drains
Joint Drain
Foundation Drains
BUILDING STRONG® 26 Jointand Taking Drain Care ofDetail People! Profile View Planar Sliding Stability – Input Parameters
Bedrock Exposures – Joint Orientations
. Sliding Resistance for Highly Weathered Granite: phi = 33 degrees, cohesion = 0 psi
. 5 degree waviness or i angle (as measured in field)
. Maximum design earthquake: horizontal PGA 0.3g, vertical PGA 0.21g. Seismic coefficient 0.2 (2/3 of 0.3g) Dam Construction Profile BUILDING STRONG® 27 and Taking Care of People! Planar Sliding – Downstream Monolith – Load Cases 2680 Required Load Case Loading Factor of Top of Ground 14o Plane Condition Safety Dry Joints 2660 Usual 1.5 no uplift Rain - Wet Joints Unusual 1.3 full uplift Flood PMF Spillway 2640 full uplift Extreme 1.1 Earthquake MDE no uplift Extreme 1.1 Uplift - Groundwater 2620
Potential Failure Plane (47.8’ length, 14 degree inclination) 2600
Approximate Base of Near-Surface 2580 Decomposed Granite
2560 -100 -80 -60 -40 -20 0 20 40 60 80 100 Cross Section – Downstream of Dam – 14o Plane BUILDING STRONG® and Taking Care of People! 28 Planar Sliding – Downstream Monolith – Load Cases 2680 Required Load Case Loading Factor of Top of Ground 20o Plane Condition Safety Dry Joints 2660 Usual 1.5 no uplift Rain - Wet Joints Unusual 1.3 full uplift Flood PMF 2640 full uplift Extreme 1.1 Spillway Earthquake MDE no uplift Extreme 1.1 2620
Potential Failure Plane (109’ length, 20 degree inclination) 2600
Approximate Base of Near-Surface Decomposed Granite 2580
2560 -100 -80 -60 -40 -20 0 20 40 60 80 100 Cross Section – Downstream of Dam – 20o Plane BUILDING STRONG® and Taking Care of People! 29 Planar Sliding – Dam Crest – Load Cases - Construction 2680 Required Load Case Loading Factor of Top of Ground 20o Plane Condition Safety Dry Joints 2660 Usual 1.5 no uplift
Rain - Wet Joints 2 Unusual 1.3 full uplift 1 DRAIN 2640 Spillway
SP Dam 2620 Uplift - Groundwater Embankment Potential Failure Plane
(47.8’ length, 14 degree inclination) 2600
Approximate Base of Near-Surface Decomposed Granite 2580
2560 -100 -80 -60 -40 -20 0 20 40 60 80 100 Cross Section – Station 102+90 BUILDING STRONG® and Taking Care of People! 30 2D Planar Sliding Equation
BUILDING STRONG® 31 and Taking Care of People! 2D Planar Sliding Stability – Summary & Sensitivity
BUILDING STRONG® 32 and Taking Care of People! 3D Wedge Analysis
Wedge - Two Joints w/ Tension Plane
Hypothetical Wedge
Major Joint Sets
BUILDING STRONG® and Taking Care of People! 33 Detrimental Wedges
Utilized Swedge program from Rocscience
Two detrimental wedges: Joint Sets A&C Joint Sets D&E
Sliding resistance of Highly Weathered Granite: phi = 33o, c = 0 psi w/ 5o waviness added
Major Joint Sets Detrimental Wedges
BUILDING STRONG® and Taking Care of People! 34 Wedge Configurations
Tension Plane Tension Plane
Joint Sets D&E Joint Sets D&E Joint Sets A&C Joint Sets A&C With Tension Plane W/O Tension Plane With Tension Plane W/O Tension Plane
BUILDING STRONG® and Taking Care of People! Wedge Analysis – Load Cases
Weight of Structure Added Weight of Added PMF Flow
Horizontal Force
Uplift Earthquake Force
Dry Joints Rain Event PMF Flood MDE Earthquake Usual Water Filled Joints Water Filled Joints Dry Joints Unusual Extreme Extreme
BUILDING STRONG® and Taking Care of People! 3D Wedge Stability – Summary & Sensitivity
Sensitivity – Wedge D&E w/ Tension Plane (wet) BUILDING STRONG® 37 and Taking Care of People! Stability Analysis for the Right Abutment Spillway – Isabella Dam, CA OUTLINE
A. PROJECT INFORMATION 1. Project Location 2. Project Description 3. Site Geology
B. SPILLWAY STABILITY 1. Founding Elevations 2. Plane Analysis 3. Wedge Analysis
C. CUT-SLOPE STABILITY 1. Stereonet Analysis 2. Construction Concerns
BUILDING STRONG® 38 and Taking Care of People! Cut-Slope Stability 2680
Cut-Slope Top of Ground
2660 Raised Dam Embankment 2 1 2640 DRAIN Spillway SP Preliminary Foundation Elevations Dam 2620 Embankment Foundation Concrete
2600
Approximate Base of Near-Surface Decomposed Granite 2580 Approximate Top of Rock
2560 -100 -80 -60 -40 -20 0 20 40 60 80 100 Cross Section – Station 102+90 BUILDING STRONG® and Taking Care of People! 39 Kinematic Analysis – Input Parameters
Existing Slope
Sliding Resistance for Highly Weathered Granite: phi = 33 degrees, cohesion = 0 psi
BUILDING STRONG® and Taking Care of People! Stereographic Projection – Planar Failure
West Side Cut Slope ½:1 East Side Cut Slope ½:1
BUILDING STRONG® 41 and Taking Care of People! Stereographic Projection – Wedge Failure
West Side Cut Slope ½:1 East Side Cut Slope ½:1
BUILDING STRONG® 42 and Taking Care of People! Stereographic Projection – Toppling Failure
West Side Cut Slope ½:1 East Side Cut Slope ½:1
BUILDING STRONG® 43 and Taking Care of People! Future Construction Concerns . Overhead boulders or rock fall during excavation.
. Mechanical excavation methods
. Joints with detrimental orientations and low sliding resistance (clay filled or fault gouge) Boulders Above Proposed Cut-Slope . Localized problematic areas of Decomposed Granite.
. Experienced on-site geologist is required
Construction Contract Status
. Plans and Specifications completed
. Advertised and Bids received
. Hillside Above Lake Isabella Notice to Proceed - soon
BUILDING STRONG® 44 . Approximately 4 years to construct and Taking Care of People! Stability Analysis for the Right Abutment Spillway – Isabella Dam, CA CONCLUSIONS / TAKE AWAYS
1. Sliding stability for structures can be determined by utilizing equations and methods typically used for cut-slope design. (If the proposed structure is on the side of a hill)
2. Bedrock weathering can have significant impact on rock strength and influence structural design.
3. How can anyone can talk so much about such a small project?
BUILDING STRONG® 45 and Taking Care of People! Stability Analysis for the Right Abutment Spillway Isabella Dam, CA
BUILDING STRONG® 46 and Taking Care of People!