ENGINEERING GEOLOGY. Landslides by U.S. Region. WV Has 1st or 2nd Highest Landslide Damage Per Capita $ /person/yr UTAH

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1 Essay Questions for New Topic: SLOPES Colluvial - Related to Hill-Slope or Mountain-Slope Processes, Especially Those Driven Directly by Gravity Colluvium - Gravity Driven Deposits U.S. Landslide Risk 1

2 Landslides by U.S. Region California West Virginia 40% of U.S. damage 13% of U.S. damage WV Has 1st or 2nd Highest Landslide Damage Per Capita $ /person/yr UTAH Regional Causes of Landslides Steep Topography Mountains Incision by Rivers in Last 1 MY Materials Red Shales - Expansive Clays Stupid or Ignorant People Oversteepening of Slopes w/o Geotechnical Consulting ENGINEERING GEOLOGY Terms to Know in Order to Talk to Civil Engineers Geotechnical Lingo 2

3 Weight (w) Resolved into 2 Vectors 1 Parallel to Slope 1 Perpendicular to Slope Vectors Vary with Tan β (beta) β β Coulomb Equation S = c + σ' tan Φ Shear Strength = Cohesion + Effective Normal Stress X Tangent of Angle of Repose S = c + σ' tan Φ Coulomb Equation Symbols Φ phi angle of internal friction σ' sigma effective normal stress β beta angle of slope, =Φ at failure c cohesion (grain-grain attraction) 3

4 Φ = Angle of Internal Friction = "Angle of Repose" Plane Friction + Interlocking Friction tan Φ Increases from 0 to Infinity as Φ Increases from 0 o to 90 o Normal Stress (σ') Influenced by Pore Pressure (μ) In Wet Soils σ' = σ - μ μ > 0 in saturated zone μ < 0 in unsaturated zone Factor of Safety = Shear Strength/Shear Stress Bearing Capacity: = Load/Area Without Yield Ultimate Bearing Capacity: = Load/Area Without Rupture 4

5 COMPACTION Artificial Compaction to Increase Bearing Capacity Void Ratio (% Voids in Soil) Void Ratio Decreases w/ Compaction Graph: Void Ratio vs. Pressure Normal Soil Void Ratio Precompacted Soil Pressure ATTERBERG LIMITS: Solid - Plastic - Liquid Plastic: Continuous Deformation With Stress Without Rupture Plastic Limit: Water Content at Which Solid Becomes Plastic Liquid Limit: Water Content at Which Plastic Becomes Liquid 5

6 ATTERBERG LIMITS: Solid - Plastic - Liquid Plasticity Index: Difference Between Plastic & Liquid Limits Liquidity Index: (at a given instant) H 2 0 Content - Liquid Limit Plasticity Index SENSITIVE CLAYS: more water than liquid limit - but retains plastic nature until disturbed How? honeycomb structure Water in Pores SENSITIVE CLAYS: more water than liquid limit - but retains plastic nature until disturbed How? honeycomb structure Water Escapes 6

7 Campbell & others (1986) Classification after Varnes See Ritter and others, 3rd Edition, 1995, p. 114) Landslides Rock Debris Soil Earth Fall Rock Fall Debris Fall Earth Fall Type of Motion Topple Planar Slide Rock Slide Debris Slide Earth Slide Rotational Slide Flow Rock Topple Rock Slump Debris Topple Earth Topple Debris Slump Earth Slump Rock Flow Debris Flow Earth Flow Rock Debris Earth Basic Landslide Classification Material Type of Motion Rock Debris Soil Earth 7

8 Material Rock = Bedrock Soil = Unconsolidated Material Debris: >20 % Big Stuff (>2 mm) Earth: <20 % Big Stuff (>2 mm) Basic Landslide Classification Material Type of Motion Rock Debris Soil Earth Landslides Rock Debris Soil Earth Fall Rock Fall Debris Fall Earth Fall Type of Motion Topple Planar Slide Rock Slide Debris Slide Earth Slide Rotational Slide Flow Rock Topple Debris Topple Earth Topple Rock Slump Debris Slump Earth Slump Rock Flow Rock Debris Flow Earth Flow Debris Earth 8

9 Landslides Rock Debris Soil Earth Fall Rock Fall Debris Fall Earth Fall Type of Motion Topple Planar Slide Rotational Slide Flow Rock Topple Debris Topple Earth Topple Rock Slide Debris Slide Earth Slide Rock Slump Debris Slump Earth Slump Rock Flow Debris Flow Earth Flow Rock Debris Earth ROCK FALL: Talus = Landform (= Block Apron) Scree = Deposit = Sediment (= Block Mantle) 70 Ton Boulder: Mon Blvd., 10 March

10 West Virginia's Ice Mountain Talus Slope: 10

11 Lower Talus Images River Mountain Crest Middle Upper Landslides - Topple gf/buildings/ltpisa/ ltpgallery/7nov99/ ltpgallery7nov99.htm Pisa Landslides Rock Debris Soil Earth Fall Rock Fall Debris Fall Earth Fall Type of Motion Topple Rock Topple Debris Topple Earth Topple Planar Slide Rock Slide Debris Slide Earth Slide Rotational Rock Slump Debris Slump Earth Slump Slide Flow Rock Flow Debris Flow Earth Flow Rock Debris Earth 11

12 Landslides Planar Slide = Slide SLIDE (Translational) Rock Slides may Parallel Weakness Rotational Slide = Slump SLUMP (Rotational Slide) Landslides Planar Slide = Slide Rotational Slide = Slump Seattle Shoreline Debris (?) Slide 12

13 Debris Slides, Venezuela, Dec 1999 Slump: the typical WV landslide. Slump scarp is at the head, and earthflow is at the toe. (Illustration by Paul Queen, WV Geol. Surv.) www/geohaz/geohaz3.htm La Conchita, California Slump 1995 &

14 Geomorphic Thresholds Intrinsic: e.g. collapse of cave Extrinsic: e.g. climate, humans Slump Slump in California 14

15 Tully Landslide, New York, 1994 Jäger, Stefan, & Wieczorek, Gerald F., 1994, Landslide Susceptibility in the Tully Valley Area, Finger Lakes Region, New York: USGS Open-File-Report FLOW: Confined to Channel or Hollow Debris Flows: Slurry Consistency Laminar Flow vs. Hyper-Concentrated Flow: Viscous Liquid Turbulent Debris flows, July 28, 1999, Interstate-70 corridor, Georgetown to the Eisenhower Tunnel, central Colorado Photo by Jeff Coe usgs.gov/i70/ New photo

16 Las Colinas, El Salvador, Jan 2001 Debris Slide (Reuters photo) November 1985 Debris Flow Track, Twin Run, Pendleton Co., WV Superelevation of Debris Flow, Twin Run 16

17 Kanawha City Debris Flow FLOW: Confined to Channel or Hollow Debris Flows: Slurry Consistency Laminar Flow vs. Hyper-Concentrated Flow: Viscous Liquid Turbulent Peeks Creek, NC, Sept

18 Peeks Creek, NC, Sept Debris Flows in Blue Ridge, Madison Co., Virginia Source: Gori, Paula L., and Burton, William C., 1996, Debris-Flow Hazards in the Blue Ridge of Virginia: U.S. Geological Survey Fact Sheet blueridge.htm 1995 Debris Flows in Virginia Blue Ridge 18

19 1995 Debris Flow in Virginia Blue Ridge A lucky family on the 2nd floor of the house (indicated by the arrow) survived the event. Goal: coarse open-framework internal drainage system without cost required to build chimney drain. Durable Rock Fill AVALANCHE: Trapped Air &/or Water Reduces Friction Snow Debris : Rapidly "Sliding" Debris - Typically Originates as Debris Slide 19

20 Mt. Huascaran, Peru, 1970 Mt. St. Helens Lahar, 1982 CVO Photo Archives - Mount St. Helens Debris MSH/Images/debris_aval_images.html 20

21 21

22 Mount St. Helens with debris avalanche in the foreground, 1990 Debris Deposits: North Toutle River, Mt. St. Helens 22

23 Debris Deposits: N Fork Toutle River Logging Camp, South Toutle River Debris Flow Track Toutle River Post 1980 Mud Flow 23

24 Landslides Debris Flow - Hazard Seattle Area DEBRIS FLOW VIDEOTAPE Costa, John E., and Williams, Garnett P., 1984, Debris-flow dynamics: U.S. Geological Survey Open File Report , 1 VHS videotape. Two WMV files of Landslides LandslideJapnAug wmv SultanRivLandslide.wmv 24

25 Creep: Slow Unconfined Flow of Soil or Rock Creep Creep 25

26 Creep Creep Creep 26

27 SOLIFLUCTION: Soil Flow Gelifluction: Solifluction Associated with Frozen Ground Frozen Soil Winter Mean Annual 0 o C Thawed Soil Summer Active Layer Permafrost Zone Landslides Rock Debris Soil Earth Fall Rock Fall Debris Fall Earth Fall Type of Motion Topple Planar Slide Rock Slide Debris Slide Earth Slide Rotational Slide Flow Rock Topple Rock Slump Debris Topple Earth Topple Debris Slump Earth Slump Rock Flow Debris Flow Earth Flow Rock Debris Earth Maximum (45 ) Angle of Generalized cross section of subsidence. The area on the surface affected by subsidence is Draw usually wider than the area mined out below. The angle of draw is formed by a line from the edge of the mined area straight up to the surface (A-B), and a line from the edge of the mined area to the edge of the surface subsidence (A-C). The angle of draw does not exceed 45 degrees. WVGES Homeowner's Guide to Geologic Hazards wvnet.edu/ www/geohaz/ geohaz3.htm 27