Stability Analysis on Clay Slopes Impacting US Highway 45 near Military Hill, Ontonagon, MI

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1 Stability Analysis on Clay Slopes Impacting US Highway 45 near Military Hill, Ontonagon, MI GE4900 Presented by: Tasha Cook, Kirsten DePrekel, Leah Meek, Megan Sprague, Luke Weidner Advisor: Dr. Thomas Oommen, GMES

2 Outline Objective Background Highway Slope Stability Field and Lab Work Slide Modeling Mitigation Regional Slope Stability Trigger Analysis Regional Model Mitigation Methods Luke Weidner

3 Objective Evaluate the stability of slopes along the US Highway 45 near Military Hill and design mitigation measures. Evaluate the slope failures occurring along the Ontonagon River and characterize the susceptibility of the slopes along the river for future slides. Image: Dr. Stan Vitton

4 Location of Study Area

5 Surface Geology Buried Keweenaw Fault Late Pleistocene glacio-lacustrine derived sediments Glacial lake Ontonagon

locations selected to cover stable and unstable areas of the slope

6 Fieldwork 3 trips to the site Collected samples for lab tests Field tests vane shear test, CPT, shelby tubes, and Lidar Test locations selected to cover stable and unstable areas of the slope Little vegetation until tree line Utility marker shows movement 60 Leah Meek

8 Sample Locations

9 Lidar: FARO Focus 4 scenes collected on Oct 29, 2017 Merged in SCENE Software to create point cloud Ultimately did not use for modeling

10 Aerial Lidar Flown by Quantum Spatial in Created 0.5 meter DEM and cross sections

11 Labwork UCS, Unconfined Compression Strength Represents undrained conditions; cohesion Atterberg Soil classification using USCS Unit Weight Used in modeling Moisture Content Specific Gravity Kirsten DePrekel

Min Mean Max Su, Undrained Shear Strength (kpa) Vane Shear 40 70 128 Lab UCS 23 31 42 DCPT 25-50 Smith (2012)* 48-96 Dyl (1979)**+ 770-1600 31 51 72 Koons (1965)*** PI, Plasticity Index (%) Current

13 Min Mean Max Su, Undrained Shear Strength (kpa) Vane Shear Lab UCS DCPT Smith (2012)* Dyl (1979)** Koons (1965)*** PI, Plasticity Index (%) Current Study Smith (2012) Dyl (1979) LL, Liquid Limit (%) Current Study Smith (2012) Dyl (1979)+ Water Content (%) Current Study Dyl (1979) Min Mean Max

14 Slide Modeling Megan Sprague Slide 7.0 2D Slope Stability Analysis Cohesion-average UCS Shear Strength Friction Angle-worst case scenario (Koons, 1965) Unit Weight-from lab testing

16 Slide Modeling: 2D/3D comparison Extruded 2D Model 3D Model

17 Slide Modeling: 2D/3D comparison

18 Slide Modeling: 3D results

19 Slide Modeling: 3D results

20 Slide Modeling: 3D results Data suggests that the slope is highly susceptible to a deep failure. The unmitigated factor of safeties were low and this is a concern. There are already surface failures on the slope and they may be a precursor to a larger failure. The data showed a very high shear strength at low cohesion and friction angles. This further stresses the need for mitigation of a deep failure.

21 Mitigation Constraints: Cost Available Resources Environmental Impacts Slope Geometry Functionality Slide 7.0 and Microsoft Excel Cost Estimates done for each design Estimates from Darren Beckstrand (AKDOT) and MDOT were used Tasha Cook

22 Design Mitigation Estimated Cost Unit Applicable Practical Total Cost Anchored Wire Mesh $ 3.00 per sq ft Yes Yes $ Debris Flow Fencing $ per ln ft Yes No n/a Soil Nails $ per nail No No n/a Lightweight Fill $ per cu yd No No n/a Excavation $ 2.00 per cu ft Yes Yes Geotextiles $ 2.96 per sq yd No No n/a Horizontal Drains $ per ln ft No No n/a Quarry Spalls $ per ton No No n/a Rock Buttress $ per ton Yes Yes Soldier Pile Wall $ per sq ft Yes No Cantilever Retaining Wall $ per sq ft concrete Yes Yes $ $ 356, ,128, , n/a $ 462,679.71

Mitigation: No Measures Variability in magnitude of damage if failure occurs Similar landslides damage cost estimated between $150,000 to $2 million

23 Mitigation: No Measures Variability in magnitude of damage if failure occurs Similar landslides damage cost estimated between $150,000 to $2 million Preventing slope failure reduces future damage costs Road resurfacing needed every years Current surface ~5 years old Monitoring can be installed to signal failure

24 Mitigation: Impractical Designs Geotextiles Slope rebuilding Horizontal Drains Water is not cause Lightweight Fill Costly Soil Nailing Nails extremely long Debris Flow Fencing Temporary solution Soldier Pile/Tieback Walls Unpractical dimensions

25 Mitigation: Excavation Head Excavation: reduces driving forces to improve stability; for rotational slides Adding Benches: reduces driving forces; for shallow failures Slope Angle Reduction: not effective in large, planar, failures Large Excavation: not recommended in soft clays; triggers deep failure surface when excavating shallow failure surface

Mitigation: Rock Buttress Increases slope stability by increasing force on the toe of the slope Creates counterforce that resists failure Greater

26 Mitigation: Rock Buttress Increases slope stability by increasing force on the toe of the slope Creates counterforce that resists failure Greater unit weight of rock than slope is preferred to decrease probability of failure Rock aggregate pricing is $15/ton from nearby quarry Chatwin, S. C. (1994)

27 Mitigation: Retaining Wall Reinforced concrete cantilever retaining wall Retains earth behind the structure and adds load to the toe of the failure surface Groundwater has little effect on the surrounding soils; very little surcharge Ensures probability of slip circle failure to be low More practical than other retaining wall systems

28 Mitigation: Rock Buttress/Excavation Intended to function as a shear key in the toe while stabilizing the weight of the slope Benched excavation for ease of mobility Varied dimensions used Basalt Aggregate with unit weight of 30 kn/m3

29 Mitigation: Rock Buttress/Excavation

30 Mitigation: Rock Buttress/Excavation

31 Final Design Choices Rock Buttress/Excavation Bishop Simplified Method Deterministic Factor of Safety increased 0.08 ( ) Probability of Failure decreased by 14.3% Mean Factor of Safety increased to nearly 1

32 Trigger Analysis Discharge Data Daily discharge data collected from USGS gauge station Aerial Imagery from EarthExplorer Kirsten DePrekel Landslide Inventory Mapping

33 Trigger Analysis: Statistical Analysis

35 Regional Model: Overview What is landslide susceptibility? The relative spatial likelihood for the occurrence of landslides of a particular type and volume (van Westen) Typical methods: Statistical (LR), Deterministic (Scoops3D) Goal: Locate areas susceptible to rapid, large-volume rotational failures Luke Weidner

36 Regional Model: Scoops 3D Scoops3D Input Parameters Material Properties Groundwater Value Units MiGDL WTD Surface Meters Cohesion 31 kpa Friction Angle 15 Degrees Unit Weight 20.5 kn/m^3 UW (Saturated) 21.5 kn/m^3 Surfaces and Other Criteria Max Volume 2,500,000 Cubic meters Min Volume 250,000 Cubic meters Max Z 210 Meters Min Z 400 Meters Vertical Resolution 10 Meters Radius Increment 10 Meters Topography LE Method NED 10m DEM Meters Bishop's simplified -

37 Regional Model: Logistic Regression Scoops3D FS Landslide Inventory Rand. Sample Coefficient Fitting, Validation (Weka) Fail? 3DFS Dist Curve Yes 0.65 C2 60 No 1.37 C β0, β1, β2, β3

38 Regional Model: Validation and Results LR 10-fold Cross-Validation Summary Class Precision Recall PRC Area Fail 81% 89% 84% Not Fail 95% 91% 97% Weighted Avg. 90% 90% 94% Susceptibility Map Performance Metrics Comparison Scoops3D LR Model Difference Sensitivity/TPR/Recall 98% 89% -9% Specificity 85% 93% +7% Precision 3% 5% +2% 85% 93% +7% Overall Accuracy

39 Selection of Sites Leah Meek

40 Mitigation Methods Leah Meek

41 Mitigation: Tree-Drop Deflector Tree trunks bundled together and anchored at the base of the slope Diverts fast flowing water Estimated cost: $17.08 Applicable and practical Image: Jon French

42 Riprap Design Parameter Peak Velocity Avg Velocity Value Units 17 ft/s 6 to 8 ft/s Channel Width 70 to 200 ft Channel Depth 7.5 ft River Gradient Bank Slope Parameter Height of riprap 2H to 1V Material Angle of Repose 40 degrees Comments 10.0 ft Thickness of riprap 4.4 ft = 1.5*D50 Base layer thickness 0.5 ft base filter layer Volume Average Unit Weight Weight MDOT Units Rock Specific Gravity Method Value D50 (ft) (peak) Cost of Material and Construction (MDOT Average Unit cost) D50 (ft) (avg) 1 1 Kansas DOT # Isbash FHWA HEC Total Cost 93.4 ft^ pcf 8.4 US tons per linear ft basalt = Unit Weight x Volume $/ton $/ft = Weight x Unit Cost

43 Mitigation: RipRap Wall of loose rock at base of slope Mean rock diameter: 2.9 ft calculated based on peak river velocity (FHWA HEC-11) Diverts fast flowing water Estimated cost: $ Applicable and practical

44 Questions?

45 References Chatwin, S. C. (1994). A guide for management of landslide-prone terrain in the Pacific Northwest (No. 18). Ministry of Forests.

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