Best Practices for Design and Construction Robert A. Gladstone, P.E. Executive Director Association for Mechanically Stabilized Earth Geotechnical Consultant Workshop Ohio Department of Transportation June 7, 2017
NOT a Best Geotechnical Practice
Common MSE Wall Systems Precast Facing Panels, Steel or Geosynthetic Reinforcements Welded Wire Facings, Steel or Geosynthetic Reinforcements Segmental Blocks, Steel or Geosynthetic Reinforcements
Design Roles and Responsibilities Owner Geotech Service Life Requirements Aesthetic Requirements Acceptable Wall Types Global Stability Bearing Capacity Settlement Acceptable Wall Types Civil / Structural Site Grading Wall Location DRAINAGE DESIGN Acceptable Wall Types Loading Internal Stability Detailed facing and reinforcement design Construction drawings MSE Designer
Design Responsibility Internal Stability MSE wall system supplier Simple check of sliding and overturning Determine eccentricity and applied bearing pressure Check reinforcement pullout and rupture Design of wall system components External Stability Owner or Consultant Owner proposing to build the structure in the specified location Therefore, owner is responsible for investigating feasibility Includes: global stability, bearing capacity, settlement analysis
Global Stability
Options for Bearing Capacity and Settlement
Specify Requirements in Contract Drawings
Contract Specifications
Contract Drawings
Design Parameters Design usually based on assumed parameters Soil Type Unit Weight Friction Angle Select Granular fill 125 pcf 34 Retained Fill 125 pcf 30 Foundation Soil * ----- 30 * These parameters are actually a good choice: 34 o is maximum value permitted by AASHTO without test data 34 o is approximately the mobilized shear that will develop 34 o has been assumed in design for 4 decades * Foundation soil design parameters should be clearly defined in the contract documents
Coherent Gravity Design Reinforced Soil Facing W E Sliding Resistance Vertical Pressure
Meyerhof Bearing Pressure Distribution V V = L - 2e e= M C V V V L e = BEARING PRESSURE = SUM OF VERTICAL LOADS = REINFORCING STRIP LENGTH = ECCENTRICITY OF STRUCTURE DUE TO APPLIED LOADS M C = SUM OF MOMENTS ABOUT CENTER LINE DUE TO APPLIED LOADS Best Practices for Design and Construction
Characteristics of the Coherent Gravity Method
Fabrication / QC and QA
Attendance Pre-Construction Meeting MSE wall Rep, Resident Engineer, Inspector, Wall Foreman and Crew Presentation by MSE wall Rep Detailed MSE wall construction procedures Compaction of backfill and installation of soil reinforcements Project specific details drainage structures, obstructions, etc Inspection What to look for, what will be required General discussion Discuss what's important to: Resident, Inspector, Contractor
MSE Wall Construction
Duties of MSE Wall Rep On site for start up of wall construction 2 to 3 Days Instruct on installation of MSE wall components Instruct on backfilling within the MSE wall volume Answer questions of contractor and inspector MSE wall rep is NOT the Inspector The MSE wall Rep is employed by the Contractor
Construction Inspection Minimum 95% Standard Proctor Density Required CONSIDER: NHI training course # 132080: Inspection of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes
Backfill Selection is Critical Clay backfill = poor friction and drainage Good friction and drainage come from granular backfill
Backfill Materials Granular Fill Crushed Stone Expanded Shale LWFC Fill
Granular Backfill for MSE Walls Gradation limits per AASHTO U.S. Sieve Size Percent Passing 4 100 3 75-100 #200 0-15 Some states use different gradation limits and/or reduce fines FHWA allowed up to 25% fines in the early 1980s Backfills often exceeded this limit, up to 35% fines Facing panel alignment was difficult to achieve FHWA and AASHTO returned to 15% limit on fines
Compaction is Important Flat Plate Tamper within 3 ft. of Wall Face Large Roller Stay 3 ft. Away Minimum 95% Standard Proctor Density Required
Installation of Soil Reinforcements
Reinforcement Connections are Critical
Accommodating Differential Settlement Perpendicular to the Face of Wall 2" Typical for Normal Construction 4" to 6" if expect large settlement Best Practices for Design and Construction
Critical Bottom of Wall Details Adequate Foundation Soils Embedment Underdrain
Drainage Within MSE Walls
Angles Shift Reinforcements at Inlets and Manholes
Pipes Behind Walls
Precast Traffic Barrier Design 4-6 Important: Coping Lip Required
Membrane with Traffic Barrier
Locate Guiderail Posts - Skew Reinforcements
Membrane with Guiderail Posts
Precast Coping Detail
There was a Reason for This! Owner Geotech Service Life Requirements Aesthetic Requirements Acceptable Wall Types Global Stability Bearing Capacity Settlement Acceptable Wall Types Civil / Structural Site Grading Wall Location DRAINAGE DESIGN Acceptable Wall Types Loading Internal Stability Detailed facing and reinforcement design Construction drawings MSE Designer
That Reason Is Implementing Best Practices Produces Beautiful Long-Performing Structures
Some of Ohio's Best I-90 Cleveland (2015) In Great Condition! (1984 33 yrs) I-75 Dayton (Wright Brothers)
Thanks for Listening Front Street City of Berea US 23 & US 30 Interchange Wyandot County Seneca-Jones Road over CSX RR, Seneca County