1. 4th Annual Construction Law Summit
Reinforced Earth Retaining Wall Structures The Importance of Continuity Between Design, Inspection & Testing and Construction, and Long Term Maintenance
Presented to
4th Annual Construction Law Summit
Alabama State Bar
Presented by
Oasis Consulting Services
5 December 2017

2. What are Reinforced Earth Structures?
Reinforced earth structures are built using reinforcing elements to strengthen the backfill material, typically soil or aggregate, by providing tensile resistance
Reinforcing members can be high strength woven fabrics, geogrids, or steel
Structures may have block, concrete panels or vegetated baskets for the face

3. Typical Reinforced Earthen Structure

4. Common Reinforced Earth Structures
Presented to: Georgia Institute of Technology
ATC Associates Inc.
Common Reinforced Earth Structures
November 19, 2010

5. Most Common Causes of Failures
Presented to: Georgia Institute of Technology
ATC Associates Inc.
Most Common Causes of Failures
Water
Unanticipated groundwater causing hydrostatic pressure
Erosion caused by excessive surface runoff
Broken water utilities, such as storm sewers, roof drains, water supply pipes
Soil Compaction, Lack of Compaction Causes
Settlement of wall
Lower soil strengths result in excessive movement of wall, rotation or sliding (wall movement occurs to mobilize shear strength of soil and engage the resistance of reinforcing elements)
Poor Planning for Installation of Utilities and Structures Built Close to Walls
Plan installation of utilities and other structures such that reinforced zone of structure does not have to be disturbed
Cutting of reinforcing elements during installation, also performing no repair
Improper backfill of excavations
Poor Soil Type
Soil does not meet design parameters for strength, gradation, plasticity index
Inadequate Design, Wall and Geotechnical
Design does not follow standard design guidelines or errors in design calculations
Inadequate geotechnical design, not all potential failure mechanisms evaluated, particulary global stability
Site conditions or groundwater regime not adequately defined
November 19, 2010

6. Most Common Causes of Failures (cont.)
Presented to: Georgia Institute of Technology
ATC Associates Inc.
Most Common Causes of Failures (cont.)
Improper Wall Construction and Oversight
Inadequate inspection during construction
Part-time testing and inspection does not guarantee that 100% of structure was constructed according to plans and specification
Long Term Operation and Maintenance
Have a regular inspection program to identify problems and correct them as soon as possible
Provide documentation to facility manager of areas where reinforced structures exist and information about not disturbing the reinforced zones without getting a competent design professional involved to design proper repairs
November 19, 2010

7. Retail Development Case Study
A problem developed with the back wall of the building which is supported by a reinforced earth retaining wall
The building and slab settled a couple inches after the development was completed
Geotechnical engineers scope of work included performing subsurface exploration and part time materials testing and inspection

8. Project Overview
Modular wall was built to support the building, 12 ft. to 14 ft. setback, geogrid length 17 feet (extends beneath building)
Max wall height about 16 feet
Gutter collection system installed after wall and building construction complete
Utility services installed after building and wall construction completed

9. Resulting Damage

10. Resulting Damage

11. Evaluation of Problem Performed visual inspection of distress
Performed exploration to evaluate soil conditions adjacent to the building
Performed laboratory testing on retaining wall backfill soil
Install crack monitors on interior floor slab and construction joints in masonry
Verify elevations of interior slab using survey equipment
Install tilt meters on the retaining wall and back wall of the building, monitored for 12 months

12. Causes of Movement
Contractor excavated into reinforced zone for utility installation and cut geogrids and did not repair
Contractor undermined foundations on west side of building during installation of building utilities
Soil type for wall backfill did not meet specification, clay soil used for backfill, may or may not have contributed to current issue but at least represented a long term potential problem
Testing and inspection was performed on a part-time basis, site personnel did not note change in soil type, no inspections or testing was performed after wall and building construction was completed
Contractor site personnel did not understand the critical issue of not disturbing reinforced wall zone after completion of construction

13. Resolution and Lessons Learned
Case settled through mediation with the contractor and geotechnical engineer splitting the cost for the repairs
Lessons Learned
Testing and inspection should be performed on a full time basis, not part time
Make sure client has a clear understanding of the role of the testing and inspection agency; it is not to guarantee that wall construction is free of defects
Know what the relationship is between the contractor and developer
Perform a detailed inspection and determine if wall area has been disturbed after wall construction was completed, if so investigate further to determine if the wall has been damaged; complete this before issuing construction certification letter
Construction documents should have specific details concerning protection of the reinforced zone of the wall, i.e. do not cut reinforcing elements, do not excavate in reinforced zone unless the wall design engineer is consulted
Need to have more experienced construction supervision on site

14. Questions and Discussion