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

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

Typical Reinforced Earthen Structure

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

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

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

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

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

Resulting Damage

Resulting Damage

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

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

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

Questions and Discussion