QC/QA Guidelines

QC/QA for column-supported embankment projects should include verification of the properties and placement of the LTP fill, embankment fill, and the geosynthetic reinforcement. Settlement and lateral displacement monitoring should be included to determine if the embankment performs as expected. Although not covered in this document, industry standard QC/QA procedures for the type of column or pile used for embankment support should be followed.

Load testing is recommended prior to production column construction to verify column capacity and settlement. Testing procedures will vary depending on the column type used, but load tests should conducted in general accordance with ASTM D-1143, Standard Test Methods for Deep Foundations Under Static Axial Compressive Load. 
 

Geosynthetics testing and verification should include the following:

• Documentation of manufacturer, model number, lot number, and roll number for each roll
• Verification of the following geosynthetic properties per manufacturer’s certified test results: ultimate strength per ASTM D6637 (geogrid) or ASTM D4595 (geotextile), creep resistance per ASTM D5262, durability, coefficient of interaction for sliding per ASTM D5321. Holtz et al. (2008) provides a complete list of geotextile properties and test methods.
• Inspection of each roll to verify that it is undamaged prior to covering with fill material
• Verification that storage and shipment are such that the geosynthetic does not receive prolonged exposure to ultraviolet radiation prior to covering
• Observation to verify removal of deleterious materials prior to placement of geosynthetic reinforcement
• Observation of geosynthetic placement to verify it is taut, unless sagging is prescribed by the design method and construction notes to enhance arching in the embankment fill as addressed in McGuire and Filz (2010)
• Observation to verify that equipment is not operated directly on the geosynthetic and that a minimum fill thickness is placed before equipment is operated over geosynthetic; equipment should not make sharp turns
• Observation to verify there are no large piles of fill material on top of the LTP which may cause a local bearing capacity failure
• Observation to verify proper orientation, overlap, and elevation within the embankment
• If geotextile seams are specified, verification that the seams are placed upwards and inspection of every stitch

A complete recommended “Geosynthetic Field Inspection Checklist” is included in Table 1-5 on page 1-25 of Holtz et al. (2008). Construction procedures for reinforced embankments are contained in Section 7.8 (pages 7-45 to 7-52) of Holtz et al. (2008); although this is written for the general category of reinforced embankments, much of it applies to column-supported embankments.

Verification for the LTP and embankment fill should include:

• Grain size distribution of fill material(s) to verify adherence to the specified gradation. The frequency of testing is determined by state DOT recommendations typical for embankment fill projects.
• Atterberg limits to verify that the liquid limit and plasticity index are below the specified maximum values. The frequency of testing is determined by state DOT recommendations typical for embankment fill projects.
• Modified Proctor compaction tests to determine the maximum dry unit weight and the optimum moisture content for use in calculating relative compaction and determining the allowable range of moisture contents. Minimum and maximum density tests can also be included to determine relative density of the granular fill placement.
• In-situ density verification with nuclear gage, sand cone, balloon densometer, or other reliable method. The specific method of density testing and frequency should follow guidelines by the state DOT.
• Observation to verify maximum lift thickness is not exceeded. A maximum lift thickness of 10 inches for large compaction equipment and 6 inches for hand operated equipment is recommended.

The following monitoring is recommended:

• Surface survey to confirm the finished embankment elevation and periodic resurvey to quantify total and differential settlement
• Settlement plates at the elevation of the geosynthetic reinforcement to monitor settlement during construction
• Inclinometers at the embankment toe to monitor lateral displacement.