Reference(s):

FHWA (2004)
Holtz et al. (2008)
Schaefer et al. (2017)

Method Summary

Column load testing should be performed prior to production column construction to verify column capacity and settlement. The tests also ensure that the proposed column construction procedures will result in the desired performance. Load tests should be conducted in general accordance with ASTM D-1143, Standard Test Methods for Deep Foundations Under Static Axial Compressive Load. The exact test specifications will vary based on the column type used. Load tests should be performed after excess pore pressures induced during construction have dissipated and enough time has elapsed for the concrete or gout to cure (if applicable).

QC/QA Method: Geosynthetics Verification

Reference(s):

FHWA (2004)
Holtz et al. (2008)
Schaefer et al. (2017)

Method Summary

In general, this method involves verification that the geosynthetics (if used) satisfy the required specifications. This should include verification of the manufacturer, model number, lot number, and manufacturer’s test data for the geosynthetic. It may also include independent testing of samples of the geosynthetic taken from the construction site. Some other specific verification methods relating to the geosynthetic reinforcement are discussed below.

Holtz et al. (2008) includes specifications and construction techniques for reinforced embankments, some of which apply to column-supported embankments. Stumps and debris should be removed prior to placement of the geosynthetic reinforcement. Sagging in the geosynthetic may be required by the design method and specifications to promote arching within the embankment fill and develop the catenary resistance within the geosynthetic; see McGuire and Filz (2010). Otherwise, the geosynthetic reinforcement should be pulled taut prior to placement of fill material on top to ensure that there is no sagging.

If a geosynthetic is used, the contractor shall provide a manufacturer’s certificate of compliance to the Engineer which includes the following information about each roll of material to be used (Holtz et al. 2008): manufacturer’s name and current address, full product name, geosynthetic structure including fiber/yarn type (if applicable), polymer type(s), roll number, and certified test results. Seams in geotextiles should be sewn as required with all seams placed up and every stitch inspected. The geosynthetic should be inspected for holes, rips, or tears. Defective material should be replaced or repaired. Geosynthetic roll identification, storage, and handling shall be in conformance to ASTM D4873. The geosynthetic shall be covered during shipment and stored such that it is protected from ultraviolet radiation or sunlight, site construction damage, precipitation, chemicals, flames or welding sparks, temperatures in excess of 70° Celsius, and other environmental conditions that may damage the physical properties of the geosynthetic. Table 1-5 of Holtz et al. (2008) on page 1-25 contains a geosynthetic field installation checklist.

Proper orientation and overlap of geosynthetic (placement details) should be verified. No changes to the reinforcement details (orientation, layout, overlap, type, elevation, etc.) should be made without approval of the Engineer. Remove slack and wrinkles from the geosynthetic prior to placing fill. Equipment should not be allowed directly on the geosynthetic; FHWA (2004) and Schaefer et al. (2017) recommend a minimum fill of 150 mm (6 inches) above the geosynthetic before it is trafficked by equipment. Vehicle turning should be kept to a minimum so as not to damage the geosynthetic. The geosynthetic should be unrolled smoothly, without dragging. It should be examined for damage before covering with fill material. The height of individual fill piles on the geosynthetic should be limited to avoid a local bearing capacity failure. The geosynthetic should be covered within 48 hours of placement.

Geosynthetics should meet the required ultimate strength per ASTM D6637, creep limited strength, and coefficient of interaction for direct sliding per ASTM D5321. Some designs may call for placement of an additional sacrificial geosynthetic layer over columns to protect the reinforcement geosynthetic.