<p><p><h2>QC/QA Guidelines</h2>Proof and verification load tests are effective in establishing the grout-ground interface strength. Verification and proof tests load the nail to a specified percentage of the design load. Verification tests load sacrificial nails to at least 200% of the design load. Results from verification tests are used to produce final design values. One or two verification load tests should be completed prior to production soil nail installation. During soil nail installation, at a minimum, two verification load tests should be performed in every different soil strata encountered. Larger projects will require more verification load tests (Lazarte et al. 2015 and Porterfield et al. 1994). Proof tests occur during production nail installation and can be conducted on production nails. Proof tests are usually performed on 5% of the installed nails (Lazarte et al. 2015). Results from proof tests are used to assure consistent and acceptable installation methods and pullout capacity. Dial gages should be used during load tests to measure nail head movement. According to Samatini and Nowatzki (2006), since the strength of the grout-ground interface for hollow bar soil nails is often irregular, there are concerns about accurately assessing the pullout strength of the soil nails from representative proof or verification tests.</p><p>A short-term creep test is normally conducted as part of a proof or verification test, in which the load test is paused at a specified load ceiling while deformations in the soil nail over time are measured. The creep test can indicate how the loaded nail will behave throughout its service life under a constant load. Long-term creep testing is typically only performed for projects where the soil nails are installed in cohesive soils where creep may be an issue. Creep tests should be performed at the same frequency as verification testing.</p><p>Records of proof, verification, and creep test results should be kept to confirm design values have been achieved and adherence to the method and performance approach specifications. These records should include information pertaining to the nail installation method, design test load, maximum test load, maximum nail movement, residual movement, whether or not failure occurred, creep rate, duration of load/creep test, pressure gage measurements, dial gage measurements, nail deflections/extensions, the unbounded length, and the bonded length. This will help to assure the wall’s longevity and ability to sustain the design load. While these testing methods are valid for drilled/grouted soil nails and have been used for hollow bar soil nails, further research is necessary to evaluate these testing methods for assigning appropriate bond strength values to hollow bar soil nails (Gomez 2010).</p><p>Surveying is useful for monitoring the entire soil nail wall during and after construction for slope movements. Visual inspection rapidly covers large areas and identifies visible problems such as cracking, seepage, and bulging, which may indicate failure. Inspection does not provide quantifiable results, but can identify major concerns that should have been addressed in the specifications. During construction, inspection of construction materials and activities verify that samples from each batch of material conform to the design specifications and that proper construction procedure and design specifications are followed. Nail installation logs should be kept throughout the construction process to assure consistent and appropriate installation procedures are followed. This is important because several factors affect the bond strength of the soil nail such as rotation rate, advancement rate, grout pressure, grout flow rate, and grout mix (Gomez 2010). Lazarte et al. (2015) provides a list of every item an inspector should verify and record in nail installation logs as part of project quality assurance.</p><p>Records of grouting should be maintained. The grouting process and any problems arising during grouting should be described. Grout quality control testing normally consists of determining the water-cement ratio by a specific gravity measurement in order to control the behavior of the grout. Grout cubes and shotcrete cores are also taken from each batch of grout for compressive testing at a later date as a quality assurance measure. The recommended frequency of cube and specific gravity tests can be found in Lazarte et al. (2015) and will vary based on the project. Cube and specific gravity tests help confirm that strength and property values defined in the specifications have been achieved. Compressive strength value from cube testing can be established at a minimum of 48 hours after sampling. The following should be recorded for every cube test performed:<br><ul> <li>Grout unit weight</li> <li>Temperature</li> <li>Air content</li> <li>Slump</li> <li>Sketch of fracture type</li> <li>Specific gravity</li> <li>Compressive strength</li></ul>The accuracy of cube testing is under debate. It is possible to get a failed cube for a passing anchor. Specific gravity tests provide the benefit of rapidly assessing the conformance of the grout to design specifications prior to grouting and are preferred.</p><p>In the laboratory, tension testing of representative nails verifies the batch’s ultimate tensile strength. Tension testing provides highly accurate and precise results for the strength of the nail, which can be used as a QC tensile strength verification test. However, because nails come with certificates, the tension test is rarely used.</p><p>Inspections, construction observations, daily logs, and record keeping are essential QC/QA activities for all technologies. These activities help to ensure and/or verify that:<br><ul> <li>Good construction practices and the project specifications are followed.</li> <li>Problems can be anticipated before they occur, in some cases.</li> <li>Problems that do arise are caught early, and their cause can oftentimes be identified.</li> <li>All parties are in good communication.</li> <li>The project stays on schedule.</li></ul>Additional technology-specific details for inspections, construction observations, daily logs, and record keeping QC/QA activities are provided in the <em>Individual QC/QA Methods </em>section below.</p></p>