How many additional inches should the drill rod be driven compared to your test?

In earthwork and drilling practices, particularly when conducting tests for soil compaction or density, it is essential to account for the potential variability and the penetration depth needed to ensure accurate measurements. The correct answer indicates that the drill rod should be driven an additional two inches compared to the initial test depth.

This extra depth allows for the possibility of any inconsistencies in the soil structure that may not be accounted for at the initial test depth. By driving the drill rod further, you ensure more accurate sampling and reduce the chance of missing layers that could affect the integrity of the test results. This practice is particularly important when evaluating the performance of the soil for construction projects, as it leads to a better understanding of the subsurface conditions.

The other options suggest a smaller increment of additional driving, which may not be sufficient to capture the necessary soil properties accurately, particularly in varied soil conditions. Thus, the additional two inches serve as a standard practice to promote thorough and reliable testing outcomes in earthwork and drilling operations.