Coastal and Floodplain Construction Inspector's Practice Exam

How should fill used to support or protect a structure be placed?

1. In lifts of not more than 6 inches loose thickness

2. In continuous pours

3. In lifts of not more than 12 inches loose thickness

4. In random layers

The correct answer is: In lifts of not more than 12 inches loose thickness

Fill used to support or protect a structure should be placed in lifts of not more than 12 inches loose thickness for several reasons related to ensuring stability and proper compaction. Placing fill in this manner allows for effective compaction of each layer, which reduces the risk of settlement and provides a stable base for the structure. The maximum thickness is important because if the lifts are too thick, the weight of the fill may not allow for adequate compaction, leading to voids and potentially compromising the integrity of the structure above. Furthermore, it enables better control over the moisture content and uniformity of the material being compacted. Each 12-inch lift can be moistened or conditioned appropriately and compacted thoroughly before the next layer is added, which creates a more stable and homogeneous fill material. This practice reduces the potential for differential settlement, which can occur if the backfill is not compacted uniformly. Other placement practices, such as continuous pours or random layers, do not allow for the same level of control over the compaction process and can lead to areas of weakness within the fill. Lifts greater than 12 inches may not achieve the necessary density throughout the layer, making stabilization less effective. Hence, placing fill in lifts of 12 inches provides