Heavy Civil Exam 2 Practice

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What distinguishes Standard Proctor from Modified Proctor tests in soil compaction?

Standard Proctor uses higher energy to determine OMC and MDD; Modified uses lower energy.

Standard Proctor uses lower energy to determine OMC and MDD; Modified uses higher energy and yields higher MDD.

Standard Proctor uses higher energy; Modified uses higher energy and yields identical results.

Standard Proctor uses lower energy to determine OMC and MDD; Modified uses higher energy and yields higher MDD.

The key idea is that the amount of compaction energy drives how densely soil can be packed. Standard Proctor uses a lower energy (fewer blows per layer), while Modified Proctor uses a higher energy (more blows per layer). Because more energy is applied in the Modified test, the soil can be packed more tightly, yielding a higher maximum dry density. The Optimum Moisture Content for achieving that maximum density is usually lower with the Modified test than with the Standard test, reflecting the denser packing at less water.

So this option correctly states that Standard uses lower energy to determine OMC and MDD, while Modified uses higher energy and yields higher MDD. The other statements misstate which test uses higher energy or imply identical results, which doesn’t reflect how increasing energy changes the achievable density.