Section 4: Soil and Water Conservation Engineering
Soil Mechanics
Subtopic: Soil compaction and Proctor test
Question Statement:
Compared to the Standard Proctor compaction test, increasing the compactive energy to Modified Proctor levels causes:
Options:
(A) Higher Maximum Dry Density (MDD) and lower Optimum Moisture Content (OMC)
(B) Lower Maximum Dry Density (MDD) and higher Optimum Moisture Content (OMC)
(C) Higher Maximum Dry Density (MDD) and higher Optimum Moisture Content (OMC)
(D) No change in MDD or OMC because compaction curves depend exclusively on soil mineralogy
Answer Key:
A
Step-by-Step Solution & Explanation
Higher compactive effort (Modified Proctor imparts 4.5 times more energy than Standard Proctor):
1. Packs soil particles closer together, driving up the Maximum Dry Density (MDD).
2. Requires less lubricating water to attain the peak density, shifting the Optimum Moisture Content (OMC) to a lower value.
Option A is correct.