Compaction I. *Definitions 1. The process of forcing air out of the soil, resulting an increase in density. 2. The effect of compaction on pore space The effect of compaction on pore space II. *Types of compaction 1. Rolling or kneading: most effective for clayey soils 2. Vibrating: most effective for non-clayey soils 3. Dropping a heavy weight: effective for both types of soils III. Control of Compaction 1. Determining the dry density of the soil as compacted and comparing it to the maximum dry density of the same soil as determined by a laboratory test. 1 Thursday, December 17, 2015

Compaction III. Control of Compaction 2. *The Proctor Tests (Standard & Modified Proctor Tests)The Proctor Tests 1) Purposes: To determine the maximum dry density and the corresponding optimum moisture content of a field sample of soil 2) Procedure: (1) Placing soils in layers (lifts) into a standard mold; (2) Compacting them by dropping a standardized hammer a specified number of times. (3) Weighing and determining the density when the mold is full; (4) Oven-drying a portion of the soil to determine the moisture content by weight 2 Thursday, December 17, 2015

Compaction III. Control of Compaction 3) Difference between standard & modified tests Difference between standard & modified tests (1) The amount of energy (the weight of hammer and the height from which it is dropped); (2) The number of lifts; 4) Typical compaction curvescompaction curves (1) The amount of compaction depends on: compaction effort and water content of the soil a. Compaction effort b. Function of water in compaction: (2) A specific relative compaction can be achieved for the soil over a range of moisture contents 3 Thursday, December 17, 2015

Compaction IV. *Misconceptions about compaction 1. The first is that 100% relative compaction implies that all of the air has left the soil (zero air voids). However, the compaction curve never reaches the zero air voids curve and it is impossible to remove all of the air voids with conventional techniques. 2. The second is that the Modified Proctor test has been standardized to approximate typical compact efforts achieved in the field with modern conventional equipment. However, it is not practical to attempt to achieve relative compactions at or above 100%. 4 Thursday, December 17, 2015

Compaction IV. Misconceptions about compaction 3. The third is that a given soil has a specific optimum moisture content. The optimum moisture content depends on the amount of compact energy and the method of compaction, and the increase in the compact energy decreases the optimum moisture content. V. Soil Compaction Equipment (Rammer, plate compactor, rollers) Soil Compaction EquipmentRammerplate compactorroller VI. Homework (Ex. II on page 224 in the textbook) 5 Thursday, December 17, 2015