Soil Compaction Lecture.

Soil Compaction Lecture

Introduction In the construction of highway embankments, earth dams, and many other engineering structures, loose soils must be compacted to increase their unit weights. To compact a soil, that is, to place it in a dense state. The dense state is achieved through the reduction of the air voids in the soil, with little or no reduction in the water content. This process must not be confused with consolidation, in which water is squeezed out under the action of a continuous static load.

Compaction of Soil Compaction increases the strength characteristics of soils, which increase the bearing capacity of foundations constructed over them. Compaction also decreases the amount of undesirable settlement of structures and increases the stability of slopes of embankments.

Purposes of compacting soil
Increased Shear Strength This means that larger loads can be applied to compacted soils since they are typically stronger. Increased Shear Strength => increased bearing capacity, slope stability, and pavement system strength Reduced Permeability This inhibits soils’ ability to absorb water, and therefore reduces the tendency to expand/shrink and potentially liquefy

Purposes of compacting soil
Reduced Compressibility This also means that larger loads can be applied to compacted soils since they will produce smaller settlements. Control Swelling & Shrinking Reduce Liquefaction Potential

Compaction of Soil Definition: Compaction, in general, is the densification of soil by removal of air, which requires mechanical energy. Simplistically, compaction may be defined as the process in which soil particles are forced closer together with the resultant reduction in air voids.

Principles of Compaction
Compaction of soils is achieved by reducing the volume of voids. It is assumed that the compaction process does not decrease the volume of the solids or soil grains· Soil before compacted compacted Soil before compacted compacted

Compaction Effect Air Air Water Water Solids Solids Loose soil Compacted soil

The degree of compaction of a soil is measured by the dry unit weight of the skeleton. The dry unit weight correlates with the degree of packing of the soil grains. yd = 1 + e yw Gs The more compacted a soil is: the smaller its void ratio (e) will be. the higher its dry unit weight ( yd ) will be

Compaction Curve The compaction curve is relationship between a soil water content and dry unit weight. Soil sample was computed at different water contents in a cylinder of volume 1000 cc and dry unit weight were obtained. y y = d 1 + w c Compaction curve is plotted between the water content as abscissa and the dry density as ordinate.

Compaction Curve It is observed that the dry density increases with an increase in water content till the max. density is attained. With Further increase in water content, the dry density decreases. 20 18 16 14 Dry unit weight(γd) Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Compaction Curve Optimum moisture content (OMC) :
The water content corresponding to maximum dry unit weight is called optimum moisture content. Note that the maximum dry unit weight is only a maximum for a specific compactive effort and method of compaction. ydmas 18 16 14 Dry unit weight(γd) OMC Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Compaction Curve Optimum moisture content (OMC) :
Each compactive effort for a given soil has its own OMC. As the compactive effort is increased, the maximum density generally increases and the OMC decreases. ydmas1 Dry unit weight(γd) 18 ydmas2 16 14 OMC1 OMC2 Water Content (Wc) 12 8 10 12 14 16 18 20 22

Compaction Curve Zero air voids curve or saturation line
The curve represent the fully saturated condition ( S= 100%). ( It can not be reached by compaction ) Theoretical unit weight is given as yw Gs yd = 1 + wc ∗ Gs ydmas Dry unit weight(γd) "Zero Air Voids" S = 100% 18 16 14 OMC Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Compaction Curve Line of Optimums
A line drawn through the peak points of several compaction curves at different compactive efforts for the same soil will be almost parallel to a zero air voids curve , it is called the line of optimums Dry unit weight(γd) "Zero Air Voids" S = 100% 18 16 14 Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Factors affecting Compaction
Water content of the soil Amount of compaction Type of soil being compacted The amount of compactive energy used Method of compaction Thickness of layer Saturation line Admixtures Stone content

Water content of the soil As water is added to a soil ( at low moisture content) it acts as a softening agent on the soil particles and becomes easier for the particles to move past one another during the application of the compacting forces. As the soil compacts the voids are reduced and this causes the dry unit weight ( or dry density) to increase.

Water content below OMC As the water content increases, the particles develop larger and larger water films around them, which tend to “lubricate” the particles and make them easier to be moved about and reoriented into a denser configuration. 20 18 16 14 Dry unit weight(γd) OMC Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Water content at OMC The density is at the maximum, and it does not increase any further. 20 18 16 14 Dry unit weight(γd) OMC Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Water content above OMC Water starts to replace soil particles in the mold and the dry unit weight starts to decrease. 20 18 16 14 Dry unit weight(γd) OMC Water Content (Wc) 12 8 10 12 14 16 18 IUST 20 22

Soil type Soil type, grain size, shape of the soil grains, amount and type of clay minerals present and the specific gravity of the soil solids, have a great influence on the dry unit weight and optimum moisture content Uniformly graded sand or poorly graded in nature is difficult to compact them.

Soil type In poorly graded sands the dry unit weight initially decreases as the moisture content increases and then increases to a maximum value with further increase in moisture content. At lower moisture content, the capillary tension inhibits the tendency of the soil particles to move around and be compacted.

Soil type At a given moisture content, a clay with low plasticity will be weaker than a heavy or high plastic clay so it will be easier to compact.

Structure of Compacted Clay Intermediate structure High Compactive Effort Low Compactive Effort Dispersed Structure or parallel Dry Unit Weight Flocculated Structure, or Honeycomb Structure, or Random Water Content

Effect of Compaction effort The compaction energy per unit volume used for the standard Proctor test can be given as No. of blows per layer No. of layer weigℎt of ℎammer ℎeigℎt of drops × × × E = Volume of mold

Effects of increasing compactive effort Increased compactive effort enables greater dry unit weight. It can be seen from this figure that the compaction curve is not a unique soil characteristic. It depends on the compaction energy. ydmas1 Dry unit weight(γd) High compactive effort curve 18 ydmas2 16 Low compactive effort curve 14 OMC1 10 12 OMC2 14 16 Water Content (Wc) 20 22 12 8 18

Effects of increasing compactive effort For this reason it is important when giving values of (γdry)max and OMC to also specify the compaction procedure (for example, standard or modified). From the preceding observation we can see that As the compaction effort is increased, the maximum dry unit weight of compaction is also increased. As the compaction effort is increased, the optimum moisture content is decreased to some extent.

General Compaction Methods
Coarse-grained soils Fine-grained soils Laboratory Falling weight and hammers Kneading compactors Static loading and press Vibrating hammer Vibration Kneading Hand-operated vibration plates Motorized vibratory rollers Rubber-tired equipment Hand-operated tampers Sheep-foot rollers Field Free – falling weight dynamic compaction Rubber-tired rollers

Laboratory Compaction Tests
Laboratory compaction tests provide the basis for determining the percent compaction and molding water content needed to achieve the required engineering properties, and for controlling construction to assure that the required compaction and water contents are achieved.

The aim of the test is to establish the maximum dry unit weight that may be attained for a given soil with a standard amount of compactive effort. When a series of samples of a soil are compacted at different water content the plot usually shows a distinct peak.

The fundamentals of compaction of fine- grained soils are relatively new. R.R. Proctor in the early 1930’s developed the principles of compaction. The proctor test is an impact compaction. A hammer is dropped several times on a soil sample in a mold. The mass of the hammer, height of drop, number of drops, number of layers of soil, and the volume of the mold are specified.

There are several types of test which can be used to study the compactive properties of soils. Standard Procter Test is not sufficient for airway and highways, Modified Procter Test was later adopted by AASHTO and ASTM

Standard Procter Test Soil is compacted into a mould in 3-5 equal layers, each layer receiving 25 blows of a hammer of standard weight. The energy (compactive effort) supplied in this test is 595 kJ/m3. The important dimensions are Volume of mould Hammer mass Drop of hammer 1000 cm^3 2.5 kg 300 mm

Standard Procter Test Standard Proctor test equipment

Standard Procter Test Proctor established that compaction is a function of four variables: Dry density (d) or dry unit weight d. Water content wc Compactive effort (energy E) Soil type (gradation, presence of clay minerals, etc.)

The soil is mixed with varying amounts
Standard Procter Test The soil is mixed with varying amounts of water to achieve different water contents Several samples of the same soil , but at different water contents, are compacted according to the compaction test specification

Standard Procter Test Apply 25 blows from the rammer dropped from a height of 305 mm above the soil.

Standard Procter Test Distribute the blows uniformly over the surface and ensure that the rammer always falls freely and is not obstructed. 4 5 4 6 2 7 8 1 etc. 3 The first four blows The successive blows Rammer Pattern for compaction in mm Mold

The soil is in mold will be divided into three lifts
Standard Procter Test The soil is in mold will be divided into three lifts Each Lift is compacted 25 times Place a second quantity of moist soil in the mould such that when compacted it occupies a little over two-thirds of the height of the mould body. Soil sample 3 layers 2.5 kg (5.5lb) 25 blows per layer 305 mm

Standard Procter Test Repeat procedure once more so that the amount of soil used is sufficient to fill the mould body, with the surface not more than 6mm proud of the upper edge of the mould body. 2.5 kg (5.5lb) 25 blows per layer 305 mm Soil sample 3 layers

Standard Procter Test The unit weight and the actual water content of each compacted sample are measured Derive the dry unit weight from the known unit weight and water content y yd = 1 + w c

Determine the maximum dry weight and OMC
Standard Procter Test Plot the dry unit weight versus water content for each compacted sample. Determine the maximum dry weight and OMC ydmas Dry unit weight(γd) "Zero Air Voids" S = 100% 18 16 14 OMC Water Content (Wc) 12 8 10 20 22

Standard Procter Test 943.3 cm^3 2124 cm^3 Method A Method B Method C
Specification of standard Proctor test ( Based on ASTM Test Designation 698) Item Method A Method B Method C 101.6 mm mm mm Diameter of mold Volume of mold 943.3 cm^3 943.3 cm^ cm^3 Weight of hammer Height of hammer drop Number of hammer blows per layer of soil 24.4 N 304.8 mm 24.4 N 304.8 mm 24.4 N 304.8 mm 25 25 56 Number of layers of compaction 3 3 3 591.3 kN.m/m^3 591.3 kN.m/m^3 591.3 kN.m/m^3 Energy of compaction

Standard Procter Test Specification of standard Proctor test ( Based on ASTM Test Designation 698) ( con.) Method A Method B Portion passing No.4 ( 457mm)sieve . May be used if 20% or less by weight of material is retained on No.4 sieve. Item Method C Portion passing 9.5 mm 19- mm sieve . sieve . May be used if more than 20% retained on No.4 by weight of sieve is more than material is 20% and 20% or retained on 9.5 less by weight of mm sieve and less than 30% by weight of mm sieve. retained on 19- Soil to be used

• Was developed during World War II
Modified Procter Test • Was developed during World War II • By the U.S. Army Corps of Engineering For a better representation of the compaction required for airfield to support heavy aircraft.

Modified Procter Test Same as the Standard Proctor Test with the following exceptions: The soil is compacted in five layers Hammer weight is 10 Lbs or 4.54 Kg Drop height h is 18 inches or 45.72cm Then the amount of Energy is calculated

Uniformly distribution of the blows over the surface
Modified Procter Test Uniformly distribution of the blows over the surface 44.5 N(10 lb) 4 6 9 457.2 mm 1 5 2 7 8 # 5 3 # 4 Rammer Pattern for compaction in 152,4 mm Mold # 3 # 2 # 1

Modified Procter Test 943.3 cm^3 2124 cm^3 Method A Method B Method C
Specification of standard Proctor test ( Based on ASTM Test Designation 698) Item Method A Method B Method C 101.6 mm mm mm Diameter of mold Volume of mold 943.3 cm^3 943.3 cm^ cm^3 Weight of hammer Height of hammer drop Number of hammer blows per layer of soil 44.5 N 457.2 mm 44.5 N 457.2 mm 44.5 N 457.2 mm 25 25 56 Number of layers of compaction 5 5 5 2696 kN.m/m^3 2696 kN.m/m^3 2696 kN.m/m^3 Energy of compaction

Modified Procter Test Specification of standard Proctor test ( Based on ASTM Test Designation 698) ( con.) Item Method A Method B Portion passing No.4 (457mm)sieve May be used if 25% or less by weight of material is retained on No.4 sieve. If this gradation requirement cannot be met, then Methods B or C may be used. Method C Portion passing 9.5 mm sieve . 19- mm sieve . May be used if soil retained on more than 20% No.4 sieve is by weight of more than 25% material is and 25% or less retained on 9.5 mm sieve and less than 30% by weight of mm sieve. retained on 19- Soil to be used

Comparison-Curves ydmas (mod.) ydmas (Stand.) OMC
Modified Procter Test ydmas (Stand.) Dry unit weight (γd) Standard Procter Test OMC Water Content (wc)

Standard Proctor Test Modified Proctor Test
Comparison-Summary Standard Proctor Test Modified Proctor Test Mold size: 943.3cm^3 304.8 mm height of drop 24.4 N hammer 3 layers 25 blows/layer Energy kN.m/m^3 Mold size: 943.3cm^3 457.2 mm height of drop 44.5 N hammer 5 layers 25 blows/layer Energy 2696 kN.m/m^3

Filed Compaction Compaction Equipment Most of the compaction in the field is done with rollers. The four most common types of rollers are: Smooth-wheel rollers (or smooth-drum rollers) Pneumatic rubber-tired rollers Sheepsfoot rollers Vibratory rollers

Filed Compaction Compaction Equipment Smooth-wheel rollers are suitable for proof rolling subgrades and for finishing operation of fills with sandy and clayey soils. These rollers provide 100% coverage under the wheels, with ground contact pressures as high as 310 to 380 kN/m^2. They are not suitable for producing high unit weights of compaction when used on thicker layers.

Compaction Equipment Smooth-wheel rollers o one steel drum and rubber tired drive wheels two steel drums one of which is the driver effective for gravel, sand, silt soils

Compaction Equipment Pneumatic rubber-tired rollers Pneumatic rubber-tired rollers are better in many respects than the smooth-wheel rollers. The former are heavily loaded with several rows of tires. These tires are closely spaced—four to six in a row. Pneumatic rollers can be used for sandy and clayey soil compaction. Compaction is achieved by a combination of pressure and kneading action.

Compaction Equipment Pneumatic rubber-tired rollers

Compaction Equipment Sheepsfoot rollers Sheepsfoot rollers are drums with a large number of projections. The area of each projection may range from 25 to 85 cm2. These rollers are most effective in compacting clayey soils. The contact pressure under the projections can range from to 7000 kN/m2.

Compaction Equipment Sheepsfoot rollers During compaction in the field, the initial passes compact the lower portion of a lift. Compaction at the top and middle of a lift is done at a later stage.

Compaction Equipment Sheepsfoot rollers

Compaction Equipment Vibratory rollers Vibratory rollers are extremely efficient in compacting granular soils. Vibrators can be attached to smooth-wheel, pneumatic rubber- tired, or sheepsfoot rollers to provide vibratory effects to the soil. The vibration is produced by rotating off-center weights.

Factors Affecting Field Compaction
For field compaction, soil is spread in layers and a predetermined amount of water is sprayed on each layer (lift) of soil, after which compaction is initiated by a desired roller. In addition to soil type and moisture content, other factors must be considered to achieve the desired unit weight of compaction in the field.

These factors include the thickness of lift, the intensity of pressure applied by the compacting equipment, and the area over which the pressure is applied. These factors are important because the pressure applied at the surface decreases with depth, which results in a decrease in the degree of soil compaction.

During compaction, the dry unit weight of soil also is affected by the number of roller passes. The dry unit weight of a soil at a given moisture content increases to a certain point with the number of roller passes.

Specifications for Field Compaction
In most specifications for earthwork, the contractor is instructed to achieve a compacted field dry unit weight of 90 to 95% of the maximum dry unit weight determined in the laboratory by either the standard or modified Proctor test.

This is a specification for relative compaction, which can be expressed as ydfield R = × 100 % yd max lab where R = relative compaction For the compaction of granular soils, specifications sometimes are written in terms of the required relative density Dr or the required relative compaction.

Relative density should not be confused with relative compaction. Correlation between relative compaction (R) and the relative density Dr Ro R = where : 1 − Dr 1 − Ro yd(min) Ro = y d max

Determination of Field Unit Weight of Compaction
When the compaction work is progressing in the field, knowing whether the specified unit weight has been achieved is useful. The standard procedures for determining the field unit weight of compaction include Sand cone method Rubber balloon method Nuclear method

Sand Cone Method Sand Cone Method (ASTM Designation D-1556)
The sand cone device consists of a glass or plastic jar with a metal cone attached at its top

(γdry)max . Worked Examples
The results of a standard Proctor test are given in the following table. Determine the maximum dry unit weight of compaction and the optimum moisture content Also, determine the moisture content required to achieve 95% of (γdry)max . Volume of Proctor Mold (cm^3 ) 944 Mass of wet soil in the mold ( kg) 1.68 1.71 1.77 1.83 1.86 1.88 1.87 1.85 Water content ( % ) 9.9 10.6 12.1 13.8 15.1 17.4 19.4 21.2

Worked Examples Example 2 Given The in situ void ratio of a borrow pit’s soil is 0.72. The borrow pit soil is to be excavated and transported to fill a construction site where it will be compacted to a void ratio of The construction project required m^3 of compacted soil fill Required Volume of soil that must be excavated from the borrow pit to provide the required volume of fill.

Soil Compaction Lecture.

Similar presentations

Presentation on theme: "Soil Compaction Lecture."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Soil Compaction Lecture.

Similar presentations

Presentation on theme: "Soil Compaction Lecture."— Presentation transcript:

Similar presentations

About project

Feedback