Compaction

Compaction

Courtesy of U.S. WICK DRAIN, INC.

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1. Soil Improvement

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1.1 Methods for Soil Improvement
Ground Reinforcement
• • • • • • • • • • • Stone Columns Soil Nails Deep Soil Nailing Micropiles (Mini-piles) Jet Grouting Ground Anchors Geosynthetics Fiber Reinforcement Lime Columns Vibro-Concrete Column Mechanically Stabilized Earth • Biotechnical

Ground Improvement
• Deep Dynamic Compaction • Drainage/Surcharge • Electro-osmosis • Compaction grouting • Blasting • Surface Compaction • • • • • •

Ground Treatment
Soil Cement Lime Admixtures Flyash Dewatering Heating/Freezing Vitrification

Compaction
Shaefer, 1997

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1.1 Methods for Soil ImprovementJet Grouting

Courtesy of Menard-soltraitement

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1.1 Methods for Soil ImprovementSoil Nailing

Courtesy of Atlas Copco Rock Drilling Equipment

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2. Compaction

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2.1 Compaction and Objectives
Compaction
• Many types of earth construction, such as dams, retaining walls, highways, and airport, require man-placed soil, or fill. 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.

Objectives:
(1) Decrease future settlements (2) Increase shear strength (3) Decrease permeability

(From Lambe, 1991; Head, 1992)

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2.2 General Compaction Methods
Coarse-grained soils Laboratory
•Vibrating hammer (BS)

dough

Fine-grained soils
•Falling weight and hammers •Kneading compactors •Static loading and press

•Hand-operated vibration plates •Motorized vibratory rollers

Field

•Rubber-tired equipment •Free-falling weight; dynamic compaction (low frequency vibration, 4~10 Hz)

•Hand-operated tampers •Sheepsfoot rollers •Rubber-tired rollers

Vibration

Kneading
(Holtz and Kovacs, 1981; Head, 1992)

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3. Theory of Compaction (Laboratory Test)

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3.1 Laboratory Compaction
Origin
The fundamentals of compaction of fine-grained soils are relatively new. R.R. Proctor in the early 1930’s was building dams for the old Bureau of Waterworks and Supply in Los Angeles, and he developed the principles of compaction in a series of articles in Engineering News-Record. In his honor, the standard laboratory compaction test which he developed is commonly called the proctor test.

Purpose
The purpose of a laboratory compaction test is to determine the proper amount of mixing water to use when compacting the soil in the field and the resulting degree of denseness which can be expected from compaction at this optimum water

Impact 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.
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3.1.1 Various Types
Various types of compaction test

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1: your test 2: Standard Proctor test

3: Modified Proctor test
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3.1.2 Test Equipment
Standard Proctor test equipment

Das, 1998

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3.1.3 ComparisonStandard and Modified Proctor Compaction Test Summary of Standard Proctor Compaction Test Specifications (ASTM D-698, AASHTO)

Das, 1998

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3.1.3 ComparisonStandard and Modified Proctor Compaction Test (Cont.) Summary of Modified Proctor Compaction Test Specifications (ASTM D-698, AASHTO)

Das, 1998

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3.1.3 Comparison-Summary
Standard Proctor Test 12 in height of drop 5.5 lb hammer 25 blows/layer 3 layers Mold size: 1/30 ft3 Energy 12,375 ft·lb/ft3 Modified Proctor Test 18 in height of drop 10 lb hammer 25 blows/layer 5 layers Mold size: 1/30 ft3 Energy 56,250 ft·lb/ft3 Higher compacting energy
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3.1.4 Comparison-Why?
• In the early days of compaction, because construction equipment was small and gave relatively low compaction densities, a laboratory method that used a small amount of compacting energy was required. As construction equipment and procedures were developed which gave higher densities, it became necessary to increase the amount of compacting energy in the laboratory test.

• The modified test was developed during World War II by the U.S. Army Corps of Engineering to better represent the compaction required for airfield to support heavy aircraft. The point is that increasing the compactive effort tends to increase the maximum dry density, as expected, but also decrease the optimum water content.

(Holtz and Kovacs, 1981; Lambe, 1991)

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3.2 Variables of Compaction
Proctor established that compaction is a function of four variables: (1)Dry density (ρd) or dry unit weight γd. (2)Water content w (3)Compactive effort (energy E) (4)Soil type (gradation, presence of clay minerals, etc.) For standard Proctor test
Weight of hammer

×

E=

Height of drop of hammer

×

Number of blows per layer

×

Number of layers

Volume of mold

E=

2.495 kg(9.81m / s 2 )(0.3048 m)(3 layers)(25 blows / layer) 0.944 × 10−3 m3

= 592.7 kJ / m3 (12,375 ft ⋅lb / ft 3 )
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3.3 Procedures and Results
Procedures
(1) Several samples of the same soil, but at different water contents, are compacted according to the compaction test specifications.
The first four blows

The successive blows

(2) The total or wet density and the actual water content of each compacted sample are measured.

ρ=

Mt ρ , ρd = Vt 1+ w

Derive ρd from the known ρ and w

(3) Plot the dry densities ρd versus water contents w for each compacted sample. The curve is called as a compaction curve.
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3.3 Procedures and Results (Cont.)
Results
Peak point
Dry density ρd (Mg/m3) Line of optimums Zero air void

Line of optimum Zero air void

ρd max

Modified Proctor Standard Proctor

wopt
Water content w (%)
Holtz and Kovacs, 1981

Dry density ρd (lb/ft3)
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3.3 Procedures and Results (Cont.)
The peak point of the compaction curve
The peak point of the compaction curve is the point with the maximum dry density ρd max. Corresponding to the maximum dry density ρd max is a water content known as the optimum water content wopt (also known as the optimum moisture content, OMC). Note that the maximum dry density is only a maximum for a specific compactive effort and method of compaction. This does not necessarily reflect the maximum dry density that can be obtained in the field.

Zero air voids curve
The curve represents the fully saturated condition (S = 100 %). (It cannot be reached by compaction)

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 100 % S curve, it is called the line of optimums

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3.3 Procedures and Results (Cont.)
The Equation for the curves with different degree of saturation is : ρd = ρwS ρ S = w ρw S w+ S w+ ρs Gs

You can derive the equation by yourself Hint:

ρs 1+ e Se = wG s ρd =
Holtz and Kovacs, 1981

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3.3 Procedures and Results-Explanation
Below wopt (dry side of optimum): 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. At wopt: The density is at the maximum, and it does not increase any further. Above wopt (wet side of optimum): Water starts to replace soil particles in the mold, and since ρw