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Dr. Khaled Hyari Department of Civil Engineering

Hashemite University

4 – Compacting and Finishing

Construction Methods 110401542

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• Principles of Compaction

• Compaction Equipment and Procedures

• Grading and Finishing

Compacting and Finishing

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• Compaction: the process of increasing the density of a soil by mechanically forcing the soil particles closer together, thereby expelling air from the void spaces in the soil.

• Consolidation: an increase in soil density of a cohesive soil resulting from the expulsion of water from the soil’s void space

• Consolidation vs. Compaction: Months vs. hours

• Compaction Why? – To improve the engineering properties of soil

Principles of Compaction

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• Compaction Advantages: – Increased bearing strength

– Reduced compressibility

– Improved volume change characteristics

– Reduced permeability

Principles of Compaction II

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• Factors Affecting Degree of Compaction: – Physical and Chemical properties of the

soil (grain size, cohesiveness, etc.) – Moisture content of the soil – The compaction method employed – The Amount of compactive effort – The thickness of the soil layer being

compacted – Soil’s initial density

Principles of Compaction III

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• FOUR basic compaction forces: – Static Weight (Pressure) – Manipulation (kneading): most effective in

plastic soils – Impact – Vibration

• Most compactors combine static weight with one or more of the other compaction forces

– Ex: Plate Vibrator combines static weight with vibration

Compaction Forces

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• Impact and vibration produce similar forces (frequency is different)

• Impact or tamping involve blows at lower frequency (usually 10 cycles per second) that is more suitable for cohesive soils

• Vibration uses higher frequency (> 80 cycles per second) that is more suitable for cohesionless soils like sand and gravel

Compaction Forces II

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• Optimum Moisture Content: The moisture content at which maximum dry density is achieved under a specific compaction effort

• Proctor Test: A standard laboratory test developed to evaluate a soil’s moisture – density relationship under a specified compaction effort – Compaction tests are performed over a range of soil

moisture contents – The results are plotted as dry density versus moisture

content – The peak of the curve represents the maximum

density obtained under the compactive effort supplied

Optimum Moisture Content I

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Proctor Compaction

Tests

Optimum Moisture Content II

Typical Compaction Test

Optimum Moisture Content III

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• Compaction specifications are intended to ensure that the compacted material provides: – The required engineering properties (minimum dry

density to be achieved) and – A satisfactory level of uniformity (A maximum variation

of density between adjacent areas) • Typical density requirements are expressed as a percentage

of Proctor (Ex. For the support of structures and for pavement base courses, requirements of 95 to 100% of Modified Proctor are commonly used

• A lack of uniformity in compaction may result in differential settlement of structures or may produce a bump or depression in pavements

Compaction Specifications

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• Why? – To verify the adequacy of compaction actually

obtained in the field • How? Methods available include:

– Traditional methods (liquid tests, sand tests) – Nuclear density devices

Measuring Field Density

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• Principal Types of Compaction Equipment: – Tamping Foot Rollers – Grid or Mesh Rollers – Vibratory Compactors – Smooth Steel Drum

Rollers – Pneumatic Rollers – Segmented Pad Rollers – Tampers or Rammers

Compaction Equipment

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• Utilize a compaction drum equipped with a number of protruding feet to achieve compaction

• These rollers come with a variety of foot shapes and sizes and include the classic sheepsfoot roller

• Achieve compaction through static weight and manipulation

• They are most effective on cohesive soils

Tamping Foot Rollers

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• Utilize a compactor drum made up of a heavy steel mesh

• They can operate at high speed without scattering the material being compacted

• Their compactive effort is due to static weight and impact

• Most effective in compacting gravel and sand • Able to crush and compact soft rock

Grid or Mesh Rollers

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• Available in a wide range of sizes and types – Size: ranges from small hand-operated compactors

through towed rollers to large self-propelled rollers) – Type: include plate compactors, smooth drum rollers,

and tamping foot rollers • Most effective in compacting noncohesive soils

Vibratory Compactors

• Many vibratory compactors permit varying the vibration frequency to obtain the most effective compaction

• Compactive forces are principally vibration and static weight

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• Widely used for compacting granular bases, asphaltic bases, and bituminous pavements

• Compaction achieved primarily through static weight

Steel Wheel or Smooth Steel drum Rollers

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• Well suited for compacting thick soil layers to high density

• Least suited for compacting sands and gravel

Rubber-tired or Pneumatic Rollers

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• Similar to tamping foot rollers except that they utilize pads shaped as segments of a circle instead of feet on the roller drum

• They produce less surface disturbance than do tamping foot rollers

Segmented Pad Rollers

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Tampers or Rammers

• Small impact-type compactors primarily used for compaction in confined spaces

• Some rammers are classified as vibratory rammers because of their operating frequency

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• Confined areas: – Trenches – Around foundations

• Equipment examples: – Vibratory plate compactors – Tampers or rammers – Walk-behind static and vibratory rollers – Attachments for backhoes and hydraulic

excavators

Compaction in Confined Areas

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Vibratory plate compactors

Compaction Equipment II

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Walk-behind static and vibratory rollers

Compaction Equipment III

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Attachments for backhoes and

hydraulic excavators

Compaction Equipment IV

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Selection of Compaction Equipment

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• Objective: Obtaining the required soil density with a minimum expenditure of time and effort

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Selection of Compaction Equipment

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• After selecting compaction equipment, a compaction plan must be developed

• Factors to be considered in the plan: – Soil moisture content – Lift thickness (layer thickness) – Number of passes used – Ground contact pressure – Compactor weight – Compactor speed – Frequency (for vibratory compactors)

Compaction Operation

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• Lifts should be kept thin for most effective compaction – A maximum lift thickness of 15 to 20 cm is suggested for

most rollers • The compaction achieved by repeated passes of a

compactor depends on the soil/compactor combination utilized

– The increase in density is relatively small after about 10 passes for most soil/compactor combinations (see Figure 5-12 in the Textbook)

• Trial operations are usually required to determine the exact values of soil moisture content, lift thickness, compactor weight and frequency that yield maximum productivity while achieving the specified soil density

Compaction Operation II

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Number of Passes

Number of Pass Effect

Compaction Operation III

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Production (CCM/h) = (10 x W x S x L x E) / P Where: P = number of passes required W = width compacted per pass (m) S = compactor speed (km/h) L = Compacted layer thickness (cm) E = job efficiency

Compaction Production

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• Problem 2 Estimate the production in compacted cubic

meters per hour for a self-propelled tamping foot roller under the following conditions: – Average speed = 8 km/h – Compacted lift thickness = 15.2 cm – Effective roller width = 3.05 m – Job efficiency = 0.75 – Number of passes = 8

Compaction Production II

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• Solution Production (CCM/h) = (10 x W x S x L x E) / P = (10 x 3.05 x 8 x 15.2 x 0.75) /8 = 347.7 CCM/h

Compaction Production III

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What? • Grading: the process of bringing earthwork to

the desired shape and elevation (or grade)

• Finishing (or finish grading): Smoothing slopes, shaping ditches, and bringing the earthwork to the elevation required by the plans and specifications

• The grader is usually the equipment used for grading and finishing

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Grading and Finishing

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• Graders are used for: stripping, grading, finishing, backfilling, mixing and spreading soil, and maintenance of haul roads

Grading and Finishing II

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• Usually calculated on – Linear basis for roadway projects (kilometers

completed per hour) – Area basis for general construction projects

(square meters per hour)

• Average speed depends on – Operator skill – Machine characteristics – Job Conditions

Estimating Grader Production

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• Typical grader operating speed

Estimating Grader Production II

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• Example 24.1 km of gravel road require reshaping and

leveling. It is estimated that 6 passes of a motor grader will be required as follows: – 2 passes at 6.4 km/h – 2 passes at 8.0 km/h – 2 passes at 9.7 km/h

• Job efficiency is estimated at 0.8 • How many grader hours will be required for this

job?

Estimating Grader Production III

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Estimating Grader Production IV

• Solution:

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• The use of skilled operators and competent supervision are required

• Use the minimum possible number of grader passes to accomplish the work

• Eliminate as many turns as possible

• Use grading in reverse for distances less than 305 meters

• Several graders may work side by side if sufficient working room is available (for large areas)

Job Management