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Construction Methods 110401542 – Compacting and Finishing Dr Khaled Hyari Department of Civil Engineering Hashemite University Compacting and Finishing • Principles of Compaction • Compaction Equipment and Procedures • Grading and Finishing 4-٢ ١ Principles of Compaction • 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 4-٣ Principles of Compaction II • Compaction Advantages: – Increased bearing strength – Reduced compressibility – Improved volume change characteristics – Reduced permeability 4-٤ ٢ Principles of Compaction III • 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 4-٥ Compaction Forces • 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 4-٦ ٣ Compaction Forces II • 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 4- ٧ Optimum Moisture Content I • 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 4-٨ ٤ Optimum Moisture Content II Proctor Compaction Tests Optimum Moisture Content III Typical Compaction Test ٥ Compaction Specifications • 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 - ١١ Measuring Field Density • 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 - ١٢ ٦ Compaction Equipment • 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 - ١٣ Tamping Foot Rollers • 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 - ١٤ ٧ Grid or Mesh Rollers • 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 - ١٥ Vibratory Compactors • 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 • Many vibratory compactors permit varying the vibration frequency to obtain the most effective compaction • Compactive forces are principally vibration and static weight - ١٦ ٨ Steel Wheel or Smooth Steel drum Rollers • Widely used for compacting granular bases, asphaltic bases, and bituminous pavements • Compaction achieved primarily through static weight - ١٧ Rubber-tired or Pneumatic Rollers • Well suited for compacting thick soil layers to high density • Least suited for compacting sands and gravel 4- ١٨ ٩ Segmented Pad Rollers • 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 tamping foot rollers - ١٩ 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 - ٢٠ ١٠ Compaction in Confined Areas • 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 - ٢١ Compaction Equipment II Vibratory plate compactors - ٢٢ ١١ Compaction Equipment III Walk-behind static and vibratory rollers - ٢٣ Compaction Equipment IV Attachments for backhoes and hydraulic excavators - ٢٤ ١٢ Selection of Compaction Equipment Selection of Compaction Equipment • Objective: Obtaining the required soil density with a minimum expenditure of time and effort This image cannot currently be display ed - ٢٦ ١٣ Compaction Operation • 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) - ٢٧ Compaction Operation II • 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 4- ٢٨ ١٤ Compaction Operation III Number of Pass Effect Number of Passes Compaction Production 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 - ٣٠ ١٥ Compaction Production II • Problem Estimate the production in compacted cubic meters per hour for a self-propelled tamping foot roller under the following conditions: – – – – – Average speed = km/h Compacted lift thickness = 15.2 cm Effective roller width = 3.05 m Job efficiency = 0.75 Number of passes = - ٣١ Compaction Production III • Solution Production (CCM/h) = (10 x W x S x L x E) / P = (10 x 3.05 x x 15.2 x 0.75) /8 = 347.7 CCM/h - ٣٢ ١٦ Grading and Finishing What? This image cannot currently be display ed • 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 - ٣٣ Grading and Finishing II • Graders are used for: stripping, grading, finishing, backfilling, mixing and spreading soil, and maintenance of haul roads - ٣٤ ١٧ Estimating Grader Production • 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 - ٣٥ Estimating Grader Production II • Typical grader operating speed - ٣٦ ١٨ Estimating Grader Production III • Example 24.1 km of gravel road require reshaping and leveling It is estimated that passes of a motor grader will be required as follows: – passes at 6.4 km/h – passes at 8.0 km/h – passes at 9.7 km/h • Job efficiency is estimated at 0.8 • How many grader hours will be required for this job? - ٣٧ Estimating Grader Production IV • Solution: - ٣٨ ١٩ Job Management • 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) - ٣٩ ٢٠ ... to static weight and impact • Most effective in compacting gravel and sand • Able to crush and compact soft rock - ١٥ Vibratory Compactors • Available in a wide range of sizes and types – Size:... 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 - ٣٣ Grading and Finishing. .. /8 = 347 .7 CCM/h - ٣٢ ١٦ Grading and Finishing What? This image cannot currently be display ed • Grading: the process of bringing earthwork to the desired shape and elevation (or grade) • Finishing