Light Compaction Equipment About compaction 011206 History of

Light Compaction Equipment About compaction 01/12/06

History of compaction • Ancient technique: Herds of cattle or sheep were used to compact soil for road construction. Their weight on small hoof used to make an effective compaction. • 18 th century Horses or oxen drawn rollers • 19 th century First steam roller in France • 1905 First sheep foot roller for dam construction in California 2 Light Construction Utility Equipment

History of compaction • 1930’s First use of vibratory compactors in Germany for highway construction. • 1940’s Tow behind vibratory roller in the USA. • 1950 – 1960’s First self-propelled units. Fast development started by the end of the 60’s because of the popularity of self-propelled units in highway construction. 3 Light Construction Utility Equipment

What is compaction? • Rearranging the particles. – Removing voids (increasing the density [kg/dm³]). – Interlocking the particles. – Compacting freshly dropped soil will generally double its density. • The action of compacting can be measured by – The density increase. – The soil hardness increase. – The particles arrangement on a sample. 4 Light Construction Utility Equipment

Compaction objectives • Reducing soil compressibility and therefore reducing further deformation: – Increasing soil strength – Improving stability and load bearing capacity • Reducing water absorption – Increasing impermeability – No soil swelling and contraction due to water seepage – Reducing frost damage • Hardening and flattening the surface – Reducing erosion – Improving the grip 5 Light Construction Utility Equipment

Importance of ground compaction • The building itself can be as strong as possible. • If the ground below cannot bear the building weight, serious problems will arise! 6 Light Construction Utility Equipment

Why does efficient compaction make the difference? • Poor compaction results into cavities and ground permeability. • A quality work requires performing proper compaction at all levels of the layers structure. 7 Light Construction Utility Equipment

Materials: usual road layers Shear resistance Asphalt wearing course Asphalt binder course Asphalt base course Pavement Bearing capacity Subbase Different materials require different compaction parameters. Capping layer Ground Loam 8 Light Construction Utility Equipment For light compaction, asphalt can be seen like a material mix + a binder.

Soil and Asphalt • In the prospect of light compaction, asphalt can be seen as a particular case. • Asphalt: On low traffic ways: Small stones – High sand content – Liquid bitumen On high traffic ways: Large aggregates – Low sand content – Thick bitumen • Asphalt specificities: – Must be worked when hot. – Water is necessary to prevent asphalt from sticking to the compacting machine – Compaction control is performed by core sampling. • The information that follows is focused on soil compaction 9 Light Construction Utility Equipment +

Material parameters Particle size Coarse granular soil Fine cohesive soil Fine sands & silts. Mixes & clays Particles stick together • Coarse grains can be seen. Feels gritty when • Grains cannot be seen by naked eye. Feels rubbed between fingers. • When moist, very little or no plasticity. • Little or no cohesive strength when dry. Soil smooth and greasy when rubbed between fingers. sample will crumble easily. • When moist, Plastic and sticky. Can be rolled. • Has high strength when dry. Crumbles with • Relatively easy to compact difficulty. Slow saturation in water. • Requires high compaction energy 10 Light Construction Utility Equipment

Material parameters Particle shape Compaction properties of granular soils will vary as according to their particle shape. Rolled aggregates Crushed aggregates E. g. : River gravel E. g. : Crushed granite • • • Lots of grip on the particle contacts: Particles easily slide on each other. Low shear resistance. Relatively easy to compact Static compaction can be enough. 11 Light Construction Utility Equipment they don’t move easily. • High shear resistance. • Requires high compaction energy • Requires vibration

Material parameters Size mix The size distribution of the particles has a strong effect over the long term stability of the compacted soils. Poor mix Good mix • Mixed aggregate sizes allow to achieve better mechanical properties of the compacted layer because of –better interlocking –more contact points –fewer voids • It is not allowed to backfill trenches or road support with any kind of soil. 12 Light Construction Utility Equipment

Material parameters Water content • There is an optimum water content that will reduce aggregate friction and therefore maximize the compaction ability: ~11% Dry Ideal moisture ~11% High water pressure • Hand test: Pick up a handful of soil, squeeze it in your hand open. § If the soil is powdery and will not retain the hand shape, it is too dry: add water. § If the soil is moldable and breaks into only a couple of pieces when dropped, it has the right moisture content for compaction. § If the soil is plastic in your hand stays in one piece when dropped, it is too wet for compaction. 13 Light Construction Utility Equipment

4 compaction processes • Impacting – Compaction is the result of material compression under relatively low frequency impacts with significant amplitude. • Static (pressure) compaction – Static rollers compact the material by their dead weight alone. These machines tend to « surface compact » only. They achieve higher density near the surface. • Vibratory compaction – The vibrations create motion of the particles in depth. They rearrange and the compaction occurs from bottom to top. • Kneading – The material undergoes a shearing force that creates particles motion toward interlocking. 14 Light Construction Utility Equipment

4 compaction processes Rammer Vibr. Sheepfoot Soils Lift Thickness Impact Static Sheepfoot Grid Roller Scraper Pressure Vibrating Plate Vibrating Roller Vibr. Sheepfoot (with kneading) Vibration Scraper Rubber-tired roll. Loader Grid roller Kneading (with pressure) Gravel >=30 cm Poor No Good Very Good Sand ~25 cm Poor No Excellent Good Silt ~15 cm Good Poor Excellent Clay ~15 cm Excellent Very good No Good • Compaction equipment usually consists in a combination of these 4 compaction processes. • In practice, the most important process is probably the compaction through vibrations. But it is still not the most obvious to understand. 15 Light Construction Utility Equipment

Compacting by vibrations • The vibrations are induced by the rotation of one or more eccentric shafts. The energy comes from the centrifugal force. • A compactor is characterized by its – Contact surface [m²] – Weight [kg] – Eccentric shaft design • Other parameters are – Frequency [Hz] – Advance rate [m/s] 16 Light Construction Utility Equipment

Compacting by vibrations • The eccentric shaft design together with the total weight of the compactor and the working frequency [vpm] will determine the vibration amplitude [cm] and the impact force [k. N]. • The « compaction energy » of an equipment is directly proportional to its impact force and to its working frequency. • Each compaction machine is designed to operate at an optimum frequency to supply the maximum force. 17 Light Construction Utility Equipment

Frequency effect • High frequencies are suitable for compacting a thin layer of asphalt* or small particles granular soil. Small particles also require more energy as more particles mean more friction. • Lower frequencies will work best to put big aggregates into motion on a thicker layer. 18 Light Construction Utility Equipment

Traveling speed • With vibratory rollers, the machine speed Rough surface finish: must be settled in adequate relation with the vibration frequency. LOW HIGH Impact spacing • A typical objective for impact spacing is at least 30 to 40 impacts per meter. A high vibration frequency of 3300 vpm (55 Hz) allows traveling at up to 1. 8 m/s. 19 Light Construction Utility Equipment Traveling too fast or too low vibration frequency

Lift thickness • The fresh soil layer to be compacted, also called the lift thickness should not be too big at a time: there is a danger that an intermediate layer will stay loose, which can generate problems in the future. • Manufacturers of compaction equipment usually specify a maximum lift depth. This is measured in ideal conditions. In real jobsite conditions, you may consider that the lift thickness is 75% of this value. 20 Light Construction Utility Equipment

Pay attention • Multiple passes are necessary to optimize the compaction. For a good result, it will be necessary to perform typically from 3 to 5 passes, depending on the soil properties. • As the soil becomes compacted, more energy returns to the compactor. This makes the apparent amplitude (as felt by the operator) grow bigger. • Over-compaction – Making too many passes can result into over-compaction. It is like constantly hitting concrete with a sledgehammer. Cracks will eventually appear, reducing density and the ground stability. – Over-compaction is a waste of time and adds unnecessary wear to the machine. 21 Light Construction Utility Equipment

Job site specifications • The general contractor can ensure the compaction performances on a jobsite in two ways: Method Specification Detailed instructions specify machine type, lift depths, number of passes, machine speed and moisture content. End result Specification Engineers indicate final compaction requirements: soil density to a specified depth, ground hardness. • The second method is better as it gives the contractor the opportunity to the choose the most economic and flexible way to do the job, taking advantage of the latest technology Choosing the right equipment for the right application. 22 Light Construction Utility Equipment

Rammers • Technology Rammers get compaction force from a small gasoline engine powering a large piston set with two sets of springs. Frequency range is 500 to 750 blows per minute. The rammer is inclined at a forward angle to allow forward travel as the machine jumps. • Application Rammers deliver a high impact force (high amplitude) on a small shoe surface. It makes them an excellent choice for cohesive and semi-cohesive soils. They are perfect for backfilling and narrow trench compaction applications. Rammers cover three types of compaction: impact, vibration and kneading. 23 Light Construction Utility Equipment

Vibratory Plates • Technology Gasoline engines drive one eccentric weight at a high speed to develop compaction force. Frequency range is usually 2500 to 6000 vpm. The resulting vibrations cause forward motion. The engine and handle are vibration-isolated from the vibrating plate. • Application Vibratory plates are low amplitude and high frequency, designed to compact granular soils and asphalt. The heavier the plate, the more compaction force it generates. Plates used for asphalt have a water tank and sprinkler system to prevent asphalt from sticking to the bottom of the base plate. Vibration is the one principal compaction effect. 24 Light Construction Utility Equipment

Reversible Vibratory Plates • Technology In addition to some of the standard vibratory plate features, reversible plates have two eccentric weights that allow smooth transition forward or reverse travel, plus increased compaction force as the result of dual weights. • Application Due to their weight and force, reversible plates are ideal for semi-cohesive soils or crushed stones, which require high compaction energy. Heavy plates with high compaction energy are good for trench works. Unlike standard plates, the reversible forward travel may be stopped and the machine will maintain its force for « spot » compaction. 25 Light Construction Utility Equipment

Double-drum Walk-behind Rollers • Technology Dual steel drum are mounted on a rigid frame and powered by a diesel engine. Steering is done manually with the machine handle. Frequency is 3300 vpm and amplitude is around 0. 5 mm. Vibration is provided by eccentric shafts placed in the drums. • Application A popular design for many years, the smooth-drum machine is ideal for both soil and asphalt. Its frequency and amplitude make it optimized for small particles material. High productivity is achieved as the double-drum works twice in one pass. 26 Light Construction Utility Equipment

Trench Padded Rollers • Technology The trench roller feature hydrostatic drive and skidsteering. Powered by a diesel engine, the trench roller is built to withstand the rigors of confined compaction. • Application This equipment has a high productivity in trenches and excavations, even on highly cohesive soils. For added safety in shored and unshored trenches, the equipment is operated by means of a remote control. Large eccentric units provide high impact force and high amplitude that are appropriate for cohesive soils. The drum pads provide a kneading action on soil. 27 Light Construction Utility Equipment

When choosing the equipment, keep in mind Physical constraint of the jobsite Dimension of the trench… Obstacles Compaction requirements Requested relative density Type of soil Granular, Cohesive… Water content Labor requirements Number of operators available Safety of operators Required productivity Size of the job… 28 Light Construction Utility Equipment

Equipment Applications Granular Soils Sand Clay Cohesive Clay Asphalt Not Recommended Testing Recommended Best Application Not Recommended Best Application Testing Recommended Not Recommended Best Application Reversible Plates Testing Recommended Best Application Not Recommended Double-drum Rollers Not Recommended Best Application Testing Recommended Best Application Trench Rollers Testing Recommended Best Application Not Recommended Rammers Forward Plates • Ground composition is not always easy to tell. Therefore it is wise sometimes to test the efficiency of different machines. 29 Light Construction Utility Equipment

Jobsite observations • Construction compaction equipment can be highly dangerous. Every operator must conform to the safety instructions, wear the proper protection equipment and be trained to a safe usage of the machinery. • Some job situations require using complementary pieces of equipment. For instance, when a picket is standing in the way of a double-drum roller compacting asphalt, this one cannot operate very next to the picket foot because of the side-clearance. Therefore it is compulsory to finish the work with a vibratory plate. • It is possible to increase the compaction pressure of a light forward vibratory plate by forcing it to rear up by pushing the handle downward. This trick helps when leveling asphalt. 30 Light Construction Utility Equipment