Light Compaction Equipment Technology Welcome remarks TBD.

4 processes producing compaction 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. Light Construction Utility Equipment

4 types of soil vs 4 compaction processes Rammer Vibr. Sheepfoot Static Sheepfoot Grid Roller Scraper Vibrating Plate Vibrating Roller Rubber-tired roll. Loader Grid roller Soils Lift Thickness Impact Pressure (with kneading) Vibration Kneading (with pressure) Gravel >=30cm Poor No Good Very Good Sand ~25cm Excellent Silt ~15cm Clay Very 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. Light Construction Utility Equipment

Families of equipment Family Compaction process Application Frequency Impact force concentr. Rammers Impact + Kneading Cohesive soils 700 BPM High Forward plates Vibration Granular soils – Asphalt 5000 - 6000 BPM Low Reversible plates Vibration + Impact Gravels – Semi cohesive soils 3000 – 4000 BPM Medium Double-drum rollers Static weight + Vibration Asphalt – Granular soils 3000 - 3500 BPM Light Construction Utility Equipment

1 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. Light Construction Utility Equipment

1 Rammers The 4 stroke engine runs the big green gear at 700 rpm. The blue crank drives the orange piston up and down. The piston is activating the rammer foot through a set of springs. Hard spring for hammering down, softer spring for bringing it up. The bottom part is dipping in oil. The purple bellows protects the mechanics against dirt. The forward motion is created by the angle between the ground and the oscillating movements. Rammers are characterized by their impact force and shoe width. Light Construction Utility Equipment

2 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. Light Construction Utility Equipment

2 Vibratory plates A 4 stroke engine drives an eccentric shaft through a belt transmission equipped with a centrifugal clutch. The shaft is strongly connected to the base plate with bearings in such a way that the centrifugal force will result into vibrating the plate. The engine is isolated from the plate thanks to silent blocks. The vibrations naturally result into a forward motion by small jumps. A plate compactor is characterized by its Impact force Contact surface, plate width Weight [kg] Light Construction Utility Equipment

Impact force [kN] Eccentric shaft design & frequency The impact force of a compaction unit depends on the design of the eccentric weight (mass m and eccentricity R) and on the rotation speed (frequency). High frequency – Small eccentricity: Vibratory plates Low frequency – High eccentricity: Rammers Light Construction Utility Equipment

3 Reversible Vibratory Plates Technology In addition to some of the standard vibratory plate features, reversible plates have two eccentric weights that allow smooth transition for 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. Light Construction Utility Equipment

3 Reversible Vibratory Plates Reversible plates have 2 eccentric shafts connected by gears and turning in opposite directions. The 2 weights will be at the same angle twice per revolution. By changing the relative position of the weights on their shafts with the lever, the operator will change the motion from forward to neutral and further, backward. The weight position modification is done through a sliding helicoidal spring system. Light Construction Utility Equipment

4 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 one eccentric shafts placed between 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. Light Construction Utility Equipment

4 Double-drum Walk-behind Rollers A diesel engine drives both the hydrostatic pump for smooth propulsion and the eccentric shaft for vibration. The shaft is located on top between the drums; it is dipping into oil and there is a clutch system allowing the operator to put it on/off. 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… Particle shape, Particle distribution, Water content Labor requirements Number of operators available Safety of operators Required productivity Size of the job… Light Construction Utility Equipment

Equipment Applications Asphalt Granular Soils Sand and Clay Cohesive Clay Ideal vibration frequency: 6000 RPM 4500 RPM  2500 RPM  750 RPM Rammers Not Recommended Testing Recommended Best Application Forward Plates Reversible Plates Double-drum Rollers Trench Rollers Ground composition is not always easy to tell. Therefore it is wise sometimes to test the efficiency of different machines. Light Construction Utility Equipment

Alternative applications Vibratory plates of all sizes are used to settle paving stones. For this purpose, a polyurethane mattress can be fixed on the unit in order to prevent the steel plate from breaking the paving stones. Another paving technique consists of imprinting fresh concrete with a plate mold. This gives the concrete a pattern and a color. Vibratory plates are used to press the mold onto the fresh concrete. Light Construction Utility Equipment

Working parameters The machines are always optimized to be operated at full engine load: this will provide the proper frequency. Other parameters are controlled by the operator: Lift thickness Number of passes Traveling speed Light Construction Utility Equipment

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. Light Construction Utility Equipment

Number of passes 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. Light Construction Utility Equipment

Traveling speed With reversible plates and duplex rollers, it is possible to adjust accurately the travel speed. Working at 1/2 speed will have the same effect as making 2 passes. Light Construction Utility Equipment

Traveling too fast or too low vibration frequency Traveling speed With vibratory rollers, the machine speed must be settled in adequate relation with the vibration frequency. 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. Rough surface finish: LOW HIGH Impact spacing Traveling too fast or too low vibration frequency Light Construction Utility Equipment

Pay attention 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. 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. 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 compaction 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. Organic soils should never be used for backfilling. As they will decay further, voids will appear, making it unstable. 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. Light Construction Utility Equipment