BAB 7:

GRADERS & COMPACTORS

GRADING Definition: Any excavating or filling or combination

thereof.” The site is graded to cut high points and fill low

areas to the desired profile elevations. the grading construction was done according to the

approved plans, including the location and extent of grading, and the finish slopes of cuts and fills.

Generally, cut material can be used as embankment fill.

However, peat, organic silt, or soil with high organic content should not be used; borrow material should be used instead.

GRADERS The function of grading equipment is to bring

the earthwork to the desired shape and elevation.

Major types of grading equipment include motor graders and grade trimmers.

The former is an all-purpose machine for grading and surface finishing, while the latter is used for heavy construction because of its higher operating speed.

GRADERS

GRADERS

GRADERS

GRADERS

GRADERS is used to level the ground for example in order to

produce a declivity so that the rain water can drain off.

For doing this the grader is equipped with a leveling blade (moldboard), which is fixed between the axles, and which is moveable to many adjusted positions.

is equipped with a steerable off-road independent front axle as well as with attachments, for example front leveling blade and a rear road raker, both are height-adjustable and detachable.

GRADERS In construction industry, the grader's purpose is to "finish grade" (refine, set precisely)

the "rough grading" performed by heavy equipment or engineering vehicles such as scrapers and bulldozers.

Graders are commonly used in the construction and maintenance of dirt roads and gravel roads. In the construction of paved roads they are used to prepare the base course to create a wide flat surface for the asphalt to be placed on. Graders are also used to set native soil foundation pads to finish grade prior to the construction of large buildings.

Graders can produce inclined surfaces, to give cant (camber) to roads. In some countries they are used to produce drainage ditches with shallow V-shaped cross-sections on either side of highways.

GRADERS

GRADERS Motor Grader or Trimmer? Subgrade preparation is about to begin. Do we use a motor grader or a trimmer? Both have their place on the job site. For many years motor graders were used for final subgrade preparation because most road building contractors owned a motor grader. They would normally be operated by an individual who had

expertise in cutting "fine grade." This was normally accomplished by a surveyor setting what were known as "blue tops." These were simply square, wooden stakes driven into the ground until the top of the stake, which was

painted blue, would be at the correct subgrade elevation. Depending on the profile of the roadway, there was usually a stake driven every 25 or 50 feet (7.6 or 15.2 m) apart on each side of the roadway and also down the centerline. The motor grader operator would make multiple passes on the roadway cutting the grade until he could see the "blue top," and consequently, the final subgrade elevation was achieved.

Because of blue tops being cut out by the moldboard, this sometimes required multiple settings of the blue tops by the surveyors. This added time and cost to the project. Just as a side note... today, after the blue top is set to elevation, a "chaser" is nailed to the top of the blue top to aid the motor grader operator in knowing how close the blue top is to his

moldboard. The chaser is made from polyurethane strands that, after being attached to the top of the blue top, stick up vertically about three or four inches (76 to 102 mm). The most common problem was that the area between the blue tops may not be exactly the same elevation as over the blue tops because the operators would push the moldboard of the motor

grader down as they approached the blue top. Another problem that the motor grader operator would encounter would be subgrade density that would vary because of different base materials and the moldboard would not maintain the same elevation as the operator desired. In other words, the moldboard may "ride up" or float over more dense material and cut in deeper in less dense material.

That is what separated the normal motor grader operator from a good "blade man." This situation is compounded by the fact many engineers specify either lime or cement-stabilized natural soils or select materials. The mixing of these materials creates a very dense and, after some time, extremely hard material that is almost impervious to a blade. The trimmer will in most cases be able to cut this material accurately.

 

The Advent of Slipform Paving Once preset stringline came into use, with the advent of slipform paving, many contractors used a combination of stringline and blue tops to attain their desired subgrade elevation. Also at this

time, the grade trimmer came onto the scene because this machine would follow the same stringline that the paver would follow. This eliminated the necessity for the surveyor to set blue tops, but sometimes they are still written in the specifications for an additional elevation check. The premise of the trimmer is that with a

rotating mandrel or trimmer wheel that has teeth evenly spaced across the width of the wheel, the teeth are cutting the subgrade. The moldboard that follows directly behind the wheel is simply containing and scraping the excess loose material to be loaded on the loading belts.

This effectively eliminates the problem of a motor grader with a blade or moldboard that may float over the high-density material and cut into the lower-density material. The composition of the subgrade makes an enormous amount of difference in the way trimmers and motor graders react to that material. One example would be a subgrade that has a lot of clay which, when compacted to density, is very hard. The trimmer, because of its cutting action, "chips" away at the material and is able to maintain an accurate grade, usually in one trimming pass if the machine is operated correctly.

The motor grader on the other hand, with this same material, will have a tendency to float over this hard material. It may take several passes to cut it down to final elevation. This process occurs whether the machine is operated manually or if it has some type of sensor system to follow the stringline or is GPS/Laser database controlled.

Another example would be a subgrade material consisting of mainly aggregates and sand with not much clay or "binder" present. This type of material shears very easily and even if compacted to high density will be easily cut by a motor grader following a stringline or GPS/Laser database control. The trimmer will also cut this material with ease.

Grade Trimmer

Grade Trimmer

Grade Trimmer

Grade Trimmer – advantages

When trimming what is known as select material, such as previously placed aggregate base, lime or cement-treated base or even lime or cement-stabilized natural soils, the excess materials that come from the trimming operation can be loaded on a truck while trimming and hauled to another area on the job site where a low-grade condition exists.

This keeps the contractor from wasting the high-cost select material. Even if select material is not used and local soils are being trimmed, the excess material can be

moved to the back side of the stringline where it can be used for backfill to the edge of slab. This saves the contractor time and money. He can accomplish a task while trimming that would

either require tearing down stringline or several extra pieces of equipment to move the material. If the local material is needed elsewhere, it can be loaded on a truck while trimming, again

saving additional equipment and expense.

COMPACTORS

Soil Compaction

Definition:

The process by which soil air space is decreased due to the pressure applied to the soil particles.

The method of mechanically increasing the density of soil.

Soil Compaction

Soil Compaction In construction, this is a significant part of the

building process. 

If performed improperly, settlement of the soil could occur and result in unnecessary maintenance costs or structure failure.

  Almost all types of building sites and construction

projects utilize mechanical compaction techniques.

Soil Compaction When it comes to road building or parking lot

construction, the subgrade has to meet the appropriate standards before the finished surface can be installed.

One of the machines designed to help meet the necessary density numbers that will make for a smooth, long-lasting surface is the compactor.

COMPACTORS

The function of compaction equipment is to produce higher density in soil mechanically.

The basic forces used in compaction are static weight, impact and vibration.

COMPACTORS

COMPACTORS The degree of compaction that may be achieved

depends on the properties of soil, its moisture content, the thickness of the soil layer for compaction and the method of compaction.

Some major types of compaction equipment includes rollers with different operating characteristics.

Vibratory roller is capable of performing a wide range of soil and asphalt compaction applications.

Some Major Types of Compaction Equipment

Sheepsfoot Compactor with Blade

Single Drum Vibratory Roller

Single Drum Vibratory Roller Features Large Compaction Force:

The larger centrifugal force allows for a thicker layer compaction, which in turn allows a fewer number of shuttle runs over the surface for reduced operating cost.

• Articulated Frame for High Mobility: The frame articulation provides a small turning radius, making the machine highly mobile even in

restricted areas. • Easy Compaction on Road Shoulders:

The frame overhang on both sides allows compaction very close to curbstones or fences. • One-Lever Hydrostatic Transmission System:

The hydrostatic transmission allows directional changes, starts, braking and stop to be achieved with only one lever. Also, it allows travel speed to be controlled to optimum levels to suit operation.

Comfortable to Operate: A rubber-mounted operator's compartment is designed to reduce vibration for improved operator

comfort. The operator seat, sliding fore and aft, provides the optimum driving position for any size operator. Additionally, full-hydraulic power steering provides light control effort.

Single Drum Vibratory Roller Economical, Durable Engine:

The engine, featuring direct injection and troidal combustion chambers, offers proven durability and low fuel consumption. The hydrostatic transmission assures excellent flat torque for very smooth operation.

Small Overhang: Small overhang of the left side of the machine facilitates quick and smooth compaction work very close

to walls, fences, or posts. Large Roll Width and Working Speed:

Large roller width and working speed allows shorter cycle time for speedy job completion. Low Noise and Vibration:

Rubber pads for vibrator shaft support, steering wheel support, and operator's compartment suppress vibration before it reached the operator.

Sprinkler System: A sprinkler system is essential for asphalt compaction work. Water is spread uniformly over the whole span

of the rollers and a large-capacity water tank allows extended operation before refilling.

Single Drum Vibratory Roller

Tire Roller Features High efficiency, high precision rolling operations

The wide rolling width provides a large hourly production, thereby reducing the project period. By using wide tires which provide a uniform ground pressure, it is possible to achieve high precision rolling with a high degree of

flatness. The amount of overlap is large and uniform, so there are no parts left unrolled, and the rolling operation can be carried out efficiently.

Side rolling is also easy The front tires are over-banked a large amount from the frame, so it is possible to carry out rolling operations right up to the edge of

walls or roads.

Optimum water spray, oil spray device installed for operation on paved surfaces A job-proven diaphragm type pump is used to spray water. This can give a uniform spray regardless of the slope of the surface

being rolled. The capacity of the water tank is a large 220 liters, which enables water spray operations to be carried out for a long period with one tank of water.

Stable, low center of gravity design The design with a low center of gravity allows a large angle of lean to the left or right, thereby ensuring stable operations even on

rough ground.

Easy operation and control A HST (hydrostatic transmission) is used. Change of direction, braking, and speed control operations can be carried out simply with

one FR lever. The knob on the steering wheel and the power steering system enable steering operations to be carried out with a light touch.

Tire Roller Features High safety brake system

For normal operations, the FR lever is placed at neutral and the HST brake is used to brake the machine. The parking brake is a mechanical type. In emergencies, the foot brake is operated to use the braking force of both the HST brake and the mechanical brake.

Comfortable, pleasant operation A wide bench seat is used to enable the operator to take the most suitable driving position, so he feels no fatigue even after long

hours of operation.

Easy maintenance The structure of the fully hydraulic system has made the drive system easier, so daily maintenance can be carried out easily.

Tire Roller