DOZERS

FAILURE TYPES Structural or mechanical: Machine parts are stressed

beyond capacity.

Stability: Machine becomes imbalanced and overturns.

Machine parts remain operable but machine isn’t in the

position to carry out the work.

FACTORS FOR

MACHINE

SELECTION

Nature of activity

Required efficiency

Cost

Site conditions

Equipment productivity

Time available

Availability of skilled labor

GENERAL

RELATIONSHIPS

Productivity is high, cost of machinery is high

Productivity is high, Unit cost of work to be done is low

Capacity of equipment is high, Productivity is high

BULLDOZER

A bulldozer is a tractor unit with a blade attached to its

front. The blade is used to push, shear, cut, and roll

material ahead of the tractor.

3 parts – blade, ripper, tractor.

Two types: Wheeled, crawler or tracked

WHY DOZERS ARE USED? AND USES

Dozers are low centre of gravity machines

The larger the difference between the transmission line of the force applied by the machine and the transmission line of the resistive force, the less effective is the utilization of the developed power.

Uses: Dozing, Land Clearing, Ripping, Towing, Assisting Scrapers

WHEELED VS

TRACKED

WHEELED TRACKED

Works on variety of soils

Works on variety of soils

Less versatility in terms of terrain

More versatility in terms of terrain

High return speeds Low return speeds

Better for loose soils Better for tight soils Moderate blade loads Larger blade loads

Long work distances Short work distances

BLADE FUNCTIONS

Pitching: Movement about horizontal axis, cutting angle adjustment

Angling: Movement about vertical axis, Side casting (material rolls off one end of blade)

Tilting: Movement about horizontal axis, concentrate cutting power to a smaller length of the blade. Used for sloping.

BLADE TYPES Universal: Best for lighter soils, used for long distance work, reduced spillage of material

Angle: Best for side casting, not recommended for harder soils

Cushion: Used for ‘on-the-go’ excavation with scrapers, use recommended for lighter soils and light excavation

Straight: Heavy-duty, used for short to medium distance work, used primarily for grading and shallow works

S and U blade: Combination of universal and straight.

FACTORS AFFECTING

DOZER PRODUCTIVITY

Blade type

Tractor type

Soil conditions

Blade load(lcy) = 0.0138(WHL) Volume (cy) = (0.375)(WHL)/27

DOZER CYCLE Dozer moves into position to excavate

Dozer digs or scoops soil

Dozer moves excavated soil

Dozer unloads excavated soil

Dozer repositions

Dozer backtracks to excavation site FACTORS FOR PRODUCTION PER CYCLE

Visibility

Slope

Transmission

Material

Operator

Blade adjustment WHY LAND CLEARING IS NECESSARY

Organic materials decompose in fill, can cause settlement of fill

Have to be removed

Make material handling difficult

LAND CLEARING

Crawlers with special land clearing blades and rakes are used

Involves: o Removal of trees, shrubs, grass and roots o Only material seen on surface is removed o Removed vegetation is stacked and burned

Production(acre/hr) = W(ft) x SPEED (mph) x5280xE/43560

Production min/acre= H [A (B) + MINI + M2N2 + M3N3 + M4N4 + DF]

RIPPER Claw like device on back of dozer

Single shank or multiple shank

RIPPER TIP USAGE

Short – high impact conditions

Intermediate – moderate impact conditions

Long- Low impact conditions, soft soils

GRADER

DEFINTION A long tractor driven piece of equipment with a blade mounted underneath it.

It is a multipurpose machine used for finishing and shaping.

FUNCTIONS Levelling

Sloping

Side casting

Spreading

Finishing

Grading

General construction FACILITATES DOZERS

Can progressively cut a ditch of upto 3 ft.

Can make shallow cuts in hard soils where the dozer can then perform heavier work

BLADE OPERATIONS

Angling

Pitching

SHOVELS

DEFINITION A machine that is designed to carry out digging above

grade and into the face of the excavation.

The shovels are usually mounted on a crawler or track to provide larger traction.

Excavated soil is dumped into trucks.

Shovels are not designed for high mobility and so hauling distances are minimized.

FACTORS AFFECTING

PRODUCTIVITY

Operator skill

Material to be excavated

Clean up of loading area

Size of hauling units

Height of cut

Condition of shovel

SELECTION OF SHOVEL

Type of material to be excavated

Operator skill

Size of hauling units

Use of auxiliary equipment

Swing angle

Height of cut

PROCESS OF SHOVEL

Excavate

Swing out

Dump

Swing back

P= 3600*Q/t*F*E*(1/(1+swell))

LOADERS

DEFINITION Versatile piece of machinery

Used for hauling, loading materials, excavation at and above wheel or track level

Rubber wheels used are thick and provide sufficient traction and reduce bearing pressure

Can transfer loads from one site to another as it can move at high speeds (wheeled)

Hydraulically powered lifting equipment exerts a heavy breakout force as the lifting occurs

TYPES Based on running gear: o Wheel mounted o Track mounted

Other classifications based on load carrying capacity, steering mechanisms etc.

FACTORS AFFECTING

PRODUCTION AND

SELECTION

Haul distance

Type of material to be excavated/hauled

Volume of material to be hauled

Cycle times

Height of lift required

Machine specifications (load carrying capacity e.g.)

WHEEL LOADERS VS TRACK LOADERS

WHEEL TRACK

More bearing pressure Less bearing pressure Best for work on soils of low to medium hardness

Best for work on soils of medium to high hardness

High mobility Low mobility

Rubber tires vulnerable to cuts from cut rock

Steel tracks are not damaged by use on cut rock

Can climb 30% grades Can climb 60% grades Operation limited on steep side slopes

Can operate better on steep side slopes

SKID STEER LOADERS

Are small in size and very versatile

Can attach a number of tools such as saws, blades, backhoes, trenchers, rotary brooms etc.

Steer by applying brakes to wheels on one side and transferring power to wheels on the other side.

PRODUCTION LOADER AND EXCAVATOR

P= E*FILL FACTOR*LOAD IN ONE CYCLE/CYCLE TIME P= E*F*Q/T CHECK FOR LOAD AGAINST CAPACITY

ROLLERS AND COMPACTORS

DEFINITION Equipment designed to compact materials such as soil, gravel, asphalt and concrete.

COMPACTION METHODS

Kneading (manipulation)

Static weight (pressure)

Impact (sharp blow)

Vibration (shaking)

ROLLER TYPES Sheep foot or tamping foot

Pneumatic (rubber tired)

Smooth drum Vibratory

Pad drum Vibratory

Grid rollers

SHEEP FOOT Angular or square projections from a drum exert pressure on soil, kneading

Can be used on fine grained soils but not on granular non-cohesive soils

SMOOTH DRUM

Widely used

Best for compacting asphalt pavements and granular bases

Works on static weight and can incorporate vibration

PAD DRUM Vibratory plus kneading

Pads emerge from drums

Lift thickness of 1 to 1.5 ft thick

Work best on cohesive soils

GRID Work on granular soils

Work on static weight along with impact and manipulation

Good for breaking lumps and soft rock

PNEUMATIC Work on kneading

Rear and front tires cover all

Work on bases, sub bases, pavements

Can work on granular and fine soils

Tire ply, Inflation pressure, tire size, wheel load determine compaction

COMPACTION WHEELS

Work on all types of soils

Can have tamping or sheepsfoot shape

Attached to an excavator boom

Work in narrow trenches

VIBRATORY PLATE

COMPACTORS

Self-propelled, gasoline or diesel powered

Compaction of crushed aggregate, concrete and asphalt

Can be walk-behind units or operated through remote control

RAMMERS Self-propelled, gasoline powered

Compact through impact

Designed to work in small spaces PRODUCTION Production (cubic Yard/hr )= 16.3xWxSxLxE/P

W= width compacted in each pass in feet

S= Compacter speed in mph

L= compacted lift thickness in inches

E= Job Efficiency

P= Number of passes required

Mixer types:

Gravity or freefall:

Reversible drum: Single axes

Tilting drum: Double axes

Power or forced mixers: Paddles move eccentrically or centrically around a shaft or axis

Pan mixers: (vertical shafts)

Planetary: Shafts eccentrically located and are able to rotate

Turbo: Shafts are centrally located and can be fixed or rotary

Even flow: drums and paddles rotary and move in same directions

Counter flow: drums and paddles move in counter directions

Trough Mixers (horizontal):

Paddles or wave shaped arms (arranged in spiral pattern)

Single shaft

Twin shaft

Transit:

Concrete mixed already but kept plastic while being transported to site

or

Concrete mixed during journey to site

Front Discharge

Rear discharge

Articulate truck mixers

PUMPS:

Piston VS Squeeze

High reliability Quiet operation

Low noise operation Low pressure operation

High pressure operation Easier to clean

High efficiency Variable delivery rate

Pumping systems:

Pump with pipeline mounted on frames, trailers or trucks

Pump mounted on truck boom

Pump mounted on tower boom