Special report - Equipment
Engineer JAGVIR GOYAL tells us about the amazing versatility
of the excavators available today.
The first activity in the construction of any new structure
is excavation for its foundations. Normally, this occurs with
much fanfare. However, the real tempo is built and the pace
is set only if excavation work moves at a fast speed. The
movement of machines at the site is an electrifying scene
and work finds its rhythm. In contrast, if excavation work
moves at a slow speed, the spirit of producing a new structure
is lost and the project dawdles.
Thus, excavation work is an activity that decides the future
pace of construction of any structure.
Excavation work needs to be planned well by drawing an excavation
plan of the area. All precautions are to be taken against
caving of sides by maintaining proper slope in them or providing
shoring and supports wherever required. Vertical cuts in excavation
should be avoided at any cost as these prove risky and costly
ultimately. All excavated earth is always stacked away from
the cutting edge to avoid its falling over the workers. A
major percentage of fatal accidents at construction sites
occur during excavation activity owing to caving in of the
sides. The Jasola Delhi accident is a recent example.
Highly versatile excavators being produced today give unbelievable
output and can handle any kind of job. These can be operated
mechanically, hydraulically or by cable. Further, they can
be track or tyre-mounted. Track-mounted excavators are preferred
as they can work in waterlogged areas or areas of low bearing
capacity. They can also move on steeper slopes than tyre-mounted
excavators. However, the speed of tyre-mounted excavators
is higher. Therefore, the choice is made according to site
requirements. Excavation equipment includes backhoes, shovels,
drag-lines, clam shells and hydraulic excavators.
In backhoes, buckets move towards the operating machine, while
in shovels, the bucket moves away from the body of the machine.
Hoes excavate earth at levels below their own position while
shovels excavate earth above their positioning level. Backhoe
loaders have an arm and bucket on the back and a loader on
the front. Draglines have buckets suspended from the booms
by means of wire ropes run from the cabin by powerful motors.
There are separate hoist ropes and drag ropes in a drag line.
The drag rope drags the bucket on the area to be excavated
and also keeps it balanced. Draglines are suitable for excavation
below their own level and have their own limitations as hoist
and drag ropes can't be extended too long. These are more
suitable for mining work. Clamshells have their buckets in
two halves with teeth on each half, opened and closed hydraulically
and supported by another hydraulic circuit to drag the bucket.
Hydraulically operated excavators have taken over the excavation
scene now. These are able to rotate in any direction, work
at a fast pace and are highly reliable. The best part of this
equipment is the forearm-like movement of the bucket with
teeth. It can be set to any angle to rip off a large chunk
of soil from the earth's surface.
The basic components of a hydraulic excavator are the track
or tyre undercarriage, cabin built over a pivot, hydraulic
system, boom, ram and bucket. The sharp teeth of the bucket
cut through the soil and the bucket scoops it up. A hydraulic
jack moves the arm. Two levers provided on the right side
of the operator help him to virtually control all the movements
of the excavator. These levers require no extra effort and
can be operated with ease. The upper body of a hydraulic excavator
can swivel through 360° by rotating on the slewing ring.
Though the excavator has been designed by taking a cue from
man's movements, it can swivel more than a man's torso.
Basically, a diesel engine at the back of the excavator provides
all the power to drive the hydraulic equipment. Further, a
hydraulic motor at the front drives the machine forward. All
hydraulic power is produced by exerting great pressure on
hydraulic oil, which further drives the motors, pushes the
pistons of jacks, and so on. Thus, the oil-carrying pipes
and their joints have to be very strong.
While buying an excavator, parameters that need to be studied
include the capacity of the bucket of the excavator; the power
of the excavator; cycle time and hourly output; reach; maintenance
requirements; POL consumption; cost; and travelling speed.
Excavators being produced today have a bucket capacity as
high as 5 cu m. The higher the bucket capacity of an excavator,
the more its weight. A 5-cu-m bucket capacity excavator weighs
around 90 tonne. A useful feature of excavators is that their
track width is adjustable according to site requirements.
Almost all excavators are now equipped with a dozer blade
as pushing the excavated earth and mounting it for collection
and dumping into dumpers are crucial to achieve optimum efficiency.
An excavator can achieve the rated output only if it is backed
by earth-carrying dumpers with earth-disposal capacity matching
the excavation capacity of the excavator. A dumper always
has to be ready and in position to receive excavated earth
when the boom of the excavator swings back with a filled bucket
for unloading. Thus, the fleet of dumpers also has to be reviewed
while assessing an excavator's performance.
Sound hydraulic system
The success of an excavator depends on the soundness of its
hydraulic system. This should always be kept in mind while
buying an excavator. Frequent breakdowns owing to the failure
of this system completely ruin momentum of work and the excavator
becomes a burden. Many hydraulic cylinder actions with variable
strokes are involved in the excavation process. Any pressure
drop owing to leakage of oil or non-operation of a valve can
steal the major advantage of the excavator.
Among the important components of the excavator hydraulic
system are its filters, pipes, hoses, seals, valves, cylinders
and oil. Filters of hydraulic systems must work efficiently
for smooth working of the hydraulic pump, to avoid cavitations
and the long life of the system. The latest range of excavators
promises almost double life of hydraulic filters. Availability
of spare pipes, hoses and seals is important as, sometimes,
one of these hoses or pipes may burst under pressure. Connections
of hoses to machine parts are the most vulnerable points.
Therefore, excavators with least hoses and more tubes should
be preferred. Filters need to take out every minor particle
of the hydraulic oil to avoid any cavitations effect or erosion
of pumps. Regular filter cleaning is a very important aspect
Hydraulic excavators can have a number of attachments and
accessories used to handle particular jobs. Some of these
Excavator rippers: These are useful in breaking up hard soil
and particularly helpful in trenching and pipeline work.
Rock buckets: These are suitable for handling hard rocks and
resist highly abrasive forces. Made of high-strength steel,
these buckets have the thickest wear plates and can achieve
better penetration than general purpose buckets.
Concrete cutter jaws: This attachment helps in demolition
and cutting of concrete structures.
Crusher jaws: They are particularly helpful in demolition
of RCC structures.
Primary pulverizer jaws: These demolish concrete and separate
the reinforcement from it in a single operation. The time
of secondary processing is thus saved.
Pin grabbers and couplers: These help excavators in picking
up and using any work tool.
Grapples: These can handle loose materials as well as irregularly
Rotation shears: These can rotate at a full 360° and demolish
even steel structures.
They can be mounted on the boom or stick of the excavator.
While the primary function of a hydraulic excavator is to
excavate soil to a larger reach and depth, it acts as the
most effective demolition tool for any type of structure,
steel or RCC.
With India in the grip of an infrastructure development boom,
the need of the hour is to make available excavators of high
capacity, thus completely eliminating the need of importing
excavation equipment and saving on high cost of spare parts.
The main manufacturers of hydraulic excavators are Caterpillar,
Hitachi, L&T, JCB, BEML, Mitsubishi, Poclain, Volvo and
Liebherr. In India, L&T, BEML and JCB rule the market
while Poclain excavators are available in plenty. In fact,
excavators are known as JCB or Poclain at sites of work! JCB,
which stands for Joseph Cyril Banford, is in fact the founder
of the UK-based company. And in February 2007, a robust excavator,
the L&T Komatsu PC 130-7, was launched in India by L&T.
JCB's JS 210 L and JS 330 L with maximum engine power of 128
HP and 239 HP are also available in India.
Caterpillar produces the larg-est variety of hydraulic excavators
to cater to all small and big jobs. Known as CAT, the machines
are divided into five categories: Mini, Small, Medium, Large
and Extra Large. Further, a number of machines are produced
under each category. A buyer can configure his machine and
get a price estimate. For example, the CAT 345C L excavator
is an amazing machine with 345 hp net power, a travel speed
of 4.4 kmph and a digging depth reach of 9 m. Its maximum
bucket capacity is 3.8-cu-m, the bucket itself weighs about
1.76 tonne. The machine has a reach of 13-m at ground level.
CAT unveiled its D series excavator 325D at Excon 2007 held
in Bangalore in November 2007. Its 330D and 320D models are
already in operation in India. CAT's D series excavators particularly
suit Indian projects owing to their comparatively lower buying
and running costs, ability to take higher hydraulic pressure
and lower oil consumption. The filter replacement period is
almost double that of C series machines. In fact, the 325D
model now introduced fills the large gap between 320D and
Manufacturers often project specifications and data showing
bucket-fill capacity, operating weight, engine output, fuel
tank capacity, rated RPM, maximum travelling speed, length
of boom, maximum dumping height, maximum horizontal reach
of excavator, maximum digging depth, tyre size and wheel base
(for wheeled excavators) or ground pressure (for track based
excavators). These should be examined with respect to specific
needs at the work site.