Familiarization with Construction Equipments

Concrete batching plant

A batching plant measures the ingredients (cement, water, sand, aggregate, admixture) accurately in the proportions of the mix design. Accurate weigh-batching improves strength and uniformity.

Main parts: aggregate storage bins/hoppers, conveyor or skip hoist, cement silo and weigh hopper, water tank and meter, admixture dispenser and control panel.

Types: manual (volume) batching for small jobs; semi-automatic; fully automatic computer-controlled plants. Stationary or mobile plants.

Concrete mixers

   Drum mixer (tilting)
        ____
      /  /\  \   charging ->
     |  |  |  |  rotating drum with
      \ \__/ /   blades inside
        ----     discharge by tilting

• Batch mixers: tilting drum (discharge by tilting, for large aggregate), non-tilting drum, reversing drum, pan (forced action), twin-shaft. Capacity: 0.1-3 m$^3$ per batch.
• Continuous mixers for large, steady output.
• Transit mixers (ready-mix trucks) carry and mix concrete from a central batching plant to the site.

Points

• Mixing time: normally 1.5-2 minutes for a drum mixer; at the correct drum speed.
• Charge in sequence: part of the water, aggregate, cement, sand, then remaining water.
• Wash the drum after use; mix at least until uniform colour and consistency.
• Machine mixing and batching give better quality, higher productivity and less labour than hand mixing, and are essential for large projects.

Equipment is therefore justified when the quantity of work is large, the time is short, and the work cannot be done economically by hand. In small projects, manual methods may be better.

The right equipment gives the required output at the lowest cost. Selection depends on the following factors.

Technical factors

1. Type and quantity of work: earthwork, lifting, concreting, compaction; large quantity favours big machines.
2. Site conditions: soil or rock, ground bearing, slope, water table, space, access, haul distance, climate.
3. Time available: tight schedule needs high-output machines or more units.
4. Capacity and output matched with the other machines in the fleet (for example, number of trucks per excavator).
5. Versatility: a backhoe loader can dig, load and lift; one machine for several jobs reduces idle time.
6. Operator skill, safety and the working conditions.

Economic and commercial factors

7. Initial cost, operating cost (fuel, repair, operator), depreciation, and owning cost against the hire rate.
8. Buy, lease or hire: depends on the utilisation hours and duration of the job.
9. Availability of spare parts, service and dealer support in the area (an important point in Nepal).
10. Resale value and standardisation of the fleet; fuel type available.
11. Mobility and transport cost to the site, mobilisation and demobilisation.
12. Reliability and past performance, warranty, and brand reputation.
13. Statutory and environmental limits: noise, emission and road limits.

Example: for 20,000 m$^3$ of excavation in a limited urban site, a hydraulic backhoe with tipper trucks is better than a dragline, which needs a big space; for a remote hill road, a bulldozer with a small excavator suits better than big heavy shovels, which are hard to transport.

Equipment for excavation and earth-moving

1. Bulldozer

     blade
    |\     cab
    | \___[_____]
    |_/ ====tracks====
   (pushes soil forward)

A crawler tractor with a front blade (straight, angle, U type) that pushes, cuts and spreads soil over short distances (up to about 100 m). Used for clearing, opening roads and levelling; the blade can be raised, lowered or tilted by hydraulic rams.

2. Backhoe (hydraulic excavator)

              boom
          ___/\___ stick
         /        \
   cab  /          \
 [____]/            \_bucket (digs toward machine)
 [==tracks==]

The excavator has a boom, a stick and a bucket that digs by pulling toward the machine. It excavates below ground level, trenches, foundations and basements, and loads trucks. It rotates 360 degrees and the bucket size of 0.3-2 m$^3$ is common.

Compaction equipment are machines that increase the density of soil, aggregate or bituminous layers by rolling, vibration, tamping or impact, to expel air and bring particles into close contact so that strength, stability and imperviousness increase.

Types

1. Smooth-wheel roller (static): steel drums (two- or three-wheel); gives a smooth surface for granular soil, aggregate base, and asphalt. Weight 8-12 t.
2. Sheepsfoot (tamping) roller: drum with projecting feet; kneads cohesive soils (clay) layer by layer, giving high pressure at the feet.
3. Pneumatic-tyred roller: several rubber tyres at close spacing; suitable for both granular and cohesive soils, sub-base and asphalt finishing; ballasted for weight.
4. Vibratory roller: vibrating drum, effective on sand, gravel and rockfill, and asphalt with thinner layers.
5. Rammers and plate compactors: hand-operated, for trenches and small areas.
6. Grid roller: heavy steel mesh drum for rocky soils and gravel breaking.

  Smooth roller        Sheepsfoot roller
   ___________          _________
  (  drum     )        ( ^^^^^^^ ) feet
  ------------         -----------

Selection: sandy/gravelly soil: vibratory; clay: sheepsfoot or pneumatic; asphalt: smooth/pneumatic. The efficiency depends on lift thickness, number of passes, moisture content (OMC) and speed.

Equipment used

Earthwork: bulldozer, scraper, excavator, grader, dump trucks, water tanker. Compaction: smooth-wheel, vibratory and pneumatic rollers. Sub-base/base: grader, aggregate spreader, roller, water tanker. Bituminous works: hot-mix plant, bitumen boiler/heater, bitumen sprayer, paver (finisher), tipper trucks, rollers, chip spreader. Concrete pavement: batching plant, transit mixer, slip-form paver, concrete finisher, vibrators, joint cutter.

1. Motor grader

        cab
      [____]
   (O)--------(O)(O)   blade under the belly
          \__blade__/

A six-wheel machine with an adjustable blade under the frame, used for spreading and fine-shaping base and sub-base to the camber and grade, mixing, ditch cutting, and for maintenance of gravel roads.

2. Paver (bituminous finisher)

   truck -> [hopper]--conveyor--[auger]--[screed]
                tracks / wheels      (levels & compacts lightly)

The paver receives hot mix from trucks into the hopper, carries it by conveyors to the auger, which spreads it in front of the screed. The screed levels and pre-compacts the mat to the desired thickness, width and camber. It is followed by rollers.

Tunnelling and rock drilling equipment

Brief explanation

• Jackhammer / pneumatic drill: air-powered hand drill, using drill steels with tungsten carbide bits to make blast holes in small tunnels.
• Drill jumbo: a rig with several booms and drifters mounted on a truck or rail-wheeled frame; drills the entire face pattern quickly with accurate hole position.
• Roadheader: a boom with a cutter head that grinds soft to medium rock without blasting.
• Rocker shovel / loader: loads blasted muck into cars or trucks behind it.
• Shotcrete machine: sprays concrete, with accelerator, on the rock to stabilise it.
• TBM: a rotating cutter head with disc cutters that excavate the full circular face, with continuous support and muck removal.
• Ventilation fans: supply fresh air and remove dust and blast fumes.

A tunnel boring machine (TBM) excavates a full-circular tunnel section in a continuous mechanised operation, without drilling and blasting. It is used for long tunnels in hydropower, metro, water supply and road projects.

   cutter head   shield     erector    conveyor
   [O|O|O]======[=========][segment]=======>  muck out
     ^ rotates   thrust rams push on lining

Main parts

• Rotating cutter head with disc cutters (hard rock) or teeth/scrapers (soft ground)
• Shield that protects the crew and supports the ground
• Thrust rams, which push the machine forward against the installed lining or grippers
• Muck removal conveyor
• Segment erector to build the precast concrete lining
• Control cabin, grout and ventilation systems

Types

Open (gripper) TBM for good hard rock; shielded TBM for fractured rock; earth pressure balance (EPB) and slurry TBM for soft, wet ground; double-shield TBM.

Advantages

Fast and continuous advance, smooth tunnel surface, less overbreak, safe working, less vibration, and less labour. Disadvantages: very high initial cost, long delivery and set-up time, difficult to change the alignment or diameter, and it is economical only for long tunnels (usually over 3-5 km).

A tower crane is a fixed or climbing crane with a tall vertical mast (tower) and a horizontal jib, balanced by a counter-jib and counterweight. It is the main lifting machine for high-rise buildings.

       counter     jib (boom)
       weight  ____________________
         [#]--|__trolley__|--hook
              |
              | mast (tower)
              |
         [========] base / tie to building

Parts

Base (fixed on a concrete foundation or on rails), mast sections, slewing unit with the operator cab, jib with trolley, counter-jib with counterweight, hoist rope and hook.

Working

The hoist lifts the load, the trolley moves it along the jib, and the slewing ring rotates the jib through 360 degrees. Capacity depends on the radius (the load moment is limited).

Types

Static (fixed), travelling (rail-mounted), self-erecting (small), climbing (tied to or climbing inside the structure), hammerhead and luffing-jib types.

Uses and merits

Lifts steel, formwork, concrete skips, precast units and materials to height; large reach and height; high speed. Limitations: high cost of erection, needs a strong foundation, and is affected by wind.

Cranes lift and move heavy loads vertically and horizontally. Types:

1. Mobile crane (truck-mounted): a telescopic or lattice boom on a truck chassis, with outriggers; used for general lifting, precast erection, with road mobility.
2. Crawler crane: a lattice boom on tracks; very high capacity, travels on rough ground, suitable for heavy lifts.
3. Tower crane: a fixed vertical mast with a rotating jib; for high-rise buildings.
4. Derrick crane: a mast with a boom held by guy ropes; used for heavy loads in a limited area.
5. Gantry (portal) crane: a bridge on legs running on rails; used in precasting yards, workshops and dam construction.
6. Overhead travelling crane: moves on rails along a building; in factories and powerhouses.
7. Rough-terrain and all-terrain cranes: four-wheel-drive for site travel.
8. Hoists and chain blocks, winches: simple lifting of light loads; goods hoists in buildings.
9. Cableway: for dams and mountain areas.

 Mobile crane:      Tower crane:
   boom  /            ____|____
   _____/ hook        counter  jib
  [cab]=O==O=         |mast|

Selection depends on the load weight, lifting radius, height, ground conditions and the duration of use.

Front-end loader

Front-end loader: a wheeled or tracked tractor with a hydraulic bucket at the front that scoops, lifts, carries and dumps loose material.

        arm
     ___/\____
    /   \    \__
   | cab|  ====\___bucket
   |____|__
  (O)======(O)   wheels / tracks

• Parts: tractor, lift arms, tilt linkage, bucket, hydraulic rams.
• Operation: the loader digs into a pile by driving forward, tilts the bucket back, lifts, carries to the truck and dumps.
• Uses: loading trucks and hoppers, stockpiling, short-haul carrying, light excavating, cleaning, and backfilling.

Dragline

Dragline: an excavator whose bucket hangs from a boom by hoist rope and is pulled toward the machine by a drag rope. It digs below the machine level and works at a distance from its own tracks.

        boom
         /\
        /  \   hoist rope
   cab /____\    |
  ____|______|   v
  [==tracks==]   \__bucket-->(drag rope pulls bucket in)

• Parts: crawler base, cab/rotating deck, long boom, hoist rope, drag rope, bucket.
• Operation: the bucket is thrown out, dragged to fill, hoisted, swung and dumped.
• Uses: soft soil, sand, wet ground, canal and drain cleaning, underwater and river dredging, long reach digging and stockpiling.

Grader (motor grader)

         cab
      [_______]
   (O)|=======|(O)(O)    blade (moldboard)
         \_____/       under the frame, can swing & tilt

A grader is a six-wheel machine with a long adjustable blade (moldboard) between the front and rear axles. The blade can be raised, lowered, tilted and angled. Uses: fine grading of sub-grade and base courses to correct levels and camber, spreading and mixing materials, cutting side drains and ditches, snow and debris removal, and maintenance of unpaved roads. It is a finishing machine; it is not suited to heavy digging.

Dragline

Dragline: an excavator whose bucket hangs from a boom by hoist rope and is pulled toward the machine by a drag rope. It digs below the machine level and works at a distance from its own tracks.

        boom
         /\
        /  \   hoist rope
   cab /____\    |
  ____|______|   v
  [==tracks==]   \__bucket-->(drag rope pulls bucket in)

• Parts: crawler base, cab/rotating deck, long boom, hoist rope, drag rope, bucket.
• Operation: the bucket is thrown out, dragged to fill, hoisted, swung and dumped.
• Uses: soft soil, sand, wet ground, canal and drain cleaning, underwater and river dredging, long reach digging and stockpiling.

(i) Power shovel (front shovel)

            boom
          _/\_
        _/    \   dipper stick
   cab /       \__
 [____]         [bucket] digs upward/forward
 [=tracks=]

Basic parts: crawler base, revolving deck with cab and engine, boom, dipper (stick), and bucket with a hinged bottom door. Operation: the bucket is crowded forward into the bank and lifted upward, curling in material; the machine swings, and the door is opened to dump into a truck. Application: digging above the track level (hillside, borrow pits, quarry), loading trucks, in hard and rocky soil with high output (bucket 1-5 m$^3$). It is not suitable for digging below its own level or for wet ground.

(ii) Backhoe (hydraulic excavator)

           boom
        __/\___ stick
       /        \
 [cab]/          \__bucket (teeth face machine)
 [==tracks==]

Parts: undercarriage (tracks or wheels), swing platform, boom, stick, bucket, hydraulic cylinders. Operation: the boom is lowered, the bucket is extended out and pulled toward the machine to dig; it is curled, lifted, swung and dumped. Application: trenches for pipes and cables, foundation pits, basement excavation, below-grade digging, ditches, demolition and loading trucks. Its 360-degree swing and precise control make it the most common site excavator.

(iii) Three-wheel steel roller

      [seat]
   ___|_____|___
  (   ) front guide wheel (steel drum)
   (  rear drive wheels - two big steel drums )

Parts: one front steering drum and two large rear drive drums, engine, frame, water spray and scrapers, ballast. Operation: it makes repeated passes at 3-6 km/h, with overlap, from the edges toward the centre; the weight is 8-12 t (ballast can be added). Application: compaction of granular sub-base, base course and macadam, initial rolling of asphalt, giving a smooth surface. Not suited to cohesive soils for deep compaction.

Equipment for road construction

Paver (finisher)

  tipper -> [hopper] -conveyor-> [auger] -> [screed]
            (receives hot mix)   spreads    levels, compacts

Functions: receives hot mix from trucks, spreads it evenly across the width, and gives the specified thickness, camber and level, with initial compaction by the vibrating screed. Sequence of operation:

1. Clean the base and apply a tack coat.
2. Set the screed height (thickness) and the guide wire or sensors; pre-heat the screed.
3. The tipper backs to the paver, which pushes it forward as hot mix is discharged to the hopper.
4. The conveyor feeds the mix to the augers, which spread it in front of the screed.
5. The screed levels and compacts the mat as the paver moves forward at a steady speed.
6. Rollers (breakdown, intermediate, finish) follow immediately to compact.

Bitumen sprayer (distributor)

  [Insulated tank + burner]  pump  spray bar
  =========truck========== |||||||||||
                           (nozzles spray hot bitumen)

Functions: sprays bitumen (tack coat, prime coat, surface dressing binder) uniformly over the road surface at a controlled rate (kg/m$^2$) and temperature. Sequence:

1. Heat the bitumen in the tank to the spraying temperature.
2. Clean the base; set the spray bar height and the nozzles.
3. Pump the bitumen through the spray bar as the truck moves at a uniform speed.
4. Check the rate of application; avoid overlap or gaps at joints.
5. Spread chippings immediately (for surface dressing) and roll.

A road paver (finisher) is a self-propelled machine that lays, spreads and partly compacts bituminous mix (or concrete in the slip-form type) to the required width, thickness, camber and level.

 truck->[hopper]==conveyor==[auger]--[screed]
         tracks or wheels      spreads  vibrates & levels

• Parts: receiving hopper, feeder conveyors, augers, tamper bar, vibrating and heated screed, levelling sensors, tracks or rubber tyres, operator platform.
• Working: tipper trucks unload hot mix (130-160 degrees C) into the hopper; the conveyor carries it to the augers, which spread it; the screed floats on the mix, and gives a uniform mat of the set thickness. Rollers follow at once.
• Types: crawler and wheeled pavers; asphalt pavers; concrete slip-form pavers.
• Advantages: uniform thickness and riding quality, high output, and less labour.
• Care: continuous feed of material, steady speed, and correct temperature to avoid segregation and cold joints.

Construction equipment used in hydropower projects

• Earthmoving: bulldozers, excavators, loaders, dump trucks, scrapers.
• Rock and tunnelling: drill jumbos, jackhammers, rock bolters, shotcrete machines, tunnel boring machines, rocker shovels, ventilation fans.
• Concrete: aggregate crushers, batching plants, transit mixers, concrete pumps, tower cranes, cableways, vibrators, and formwork travellers.
• Lifting: mobile and crawler cranes, gantry cranes for powerhouse and gates.
• Compaction: vibratory rollers (earth/rockfill dams).
• Dewatering: pumps, well points; grouting plant for curtain grouting.
• Transport: tippers, trailers, ropeways.

1. Drill jumbo

       boom1  boom2  boom3
        \    |    /
  [cab]  drifters at the face
  [==rubber tyre or rail carriage==]

A truck-mounted frame with two or three hydraulic booms, each carrying a rock drill (drifter). The operator positions the drills in the blast pattern. It drills the holes for the explosives rapidly in headrace tunnels, adits and caverns. Advantage: speed, accuracy of holes and safety.

2. Tower crane or cableway for concrete placing

   head tower ======cable======= tail tower
                    |bucket|
                 (concrete bucket over the dam block)

A cableway carries concrete buckets across the dam site, from the batching plant to the blocks, over a long span. A tower crane serves the powerhouse and intake structures for lifting formwork, reinforcement and concrete.

Tunnel excavation methods depend on the type of ground, the size and length of the tunnel, time, and cost.

1. Drilling and blasting (drill and blast)

Holes are drilled on the face, charged with explosives and blasted; the muck is removed and the roof supported. Used in hard rock; flexible for any shape. Steps: drilling, charging, blasting, ventilation, mucking, scaling and support.

2. Mechanical excavation

• TBM (full face): a rotating cutter head cuts the whole section and the muck goes by conveyor. Fast and safe for long tunnels.
• Roadheader: boom-mounted cutting head for soft to medium rock and for tunnels of variable shape.

3. Heading and bench method

The tunnel is excavated in two stages: a top heading first (and supported), then the bench below. Used in large sections.

4. Soft-ground methods

Shield tunnelling, pipe-jacking or micro-tunnelling, cut-and-cover (open trench and roof), and the New Austrian Tunnelling Method (NATM) with shotcrete and rock bolts.

5. Other: multiple drifts (side drift, centre drift), and the use of ripping or hydraulic breakers.

Choice factors: geology and rock quality, tunnel length and diameter, water inflow, available equipment, and the schedule and cost. Support (rock bolts, shotcrete, steel ribs) follows each method to keep the opening stable, and the lining is built afterward.

Conventional (drill and blast) method: steps in sequence

1. Survey and marking of the face profile, centre line and level.
2. Drilling blast holes in the planned pattern using a drill jumbo.
3. Charging the holes with explosives and detonators, and connecting.
4. Blasting after everyone leaves, using the proper delay sequence.
5. Ventilation to clear fumes and dust.
6. Scaling: removing loose rock from the roof and sides.
7. Mucking (muck removal) by loader and trucks, or rail cars.
8. Temporary support: rock bolts, shotcrete, wire mesh or steel ribs, as per the rock class.
9. Advancing and repeating the cycle; drainage, services, and survey control.
10. Final lining: concrete lining, with waterproofing and grouting.

 Drill -> Charge -> Blast -> Ventilate -> Scale
    -> Muck -> Support -> (repeat) -> Lining

Tunnel boring machine (TBM)

A TBM is a machine with a rotating circular cutter head that excavates the whole tunnel section continuously, supports the tunnel with a shield and lining, and removes muck by a conveyor.

Advantages of TBM

• High speed of advance and continuous operation
• Smooth tunnel wall and less overbreak, so less lining concrete
• Safer working and less vibration and ground disturbance
• Less labour, and consistent quality
• Suited to long tunnels, with less ventilation problem than blasting

(High cost and long mobilisation time are its limits.)

Tunnel excavation by blasting (drill and blast) is the traditional method for hard rock tunnels, widely used in Nepal's hydropower and road tunnels.

Cycle

1. Drilling: holes (32-45 mm diameter, 3-4 m deep) are drilled with a drill jumbo according to the blast pattern.
2. Charging: explosives (dynamite, emulsion or ANFO) and detonators are placed, and the holes are stemmed.
3. Blasting: firing in sequence using delay detonators.
4. Ventilation: clearing of fumes and dust.
5. Scaling and mucking: loose rock is removed, and the muck is carried away.
6. Support: rock bolts, shotcrete, or steel ribs.

   Face drilling pattern (cut holes in middle)
        o   o   o   o
      o   o  [x x]  o   o      x = cut / empty holes
        o   o   o   o
      Cut - stopers - contour (perimeter) holes

Hole types

Cut holes (open the face first), easers/stopers (enlarge), contour holes (smooth blasting for a clean profile), and lifters (floor).

Merits and limits

It is flexible for any section and rock, uses cheap equipment, and has a low initial cost. But it is slower than a TBM, causes overbreak, vibration, fumes and noise, and needs strict safety control, licensed blasters and explosive storage.

Use: a typical building uses a batching plant or ready mix, a transit mixer, a pump or crane, and needle vibrators; for large pavements a slip-form paver is used. Choice depends on the volume, the placing rate, height, and distance of the pour.

A contractor can obtain construction equipment by purchase, lease, or hire (rent).

Purchase

• The contractor owns the machine; it is suitable where utilisation is high and continuous over a long period.
• Merits: full control, lower cost per hour at high use, resale value, and tax benefit on depreciation.
• Demerits: heavy initial investment, depreciation, repair and maintenance cost, idle cost when there is no work, and risk of obsolescence.

Lease

• A long-term contract where the lessor owns the machine and the contractor pays regular rent; at the end it may be returned or bought (finance lease, operating lease).
• Merits: no large capital outlay, the latest technology, and fixed monthly payments; maintenance may be included.
• Demerits: total payments exceed the purchase price in the long run; the contractor does not own the machine; there are lease conditions.

Hire (rental)

Short-term use by the day, hour or month; suited to occasional or short-duration work.

Decision

Compare the owning cost per hour (depreciation, interest, insurance, tax, storage) plus operating cost (fuel, repair, operator) with the lease or hire cost at the expected utilisation. Buy if the use is high and long, lease or hire if the use is low or the job is short. Other factors include the availability of capital, local dealer support, and the contractor's future work.