32

CONSTRUCTION EQUIPMENT

32.1 INTRODUCTION

The type of equipment to be used for a specific project depends on the scope of the project involved. Every project is executed not by department but by contracting the work. So it is the choice of contractor to use suitable equipment. If a particular equipment is required to be purchased, he has to think whether he could get the amount of investment for the equipment during the project itself.

32.2 COST OF EQUIPMENT

32.2.1 Procurement Cost

Procurement cost includes (i) the cost price of the equipment, (ii) interest on money invested on the purchase, (iii) taxes paid and (iv) insurance cost.

Evidently the owner of the equipment pays cash for the procurement of the equipment. It is to be noted that if the same amount is invested in some other scheme what would be the turnover. One should get a higher amount annually by investing in the equipment. Each year the equipment earns for the owner and in the process its value gets depreciated. Thus the investment in the equipment is therefore reduced by the amount of depreciation. A realistic rate of interest would be the one based on the average value of the equipment during its useful life. The average value of the equipment has to be determined.

On the depreciated value of the equipment the insurance and taxes are paid. The expenses also should be worked out on the average value of equipment. These aspects are to be considered before investing on the procurement of equipment.

32.2.2 Operating Cost

Operating cost of an equipment is based on the following factors:

1. Cost of investment
2. Depreciation cost
3. Cost of major repair
4. Cost of fuel and lubricants
5. Cost of labour
6. Servicing and field repairs
7. Overheads

1. Cost of Investment

By investment made on the equipment the owner is losing an amount equal to the interest or return one would have otherwise received from bank or other sources of investment. For the purpose of calculating the total cost of investment, the interest, the taxes, insurance, etc., may be taken as 10–15% of the cost of equipment.

2. Depreciation Cost

Because of wear and tear the cost of equipment gets depreciated. An amount of earning has to be set aside, to balance the depreciation, so that the accumulated amount can be used at the end. This amount is recovered from the earnings of the equipment and forms a charge on the operating cost.

3. Cost of Major Repair

Major repairs are those which are incurred when the equipment is taken to a workshop. This repair involves replacement of major parts of the equipment, overhauling and servicing. This incurred expense is added to the capital cost so that the expenditure is distributed over the years and included in the operating cost of the machine.

4. Cost of Fuel and Lubricant

While calculating the fuel consumption of the equipment, it is the general practice to consider the full load condition and constant speed under favourable conditions. As the equipment would not be working always at the ideal condition and so a reduction factor of 60% is considered.

5. Cost of Labour

The cost of labour includes (i) the wages of the working crew and (ii) wages of supervisory staff.

6. Servicing and Field Repair

All expenses involved in the maintenance normally met during the operation of equipment except major repairs are included under this. This demands periodical service of the equipment.

7. Overhead

In a large project the whole establishment is work charged. Any unforeseen expenses which are not work charged or non-productive are distributed to the various work producing elements for purpose of cost control.

32.3 TYPES OF EQUIPMENT

For a building project the selection of equipment depends on:

1. The magnitude of the building project, viz., a single unit, multi-storeyed building, housing complex, etc.
2. The type of equipment, its size and other particulars.
3. Whether the equipment are to be purchased, rented or contracted for the work.

Major equipment needed for a building project are the following:

1. Earthwork equipment
2. De-watering equipment
3. Compaction equipment
4. Pile driving equipment
5. Movement and hoisting equipment
6. Hauling equipment

32.3.1 Earthwork Equipment

Earthwork and moving equipment are available to suit different field conditions which are discussed below.

1. Excavators

Excavators are digging machines. These machines consist of the following components (Fig. 32.1):

1. An undercarriage – this gives mobility to the excavator. This may be mounted with crawler track or wheel.
2. A superstructure with operator’s cabin – this could traverse through 360° or fitted on a rigid frame.
3. Hydraulically articulated booms and dipper arms with bucket.

Figure 32.1 Excavator

Excavators may be of mechanical (or cable operated) or hydraulic types. Hydraulic excavators have more advantages. They can be fitted with various multi-purpose attachments for various earth moving works. Most efficient action of the machine is that the hydraulic unit of action of the excavator which directs the bucket teeth at their most efficient angle during dipping operation.

Mechanical or cable operated excavators are of either hoe or shovel type. In hoe type the bucket opening fences towards the machine whereas in shovel the bucket opening faces away from the machine.

Excavators are of four types, viz., crawler-mounted excavator, truck-mounted excavator, self-propelled excavator, and excavator mounted on barge or rail.

Excavators include dipper or power shovel, dragline, clamshell and drag shovel. All these machines basically fall under shovel family in that the front end only is changed. Shovel based machines have a common type of operating and tracking mechanism.

2. Shovels

Shovel is often used for a specific type of excavating machine fitted with a short length boom and working with forward strokes. The following are the four types of machines which have the same basic structure but the front-end attachments are different:

1. Dipper shovel
2. Drag shovel or hoe
3. Dragline
4. Clamshell

The frontline attachments are as follows:

1. Shovel boom and dipper stick for a dipper shovel.
2. Shovel boom, jack boom and stick for a drag shovel.
3. Crane boom with a failed and a loosely attached bucket for dragline.
4. Crane boom with a special type of bucket for a clamshell.

(i) Dipper Shovel

The dipper shovel or power shovel is the most popular of the shovel excavator. It consists of a boom, dipper stick, the bucket and the mechanism of operation. The lower end of the boom is hinged to the support bracket and the upper end carries the bucket hoist sheaves. The dipper stick moves back and forth on a dipper drum through a guide formed by a saddle block. In order to cause the stick to slide back and forth, the dipper drum is rotated (Fig. 32.2). The bucket of the power shovel is strongly built of steel. These are generally used for digging hard rock in quarries or ores in mines. The digging is done above the machine base level

Figure 32.2 Dipper shovel

(ii) Drag Shovel or Hoe

It is also called as a Pull shovel. As this machine resembles the digging mechanism of an ordinary garden hoe it gets the name. The digging action results from the drag or pull of the bucket towards the machine. This action helps for digging below the machine level particularly while digging for trenches, footings, basements, etc., Fig. 32.3 (Mahesh Varma, 1979).

Figure 32.3 Drag shovel (Source: Mahesh Varma 1979) (Construction Equipment: It’s Planning & Applications, 1979, Metropolitan, New Delhi)

This shovel consists of a boom, a stick, a jack boom and a bucket which is attached at the end of the stick. The stick is hinged by a pin with a boom. This enables to turn over the pin to take any desired direction best suited for digging or dumping operations. The lower end of the stick carries the bucket and the upper end carries a sheave having the hoist cable supported on a jack bottom at the other end. This arrangement enables to hoist the cable when pulled and the reaction at the stick enables to move the boom with stick up or down. Thus the boom is capable of taking any position in vertical plane.

Drag shovels have application in

1. Digging trenches, footings or basements
2. Digging for hard materials
3. Providing close trimming whenever needed, and
4. Where excavated materials need to be dumped at a short distance.

(iii) Dragline

As this machine drags the bucket against the material to be dug it attains this name. This consists of a boom, a bucket, a fairlead and hoist, dump and drag cables, Fig. 32.4 (Mahesh Varma, 1979). The boom is similar to that of a crane boom. The top and bottom ends of the boom are known as the point and the foot respectively. The boom is attached to the deck with pin at foot and supported at the point through the boom hoist cable. This cable passes over a pair of sheaves placed one on each side. They have three types of buckets, viz., light, medium and heavy, which are used depending on the nature of material.

Figure 32.4 Dragline (Source: Mahesh Varma, 1979) Construction Equipment: It’s Planning & Applications, 1979, Metropolitan, New Delhi

A dragline can dig and dump over longer distance than an ordinary shovel can do. Because of its long boom the machine need not be seated close to the pit. Thus it can handle digging of underwater excavation while stationing the machine on a firm soil away from the location of the pit. This can dig below the track level and can handle soft materials comfortably.

(iv) Clamshell

It gets the name as its bucket resembles to a clam which is a shellfish with a hinged double shell. It is having most of the characteristics of dragline and crane. Digging is done as in a dragline and soon after the bucket is filled, it works like a crane. It has a crane boom with a specially designed bucket attached to it at the upper end through cables. The bucket is hinged at top and has either sharp edge or the teeth at the bottom (Fig. 32.5).

Figure 32.5 Clamshell

During digging process the bucket is lowered with shells open. When reaching the surface to be dug it makes a good contact with it. The weight of the bucket helps the sharp-edge or the teeth at the bottom of the bucket to dig into the surface or material, thereby filling the bucket. Once the bucket is filled the shells close.

The bucket is then hoisted and swung to the position where dumping has to be done and contents are dropped. Buckets may be light or heavy weight and used depending on the type.

Its applications are widely used where

1. The digging or dumping vertically is needed.
2. The material is relatively soft or medium hard.
3. Digging of trenches.
4. Loading materials in a bin or a stock pile.
5. Accurate dumping of materials.

3. Bulldozers

It is an important equipment on a construction project. It is basically a scraping and pushing unit. However, it is a multi-purpose equipment which can be used for different purposes with some modifications. Accordingly they are called as angle dozer, tilt dozer, tree dozer, and push dozer. Up to 100 m distance these can be used to haul.

Angle dozer pushes its load at an angle (nearly 25°) to the direction of travel. This is helpful (i) when the material has to be pushed down the slope on hill work and (ii) where a long windrow has to be made during the travel of the dozer.

Tilt dozer is used to start excavating a ditch or a trench or for excavation in hard ground. For this the blade is required to be tilted by raising one end up to 25 cm above the other. Push dozer is used to push the scraper unit after digging and also during loading operation using the pusher plate.

Tree dozer is used to uproot and remove trees.

4. Tractors

A tractor is a multi-purpose machine. This comes in varied type of light model to heavy model. The light model is used for agricultural or small haulage purposes. Heavy model equipped with several special rings are used for earth moving work. This is an important piece of equipment which is indispensable on all important projects.

Two principal applications of tractors are as follows:

1. Clearing and excavating machinery.
2. Hauling and conveying machinery.

There are two types, viz., wheeled tractors and crawler tractors. The wheeled type is used for light and speedy jobs. As regards to its applicability it falls between the crawler tractor and the truck. The crawler tractors are rugged machines which are used for heavy duty work. It is used particularly when there is a demand for more tractor power and speed of movement. Now-a-days wheeled units have been made to work on the jobs which are intended for the crawler type. Wheel tractors are now available for all practical earth moving jobs including nipping and dozing.

5. Motor Graders

A grader is primarily a device for loading or finishing earth work. Sometimes it is also used for mixing gravel, making windrows and trimming slopes. There are two types of graders, viz., towed and motorised.

The towed type is of small size with a tractor. The controls are in general manual and sometimes a small petrol engine is fitted on the framework of the grader to operate the controls. It is operated by separate operator.

Attachments to the grader include the blade (also called as moldboard), the scarifier, the bulldozer or the snowplow, the elevator and the roller. The versatility of the machine is increased by the addition of these tools. The blade is thick and like a blade of dozer and can swivel through 180°. The scarifier is the tool for loosening hard soil and may be mounted in the front or in the rear of the machine. The bulldozer and the snowplow (a V-shaped/blade) are front-cut attachments enables the grader to pick up the material cut by the blade and drop it over an inclined belt conveyor which transmits it into carrier unit or discharges it aside the windrow. In order to compact or smoothen the ground surface, a roller may be attached to the rear of the grader.

6. Scrapers

Scrapers are the devices to scrap the ground to load the material, to transport to the required distance, to dump at the intended place, to spread the dumped material over the required area, to attain the desired thickness and to return back to do the next cycle. In simple terms scrapers are designed to dig, load, haul, dump and spread. As a scraper does a multiple works it is also called a carry all.

A scraper is provided with a bowl, apron, ejector and a hydraulic system which are explained below (Fig. 32.6).

Figure 32.6 Scraper

(i) Bowl

It is a pan which is to hold the scraped material. It is hinged at the rear corners to the rear axle inside the wheels. It can tilt down for digging or ejecting. The size of a scraper is specified by the size of the bowl. At the bottom of the bowl a cutting edge is attached. In order to make a shallow cut, the cutting edge is lowered into material or dirt.

(ii) Apron

It is a wall located in front of the bowl to open or close in order to regulate the flow of the material in and out of the bowl. Further it is capable to open or to close during the carrying position also.

(iii) Ejector

It is also called as a tail gate which is the rear of the pan. It is provided with forward and backward movement inside the bowl. During loading it remains at its rear wall and moves in the forward direction to help in the ejection of the load during dumping.

(iv) Hydraulic System

All these operations are controlled by hydraulic cylinders.

The operation of a conventional scraper comprises of (i) digging or loading, (ii) transporting and (iii) unloading.

(i) Digging or Loading

Keeping the ejector at the rear and the apron raised (approximately to 40 cm) the operator moves to the cut. The bowl is then lowered to the required depth of cut, and the engine speed is increased and moved forward keeping the optimum depth of cut. After filling the bowl the apron is closed and the bowl is then raised.

(ii) Transporting

The bowl is transported in raised position so as to provide sufficient clearance from the ground. In order to prevent the loss of the collected material the apron is fully closed.

(iii) Unloading

The process of unloading by the scraper is called as dumping and spreading operation. In this operation the bowl is positioned so as to spread the material. So as to have an even spreading, a partial opening of the apron in the stage of unloading will be helpful. In the case of wet and sticky material, the apron should be raised and lowered separately. This helps the material behind it is get loosened and material drops out of the bowl by moving the ejector forward, the remaining material is pushed out at a uniform rate. After the dumping is complete, the tail gate is fully retarted, the apron is dropped and the bowl is raised to the transporting position. Using the cutting edge final finishing is done.

7. Loaders

Loader is a machine in which a bucket is attached to the arms and capable of being raised, lowered and dumped through mechanical or hydraulic controls. A very common type is one in which the loader is having the bucket in the front which is known as front-end loader.

Loaders are self-propelled and versatile equipment which are mounted either on crawler or wheel-type running gear. These loaders are fitted with front mounted general purpose bucket.

These loaders are operated through hydraulic rams with which they dig, scoop, lift, transport, carry, dump or load into hauling units, bins, hoppers, conveyors and stockpiles. With the additional parts added to the front and rear mounted attachments these can doze, scrap, grab, forklift, trench, grade, ditch, rip, clamp and winch.

Loaders are used for handling coal, sugar, sand, salt, stone, etc., to earth moving and digging works. Two types of loaders are crawler loaders and wheeled loader.

8. Trenchers

Trenchers are used to make trenches. Trenchers are used for excavating trenches or ditches of variable width and depth. The present day trenchers can be used to make trenches of width up to 12 m and depth up to 3 m can be excavated in one pass. Basically a trencher consists of :

1. Self-propelled tractor (Fig. 32.7) or carrier mounting fitted with crawler or wheel-type running gear (Fig. 32.8).
2. An excavating device consisting of several buckets on the periphery of the wheel and alternatively several cutters are provided for digging and discharging continuously.
3. A provision conveying the excavated material.

Figure 32.7 Trencher with tractor

Figure 32.8 Wheel-type trencher or ditcher

The common type of trench excavator is the wheel trenchers. It consists of a pair of circular rims whose outside diameters are connected by V-shaped buckets or cutters. The wheel is turned by a chain drive which connects to the power source. The wheel moves to the top position when discharging the material and at the bottom position while digging. The buckets or cutters on the wheel perform the work of excavator while travelling upward. When the wheel reaches the top position the excavated material drops. The dropped material is carried on conveyors and discharged alongside of the trench.

The selection of a trenching equipment depends on various factors, viz., depth and width of trench, type of soil, disposal of excavated earth, ground water position, and the nature of the job.

32.3.2 De-watering Equipment

Groundwater and seepage control needs a most significant consideration in the construction of buildings. Groundwater can be controlled depending on the geological conditions and characteristics of the soil. In such a situation, groundwater can be controlled by adopting one or more types of de-watering systems or drain appropriate to the size and depth of excavation.

Following are some of the de-watering methods:

1. Pumping Methods
   1. From open sumps and ditches
   2. From well-point systems
   3. From deep-well drainage
   4. From vacuum de-watering.
2. Electro-osmosis
3. Elimination or reduction of ground water by
   1. Cement grouting
   2. Displacement grouting
   3. Chemical consolidation
   4. Freezing

Pumping and electro-osmosis methods are discussed below. For other methods, reference may be made to Purushothama Raj (2013).

1. Pumping Methods

(i) Open Sumps and Ditches

The essential feature of the method is a sump below the ground level of the excavation at one or more corners or sides (Fig. 32.9).

Figure 32.9 De-watering through sumps

In fairly permeable soils the head is low and flow does not emerge through the excavation slopes. In such cases pumping out can be done by collecting the seepage in the sump and pumping out.

In case of excavation in clays the groundwater seeps from fissures and can readily pumped out from sumps. Salty soils generally pose problems. In rocks ground water discharges in the form of sprays or weeps from fissures. Therefore no instability problem in rocks except the water seeps through a weak or shattered rock. The discharges can be collected in an open sump and pumped out.

In order to provide the required number and capacities of pumps the quantity of water to be pumped should be known. This is calculated from Dupit’s formula.

(ii) Well-Point Systems

Filter wells or well-points are small well screens of sizes 50–80 mm in diameter and 0.3–1 m length. Well-points are made of brass or stainless steel screens and of closed ends or self-jetting types. When well-points are required to remain in the ground for a long period disposable plastic well-points are used. The plastic well-points are of nylon mesh screens surrounded by flexible plastic riser pipes. Water drawn through the screen enters the space between the gauze and the outside of the riser pipe through holes drilled in the bottom of the pipe and then reaches the surface. The well-points are installed by jetting them into the ground. A typical layout of a single stage well-point is shown in Fig. 32.10.

Figure 32.10 Single stage well-point installation

A well-point system, in general, comprises of well-points which are attached to riser pipes, which extend a short distance above the surface of the ground, where they are connected to a large pipe called header. The header pipe is connected to the suction of a centrifugal pump. A well-point system may include a few or several hundred well-points (generally 50–60 well points) all connected to one or more headers and pumps.

Well-point systems are very effective in solving subsurface water problem on construction sites. These systems are used to provide dry work areas below the water table for the following works:

1. Foundation work including buildings, bridges, dams and dry dock.
2. Trench work including buildings, bridges, dams and dry dock.
3. Tunnel work such as subway construction.

(iii) Deep-well Drainage

If the soil formation is such that it is pervious with depth, large diameter deep-wells are suitable for lowering the ground water table. An advantage of the system is that it can be installed outside the zone of construction operation and drainage is effected to the depth of excavation. Deep-wells may be combined with the well-point system on certain occasions for lowering the ground water table (Fig. 32.11).

Figure 32.11 Deep-well de-watering

Presence of artesian pressure in some field conditions may be relieved by deep-wells. The cost of installation of deep-well is high. Thus it is preferred in jobs which have a long construction period.

The deep wells are installed by sinking a cased borehole having a diameter of about 300 mm larger than the well casing. The diameter of the latter depends on the size of the submersible pumps. The inner well casing is inserted after the completion of the bore hole.

A perforated screen is provided over the lengths where de-watering of the soil is required. Graded filters of gravel are provided between the well casing and the outer borehole casing over the length to be de-watered. The outer casing is withdrawn in stages as the filter material is placed. The space above the screen is backfilled with any available material. The details of such a deep well are shown in Fig. 32.12. The spacing of deep well vary from 10 to 100 m depending on the field condition.

Figure 32.12 Details of deep-well installation

(iv) Vacuum De-watering System

Gravity methods explained so far are not very effective in fine-grained soils. Such soils can be stabilised by means of a vacuum well or well-point system. A vacuum de-watering system primarily consists of well or well-points with the screen and riser pipes.

A stabilising fine soil such as bentonite or impervious soil seal is provided at the remaining portion of the hole. By creating and maintaining a vacuum in the well screen and the sand filter, the flow towards the well is increased. A closer spacing is required (Fig. 32.13) for proper de-watering.

2. De-watering by Electro-osmosis

This is also a method applicable for fine-grained soils. This is not a general pumping method but collecting the water through some process to a well and pumping out.

If the vacuum well-point or well-point system is ineffective, application of an electrical gradient may be made. In a fine-grained soil stratum, when a direct electric current is passed through a saturated soil stratum, water moves towards the cathode. If the water is removed at the cathode, the soil decreases in volume resulting in increased shear strength. This process is called de-watering by electro-osmosis.

The general layout of the electrode is based on the purpose for which they are intended. Electrode arrangement for sheeted excavation is shown in Fig. 32.14.

Figure 32.14 Electrode arrangement for sheeted excavation

Sheet piles of any shape and old pipes of 25–50 mm diameter can be made as anodes. Since the anodes corrode considerably in the course of a few weeks of electro-osmotic treatment, they should be replaced as soon as the current drops to less than 30% of the initial consumption. For cathode perforated tubes are used and the cathode wells are connected to a pumping system.

Electro-osmotic method is used only when other methods fail as the cost of installation and maintenance are very high.

32.3.3 Compaction Equipment

Compaction is the process by which particles of materials are packed closely together by reducing air void content. In general the compaction is achieved by mechanical means.

1. Mechanical Forces

Mechanical forces may be applied by the following ways, viz., by rolling, by kneading, by vibration and by ramming.

(i) Rolling

In the rolling process heavy weights in the form of rollers are used to press the soil particles together. Smooth-wheeled rollers are the typical example which falls under this category.

(ii) Kneading

In the kneading process the soil while at kneading will be subjected to some pressure. Sheepsfoot roller is a typical example of this type of compaction.

(iii) Vibrations

In the vibrations process the soil particles are shaken together to form a compact mass. Vibrating rollers are typical example of compaction equipment which operate on this principle.

(iv) Ramming

In this process the soil particles are forced to move closer together by pounding action. Hand-tampers and mechanical tampers are the typical examples of compaction equipment which operate under this principle.

2. Rollers

(i) Smooth-Wheeled Rollers

These rollers are used with or without ballast and may be provided with three wheels or two wheels of equal width called tandom type. These rollers are generally used for most of the works. But these rollers are not effective in uniformly graded sand, gravel or silt and on cohesive soil with high moisture content due to poor traction.

These static rollers, also called as dead weight rollers, are diesel powered. These rollers rely on the weight only to compact the materials by passing over them. Units of 8–10 tonnes can impact a pressure of 20–40 kg per linear cm are generally in use. Rollers with weight up to 1 tonnes are used for light work.

(ii) Sheepsfoot Rollers

Sheepsfoot or Padfoot rollers are suitable for cohesive soils. These may be self-driven or tractor driven and are especially useful when the water content is on the higher side. The mass of the drum can be varied by adding ballast. For effective rolling, the lift thickness should be small and the contact pressure under the projection very high. These rollers are specially recommended for water-retaining earth works.

(iii) Pneumatic-tyred Rollers

In pneumatic-tyred rollers wheels are placed close together on two axles and placed such that the rear set of wheels overlap the lines of the front set to ensure complete coverage of the soil surface. In order to avoid the lateral displacement of soil, wide tyres with flat threads are provided. The compaction produced by these types is better than that of the smooth wheel rollers.

(iv) Tandom Compactors

Tandom compactors have two equal sized rollers and are centred in line-tandon. These rollers have smooth surface. Improvements have been made on these type of compactors as tandom vibratory compactors. Large size tandom vibratory compactors are generally preferred now-a-days as they can be used either as static compactor or as a vibratory compactor as per the requirement.

32.3.4 Pile Driving Equipment

As discussed earlier piles are generally classified as bored piles or driven piles depending on the method of installation. Only driven piles are to be installed by driving using an equipment. Bored piles are installed after making a hole in the ground and inserting a cage of reinforcement followed by concreting. In some cases reinforcement is not provided.

Driven piles are made out of some materials like wood, concrete, steel and sometimes with composite section of wood and steel, wood and concrete or steel and concrete. They are manufactured in special lengths.

Sheet piles, as discussed earlier, may be wood, concrete or steel. These piles are also driven.

1. Process of Pile Driving

The process of pile driving consists of lifting the pile into position, holding it and driving it to refusal or a desired depth. In this exercise, long piles need to be cut to the required length and the short piles need to be extended for safe and economical driving operations, proper judgement, experience and the combined skill of the crew. Driving of sheet piles greatly affect the seepage of the ground water and thereby pose special problem. As a guide to decide the depth of penetration pile driving formula is used.

2. Components of Equipment

Pile driving equipment comprises of the following components (Chellis, 1951):

1. Driving Rigs
2. Guiding leaders
3. Pile hammer with Accessories
4. Additional aids for pre-boring and jetting
5. Boiler for steam raising or air compressor

(i) Driving Rigs

Driving rig provides basic operations of lifting the pile, holding the pile in position, hammering it into the ground or of pulling it out of the ground and guiding the pile in the desired direction of movement. The rig supports the boom and winch mechanism, driving hammer, the guiding leaders, and a platform for mounting of auxiliary equipment such as a jet pump, drilling auger steam boiler or air compressor.

(ii) Guiding Leaders

The leaders guide the pile and the hammer during operation which extends to the entire height of the rig. In case of piles to be driven below the level of the rig into excavations, trencher or water, telescopic or extensible leaders can be used. The leader should enable the hammer to deliver blows axially to the pile.

During the process of driving, the driving rig should be strong and stable. In case a boom is used, adequate space should be available between the pile top and the point for the hammer to work.

There are two types of rigs, viz., skid-mounted and crane-mounted. The skin-mounted rigs are provided with rail wheels or with long steel rollers for movement. The crane mounted rigs are mounted with a crawler or a truck chassis with a swinging deck. In the case of floating pile driving, both the rigs can be mounted on a barge.

(iii) Driving Hammers

Pile driving hammers impart energy required to drive the pile into the soil. The routinely used pile hammers work by hitting the pile on its head. The vibratory and sonic type of hammers are the two new types.

Hammers are classified as follows:

1. Drop hammers
2. Single-acting hammers
3. Double-acting hammers
4. Differential-acting hammers
5. Diesel hammers
6. Hydraulic hammers
7. Vibratory hammers
8. Sonic hammers.

Out of these hammers drop hammer and single-acting hammer are generally used which are explained below. For details of other hammers reference may be made to Purushothama Raj (2015).

1. Drop Hammer: This is the simplest form of hammer which does not use any external sources of power. The only mechanism needed is to lift the hammer through a cable. Although the process is slower, it is more efficient as it uses only the gravity. The drop hammer is basically a block of suitably shaped cast-iron with its centre of gravity centred near the base in order to facilitate smoothness of fall.
2. Singe Acting Hammer: The functioning of single acting hammer differs from drop hammer only in the manner of lifting of the ram after each blow. A conventional single acting hammer employs a piston connected to a ram at its bottom end and moving inside a cylinder. The hammer may be of an open type or closed type. Steam power or compressed air is used in the single acting hammer wilthout any adjustment or alterations and the pressure remains unchanged. This pressure ranges from 5.6 to 10.5 kg per cm² and used depending on the size of the hammer and its weight. The operation of the single-acting hammer costs less compared to a double acting hammer but its speed is slower.

32.3.5 Movement and Hosting Equipment

Materials needed for construction are to be shifted from one place to another which may involve horizontal movement, vertical movement or other type. In such cases the following movement devices, are used:

1. Vertical Movement Devices
2. Horizontal Movement Devices
3. Combined Movement Devices

1. Vertical Movement Devices

The vertical movement devices are:

1. Block and Tackle
2. Winch
3. Hoist
4. Elevators

(i) Block and Tackle

This is a vertical distance movement device which is the oldest and the simplest device. It depends on mechanical power and gives only mechanical advantage. It is the most expensive device but waste of manpower (Fig. 32.15(a)).

(ii) Winch

By winding the rope of cable on the drum vertical movement is attained. Manpower or other power can be used to wind and a greater mechanical advantage than that of block and tackle. It is after used to load heavy equipment into ships, construction equipment, etc. (Fig. 32.15(b)).

Figure 32.15 Vertical movement devices

(iii) Hoist

Hoist is operated between fixed guide rails for vertical lifting of things. Hoists are operated by hand, compressed air or by electric power. Variety of hoists is available to suit a specific purpose. The simplest is the chain hoist. Hoists are similar to elevators except that operator does not go up but operated from one point to the other (Fig. 32.15(c)).

(iv) Elevators

This is similar to hoist but with a difference that the operator can ride with the load. Among the different types of elevators, the electrical one is often used. In places where electric power can not be used hydraulic elevators are used.

2. Horizontal Movement Devices

The horizontal movement devices are:

1. Hand Trucks
2. Narrow-gauge Rail Road
3. Tractors and Trailers
4. Skids

(i) Hand Trucks

Wheel barrows and hand trucks are the simplest transporting devices which are still in use. These devices involve large amount of manpower to move a small load. The advantages of these devices are small cost, flexibility, easy transportation from one place to another (Fig. 32.16(a)).

Figure 32.16 Horizontal movement devices

(ii) Narrow-gauge Rail Road

As it is very expensive, this is adopted only in very large projects. It is used to industries like blast furnace, copper refineries and steel-rolling operations.

(iii) Tractors and Trailers

These are the commonest modes of horizontal transportation. Trailers can be lift-loaded and can be towed to tractors. Different types of trailers can be picked up by tractors. This is one of the mostly used methods of handling materials from one place to another. This is less costly compared to narrow-gauge rail.

(iv) Skids

Skids are wheeled or plain trollies over which materials can be loaded and then picked up with lift trucks. Skids can be used to load and transfer from position to position without subsequent loading and unloading. The most common skids, which can be picked up in either direction, consist of a wooden platform and four steel legs (Fig. 32.16(b)).

3. Combined Devices

Combined devices comprise the actions of lifting, lowering or transportation. Combined devices are as follows:

1. Chute
2. Lift truck
3. Forklift truck
4. Cranes
5. Conveyers

(i) Chute

Chutes are the devices which are adopted for horizontal and vertical movements. The chutes may be straight or of spiral form.

(ii) Lift Truck

These are similar to roller skids but provide provision for a large platform to lift and place the materials and move them horizontally through power to another location (Fig. 32.17).

Figure 32.17 Lift truck

(iii) Fork Lift Truck

It is provided with fork which receives the load at ground level and elevates it hydraulically to the desired height. There is no need for manual lifting. Self-loading or unloading can be carried out by providing a fork at the front end of the truck. Fork lift trucks are used in construction industry (Fig. 32.18).

(iv) Cranes

Cranes are electrically or diesel operated equipment used to lift and move heavy materials and machinery. Cranes have wide application in construction projects, industries and in shipping yard. Cranes have three motions, viz., hoisting, derricking and slewing.

Cranes are classified as given below:

1. Derrick cranes
2. Tower cranes
3. Pillar cranes
4. Overhead or gantry cranes
5. Self-propelling boom cranes
6. Crane trucks

1. Derrick Cranes: They consist of a mast, a boom and a bull wheel on which it rotates about a vertical axis and with supporting members (also referred to as guys).

   Most of the derrick cranes are supported by a number of guys. The boom can revolve through 360° and passes below these guys. A bull wheel is attached to the mast and rotates it. These cranes are operated by diesel engine or by an electric motor.

   Guy derricks are available in lifting capacities of 5–200 tonnes and used mainly for erecting heavy structures, Fig. 32.19 (Ataev, 1985).

   

   Figure 32.19 200-tonne guy derrick

   These cranes are used in construction projects like industries or multi-storeyed buildings, loading and unloading of cargoes at ports, in ship building, etc.

2. Tower Cranes: These are used mainly in erection of apartment and high-rise industrial buildings.

   Main advantages of tower rail-mounted cranes are their stability and a large reach of hook. Main construction is served by tower cranes of capabilities varying from 8 to 10 tonnes lifting capacities (Fig. 32.20).

   

   Figure 32.20 Tower crane for high-rise house construction

3. Pillar Cranes: Pillar cranes may be a stationary or mobile type. It is used for light load (up to 20 tonnes). In order to lift up or lower down the load a job or inclined boom is fixed to the lift and the lifting is done with the help of rope and pulley arrangement. All the movements to the crane required for a particular situation are provided by gearing and electric power drive (Fig. 32.21).
   

   Figure 32.21 Pillar crane

4. Overhead Cranes: Overhead cranes are fixed in one location and can not be moved to place to place. These are provided in big workshops, boundaries, powerhouses, chemical plants, research stations, etc. These are operated by electric power. These cranes have the advantage of providing large service area. All the operations can be done by an operator seated in the cabin (Fig. 32.22).
   

   Figure 32.22 Overhead crane

5. Self-propelling Boom Cranes: These are available in caterpillar-tracked wheeler, truck and tractor mounted varieties with diesel or electric drivers. The lifting capacity ranges from 3–160 tonnes. Caterpillar-mounted boom cranes are widely used.

   In order to increase the reach and the height of lift of a crane hook, a standard boom may be provided. Now-a-days cranes with telescopic booms are being increasingly employed (Fig. 32.23).

   

   Figure 32.23 Crane with telescopic boom

6. Crane Truck: Crane trucks of small size function as that of a lift truck (Fig. 32.24). These are used where the material to be moved is of heavy weight which can not be moved using skids. This can be moved easily to a desired place and handling is much easier. The cranes are rotary type so that the load can be lifted from any position.
   

   Figure 32.24 Crane truck

7. Conveyors: These are the material transportation devices used when the parts of flow of material is fixed. Because of this desired fixity, lifting and lowering of materials are done automatically. Conveyors require no stopping or starting but the operation is continuous. The transportation is effected by friction between materials being transported and the belt or roller.

32.3.6 Hauling Equipment

Hauling of materials, machines and/or personnel around and between building sites can be very time consuming, expensive and unproductive. Movement of materials within a short distance can be done by using any one of the movement-equipment explained in the previous section.

Transportation between sites of men, machines and materials is usually carried out by using lorries, trucks, rubber-tire tractors with wagons or crawler tractors with wagons. Such transport equipments are discussed below.

1. Trucks

These are essential equipment on any construction project. They are available in various sizes and types. The capacity varies from 0.4–20 m³. The average speed of the truck varies from 10–20 kmph and top speed from 30–100 kmph. They are classified into three categories based on the capacity as (i) light (1/2–1 tonne), medium (1.5–3 tonne) and heavy (3.5–10 tonne) trucks. Trucks are also specified by their total number of wheels and the number of wheel drives. For normal load condition of road a 4 × 2 truck having four wheels, two of them only being driving wheels is quite popular. Under poor road condition and for heavy loads a 6 × 6 or 4 × 4 truck would be required.

2. Dump Trucks

These trucks are fitted with automatic unloading devices. The loading is done either by loading shovels or loaders. These trucks may have capacities as high as 50 tonnes. These trucks can be rear dump trucks, bottom dump trucks and side dump trucks.

3. Dumpers

Trucks with special pneumatic wheels and capable of moving at high speeds having short chassis and strong dumping bodies are known as dumpers. The material can be dumped in front or at the back. The loading, transporting and dumping can be done in quick succession. They are available in capacities up to 4.5 m³.

4. Trailers

Trailers are carriages hauled by power units such as tractors or trucks. Trailers are of two types, viz., full trailer or wagons and semi-trailers. Full trailers are provided with power unit with swivelling axle and drawbar. The semi-trailers are supported in the front by the power unit and at the rear on their own wheels. These trailers can also be operated in a smaller space. Both these trailers are provided with hydraulically-operated breaking systems.

1. Procurement cost includes (i) the cost price of the equipment, (ii) interest on money invested on the purchase, (iii) taxes and (iv) the insurance cost.
2. Operation cost of an equipment is based on the following factors: (i) cost of investment, (ii) depreciation cost, (iii) cost of major repair, (iv) cost of fuel and lubricants, (v) cost of labour, (vi) servicing and field repairs and (vii) overheads.
3. Major equipment needed for a building project are (i) earthwork equipment, (ii) de-watering equipment, (iii) compaction equipment, (iv) pile-driving equipment and (v) movement equipment.
4. Earthwork equipment comprises of excavators, shovels, bulldozers, tractors, motor graders, scrapers and loaders.
5. Shovels are classified as (i) dipper shovel, (ii) drag shovel or hoe (iii) dragline and (iv) clamshell.
6. Bulldozers are classified as angle dozer, tilt dozer and tree dozer.
7. Scrapers are provided with bowl, apron, ejector and hydraulic system.
8. Operations of a conventional scraper are digging or loading, transporting and unloading.
9. Loaders are of two types, viz., crawler loader and wheeled loader.
10. De-watering methods are: (i) pumping methods, (ii) electro-osmosis and (iii) elimination of groundwater by cement grouting, chemical consolidation, displacement grouting and freezing.
11. Pumping methods comprise of open sumps and ditches, well-point systems, deep-well drainage and vacuum de-watering.
12. Compaction of material is obtained by mechanical means such as rolling, kneading vibrations and ramming.
13. Rollers are classified as smooth-wheeled rollers, sheepsfoot rollers, pneumatic-tired rollers and tandom compactors.
14. Pile driving equipment comprises of the following components: (i) driving rigs, (ii) guiding loaders, (iii) pile hammer with accessories, (iv) additional aids for pre-boring and jetting and (b) boiler for steam raising or air compressor.
15. Moving equipment are (i) vertical movement devices, (ii) horizontal movement devices and (iii) combined movement devices.
16. Vertical movement devices are (i) block and tackle, (ii) winch, (iii) hoist and (iv) elevators.
17. Horizontal movement devices are (i) hand trucks, (ii) narrow-gauge rail load, (iii) tractors and trailers and (iv) skids.
18. Combined devices are (i) chute, (ii) lift truck, (iii) fork-lift truck, (iv) cranes and (v) conveyers.
19. Hauling equipment are trucks, dump trucks, dumpers and Trailors.

1. Explain the factors to be considered in the selection of construction equipment.
2. How do you select equipment for earthwork?
3. What are the different types of excavators? Explain any one in detail.
4. Distinguish between dipper shovel and drag shovel.
5. Explain a clamshell along with its applications.
6. How a dragline works? In what situation can they be used?
7. Suggest the method of dewatering the foundation trenches under the following condition.

   (i) Excavation is to be carried out at a location where the area is water-logged.

   (ii) If the permeability of a site very much less than 10^–4 cm per second.

   (iii) Relatively homogeneous soft day.

8. Briefly explain the process of electro-osmosis for dewatering the foundation trenches.
9. What are the different types of tractors? Explain.
10. Explain the different parts of a scraper.
11. Discuss the operations of a scraper.
12. What is a front-end loader?
13. Explain the well-point system of de-watering.
14. What is deep-well drainage?
15. Explain vacuum de-watering system.
16. Explain the methods of de-watering foundation excavation.
17. What are the different types of rollers? Explain.
18. Distinguish between drop hammer and single-acting hammer.
19. Name the different components of a pile-driving equipment.
20. Explain briefly different horizontal movement devices.
21. What are different types of handling devices? Explain.
22. What are the different types of cranes? Explain the types in detail.
23. Explain different types of hauling equipment.