Chapter 3

Chapter 3

Excavating and

Lifting

Part 2

3-4 DRAGLINES

Operation and Employment

Production Estimating

Job Management

Operation and Employment

The

dragline

is a very versatile machine that has the longest reach for digging and dumping of any member of the crane-shovel family.

It can dig from above machine level to significant depths in soft to medium-hard material. The components of a dragline are shown in Figure 3-10.

FIGURE 3-10

: Components of a dragline.

3-4 DRAGLINES

Bucket teeth and weight produce digging action as the drag cable pulls the bucket across the ground surface.

Digging is also controlled by the position at which the drag chain is attached to the bucket (Figure 3-11).

The higher the point of attachment, the greater the angle at which the bucket enters the soil.

FIGURE 3-11:

Dragline bucket.

3-4 DRAGLINES

During hoisting and swinging, material is retained in the bucket by tension on the dump cable.

When tension on the drag cable is released, tension is removed from the dump cable, allowing the bucket to dump.

3-4 DRAGLINES

Buckets are available in a wide range of sizes and weights, solid and perforated.

Also available are archless buckets which eliminate the front cross-member connecting the bucket sides to provide easier flow of material into and out of the bucket.

3-4 DRAGLINES

While the dragline is a very versatile excavator, it does not have the positive digging action or lateral control of the shovel.

Hence the bucket may bounce or move sideways during hard digging.

3-4 DRAGLINES

Also, more spillage must be expected in loading operations than would occur with a shovel.

While a skilled dragline operator can overcome many of these limitations, the size of haul units used for dragline loading should be greater than that of those used with a similar-size shovel.

3-4 DRAGLINES

The maximum bucket size to be used on a dragline depends on machine power, boom length, and material weight.

Therefore, use the dragline capacity chart provided by the manufacturer instead of the machine's lifting capacity chart to determine maximum allowable bucket size.

Production Estimating

The Association of Equipment Manufacturers [formerly the Construction Industry Manufacturers Association (CIMA)], through its PCSA Bureau, has made studies of cable-operated dragline operations and has developed production tables that are widely used by the construction industry.

Tables 3-7 to 3-9 are based on PCSA data. Note, however, that these tables are applicable only to diesel-powered, cable-operated draglines.

3-4 DRAGLINES

To estimate dragline production using the tables,

determine the ideal output of the dragline for the machine size and material (Table 3-7),

then adjust this figure by multiplying it by a swing-depth factor (Table 3-9) and a job efficiency factor, as shown in Equation 3-3.

Expected production = Ideal output × Swing-depth factor × Efficiency (3-3)

Notice the conditions applicable to Table 3-7 given in the footnote..

3-4 DRAGLINES

To use Table 3-9 it is first necessary to determine the optimum depth of cut for the machine and material involved from Table 3-8. Next, divide the actual depth of cut by the optimum depth and express the result as a percentage.

3-4 DRAGLINES

The appropriate swing-depth factor is then obtained from Table 3-9, interpolating as necessary.

The method of calculating expected hourly production is illustrated in Example 3-4.

EXAMPLE 3-4

Determine the expected dragline production in loose cubic yards (LCM) per hour based on the following information.

Dragline size = 2 cu yd (1.53 m

3

)

Swing angle = 120

o

Average depth of cut = 7.9 ft (2.4 m)

Material = common earth

Job efficiency = 50 min/h

Soil swell = 25%

EXAMPLE 3-4

Solution

 Ideal output =230 BCY/h (176 BCM/h)

(Table 3-7)

Optimum depth of cut = 9.9 ft (3.0 m)

(Table 3-8)

Actual depth/optimum depth = 7.9/9.9

× 100

= 80%

[= 2.4/3.0 × 100

= 80%]

EXAMPLE 3-4

Swing-depth factor=0.90 (Table 3-9)

Efficiency factor =50/60

= 0.833

Volume change factor = 1 + 0.25 = 1.25

Estimated production = 230 × 0.90 × 0.833

×1.25 = 216 LCY/h

[= 176 × 0.90 × 0.833

×1.25 = 165 LCM/h]

Job Management

Trial operations may be necessary to select the boom length, boom angle, bucket size and weight, and the attachment position of the drag chain that yield maximum production.

As in shovel operation, maximum production is obtained with a minimum swing angle.

Job Management

In general, the lightest bucket capable of satisfactory digging should be used, since this increases the allowable bucket size and reduces cycle time.

It has been found that the most efficient digging area is located within 15° forward and back of a vertical line through the boom point, as illustrated in Figure 3-12.

Job Management

Special bucket hitches are available which shorten the drag distance necessary to obtain a full bucket load.

Deep cuts should be excavated in layers whose thickness is as close to the optimum depth of cut as possible.

FIGURE 3-12

: Most efficient digging area for a dragline

3-5 CLAMSHELLS

Operation and Employment

Production Estimating

Job Management

3-5 CLAMSHELLS

Operation and Employment

When the crane-shovel is equipped with a crane boom and clamshell bucket, it becomes an excavator known as a

clamshell.

The clamshell is capable of excavating to great depths but lacks the positive digging action and precise lateral control of the shovel and backhoe.

3-5 CLAMSHELLS

Clamshells are commonly used for :

excavating vertical shafts and footings,

unloading bulk materials from rail cars and ships, and

moving bulk material from stockpiles to bins, hoppers, or haul units.

3-5 CLAMSHELLS

The components of a cable-operated clamshell are identified in Figure 3-14. Clamshell attachments are also available for the hydraulic excavator.

A clamshell bucket is illustrated in Figure 3-14.

Notice that the bucket halves are forced together by the action of the closing line against the sheaves.

FIGURE 3-13

: Components of a Clamshell

FIGURE 3-14:

Clamshell bucket

3-5 CLAMSHELLS

When the closing line is released, the counterweights cause the bucket halves to open as the bucket is held by the holding line.

Bucket penetration depends on bucket weight assisted by the bucket teeth.

3-5 CLAMSHELLS

Therefore, buckets are available in light, medium, and heavy weights, with and without teeth.

Heavy buckets are suitable for digging medium soils.

Medium buckets are used for general-purpose work, including the excavation of loose soils.

Light buckets are used for handling bulk materials such as sand and gravel.

3-5 CLAMSHELLS

The orange peel bucket illustrated in Figure 3-15 is principally utilized for underwater excavation and for rock placement.

Because of its circular shape, it is also well suited to excavating piers and shafts.

It operates on the same principle as does the clamshell.

FIGURE 3-15

: Orange peel bucket.

(Courtesy of ESCO Corporation)

3-5 CLAMSHELLS

Production Estimating

No standard production tables are available for the clamshell.

Thus production estimation should be based on the use of Equation 2-1.

The procedure is illustrated in Example 3-5.

EXAMPLE 3-5

Estimate the production in loose cubic yards per hour for a medium-weight clamshell excavating loose earth. Heaped bucket capacity is 1 cu yd (0.75 m3). The soil is common earth with a bucket fill factor of 0.95. Estimated cycle time is 40 s. Job efficiency is estimated at 50 min/h.

EXAMPLE 3-5

Solution

Production = 3600/40 × 1 × 0.95 × 60/50

= 71 LCY/h

B = 3600/40 × 0.75 × 0.95 × 60/50 = 53 LCM/h

Job Management

The maximum allowable load (bucket weight plus soil weight) on a clamshell should be obtained from the manufacturer's clamshell loading chart for continuous operation.

Job Management

If a clamshell loading chart is not available, limit the load to 80% of the safe lifting capacity given by the crane capacity chart for rubber- tired equipment or 90% for crawler-mounted equipment.

Since the machine load includes the weight of the bucket as well as its load, use of the lightest bucket capable of digging the material will enable a larger bucket to be used and will usually increase production.

Job Management

Tests may be necessary to determine the size of bucket that yields maximum production in a particular situation.

Cycle time is reduced by organizing the job so that the dumping radius 3-6 Trenching and Trenchless Technology 65 is the same as the digging radius.

Job Management

Keep the machine level to avoid swinging uphill or downhill.

Nonlevel swinging is hard on the machine and usually increases cycle time.

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

Trenching Machines and Plows

Trenchless Technology

Repair and Rehabilitation of Pipelines

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

The use of backhoes and other excavators for digging trenches was discussed earlier in this chapter.

In addition, there is a growing demand for methods of installing utility systems below the ground with minimum open excavation.

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

Some methods available for achieving this objective include specialized trenching machines and plows as well as trenchless technology (also called trenchless excavation).

Safety considerations in trenching operations are discussed in Section 10-6.

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

Trenching Machines and Plows

Some of the types of trenching machines available include chain trenchers, ladder trenchers, and bucket wheel trenchers.

Figure 3-14 shows a large chain trencher capable of digging 14 to 36 in. (356-914 mm) wide vertical sided trenches to a depth of 10 ft (3.1 m).

Ladder trenchers are similar to chain trenchers but are larger.

FIGURE 3-16

: Chain trencher.

(Courtesy of Vermeer Manufacturing Co.)

FIGURE 3-16

: Chain trencher.

(©Vermeer Manufacturing Company, All Rights Reserved.)

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

They are capable of digging trenches up to 10 ft (3.1 m) wide and 25 ft (7.6 m) deep.

Bucket wheel trenchers use a revolving bucket wheel to cut a trench up to 5 ft (1.5 m) wide and 9 ft (2.7 m) deep.

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

Plows can be used to cut a narrow trench and simultaneously insert a small diameter cable or pipeline in most soils.

Vibratory plows such as those shown in Figure 3-17 deliver a more powerful cutting action than static plows and can be used to insert utility lines in hard soil or soft rock.

FIGURE 3-17

: Hydrostatic vibratory plow.

(Courtesy of Vermeer Manufacturing Company, All Rights Reserved)

Trenchless Technology

While a number of different techniques are used in trenchless technology, the principal categories include pipe jacking, horizontal earth boring, and microtunneling.

Trenchless Technology

The process of

pipe jacking

(Figure 3-18) involves forcing pipe horizontally through the soil.

Working from a vertical shaft, a section of pipe is carefully aligned and advanced through the soil by hydraulic jacks braced against the shaft sides.

As the pipe advances, spoil is removed through the inside of the pipe.

FIGURE 3-18: Installing a utility line by pipe jacking

Trenchless Technology

After the pipe section has advanced far enough, the hydraulic rams are retracted and another section of pipe is placed into position for installation.

The process often requires workers to enter the pipe during the pipe jacking operation.

Trenchless Technology

In

horizontal earth boring

a horizontal hole is created mechanically or hydraulically with the pipe to be installed serving as the casing for the hole.

Some of the many installation methods used include auger boring, rod pushing (thrust boring), rotational compaction boring, impact piercing, horizontal directional drilling, and fluid boring.

Trenchless Technology

A track-mounted thrust boring machine with percussive hammer action is shown in Figure 3-19.

Many of these techniques utilize lasers and television cameras for hole alignment and boring control.

A number of types of detectors are available to locate the drill head and ensure that the desired alignment and depth are being maintained.

FIGURE 3-19: Grundodrill & Thrust boring machine with percussive action.(Courtesy of TT Technologies, Inc.)

Trenchless Technology

The use of a pneumatic piercing tool to create a borehole for a utility line is illustrated in Figure 3-20.

FIGURE 3-20:

Installing a utility line by horizontal earth boring.

Trenchless Technology

After the bore has been completed, several methods are available to place pipe into the borehole.

In one method, pipe is pulled through the bore using the tool's air hose or a steel cable pulled by the air hose.

Another method uses the piercing tool to push the pipe through the borehole.

A third method uses a pipe pulling adapter attached to the piercing tool to advance the pipe at the same time as the piercing tool advances the bore.

Trenchless Technology

Microtunneling

or

utility tunneling

is similar to the conventional tunneling described in Section 8-1 except for the tunnel size and use.

Since the tunnels are used for utility systems rather than for vehicle passage, they are normally smaller than road or rail tunnels.

Trenchless Technology

They differ from other trenchless methods in their use of a conventional tunnel liner instead of using the pipe itself as a liner.

Small moles (see Section 8-1) are frequently used in creating such tunnels.

Repair and Rehabilitation of Pipelines

The repair and rehabilitation of existing pipelines without excavation is another form of trenchless technology.

Repair and Rehabilitation of Pipelines

While a number of methods exist, most involve the relining of the existing pipeline or the bursting of the existing pipe while inserting a new pipe.

The relining of a pipeline is accomplished by pulling a new plastic pipe into the existing pipe or by inserting a liner into the existing pipe.

Repair and Rehabilitation of Pipelines

When a new pipe is used to reline the pipe, the resulting pipe must be slightly smaller than the original pipe.

Another relining technique involves pulling a folded liner into the existing pipe, expanding the liner, treating the liner with an epoxy, and curing it in place.

Repair and Rehabilitation of Pipelines

Pipe bursting

(Figure 3-21) uses a high-powered hydraulic or pneumatic piercing tool equipped with a special bursting head to shatter the existing pipe and enlarge the opening.

A new, often larger, pipe is then pulled into the opening by the piercing head.

FIGURE 3-21: Schematic of pneumatic pipe bursting method.(Courtesy of Earth Tool Company LLC)

FIGURE 3-21

: Schematic of pipe bursting.

(Courtesy of Vermeer Manufacturing Co.)