unit 3 ( the technique of planning and pre-construction road work ( part 2 ) )

THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 /

UNIT3

THE TECHNIQUE OF PLANNING AND PRE-

CONSTRUCTION ROAD WORK

( Part 2 )

OBJECTIVES

General Objective

To understand the earth work operation and its problems occurred.

Specific Objectives

At the end of the unit you should be able to :-

describe the earth work operation. state the highway machinery state the types of slope. state the problem and its solutions. describe the method of slope protection.

UNIT 3UNIT 3


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PLANNING TECHNIQUE AND PRE-

CONSTRUCTION

ROAD WORK – ( Part 2 )

3.0 INTRODUCTION

The sub-grade soil is prepared by bringing it to the desired grade and

camber and by compacting adequately. The sub-grade may be either in

embankment or in excavation, depending on the topography and the finalized

vertical alignment of the road to be constructed.

3.1 EARTH WORH OPERATION

The earth work quantities are estimated based on longitudinal and transverse

section along the alignment of the road. In order to reduce the cost of

construction, it is necessary to plan the movement of materials from cuts to the

nearest fills. It is necessary to decide the limits of economical haul and lift. It is

advantageous to plot a mass haul diagram to compute the haulage details. The

swelling and shrinkage factor may also be considered in the excavation and

compaction of earth.

INPUTINPUT


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3.1.1 Excavation

Excavation is the process of cutting or loosening and removing earth

including rock from its original position, transporting and dumping it as a fill or

spoil bank. The excavation or cutting may be needed in soil, soft rock or even in

hard rock, before preparing the sub-grade. The selection of excavation

equipment and the cost analysis is made based on the stiffness of the materials

to be excavated.

Earth excavation work may be divided as excavation or cutting, grading

and compaction. The depth of the excavation is decided, among other factors, on

requirement of vertical profile of the road. The slope to be provided is governed

by the type of soil including stratification, if any, and the depth of the cutting. The

stability computations may help in arriving at maximum permissible slope for the

complex problems. However highway cuts much flatter slopes are preferred from

other considerations including aesthetics construction of side drains also require

excavations along road side.

a. Excavation equipment

The excavation equipment commonly used in highway projects includes

bull dozers, scrapers, power shovels, draglines, clamshells and hoes. However,

in small projects excavation is carried out manually using hand tools.

The machines that used are:-

i. Bull dozer and scraper

Bull dozer and scraper may be used for shallow excavation work

and for hauling the earth for relatively short distances. Bull dozer is


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considered to be versatile machine for many construction projects as it

may be used for clearing site. It can used for opening up pilot roads,

moving earth for short haul distances of about 100m and also in several

other jobs. Scraper is considered as one of the useful earth-moving

equipment as it is self operating - it can dig, haul and discharge the

material in uniformly thick layers. However scrapers are not capable of

digging very stiff material.

Figure 3.1: Bull dozer

ii. Power shovel

Power shovel used primarily to excavate earth of all classes except

rock and to load it into wagons. Power shovels may be mounted on

crawler tracks and so they can move at low speeds. Figure 3.2 shows the

operation and basic parts of a power shovel, these including the mounting,

cab, boom, dipper stick, dipper and hoist line. The power shovel can

effectively operate the excavate earth from a lower level where it stands

and when the depth of the face to be excavated is not too shallow.


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iii. Dragline

Dragline is used to excavate soft earth and to deposit in nearly

banks or to load into wagons. Dragline may also be mounted on crawler. It

can operate on natural ground while excavating from a pit with the bucket,

thus it is not necessary for the dragline to go into the pit in order to

excavate. The basic parts and operation of a dragline are shown in figure

3.3. The bucket is thrown out from the dragline on the top of the earth to

be excavated and then pulled back towards the base of the machine.

Figure 3.2: Power Shovel

Figure 3.3: Dragline


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iv. Clamshell

Clamshell consists of a bucket of two halves or shell which is

hinged together at top. The shells may be attached to the shovel-crane

units or at the boom of a drag line. The open clam-shell bucket is thrown

on the top of the loose material to be dug and as the bucket is lift, the two

halves close en trapping the material into the bucket. Figure 3.4 shows the

clamshell bucket. This equipment is useful for excavation of soft to

medium materials and loose material at or below existing ground surface.

v. Hoe

Hoe is an excavating equipment of the power-shovel family. Hoe is

meant to excavate below the natural surface where the machine is

stationed and is capable of having precise control of depth of excavation

at close range work (see figure 3.5). Hoe can exert high tooth pressures

and hence can excavate stiff material which normally can not be

excavated by dragline.

Figure 3.4: Clamshell


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The excavation equipment is selected depending on the natural of the

material, the distance, to be hauled and the method of disposal. At times the

selection may be made based on the availability also.

3.1.2 Embankment

When it is required to raise line of a highway above the existing ground

level it becomes necessary to construct embankments. The grade line may

raised due to any of the following reasons:

i. to keep the sub grade above the high ground water table.

ii. to prevent damage to pavement due to surface water and capillary

water.

iii. to maintain the design standards of the highway with respect to the

vertical alignment.

The design elements in highway embankments are:

i. height

ii. fill material

Figure 3.5 Hoe


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iii. settlements.

iv. stability of foundation, and

v. stability of slopes

a. Height

The height of the embankments depends on the desired grade line of the

highway and the soil profile or topography. Also the height of the fill is some

times governed by stability of foundation, particularly when the foundation soil is

week.

b. Fill material

Granular soil is generally preferred as highway embankment material. Silts

and clays are considered less desirable. Organic soils, particularly peat are

unsuitable. The best of the soils available locally is often selected with a view to

keep the lead and lift as lowers possible. At times light-weight fill material like

cinder may be used to reduce the weight when foundation soil is weak.

c. Settlement

The embankment may settle after the completion of construction either

due to consolidation and settlement of the foundation or due to settlement of the

fill or due to both. If the embankments foundation consists of compressible soil

with high moisture content, the consolidation can occur due to increase in the

load. The settlement of the fill is generally due to inadequate compaction during

construction, and hence by proper compaction this type of settlement may be

almost eliminated. Whatever be the type of settlement, it is desired that the

settlement is almost complete before the construction of saturated. Foundation

clay, vertical sand drains are sometimes constructed. These are vertical columns


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of sand installed in the compressible foundation like marshy soils in order to

decrease drainage path and thus accelerate the rate of consolidation. The

vertical sand columns may be of 30 to 60 cm diameter and 2.5 to 6 meter

spacing, arranged in hexagonal pattern. A horizontal sand blanket, 40 to 60 cm

thick is placed at the top of the drains extending across the entire width of

embankment at its bottom. This helps the water to flow out with ease.

d. Stability Of Foundation

When the embankment foundation consists of weak soil just beneath are

at a certain depth below in the form of a weak stratum, it is essential to consider

the stability of the foundation against a failure. This is more essential in the case

of high embankment. The foundation stability is evaluated and the factor of

safety is estimated by any of the following approaches.

i. Assuming a certain failure surface such as a circular arc or any other

composite shape and analyzing it with Swedish circular arc analysis

or method of wedges. As the case may be.

ii. Estimating the average shear stress and strength at the foundation

layers by approximate methods and estimating the factor of safety.

iii. Using theoretical analysis base on elastic theory.

The factor of safety in the case of compressible soil foundation is likely to be

minimum just after the completion of the embankment. Later due to

consolidation of foundation and consequent gain in strength there will be an

increase in the foundation factor of safety. Thus it is evident that in such

compressible foundation soils, the vertical sand drains would be useful also to

increase the rate of gain in strength. By proper design of vertical sand drains, it

is possible to limit the decrease in foundation factor of safety due to the

construction, within the allowable value.


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e. Stability Of Slopes

The embankment slopes should be stable enough to eliminate the

possibility of a failure under adverse moisture and other conditions. Hence the

stability of the slope should be checked or the slope should be designed

providing minimum factor of safety of 1.5. Often much flatter slopes are

preferred in highway embankment due to aesthetic and other reasons.

3.1.3 Construction of embankment

The embankment may be constructed either by rolling in relatively thin

layers or by hydraulic fills. The former is called rolled-earth method and is

preferred in highway embankments. Each layer is compacted by rolling to a

satisfactory degree or to a desired density before the next layer is placed.

Compaction is carried out at optimum moisture content so as to take advantages

of maximum dry density using a specified compacting effort and equipment. The

thickness of the layers may vary between 10 and 30 cm depending on various

factors such as soils type, equipment, specifications etc.

The practice of dumping the earth without compacting properly and

allowing the fill to get consolidated under weather during few subsequent

seasons should be avoided as the settlement will continue for a very long period.

If pavement is constructed before the settlement of the fill is almost complete, the

pavement is likely to become uneven and also fail later-on. Compaction of soil is

discussed separately in topic Soil Compaction.


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Let’s test your understanding before we continue to the next input…. GOOD LUCK….

3.1 Earth work operation can be divided into two categories. Name the work by filling in the chart below.

3.2 Match the excavation equipment listed below with its description. Then unite the words in the boxes provided.

HOE CLAMSHELL

POWER SHOVEL BULLDOZER/SCRAPPER

DRAGLINE

EARTH WORK OPERATION

ACTIVITY 3A


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“I’m used for shallow excavation work and for hauling the earth for relatively short distances.”

“I’m used primarily to excavate earth of all classes except rock and to load it into wagons.”

“I’m used to excavate soft earth and to deposit it nearby banks or into wagons.”

“I’m useful for excavation of soft to medium materials and loose materials at or below existing ground surface.”

“I’m useful to excavate below natural surface.”


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3.3 Complete the chart of design elements in highway embankments below

HEIGHT

DESIGN ELEMENTS IN HIGHWAY

EMBANKMENTS STABILITY OF SLOPE


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3.1

EARTH WORK OPERATION

EXCAVATION EMBANKMENTS

FEEDBACK ON

ACTIVITY 3A


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3.2

3.3


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HOW DO YOU FIND THE ACTIVITIES? FUN AREN’T THEY? LET’S PROCEED TO THE NEXT

INPUT…..

HEIGHT

DESIGN ELEMENTS IN HIGHWAY

EMBANKMENTS STABILITY OF SLOPE

FILL MATERIAL

SETTLEMENTS

STABILITY OF FOUNDATION


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3.2 SIDE SLOPE OPERATION

There are two types of side slope in Highway Engineering. Alignments of

highways through hilly and rolling topography result in many cut and fill slopes of

exposed soil. Highway construction until recently has been simply a matter of

location and design. Very little consideration has been given to the possibility of

erosion or sloughing on cut and fill.

3.2.1 CUT SLOPES

There have several types of strata in the soil and rock. When the soil and

the rock are being cut and excavated, the stability of the content will decrease,

meanwhile, the renovating have to be done to get the slope cutting ready and

safe. The safety works are important to prevent erosion and sloughing. Slope

excavation takes place when the original soil level higher then the level of new

road formation to be built.

Figure 3.1 : Cut slope for equivalent soil strata.

i. Shallow cutting ii. Deep cutting ( by storey )


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Figure 3.2: Cut slope for variable soil strata.

Type of soil Cutting depth sloping

Solid rock 1:0.3 – 1:0.0

Rock 1:0.5 – 1:1.2

Sand 1:0.5 – 1:1.0

Sandy soil 0 – 5 1:0.8 - 1:1.2

Compact earth 5-10 1:1.0 – 1:1.2

Sand, loose 5-10 1:1.2 – 1:1.5

Clay soil 0-10 1:0.8 – 1:1.2

Clay-stone 5-10 1:1.2 - 1:1.5

Table 3.1: Table for safety slope cutting

Sand Granular Rock


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3.2.1.1 Problems in cut slope

There are several problems that will be stated in cut slope.

a. Landslide

Land slide is a problem that always happens in the work of slope cutting. It

is because the cut of soil influence the stability of the soil. There are a few ways

to overcome the problem.

i. Prepare the slope with suitable slanting degrees.

ii. Turfing the slope areas to maintain the soil stability

iii. Hydro ‘seeding’ is use to plant the plant on the alkali soil.

iv. By using Geofabric or geotextile to avoid the diffusion of ground

water.

Rock slope is dangerous because the area of cutting does not have stable

binding ability. If the failure of stone happen, it will cause the accident and

dangerous for us. There are some methods which had being used in our country

to overcome the problems.

i. Build the fencing along the slope areas.

ii. Use a net.

iii. Gabion block.

b. Water Infiltration


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Water infiltration in soil also influences the soil stability. Storey and soil

drainage system are important. Sub-soil drains are always used to control the

flow of infiltration.

3.2.2 EMBANKMENT SLOPE

Slope embankment takes place when the original soil is under the level of

new road formation to be built. Embankment slope is built by equivalent or

different types of materials depend on soil strata.

Figure 3.3: Embankment by equivalent materials

Figure 3.4: Embankment by different materials

i. Normally Cut Slope

1:1.5

1:1.8

1:2.0

ii. Step Slope

1.5 – 2.0m

Compact earth

Sand

Rock1:0.5

1:1.0

1:2.0


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Tables 3.2: of safety sloping degree in soil banking

Types of material Height ( m ) Slope: Hor. To Ver.

( well graded sand )0 – 6

6 – 15

1:1.5 – 1:1.8

1:1.8 – 1:2.0

( poorly graded sand ) 0 – 10 1:1.8 – 1:2.0

Rock0 – 10

10 – 20

1:1.5 – 1:2.0

1:1.8 – 1:2.0

Clay 0 - 6 1:1.8 – 1:2.0

3.2.2.1 Problems in slope banking

There are several problems that are related to the embankment slope.

a. Landslide

There are some ways to overcome the problem.

i. Turfing - Planting the plants for slope protection

ii. Prepare the slope with suitable slanting degrees.

iii. Use Geofabric and geotextiles to avoid the diffusion of

ground water.

b. Erosion

Soil erosion happens because of infiltration and the flow of water

run-off. To prevent the erosion, a few methods can be used:

i. Prepare the drainage system to let the water flow easily.

ii. Grow plants to cover the slope surface.


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Let’s test your understanding before we continue to the next input…. GOOD LUCK….

3.4 There are two types of side slope in Highway Engineering. Name the types by filling in place below.

3.5 Match the two type slope as the answer from question 3.4 with its description. Write the words in the boxes provided.

ACTIVITY 3B

Its take place when the

original soil is under the

level of new road formation

to be built.

Its takes place when the

original soil level higher

then the level of new road

formation to be built.

Two types of slopes?

……………………

……………………


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3.6 Name the problems of the fffembankment slope by filling the chart

below.

Embankment Slope


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3.4

3.5

FEEDBACK TO

ACTIVITY 3B

The answers are…..

Cut SlopeEmbankment Slope

Its take place when the

original soil is under the

level of new road formation

to be built.

Embankment Slope

Its takes place when the

original soil level higher

then the level of new road

formation to be built.

Cut Slope


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3.6

HOW DO YOU FIND THE ACTIVITIES? FUN AREN’T THEY? LET’S PROCEED TO THE NEXT

INPUT…..

Embankment Slope

Landslide Erosion


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The excavation equipment commonly used in highway projects. Describe

about the machine as listed below.

a. Bulldozer and scraper.

b. Power shovel.

c. Hoe.

Describe all the problems in slopes and the solution to overcome the

problem.

There are several factors that contribute to the increase of design. Explain

briefly two factors that contribute to the increment.

Question 3 - 1

Question 3 - 2Question 3 - 2

Question 3 - 3


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a. Bull dozer and scraper

Bull dozer and scraper may be used for shallow excavation work

and for hauling the earth for relatively short distances. Bull dozer is

considered to be versatile machine for many construction projects as it

may be used for clearing site. It can used for opening up pilot roads,

moving earth for short haul distances of about 100m and also in several

other jobs. Scraper is considered as one of the useful earth-moving

equipment as it is self operating - it can dig, haul and discharge the

material in uniformly thick layers. However scrapers are not capable of

digging very stiff material.

b. Power shovel

Answer 3.1


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Power shovel used primarily to excavate earth of all classes except

rock and to load it into wagons. Power shovels may be mounted on

crawler tracks and so they can move at low speeds. Figure 1 shows the

operation and basic parts of a power shovel, these including the mounting,

cab, boom, dipper stick, dipper and hoist line. The power shovel can

effectively operate the excavate earth from a lower level where it stands

and when the depth of the face to be excavated is not too shallow.

c. Hoe

Hoe is an excavating equipment of the power-shovel family. Hoe is

meant to excavate below the natural surface where the machine is

stationed and is capable of having precise control of depth of excavation

at close range work (see figure 2). Hoe can exert high tooth pressures and

hence can excavate stiff material which normally can not be excavated by

dragline.

Figure 1: Power Shovel

Figure 2: Hoe


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1. Problems in cut slope

There are several problems that will be stated in cut slope.

a. Landslide

Land slide is a problem that always happens in the work of slope cutting. It

is because the cut of soil influence the stability of the soil. There are a few ways

to overcome the problem.

i. Prepare the slope with suitable slanting degrees.

ii. Turfing the slope areas to maintain the soil stability

iii. Hydro ‘seeding’ is use to plant the plant on the alkali soil.

iv. By using Geofabric or geotextile to avoid the diffusion of ground

water.

Rock slope is dangerous because the area of cutting does not have stable

binding ability. If the failure of stone happen, it will cause the accident and

dangerous for us. There are some methods which had being used in our country

to overcome the problems.

i. Build the fencing along the slope areas.

ii. Use a net.

Answer 3.2


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iii. Gabion block.

v. Water Infiltration

Water infiltration in soil also influences the soil stability. Storey and soil

drainage system are important. Sub-soil drains are always used to control the

flow of infiltration.

2 Problems in slope banking

There are several problems that will be stated in embankment slope.

c. Landslide

There are some ways to overcome the problem.

iv. Turfing - Planting the plants for slope protection

v. Prepare the slope with suitable slanting degrees.

vi. Use Geofabric and geotextiles to avoid the diffusion of

ground water.

d. Erosion

Soil erosion happens because of infiltration and the flow of water

run-off. To prevent the erosion, a few methods can be used:

iii. Prepare the drainage system to let the water flow easily.

iv. Grow plants to cover the slope surface.


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a. Height

The height of the embankments depends on the desired grade line of the

highway and the soil profile or topography. Also the height of the fill is some

times governed by stability of foundation, particularly when the foundation soil is

week.

b. Fill material

Granular soil is generally preferred as highway embankment material. Silts

and clays are considered less desirable. Organic soils, particularly peat are

unsuitable. The best the soils available locally is often selected with a view to

keep the lead and lift as lowers possible. At times light-weight fill material like

cinder may be used to reduce the weight when foundation soil is weak.

Answer 3.3


UNIT3

unit 3 ( the technique of planning and pre-construction road work ( part 2 ) )

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