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 3
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
INPUT
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
considered to be versatile machine for many construction projects as it
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
iii. settlements.
Figure 3.5 Hoe
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
of sand installed in the compressible foundation like marshy soils in order to
decrease drainage path and thus accelerate the rate of consolidation. The
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
“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.”
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
3.3 Complete the chart of design elements in highway embankments below
HEIGHT
DESIGN ELEMENTS IN HIGHWAY
EMBANKMENTS STABILITY OF SLOPE
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
3.1
3.2
“I’m used for shallow excavation work and for hauling the earth for relatively short distances.”
BULLDOZER/SCRAPPER
“I’m used primarily to excavate earth of all classes except rock and to load it into wagons.”
POWER SHOVEL
“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.”
DRAGLINE
CLAM SHELL HOE
EARTH WORK OPERATION
EXCAVATION EMBANKMENTS
FEEDBACK ON
ACTIVITY 3A
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
3.3
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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 slopingSolid rock 1:0.3 – 1:0.0Rock 1:0.5 – 1:1.2Sand 1:0.5 – 1:1.0Sandy soil 0 – 5 1:0.8 - 1:1.2Compact earth 5-10 1:1.0 – 1:1.2Sand, loose 5-10 1:1.2 – 1:1.5Clay soil 0-10 1:0.8 – 1:1.2Clay-stone 5-10 1:1.2 - 1:1.5
Table 3.1: Table for safety slope cutting
3.2.1.1 Problems in cut slope
Sand Granular Rock
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
Tables 3.2: of safety sloping degree in soil banking
Types of material Height ( m ) Slope: Hor. To Ver.( well graded sand ) 0 – 6 1:1.5 – 1:1.8
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
6 – 15 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 – 1:2.0Clay 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.
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.
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.
ACTIVITY 3B
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
3.6 Name the problems of the fffembankment slope by filling the chart
below.
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?
……………………
……………………
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
Embankment Slope
FEEDBACK TO
ACTIVITY 3B
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
3.4
3.5
3.6
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
Embankment Slope
Landslide Erosion
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
HOW DO YOU FIND THE ACTIVITIES? FUN AREN’T THEY? LET’S PROCEED TO THE NEXT INPUT…..
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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
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.
Answer 3.1
Figure 1: Power Shovel
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
1. Problems in cut slope
Answer 3.2
Figure 2: Hoe
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
v. Water Infiltration
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
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.
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.
a. Height
Answer 3.3
THE TECHNIQE OF PLANNING AND PRE-CONSTRUCTION ROAD WORKHighway Engineering C3010 / UNIT3
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.
Recommended