Chapter 6

Question 1

What is earth work?

Answer 1

Changing the configuration of the ground surface by removing soil and or rocks by either cut or excavation or adding soil or rocks by back filling or embankment.

Question 2

Example of projects requiring earth work.

Answer 2

Highways
Rail roads
Building construction

Question 3

What are properly graded tract less prone to

Answer 3

Land slides
Excessive settlements
Flooding

Question 4

What is the fundamental objective of earthwork construction?

Answer 4

Is to change the ground surface from its initial configuration, typically described by a topography map, to some final configuration, as described on a new topographic map known as grading plan. Also to create slope stability on hilly terrain.

Question 5

Fills

Answer 5

Must have sufficient shear strength to support own weight and external weight
Must be sufficiently still to avoid excessive settlement- eve when wet
In areas that prone to freezing, fills must be made with non- frost susceptible soil.

Question 6

Historic Methods and Equipment in construction

Answer 6

Slaves, animals and carts were used.

Question 7

Hydraulic Fills

Answer 7

Process of mixing soil and water together and then transporting it to its designated location and allowing it to settle. After it settles, the remaining water is directed away. This is no longer used

Question 8

Modern earth moving equipments

Answer 8

Tractor- moves its self plus other equipment, first designed for military and agriculture. Designed for rough terrains

Question 9

Modern earth moving equipments

Answer 9

Wheel-mounted tractors: operates at greater speeds, not well suited for rough terrains, equipments can be attached like bulldozer. Can be used for cutting, moving and spreading.

Question 10

Conventional earthwork

Answer 10

Is described at the excavation, transport, placement, and compaction of soft rocks and or soils in areas where equipment can move freely

Question 11

Clearing and grubbing

Clearing(Above Ground)
Grubbing( Below Ground)

Answer 11

Step one in earthwork projects: removal or trash, debris and vegetation from site. Most of these materials would have detrimental effect on fills, and must be hauled offsite.

Question 12

Clearing and Grubbing

Answer 12

Inorganic debris such as chunks of concrete, bricks, or asphalt pavement does not need to be hauled away. They can be reused during filling.

Question 13

Excavation

Answer 13

Occurs in areas where the proposed ground surface is lower than the existing ground surface. The excavated material is used for site fills, or site fills material is obtained from borrow “sites”.

Question 14

Transport and placement

Answer 14

Bulldozers and Wheel loaders can be used for long hauls but are very no economical.

Question 15

Transport and Placement

Answer 15

Scrapers are very different at moderate- length hauls, and earth work projects falls into this category

Question 16

Transport and placements

Answer 16

Dump Trucks: can be used instead of scrapers especially when the soil is being excavated by scrapers. Ability to travel on public highways.

Question 17

Transport and placement

Answer 17

Wagons: used for hauling soils over long distances on highways

Question 18

Transportation and Placement

Answer 18

Soil transportation equipment depends on the haul distance. When ever it arrives on a site that requires filling, it must be laid out into “lifts” typically 200 mm thick. Each “lift” must be moisture conditioned and compacted before next lift is placed.

Question 19

Moisture conditioning

Answer 19

Soils must be at the proper moisture content before compacting.
They wont compact well if too dry or too wet.
If moisture is needed, soil is sprayed with water by a water truck.
After being sprayed, it is then mixed by a bulldozer for uniformity.

Question 20

Moisture Conditioning

Answer 20

Mixing good wet soils with dry soils is very difficult, especially when mixed wit clays because it results in alternating clumps instead of uniformity

Method used for this is to spread wet soil over large areas and allow it too dry naturally.

Question 21

Compaction

Answer 21

Use of equipment o compress soil into smaller volume, thus increasing dry unit weight

Soils and water are virtually incompressible, so during compaction the volume of air is reduced while the volume of the soil and water remains unchanged.

Question 22

Compaction

Answer 22

In the stages of development, animals were used for compaction.
Earth dam near Santa Fe New Mexico used 115 goats.
Rollers were initially pulled by horses which was replaced by tractors in 20 th century

Question 23

Compaction

Answer 23

Basically anything the moves across a compaction site does some form of compression, like pickup trucks

We cannot depend on accidental forms of compaction because some pick up trucks amongst other compaction equipment were designed to have low pressures between tires and soils which allowed them to move across soft ground more easily

Question 24

Compaction (Pressure)

Answer 24

The compact pressure between the ground and the equipment is most important factor resulting in compaction of the ground underlining

Question 25

Compact (Impact)

Answer 25

Some equipment imparts a series of blows to the soils, such as by dropping weight. This adds a dynamic component to the compactive efforts

Question 26

Compaction (Vibration)

Answer 26

Vibratory compaction equipment utilizes eccentric weights or some other device to induce strong vibrations into the soil, which can enhance its compaction

Question 27

Compaction (Manipulation)

Answer 27

Compaction equipment that imparts some shearing forces to the soil can also contribute to better compaction. This action is called “Kneading” or “manipulation”. Excessive manipulation such as overly wel fill, can be detrimental. When such fills are simply being moved around with no compaction, we have a condition called pumping.

Question 28

Compaction Machines

Answer 28

Speed foot Rollers: consists of one or more rotating drums with numerous feet that concentrate its weight onto a small area. They compact soils by pressure manipulation

Question 29

Tamping foot rollers

Answer 29

Similar to sheep foot rollers, except they have larger feet with a correspondingly smaller contact pressure

Question 30

Pneumatic rollers

Answer 30

Are heavy units resting on several tires. The contact pressure is typically about 600 kPa. Since each tire is able to move independently, this device is good at finding small soft spots that rigid compaction equipment such as sheepfoot rollers can miss

Question 31

Vibratory rollers

Answer 31

Similar to sheep foot rollers with vibration mechanism

Question 32

Smooth steel wheel rollers

Answer 32

Leaves smooth compacted soil surfaces.

Question 33

Fine Grading

Answer 33

After last lift has been placed and right elevation achieved - this completes rough grading. Fine grading which consists of careful trimming and filling to produce the desired configuration. Requires different equipment

Question 34

Utility trenches

Answer 34

Are need for trenches when installing utility pipes, sewer pipes and electrical lines. Holes are back filled, but no fully compacted due to sensitivity. Allowed to settle naturally. “Jetting” process of mixing sand with water, and injecting it into trenches around pipes, while allowing gravity and lubrication to settle it in trenches.

Question 35

Small Backfills

Answer 35

Used for earth work in small confined areas

Question 36

Soil Compaction Concepts

Answer 36

Increased shear strength: reduces potential for slope stability Decreased compressibility: reduces potential for excessive settlement Decreased Hydraulic conductivity: Inhibits the flow of water through soil Decreased void ratio: reduces amount of water that can be held in soil, maintain soil strength Increased erosion resistance: helps maintain ground surface in serviceable condition