CONSTRUCTION AND MAINTANANCE OF ROAD PAVEMENT

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Soil classification

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PurposeArrange various types of soils into groups according to their engineering or various other characteristicSoil possessing similar characteristics can be placed in the same group.

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Soil Classification Systems

Unified Soil Classification System (USCS)

AASHTO Soil Classification System

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AASHTO Soil Classification System

The AASHTO system uses both grain-size distribution and Atterberg limits data to assign a group classification and a group index to the soil. The group classification ranges from A-1 (best soils) to A-8 (worst soils). Group index values near 0 indicate good soils, while values of 20 or more indicate very poor soils. However, a soil that may be "good" for use as a highway subgrade might be "very poor" for other purposes, and vice ver. Group Index (GI)Used to describe performance of soil when used for pavements.Not used to place a soil in a particular group.

It means rating the value of soil as a subgrade material within its

own group.

Unified soil classification system• The USCS is based on those characteristics

of the soil that indicate how it will behave as an engineering construction material.

• USCS is based on identifying soils according to their textural and plasticity qualities and on their grouping with respect to behavior.

• Each group is designated a symbol consisting of two capital letters.

• The first letter is based on main soil type.• The second letter is based on gradation

and plasticity .5

Group Symbol Typical NameGW Well-graded gravels.GP Poorly-graded gravels.GM Silt gravels.GC Clayey gravelsSW Well-graded sands.SP Poorly-graded sands.SM Silt sands.SC Clayey sands.

CL Inorganic clays of low plasticity.ML Inorganic silts with slight plasticity.OL Organic soil of low plasticity.CH Inorganic clays of high plasticity.MH Inorganic silts with high plasticity.OH Organic soil of high plasticity.

EARTHWORK EQUIPMENTS

Advantages of Earthwork equipments:• Increase the rate of output through work

progress with the best effective and efficient methods.

• Reduce the overall construction costs especially for large contracts.

• Carry out activities which cannot be done manually or to do them more economically and much faster.

• Eliminate the heavy manual work by human thus eliminates various other hazards and health issues.

• Maintain the planned rate of production where there is a shortage of skilled or unskilled labors.

• Maintain the high quality standards often required by present-day design and specifications (technical standards).

CLASSIFICATION OF CONSTRUCTION EQUIPMENTS

Depending on the application, construction machines are classified into various categories which we are discussing here.

• Earth-moving equipment• Earth-compacting equipment• Hauling equipment• Hoisting equipment• Conveying equipment• Aggregate production equipment• Equipments used in Concrete

Construction.• Pile-driving equipment

DEFINATION OF COMPACTION

The densification of soil by the application of mechanical energy is known as compaction

2 > 1

1=W1V12=W1/V2

REQUIREMENT OF SOIL COMPACTION

To increase

soil strength

To improve

the stability of

soilTo reduce soil

permeability

To reduce erosion

damage

FACTOR AFFECTING COMPATION

WATER CONTENT

COMPACTING EFFORT

TYPE OF SOIL

METHOD OF COMPACTION

WATER CONTENT

COMPACTIVE EFFORT

TYPE OF SOILThe maximum dry density and the optimum water content for different soils are different. In general, coarse grained soils can be compacted to higher dry density than fine-grained soils.Cohesive soils have high air voids. These soils attain a relatively lower maximum dry density as compared with the cohesion less soils.METHOD OF COMPACTIONThe dry density achieved depends also on the method of compaction. For the same amount of compactive effort, the dry density will depend upon whether the method of compaction utilizes kneading action, dynamic action or static action. The compaction curve obtained is different for different method though equal compactive effort is applied.

SOIL COMPACTION IN THE FIELD

Smooth steel drum roller

Pneumatic tyred rollers

Sheep foot rollers

Grid rollers

Vibrating plates

Tampers and rammers

Consolidation:• Consolidation is a process by which soils decrease

in volume. According to Karl Terzaghi consolidation is any process which involves decrease in water content of a saturated soil without replacement of water by air. In general it is the process in which reduction in volume takes place by expulsion of water under long term static loads.

(a)

W W W(b) (c)

Figure : Terzaghi Spring analogy.

Types of Consolidation: Immediate Consolidation:

Caused by elastic deformation of dry soil or moist and saturated soil without change in moisture content.

Primary Consolidation: Caused as a result of volume change in saturated cohesive soils due to exclusion of water occupied the void space.

Secondary Consolidation: Occurs in saturated cohesive soils as a result of the plastic adjustment of soil fabrics.

Initial compression

Primary Consolidation

Secondary Consolidation

Time (log scale)

Defo

rmat

ion

Pranamesh Chakraborty

Consolidation Test•The main purpose of consolidation tests is to obtain soil data which is used in predicting the rate and amount of settlement of structures founded on clay.

The four most important soil properties determined by a consolidation test are: • The pre-consolidation stress, ’, This is the maximum stress that the soil has “felt” in the past. • The compression index, Cc , which indicates the compressibility of a normally-consolidated soil. • The recompression index, Cr , which indicates the compressibility of an over-consolidated soil. • The coefficient of consolidation, cv , which indicates the rate of compression under a load increment.

Pranamesh Chakraborty

LABORATORY TESTS TO DETERMINE SOIL COMPACTION AND

CONSOLIDATIONStandard Proctor test(Light compaction Test)

Modified Proctor Test(heavy compaction Test)

Oedometer Test(Consolidation)

Consolidation vs. Compaction

21Thank You