mujaddad pavement assignment

7/30/2019 Mujaddad Pavement Assignment

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PAVEMENT EVALUATION AND REHABILITATION

TECHNIQUES

ASSIGNMENT # 1

SUBMITTED TO:-

Dr. NAVEED AHMAD

SUBMITTED BY:-

MUJADDAD AFZAL

2K12-FT-MSc-TRANS-04

DEPARTMENT OF TRANSPORTATIONENGINEERING

UNIVERSITY OF ENGINEERING & TECHNOLOGY

TAXILA


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California Bearing Ratio (CBR)

Mr (resilient modulus) of sub-grade is

required to design flexible pavement. It

can be calculated directly from triaxial

test, but conventionally we calculate Mrfrom an empirical equation by using CBR

value.

The basic CBR test

It consists of causing a plunger of

standard area to penetrate a soil sample,

(this can be in the laboratory or on site).

The force (load) required to cause the

penetration is plotted against measured penetration, the readings noted at regular time intervals.

This information is plotted on a standard graph, and the plot of the test data will establish the

CBR result of the soil tested.

The test is fully covered in:-

BS 1377: Soils for civil engineering purposes: Part 4, Compaction related tests.

THE REASON FOR THE CBR TEST

It sounds complicated, but the basis behind it is quite simple.

We are determining the resistance of the sub grade, (i.e. the layer of naturally occurring material

upon which the road is built), to deformation under the load from vehicle wheels.

Even more simply put, ''How strong is the ground upon which we are going to build the road''.

The CBR test is a way of putting a figure on this inherent strength, the test is done in a standard

manner so we are able to compare the strengths of different sub grade materials, and we are able

to use these figures as a means of designing the road pavement required for a particular strength

of sub grade.

The stronger the sub grade (the higher the CBR reading) the less thick it is necessary to design

and construct the road pavement, this gives a considerable cost saving.

Conversely if CBR testing indicates the sub grade is weak (a low CBR reading) we must

construct a suitable thicker road pavement to spread the wheel load over a greater area of the

weak sub grade in order that the weak sub grade material is not deformed, causing the road

pavement to fail.TABLE OF CBR's FOR COMMONLY FOUND SUB-GRADE CONDITIONS


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CBR VALUE SUBGRADE STRENGTH COMMENTS

3% and less Poor " Capping is required

3% - 5% NormalWidely encountered CBR range capping

considered according to road category

5% - 15% Good"Capping" normally unnecessary except on

very heavily trafficked roads.

CBR VALUES IN RELATION TO SITE CONDITIONS AT THE TIME OF

CONSTRUCTION

CBR values "on site" may not bear any relationship to the CBR values employed in the road

design, due to softening from wet weather and trafficking from site vehicles.

This is of course true for any design method you employ if the soil conditions at the time of

construction are different to the soil conditions upon which you based your design.

It could be some time before the properties of the soil revert back to their original engineering

condition and by this time failure could have occurred.

"Capping layers" have been introduced to help solve the problem of sub-grades wetting up and

losing strength during construction by protecting the sub grade from the worst of the damage

caused by site traffic.

The opposite is also true, if CBR values are taken on site after the sub-grade has been exposed

and dry weather has caused the moisture content of the soil to decrease, increasing soil stiffness,

the CBR value will be higher than natural moisture content, this is an incorrect value for design

purposes and if accepted will cause a serious under design of the road pavement.

Natural soil moisture content, after drainage, is the correct moisture content for determining

CBR values for highway design purposes because in the course of time natural soil moisture

conditions will be re-established.

Good drainage is an essential part of road construction to allow the optimum strength/CBR to be

obtained, and maintained, from the soil foundation, whether it be in-situ soil or imported fill.

It of course follows that the drainage must be kept operating efficiently during the life of the road

prevent the strength/CBR decreasing through weakening of the foundation by a rising water

table.


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If water is able to enter the road pavement, for whatever reason, the design of the road pavement

should be such that the water has a way out; this is usually through a sub-base layer that is

drained to an installed drainage system or road side ditch.

If water cannot find a path out the road pavement failure of the highway will be premature and

swift, as the wheel loads will no longer be correctly, and directly, transferred downwards through

the road pavement to the underlying sub grade.

TOP-Down Fatigue Cracking

In thick pavements, the cracks most likely initiate from the top in areas of high localized tensile

stresses resulting from tire-pavement interaction and asphaltbinder aging (top-down cracking).

Possible Causes

Inadequate structural support, which can be caused by a myriad of things. A few of the more

common ones are listed here:

Decrease in pavement load supporting characteristics

Loss of base, sub base or sub grade support (e.g., poor drainage or spring thaw resulting in a less

stiff base).

Stripping on the bottom of the HMA layer (the stripped portion contributes little to pavement

strength so the effective HMA thickness decreases)

Increase in loading (e.g., more or heavier loads than anticipated in design)

Inadequate structural design

Poorconstruction (e.g., inadequate compaction)
http://www.pavementinteractive.org/category/materials/asphalt/http://www.pavementinteractive.org/article/fatigue-cracking/top-down-crackinghttp://www.pavementinteractive.org/article/fatigue-cracking/strippinghttp://www.pavementinteractive.org/category/design/structural-design/http://www.pavementinteractive.org/category/construction/http://www.pavementinteractive.org/category/construction/compaction-construction/http://www.pavementinteractive.org/category/construction/compaction-construction/http://www.pavementinteractive.org/category/construction/http://www.pavementinteractive.org/category/design/structural-design/http://www.pavementinteractive.org/article/fatigue-cracking/strippinghttp://www.pavementinteractive.org/article/fatigue-cracking/top-down-crackinghttp://www.pavementinteractive.org/category/materials/asphalt/


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Rutting

Surface depression in the wheel path. Pavement uplift (shearing) may occur along the sides of

the rut. Ruts are particularly evident after a rain when they are filled with water. There are two

basic types of rutting: mix rutting and sub grade rutting. Mix rutting occurs when the sub grade

does not rut yet the pavement surface exhibits wheel path depressions as a result of

compaction/mix design problems. Sub grade rutting occurs when the sub grade exhibits wheel

path depressions due to loading. In this case, the pavement settles into the sub grade ruts causing

surface depressions in the wheel path.

Possible Causes

Permanent deformation in any of a pavements layers or sub grade usually caused by

consolidation or lateral movement of the materials due to traffic loading. Specific causes of

rutting can be:

Insufficient compaction of HMA layers during construction. If it is not compacted enough

initially, HMA pavement may continue to densify under traffic loads.

Sub grade rutting (e.g., as a result of inadequate pavement structure)

Impropermix design or manufacture (e.g., excessively high asphalt content, excessive mineral

filler, insufficient amount of angularaggregateparticles)

Ruts caused by studded tire wearpresent the same problem as the ruts described here, but they

are actually a result of mechanical dislodging due to wear and not pavement deformation.

Roughness

Pavement roughness is generally defined as an expression of irregularities in the pavement

surface that adversely affect the ride quality of a vehicle (and thus the user). Roughness is an

important pavement characteristic because it affects not only ride quality but also vehicle delay

costs, fuel consumption and maintenance costs. The World Bank found road roughness to be a

primary factor in the analyses and trade-offs involving road quality vs. user cost. Roughness is

also referred to as smoothness although both terms refer to the same pavement qualities.

Methods to find roughness index

Dipstick Profiler Profilographs Response Type Road Roughness Meters (RTRRMs)
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Correlations Between PSR and IRI

Various correlations have been developed between PSR and IRI. Two are presented here. One

was reported in 1986 by Paterson:

Another correlation was reported in a 1992 Illinois funded study performed byAl-Omari and Darter (1992)

Fig : Present serviceability rating form

PSR(PSI & TSI) used in ASSHTO Empirical design equation to design pavement thickness, in

both rigid and flexible pavement.

FWD (Falling Weight Deflectometer)

Deflection

Pavement surface deflection measurements are

the primary means of evaluating a flexible

pavement structure and rigid pavement load

transfer. Although other measurements can be

made that reflect (to some degree) a

pavements structural condition, surface

deflection is an important pavement evaluation

method because the magnitude and shape of pavement deflection is a function of traffic (type

and volume), pavement structural section, temperature affecting the pavement structure and

moisture affecting the pavement structure. Deflection measurements can be used in back

calculation methods to determine pavement structural layer stiffness and the sub grade resilient

modulus. Thus, many characteristics of a flexible pavement can be determined by measuring its

deflection in response to load. Furthermore, pavement deflection measurements are non-

destructive.
http://www.pavementinteractive.org/category/pavement-management/pavement-evaluation/http://www.pavementinteractive.org/article/deflection/backcalculationhttp://www.pavementinteractive.org/article/deflection/backcalculationhttp://www.pavementinteractive.org/article/deflection/resilient-modulushttp://www.pavementinteractive.org/article/deflection/resilient-modulushttp://www.pavementinteractive.org/article/deflection/resilient-modulushttp://www.pavementinteractive.org/wp-content/uploads/2010/01/Fwd1.jpghttp://www.pavementinteractive.org/wp-content/uploads/2007/08/PSR.gifhttp://www.pavementinteractive.org/wp-content/uploads/2010/01/Fwd1.jpghttp://www.pavementinteractive.org/wp-content/uploads/2007/08/PSR.gifhttp://www.pavementinteractive.org/wp-content/uploads/2010/01/Fwd1.jpghttp://www.pavementinteractive.org/wp-content/uploads/2007/08/PSR.gifhttp://www.pavementinteractive.org/wp-content/uploads/2010/01/Fwd1.jpghttp://www.pavementinteractive.org/wp-content/uploads/2007/08/PSR.gifhttp://www.pavementinteractive.org/article/deflection/resilient-modulushttp://www.pavementinteractive.org/article/deflection/resilient-modulushttp://www.pavementinteractive.org/article/deflection/backcalculationhttp://www.pavementinteractive.org/article/deflection/backcalculationhttp://www.pavementinteractive.org/category/pavement-management/pavement-evaluation/


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Impact (Impulse) Load Response

All impact load devices deliver a transient impulse load to the pavement surface. The subsequent

pavement response (deflection basin) is measured by a series of sensors. The most common type

of equipment is the falling weight deflectometer (FWD) (Figures 9 through 26). The FWD can

either be mounted in a vehicle or on a trailer and is equipped with a weight and several velocitytransducer sensors. To perform a test, the vehicle is stopped and the loading plate (weight) is

positioned over the desired location. The sensors are then lowered to the pavement surface and

the weight is dropped. Multiple tests can be performed on the same location using different

weight drop heights (ASTM, 2000[2]

). The advantage of an impact load response measuring

device over a steady state deflection measuring device is that it is quicker, the impact load can be

easily varied and it more accurately simulates the transient loading of traffic. Results from FWD

tests are often communicated using the FWD AREA Parameter.

Figure 9. FWD impulse loading mechanism Figure 10. Dynatest 8000 FWD

(Foreground) and sensors (background).

Figure 11. KUAB FWD.Figure 12: JILS FWD.
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The standard impact load response test method is:

ASTM D 4694: Standard Test Method for Deflections with a Falling Weight Type Impulse Load

Device

Correlations between Deflection Measuring Equipment

In general, correlations between deflection devices should be used with caution. Too often, a

correlation is developed for a specific set of conditions that may not be present for those using

the correlation. It appears that the best approach is to obtain pavement parameters (such as layer

moduli) from the specific device being used. However, that said, a few of many such correlations

that have been developed follow.

Benkelman Beam to FWD

Based on unpublished data collected by the Washington State DOT Materials Laboratory in

1982-1983[3]
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