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Code Document No.
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ENGINEERING DESIGN OF PROJECT FRONTIER TANUAN FACTORY
2nd Street FPIP Barangay Ulango,
Tanuan City, Batangas
Rigid Pavement Design
Client:
NESTLE Philippines Inc.
No. 31 Plaza Drive Rockwell Center Makati City
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Code Document No.
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1.0 PAVEMENT DESIGN
There are three main steps which the designer must consider when designing
a new road pavement. These are:
a) preparing estimate of the amount of traffic and its approximate axle load
distribution –that will use the road over its expected design life,
b) determining the strength of the subgrade soils upon which the road will be
built, and
c) evaluating a) and b) to select the most economical combination of
pavementmaterials and layer thicknesses that will provide satisfactory service
over the design life of the pavement considering normal routine maintenance.
Recommended surface types in accordance with DPWH Design guide, Chart
4.10 with the following as general guidelines:
DBST surface for ESALs up to 2,500,000
DBST or Asphaltic Concrete for ESALs 1,000,000 to 2,500,000
Asphaltic Concrete or PCCP for ESALs 2,500,000 to
5,000,000
PCCP for ESAL's over 5,000,000
Portland Cement Concrete Pavement (PCCP) surface option was considered
for the Car Park area and access road at 210-Warehouse of Egron 2.
1.1 TRAFFIC LOADING
For the Car park area the loads imposed by private cars and other light
vehicles do not contribute significantly to the structural damage caused to road
pavements by traffic. As a result, it is widely accepted that for the purpose of
structural design, cars, motorcycle or bicycle can be ignored and only the axle loading
of the light rigid vehicle the heaviest unit that will use the road during its design life
need to be considered. For this Study the light rigid vehicle then will be defined as
any private or public service vehicle of 3500 kg or less(3.85 tons). includes bicycle,
motorcycles, cars and light van.
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For the access road of 210-warehouse of Egron 1 will consider HS20-44 load
for design purposes. the HS indicates truck with three axels with average weight of
32000 kg(36 tons). These are fictituos trucks used only for design and does not
resemble any real truck on the road. The HS20-44 truck is defined below as one 8 kip
axle load and two 32 kip axle loads spaced as shown.
HS20-44
In order to estimate the number of vehicles on a pavement segment during its
designlife, the geotechnical report on item 5.3.8 recommends the following average
daily traffic (ADT) of approximately 200 HS 20-44 (truck trailer types) for the
loading bay warehouse and about 400 light rigid vehicles for the car park.
Another factor which must be considered when determining pavement
deterioration over time is the number of repetitions of loaded axles. For design
purposes then, it is necessary to consider not only the total number of commercial
vehicles that will use the road, but also the wheel loads (or, for convenience, the axle
loads) of these vehicles. Current practice is to assign as a "standard" the 8,200 kg
(18,000 lb) axle load and to design on the basis an equivalent number of standard
axles. Different pavement design criteria utilize varying terminology such as
equivalent daily load applications (EDLA), equivalent standard axle load (ESAL), or
design traffic number (DTN). Use of these three terms relative to total "standard"
axles yields basically the same number. This design will utilize the term ESAL when
considering "standard" axle.
Computed Esal/Lane Value, 20 Yr Design Life
Esal Type
Car Park 13,432 Light Rigid Vehicle
Warehouse loading bay 1,355,610 HS20-44
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1.2 Rigid Pavement Design
A rigid pavement, Portland Cement Concrete Pavement, (PCCP), is normally
designed based on a structure consisting of two layers, the pavement slab and the
subbase course. When the roadbed soils are of subbase quality, ie. when the soil
support value is high, the subbase course is often omitted. The design procedure
determines the thickness of portland cement concrete pavement and any base/subbase
thickness. The pavement slab thickness is determined by the use of 1993
AASHTO Guide basic design equation for rigid pavement.
1993 AASHTO Empirical Equation for Rigid Pavement
where:
W18 = predicted number of 80 kN (18,000 lb.) ESALs
ZR = standard normal deviation
So=combined standard error of the traffic prediction and performance
prediction
D=slab depth (inches)
pt=terminal serviceability index
PSI = difference between the initial design serviceability index, po,
and the terminal serviceability index, pt
S’c=modulus of rupture of PCC (flexural strength)
Cd = drainage coefficient
J=load transfer coefficient (value depends upon the load transfer
efficiency)
Ec=Elastic modulus of PCC
k=modulus of subgrade reaction
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The W18 is the predicted number of 80 kN (18,000 lb.) ESALs that the
pavement will experience over its design lifetime. For this project we considered 20
years as the design lifetime.
The reliability of the pavement design-performance process is the probability
that a pavement section designed using the process will perform satisfactorily over the
traffic and environmental conditions for the design period. In other words, there must
be some assurance that a pavement will perform as intended given variability in such
things as construction, environment and materials. The ZR and So variables account
for reliability.
Each agency that uses the 1993 AASHTO Guide design equation can choose
their own levels of reliability to use, however the 1993 AASHTO Guide (Table 2.2, p.
II-9) provides some recommended levels.
Suggested Levels of Reliability for
Various Functional Classifications
Recommended level of reliability
Functional Classification
Urban Rural
Interstate and Other Freeways 85 – 99.9 80 – 99.9
Principal Arterials 80 - 99 75 – 95
Collectors 80 -95 75 – 95
Local 50 -80 50 – 80
Typical values of So used are 0.40 to 0.50 for flexible pavements and 0.35 to
0.40 for rigid pavements.
The pavement structure is best characterized by slab depth (D). The number of
ESALs a rigid pavement can carry over its lifetime is very sensitive to slab depth. As
a general rule, beyond about 200 mm (8 inches) the load carrying capacity of a rigid
pavement doubles for each additional 25 mm (1 inch) of slab thickness.
The difference in present serviceability index (PSI)between construction and
end-of-life is the serviceability life. The equation compares this to default values of
4.2 for the immediately-after-construction value and 1.5 for end-of-life (terminal
serviceability).
Typical values used now are:
Post-construction: 4.0 – 5.0 depending upon construction quality,
smoothness, etc.
End-of-life (called “terminal serviceability” and designated “pt“): 1.5 –
3.0 depending upon road use (e.g., interstate highway, urban arterial,
residential)
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The modulus of rupture (S’c) is typically obtained from a flexural strength
test. If no compressive strength data are available (or cannot be assumed), assume
Ec = 27,500 MPa (4,000,000 psi), which corresponds to a compressive strength of
34.5 MPa (5000 psi). The formula is given as:
S’c = 7.5*fc’^1/2
Rigid pavement is assigned a drainage coefficient (Cd) that represents the
relative loss of strength due to its drainage characteristics and the total time it is
exposed to near-saturation moisture conditions. Generally, quick-draining layers that
almost never become saturated can have coefficients as high as 1.2 while slow-
draining layers that are often saturated can have drainage coefficients as low as 0.80.
If subsurface drainage is expected to be a problem, positive drainage measures should
be taken. In general, the use of drainage coefficients to overcome poor drainage
conditions is not recommended (i.e. more slab thickness does not necessarily solve
water-related problems). Because of the peril associated with its use, often times the
drainage coefficient is neglected (i.e., set as Cd = 1.0).
Load Transfer Coefficient (J Factor) accounts for load transfer efficiency.
Essentially, the lower the J Factor the better the load transfer. Typical J factor values
are as shown below.
Condition J Factor
Undoweled PCC on crushed aggregate surfacing 3.8
Doweled PCC on crushed aggregate surfacing 3.2
Doweled PCC on HMA (without widened outside
2.7
lane) and tied PCC shoulders
CRCP with HMA shoulders 2.9 – 3.2
CRCP with tied PCC shoulders 2.3 – 2.9
Rigid pavement design incorporates a term entitled modulus of subgrade
reaction (K) in the determination of slab thickness. This K represents the load in
pounds per square inch on a loaded area, divided by the deflection in inches of that
loaded area. The K value can be determined from the data in figure below.
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In order to properly utilize the various design formulae and nomographs, the
structural support(CBR) available from the roadbed soils must be known and factored
into the equations.Geotechnical data obtained for this project reveal that the roadbed
soil support values (CBR) ranges from 21% to 45% max.
1.3 Subgrade and Subbase Thickness
The DPWH design guide also refers to the Road Note 29 Method of PCCP
design. From that method, the minimum concrete slab thickness equals 180
millimeters (unreinforced). Subgrade and subbase thicknesses are as shown on:
Minimum
Type of Thickness of
Definition
Subgrade Subbase
Required
Very weak All subgrade of CBR value 2 percent or less 280 mm
Weak All subgrade of CBR value 2-4 percent 180 mm
Subgrades with CBR > 4 percent but less than
Normal 15 and with subgrade CBR > 15 percent but 100 mm
not free draining subgrade
All subgrades with CBR value over 15
Very stable 0 mm
percent
Based on subsurface soil exploration report submitted by EM2A Partners &
Co., the project site has CBR values from 21% to 45% at max 15 blows per layer
specified for modified proctor criteria for use in heavy haul roads (refer to appendix
A).
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2.0 PAVEMENT ANALYSIS
FOR WAREHOUSE
HS 20‐44
Axle Loading
front wheel = 36 kN
rear wheel = 142 kN
rear wheel = 142 kN
design life = 20 years
Average Daily Traffic = 200
Reliability R = 85 %
Standard Error (So) = 0.35
Serviceability Index
initial servicibility index (Pi) = 4.5
terminal servicibility index (Pt) = 2.5
Portland Cement Concrete Parameters
28 days Concrete Strength, fc' = 4000 psi(28MPa)
Elastic Modulus, (Ec) = 57000 (fc')^1/2 = 3600000 psi
Modulus of Rupture, (S'c) = 7.5 fc'^1/2 = 400 psi
Other Design Parameters
Drainage Factor, (Cd) = 1 (common value)
Load Transfer Coefficient, (J) = 3.2 (no dowel at joint)
Field California Bearing Ratio (CBR) = 21
Modulus of subgrade reaction, (k) = 252
ESAL per truck = (front wheel/80)^4 + (rear wheel*0.55/80)^4
+ (rear wheel*0.55/80)^4
= 1.857 Esals/truck
design esals per lane = Esal*ADT*(365 days)*design life
= 1,355,610.00 Esals/lane
assumed thickness of
concrete pavement = 250 mm
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FOR CARPARK AREA
Light Rigid Vehicle
Axle Loading
front wheel = 17.5 kN
rear wheel = 17.5 kN
design life = 20 years
Average Daily Traffic = 400
Reliability R = 85 %
Standard Error (So) = 0.35
Serviceability Index
initial servicibility index (Pi) = 4.5
terminal servicibility index (Pt) = 2.5
Portland Cement Concrete Parameters
28 days Concrete Strength, fc' = 4000 psi(28MPa)
Elastic Modulus, (Ec) = 57000 (fc')^1/2 = 3600000 psi
Modulus of Rupture, (S'c) = 7.5 fc'^1/2 = 400 psi
Other Design Parameters
Drainage Factor, (Cd) = 1 (common value)
Load Transfer Coefficient, (J) = 3.2 (no dowel at joint)
Field California Bearing Ratio (CBR) = 21
Modulus of subgrade reaction, (k) = 252
ESAL per vehicle = (front wheel/80)^4 + (rear wheel/80)^4
= 0.0046Esals/vehicle
design esals per lane = Esal*ADT*(365 days)*design life
= 13,432.00 Esals/lane
assumed thickness of
concrete pavement = 100 mm
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3.0 RECOMMENDATION
Based on the result for the access road at 210 - warehouse it is recommend that we use
9.5 in (240.13mm) thick concrete pavement. To conform with the existing pavement
thickness we use 250mm.
For the car park area it is recommend that we use 3.5 in (88.90mm) thick concrete
pavement. For this we use the minimum concrete pavement thickness 100mm.
For the basecourse and subgrade, considering that we have CBR of 21% min and 48%
max on site it is very stable, based on table given on sec 1.3 the minimum thickness needed is
0 mm but for standard practice we recommend 100mm subgrade and 100mm subbase.
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ANNEX A
