SUBGRADE in RIGID PAVEMENT
Reference of Rigid Pavement Design in Indonesia
1. Perencanaan Jalan
Beton Semen Pd T-142003
2. Manual Perkerasan
Jalan (Revisi Juni
2013) No.
04/SE/Db/2017
3. Austroad, Pavement
Design, A Guide to the
Structural Design of
Pavement
SUBGRADE
The Subgrade definition according to specification is :
Briefly, the meaning of subgrade is in
situ material upon which the
pavement structure is placed
Typical Rigid Pavement by Manual Perkerasan Jalan
(Revisi Juni 2013) No. 04/SE/Db/2017
SUBGRADE AND REFERENCE
Subgrade Requirement base on the specification:
a. Soak CBR value min 6%, Specification ( S.4.05-(3) Material and S.7.01(2)(d) Subgrade on excavated area
b. Properly shaped, elevation meets specification, Specification S.7.01(2)(b) Preparation of workplace
c. Well compacted to the required layer thickness, Specification S.7.01(2)(c) Density degree
Depth of Subgrade :
a. Refer to Austroad, Pavement Design, A Guide to the Structural Design Pavement, (5.3.7
Presence of weak layers bellow the design subgrade level ) , mentioned about 1 m
b. Pavement Design Supplement Supplement to ‘Part 2: Pavement Structural Design’ of
the Austroads Guide to Pavement Technology, about 1,5 m
c. Manual Perkerasan Jalan (Revisi Juni 2013) No. 04/SE/Db/2017 about 0,85 m
d. Handbook of Geotechnical Investigation and Design Tables Burt Look, abot 0,75 m
e. Geotechnical Aspects of Pavement FHWA NHI-05-037, about 1,5 m
The Method for Evaluate Subgrade in site :
a. Refer to Austroad, Pavement Design, A Guide to the Structural Design Pavement, CBR in site by
DCP
b. Pavement Design Supplement Supplement to ‘Part 2: Pavement Structural Design’ of the
Austroads Guide to Pavement Technology, CBR in site by DCP
c. Manual Perkerasan Jalan (Revisi Juni 2013) No. 04/SE/Db/2017 , CBR in site by DCP
DEPTH of SUBGRADE
a. Refer to Austroad, Pavement Design, A Guide to the
Structural Design Pavement, (5.3.7 Presence of weak layers
bellow the design subgrade level )
DEPTH OF SUBGRADE :
Pavement Design Supplement Supplement to ‘Part 2: Pavement
Structural Design’ of the Austroads Guide to Pavement Technology
DEPTH OF SUBGRADE :
By Handbook of Geotechnical Investigation and Design Tables Burt Look
DEPTH OF SUBGRADE :
Finite Element Method
DISPACEMENT IN RIGID
PAVEMENT by FINITE
ELEMENT
DEPTH OF SUBGRADE :
By Geotechnical Aspects of Pavement FHWA NHI-05-037
The zone of influence under the
completed pavement varies with the
pavement section, but typically 80 –
90 percent of the applied stress is
dissipated within 1,5 m (50 inc) below
the asphalt section
KEY POINT DESIGN PRINCIPLE OF SUBGRADE AND SUBBASE
By Subgrades and Subbases for Concrete Pavements
● Roadbed (subgrade and subbase) design is key to long-term performance and smoothness of concrete pavements.
● The pavement structure of a concrete pavement typically consists of a concrete surface and subbase(s) placed upon a
prepared subgrade (a “base” is part of an asphalt pavement structure, while a subbase is an optional element of a
concrete pavement structure).
● Every foundation for a concrete pavement structure should be free from abrupt changes in character of the materials
(should be uniform), should resist erosion, and be engineered to control subgrade soil expansion and frost heave.
● Above all other design concerns, uniformity is of utmost importance.
● Because of the rigid nature of concrete pavements, loads are distributed over relatively large areas, greatly reducing
stresses on the subgrade/subbase; thus, concrete pavements do not necessarily require exceptionally strong foundation
support.
● The pavement design engineer should consider all subbase types (stabilized or unstabilized) and available materials
(recycled or virgin) for each pavement design; there is no standard recommended subbase for any concrete
pavement. Subbase selection is the designer’s option, but should consider fundamentals and decision factors described
in this guide.
● Concrete pavement design thickness is relatively insensitive to support stiffness (modulus of subgrade reaction), so it
is improper engineering to make a subgrade/subbase stronger or thicker in an attempt to decrease concrete pavement
thickness.
● Free-draining subbases are preferred over permeable subbases.
● Daylighted subbases are more economical and yield better long-term performance than edge drain piping.
The principle of pressure distribution by surface loading
By Geotechnical Aspects of Pavement FHWA NHI-05-037
PRESSURE ON SUBGRADE
Tech Brief
Bases and Subbases for Concrete Pavements
As shown in Figure 4, loads applied to a PCC-surfaced rigid pavement are spread over a large area of subgrade,
compared to loads applied to an asphalt concrete-surfaced flexible pavement. This permits the use of thinner
bases for rigid pavements than for flexible pavements.
PRESSURE ON SUBGRADE
By Subgrades and Subbases for Concrete Pavements
= 32 kN
Subgrade Requirement base on the specification:
a. Soak CBR value min 6%, Specification ( S.4.05-(3) Material and S.7.01(2)(d) Subgrade on excavated area
Subgrade Requirement base on the specification:
b. Properly shaped, elevation meets specification, Specification S.7.01(2)(b) Preparation of workplace
Subgrade Requirement base on the specification:
c. Well compacted to the required layer thickness, Specification S.7.01(2)(c) Density degree
Subgrade Requirement base on the specification:
d. Soak CBR value min 6%, Specification ( S.4.05-(3) Material and S.7.01(2)(d) Subgrade on excavated area
By ACPA, Subgrades and Subbases for Concrete Pavements, P_
A minimum CBR of 6 in the top 24 in. (610 mm) of subgrade provides an
adequate
working platform for construction, while limiting subgrade rutting under
construction
traffic to ½ in. (13 mm) or less.
Typically, a specified percentage of compaction of 95 percent, according to
AASHTO T99 will provide an adequate working platform for construction
equipment
and for excellent in-service performance of the subgrade portion of a concrete
pavement
structure.
STRUCTURAL MODEL
By Subgrades and Subbases for Concrete Pavements
Strength Limitation
Cement-treated subbases should be in a strength target
range of 300 to 800 psi (2.1 to 5.5 MPa) (PCA 2006), while lean
concrete subbases require a maximum strength limit of 1,200
psi (8.3 MPa).
SUBGRADE STRENGTH AND
WORKING PLATFORM
By Geotechnical Aspects of Pavement FHWA NHI-05-037
● Research conducted by the Wisconsin Depart ment of Transportation has concluded that a minimum California
Bearing Ratio (CBR) of 6 in the top 24 in. (610 mm) of subgrade provides an adequate working platform, while limiting
subgrade rutting under construction traffic to 1⁄2 in. (13 mm) or less (Crovetti and Schabelski 2001).
● Compacting the subgrade to a density that provides an adequate working platform for construction equipment
will provide adequate subgrade strength for the in-service concrete pavement.
● State departments of transportation recommend values ranging from 84 to 100 percent of the standard proctor,
but a value of 95 percent is by far the most specified and, thus, is the recommended value for most applications
(ACPA 2005).
● Soils that are compacted to a given density at dryer than optimum moisture contents will lose strength if the soils
become saturated over time
● experience also shows that uncontrolled shrinking and swelling of expansive soils can lead to increased stresses in a
concrete pavement due to non-uniform support, which accelerates pavement degradation and negatively impacts
pavement smoothness
● It should be noted that subgrade strength is a function of both density and moisture content.
By ACPA, Subgrades and Subbases for Concrete Pavements, P_4
Preparation of the subgrade includes:
 Compacting soils at moisture contents and densities that will ensure uniform and stable pavement
support.
 Whenever possible, setting the profile gradeline at an elevation that will allow adequate depth in the
side ditches to protect the pavement structure from the water table.
 Improving expansive or weak soils by treatment with portland cement, fly ash, cement kiln dust (CKD),
lime, or alternatively, importing better soils.
 Cross-hauling and mixing of soils to achieve uniform conditions in areas where there are abrupt
horizontal changes in soil types.
 Using selective grading in cut-and-fill areas to place the better soils closer to the top of the final
subgrade elevation.
 Fine grading the top of the subgrade to meet specified grade tolerances in the specifications and for
thickness control of the subbase and/or the concrete pavement.
Performance surveys have been conducted over many miles of old concrete pavements that were constructed without
proper subgrade compaction control and without subbases. Where the subgrade was naturally uniform, many of these old
pavements are still in excellent condition. Distress is limited to cut-fill transitions and other locations where there are abrupt
changes in subgrade materials and moisture conditions. Surveys show that low-strength soils where construction methods
provided reasonably uniform support perform better than stronger soils lacking uniformity (ACPA 1995).
SUBGRADE STRENGTH CLASSIFICATION
By Handbook of Geotechnical Investigation and Design Tables Burt Look
OBTAINING UNIFORM SUPPORT
By ACPA, Subgrades and Subbases for Concrete Pavements
Long-term subgrade performance depends heavily on three
interdependent factors:
• Moisture content and density.
• Load bearing capacity.
• Volume stability.
To obtain a subgrade that provides uniform support,
the four major causes of non-uniformity must be
addressed:
• Expansive soils.
• Frost-susceptible soils (frost heave).
• Pumping (from erodible layers underneath the
pavement slabs).
• Wet soils.
By Guide to Pavement Technology art 2, Ausroad
WATER MIGRATION within SUBGRADE and PAVEMENT
By Geotechnical Aspects of Pavement FHWA NHI-05-037
As is the case for all geotechnical structures, pavements will be
strongly influenced by moisture and other environmental factors.
Water migrates into the pavement structure through combinations of
surface infiltration (e.g., through cracks in the surface layer), edge
inflows (e.g., from inadequately drained side ditches or inadequate
shoulders), and from the underlying groundwater table (e.g., via
capillary potential in fine-grained foundation soils).
In cold environments, the moisture may undergo seasonal
freeze/thaw cycles. Moisture within the pavement system nearly
always has detrimental effects on pavement performance.
It reduces the strength and stiffness of the unbound pavement
materials, promotes contamination of coarse granular material due
to fines migration, and can cause swelling (e.g., frost heave and/or
soil expansion) and subsequent consolidation. Moisture can also
introduce substantial spatial variability in the pavement properties
and performance, which can be manifested either as local distresses,
It is widely recognized today that excess moisture in pavement
like potholes, or more globally as excessive roughness.
layers, when combined with heavy traffic and moisture-susceptib
materials, can reduce service life.
FACTOR TO CONSIDERING SUBGRADE CONDITION
By Geotechnical Aspects of Pavement FHWA NHI-05-037
The three main approaches
for controlling or reducing moisture problems follow below:
By Guide to Pavement Technology art 2, Ausroad
Many factors must be considered in determining the design
support conditions, including:
• subgrade variability
• Prevent moisture from entering the pavement system.
• consequences of premature distress
• Use materials and design features that are insensitive to the • sequence of earthworks construction
• target compaction moisture content and field density
effects of moisture
achieved
• Quickly remove moisture that enters the pavement system.
• moisture changes during service life
• pavement cross-section
• subsurface drainage and the depth to the watertable
• the presence of weak layers below the design subgrade level
DEPTH OF GWL TO CONSIDERING SUBGRADE CONDITION
By Manual Perkerasan Jalan (Revisi Juni 2013) No. 04/SE/Db/2017
By Guide to Pavement Technology art 2, Ausroad
EQUILIBRIUM MOISTURE CONTENT
By Handbook of Geotechnical Investigation and Design Tables Burt Look
MOISTURE AND VOLUME CHANGE
By Subgrades and Subbases for Concrete Pavements
SUBGRADE VOLUME
CHANGE
CLASSIFICATION
By Handbook of Geotechnical
Investigation and Design Tables
Burt Look
MINIMISING SUBGRADE
VOLUME CHANGE
By Handbook of
Geotechnical
Investigation and
Design Tables Burt
Look
MOISTURE AND CBR IN SERVICE PAVEMENT
By Guide to Pavement Technology art 2, Ausroad
By Manual Perkerasan Jalan (Revisi Juni 2013) No.
04/SE/Db/2017
IMPACT OF SUBGRADE/BASE STRENGTH FOR RIGID PAVEMENT
IMPACT OF SUBGRADE/BASE STRENGTH FOR FLEXIBLE PAVEMENT
By Geotechnical Aspects of Pavement FHWA NH-05-037
IMPACT OF SOIL SUPPORT/REGIONAL FACTOR FOR FLEXIBLE PAVEMENT
By Geotechnical Aspects of Pavement FHWA NHI-05-037
THE METHOD FOR EVALUATE SUBGRADE:
By Austroad, Pavement Design, A Guide to the Structural Design Pavement,
The Method for Evaluate Subgrade:
Pavement Design Supplement Supplement to ‘Part 2: Pavement
Structural Design’ of the Austroads Guide to Pavement Technology
DCP TEST
For In Situ CBR
1. Depth range test about
1m
2. Value of Site CBR
readable per blow and
penetration
3. There are many
formulas to calculate
CBR
1. One factor related strength of soil is about water
content. Where water content exceeds optimum
moisture will tend to reduce of soil strength
2. At site, on existing condition regarding to the note
above, Manual Perkerasan Jalan , recommend using
correction factor adapted to seasonal conditions