CSTR: Part D025 Design – Earthworks for Roads
Edition: February 2011
PART D025
DESIGN – EARTHWORKS FOR ROADS
CONTENTS
1.
2.
3.
4.
5.
6.
7.
8.
1.
General
References
Design Requirements
Dewatering
Materials for Fill
Settlement
Acid Sulphate Soils
Records
GENERAL
This Part specifies the requirements for the design of earthworks for roads and associated structures. This includes
excavation, fills, verges, levees, sub-soil drainage, catch drains, side drains and open drains, spreading of topsoil and
spreading of mulch. It excludes backfill of Reinforced Soil Structures (refer Part 420 "Reinforced Soil Structures").
The requirements of this Part are in addition to those specified in Part 210 "Construction of Earthworks".
2.
REFERENCES
Unless specified otherwise, all design shall be undertaken in accordance with the following:
3.
1) AS 3798
Guidelines on Earthworks for Commercial and Residential Developments.
2) AS 5100
Bridge Design.
DESIGN REQUIREMENTS
3.1
Design Life
The Contractor shall design assets for the following minimum design life:
ELEMENT
DESIGN LIFE (YEARS)
Embankments, including reinforced embankments
100
Cut batters, including batter treatments
100
3.2
General
The Contractor shall give due consideration to the following requirements in the design of the earthworks:
(a)
providing a safe run off area for errant vehicles;
(b)
providing a natural fit into the surrounding terrain;
(c)
minimising ongoing maintenance costs;
(d)
minimising the length of traffic barriers consistent with safety requirements;
(e)
limiting level changes and undulations in the finished pavement surface; and
(f)
limiting seasonal or permanent changes in the subsurface moisture regime.
Earthworks shall be designed so that detrimental effects from water (e.g. concentrated flows, erosion, ponding of
water) are kept to the minimum practicable.
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CSTR: Part D025 Design – Earthworks for Roads
Edition: February 2011
3.3
Stability and Surface Condition
The earthworks shall be designed to achieve the following:
(a)
there is no detectable instability or evidence of impending loss of stability;
(b)
the surface is highly resistant to surface scour and erosion and will not suffer detrimental effects from a
1 in 10 year Average Recurrence Interval storm event;
(c)
in cuts, any material which becomes detached is prevented from reaching the road shoulder; and
(d)
there is no undermining or destabilisation of any existing batter slopes or structures.
3.4
Provision for Maintenance
The Works shall be designed and constructed such that maintenance that would normally be required of the road and
environs can be readily and economically undertaken. Plant and equipment access must be available to the final
batter slope to allow ready installation of any treatment measures which may become necessary and to facilitate
inspection and maintenance of the face of the batter.
4.
DEWATERING
Any existing groundwater table level must not be permanently affected by the Works. The Contractor shall make
every reasonable endeavour to design structures and embankments to avoid temporarily lowering the existing
groundwater table by dewatering.
If dewatering cannot be avoided the Contractor shall:
5.
(a)
ensure that the extent and depth of the area to be dewatered is held to a practicable minimum;
(b)
ensure that the duration of any dewatering is held to a practicable minimum;
(c)
provide full details of any dewatering system, including the quantity and proposed method of disposal in
the Quality Plan; and
(d)
ensure that dewatering water is disposed of in such a manner that it does not harm the environment and is
in accordance with the Environmental Protection Act.
MATERIALS FOR FILL
Only Type A Material shall be used within 1.0 m of the finished surface of the pavement
Fill material with a WPI greater than 1 200 shall not be used at any level directly below the pavement.
The maximum allowable design modulus for fill materials is 100 MPa
Design parameters for standard fill materials shall not exceed the following value unless the contractor can
demonstrate higher values are appropriate:
Material (Refer to Part 210 for definitions)
Design Parameter
Type A Fill
E  70MPa,  = 0.45
Type B Fill
E  50MPa,  = 0.45
E = Vertical Resilient Modulus,  = Poisson Ratio of all sub-layers.
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Grading Sieve Size
% Passing
106
100
75
90 - 100
0.075
0 - 35
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CSTR: Part D025 Design – Earthworks for Roads
Edition: February 2011
4.
Plasticity Index
Max 20
Linear Shrinkage
Max 7
Natural Subgrade Strengths
The design CBR values of the natural subgrade shall not exceed the values in the following table:
Section Description
CBR of Natural Subgrade
….
1%
3%
6.
SETTLEMENT
Calculations
Prior to the commencement of works, the Contractor shall provide calculations and details of estimated gross
settlement, grade changes and creep at Practical Completion and at the Date of Final Completion. If methods for
limiting or accelerating settlement are to be used, full details must be provided with the calculations.
Settlement Limitations
Level changes in the finished pavement surface shall comply with the following:
(a)
no increase in levels after completion of construction of the pavement;
(b)
maximum decrease in level of the pavement surface of 30 mm over any 12 month period following the
construction of the pavement;
(c)
maximum differential settlement of 30 mm in a longitudinal direction, measured between Settlement
Measurement Points spaced at 50 m, following construction of the pavement until the Date of Final
Completion;
(d)
maximum differential settlement of 12 mm in a longitudinal direction, measured between Settlement
Measurement Points spaced at 20 m, following construction of the pavement until the Date of Final
Completion;
(e)
maximum differential settlement of 15 mm in a transverse direction, when measured between Settlement
Measurement Points on opposite sides of each carriageway following construction of the pavement until
the Date of Final Completion;
Estimated settlement creep (extrapolated on a logarithmic time scale) at any point over this length shall not exceed
50 mm over the period of 10 years following the Date of Practical Completion.
Monitoring
The Contractor shall implement a monitoring program that records settlement for the period between completion of
the embankment and expiry of the defects liability period. Settlement shall be recorded each fortnight for the first
6 months and monthly thereafter. A total of 4 settlement recording points is required, located 5 m and 15 m from
each bridge abutment.
Settlement shall be measured by a Surveyor meeting the requirements of Clause 130.1. Measurements shall be
plotted graphically creep (on a logarithmic time scale) and forwarded to the Principal within 1 week. If
calculations of predicted settlement have been prepared, these shall also be shown on the plot.
If a Settlement Measurement Point is disturbed or lost it must be replaced as close as practicable to the original
point before the next survey. Settlement must be determined by reference to a stable benchmark (eg a deep
benchmark).
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CSTR: Part D025 Design – Earthworks for Roads
Edition: February 2011
7.
ACID SULPHATE SOILS
Potential acid sulphate soils may be present below the proposed route of the project, particularly in the northern
section. In situ soil that is excavated from below the equilibrium groundwater level, or in situ soil below the natural
equilibrium ground level that lies within the draw down zone of a groundwater dewatering system, has the potential
to become actual acid sulphate soil. Potential acid sulphate soil that is excavated or dewatered shall be managed in
accordance with the acid sulphate soils component of the Environmental Management Plan for the project and Part
D020 – Design - Environmental.
8.
RECORDS
The following records shall be provided to the Principal:
Drawings
Construction drawings.
Drawings of any temporary earthworks, including settlement limiting or accelerating methods or dewatering
temporary works.
Reports
All relevant calculations and analysis, including those for settlement, slope stability, shrink – swell
movement, the effect of any water table and any requirements for monitoring.
Implementation Records
Settlement records.
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