shaped leading edge (concave outward) to contain the mud
ɷ Traffic on the first lift should be parallel to the embankment alignment; no
turning of construction equipment should be allowed.
ɷ Construction vehicles should be limited in size and weight to limit initial
lift rutting to 75 mm (3 in.). If rut depth exceeds 75 mm (3 in.), decrease
the construction vehicle size and/or weight.
ɷ The first lift should be compacted only by tracking in place with dozers
ɷ Once the embankment is at least 0.6 m (2 ft) above the original ground,
subsequent lifts can be compacted with a smooth drum vibratory roller or
other suitable compactor. If local liquefied soil conditions occur, any
vibration should be turned off and the weight of the drum alone should be
used for compaction. Other types of compaction equipment also can be
used for nongranular fill.
ɷ After placement, the geosynthetic should be covered within 48 hours.
ɷ For less severe conditions (i.e., when no mudwave forms):
• Place the geosynthetic with no wrinkles or folds; if necessary,
manually pull it taut prior to fill placement.
ɷ Place fill symmetrically from the center outward in an inverted U (convex
outward) construction process. Use fill placement to maintain tension in
ɷ Minimize pile heights to avoid localized depressions.
ɷ Limit construction vehicle size and weight so initial lift rutting is no
greater than 75mm (3 in.)
ɷ Smooth-drum or rubber-tired rollers may be considered for compaction of
the first lift; however, do not over compact. If weaving or localized quick
conditions are observed, the first lift should be compacted by tracking with
c. Monitoring should include piezometers to indicate the magnitude of excess
pore pressure developed during construction. If excessive pore pressures are
observed, construction should be halted until the pressure drops to a
predetermined safe value.
d. Settlement plates should be installed at the geosynthetic level to monitor
settlement during construction and to adjust fill requirements appropriately.
Benefits can be realized in two ways. Adding a geosynthetic to a standard
pavement system design may increase the stiffness of the system, increasing the stability.
This method does not quantify the mechanistic properties of geosynthetics during the
design by reducing other material requirements. An alternative to this approach is to
modify the design using the properties of geosynthetics. Savings associated with
geosynthetic designs are realized by decreasing the thickness of granular material
required to protect a soft subgrade and create a construction platform. A cost savings of
more than 15% has been realized for geogrid stabilization of soft subgrades in
Pennsylvania (59). The cost savings are commonly a function of the haul distance for the
4.5.6. Subgrade Enhancement using Substitution
Substitution is a method that directly enhances the subgrade by removing unstable or
unsuitable soil and replacing or covering it with other suitable material.
If the use of in situ soil or available borrow is not practical from an engineering or
financial standpoint then substitution with lightweight fill materials may be a solution.
The following materials have been used in Minnesota to replace unstable subgrade
materials. Select granular and/or Breaker Run Limestone have been used where the
weight of the fill is not a concern. Wood fibers, shredded tires, or geofoam have been
used in areas where the weight of the fill can cause consolidation of a submerged layer of
peat or other compressible material.
Each section summaries the use of these materials. References and contacts for more
detailed information are included in each of the summaries.
188.8.131.52. Substitution Using Select Granular Materials
Purpose: Select Granular has been used as a substitute subgrade material for regions
having poor soils.
Conditions: Areas with high moisture content fine-grained soils near the water table.
Materials: Mn/DOT specification 3149.2 identifies Select Granular borrow is either
pit-run or crushed material graded from coarse to fine, having:
“The material shall not contain oversize salvaged bituminous particles or stone, rock
or concrete fragments in excess of the quantity or size permissible for placement as
specified. This is a very open gradation specification. The material should not be very
frost or moisture susceptible. To minimize frost and moisture susceptibility there should
be less than seven percent passing the 0.075-mm (No. 200) sieve (4).”
Design Considerations: Reported practice is to subcut and then fill with 0.6 m (24
in.) of select granular followed by 0.3 m (12 in.) of Mn/DOT Class 5 material.
Depending on the existing soil it may be desirable to use a geofabric separation layer
between soft, wet soils and the granular material.
Construction: Construction with Select Granular material should be governed by the
standard practices given in Mn/DOT 2105 and 2112.
Contacts: Mn/DOT District Materials Engineer
184.108.40.206. Substitution using Breaker Run Limestone
Breaker run limestone has been used in Minnesota as a substitute for undesirable
subgrade materials, particularly where fine grained, wet soils occur. Satisfactory
compaction is achieved using the Quality Compaction Method given by 2211.3C2 in the
Minnesota Standard Specifications for Construction (9) After compaction and grading
the embankment is ready for placement of granular base materials (Class 5 or 6
recommended) and bituminous surfacing.
The term breaker run limestone shall refer to a limestone/dolostone material that has
been run through a crusher one time and then screened for maximum size. The material
has a maximum particle size of 150 mm (6 in.) and is well graded from the top size down
to the 0.075-mm (No. 200) sieve. Item S-4.1 from the specifications for S.A.P. 20-625-
01 states that 100% breaker run limestone material shall be graded from coarse to fine
and pass the 150-mm (6 in.) sieve. Column (A) of Table 4.10 shows the results of sieve
analyses performed on breaker run samples collected from a construction site. Column
(B) contains the same information but with some interpolated values. Column (C) is the
gradation band for MnDOT Class 5 aggregate containing more than 60 percent crushed
Table 4.10 Breaker-Run Limestone and MnDOT Class 5 Gradations
MnDot Class 5
(+ 60% crushed)
90 – 100
50 – 90
35 – 70
20 – 55
10 – 35
3 – 10
Breaker run material may contain amounts of magnesium. Materials normally used
for this type of backfill will not meet the insoluble residue requirements given in
Minnesota specification 3138.2A3.
Sunny and dry weather conditions are best when constructing with breaker run
limestone. The worst weather conditions would be overcast/misty or frozen.
Recommended practice is to end dump the breaker run material then spread it with a
bulldozer. Compacted lift thickness should not exceed 225 mm (9 in.). The lift moisture
content should be adjusted to 4 to 5 percent then followed by compaction. Compaction is
carried out using a vibratory steel-wheeled roller.
In cases where the design includes geofabric there is a danger of the coarse breaker
run material causing tears or otherwise damaging the geofabric. To prevent this damage
a 150-mm (6-in.) separation layer of granular material (Class 5 recommended) should be
included. In keeping with good construction practice the geofabric should be sewn or
overlapped. Sewing shall be J-seam or prayer-seam according to Minnesota specification
3733.2B(D). An overlap of 0.3 to 1 m (1 to 3 ft) is adequate. Granular separation
material should be initially spread along the centerline. This keeps the geofabric taut and
wrinkle free. The construction sequencing and procedures presented in Section 4.5.5.
should be followed.
Costs in 2002.
Breaker run limestone has been priced at $8.39 per ton from the Mantorville quarry.
This bid was contingent upon the purchase of 14,000 cubic yards.
For more information on breaker run limestone contact Guy Kohlnhofer, Dodge
County Engineer at firstname.lastname@example.org
Figure 4.12 Overlapping Layers of Type V Nonwoven Geofabric Separate Granular
Material from Wet, Fine Soil. 150-mm (6-in.) of Class 5 Granular Material Protects the
Geofabric from the Breaker Run Material.
Figure 4.13 Steel-wheeled Roller Applies Compactive Effort to a 225-mm (9-in.) Lift of
Breaker Run Limestone.
220.127.116.11. Lightweight Fills
Wood chip, shredded tires and geofoam have been used as lightweight fills to decrease
the weight on in areas where the lower layers can consolidate or are otherwise unstable.
Table 4.11 lists some of the factors used to help design an embankment using wood chips or
shredded tires. A summary of the use of wood chips is presented in Section 18.104.22.168.1.,
shredded tires in Section 22.214.171.124.2. and geofoam in Section 126.96.36.199.3. Each of the summaries
include 1. Purpose, 2. Conditions, 3. Materials, 4. Construction specifications and
procedures, 5. Value, and 6. Contacts which includes people who have had experience with
the given material.
Table 4.11 Characteristics of Common Lightweight Fill Materials (52)
24 – 36
Readily available, renewable.
Easily placed with standard construction equipment.
Should remain saturated at all times.
Sawdust form is a relatively inexpensive byproduct of
No formal design parameters, based on field experiments.
20 – 45
Considered a by-product, relatively inexpensive.
Easily placed by standard construction equipment.
Design parameters are based on field experiments.
Use restricted to above the water table by MPCA
188.8.131.52.1. Use of Wood Chips for Lightweight Fill
Wood Chips have been used in Minnesota as a lightweight substitute for undesirable
subgrade materials. Wood chips have a unit weight of approximately 30 pcf and are
particularly suited to swamp-like conditions where the water table is close to the surface.
Wood chip construction can be combined with the use of other lightweight fills and the
use of geotextiles.
Mn/DOT conducted a 1976 study that included log and wood chip construction. The
methods were described as corduroy and wood chip and were used to widen sections of
road over a swamp (60).
• Corduroy – Place tied logs perpendicular to the road. The corduroy creates a
working platform for further construction.
• Wood chip working platform – Create a working platform using a layer of wood
chips. Place a 0.7-m (2-ft) thickness then cover with a minimum of 150 mm (6
in.) of clay to reduce exposure to air.
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