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the project. As the project is started variations in the soils may be encountered and
therefore the field Engineer and Inspector must be aware of the effect of these possible
changes. The following considerations are presented in Section 4.5.3.
• Excavation and Embankment Construction: 1. The finished grade must be kept at
least 1.7 m (5 ft) above the water table. 2. The finished grade should be at least
the depth of frost penetration to minimize frost heave and 3. The existing soils or
materials and their preparation including subgrade correction embankment
placement and protection of the completed embankment need to be considered.
• Soils Evaluation: Soils must be evaluated based on whether they are, 1. Suitable
or unsuitable, 2. Excavated soils, 3. Salvaged Materials, 4. Borrow,
• Soils Preparation: Proper preparation of the soils for good uniformity involves
reworking and enhancing the existing materials and eliminating pockets of high
moisture and unstable soils. Soil preparation must also include proper compaction
using test rolling or specified densities, and possible lime treatment for moisture
• Subgrade Correction: Subcuts must be made in areas with pockets of high
moisture, unstable materials or other non-uniform conditions. Subcuts must be
used especially where there are silty type soils, which are particularly frost
susceptible. Subcuts can vary from 0.3 m to 1.3 m (1 ft to 4 ft). Tapers must be
provided with the subcuts.
• Placement of Embankment and Backfill Materials: As embankment materials are
placed the same soil must be used for each layer. Specific design considerations to
accomplish uniformity are listed in Section 188.8.131.52.
• Compaction: Compaction must be performed to MnDOT Specification 2105
and/or 2111 using the equipment specified in Specification 2123. These are Proof-
Rolling, Specified Density and Quality/Ordinary Compaction. The situations
where one method is appropriate relative to the others are listed in Section 184.108.40.206.
220.127.116.11. Construction Notes and Procedures
The MnDOT Office of Construction, Technical Certification Section has published an
“Inspector’s Job Guide for Construction” (11). This Guide gives the inspector a checklist
that will help get a project started and document the parameters forms and procedures
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that need to be considered based on the specifications to be used. One of the items that
will help keep a project under control is for the Inspector to keep a good diary. This will
help all people involved make sure that work is progressing at an appropriate rate and
that the inspection work is being accomplished.
18.104.22.168. Subgrade Enhancement
Various methods of subgrade enhancement are presented in Section 4.5.
• Enhancement of in-place soils using proper design of drainage and good
compaction are summarized in Sections 4.5.2.
• Modification using lime, bituminous materials and chlorides (Sections 22.214.171.124.,
126.96.36.199. and 188.8.131.52.)
• Stabilization using Fly Ash (Section 4.5.4.).
• Use of Geosynthetics
o Separation (Section 184.108.40.206.2.)
o Reinforcement (Section 220.127.116.11.)
General design considerations along with factors affecting of geosynthetic
lifespan are presented in Section 18.104.22.168.
• Substitution using higher quality granular and lightweight materials is presented
in Section 4.5.6.
o Higher quality granular materials presented are Select Granular (Section
22.214.171.124. and Breaker Run Limestone (Section 126.96.36.199.). Design and
construction procedures along with specifications are presented.
o Design and construction of lightweight fills using Wood Chips, Shredded
Tires and Geofoam are covered in Sections 188.8.131.52.1., 184.108.40.206.2., and
Summaries using each of the materials and procedures recommendations are
summarized for design and construction control. Specifications for materials and
procedures to use in Minnesota along with contacts for further information are presented.
Based on a review of the literature, questionnaires and interviews with Mn/DOT
and county engineers and review of specific projects recommendations are made for
when and how the various procedures should be used. Recommendations are presented in
Tables 4.14, 4.15, and 4.16 for Granular, Semi-plastic and Plastic soils respectively. The
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parameters used for the recommendations are “Grade above Water Table” and “Moisture
Conditions”. There are essentially no conditions recommended for soil enhancement for
granular soils. Methods of Modification, Stabilization, Separation and Reinforcement are
recommended for various conditions in the tables.
Table 4.17 lists the conditions and including “Thickness of Peat” for which the
various lightweight fills are recommended.
A database has been developed to document installations using the procedures
listed. Projects were located during visits to the cities and counties during the Summer,
2002. Sixty five projects have been identified. It recommended that:
• The projects identified should be reviewed every three years or more often.
• The location and parameters for additional projects should be added to the
In this way actual performance of the various methods of subgrade enhancement
can be documented.
1.5. Pavement Section Materials
Pavement section materials are all materials that are added above the subgrade soil to
more effectively withstand the loads caused by the traffic. The materials must be stronger
and more durable closer to the surface. All pavement section materials must be non-frost
susceptible. Chapter 5 presents many different materials that are now used in pavement
sections in Minnesota. There are others that are and will be tried in the future. With the
MnPAVE program it will be possible to simulate the new materials as input for the software
and make predictions of how the material will perform in a pavement.
Chapter 5 follows the same format as Chapter 4 for subgrade design and construction.
Definitions of the various materials are first presented. The materials range from Select
Granular to a high type Hot Mix Asphalt mixture.
The specifications that define each of these materials are listed in Section 5.4.1. The
granular equivalency factors for the Soil Factor and R-Value design procedures are based on
the specification that the material passes.
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Section 5.3 summarizes how the specifications relate to the granular equivalent thickness
factors. The moduli for the pavement layers that can be input for the MnPAVE software are
also presented in Section 5.3.3. The pavement moduli are varied by season just as those of
the subgrade soil. As the MnPAVE procedure and its input are developed further it will be
possible to assign different moduli to various materials that pass a particular specification.
For instance, a Specification 3138, Class 5 material with 10% passing the 0.075-mm (No.
200) sieve may have a different set of moduli than one with 5% passing the same sieve.
Other variations in gradation and particle angularity may also result in different moduli.
When a reliable laboratory test is finalized these moduli can be measured and then checked
with back-calculated moduli from the falling weight deflectometer or other non-destructive
The design factor inputs for the two HMA mixes used by MnDOT are presented in
1.5.2. Pavement Layer Construction
To obtain the design values discussed above for the granular, stabilized and HMA
pavement materials in the field, proper construction practices must be followed. These
start with specifications which when followed to assure good construction. Field control
procedures to help meet the specifications are then presented in Section 5.4.2. This
includes a summary of the Inspector’s Job Guide for Construction (11). MnDOT has also
published a “Materials Control Schedule” in the Grading and Base Manual (10), which
summarizes the testing frequency and quantities of materials needed to conform to the
In Section 5.4.1.the specifications pertaining to the construction of the pavement
layers are summarized. These include:
• Select Granular (MnDOT Spec. 3149.2B2) Section 220.127.116.11.1.
• Granular Base and Subbase Materials Gradations (MnDOT Spec. 3138) Section
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• Salvaged/Recycled Materials Gradations (MnDOT Spec 3138, Class 7) Section
• Aggregate Base/Subbase Construction (MnDOT Spec. 2211) Section 18.104.22.168.
• HMA Combined Mix Design (MnDOT Spec. 2350) Section 22.214.171.124.1.
The specifications are summarized in the indicated sections.
The specifications for Hot Mix Asphalt mixtures cover the materials, mixture design
and construction of the mixtures. Currently, MnDOT uses the 2360/2350 specifications
mixture designs. The 2350 mix design uses the gyratory or Marshall hammer for
compaction for developing the Job Mix Formula and construction control. Both of the
procedures use volumetrics including Voids in the Mineral Aggregate (VMA) and total
air voids. Before the 2350 specification was adopted VMA was used in the design phase
of the mixture, but not checked in the field. Some mixtures were experiencing “VMA
collapse” in the field (13); therefore, the current specifications require that VMA be
controlled in the final mixture. Ride (smoothness) requirements have also been added to
the 2360/2350 specifications. Both incentives and disincentives are included for control
of ride quality.
MnDOT also has Specifications 2331 and 2340 included in the 2000 Specification
Book (9). Some of these mixtures are still being produced. The field control procedures
for these mixtures also need to be followed carefully, especially for adequate compaction.
Currently, MnDOT uses the mixes only for Superpave (2360) for all new construction
and mid and long life (> 5 years) overlays.
126.96.36.199. Field Control Procedures to Meet Specifications
Section 5.4.2. summarizes procedures presented in the MnDOT Grading and
Base, Geotechnical and Bituminous Manuals (10)(5)(14). Checklists for field
personnel from the Field Notes for Construction Engineers and Inspectors are also
presented (11). Recommendations are made indicating which method is best for field
control. Field control procedures for cold in-place recycling and full depth
reclamation have not been finalized.
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188.8.131.52.2. Granular Bases
The construction of granular bases and subbases involves the following
• Manufacture of the material from a gravel pit or quarry
• Storage of the materials
• Transport to the grade
The material is initially tested for general quality and gradation and uniformity of
these characteristics. Segregation must be minimized during the entire construction
The current Schedule of Materials Control must be followed for each project.
It is important that the Contractor use exactly the same procedures and the State
when doing Quality Control and Quality Assurance companion testing is being done.
MnDOT specifications define three methods that can be used for compaction
• Specified Density
• Dynamic Cone Penetrometer (DCP)
• Quality (Ordinary) Compaction
The specified density is measured using the 150-mm (6-in.) Sand Cone Method
(ASTM D 1556-90. Random sampling procedures should be followed to establish
density test locations.
The DCP is a quick and easier test to run than the sand cone. It also gives a direct
measure of stiffness. The DCP needs to be run using the prescribed procedure
carefully and within 24 hours of compaction so that crusting does not occur.
Quality (Ordinary) Compaction should only be used if the equipment is not
available to do either Specified or DCP testing. If quality compaction is used the
Inspector and Engineer must be experienced in the construction of granular base and
embankment materials. The compaction operation must be observed continuously. It
generally is only appropriate for small areas where a limited amount of granular
material is being placed.
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The Field Notes for Construction Engineers and Inspectors (11) includes a section
for inspection of granular base construction. This checklist will help the field
personnel carry out the specifications well. Just as for the construction of
embankment soils one of the most important items to maintain is a good diary which
includes such things as hours, location, lift thickness, test results, quantity, yield and
other events including weather which may have an effect on the work.
184.108.40.206.3. Hot Mix Asphalt Mixtures
The current Schedule of Materials Control should be reviewed and used for
setting up the field control for each HMA construction project. That document will
• The specification applicable for the project
• The minimum required field acceptance testing rate
• Form number to use
• Minimum required sampling rate for laboratory testing
• Sample size required for laboratory testing
The construction of an HMA pavement layer includes the following operations:
• Materials delivery or manufacture and storage (asphalt and aggregate)
• Materials proportioning and mixing
• HMA storage and/or transfer to trucks
• Delivery to the construction project
Each of these steps requires some Quality Control (QC) testing by the Contractor
and the Quality Assurance (QA) testing by the Agency as spelled out in the
Specification. The testing will help assure that the material is uniform (not
segregated) is placed to specification density and that a surface is provided which
passes the ride specifications.
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