SECTION 8
SUBGRADE DESIGN REQUIREMENTS Original Ordinance Number: 06-03-20
SECTION 8 – SUBGRADE DESIGN REQUIREMENTS
ENGINEERING DESIGN AND CONSTRUCTION PROTOCOL for Pavements within the Eagle Ford formation in the City of Frisco. (The Eagle Ford formation is defined as an area with eastern limits generally following Preston Road and extending to the western city limits.)
澳门简介8.01GENERAL:
All pavement projects shall have a subgrade investigation and pavement design. This protocol provides for two methods: the Swell Test Alternative and the calculated Potential Vertical Ri (PVR) - TxDOT Tex-124-E Alternative. The information and recommendations contained in the report must be approved in writing by the Engineer1. As a minimum, the investigation shall consist of:
A.Field Investigation胶原带白
1.1.(Swell Test Alternative) Borings shall be drilled on center of roadway at 250 feet spacing (or less),
alternating between each roadway direction or on a 200 feet grid throughout a subdivision to a depth
of at least 10 feet below finished subgrade.
1.2.(PVR-TxDOT Tex-124-E Alternative) Borings shall be drilled on center of roadway at 250 feet spacing
(or less), alternating between each roadway direction or on a 200 feet grid throughout a subdivision to
a depth of at least 20 feet below finished subgrade.
2.Borings shall be sampled at 3 feet intervals or less to a depth of 10 feet and at 5 feet intervals or less
thereafter.
3.Bulk samples of each soil type encountered in the upper 5 feet shall be taken.
4. Logs shall be developed to provide a lithographic log of the soil types encountered in each boring,
descriptions of each layer and groundwater conditions.
B. Determination of swell characteristics and movement potential can be accomplished by either the Swell Test
Alternative (C.1.1) or calculated Potential Vertical Ri (Alternative C.1.2) for a 20 foot depth of moisture penetration at the option of the Design Engineer2. The Design Engineer shall submit all calculations and assumptions involved in calculating the PVR and the recommended depth of moisture treatment to the City for review.
机器姬C. Laboratory Investigation
1. Soil types in each boring shall be subjected to classification tests; Atterberg limits (ASTM D 4318) and
Percent Passing the No. 200 sieve (ASTM D 1140) and moisture/density. Where logs show uniform
conditions, the number of tests can be reduced by visual classification, as long as there is at least one
t of classification tests per each 2 borings.
1.1. (Swell Test Alternative) Test for swell potential using ASTM D 4546 at 200 psf stress at least two
(2) samples per boring at varying depths from 0 to 10 feet to determine with reasonable certainty
the average swell potential of the subgrade.
1.2. (PVR-TxDOT Tex-124-E Alternative) Test for swell potential using swell tests (ASTM D4546) and/or
soil suction tests (ASTM D5298) necessary to calculate PVR for a 20 foot moisture penetration.
1
The term “Engineer” as ud in the specifications shall mean the City of Frisco Director of Engineering Services or his/her designee.
2The term “Design Engineer” as ud in the specifications shall mean an individual or entity with whom the Owner has entered into an agreement for professional geotechnical engineering rvices.
2. Due to the variability in moisture contents over the year, the Design Engineer shall asss the condition
of the samples and the ason. Moisture Content Tests (ASTM D 2216) shall be performed. When in
the Design Engineer’s opinion the samples are wetter than should normally be expected, the samples
shall be air dried such that the samples reprent the drier portion of the year.
3. Average all swell test results to determine the mean maximum swell percentage and the standard
deviation. In the months of June through September u the mean swell percentage. For all other
time periods u the mean plus one standard deviation to determine the design swell percentage.
4. Test for sulfates in the upper 3 feet of the subgrade in each boring using EPA 9038 or EPA 37
5.4 with
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10:1 dilution ratio. Provide sufficient testing to determine with reasonable certainty the levels of sulfate
prent. Note: Majority of testing should be performed in the light brown clays.
5. Bad upon the results of classification tests, group the samples and identify the subgrade soil types in
the upper 5 feet which impact the pavement design.
6. Perform a lime stabilization ries for each soil type expected to be in the upper 12 inches of the
subgrade3. The Eades-Grimm method of pH testing shall be ud to obtain a beginning point.
到远方去Additional testing shall be performed for each soil type to determine lime content. Minimum Design
Criteria are:
a. pH = 12.4 after mellowing (ASTM D 2976)
b. Swell potential <1.0 percent under 200 psf stress test4 (ASTM D 4546)
c. Unconfined Compressive strength >160 psi4 (ASTM D 2166)
The minimum lime content shall be the percentage, by weight, of hydrated lime required to meet the
Minimum Design Criteria plus 1.0%.
7. Light brown clays having over 5,000 ppm (0.5 percent) sulfate, dark brown clays having over 25,000
ppm (2.5 percent) sulfate, and weathered shale having over 15,000 ppm (1.5 percent) sulfate shall be
stabilized using double application method.
8.02ENGINEERING AND CONSTRUCTION:
The Design Engineer shall utilize the results of the field and laboratory investigation to provide an engineered pavement ction consisting of moisture treated subgrade, lime stabilized subgrade and continuously reinforced concrete. The continuously reinforced pavement shall consist of City of Frisco standard ctions for the street classification or bad on rigid pavement design in accordance with The City of Frisco “Thoroughfare and Circulation Design Requirements.” The following engineering requirements will apply to the design and report.
A.Weathered shale material encountered within 8 feet below finish subgrade shall be subexcavated t
o a depth
of at least the depth of required moisture treatment and replaced with on-site light brown or dark brown
clays or other approved material.
B.1 (Swell Testing Alternative) U Figure 8.1 to determine the minimum depth of moisture treatment bad
on average swell potential percentage to 10 feet (mean plus one standard deviation) and anticipated speed
limit.
B.2 (PVR-TxDOT Tex-124-E Alternative) The Design Engineer shall calculate the PVR bad upon a 20 feet
moisture penetration and shall provide moisture treatment depth to limit the PVR to 4.5 inches. The Design
Engineer shall submit all calculations and assumptions involved in calculating the PVR and the recommended depth of moisture treatment to the City for review.
3 Note: The minimum lime percentage shall be 7.0 percent hydrated lime for light brown clays and 10.5 percent hydrated lime for dark brown clays. The weathered shale is not suitable for stabilization without permission from the Engineer and appropriate detailed engineering and laboratory design.
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4Soil mixed with lime at +3% of its optimum moisture content, with 2 days of mellowing time, remolded to 95% ASTM D 698. Cure remolded samples @ 100°F for 5 days, then followed by capillary soak for 24 hours for unconfined compression test. The lime source ud in the laboratory design shall be specified for u in the field construction.
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Percent Swell, 200 psf
M o i s t u r e T r e a t m e n t , f e e t
C. Moisture treatment to a minimum of 3 percentage points above optimum moisture content at a minimum of 95 percent standard Proctor (ASTM D 698) shall be required for at least 2 feet of the subgrade. Thicker zones of moisture treatment may be required depending upon the average swell potential. The thickness shall be determined in accordance with Figure 8.1 or as determined by calculations from B.2.
D. Trench backfill shall consist of clay soils and shall be placed in thin, loo lifts, moisture conditioned to a minimum of 3 percentage points above optimum moisture content, and compacted to a minimum of 95 percent of standard Proctor (ASTM D 698) maximum dry density. Sands containing less than 20% passing the No. 200 sieve shall be placed in thin, loo lifts and moisture conditioned to within 2 percentage points of optimum moisture content and compacted to a minimum of 95 percent of standard Proctor (ASTM D 698). The placement and compaction of trench backfill shall be obrved and density tested during construction.
E. The upper 8 inches (residential) to 12 inches (arterial) of the subgrade shall be lime stabilized in accordance with the laboratory determined lime percentage and shall meet the requirements listed above in Item C.6. The lime stabilized subgrade shall be moisture treated to a minimum of 4 percentage points above optimum moisture content, allowed to mellow before final compacting to a minimum of 95 percent standard Proctor (ASTM D 698) at a minimum of 2 percentage points above optimum moisture content.
F. Moisture treatment and lime stabilization shall extend at least four feet beyond the edge of pavement. A moisture barrier consisting of at least 10 mil poly sheeting shall be placed horizontally on the subgrade beyond the pavement edge and extend at least 6 feet on either side of the paveme
nt neat line after final compaction. The barrier shall be covered with at least 8 inches of lightly compacted soil. Care should be taken not to rip or tear the poly sheeting during placement of the cover fill.
G. The thickness and reinforcement shall be the greater of either the City of Frisco design standards or a design signed and aled by a qualified Professional Engineer in accordance with an approved design methodology such as AASHTO for continuously reinforced concrete pavements. All calculations and assumptions ud by the Design Engineer shall be provided to the Engineer for review.
H. Stabilized subgrade soils shall be subjected to testing to determine Resilient Modulus (M R ). The testing can be either direct M R testing or u of correlation testing methods which are accepted by the City of Frisco. FIGURE 8.1 - RECOMMENDED DEPTH OF MOISTURE TREATMENT
I.All concrete, which comes into contact with soils containing more than 0.1% (1,000 ppm) sulfate shall be
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designed to resist sulfate attack. As a minimum, the concrete shall have a maximum water/cementiti
ous materials ratio of 0.45, with 25% ASTM C 618 Class F fly ash and ASTM C 150 Type II cement (or Type V).
J.Detailed mix design shall be performed for concrete pavement in high sulfate areas.
K.Finished pavement grades shall have at least 0.8 percent longitudinal slope to provide for drainage in the event that isolated heave features occurred.
L.Results of the field and laboratory investigations, engineering analys and recommendations shall be prented in a report and is subject to the approval of the Engineer. The report shall contain a specific list of design thickness, reinforcement, subgrade and stabilization requirements including lime source, type, and concentration (by dry weight) which can be easily incorporated to plans and specifications. All calculations and laboratory tests shall be included in the report along with boring location plan and geology maps. The report shall be signed and aled by a qualified Professional Engineer.
8.03LIME STABILIZATION OF SUBGRADE SOILS:
A.SCOPE:
This Item shall govern stabilization of the new or existing subgrade and shall consist of all labor, equipment
and material necessary to pulverize the subgrade clays or existing pavements, add the specified percentage
of hydrated lime, mix, mellow, remix and compact the mixture as specified in this Item. The Contractor5
shall be responsible for making allowances for subgrade bulking during stabilization to achieve design
finished subgrade elevation and meeting specified thickness. The finished item shall be a compacted and
finished subgrade meeting the grades, thickness, lines and typical cross ctions shown on the plans and
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specifications and having:
1. A minimum unconfined compressive strength of 160 psi (ASTM D 2166 / AASHTO T 208 or ASTM D
1633 / AASHTO T 220), (information only)
2.Less than 1 percent swell when tested under a 200 psf stress (ASTM D 4546 / AASHTO T 216),
3. A minimum pH of 12.4 (ASTM D 2976 / AASHTO T 289)
B.MATERIALS:
All materials ud in the construction shall meet the following requirements. In the event the Contractor
wishes to u materials not listed in this ction, the Contractor shall submit to the Engineer mix design
data and proof of performance data as required by the Engineer who shall review the submittal and
determine whether the materials will meet the design intent. No other materials shall be ud without the
written permission of the Engineer.
1.Lime – The lime shall meet the requirements of ASTM C977 / AASHTO M 216; contain at least 92
percent calcium and magnesium oxide, and the rate of slaking test for moderate reactivity per ASTM
C110 / AASHTO T 232. All lime shall come from a single source, shall be the same source as ud in
the design, and shall be subject to periodic testing to confirm properties. Each shipment of lime shall
be accompanied by a Certificate of Compliance stating the conformance of the product to the
specifications. Certificates shall be provided to the Engineer.
In the event the Contractor changes lime sources, no work shall be done until the Engineer accepts, in
writing, a new lime-soil mix design using the new lime source.
5
The term “Contractor” as ud in the specifications shall mean an individual or entity with whom the Owner has entered into an agreement for construction rvices.
