ST0301A-CN100910 (2)
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Keith Marvin - Bethel Road Reconstruction - Response to RFI 014
From: Caleb Thornhill <bct@freese.com>
To: Keith Marvin <kmarvin@coppelltx.gov>
Date: 9/10/2010 10:13 AM
Subject: Bethel Road Reconstruction - Response to RFI 014
CC:CPL03243 <CPL03243@freese.com>, Mike Shiflett <mms@freese.com>, ChrisPoteet
<cjp@freese.com>
Attachments:Memo Response to RFI #14.docx; Response to RFI 014 - AASHTOGuide of Design of
Pavement Structures.pdf; Response RFI 014 - Construction Methods.doc
Keith,
Attached is the response to RFI 014. I’ve also attached supplemental information for your records.
Please contact me with any questions you might have.
B. Caleb Thornhill P.E.
Project Manager
Freese and Nichols, Inc.
Main: 214-217-2200
Direct: 214-217-2282
Fax: 214-920-2565
Email: bct@freese.com
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file://C:\Documents and Settings\radloo\Local Settings\Temp\XPgrpwise\4C8A04DECity_...1/25/2011
MEMORANDUM
TO: Keith Marvin, P.E.
CC: Mike Shiflett
FROM: B. Caleb Thornhill, P.E.
SUBJECT: Bethel Road Reconstruction – Response to RFI #14 – Sulfates West Side of Bridge
DATE: September 10, 2010
This memo was prepared in response to RFI #14 for the Bethel Road Reconstruction, Phase I project. RFI
#14 notes the detection of soluble sulfates west of the Grapevine Creek Bridge.
Based on the information provided from the Alliance Geotechnical Group (City’s testing lab), Report
#1_26231_1 states the sulfate readings west of the bridge along Bethel Road varied from 1,420 to 3,720
psf.(assume this is a typographic error and ppm is intended)
According to the Lime Association of Texas, sulfate levels below 3000 ppm “should not be of significant
concern. The potential for a harmful reaction is low.” Sulfate levels between 3000 ppm and 5000 ppm
“are of moderate concern. Generally, these sulfate levels do not result in harmful disruption, but on
occasions have caused localized distress.” Based upon the mentioned test results along Bethel Road,
the risk of sulfate induced heave is low to moderate, therefore not being of critical concern based upon
this data.
Eliminating the lime treatment and adding concrete is not recommended. Although the concrete
pavement would have an increased loading capacity, the overall quality of the structure could suffer due
to a poor or unpredictable “working platform.” AASHTO Guide of Design of Pavement Structures
recommends, for rigid pavements, a subbase structure consisting of one or more compacted layers of
granular or stabilized material placed between the subgrade and the rigid slab for several purposes, one
purpose being “ to provide a working platform for construction equipment”. (1.6.2 Rigid Pavements).
Even with the other benefits of the subbase layer being potentially overcome with a thickened concrete
section, the working platform for construction equipment , uniform pavement support, and resulting
quality construction is sufficiently important to justify constructing a subbase.
The City of Arlington contains an area located on the Eagle Ford Shale geologic formation similar to this
particular area of Coppell. Arlington has implemented construction methods to deal with the sulfate
rich soil environment. The modified lime application specification was developed in general accordance
with the Lime Associaton of Texas guidelines, and Arlington has had success in incorporating this
approach to lime treated subgrades for roadways in this formation. Attached is Arlington’s construction
practices for constructing the subbase for a municipal roadway.
FNI recommends implementing the attached construction methods and proceeding with the pavement
structure as shown in the plans.
Bethel Road Reconstruction - RFI 12 Response
Click here to enter a date.
Page 2 of 2
City of Arlington Standard Specification for
11-32A Modified Lime Stabilization of Subgrade:
A.Prior to beginning any lime modification, the subgrade shall be brought to the
required line, grades, and cross-section, and proof rolled in accordance with the
specification requirements. Proof rolling shall be in accordance with Texas
Department of Transportation Standard Specification for Construction of
Highways, Streets and Bridges, 1993, Item 216. The cost of proof rolling shall be
considered subsidiary to this item.
B. After the subgrade has been shaped, the roadway will be scarified to full depth
and width of modification. Full depth will be eight inches (8") below finished
grade and full width will be that distance from one foot (1') behind the back of
curb on each side of the roadway.
After the roadway has been scarified, but before adding lime, water shall be
applied to the subgrade and the soil shall be kept at or above the optimal moisture
content for 72 hours prior to adding lime. If the subgrade has naturally been at or
above the optimal moisture content for 72 hours this step can be deleted.
This will be paid for at the unit price bid for adding moisture to subgrade in the
proposal.
B.Lime will be applied to that area defined in Part B of this section so that the initial
mixing operation can be completed during the same working day. Lime will be
applied by the “slurry method” when application is in the corporate limits of the
City of Arlington, Texas.
1.Lime and water shall be combined to form a mixture for the lime
application. Past experience has proven that approximately 3200 pounds
of lime to 500-600 gallons of water will produce the satisfactory mixture.
The slurry mix must be made within the city limits of the City of
Arlington.
2.The slurry will be applied with an approved distributor or water truck by
making multiple passes, if necessary, to apply the correct amount of lime.
The distributor or water truck will be equipped with an agitator to keep the
slurry in a consistent mixture.
3.For applications greater than or equal to 40 pounds per square yard, the
initial application shall be applied in halves (two equal parts) on day one
(1) and day two (2). This is subsidiary to the lime stabilization item.
B-1
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4.Mixing with a pulvimixer will immediately follow the lime application
until 100% of all material will pass a two-inch (2") sieve. The lime treated
subgrade shall then be sealed with a pneumatic roller and left for an initial
curing (mellowing) period of no less than 96 hours (4 days) and no more
than 168 hours (7 days) measured from day one (1) of the initial
application. During the initial curing (mellowing) period, the lime treated
subgrade shall be maintained at the optimal moisture content to plus (+)
four percentage points. The final remix and compaction shall be
completed within 168 hours (7 days) measured from day one (1) of the
initial application. If the final remix and compaction are not completed
within 168 hours (7 days) measured from day one (1) of the initial
application, then an additional lime application will be required. The
additional lime application amount shall be 50% of the original total
application rate and shall be added to the lime treated subgrade in
accordance with section 11-32A. NO additional payment shall be made
when this additional lime application is required.
5.For the final remix the subgrade shall be re-scarified to a depth of six
inches (6") and pulverized until all material conforms to the following:
Passing 1" Sieve 100%
Passing #4 Sieve 60%
Final compaction shall be accomplished in two (2) three-inch (3") lifts and
compacted to at least 95% of Standard Proctor Density as defined by
ASTM D 698. The allowable field moisture content at 95% Standard
Proctor Density shall be maintained at optimum to plus (+) four
percentage points. The compacted subgrade shall then be cured until 240
hours (10) days have elapsed from day one (1) of the initial application. A
curing seal of Emulsified asphalt, MS-1 shall be applied to the compacted
base material at a rate of 0.15 gallons per square yard within 24 hours of
passing density tests. This is subsidiary to the lime stabilization item.
6.Any subgrade exhibiting heave shall be brought to the attention of the
project engineer or inspector and these areas will be evaluated. The
project engineer or inspector will be given five (5) days to make a decision
on which areas will require additional treatment. Areas that require
additional treatment shall then be re-scarified to a depth of six inches (6")
and additional lime slurry will be applied with an approved distributor or
water truck by making multiple passes, if necessary, to apply 50% of the
original application rate. The distributor or water truck will be equipped
with an agitator to keep the slurry in consistent mixture.
B-2
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Compensation for this additional work will be paid by the ton at the unit
price bid for hydrated lime and by the square yard at the unit price bid for
subgrade preparation.
C.No stabilizer, either concentrated or diluted, shall be allowed to enter a storm
drain system or a natural waterway. The stabilizer shall be applied in a manner
that prevents puddling and /or runoff. Runoff will be considered a spill. All spills
shall be immediately reported to the City of Arlington’s Environmental
Management Division at (817) 459-6550 during City Hall working hours and to
the Arlington Fire Department Dispatcher (817) 543-5920 during evenings and
weekends. The spill shall be contained, neutralized, cleaned up, and removed
from the site. Washing down the spill is not allowed. This is subsidiary to the
lime stabilization items.
B-3
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