HomeMy WebLinkAbout215 MATHEWS OFFICE BUILDING - PDP - PDP150020 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT (3)Soilogic, Inc.
3050 67th Avenue, Suite 200 Greeley, CO 80634 (970) 535-6144
P.O. Box 1121 Hayden, CO 81639 (970) 276-2087
April 15, 2015
Greg D. Fisher. Architect pllc
3115 Clyde Street
Fort Collins, Colorado 80524
Attn: Mr. Greg Fisher
Re: Addendum #1 to Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic Project # 15-1056
Mr. Fisher:
Our geotechnical subsurface exploration report was submitted to your attention dated
April 7, 2015. At this time we understand a portion of the site pavement areas will be
surfaced with hot-mix asphalt and/or Portland cement concrete. Recommendations
concerning development of flexible and rigid pavement subgrades and pavement section
design options are included with this letter.
Hot Mix Asphalt and Portland Cement Concrete Pavements
After completing the minimum 2-feet of overexcavation as recommended in our original
geotechnical subsurface exploration report, we recommend suitable overexcavation/
backfill soils consisting of the site lean clay or similar soils be placed in loose lifts not to
exceed 9 inches thick, adjusted to within ±2% of standard Proctor optimum moisture
content and compacted to at least 95% of the materials standard Proctor maximum dry
density.
Care should be taken to maintain the proper moisture content in the subgrade soils prior
to paving. The prepared structural mat should not be left exposed for extended periods of
time. In the event that the reconditioned soils are allowed to dry out or if rain, snowmelt
or water from any source is allowed to infiltrate the subgrade soils, reworking of those
materials or removal/replacement procedures may be required.
Addendum #1 to Geotechnical Subsurface Exploration Report
Proposed Office Building (215 Matthews Street)
Fort Collins, Colorado
Soilogic # 15-1056
2
Pavement subgrades are expected to consist of reconditioned sandy lean clay. The lean
clay would be subject to low remolded shear strength. A resistance value (R-value) of 5
was estimated for the subgrade soils and used in the pavement section design. Traffic
loading on the site pavements is expected to consist of areas of low volumes of
automobiles and light trucks, as well as areas of higher light vehicle traffic volumes and
occasional heavier trash and delivery trucks. Equivalent 18-kip single axle loads
(ESAL’s) were estimated for the quantity of site traffic anticipated. Two (2) general
pavement design classifications are outlined below in Table I. Standard duty pavements
could be considered in automobile drive and parking areas. Heavy duty pavements
should be considered for access drives and other areas of the site expected to receive
higher traffic volumes or heavy truck traffic.
Proofrolling of the pavement subgrades should be completed to help identify unstable
areas. Depending on the in place moisture content of the subgrade soils immediately
prior to paving, the time of year when construction occurs and other hydrologic
conditions, stabilization of the subgrade soils may become necessary to develop a
suitable paving platform. If required, we recommend consideration be given to
stabilization of the pavement subgrades with class C fly ash. With the water-soluble
sulfate concentration of the site soils determined in laboratory testing, it is our opinion
stabilization with Portland cement could also be considered for this project. With the
increase in support strength developed by the chemical stabilization procedures, it is our
opinion some credit for the stabilized zone could be included in the pavement section
design, reducing the required thickness of overlying asphaltic concrete and aggregate
base course. Fly ash and cement stabilization can also eliminate some of the uncertainty
associated with attempting to pave during periods of inclement weather. Pavement
section design options incorporating some structural credit for the chemically stabilized
subgrade soils are outlined below in Table 1.
Addendum #1 to Geotechnical Subsurface Exploration Report
Proposed Office Building (215 Matthews Street)
Fort Collins, Colorado
Soilogic # 15-1056
3
TABLE 1 – PAVEMENT SECTION DESIGN
Standard Duty Heavy Duty
Option A – Composite
Asphaltic Concrete (Grading S or SX)
Aggregate Base (Class 5 or 6)
4”
6”
5”
8”
Option B – Composite on Stabilized Subgrade
Asphaltic Concrete (Grading S or SX)
Aggregate Base (Class 5 or 6)
Fly Ash of Cement Stabilized Subgrade
3”
4”
12”
4”
6”
12”
Option C - Portland Cement Concrete Pavement
PCCP
5”
6”
Asphaltic concrete should consist of a bituminous plant mix composed of a mixture of
aggregate, filler, binders and additives if required meeting the design requirements of the
City of Fort Collins. Aggregate used in the asphaltic concrete should meet specific
gradation requirements such as Colorado Department of Transportation (CDOT) grading
S (¾-inch minus) or SX (½-inch minus) specifications. Hot mix asphalt designed using
“Superpave” criteria should be compacted to within 92 to 96% of the materials Maximum
Theoretical Density. Aggregate base should be consistent with CDOT requirements for
Class 5 or Class 6 aggregate base, placed in loose lifts not to exceed 9 inches thick and
compacted to at least 95% of the materials standard Proctor maximum dry density.
If chemical stabilization procedures will be completed, we recommend the addition of
13% class ‘C’ fly ash or 5% Portland cement based on component dry unit weights. A
12-inch thick stabilized zone should be constructed by thoroughly blending the fly
ash/cement with the in-place subgrade soils. Some “fluffing” of the finish subgrade level
should be expected with the stabilization procedures. The blended materials should be
adjusted in moisture content to within the range of ±2% of standard Proctor optimum
moisture content and compacted to at least 95% of the material’s standard Proctor
maximum dry density within two (2) hours of fly ash addition and immediately after
cement addition.
For areas subjected to truck turning movements and/or concentrated and repetitive
loading such as dumpster or truck parking and loading areas, we recommend
consideration be given to the use of Portland cement concrete pavement with a minimum
thickness of 6 inches. The concrete used for site pavements should be air entrained and
Addendum #1 to Geotechnical Subsurface Exploration Report
Proposed Office Building (215 Matthews Street)
Fort Collins, Colorado
Soilogic # 15-1056
4
have a minimum 28-day compressive strength of 4,000 psi. Woven wire mesh or fiber
entrained concrete should be considered to help in the control of shrinkage cracking.
The proposed pavement section designs do not include an allowance for excessive
loading conditions imposed by heavy construction vehicles or equipment. Heavily
loaded concrete or other building material trucks and construction equipment can cause
some localized distress to site pavements. The recommended pavement sections are
minimums and periodic maintenance efforts should be expected. A preventative
maintenance program can help increase the service life of site pavements.
We appreciate the opportunity to be of service to you on this project. If you have any
questions concerning the enclosed information or if we can be of further service to you in
any way, please do not hesitate to contact us.
Very Truly Yours,
Soilogic, Inc. Reviewed by:
Wolf von Carlowitz, P.E. Darrel DiCarlo, P.E.
Principal Engineer Senior Project Engineer
36746 44271