HomeMy WebLinkAbout3957; EL CAMINO REAL ROAD WIDENING; PAVEMENT RECOMMENDATIONS; 2016-03-02CLce-
'
SDV0SB.DVB
SCSI, Inc.
Corporate Healquarters
6280 Pivercjale Street
San Diego, CA 92120
P 619.280.4321
T 877.215.4321
619.280.4717
W www.scst.com
March 2, 2016
Mr. Casey Arndt
City of Carlsbad
Construction Inspection Division
5950 El Camino Real
Carlsbad, California 92008
SCSI No. 150105P3
Report No. 4
Subject: PAVEMENT SECTION RECOMMENDATIONS
ASPHALT ROADWAY BUS STOP PADS
EL CAMINO REAL STATIONS 497+30 TO STATION 537+95
CARLSBAD, CALIFORNIA
Reference: "Geotechnical Engineering Investigation Report, El Camino Real Road
Widening Project, City of Carlsbad, California" prepared by Testing Engineers -
US Labs, Inc. dated March 28, 2006.
Dear Mr. Arndt:
In accordance with your request, SCST, Inc. has evaluated alternative pavement sections for
the subject project stations. We understand that two bus stop pads will be constructed at the
subject project site. For this particular project, an asphalt concrete (AC) pavement section
is desired to allow for future asphalt overlay projects. The The North County Transit District
(NCTD) design standards specifies pavements be underlain by concrete treated base. The
purpose of our work is to provide an appropriate pavement section alternative consisting of
aggregate base (AB) and geogrid as a substitute to Cement Treated Base (CTB).
CONCLUSIONS AND PAVEMENT SECTION RECOMMENDATION
SCSI reviewed project geotechnical reports to develop conclusions regarding the subgrade
conditions anticipated at the project site. R-value tests performed on representative subgrade
samples ranged between 8 and 72 (Testing Engineers, 2006). Based on our experience at the
site, the pavement support characteristics of the subgrade soils are considered poor. SCST
used the Caltrans Highway Design Manual pavement design procedures and methods to assist
us in determining the pavement section suggested by the NCTD Design Standards for bus stop
pad pavement sections.
New Pavement Section Recommendations
A design R-value of 5 was selected for our pavement design to calculate the standard
asphalt pavement section provided in the NCTD Design Standards. The following pavement
section is recommended for the assumed Traffic Index for 20-year life cycles (Table 1).
The City of Carlsbad March 2, 2016
El Camino Real Road Widening - Bus Stop Pads SCST No. 150105P3-4
Carlsbad, California Page 3
Table I
Flexible Pavement Sections (20-year life)
Pavement Design R- Asphalt Aggregate Geogrid
Section value Traffic Index Concrete Base* Reinforcement**
(inches) (inches) (layers)
Bus Stop Less than 5 12 8.0 17.0 1 Pad
Aggregate Base should conform to Class 2 Aggregate Base in accordance with the Caltrans Standard Specifications or
Crushed Miscellaneous Base in accordance with the Standard Specifications for Public Works Construction.
**Geogrid reinforcement such as Tensar TX-5 or equivalent placed between subgrade and aggregate base.
Subgrade Preparation for Bus Stop Pad Construction
Where the pavement is to be removed and reconstructed, the subgrade surface exposed should
be proof rolled. Areas judged unsuitable for pavement support by the proof roll should be
excavated to remove unsuitable materials as determined by the geotechnical engineer or their
representative. Excavations of up to 2 feet should be anticipated. The excavations may be
backfilled with suitable onsite soil materials or imported aggregate base materials in accordance
with project specifications.
Unsuitable materials may be encountered deeper than 2 feet requiring additional excavation. In
lieu of deeper excavations, geotextile such as Tensar® TX-5 or equivalent can be placed at 2
feet below planned subgrade elevations and backfilled with suitable material in accordance with
project specifications. This layer of geotextile reinforcement is in addition to recommended
pavement schedule.
The surface exposed should be scarified to a depth of 12 inches, moisture conditioned to near
optimum moisture content and compacted to at least 95% relative compaction in accordance
with ASTM D 1557.
Existing soils that are free of organic material and that do not contain rocks larger than 3 inches
in maximum dimension will be suitable for placement as compacted fill, provided they are
moisture conditioned to near the optimum moisture content. Imported soils, if any, should not
contain organic material or rocks greater than 3 inches in maximum dimension. Imported
material should be granular, and should be reviewed by the Engineer prior to placement.
New fill soils and base courses for pavements, should be placed in 6-inch to 8-inch loose lifts,
moisture conditioned to near optimum moisture content and compacted to at least 95% relative
compaction. Materials and methods of construction should conform to good engineering
practice.
GEOTECHNICAL ENGINEERING DURING CONSTRUCTION
SCST should observe pavement construction and perform appropriate laboratory tests to
evaluate the degree of compaction achieved and that material characteristics conform to the
specified criteria. In the event unusual or unanticipated conditions are encountered, the
presence of the geotechnical engineer during construction will enable modification of the
ESI2
I
The City of Carlsbad March 2, 2016
El Camino Real Road Widening - Bus Stop Pads SCST No. 150105P3-4
Carlsbad, California Page 4
recommendations in this report or the development of additional recommendations on a timely
basis.
If you have any questions, please call our office at (619) 280-4321.
Respectfully Submitted,
SCST, INC.
cent .U,IT1514
Staff Engineer
VAU:ER:aw
UnUNdol,GE
Principal Engineer
(1) Addressee via e-mail: Casey.Arndt@carlsbadca.gov
(1) Mr. Dave Carlin via e-mail: DCarlin@kleinfelder.com