HomeMy WebLinkAboutCT 06-27; MUROYA SUBDIVISION; PAVEMENT RECOMMENDATIONS; 2012-04-174%) Z FO/Z AS -
I.
V. GEOCON
INCORPORATED
GEOTECHNICAL . ENVIRONMENTAL.
C-ro(-7-7
M A T E R I A I S
Project No. 07671-52-02
March 30, 2012
Revised April 17, 2012
Taylor Woodrow Homes Incorporated
8105 Irvine Center Drive, Suite 1450
Irvine, California 92618
Attention: Mr. Tom Baine
Subject: PAVEMENT RECOMMENDATIONS
MUROYAPROPERTY
CARLSBAD, CALIFORNIA
Reference: Interim Report of Testing and ObservatiOn Services Performed During Site Grading,
Muroya Property, Buildings 1 Through 12 and 19 Through 37, Carlsbad, Cal/oi-nia,
prepared by Geocon Incorporated, dated February 13, 2012 (Project No. 07671-52-02).
Dear Mr. Baine:
We have prepared letter to provide pávëment recOmmendations for the construction of Holly Leaf
Court, Sweet Clover Lane, White Sage Way, and private driveways within the proposed
development We understand that the planned roadways are proposed for automobile and light truck-
traffic with a traffic index (Ti) of 5.0 for the roadways and a TI of 4.0 for the private driveways as
provided by Pangaea Land Consultants, Inc. We prepared this letter to provide recommendations for
asphalt concrete (flexible) and Portland cement concrete (rigid) pavement structural sections for the
planned roadways and interlocking concrete paver pavement structural sections for the private
driveways at the subject project.
The recommendations provided herein are based on laboratory test results obtained from subgrade
soils. After soil collection, we performed laboratory resistance value (R-Value) testing in accordance
with ASTM D'1844 (California Test Method No..301) Subgrade soils consist predominately of silty
sand with some clay and typically exhibit low R-Value strength characteristics. Table I presents the
laboratory R-Value test results.
6960 Flanders Drive 0 San Diego, California 92121.2974 a Telephone 858.558.6900 I Fox 858.558.6159
TABLE I
SUMMARY OF LABORATORY R-VALUE TEST RESULTS
ASTM 02844
Sample No. Location R-Value
R-1 Holly Leaf Court - Sta. 11+00 14
R-2 White Sage Way - Sta. 13+50 11
R-3 White Sage Way - Sta. 11+20 14
R4 Sweet Clover Lane - Sta. 12+00 13
R-5 Sweet Clover Lane - Sta. 14+00 11
As indicated on Table 1, the laboratory R-Value tests results for Sample Nos. R-2 and R-5 are less
than 12. We understand the City of Carlsbad typically requires lime treatment of subgrade soils when
the R-Value is less than 12. It has been our experience that lime treatment is most effective when
used in situations where clays of "high" to "very high" expansion potential (Expansion Index greater
than 90) are present. Due to the presence of silty sands with "very low" expansion potential (El of 20
or less), it is our opinion, from a geotechhical standpoint, that the construction of a conventional
pavement section along the subject alignments would be more appropriate. Therefore, we are
recommending the implementation of the conventional pavement section recommendations provided
on Table 2.
If an alternative pavement section that incorporates a limetreated subgrade is required by the city,
Geocon Incorporated should be retained to provide additional recommendations Additional
laboratory testing will be required to evaluate the percentage of lime required to treat the subgrade
soils.
FLEXIBLE PAVEMENT RECOMMENDATIONS
We calculated the flexible pavement sections in general conformance, with the Caltrãns Method of
Flexible Pavement Design (Highway Design Manual, Section 608.4). Based on discussions with the
project civil engineer, the planned roadways will possess a TI of 5.0. Table 2 presents the calculated
pavement sections using the City of Carlsbad minimum design sections in accordnce with
Supplemental Standard No. GS-17.
PE
March 30, 2012 Project No. 07671-52-02 -2-
Revised April 17, 2012
TABLE 2
FLEXIBLE PAVEMENT SECTION
Traffic Subgrade Calculated Asphalt Calculated
Location Index R-Value Concrete Thckness Class 2 Aggregate Base
(inches) Thickness (inches)
Holly Leaf Court 5.0 14 4* 6
Sweet Clover Lane 5.0 11 4* 7
White Sage Way 5.0 11 4* 7
* Minimum thickness required by the City of Carlsbad.
Prior to placing the base materials, the upper 12 inches of pavement subgrade soil should be scarified,
moisture conditioned as necessary, and compacted to a dry density of at least of 95 percent of the
laboratory maximum dry density near to slightly above optimum moisture content as determined by
ASTM D 1557. Base materials should be moisture conditioned to near optimum moisture content and
compacted to a minimum density of 95 percent of the laboratory maximum dry density Asphalt
concrete should be compacted to a density of at least 95 percent of the laboratory Hvéem density in
accordance with ASTM D 2726.
The placement of new base materials should conform to Section 26-1.02A of the Standard
Specifications for The State of California Department of Transportation (Caltrans) with a 3/4-inch
maximum size aggregate and the City of Carlsbad specifications.
The placement of new asphalt concrete should conform to Section 203-6 of the Standard
Specifications for Public Works Construction (Greenbook) Asphalt concrete should be compacted to
a density of at least 95 percent of the laboratory Hveem density in accordance with ASTM D 2726
RIGID PAVEMENT RECOMMENDATIONS
A rigid Portland cement concrete (PCC) pavenient section should be placed in driveway entrance
aprons, cross gutters and trash bin loading/storage areas. The concrete pad for trash truck areas
should be large enough such that the truck wheels will be positioned on the concrete during loading.
We calculated the rigid pavement section in general conformance with the procedure recommended
by the American Concrete Institute report ACI 330R-08 Guide fOr Designand Construction of
Concrete Parking Lots rising the parameters presented in Table 3.
Project No. 07671-52-02 - 3 - March 30, 2012
Revised April 17, 2012
S
TABLE 3
RIGID PAVEMENT DESIGN PARAMETERS
Design Parameter Design Value
Modulus of Subgrade Reaction, k 100 pci
Modulus of Rupture for Concrete, MR 500 psi
Traffic Category, TC A and C
Average Daily Truck Traffic, ADTT 10 and 100
Based on the criteria presented herein, the PCC pavement sections should have a minimum thickness
as presented in Table 4.
TABLE 4
RIGID PAVEMENT RECOMMENDATIONS
Location Portland Cement Concrete (inches)
Automobile Parking Stalls (TC=A) 5.5
Heavy Truck and Fire. Lane Areas (TC=C) 7.0
The PCC pavement should be placed over subgrade soil that is compacted to a dry density of at least
95 percent of the laboratory maximum dry density near to slightly above optimum moisture content.
This pavement section is based on a minimum concrete compressive strength of approximately
3,000 psi (pounds per square inch).
A thickened edge or integral curb should be constructed on the outside of concrete slabs subjected to
wheel loads. The thickened edge should be 1.2 times the slab thickness or a minimum thickness of
2 inches, whichever results in a thicker edge, and taper back to the recommended slab thickness 4 feet
behind the face of the slab (e.g., a 7-inch-thick slab would have a 9-inch-thick edge). Reinforcing
steel will not be necessary within the concrete for geotechnical purposes with the possible exception
of dowels at construction joints as discussed herein.
To control the location and spread of concrete shrinkage cracks, crack-control joints (weakened plane
joints) should be included in the design of the concrete pavement slab. Crack-control joints should
not exceed 30 times the slab thickness with a maximum spacing of 12.5 feet and 15 feet for the 4 and
7-inch-thick slabs, respectively (e.g., a 7-inch-thick slab would have a 15-foot spacing pattern), and
should be sealed with an appropriate sealant to prevent the migration of water through the control
joint to the subgrade materials. The depth of the crack-control joints should be detennined by the
referenced ACI report.
March 30, 2012 Project No. 07671-52-02 4
Revised April 17, 2012
To provide load transfer between adjacent pavement slab sections, a butt-type construction
joint should be constructed. The butt-type joint should be thickened by at least 20 percent at the edge
and taper back at least 4 feet from the face of the slab. As an alternative to the butt-type construction
joint, dowelling can be used between construction joints for pavements of 7 inches or thicker. As
discussed in the referenced ACT guide, dowels should consist of smooth, 1-inch-diameter reinforcing
steel 14 inches long embedded a minimum of 6 inches into the slab on either side of the construction
joint. Dowels should be located at the midpoint of the slab, spaced at 12 inches on center and
lubricated to allow joint movement while still transferring loads. In addition, tie bars should be
installed at the as recommended in Section 3.8.3 of the referenced ACT guide. The structural engineer
should provide other alternative recommendations for load transfer.
PAVER PAVEMENT RECOMMENDATIONS
We calculated the paver pavement sections in general conformance with the Caltrans Method of
Flexible Pavement Design (Highway Design Manual, Section 608.4) using an estimated Traffic Index
(TI) of 4.0 for the private driveways. We used an R-Valué of 11 and an R-value of 78 for the
subgrade soil and the base materials, respectively. Table 5 presents the recommended pavement
section. We calculated the section based on a full depth base section and subtracted the thickness of
the payers. We estimate the paver and sand thickness will be 3 inches and 1 inch, respectively. The
sand should be properly vibrated to seat the paver blocks to reduce settlement potential of individual
blocks. Geocon Incorporated should be informed if the paver block thickness is less than 3 inches to
update the pavement section.
TABLE 5
PAVER PAVEMENT SECTION
Assumed Estimated Estimated Base
Location Assumed Subgride Paver Sand Material
Traffic Index R-Value Thickness Thickness Thickness
(Inches) (Inches) (Inches)
Private, Driveways 4.0 11 f 3'/s I 1 I 1 9%,
The payers should be located at least 5 feet from the planned residences. In addition, the subgrade
should be sloped to allow water to flow to a subdrain. The stibdrain should be placed at the bottom of
the base section along the low point of the driveway subgrade to reduce the potential for water to
build up within the pavement section. The drain should consist of a 4-inch diameter, perforated
Schedule 40, PVC pipe and placed adjacent to the concrete band. The drain should be connected to an
approved drainage device. Based on discussions with the project engineer from the City of Carlsbad,
Project No. 07671-52-02 -5 - March 30, 2012
Revised April 17,2012
an impermeable liner is required by the city such as a 12-mil HDPE or equivalent should be placed on
the sides and bottom of the base material. However, the impermeable liner is not a geotechnical
requirement as long as the subgrade soil' slopes to the subdrain. The subdrain shOuld be installed
along the low point of the base materials.
Prior to placing the impermeable liner (if required) and base materials, the subgrade soil should be
scarified, moisture conditioned as necessary, and recompacted to a dry density of at least 95 percent
of the laboratory maximum dry density near to slightly above optimum moisture content as
determined by ASTM D 1557. The depth of compaction should be at least 12 inches. Similarly, the
base materials should be compacted to a dry density of at least 95 percent of the laboratory maximum
dry density near to slightly above optimum moisture content.
Concrete paver installation should be performed in accordance with Interlocking Concrete Pavement
Institute (ICPI) guidelines. Stable edge restraints such as concrete bands and curbs are essential to
maintain horizontal interlock while the paver units are subjected to repeated vehicular loads. Concrete
edge bands or curbs should be incorporated into the concrete paver sections to maintain horizontal
interlock while the payers are subjected to vehicular loads. The payers should be installed and
maintained in accordance with the manufacturer's recommendations. The payers normally require a
concrete border to prevent lateral movement from traffic. The concrete border surrounding the payers
should be embedded at least 6 inches into the subgrade to reduce the potential for water migration to
the adjacent landscape areas and pavement areas. The payers should be placed tightly adjacent to
each other and the spacing between the paver units should be filled with polymer sand (Poly-Sand) to
help prevent the water infiltration. Contraction joints should be covered with a minimum of 12-inch-
wide woven geotextile strips to prevent sand loss wider concrete payers in accordance with the ICPI
guidelines.
The performance of pavement is highly dependent on providing positive surface drainage away from
the edge of the pavement. Ponding of water on or adjacent to the pavement will likely result in
pavemetit distress and subgrade failure. Drainage from landscaped areas should be directed to
controlled drainage structures. Landscape areas adjacent to the edge of asphalt pavements are not
recommended due to the potential for surface or irrigation water to infiltrate the underlying
permeable aggregate base and cause distress. Where such a condition cannot be avoided,
consideration should be given to incorporating measures that will significantly reduce the potential
for subsurface water migration into the aggregate base. If planter islands are planned, the perimeter
curb should extend at least 6 inches below the level of the base materials.
Project No. 07671-52-02 26 - March 30, 2012
Revised April 17, 2012
r
Should you have any questions regarding this report, or if we may be of further service, please
contact the undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Cri stianA.Li
Senior Staff Engineer GE 2714
CAL:SFW:vb:dmc
CIO
(3) Addressee 0
(email) Pangaea Land Consultants
Attention: Mr. Dale Mitchell
OF
Project No. 07671-52-02 -7- March 30, 2012
Revised April 17, 201