HomeMy WebLinkAboutCT 13-03; ROBERTSON RANCH WEST VILLAGE; PRELIMINARY PAVEMENT DESIGN; 2015-04-24LGC Valley, Inc.
Geotechnical Consulting
April 27, 2015 Project No. 133023-03
Mr. Kevin Brickley
Toll Bros., In
725 W. Town and Country Road, Suite 200
Orange, California 92868
Subject: Preliminary Pavement Design, Robertson Ranch, Carlsbad Tract No. 13-03, 4980 El
Camino Real, Carlsbad, California
References: Carlsbad, City of 2012, Engineering Standards, Volume 1 - General Design Standards,
Carlsbad, California, 2004 Edition, revised November 21, 2012
O'Day Consultants, 2015, Improvement Plans for Rancho Costera, Robertson Ranch
West Village, Carlsbad Tract No. 13-03, Carlsbad, California, Drawing No. 480-3,
111 Sheets, dated January 27, 2015
Introduction
In accordance with your authorization, LGC Valley, Inc. (LGC) has been performing geotechnical
observation and testing services during the development of the Robertson Ranch project located in
Carlsbad, California. This letter has been prepared to provide preliminary pavement design
recommendations for the streets within Robertson Ranch. It should be noted that the actual pavement
sections for the streets within Robertson Ranch will need to be based on R-value testing of the street
subgrade soils after the installation of underground utilities and in accordance with the City of Carlsbad
ôriteria.
or-
The following preliminary pavement sections are based on four preliminary R-Value tests of representative
street subgrade soils at the site; our review of the available improvement plans (which provides the proposed
Traffic Index for each street); the City of Carlsbad minimum standards for street pavement sections; and our
professional experience (both on the Robertson Ranch project and on similar projects within the City of
Carlsbad) with respect to the anticipated R-value range of the soils that may be present at the street subgrade
elevations.
We anticipate that the RValue test results of the street subgrade soils will likely range from less than 5 to 25.
The actual R-value of the Street subgrade soils will depend upon the type of soil placed in the upper 3 to 5 feet
of the street subgrade elevation. It should also be noted that a lime-treated subgrade/aggregate base
material/asphalt concrete section design is required by the City of Carlsbad for streets having an R-value of
12 or less.
2420 Grand Avenue, Suite F2, • Vista • CA 92081 9 (760) 599-7000 • Fax (760) 599-7007
Based on the project improvement plans (O'Day Consultants, 2015) and the city requirements (Carlsbad,
2012) we understand that:
West Ranch Street has a Traffic Index (TI) of 8.5 and a minimum pavement section of 5 inches of Asphalt
Concrete (AC) over 6 inches of Aggregate Base (AB);
The 60-foot wide collector streets have a TI of 6.0 and a minimum pavement section of 4 inches of AC
over 6 inches of AB;
The 60-foot wide residential streets have a TI of 6.0 and a minimum pavement section of 4 inches of AC
over 4 inches of AB; and
The 56-foot wide cul-de-sac streets have a TI of 4.5 and a minimum pavement section of 4 inches of AC
over 4 inches of AB.
Laboratory R- Value TestinR
Representative street subgrade soils were collected, at four locations across the site, and R-value testing was
performed on the samples. The resistance or "R"-value was determined by the California Materials Method
No. 301 for subgrade soils. The test results summarized in the table below:
Table 1
R-Value Test Results
Sample Number Sample Location Sample Description R-Value
R-1 West Ranch Street (Station 15+50) Light gray brown clayey to 11 silty fine SAND
R-2 Robertson Road (Station 26+00) Light gray clayey to silty 10 fine SAND
R-3 Wadsworth Street (Station 12+00) Light brown silty Fine 23 SAND
R-4 Gage Street (Station 30+00) Medium Olive clayey 7 SILT to silty CLAY
Preliminary Typical Pavement Design Recommendations
Based on the Traffic Indices and the R-Value test results presented above, we recommend the following
minimum pavement sections. The calculations for the pavement design sections were performed using the
computer program, NEWCON90 and is in accordance with Chapter 600 of the California Highway Design
Manual. The designs were then compared with the City of Carlsbad's minimum section thickness
requirements and revised as necessary. The pavement sections are presented on Table 2.
Project No. 133023-03 Page 2 April 27, 2015
Table 2
Preliminary Minimum Pavement Design Sections Based on Assumed RVaIues*
Traffic Minimum
Pavement Sections*
Street*** Index Section*
R-Value R5** R-Value R10** R-Value R=20**
Major Arterial 5.0 inches AC 5.0 inches AC 5.0 inches AC 5.0 inches AC
- -
LWest RanCh Strt 8.5 over over over over
6.0 inches AB 20.0 inches AB 18.0 inches AB 15.0 inches AB
60-Foot Wide Collector Streets 4.0 inches AC 4.0 inches AC 4.0 inches AC 4.0 inches AC
'Gage Drive (Sta. 10+50 to 17+10 6.0 over over over over
Robertson Road (Sta. 27+00 to 34+25) 6.0 inches AB 11.0 inches AB 10.5 inches AB 8.0 inches AB
60-Foot Wide Residential Streets
______
asgo
Wadsworth Street
3lw Drive (Sta. 11+45 to
Glasgow Drive (Sta. 30+00 to 38+54)
Wellspring Street (Sta. 10+00 to 23+35)
ellspring Street (Sta. 23+35 to 38+54) 4.0 inches AC 4.0 inches AC 4.0 inches AC 4.0 inches AC ::Gage Street (Sta. 17+10 to 33+40),"over over over over Robertson Road (Sta. 10+40 to 3+05 6.0 4.0 inches AB 11.0 inches AB 10.5 inches AB 8.0 inches AB 17+00 to 27+00) _and
Borden Court (Sta. 13+60 to 18)
Portola Court (Sta. 12+25 to 15+58)
Nelson Court (Sta. 13+60 to 17+11)L
Paz Court (Sta. 13+50 to 16+58)
EdinburghDiiy
56-Foot Wide Cul-de-Sac Streets
Frai1b1azer Wa______
Borden Court (Sta. 9+60 to 13+60
re pi Court (Sta. 9+60 to 12+75 andi 4.0 inches AC 4.0 inches AC 4.0 inches AC 4.0 inches AC 13+30 to 17+65) 4.5 over over over over Kentner Court (Sta. 9+60 to 12+15 and 4.0 inches AB 6.0 inches AS 5.0 inches AS 4.0 inches AB Sta. 12+50 to 16+35)
chase Court (Sta. 9+60 to 11+50 and S
72+00 to 14+15)
Portola Court (Sta. 9±60 to 12+25)
Nelson Court (Sta. 9+60 to 13+60)
La Paz Court (Sta. 9+60 to 13+50)
* AC = Asphalt Concrete; AS = Aggregate Base
** Anticipated street subgrade R-Values based on the preliminary R-Value testing and our professional experience on the project
*** Streets are color-coded according to the likely pavement section based on the preliminary R-Value testing and our professional experience
on the project
Project No. 133023-03 Page 3 April 27, 2015
Prior to placement of the street aggregatejbase material, the upper 12 inches of subgrade soils in the street
(including beneath the curb and gutter) sl®kI be scarified, moisture-conditioned (or dried back) as necessary
to at least optimum moisture content and compacted to a minimum 95 percent relative compaction based on
American Standard of Testing and Materials (ASTM) Test Method D1557.
Class 2 Aggregate Base should then be placed and compacted at a minimum 95 percent relative compaction
in accordance with ASTM Test Method D1557. The aggregate base material should be a maximum of 6
inches thick (or equal to the thickness of aggregate base for the design pavement section if less than 6 inches)
below the curb and gutter and extend a minimum of 6 inches behind the back of the curb (per the city
requirements). The Class 2 Aggregate Base should conform to and be placed in accordance with the latest
revision of the California Department of Transportation Standard Specifications (Section 26), the Greenbook
specifications, and/or the City of Carlsbad requirements. Asphalt Concrete should conform to and be placed
in accordance with the "Greenbook" Standard Specifications for Public Works Construction and the City of
Carlsbad requirements.
If pavement is planned adjacent to landscaped areas, we recommend that appropriate measures be taken (such
as keeping the amount of landscape irrigation to a minimum, installing area drains or other devices, etc.) to
reduce the possible adverse effects of water on the pavement subgrade.
Preliminary Minimum Pavement Desi2n Sections Utiizi, Lime-Treated Subgrade Soils
The following pavement design recommendations utilizing a lime-treated subgrade section are provided in
accordance with the City of Carlsbad guidelines. Based on our experience with similar soils on nearby sites
within the City of Carlsbad, soils having an R-Value of less than 12 typically require an optimum hydrated
lime content between 4 to 6 percent and subsequent testing of the lime-treated samples results in minimum R-
Values in the range of 60 to 80+. The actual percentage of lime should be determined during the final
pavement section evaluation based on ASTM Test Method C977 and the city requirements. The City of
Carlsbad requires a minimum lime-treated subgrade thickness of 8 inches.
Based on the above information, the preliminary lime-treated pavement sections were calculated using the
computer program, NEWCON90 and in accordance with Chapter 600 of the California Highway Design
Manual and compared with the City of Carlsbad's minimum section thickness requirements. The lime-treated
pavement sections are presented on Table 3.
Project No. 133023-03 Page 4 April 27, 2015
Table 3
Preliminary Lime-Treated Subgrade Pavement Sections Based on Assumed R'Ialues*
Traffic Assumed AC Class 2 Base Lime Treated
Street Index R Value** Thickness Thickness Subgrade Layer
(inches) (inches) (inches)
Major Arterial 8.5 60 5 4 13 West Ranch Street
60-Foot Wide Collector Streets
Gage Drive (Sta. 10+50 to 17+ 10) 6.0 60 5 0 12
Robertson Road (Sta. 27+00 to 34+25)
60-Foot Wide Residential Streets
Glasgow Drive (Sta. 30+00 to 38+54)
Wellspring Street (Sta. 23+35 to 38+54)
Gage Street (Sta. 17+10 to 33+40)
Robertson Road (Sta. 10+40 to 13+05 6.0 60 5 0 12 and 17+00 to 27+00)
Borden Court (Sta. 13+60 to 18+22)
Portola Court (Sta. 12+25 to 15+58)
Nelson Court (Sta. 13+60 to 17+11)
La Paz Court (Sta. 13+50 to 16+58)
Edinburgh Drive
56-Foot Wide Cul-de-Sac Streets
Trailblazer Way
Borden Court (Sta. 9+60 to 13+60)
Crespi Court (Sta. 9+60 to 12+75 and Sta.
13+30t017+65) 4.5 60 4 0 8 Kentner Court (Sta. 9+60 to 12+15 and
Sta. 12+50 to 16+35)
Chase Court (Sta. 9+60 to 11+50 and Sta.
12+00 to 14+15)
Portola Court (Sta. 9+60 to 12+25)
Nelson Court (Sta. 9+60 to 13+60)
La Paz Court (Sta. 9+60 to 13+50)
* AC = Asphalt Concrete; AB = Aggregate Base; LTS = Lime-Treated Subgrade
** Anticipated Street subgrade R-Values are based on our professional experience with similar projects where lime-treated
subgrade soils were utilized as part of the pavement section; and with an assumed Unconfined Compressive Strength of
400psi
Prior to placement of the asphalt concrete and Class 2 Aggregate Base, the subgrade soils (including beneath
the curb and gutter) should be scarified, moisture-conditioned to at least optimum moisture content, and
thoroughly mixed with 4- to 6-percent quick lime (or an equivalent percentage of hydrated lime-slurry) to the
depth recommended in Table 3. After setting for a minimum of 24 hours, the thoroughly mixed lime-treated
subgrade soils should be compacted to a minimum 95 percent relative compaction based on ASTh4 Test
Method D1557. After the minimum 95 percent relative compaction is achieved for the lime-treated subgrade
soils, we recommend that a curing compound be applied to the surface of the lime-treated subgrade soils and
the materials allowed to cure.
Project No. 133023-03 Page 5 April 27, 2015
After the completion of the curing period, Class 2 Aggregate Base, where designed, should then be placed
and compacted at a minimum 95 percent relative compaction in accordance with ASTM Test Method D1557.
The aggregate base material should extend below the curb and gutter (where base is in the design pavement
section) and extend a minimum of 6 inches behind the back of the curb. After the placement and compaction
of the Class 2 Aggregate Base, a minimum of 4 or 5 inches of asphalt concrete should be placed.
Asphalt Concrete, Aggregate Base, and lime-treated subgrade soils should conform to and be placed in
accordance with: I) the latest revision of the California Department of Transportation Standard
Specifications; 2) in accordance with State of the Art Report 5, Lime Stabilization of the Transportation
Research Board, National Research Council; 3) the "Greenbook" Standard Specifications for Public Works
Construction (Sections 203 and/or 400); and/or 4) the City of Carlsbad requirements.
Portland Cement Concrete (FCC) Pavement Section
The gradient of a portion of Robertson Road between Stations 13+05 to 17+00 is greater than 10 percent; and
consequently, the street pavement section is required to be a Portland Cement Concrete (PCC) pavement
section (per City of Carlsbad criteria). Based on an assumed R-Value of 5 and a TI of 6, we recommend a
minimum of 8-inches of Portland cement concrete over 6-inches of compacted aggregate base. The modulus
of rupture of the concrete should be a minimum of 500 pounds per square inch (psi) at 28 days. Contraction
joints should be placed at maximum 15-foot spacings. Where the outer edge of a concrete pavement connects
to an asphalt pavement, the concrete slab should be thickened by 50 percent at a taper not to exceed a slope of
1 in 10. In addition, additional sections can be provided based on other desired anticipated traffic loadings.
Aggregate base should conform to the requirements of the latest edition of the Standard Specifications for
Public Works Construction ("Greenbook"). Aggregate base should be compacted to a minimum of 95
percent relative compaction over subgrade compacted to a minimum of 95 percent relative compaction per
ASTM- D1557.
Limitations
Our services were performed using the degree of care and skill ordinarily exercised, under similar
circumstances, by reputable engineers and geologists practicing in this or similar localities. No other
warranty, expressed or implied, is made as to the conclusions and professional advice included in this letter
report.
This letter report is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are
taken to see that the contractor and/or subcontractor properly implements the recommendations in the field.
The contractor and/or subcontractor should notify the owner if they consider any of the recommendations
presented herein to be unsafe.
The findings of this report are valid as of the present date. However, changes in the conditions of a property
can and do occur with the passage of time, whether they be due to natural processes or the works of man on
this or adjacent properties.
Project No. 133023-03 Page 6 April 27, 2015
Closure
If you should have any questions, please do not hesitate to contact us. The undersigned can be reached at
(661) 702-8474.
Respectfully submitted,
LGC Valley, Inc.
Owo-~'
Randall Wagner, CEG 1612
Senior Project Geologist
94-
Basil Hattar, GE 2734
Principal Engineer
Distribution: (1) Addressee (via e-mail)
Project No. 133023-03 Page 7 April 27, 2015