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Home My WebLink AboutCT 02-14; BRESSI RANCH RESIDENTIAL; RESPONSE TO CITY OF CARLSBAD REVIEW COMMENTS CONCERNING; 2004-12-274 cf 61 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY December 27, 2004 Project No. 971009-024 To: City of Carlsbad Public Works - Engineering 5950 El Camino Real Carlsbad, California 92008 Attention: Mr. Donald Moore Subject: Response to City of Carlsbad Review Comments Concerning the Pavement Design Recommendations for a Portion of Plumeria Drive, Live Oaks Drive, and Arches Way, Planning Area PA-12, Bressi Ranch, Carlsbad, California lntTpdurtjpp This letter presents our response to the City .of Carlsbad review comments (Carlsbad City, 2004b) concerning the asphalt concrete (AC) pavement design recommendations for a portion of Plurneria Drive, Live Oaks Drive, and Arches Way, within Planning Area PA-12 of the Bressi Ranch project, located in Carlsbad, California. While we have not received a copy of the review comments concerning the Alleys within Planning Areas PA-7 and PA-8 of the Bressi Ranch project, we understand the City of Carlsbad has similar concerns. Our review of the Bressi Ranch Improvement Plans indicates that Plumeria Drive, Live Oaks Drive, and Arches Way within Planning Area PA-12 have a Traffic Index of 6, while the alleys of Planning Areas PA-7 and PA-8 have a Traffic Index of 5. Based on a conversation on December 23, 2004 with Eduardo Cardena of Project Design Consultants, the City of Carlsbad assigned the traffic indexes presented on the Improvement Plans. Prior to our work at the Bressi Ranch project, our pavement design recommendations for projects within the City of Carlsbad were determined by using the Caltrans 20-year pavement design calculations and the City of Carlsbad minimum AC and aggregate base (AB) material thicknesses (Carlsbad, 1996). However, during the initial sfreet section grading operations for the Bressi Ranch project, we were told we had to base our pavement recommendations on the minimum structural sections provided on the City of Carlsbad Drawing GS-17. Consequently, all subsequent pavement section design letters (including the two letters pavement design letters for Plumeria Drive, Live Oaks Drive, and Arches Way"'[Leighton, 2004b] and for Alleys 'T', 'X', 'Y', 'ZZ', and 'W' within 3934 Murphy Canyon Road, Suite B205U San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 971009-024 Planning Areas PA-7 and PA-8 [Leighton, 2004a]) used Drawing GS-17 to determine the pavement section design recommendations. Although the Drawing GS- l 7 omits any design thicknesses for R- Values of less than 8, we were directed by the City of Carlsbad to add an additional inch to the thicknesses provided for an R-Value of 8. With respect to our conclusions in our Bressi Ranch pavement design recommendation letters that always recommended that the AC and AB section be used instead of the lime-treated subgrade soil design; the unl.y reason we even mention a lime-treated design is because the City of Carlsbad Standards indicate we have to provide a lime-treated design if the subgrade soils have an R-Value of less than 12. As far as we are aware of, the City of Carlsbad is the only city in San Diego County where a lime-treated subgrade design is ever considered. If we didn't have to provide a lime-treated design, I can't think of any significant reason that would dictate the use of a lime-treated design. Finally, it has been our experience that the added cost, longer construction period (due to the need to have the lime-treated soils cure), and uncertainties involved with the lime-treated processing of the subgrade soils (not to mention the unfamiliarity of the paving contractors with constructing a lime-treated section) all make it pretty easy to conclude that a lime-treated section is not in the best interest of all parties involved with the design, construction, and maintenance of the street pavement section. Recommended and CaIruptrj Payemant Section Dcignc With respect to the review comment• concerning the justification of our recommended pavement sections (Carlsbad, 2004b), we have provided our pavement design calculations in Appendix B. The pavement section designs presented include a number of different traffic indexes for subgrade soils having an R-Value of 5, 22, and 25. Where necessary, the thicknesses were adjusted to meet the minimum City of Carlsbad AC and AB thicknesses (i.e. a minimum of 4 inches of AC and a minimum of 4 or 6 inches of AB). As noted in Appendix B, the calculated pavement section for a traffic index of 6 and an R-Value of 5 (used for the design of the recommended pavement sections for Plumeria Drive, Live Oaks Drive, and Arches Way) is 4 inches of AC over 12 inches of A.B. This is less than the recommended section presented in our letter dated December 20, 2004 (Leighton, 2004b) of 4 inches of AC over 14 inches of AB (based on adding 1-inch of AB to the thickness for an R-value of 8 shown on Drawing GS-17). The calculated pavement section for the alleys having a traffic index of 5 and an R-Value of 22 is 4 inches of AC over 5 inches of AB while the calculated pavement section for the alleys having a traffic index of 5 and an R-Value of 25 is 4 inches of AC over 4 inches of AB. Both of these -2- Leighton 971009-024 calculated pavement sections are the same as the sections recommended in our letter dated December 17, 2004 (Leighton, 2004a). : Cnnrhiipfl Based on our additional analysis performed as part of our response, it is our professional opinion that the conclusions and recommendations resented in the two pavement recommendations letters for Plumena Drive, Live Oaks Drive, ,and Arches Way (Leighton, 2004b) and for Alleys 'T', 'X', 'Y', 'ZZ', and 'W' within Planning Areas PA-7 and PA-8 (Leighton, 2004a) are still considered valid and applicable for the construction of the subjecf streets and alleys If you have any questions regarding our letter, please contact this office We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. 4 'Mi K Ran a r, EG 1612 Senior Associate ED Gco K<OQ Q ) 1612 Attachments: Appendix A - References I ( CERTIFIED Appendix B -Pavement Design Calculations ENGINEERING GEOLOGIST 1' Distribution: (2) Addressee - (2) Lennar Communities, Attention Mr. Sean Scholey (1) Lennar Communities, Attention: Mr. Steve Hansen )9 3.31 -I Leighton APPENDIX A Reference Carlsbad, City of, 1996, Standards for Design and Construction of Public Works Improvements in the City of Carlsbad, California, Project No 05332-12-01, dated April 20, 1993, revised December 10, 1996. 2004a, City of Carlsbad Engineering Standards, Volume 1 - General Design Standards, 2004 Edition 2004b, Pavement Section Design Recommendations for a Portion of Plumena Drive, Live Oaks Drive, and Arches Way, Planning Area PA-12, Bressi Ranch, Carlsbad, California, dated December 22, 2004. Leighton and Associates, 2004a, Pavement Section Design Recommendations for Alleys 'T', 'X', 'Y', 'ZZ', and 'W', Planning Areas PA-7 and PA-8, Bressi Ranch, Carlsbad, California, Project No. 971009-030, dated December 17, 2004. 2004b, Pavement Section Design Recommendations for a Portion of Plumena Drive, Live Oaks Drive, and Arches Way, Planning Area PA-12, Bressi Ranch, Carlsbad, California, Project No. 971009-024, dated December 20, 2004. 4, Leighton :TRAFFIcINpEx. 4.5 5. 6 7 8, 1' SUBORADE R VALUE 5 5 5 5 5 SUBBASE R VALUE 5 5 5 5 5 CRUSHED AGG BASER VALUE 78 78 78 78 78 `STRUCTURAL CALCULATIONS REQUIRED GE TO AL 1.368 —1.520, 1.824 2.128 2.432 AC GRAVEL FACTOR 2 54 2.54 2.32 2 14 2.01 GEAC 0317 0352 .0.422 6.493 0.563 GEAC+SF 0.517 0.552 0622 0.693 0.763 THICK.NESSAC 2.442 2.608 3.219, 3 885 4.556 DESIGN THICKNESSAC . 40 40 40 40 5.0 GEDESIGNAC 0847 ., 0.847 0.773 0713 0838 GEBASE 0.521 0.673 1 051 A.415 1595 BASE GRAVEL FACTOR 11 11 11 11 11 THICKNESSBASE 5.687 7345 11 462 15.433 17.395 DESIGN THICKNESSBASE 6.0 8.0-1 120 160 18.0 DESIGN SECTIONS 4 41 AC 4.0 in 4.0 in 4.0 in 4.0 in CRUSHED AGGREGATE BASE 60 in 80 in 120 in 160 in 5.01 in 180 in - - . 0, - S 4 t 4 4 I- t -- I - - 0 0 • 0•,• * 4 4 .5. 0 0 • a. - 0 £ 0 Bi * I 4.5 5 6 25 .25 25. 25 25 25 !- 78 78 78 971009-024 4- 4 . 4 p4 - .. - - - -, •, Appendix B Caltrans 20-Year Asphalt Pavement Sction Design Calculation • -, .• for Asphalt Concrete and Aggregate Base Material Section Based on Different Traffic Indexes and a Subgrade Soil R-Values of 22 and 25 • DESIGN INPUT •. __________________________ SUBBASE R-VALUE - * CRUSHED AGG BASE R-VALUE STRUCTURAL CALCULATIONS REQUIRED GE.-TL t . . 1.123 ,. 1.248 1.498 - - 1.080 1.200 1.440 ,AC GRAVEL FACTOR - 2.54 2.54 , 2.32 ' 2.54 2.54 2.32 - GEAC 0.317 0.352 0.422 0.317 0.352 0.422 GE1+ SF 0.517 . 0.552 0.622 0.517 0.552 0.622 THIçKNESSAC- - 2.442 2.608 3.219 2.442 2.608 - 3.219 - DESIGN THICKNESSAc 4.0 ___4.0 ___4.0 .4.0 _I . GE D IAC . . • 0.847 ' 0.847 0.773 , . 0.847 0.847 0.773 . GEBASE • . 0.277 0.401 0.724 0.233 0.353 0.667 BASE GRAVEL FACTOR 1.1 1.1 1.1 :- 11 1. F . 1.1'• THICKNESSBASE 3.017.4.378 _•7.901 2.545 __3.855 _-7.273 -. DESIGNTFIICKNESSBASE . I_I_8.0 I. 4.0 __4.0, _.._8.0 DESIGN SECTIONS " . •AC 4.0 in 4.0 in ' 4.0 in 4.0 in 4.0 in CRUSHED AGGREGATE BASE 4.0 in _ 5.0 in _40in _8.0 in . 4.0 in _4.0 in _8.0 in - - 4 .. ,i. - _4- -, - .' 4 - . - 4 - -. . .4 ç 4 . . . . . 5 . I - - •- - . I . . - - • . . . -- 1 - . •- , •• . . 4 4 4 • . - - . . I- - . I • - II . - - - •' . . - .-. --. - . : .'4 - _•(•'_ ,*- -,- I • . I - -4 B-2 • . - - I, , - - - TRAFFIC INDEX 4.5 • 5 6 SUBGRADE R-VALUE 22 22 - 22 22 22 22 78 78 78 -