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Home My WebLink AboutCT 02-24; VILLAGES OF LA COSTA GREENS 1.11, 1.13, 1.14; PAVEMENT RECOMMENDATIONS COLDSTONE ROAD; 2004-12-27Cl- O2-'2-'- GEOCON INCORPORATED Project No. 06403-52-16A December 27, 2004 GEOTECHNICAL CONSULTANTS 0 John Laing Homes 6183 Paseo Del Norte, Suite 160 Carlsbad, California 92009 Attention: Ms. Liz Albano Subject: ..VILLAGES OF LA COSTA - THE GREENS NEIGHBORHOOD 14' GOLDSTONE ROAD STATION 9+00 TO 13+00 CARLSBAD, CALIFORNIA PAVEMENT RECOMMENDATIONS Dear Ms. Albano: In accordance with your request, we have performed supplemental geotechnical services for the subject roadway within Villages of La Costa - The Greens development. The scope of our services included obtaining representative subgrade soil samples within the street areas and performing Resistance Value (R-Value) tests. The purpose of our work was to provide pavement design recommendations. To aid in preparing this letter, we have reviewed the improvement plans entitled Improvement Plans for. La Costa Greens - Neighborhood 1. 11, 1. 13, 1.14, prepared by Hunsaker and Associates (Drawing No. 406-3), City of Carlsbad approval dated May 6, 2004, and our report entitled Update Geotechnical Report, Villages of La Costa - The Greens, Neighborhoods 1. 11, 1. 13, and 1. 14, Carlsbad, California, dated July 28, 2004 (Project No. 06403-52-16). Subgrade soils in the area are predominately sandy clays and silty sand, and typically exhibit relatively low R-Value characteristics. Based on field observations and previous laboratory tests, subgrade materials possess an expansion potential of "low" to "medium" (Expansion Index of 90 or less) as defined by Uniform Building Code (UBC) Table 18-I-B. R-Value laboratory tests were performed in accordance with ASTM D 2844-01 (California Test Method No. 301) and the laboratory test results are presented on Table I. Based on conversations with Hunsaker and Associates, the project civil, engineer, we understand that a Traffic Index (TI)6f.5:0 has been assigned to the Goldstone Road. Based on the above information and laboratory testing, we recommend the pavement sections indicated on Table II. Pavement section calculations were performed in accordance with California Department of Transportation Highway Design Manual; Section 608.4 and the City of Carlsbad Minimum Structural Standard GS-17. Pavement section calculations are presented on Figure 1. These recommended sections should be considered preliminary with final sections to be determined and approved by the City of Carlsbad. As indicated on Table I, the R-Value laboratory test results for Sample Nos.tR77añdR8 iefë1es ¶Iith 12 It is our understanding that the City of Carlsbad requires testing for lime treatment of subgrade soils when the R-Value is less than 12. Therefore, additional laboratory testing was performed to assess the actual amount of lime required to effectively treat the subgrade soils. We selected 'a sample of a similar soil type from an adjacent roadway section (Sample No. R-4, Goldstone Road) with the R-Value test result of 5. 6960 Flanders, Drive U San Diego, California 92121.2974 U Telephone (858) 558.6900 0 Fax (858) 558.6159 The laboratory test method was based on Texas Method; which consists Of performing a series of Plasticity Index (P1) tests at different lime contents until the PT stabilizes Table III shows the result of the P1 tests versus lime content. It' is our opinion that 3.5 percent Quick Lime by dry weight (or 4.5 percent hydrated lime) is required to stabilize clayey subgrade'. Supplemental R-Value testing of the• lime treated materials. shows that the R-Value increased to 70 Table IV provides alternative recomn'iendéd pavement sections thai incorprate a lime-treated subgrade. The minimum thickness of lime-treated subgrade is estimated to be 6 inches. It has been oir experience that lime treatment is most effective when used in situations where clays of "high" expansion potential (Expansion Index of 90 of higher) are present. Due to the presence of silty lands and clays with "low' to 'medium___expansion potential, (itTiñiiöiffOTh' 71 are recommending4he .implementation. of-th onalpavemenftion recommendations provided'on-T Prior to placing base material for roadways as well as curb and gutter, we recommend the upper 12 inches of subgrade be scarified, moisture conditioned as necessary, and compacted to a dry density of at least 95 percdnt of the laboratory maximum dry density near to slightly above optimum moisture content' in accordance with ASTM D 1557-02: In addition, the Class 2 aggregate base; should be , compacted to a dry density of at least 95 percent of the laboratory maximum dry density near to slightly above optini'um moisture content. Asphalt concrete should be compacted to a deiisity of at least 95 percent Of the laboratory Hveem density in accordance with ASTM. D 2726-00. The upper 12 in'hes of subgrade beneath areas to receive concrete sidewalks should be 'compacted to a dry density of 90 percent of the laboratory maximum 'dry density near to slightly above optimum moisture content. Fill soil and base lift thickness should not exceed 6.inches. Class 2 aggregate base and asphalt concrete should conform to the City of Carlsbad specifications. The performance of asphalt concrete pavement is highly dependent on providing positiie surface drainage away' from the edge of the pavement. Ponding of water 'on 'or adjacent to the pavement will likely result in pavement distress and subgrade failure. To reduce the occurrence for such situations, we recommend that a minimum drainage gadient of 1 percent be maintained for pavement surfaces. Drainage form landscaped areas should be directed to controlled drainage structures. Should you have any questions regarding this correspondence, or if we may be of further' service, please contact the undersiged at your convenience. Very truly yours, GEOCON iNCORPORATED ; ?9'°S/o . 2 ,.'Ro Ui Exp. 6130106 Shane Rodacker CC rn RCE 63291 VIL (2) Addressee . .'. (1) Hunsaker and Associates Attention: Mr. David Blalock (3/del) John Laing Homes % Devenco; La Costa Greens Jobsite Attention: Mr. Will Bigler Project No. 06403T5216A -2 - December 27, 2004 TABLE I SUMMARY OF R-VALUE TEST RESULTS ASTM D 2844-01 (CALIFORNIA TEST METHOD NO. 301) Sample No. Location R-Value R-7 Goldstone Road - Station 9+00 to. 11+00 8 R-8 Goldstone Road - Station 11+00 to 13+00 5 (11) (inches) / - (inches) Goldstone Road - Station 9+00 to 11+00 5.0 4 ;Vg Goldstone Road -Station 11+00 to 13+00 5.0 4 \ 8 TABLE III' SUMMARY OF PLASTICITY INDEX VS. LIME CONTENT SAMPLE NO. R-4 - GOLDSTONE ROAD Plasticity Index (Fl) Percent Lime 29 0 22 . . 3 19 4 18 . . 5 16 6 TABLE IV ALTERNATIVE PAVEMENT SECTION RECODAfI -4E-TREATED SUBGRADE Lraffic Asphalt Class 2 Minimum Location Concrete Aggregate Lime-Treated inches) Base Subgrade (inches) . (inches) Goldstone Road - Station 9+00 t.H0 5.0 4 4 6 Goldstone Road - Station p.'56to 13+00 5.0 4 6 TABCE 11 PAVEMENT SECTION RECOMMENDATIONS Traffic Index Asphalt Concretl Location ,,..,. I ... . i Aggregate Base Class 2 / Project No. 06403-52-16A . December 27, 2004 FIGURE 1 PAVEMENT SECTION CALCULATIONS VILLAGES OF LA COSTA - THE GREENS Goldstone Road - Station 9+00 to 11+00 Use subgrade R-Value = 8.0 Traffic Index (TI) =- 5.0 Methodology = Caltrans HighwayDesign Manual Section 608.4 Safety Factor = 0.2 - Applied to Asphalt Concrete (AC) GE for AC = (0.0032)(5.0)(100-78.0)+0.2 = .55 feet from Table 608.4B Highway Design Manual GE = .55 feet for AC yields actual thickness = 2.65 inches Use 4.0 inches of AC - City Minimum y GE for 4.0 inches of AC =.83 feet GE for base = (0.0032)(5.0)(100- 8.0) - .83 = .64 feet from Table 608.4B Highway De Manual with GF for Class 2 base = Base thickness = 6.97 inches' Use base thickness = 7.0 inches Design Street Structural Section Asphalt Concrete Thickness= 4.0 inches Class 2 Aggregate Base Thickness =00 inches. B' Goldstone Road - Station 11+00 to 13+00 Use subgrade R.-Value = 5.0 Traffic Index (TI) = 5.0 Methodology = Caltrans Highway Design Manual Section 608.4 Safety Factor = 0.2 - Applied to Asphalt Concrete (AC) GE for AC = (0.0032)(5.0)(100-78.0)+0.2 = .55 feet from Table 608.4B Highway Design Manual GE = .55 feet for AC yields actual thickness = 2.65 inches Use 4.0 inches of AC - City Minimum GE for 4.0 inches of AC = 83 feet GE for base = (0.0032)(5.0)(100- 5.0) - .83 = .69 feet from Table 608.4B Highway Design Manual with GF for Class 2 base = 1.1 Base thickness = 7.49 inches Use base thickness = 8.0 inches *** Design Street Structural Section Asphalt Concrete Thickness = 4.0 inches. Class 2 Aggregate Base Thickness = 8.0 inches. Project No. 06403-52-16A December 27, 2004