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Home My WebLink AboutCT 02-24; VILLAGES OF LA COSTA GREENS 1.11, 1.13, 1.14; PAVEMENT RECOMMENDATIONS AMMONITE PLACE AND GALENA ROAD; 2004-12-06Cl 02-24 GEOCON INCORPORATED Project No. 06403-52-16A December 6, 2004 GEOTECHNICAL CONSULTANTS f 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 1.13 AMMONITE PLACE STATION 10+00 TO 15+60 GALENA ROAD STATION 20+63 TO 22+00 CARLSBAD, CALIFORNIA PAVEMENT RECOMMENDATIONS Dear Ms Albano: In accordance with your request, we have performed supplemental geotechnical services for the subject roadway alignments 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) of 5.0 has been assigned to the roadway alignments. It should be noted that a portion of Galena Road was paved during the construction of Alicante Road. Based on discussions with the City of Carlsbad construction inspector, the pavement section for the subject section of Galena Road should match that of the existing portion. 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 gimICNoS.-k- I and R-2 were less fthãn 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 neighborhood (Sample No. R-4, Goldstone Road from Neighborhood 1.14) with the same R-Value test result of 5. 6960 Flanders Drive 0 San Diego, California 92121-2974 0 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 (PT) tests at different lime contents until the P1 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 recommended pavement sections that incorporate a lime-treated subgrade. The minimum thickness of lime-treated subgrade is estimated to be 6 inches. It has been our experience that lime treatment is most effective when used in situations where clays of "high" expansion potential (Expansion Index of 90 or higher) are present. Due to the presence of silty sands and clays with "low" to "medium" expansion potential, it is our opinion, from a geotechnical 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 II. 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 percent 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 optimum moisture content. Asphalt concrete should be compacted to a density of at least 95 percent of the laboratory Hveem density in accordance with ASTM D 2726-00. The upper 12 inches 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 positive 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 gradient 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 undersigned at your convenience. Very truly yours, GEOCON INCORPORATED LC Michael C. Ertwine Staff Geologist MCE: SR: dmc RCE 63291 (2) Addressee (1) Hunsaker and Associates Attention: Mr. David Blalock (3/del) John Laing Homes Cf Devenco; La Costa Greens Job Site Attention: Mr. Will Bigler Project No. 06403-52-16A - 2 - ' December 6, 2004 S TABLE I SUMMARY OF R-VALUE TEST RESULTS ASTM D 2844-01 (CALIFORNIA TEST METHOD NO. 301) Sample No. Location R-Value R-1 Ammonite Place Station 10+00 to 13+00 10 R-2 Ammonite Place Station 13+00 to 15+60 5 TABLE II PAVEMENT SECTION RECOMMENDATIONS - CONVENTIONAL Traffic Index Asphalt Class 2 Location (TI) Concrete Aggregate Base (inches) (inches) Ammonite Place Station 10+00 to 13+00 5.0 4 7 ' Ammonite Place Station 13+00 to 15+60 5.0 4 8 Galena Road Station 20+63 to 22+00 5.0 4 -S TABLE III SUMMARY OF PLASTICITY INDEX VS. LIME CONTENT SAMPLE NO. R-4 - GOLDSTONE ROAD Plasticity Index (P1) Percent Lime 29 . 0 22 3 19 4 18 5 16 6 TABLE IV ALTERNATIVE PAVEMENT SECTION RECOMMENDATIONS LIME-TREATED SUBGRADE Traffic Asphalt Class 2 Minimum Location Index Concrete . Aggregate Lime-Treated (TI) (inches) Base Subgrade (inches) (inches) Ammonite Place Station 13+00 to 15+60 5.0 . 4 4 6 Project No. 06403-52-16 A December 6, 2004 FIGURE 1 PAVEMENT SECTION CALCULATIONS VILLAGES OF LA COSTA- THE GREENS Ammonite Place - Station 10+00 to 13+00 Use subgrade R-Value = 10.0 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)(100-100) - .83 = .61 feet from Table 608.4B Highway Design Manual with GF for Class .2 base = 1.1 Base thickness = 6.62 inches Use base thickness = 7.0 inches Design Street Structural Section *** Asphalt Concrete Thickness = 4.0 inches. Class 2 Aggregate Base Thickness = 7.0 inches. Ammonite Place - Station 13+00 to 15+60 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)+02 =.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 6, 2004