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HomeMy WebLinkAboutCT 90-03; SHELLEY PROPERTY; GEOTECHNICAL REPORTS; 2003-03-14> RECEIVED [ 2'IM 1 CITY OF CARLSBAD Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY March 14, 2003 Ch I Lir 8511855-011 iPRC'JD To: Continental Homes D Ns 5927 Priestly Drive, Suite Carlsbad, California :8200 41 Attention: Mr. Dave Lother Subject: Toe-of-Slope Subdrain Recommendations, West Side of Rancho Santa Fe Road Between Station No. 29+58 and 40+00, Arroyo Vista, Carlsbad, California In accordance with the request of representatives of the City of Carlsbad and Continental Homes, we have been performing geotechnical observation and testing services during the construction of improvements on a portion of Rancho Santa Fe Road located in Carlsbad, California. This letter summarizes our geotechnical observations of the existing conditions and provides our recommendations concerning the installation of a subdrain along the toe-of-slope on the west side of Rancho Santa Fe Road between approximate Station No. 29+58 and 40+00. We understand that groundwater seepage conditions are occurring along the western side of Rancho Santa Fe Road south of Calle Acevo. Based on our geotechnical observations, it appears that groundwater seepage along the toe of the existing east-facing fill soil is saturating the parkway and street aggregate base and subgrade soils. Saturated street subgrades were present during the grading and construction of the new street pavement section, which resulted in the overexcavation and replacement of some of the Street subgrade soils. Continued seepage is likely to saturate the new pavement section and may cause future distress of the asphalt concrete pavement section. As a result, a subdrain system placed adjacent to the toe-of-slope should be installed to intercept the ground water and reduce the potential saturation of the street aggregate base and subgrade soils. The recommended subdrain system should consist of a 4-inch diameter perforated PVC pipe installed (holes down) in a trench having a minimum fall of at least 1-percent toward the outlet location. Due to possible conflicts with existing underground utility lines, the subdrain may have to be placed right at the toe-of-slope rather than closer to the street. The trench should have a minimum depth of 4 feet and a minimum width of 12 inches. The trench should be backfilled to 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 851855-011 within 6 inches of the ground surface with clean 3/4-inch gravel wrapped in filter fabric (Mirafi 140N or equivalent). The subdrain outlet or "tightline" should consist of a 4-inch solid PVC pipe. The upper end of the subdrain should start at Station 40+00 and should be outletted into the existing storm drain inlet box at Station No. 29+58. The solid "tightline" pipe should also have a minimum 1-percent fall toward the outlet location. The approximate location of the recommended subdrain system is presented as Figure 1. A typical detail of the subdrain construction is presented as Figure 2. We also recommend that three clean-outs be placed along the subdrain system at the high point (i.e. at Station No. 40+00), at the halfway point of the subdrain (i.e. at approximate Station No. 35+00), and where the perforated pipe transitions into solid pipe. The clean-outs should consist of a capped solid pipe placed vertically from the subdrain pipe to the ground surface. A concrete cutoff wall should also be constructed where the perforated pipe transitions to a solid tight-line pipe. The cutoff wall should have a minimum width of 6 inches, be notched 6 inches into the bottom and sides of the trench wall, and extend at least 12 inches above the top of the pipe. Between the cutoff wall and the outlet point, solid (non-perforated) pipe should be utilized. The outlet location, subdrain pipe, and clean-outs should be surveyed by a civil engineer to ensure the subdrain outlet pipe has the minimum fall of 1- to 2-percent. We also recommend that a representative of Leighton and Associates observe the toe-of-slope subdrain installation and document the placement and construction operations. 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. (. No. 1612 i CERTIFIED ENGINEE 'IN GEOLOGIST Randall K. Wagner, CEG 1612. Director of Geology Attachments: Figure 1 - Recommended Toe-of-Slope Subdrain Figure 2 - Typical Toe-of-Slope Subdrain Detail Distribution: (2) Addressee (6) Continental Homes, Attention: Mr. Canton Clark (2) City of Carlsbad, Attention: Mr. Tim Fennessy - 2 - 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY - rix LIMITS RECOMMENDED SUBDRAJN CONCRETE FILL SLOPE - - - - - _OUTLET SUBDRAINU4T0 STORM DRAIN BOX ROAD' — T i 35+00 -- JQ0- REF _—_/_------- --- - -° - - -i--- - ------ -- ___ 28+00 - - 4 - - - L - I L - - -_-=-- 24*00 - - Iva ~Ir A~o vv - — ;10 .;-;;-r —----- - I i'-: - EW 0 100 200 L___J Scale in Feet BASE MAP: Project Design Consultants, 2001, Grading and Erosion Control Plans for Shelley Property Unit No. 3, Carlsbad Tract No. CT 90-03, Carlsbad, California, Drawing No. 380-1G. dated March 28, 2001 2:1 fill slope Grass Wood chips Sidewalk, curb and street I 4' '•. ..: 0 'N o .o 'N .0 N 9,, 0 0 0' 9 / 12" Backfill with compacted native soils or loose gravel Mirafi 140N or equivalent filter fabric 3/4" clean gravel 4" diameter perforated pipe (PVC schedule 40) Project No. 851855-011 Not to scale 4 4ftP, TYPICAL TOE-OF-SLOPE Engr./Geol. SAC/RKW &W SUBDRAIN DETAIL Drafted By KAM Date 3-14-03 Leighton and Associates, inc. Figure No. 2 I! 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY ,. : March 13, 2003 \ Li° s q/3 To: Contihentalilomes 5927 PriestliDrive, Suite 200 Carlsbad, California 92008 RECEIVED 1MAR 2O3] CITY OF CARLSBAD Project No. 851855-011 Attention: Mr. Dave Lother Subject: Evaluation of Street Subgrade Soil Conditions and Addendum Geotechnical Recommendations, Western Side of Ranchó Santa Fe Road, Station No. 14±55 to 25+00, Carlsbad Tract No. 90-03, Carlsbad, California Reference: Project Design Consultants, 2002, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No. 380-1K, dated March 29, 2001, revised February 12, 2002 This letter presents our geotechnical evaluation and addendum recommendations relative to the existing street subgrade soils on the western side of Rancho Santa Fe Road between approximate Station No. 14+55 and 25+00 (Carlsbad Tract No.90-03) located in Carlsbad, California. During the pavement subgrade preparation operations on the western side of the road (north of Las Olas Court),. saturated soil and pumping street subgrade conditions were encountered. Based on our gèotechnical evaluation of the pavement subgrade soils, the subgrade soils underlying the previously existing portion of Rancho Santa Fe Road consisted of saturated clayey fill soils or saturated sandy alluvial soils. In addition, erosion control measures implemented during the recent precipitation events resulted in the ponding of surface run-off within the low lying areas of the street, further saturating the street subgrade soils. During the preparation of the subgrade soils, it became apparent that the subgrade soils were overly wet and pumping conditions were present. To mitigate the pumping subgrade conditions, we recommend the saturated soils either: 1) be removed to competent material; 2) dried back until unyielding conditions are present; or 3) a geotextile fabric and additional aggregate base material be placed after partially removals of the, saturated subgrade soils are made to allow for an increase in base section. However, due to the presence of a relatively shallow fiber optic line and the near-surface ground water elevation, removals of the saturated subgrade soils to competent material or drying back the material by ripping and mixing are not considered feasible. Therefore, we recommend that a geotextile fabric (Mirafi 600X or equivalent) beneath the aggregate base and asphalt concrete section. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 851855-011 We recommend that an additional 6 inches of the street subgrade soils be removed prior to the placement of the geotextile fabric and aggregate base material. This corresponds to a depth of at least 23 inches below the proposed street subgrade elevation. Areas below this elevation where significant pumping conditions are present should be removed and replaced with compacted aggregate base material. This material should consist of imported Class 2 aggregate base or the on- site pulverized AC and aggregate base mixture. A minimum 6-inch section of the pulverized AC and aggregate base mixture should then be placed and compacted prior to the placement of the street pavement section and the geotextile fabric. Once a 6-inch layer of aggregate base material is placed, the geotextile fabric should be installed with a minimum 12-inch overlap of adjacent layers. Aggregate base material should then be placed and compacted prior to the placement of the AC. Due to the saturated conditions, the street subgrade soils and aggregate base material beneath the geotextile fabric should be compacted to a minimum 90 percent relative compaction (based on American Standard of Testing and Materials [ASTM] Test Method D1557). The aggregate base material above the geotextile fabric should be compacted to a minimum 95 percent relative compaction (based on ASTM Test Method D1557). If you have any questions regarding this letter, please contact this office. We appreciate this,. opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. "Ne. 1612 CERTIFIED ' * ENGINEERING GEOLOGIST Randall K. Wa Cr, CEG 1612 Director of Geology N 0% No. 2507 Op-n Exp. 12/31/03 Sean'€ Director Distribution: (4) Addressee (2) Continental Homes Attention: Mr. Canton Clark (2) City of Carlsbad Attention: Mr. Tim Fennessy 4 -2- Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY February 12, 2003 Project No. 851855-011 To: Continental Homes 5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother Subject: R-Value Test Results of Sub-Base Material and Addendum Geotechnical Recommendations for Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 15+00 to 29+00, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California References: Leighton and Associates, 2003, Addendum Geotechnical Recommendations for Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 15+00 to 29+00, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California, Project No. 851855-011, dated February 6, 2003 Project Design Consultants, 2001, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No.380-1K, dated March 29, 2001, revised December 21, 2001 This letter presents the results of the R-Value testing of a representative sample of the sub-base materials and provides addendum geotechnical recommendations concerning the proposed asphalt concrete pavement section for the westside of Rancho Santa Fe Road between approximate Station No. 15+00 and 29+00 located in Carlsbad, California. On February 7, 2003, the existing section of asphalt concrete on the western side of Rancho Santa Fe Road between approximate Station No. 15+00 and 29+00 was pulverized. On February 10, 2003, one representative sample was obtained from the sub-base material stockpile. The sample was transported to our laboratory and R-value testing (in accordance with California Test Method 301) was performed. The test results indicated the sub-base material sample has an R-value of 57. The results of the laboratory testing are summarized in the following table. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com :851855-011 Table 1 R-Value Test Result Sample Sample Location Sample Description R-Value Number FSB-3 Stockpile Coarse Silty Sandy GRAVEL with AC 57 Based on the results of the R-Value testing, we anticipate that the street sub-base materials will possess an R-Value of at least 50. During establishment of grade, the contractor should take care to avoid contamination of sub-base materials with the underlying subgrade soils. We recommend that the proposed pavement section for the western side of Rancho Santa Fe Road between Station 15+00 and 29+00 consist of the section presented on Table 2. Table 2 Design Asphalt Concrete and Aggregate Base Pavement over Granular Sub-Base Section Traffic Index Design Subgrade R- AC Thickness Aggregate Base Sub-base Thickness R-Value (inches) Value Thickness (inches) (inches ) 50 1 8.5 j 13 6 7 10 All aggregate base material, sub-base and the upper 12-inches of the subgrade should be compacted to a minimum 95 percent relative compaction based on American Standard of Testing. and Materials (ASTM) Test Method D1557. Compacted materials should be placed at near optimum moisture content. Aggregate base material and Asphalt Concrete should conform to and be placed in accordance with the "Greenbook" Standard Specifications for Public Works Construction and/or Caltrans Specifications., -2- Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 851855-011 If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. 16,12 CiRTIFIED VAGINEENING Randall KWagner, G 1612 Director of Geology OF At. Sean Director of Engineering Distribution: (4) Addressee (2) Continental Homes Attention: Mr. Canton Clarke (2) City of Carlsbad Attention: Mr. Tim Fennessy (7COLo 1 1 2507 c Exp. 12/31/03 / -3- Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY \• February 6, 2003 Project No. 851855-011 N To: Continental Homes ,i5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother Subject: Addendum Geotechnical Recommendations for' Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 15+00 to 29+00, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California References: Leighton and Associates, 2002a, Geotechnical Recommendations for Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 29+00 to 42+31, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California, Project No. 851855-011, dated November 20, 2002 2002b, Geotechnical Recommendations Concerning the Existing Asphalt Concrete Pavement Section in Areas of Proposed Fill, Westerly Side of Rancho Santa Fe Road, Station Nos. 15+00 to 29+00, Arroyo Vista, Carlsbad Tract No. 90- 03, Carlsbad, California, Project No. 851855-011, dated October 31, 2002, revised December 11, 2002 Project Design Consultants, 2002, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No.380-1K, dated March 29, 2001, revised February 12, 2002 This letter presents our revised preliminary geotechnical recommendations concerning the existing and proposed asphalt concrete (AC) pavement section for the westside of Rancho Santa Fe Road between approximate Station No. 15+00 and 29+00 associated with the Arroyo Vista project (Carlsbad Tract No.90-03) located in Carlsbad, California. We understand that the existing AC pavement section is located approximately 2 to 4 feet below the proposed street grade elevation on the west side of Rancho Santa Fe Road between approximate Station No. 15+00 and 29+00. We also understand that the existing pavement section (i.e. AC and the base material below) will be ground up and utilized as a sub-base material beneath the new pavement section. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 • 858.292.8030 • Fax 858.292.0771 . www.leightongeo.com 851855-011 To allow for reuse of the existing base and pulverized asphalt concrete as a sub-base below the base layer, we have prepared the sections in Table 1 below. Three sections are provided in Table 1 that allow for consideration of the influence of sub-base R-Value on the base layer thickness. For our analysis, we have assumed sub-base R-Values of 40, 50, and 60. Table 1 Design Asphalt Concrete and Aggregate Base Pavement over Granular Sub-Base Section Sub-base R- Design AC Thickness Aggregate Sub-base Value Traffic Index Subgrade R- (inches) Base Thickness Value Thickness (inches) (inches) 40 8.5 13 5 12 7 50 8.5 13 6 7 10 60 8.5 13 6 4 13 Where the pulverized AC and base are to be reused as a sub-base, selective grading and/or stockpiling of the material may be necessary to allow design subgrade elevations to be fine graded. Testing to confirm the sub-base R-Value should be performed after the asphalt concrete is pulverized and the sub-base materials are generated so that the design sub-base thickness can be confirmed. Additional testing to confirm R-Values should be coordinated with the City inspector. All aggregate base material, sub-base and the upper 6-inches of subgrade should be compacted to a minimum 95 percent relative compaction based on American Standard of Testing and Materials (ASTM) Test Method D1557. Compacted materials should be placed at near optimum moisture content. Aggregate base material and Asphalt Concrete should conform to and be placed in accordance with the "Greenbook" Standard Specifications for Public Works Construction and/or Caltrans Specifications. -2 ;4 - Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 851855-011 If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. CO a5403 ( (No. 54033 ) Director of Engineering Exp. 12/31/03 OF C Randall K. Wagner, CEO 1612 Director of Geology Distribution: (4) Addressee (2) Continental Homes Attention: Mr. Carlton Clark * CERTIFIED * ENGINEERING GEOLOGIST OF C -3- Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY November 20, 2002 Project No. 851855-011 To: Continental Homes 5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother Subject: Geotechnical Recommendations for Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 29+00 to 42+31, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California Reference: Project Design Consultants, 2002, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No.380-1K, dated March 29, 2001, revised February 12, 2002 This letter presents our geotechnical recommendations concerning the existing and proposed asphalt concrete pavement section for the westside of Rancho Santa Fe Road between Station No. 29+00 and 42+31 associated with the Arroyo Vista project (Carlsbad Tract No.90-03) located in Carlsbad, California. During our site reconnaissance on October 14, 2002, the existing roadway was observed to evaluate the general condition of the road. The existing road surface was observed to contain local and broad areas of distress along the alignment. Where observed, the typical distress consists of depressed alligator cracking suggestive of poor subgrade or base support. We understand existing plans call for grinding and overlaying of the existing street along certain sections and removal and reconstruction along the remaining areas. We also understand that two alternative approaches are being considered with respect to the construction of the western half of the road; 1) overlaying more of the existing roadway, or 2) pulverizing the existing roadway and constructing a new pavement section. Where overlaying is planned, we recommend remedial repairs be performed to mitigate the potential for reflective cracking through the overlay section. It is further noted that along sections of the roadway, the area of distress is such that removal and replacement is likely preferred. For further consideration in evaluating the alternative approaches, coring and measurement of the existing sections were previously performed at various locations between Station 29+70 and 35+45 along the westerly lane. The measurements from that investigation are summarized in Table 1. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 851855-011 Table 1 Measured Pavement Sections Approximate Station No. Asphalt Concrete Thickness (inches) Aggregate Base Thièkness (inches) 29+70 6 15 31+60 6 14 33+10 17 9 35+45 6 12 To develop design pavement sections, a representative from our firm previously collected samples from four exploratory cores excavated along the existing portion of Rancho Santa Fe Road Station between Station Nos. 29+70 and 35+45). Samples were collected by coring through the existing pavement section and sampling the underlying subgrade. Visual descriptions of the samples are provided in Table 2. Table 2 Visual Description of Subgrade Materials Sample Location Sample Description Station No. 29+70 Gray-green ,fine to medium, very fine sandy silty with clay Station No. 31+60 Brown, fine to medium silty clayey sand Station No. 33+10 Gray-green, fine to medium silty. clayey sand Station No. 35+45 Light yellow-tan, fine to medium silty sand Based on our visual observation, the materials from Station 29+70 were judged to represent lowest traffic support material of the four samples. Laboratory testing of the materials resulted in an R-Value of 13. The design of the asphalt concrete (AC) over aggregate base section presented below was performed using Caltans design methodology and an R-Value of 13. -2- 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 851855-011 Table 3 Design Asphalt Concrete and Aggregate Base Pavement Section Location Traffic Design Subgrade AC Thickness Aggregate Base Index R-Value (inches) Thickness (inches) Station No. 29+00 to 42+14 8.5 13 5 13 As an alternative, to allow for reuse of the existing base and pulverized asphalt concrete as a sub-base below the base layer, we have prepared the sections in Table 4 below. Three sections are provided in Table 4 that allow for consideration of the influence of sub-base R-Value on the base layer thickness. For our analysis, we have assumed sub-base R-Values of 40, 50, and 60. Additional sections having a 6-inch asphalt concrete pavement section are also presented.. Table 4 Design Asphalt Concrete and Aggregate Base Pavement over Granular Sub-Base Section Sub-base R- Value Traffic Index Design Subgrade R- Value AC Thickness (inches) Aggregate Base Thickness (inches) Sub-base Thickness (inches) 40 8.5 13 5 12 7 50 8.5 13 5 9 10 50 8.5 13 6 7 10 60 8.5 13 5 6 13 60 8.5 13 6 4 13 Where the pulverized AC and base are to be reused as a sub-base, selective grading and/or stockpiling of the material may be necessary to allow design subgrade elevations to be fine graded. Testing to confirm the sub- base R-Value should be performed after the asphalt concrete is pulverized and the sub-base materials are generated so that the design sub-base thickness can be confirmed. Additional testing to confirm R-Values should be coordinated with the City inspector. All aggregate base material, sub-base and the upper 6-inches of subgrade should be compacted to a minimum 95 percent relative compaction based on American Standard of Testing and Materials (ASTM) Test Method D1557. Compacted materials should be placed at near optimum moisture content. Aggregate base material and Asphalt Concrete should conform. to and be placed in accordance with the "Greenbook" Standard Specifications for Public Works Construction and/or Caltrans Specifications. -3- 40 Leighton. and Associates, Inc. A LEIGHTON GROUP COMPANY 851855-011 If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, K. Distribution: (4) Addressee (2) Continental Homes Attention: Mr. Jerry Sims LEIGHTON AND ASSOCIATES, INC. Randall K. Wagner, CEG 1612 Director of Geology Cot Sean Col'GE23 No. 2507 rn Director of Engineering I Exp. 12/31/03 OF C -4- 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY October 31, 2002 (revised December 11, 2002) Project No. 851855-011 To: Continental Homes 5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother Subject: Geotechnical Recommendations Concerning the Existing Asphalt Concrete Pavement Section in Areas of Proposed Fill, Westerly Side of Rancho Santa Fe Road, Station Nos. 15+00 to 29+00, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California References: Leighton and Associates, 2002, Geotechnical Recommendations for Asphalt Concrete Pavement, Western Side of Rancho Santa Fe Road, Station No. 29+00 to 42+3 1, Arroyo Vista, Carlsbad Tract No. 90-03, Carlsbad, California, Project No. 851855-011, dated November 20, 2002 Project Design Consultants, 2002, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No.380-1K, dated March 29, 2001, revised February 12, 2002 This letter presents our revised geotechnical recommendations concerning the existing asphalt concrete (AC) pavement section for the westside of Rancho Santa Fe Road between Station No. 15+00 and 29+00 within the Arroyo Vista project (Carlsbad Tract No.90-03) located in Carlsbad, California. We understand that up to approximately 2 to 4 feet of fill is proposed above the existing AC pavement section on the western side of Rancho Santa Fe Road between approximate Station No. 15+00 and 29+00. We recommend that in areas where fill soils are required to reach the proposed subgrade elevation of the roadway (i.e. areas where the existing roadway surface is more than 18 to 24 inches below the proposed roadway surface), the existing AC should either be ripped and broken up or pulverized in-place. If the, alternative to rip the AC is performed, we recommend that the AC be broken into pieces 8 inches or less, mixed with the fill soils, and compacted to a minimum 90 percent relative 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 851855-011 compaction based on American Standard of Testing and Materials (ASTM) Test Method D1557. If the alternative to pulverize the AC is performed, the pulverized asphalt and aggregate base material should be moisture conditioned and mixed together; and the material compacted to a minimum 90 percent relative compaction (based on ASTM Test Method D1557). After the existing pavement section is processed (by either method), fill soils then can be placed and compacted to the proposed street subgrade elevation. In accordance with the City of Carlsbad requirements, the upper 12 inches of the Street subgrade soils should be compacted to a 95 percent relative compaction (based on ASTM Test Method D1557). In areas where the existing AC pavement section is within 18 to 24 inches of the planned finish grade surface of the road, either 1) the AC and/or aggregate base should be removed (after it is either ripped and broken-up) to the anticipated subgrade elevation; or 2) aggregate material should be placed above the pulverized and mixed pavement (that has been compacted to 95 percent in the upper 12 inches). If pulverizing of the AC is performed, the recommendations presented in our letter dated November 20, 2002 (Leighton, 2002) concerning the existing pavement section between Station Nos. 29+00 to 42+31 may be followed. The fill soils or material placed above the existing pavement section will need to be R-value tested to determine the appropriate pavement section. For planning purposes, the asphalt pavement section may be assumed to consist of 6 inches of asphalt concrete underlain by 18 inches of Class 2 or Class 2 Recycled aggregate base material. The upper 12 inches of the subgrade soils (that may consist of fill soils or aggregate base material and pulverized AC) should be compacted to a minimum 95 percent relative compaction based on ASTM Test Method D1557. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. £€K. Randall K. Wagne 1612 Director of Geology 11* CERTIFIED * ENGINEERING GEOLOGIST 00 -2- 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY Distribution: (2) Addressee (4) Continental Homes Attention: Mr. Jerry Sims /E7 s-F SO&Th' Leighton and Associates A GTG Company GEOTECHNICAL CONSULTANTS L Y Lir UAr-iLL.,AD To: Continental Homes 5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother APPROVEroiectNo. 851855-011 bITfOTJS 7 Z 9/s e/02, EY (.1 DATE Subject: Pavement Design Recommendations for the East Side of Rancho Santa Fe Road, Between Olivenhain Road and Calle Acervo, Station No. 12+38 to 42+31 and the Right Turn Lane at Olivenhain Road, Station No. 1+00 to 4+28, Carlsbad, California References: 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 Leighton and Associates, Inc., 2002, Preliminary Pavement Design Recommendations, Eastside of Rancho Santa Fe Road, Arroyo Vista, Carlsbad Tract No. 90-03, Project No. 851855-011, dated June 27, 2002, revised June 28, 2002 Project Design Consultants, 2002, Improvement and Grading Plans for Rancho Santa Fe Road, Carlsbad, California, Drawing No. 3 80-1K, dated March 29, 2001 Introduction In accordance with the requirements of the City of Carlsbad, this letter presents our pavement design recommendations for the east side of Rancho Santa Fe Road between Olivenhain Road and Ca lie Acervo (Station No. 12+38 to 42+31) and the right turn lane at Olivehain Road (Station No. 1+00 to 4+28) located in Carlsbad, California. Eight representative subgrade soil samples were obtained along the eastern side of the Rancho Santa Fe Road alignment. The samples were transported to our laboratory and R-value testing (in accordance with Caltrans Test Method 301) was performed. The test results indicated the subgrade soils have R-values ranging from 5 to 21. The approximate sample locations and results of the laboratory testing are presented in Appendix A. Based on the project Improvement Plans (Project Design Consultants, 2002), we understand that Rancho Santa Fe Road has a traffic index (TI) of 8.5. According to the City requirements (Carlsbad, 1996), the minimum pavement section for streets having a TI of 8.5 is 5 inches of Asphalt Concrete (AC) over 6 inches of Aggregate Base (AB) regardless of the R-Value. 3934 Murphy Canyon Road, #13205, San Diego, CA 92123-4425 (858) 292-8030 • FAX (858) 292-0771 • www.leightongeo.com 851855-011 Pavement Section Utilizing Class 2 Aggregate Base Material Based on the above information, the recommended Class 2 Aggregate Base pavement section was calculated using the Caltrans Highway Design Manual Method and compared with the City of Carlsbad's minimum section thickness requirements. The recommended pavement sections are presented on Table 1. Table 1 14b7 AgWQO , Recommended Pavement Section Utilizing Class 2 Aggregate Base Traffic Design Asphalt Concrete Class 2 Aggregate Location Index R-Value Thickness Base Thickness (in inches) (in inches) Right Turn Lane and Rancho Santa 8.5 5 t / _(Station _12+3 Fe Road 8 to_14+33) Rancho Santa Fe Road 8.5 12 18 (Station 14+33 to 24+00) Rancho Santa Fe Road 8.5 . 8 (Station 24+00 to 42+31) Prior to placement of the Class 2 aggregate base material, the upper 12 inches of subgrade soils (including beneath and a minimum of 6 inches beyond the back of the curb and gutter) should be scarified, moisture- conditioned 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 Dl 557. 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 at least 6 inches thick below the curb and gutter and extend a minimum of 6 inches behind the back of the curb. 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. Pavement Section Utilizing Lime-Treated Subgrade Soils The following pavement design recommendations utilizing a lime-treated subgrade section is provided in accordance with the City of Carlsbad guidelines. However, it is our professional opinion that due to the potential for differential settlement of the left-in-place alluvial soils along Rancho Santa Fe Road, a more flexible pavement section (i.e. aggregate base without a lime-treated subgrade layer) rather than a more rigid section utilizing a lime-treated layer, would be expected to provide improved performance over the life of the roadway. A representative subgrade soil sample from the Arroyo Vista project having a R-Value of less than 12 was -2- Lf- 851855-011 previously tested for optimum lime content per American Standard of Testing and Materials (ASTM) Test Method C977. The optimum lime content was determined to be 5 percent quick lime. Testing of the lime treated sample resulted in an R-value of 69. Based on the above information, the lime-treated pavement section was calculated using the Caltrans Highway Design Manual Method and compared with the City of Carlsbad's minimum section thickness requirements. The pavement section is presented on Table 2. Table 2 107 14OVIXIIv.c.I 24' Pavement Section Utilizing Lime Treated Subgrade Soils Traffic Design AC Class 2 Base Lime Treated Location Index R-Value Thickness Thickness Subgrade Layer (in inches) (in inches) (in inches) East Side of Rancho Santa Fe 8.5 5 8 4 12 Road and the Right Turn Lane Prior to placement of asphalt concrete and Class 2 Aggregate Base, the upper 12 inches of subgrade soils (including beneath the curb and gutter) should be scarified, moisture-conditioned to at least optimum moisture content, and thoroughly mixed with 5 percent quick lime (or equivalent percentage of hydrated lime slurry). 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 ASTM 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. After the completion of the curing period, a minimum of 4 inches of 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 at least 6 inches thick below the curb and gutter 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 8 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 1) 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. Pavements Adjacent to Landscape Areas 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 to reduce the possible adverse effects of water on the pavement subgrade. zgj 4. 851855-011 If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. CoLo,% Seeie ;RCE 54033 CO Director of Exp. 12131/03 LQh OF C Randall K. Wagner, CEG 1612 Director of Geology Attachments: Appendix A -Laboratory Testing Procedures and Test Results * S * CERTIFIED ENGINEERING Distribution: (4) Addressee GEOLOGIST (2) Continental Homes OF CA Attention: Mr. Jerry Sims (2) City of Carlsbad, Public Works Department Attention: Mr. Tim Fennessy S 851855-014 APPENDIX A Laboratory Testing Procedures and Test Results "R"-Value: The resistance "R"-value was determined by the California Materials Method No. 301 for subgrade soils. Three samples were prepared and exudation pressure and "R"-value determined on each one. The graphically determined "R"-value exudation pressure of 300 psi is summarized in the table below: Sample Number and Location Representative Location Sample Description R-Value Right Turn Lane Right Turn Lane Gray-olive sandy lean clay 6 (Station 2+00) (Station 1+00 to 4+28) Rancho Santa Fe Road Rancho Santa Fe Road Dark olive sandy lean clay (Station 14+10) (Station 12+38 to 14+33) Rancho Santa Fe Road Rancho Santa Fe Road Dark olive-gray silty to clayey (Station 16+00) (Station 14+33 to 19+50) sand 21 Rancho Santa Fe Road Rancho Santa Fe Road Pale olive sandy lean clay 12 (Station 2 1+00) (Station 19+50 to 24+00) Rancho Santa Fe Road Rancho Santa Fe Road Dark olive silty clayey sand 6 (Station 26+50) (Station 24+00 to 28+00) Rancho Santa Fe Road Rancho Santa Fe Road Pale olive sandy lean clay (Station 30+00) (Station 28+00 to 33+00) Rancho Santa Fe Road Rancho Santa Fe Road Pale olive-gray silty clayey (Station 35+00) (Station 33+00 to 38+00) sand 14 Rancho Santa Fe Road Rancho Santa Fe Road (Station 40+00) (Station 38+00 to 42+31) Olive sandy lean clay 12 FEW RECEIVED JAN 31 2003J HORTON - CON TLNENTAL Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY January 29, 2002 Project No. 851855-011 To: Horton Continental 5927 Priestly Drive, Suite 200 Carlsbad, California 92008 Attention: Mr. Dave Lother Subject: Summary of Settlement Monitoring, Rancho Santa Fe Road Widening - West Side, Approximate Station. No. 15+00 to 25+00, Arroyo Vista, Carlsbad, California This letter presents the results of our geoteclmical evaluation of the survey readings of the settlement monuments on the western side of Rancho Santa Fe Road between approximate Station No. 15+00 and 25+00 within the Arroyo Vista project in Carlsbad, California. Based on the project geotechnical recommendations, wick drains and a surcharge fill were placed in the areas along the western side of Rancho Santa Fe Road where saturated alluvial soils were left in place. Theses areas included the roadway fill on the western side between Station No. 15+10 to 17+20, 18+30 to 20+80, and 22+20 to 24+90 (as indicated on Figure 1). The areas of the proposed culverts and the existing sewer line were not wicked or surcharged. Prior to the placement of the proposed fill, the alluvial soils were removed to within a few feet of the ground water elevation. After the fill soils were placed with a minimum 1-percent fall toward the proposed toe-of-slope, the wick drains (on 10-foot centers) were placed and outletted to the toe-of-slope with horizontal drains. The roadway fill soils and the recommended fill surcharge were then placed. The wick drains were installed as of December 20, 2002. The placement of roadway and surcharge fills was completed as of December 24, 2202. A total of 5 settlement monuments were installed in the three surcharge areas on January 2, 2003. Starting January 3, 2003, the project surveyor took periodic survey readings of the settlement monuments. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 851855-011 Evaluation of the survey data of the settlement monuments obtained to date and the previous geotechnical findings of the settlement areas on the eastern side of the road, we constructed models to estimate future settlements due to consolidation of the underlying saturated alluvium. Based on our evaluation of the survey data obtained from the settlement monuments within the surcharge areas of the western side of Rancho Santa Fe Road, it is our professional opinion that the majority of the primary consolidation settlement of the material is essentially complete. Therefore, from a geotechnical standpoint, the surcharge fill may be removed and the completion of the roadway improvements on the western side of the road commenced. Secondary compression settlement of the fill soils and left-in-place saturated alluvium may add to future settlements. Secondary consolidation settlements are expected to be less than 1/2-inch over the next year and less than 3/4-inch for the next 5 years. Due to the limited monitoring data within the initial period of the embankment construction and various assumptions made in preparing the model, actual settlements may vary from those presented. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. 11 I1o.16Y ca— CERTiFiED *0 ENGINEER dGE0LOGIST Randall K. Wagner, CEG 1612 Directory of Geology voESSIo,p4 . COLo ry , %. LU Sean CE 54033 uJ No 54033 0 Ir Director of Engineering t cc xp 12(31/03 I CM\- OF C Attachment: Figure 1 - Surcharge and Settlement Monument Location Map Distribution: (4) Addressee (2) Horton Continental Attention: Mr. Carlton Clark -2- 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY :'• '\\\!IELLEY I I LJPU If! I /Jft I I I - • 'rT ': 1 /~- R~ I —, i -- k--(- - " \--\"I T S1.5 :g • SM-4 SM-i SM-2 - SM-3 I + -t - - _ / ii' - - .1_I .. 4 I 0 50 100 200 r Scale in Feet NORTH SURCHARGEAND LEGEND I SETTLEMENT MONUMENT SM-5 • Approximate location of settlement monument LOCATION MAP 1 West Side of RSF Road Carlsbad California Approximate limits of surcharge fill and wick drains . - Project No 851855-011 - - Scale 1" =100' - Engr /Geol SAC/RKW -' Drafted By KAM - Date 1-29-03 I Leighton and Associates, Inc - .- - F N A LEIGHTON GROUP COMPANY g --- 4 - - I I ' 14 M MUMA 1961 - 2001 Leighton and Associates GEOTECHNICAL CONSULTANTS November 14, 2001 To: Continental Homes 2237 Faraday Avenue, Suite 100 Carlsbad, California 92008 Attention: Mr. Dave Jones F a —7 I i! ! gn i, , PropctNo. 4855 011 Cl IY OFGAPLs0 - -- Subject: Revised Geotechnical Recommendations Concerning Saturated Sandy Soils Beneath Storm Drain, Rancho Santa Fe Road Station No. 10+00 to 14+00, Arroyo Vista, Carlsbad, California References: Leighton and Associates, 2001a, Geotechnical Recommendations Concerning Saturated Sandy Soils in Rancho Santa Fe Road, Arroyo Vista, Carlsbad, California, Project No. 851855-011, dated August 22, 2001 2001b, Pipe Bedding Support Layer, Proposed 60-inch Storm Drain, Rancho Santa Fe Road, Arroyo Vista Development, Carlsbad, California, Project No. 851855-011, dated August 3 1, 2001 Project Design Consultants, 2001, Preliminary Improvement Plans for Rancho Santa Fe Road, (Olivenhain Road to Calle Acervo), Carlsbad, California, CT 90-03, Drawing No.380-1K, dated March 29, 2001, revised September 28, 2001 Based on our geotechnical observations along the eastern side of Rancho Santa Fe Road between approximate Station No. 10+00 and 14+00, a perched groundwater condition and saturated sandy soils are present at the depth of and beneath the proposed 60-inch storm drain. The perched groundwater condition is likely the result of upslope irrigation water moving laterally through the sandy colluvial soils present beneath the existing fill soils (placed during the grading of Rancho Santa Fe Road) and from the storm drain outlets present on the east side of the roadway (near the intersection of Calle Acervo). Canyon subdrains were installed during rough grading along the base of the fill soils beneath the lots east of Rancho Santa Fe Road. We understand that after recommencement of work, saturated soils in the bottom of the storm drain excavation experienced instability in the vicinity of Rancho Santa Fe Road Station No. 10+00. The bottom instability in the excavation has resulted in flowing sands, side-wall instability problems, loose soil conditions, and pipe settlement. 3934 Murphy Canyon Road, #13205, San Diego, CA 92123-4425 (858) 292-8030 • FAX (858) 292-0771 • www.leightongeo.com 851855-011 Based on our geotechincal analysis of the site conditions and professional experience with similar conditions on other sites, it is our opinion that the most effective way to deal with the saturated sandy conditions is to dewater the soils. We recommend a dewatering system be installed and activated prior to trenching. At a minimum, the dewatering system should lower the water table to a depth of 2 to 3 feet below the proposed excavation bottom and incorporate proper filtration so as to avoid rilling of the ground surface. Dewatering may include construction of a number of dewatering well points along the storm drain alignment (the spacing of the well points, which should be determined by the dewatering contractor). A subdrain system placed along the side proposed storm drain alignment at least 3 to 4 feet below the proposed excavation bottom and connected to a sump pump(s) was considered but may be impractical to construct due to difficulty in maintaining an open trench with the flowing saturated sand condition. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. K. kR' NX Respectfully submitted, f4 Np. 1612 ml LEIGHTON AND ASSOCIATES, INC. CERTIFIED . ENGINEERING j GLIS/ ESSI Randall K. Wagner, CEG 1612 Oo,v Director of Geology ,cOL CO "ff(1No.54o33° rn Y Exp. 12/31/0 CIVIV ) ) Sean 33 Director of Engineering OF cc'-'-" Distribution: (4) Addressee (2) City of Carlsbad, Attention: Mr. Duane Soileu -2- LEiGHTON. 09/10/2001 15:25 8582920771 '., mmBMW o-I'M4,4AWN LEIGHTON SAN DIEGO Leighton and Associates PAGE 02 ACTOCompany GEOTECNNJCAL CON$ULTANT$ September 10,2001 Project No. 851855-012 To: Continental Homes 2237 Faraday Avenue, Suite 100 Carlsbad, Califbtnfa 92008 Attention: Mr. Dave Jones Subject: Results of Laboratory Tests on Crushed Miscellaneous Base Samples, Avenida de Suano and Calle Cordoba, Arroyo Vista Unit 2, Catlsbad Tract No. 90-03, Carlsbad, California Reference: Southern California Chapter, American Public Works A.ssoc2alion and Southern California Districts. .4.csociated Genera) Contractors, 1997, Standard Specifications for Public wodm Construction "Green Book" In accordance with the requirements of the City of Carlsbad, we have performed laboratory tests on the imported Ctusbad Miscellaneous Base placed during the construction of the curb and gutter on Avenida de Sueno and Calle Cordoba (Arroyo Vista Unit 2, Carlsbad Tract No. 90-03) located in Carlsbad, California. A total of two samples of the Crushed Miscellaneous Base material were obtained (one in the morning and one in the afternoon) during the placement operations at the site. Laboratory tests performed on each of the representative samples included sand equivalent (in accordance with California Test No. 217) and sieve analysis (in accordance with ASTM TestMethod D422). A durability index (in accordance with California Test No. 229) and a maximum dry density test (in accordance with ASTM Test Method D1557) were rim on the first sample. The results of the laboratory tests are presented in the attached tables. Based on the City of Carlsbad requirements, the Green Book specifications (Section 200-2.4) and as indicated in the attached tables, the representative Crushed Miscellaneous Base samples generally met the City of Carlsbad requments. However, the second sample was slightly out of specification with respect to the percent passing the No.4 sieve (the sample was 2 percent above the maximum passing gradation of SO percent). The results of the field density testing perlbrmed during the aggregate base material placement and compaction operations on the street will be summarized under separate cover upon completion of the street pavement section grading and placement operations. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, Distribution: (2) Addressee (2) City of Carlsbad Attention Mr, Duane Soileu 3934 Murphy Canyon Road, *A205, San Diego, CA 92123-4425 (658) 292-8030 FAX (958) 292-0771 • Www.IeIghtonaeo.com S9/10/2001 15:25 8582920771 LEIGHTON SAN DIEGO PAGE 03 851855-012 Laboratory Test Results of Crushed Miscellaneous Base Sample No. I Sieve Analysis (in accordance with ASTM 1)422) Sieve Size Required Percentage Passing* Sample Result In Conformance? 1-1/2inch 314 inch -. 100 85400 - 100 95 Yes Yes 3/8-Inch 55-75 65 Yes No.4 30-50 46 Yes No. 30 12-28 21 Yes - No. 200 2-10 - 8 Yes -. Sand Equivalent (in accordance with California Test No. 217) - Required Minimum* Sample Result In Conformance? 40 60 Yes Durability Index (in accordance with California Test No. 229) Required Minimum* Sample Result In Conformance? 40_ 42 Yes per Greenbook Section 200-2.4. 09/18/2881 15:25 8582928771 LEIGHTON SAN DIEGO PAGE @4 851855-012 Laboratory Test Results of Crushed Miscellaneous Base (continued) Sample No.2 Sieve Analysis (in accordance with ASW 1)422) Sieve Size Required Percentage Passlng* Sample.ReSU1t In Conformance? 1-1/2 inch. 100 100 Yes 314 inch 85-100 - 96 Yes' 3/8 inch 55-75 71 Yes No.4 30-50 52 No No. 30 12-28 19 Yes No. 200 2-10 5 Yes Sand Equivalent (in accordance with California Test No. 217) - Required Mjnjmum* Sample Result f - In Conformance? 40 66 I Yes * per (3reenbook Setion 200-2.4. ............ Maximum Dry Density (in accordance with ASTM Test Method 1)1557) Sample Sample Description Maximum Dry Density. Optimum Moisture Content Number - (pci) (%) 24a ( Crushed Mimllaneous. Base 1 128.5 9.0 -3- 09/10/2@@1 15:25 8582920771 LEIGHTON SAN DIEGO PAGE 05 JQB SITE INFORMATION Contractor: TC CONSTRUCTION 0 Project Address: RANCHO SANTA FE ROAD -. Jurisdictional Information: - SUppliar ESCONDIDO READY MIX Permit # - Field Data Date Placed: Material Type: Mix Design: Ticket No.: Truck No.: Admixtures: 8-9-01 Yards in Truck: Total Yards: Time Batched: Time Sampled: Drum Revolution Weather Condition: Air Temperature: Conc. Temp. (C 1064): Slump (C 143): SUNNY - CONCRETE 801, - 870 577481_ -- 12:45 - 3 - Unit WeIrht (C 138): '. . - . - Air Content (C 21): Structure: CULVERT 2 Location: BOTTOM Special Instructions! Remarks: . 0 Required Strength: 3250 psI at - 28 days -- Field Tech: CARLETON CLARK - — SET# LaboratorvOpta Field Identity Required Test Age Lab Control Number Date Received In Lab Date Tested Nominal Dimensions (InchesI -. Test Area (So. Max. Load (Pounds) Compression Strength 1 4 74 - 8/10/01 8/13/01 6 X 12 _28.27 74,000 2,620 2 7 75 - 8/10/01 8/16/01 6 X 12 28.27 92,000 3,250 3- 28 76 8/10/01 1 9/6/01 1 6 X 12 28.27 122,500 4,350 4 -28 77 10/01 9/6/01 6 X 12 - 2827 12-11-00-0- 4,280 Remarks: Laboratory Technician: PAUL R. CHAPIF'I Cylinders molded in accordance with ASTM C 31, Length of Cylinders within ASTM tolerance. Cylinders tested in accordance with ASTM C 39 / C 1231. . Fracture type is conical unless otherwise noted. 0 Project No.: 851855-011 Project Name: ARROYO VISTA Reviewed by: Date: September 6, 2001 Compressqn TO Report ft L"t Qt=Signed: _II4kj 'VtJ brAP,___'1rQjr •fiu __ Date: q[ei7o -. ' %$$c4' 3934 Murphy Canyon Road, R-105 Sari Diego, CA 92123 (858) 2681319 Fax (858) 498-4543 Rev.6-OO Leighton and Associates A GTG Company GEOTECHNICAL CONSULTANTS August 22, 2001 Project No. 851855-011 To: Continental Homes 2237 Faraday Avenue, Suite 100 Carlsbad, California 92008 Attention: Mr. Dave Jones Subject: Geotechnical Recommendations Concerning Saturated Sandy Soils in Rancho Santa Fe Road, Arroyo Vista, Carlsbad, California Based on our geotechnical observations and geologic mapping along the eastern side of Rancho Santa Fe Road, seepage conditions and saturated sandy soils are present along the eastern portion of the proposed section of Rancho Santa Fe Road. The seepage conditions are likely the result of upslope irrigation water moving laterally through the sandy. colluvial soils and existing trench backfill soils in Rancho Santa Fe Road, and from the storm drain outlets present on the east side of the roadway. Canyon subdrains were installed along the base of the fill soils beneath the lots east of Rancho Santa Fe. During the rough grading operations, removals were started as close as possible to the eastern edge of the existing roadway and excavated down at an approximate 1:1 (horizontal to vertical) inclination. However, due to the seepage conditions and saturated condition of the sandy soils (causing instability problems of the temporary slope along the excavation adjacent to the existing roadway), complete removals of the saturated sandy soil could not be made. While settlement of these sandy soils are not anticipated to be a significant concern, the presence of these saturated sandy soils in the excavation of the storm drain has resulted in flowing sands and sidewall instability problems and loose soil conditions below the storm drain flowline. Based on our geotechincal analysis of the site conditions and professional experience with similar conditions on other sites, it is our opinion that the most effective way to deal with the saturated sandy conditions is to dewater the soils. At a minimum, the dewatering system should lower the water table to a few feet below the proposed excavation bottom and incorporate proper filtration so as to avoid rilling of the ground surface. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, Randall K. Wagner, CEG 1612 Directory of Geology 1'No. 1612 * CERTIFIED * ENGINEERING Distribution: (4) Addressee (2) City of Carlsbad, Attention: Mr. Duane Soileu 3934 Murphy Canyon Road, #B205, San Diego, CA 92123-4425 (858) 292-8030 • FAX (858) 292-0771 • www.leightongeo.com