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Home My WebLink About3537; Vista/Carlsbad Interceptor Sewer; Agua Hedionda Sewer Access Road; 1998-07-14AGRA Earth & Environmental AGRA Earth & Environmental, Inc. 16760 West Bernardo Drive San Diego, CA 92127 Inlv-U 1QQR Tel <619>487-2113July ^e^, nyyo Fax (619)487-2357 Job No. 8-252-102100 Ms. Meleah Ashford Dudek & Associates 605 Third Street Encinitas, California 92024 RE: GEOTECHNICAL INVESTIGATION AGUA HEDIONDA SEWER ACCESS ROAD CARLSBAD, CALIFORNIA Dear Ms. Ashford: INTRODUCTION This report presents the results of the geotechnical investigation AGRA Earth & Environmental (AEE) performed for the new access road planned for the alignment of the existing Agua Hedionda Sewer line in Carlsbad, California. The location of the new road is shown on the Vicinity Map on Page 2. The access road is to be constructed along the 15-foot wide easement for the sewer line adjacent to the north shore of the Agua Hedionda Lagoon between Hoover Street and Cove Drive, a distance of about % mile. The road is to be 12 feet wide and will be used by the Carlsbad Municipal Water District for maintenance of the sewer. The road also is to provide protection from erosion. SCOPE OF WORK The scope of work consisted of a geologic reconnaissance, field exploration, laboratory testing, analysis of data and preparation of this report. The field exploration program included six test borings advanced to depths of four to five feet using a hand auger. The logs of the test borings are contained in Appendix A. Soils are classified according to the Unified Soil Classification System which is explained in Appendix A. The laboratory program consisted of moisture content determinations, a direct shear test and a sieve analysis. Based on the results of the sieve analysis and visual classification of subsurface materials encountered in the borings, an R-value was estimated for pavement design. The results of the field exploration and laboratory test programs were analyzed to develop conclusions and recommendations regarding: } Recycled Paper North Reference: Microsoft® Expediaru Streets98 AGUA HEDIONDA SEWER ACCESS ROAD CARLSBAD, CALIFORNIA VICINITY MAP AGRA Earth & Environmental JJS JJS 07/07/98 8-252-10210C -2- Ms. Meleah Ashford Dudek & Associates Agua Hedionda Sewer Access Road Job No. 8-252-102100 July 14, 1998 PageS 1. Grading for the access road. 2. Erosion potential. 3. Slope stability. 4. Gravel thickness for road construction. SURFACE AND SUBSURFACE CONDITIONS The ground surface above the existing sewer line is nearly flat along most of the alignment. The ground surface adjacent to the alignment on the east and west ends is nearly level. Slopes typically about 2:1 (horizontal:vertical) with local near-vertical portions abut the central part of the alignment on the north and south sides. The slopes ascend to the north and east and descend toward the lagoon on the south and west sides. The six test borings drilled for this investigation encountered fill soils to the maximum depth explored, five feet, except for Boring 3. Natural materials were encountered at a depth of three feet in this boring. These natural soils continued to the depth explored in this boring, five feet. The fill soils, probably backfill placed during sewer line installation, typically consist of medium dense silty or clayey sand, with some local zones of relatively clean sand. The natural materials consist of medium dense clayey sand and medium stiff clayey silt lagoon deposits. Formational materials observed at the ground surface in numerous exposures both north and south of the alignment consist of Santiago Formation sandstone and Terrace Deposits sandstone or conglomerate. The Santiago Formation at some locations contains siltstone and claystone layers that pose potential stability problems. No siltstone or claystone materials were observed during the site reconnaissance, but these materials could be exposed by excavation. Free groundwater was not encountered in the borings, although abundant seepage was noted in those borings drilled near sea level. The relatively fine-grained soils comprising the fill at most locations retard the flow of water, and seepage is expected in excavations open more than a few hours. Groundwater can be anticipated to be at, or slightly above, the level of the water in the lagoon. The groundwater level will vary somewhat with tidal fluctuations. AGRA Earth & Environmental^•r | Recycled Paper Ms. Meleah Ashford Dudek & Associates Agua Hedionda Sewer Access Road Job No. 8-252-102100 July 14, 1998 Page 4 CONCLUSIONS AND RECOMMENDATIONS General The minor grading expected for construction of a new access road can be accomplished with medium-duty equipment. No evidence for slope instability was observed during the site reconnaissance and field exploration program. However, excavations should be observed by an engineering geologist who will check for the presence of adversely-oriented siltstone or claystone layers which may have a potential for sliding. Slopes can be as steep as 2:1 (horizontakvertical) in fill and 1-1/2;1 in formational materials from an overall stability standpoint. However, erosion potential increases significantly on steeper slopes, and slopes as flat as practical will assist in minimizing erosion. Outside of the roadway area, exposed soil areas should be planted as soon as possible following grading with vegetation suitable for the near-shore environment and which will reduce erosion potential. The new road can be constructed with a gravel surface course, or asphalt concrete pavement surface course can be used. Alternatives for both types of road surface are described below. Site Preparation and Grading The roadway alignment and any adjacent areas where fill will be placed should be stripped of grass, weeds and the upper 4 inches of soil containing roots and organic debris. Along the road alignment where the existing ground level will be at final subgrade, the surface exposed by stripping should be scarified to a depth of 12 inches. Beneath new fill areas, the surface should be scarified to a depth of at least 8 inches. Following scarification, the soils should be moisture conditioned to between 1 and 3 percentage points above optimum moisture content and compacted to at least 95% relative compaction within 12 inches of the bottom of the roadway gravel or base course, and 90% elsewhere. If cuts will be made for the new road, existing soils should be over-excavated, replaced and compacted as necessary to obtain a 12-inch thick subgrade layer compacted to 95% relative compaction. Optimum moisture content and relative compaction should be based on the ASTM D 1557 laboratory test method. On-site materials can be used as fill. Imported material, if any, should not contain rocks or lumps greater than 4 inches in maximum dimension or organic debris. Imported material should have an Expansion Index of 40 or less. Fill should be placed in lifts 8 inches or less in loose thickness, moisture conditioned to between 1 and 3 percentage points above optimum moisture content and compacted to at least 90% relative compaction. The upper 12 inches of subgrade soil beneath the new roadway should be compacted to at least 95% relative compaction. 4^ AGRA Earth & Environmental I Recycled Paper Ms. Meleah Ashford Dudek & Associates Agua Hedionda Sewer Access Road Job No. 8-252-102100 July 14, 1998 Page5 Cut and Fill Slopes As noted above, fill slopes should not be steeper than 2:1. Due to the potential for erosion along the lagoon edge, flatter slopes should be provided if practical. Fill slopes should be over-built and then trimmed back to expose the compacted surface. Cut slopes in existing fill should not be steeper than 2:1 and cut slopes in formational materials should not be steeper than 1-!4:1 from the standpoint of stability. Due to the potential for erosion, flatter slopes would be desirable. Final surface grades should be designed to prevent the flow of rainfall runoff over the faces of slopes. Attention should be given to existing natural drainage channels, and existing grades modified as necessary to prevent flow in the channels from eroding the new roadway. A cut-off trench or v-ditch may be appropriate along the side of the road away from the lagoon. Erosion-resistant vegetation should be planted as soon as possible after grading. It is recommended that a landscape architect familiar with vegetation appropriate for the coastal environment be consulted to determine suitable ground cover for graded locations outside of the roadway. New Road Structural Section It is understood that new road will provide access along the sewer line for routine maintenance and improvement. Relatively light traffic consisting of light-to medium-weight trucks is anticipated. Based on inspection of samples collected during the subsurface exploration program and the results of a sieve analysis on the soil sample judged to have the highest clay content, an R-value of 25 was estimated for most of the material along the new road alignment. On this basis, a gravel road surface consisting of 12 inches of Caltrans Class 2 Aggregate Base (AB), or equivalent, is considered appropriate. An additional 6 inches of AB can be added to provide additional erosion protection or if heavy truck traffic is expected. A flexible pavement section consisting of an asphalt concrete surface course over aggregate base course may be more resistant to erosion and have a longer service life than a gravel road. The determination of which type of road to construct can be based on relative economics. For light truck traffic, a section consisting of 2-Yz inches of asphalt concrete (AC) over 6 inches of AB will be appropriate. For heavy truck traffic, the structural section should be increased to 3-Yz inches of AC over 11 inches of AB. AGRA Earth & Environmentalw ) Recycled Paper Ms. Meleah Ashford Dudek & Associates Agua Hedionda Sewer Access Road Job No. 8-252-102100 July 14, 1998 Page 6 CLOSURE We trust that this report provides the information you need. If you have any questions, or need additional information, please call me at (619) 487-2113. Sincerely yours, AGRA Earth & Environmental /Games J^/Stone, RGE 808 Principal Engineer JS/jjs Distribution: (6) Addressee Attachment: Appendix A - Logs of Test Borings Appendix B - Laboratory Testing Figure 1 - Site Plan 8-252-102100/f\report AGRA Earth & Environmental ( Recycled Paper APPENDIX A UNIFIED SOIL CLASSIFICATION »•»••-»•"••'••*-**• Pt Highly Organic soils 44 OH ^CH MH Silts and clays Liquid Limit >50% Him HI OL // CL ML Silts and days Liquid Limit <50% Fine grained soils (More than 50% is smaller than No. 200 sieve) msc SM Sands with fines>12% fines SP sw Clean sands<5% fines Sands - more than 50% of coarse fraction is smaller than No. 4 sieve _--> GC i*\- GM Gravels with fines> 12% fines -vj GP • *•* " GW Clean gravels<5% fines Gravels - more than 50% of coarse fraction is larger than No. 4 sieve Coarse grained soils (More than 50% is larger than No. 200 sieve) 60 20 CL CL 41^ OH4MH LABORATORY CLASSIFICATION CRITERIA GW and SW - Cu = D«, /D,« greater than 4 for GW and 6 for SW Cc = $ I(Q xQ ) between 1 and 3 GP and SP - Clean Gravel or sand not meeting requirements for GW and SW GM and SM - Atterberg Limit below "A-LINE" or P.I. less than 4 GC AND SC - Atterfaerg Limit above "A-LINE" or P.I, greater than 4 SILT OR CLAY FINE SAND MEDIUM SAND COARSE i SAND : SIEVE SIZE 200 40 10 4 FINE GRAVEL COARSE GRAVEL COBBLES BOULDERS! Vf 3' 10- 20 40 60 80 LIQUID LIMIT 100 Classification of earth materials is based on field inspection and should not be construed to imply laboratory analysis unless so stated. MATERIAL SYMBOLS Extrusive Igneous Rock Asphalt Claystone Clayey Sandstone Clayey Siltstone Metamorphic Rock Intrusive Igneous Rock Interbedded Limestone and Shale Limestone Sandy Claystone Sandstone Sandy Siltstone Siltstone Silty Claystone Silty Sandstone LEGEND OF PENETRATION TEST i ,<D 0 O 5 15 30 10 20 55 15 *-!_ ^ — I /Graphi / i | c representat driving rate u on of Blows per foot =25 50 75 Blows per foot (using 140 Ib. hammer with 30" drop = 350 ft-lb blow) Consistency Classification for Soils According to the Standard Penetration Test Blows/Ft.* 0-5 Granular Very loose 6-10 Loose 11-30 31-50 >50 Medium Dense Dense Very dense Blows/Ft.* Cohesive 0-5 Very soft 6-10 Soft 11-20 21-35 36-70 Medium Stiff Stiff Very Stiff >70 Hard LEGEND OF BORING G.W.S. ^ — Conformable material change Approximate material change Unconformable material change Bottom of boring "NSR" indicates "no sample recovery" Job No. 8-252-102100 A-1 AG RA EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH-SPECIFICNOTESDRY DENSITY<PCf)9.3 MOISTURE(X)BLOWS/FOOTbag SAMPLE SIZE( i nches)1 SAMPLE NO.1 2 3 - •T™ QJfl^ J!j ELEVATION "7.Q feet BORING B- 1 ''& $/'w p ^•'•'••. -.';;' I '. . y _i HOa; CQIJE sc SM 0(/>LU<T J-OH O FILL: Brown and gray-black CLAYEY SAND, medium dense, moist, with some GRAVEL Mottled brown and red-brown fine to medium SILTY SAND, medium stiff, saturated, with some CLAY and GRAVEL NOTES: 1. Total depth of boring = 4 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY WMC DATE 6-11-98 Job No. 8-252-102100 - July 7, 1998 A-2 AG RA EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH -SPECIFICNOTESDRY DENSITY(pcf)8.4 18.7 MOISTURE(*)BLOWS/FOOTbag bag SAMPLE SIZE( inches)1 2 d LU Q_ to 1 2 3 — — . n~ <U LJ£ i ^ C ELEVATION "6.0 feet BORING B- 2 ^Ii in i di\j.ni_SYMBOLSM SM coOCOLUC: U.CJHZ_JZ3H OCO FILL: Brown and yellow-brown fine SILTY SAND, medium dense, moist, with some roots wet below 1.2 feet Brown fine to coarse SILTY SAND, medium dense, wet, with some CLAY and GRAVEL NOTES: 1. Total depth of boring = 4 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY UMC DATE 6-11-98 Job No. 8-252-103100 - July 7, 1998 A-3 AG RA EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH-SPECIFICNOTESDRY DENSITY<pcf)9.0 21.7 MOISTURE<X)BLOUS/FOOTbag bag SAMPLE SIZE( \ nches)1 2 O UJ Q_ CO 1 2 3 4 — —DEPTH(feet)ELEVATION ^2.0 feet BORING B- 3 i ifi/% f , ^I MATERIALI SYMBOLSM SC SC ML COQCOLU<C U_OH OCO FILL: Brown fine to coarse SILTY SAND, medium dense, moist, with some CLAY Brown fine to coarse CLAYEY SAND, medium dense, wet NATURAL: Gray-black CLAYEY SAND, medium dense, saturated Gray CLAYEY SILT, stiff, saturated NOTES: 1. Total depth of boring = 5 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY UMC DATE 6-11-98 Job No. 8-252-102100 - July 7, 1998 A-4 AG R A EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH-SPECIFICNOTESDRY DENSITYCpcf)5.3 11.2 MOISTURE(X)BLOWS/FOOTbag bag SAMPLE SIZECinches)1 2 *o LU QL <E 1 2 4 — • — ; a""''' a §5 : ELEVATION ^9.0 feet BORING B- 4 '••'loauAS ISM SM SM SM QU)LU<C u-dH I3HOU) FILL: Black fine SILTY SAND, medium dense, moist Black fine to coarse SILTY SAND, medium dense, moist, with some CLAY Black fine to coarse SILTY SAND, medium dense, wet, with some GRAVEL and CLAY Yellow-brown fine to coarse SILTY SAND, medium dense, wet NOTES: 1. Total depth of boring = 5 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY UMC DATE 6-11-98 Job No. 8-252-102100 - July 7, 1998 A-5 AG R A EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH-SPECIFICNOTESDRY DENSITY<PCf)13.0 14.0 MOISTURE<X)BLOWS/FOOTbag bag SAMPLE SIZEC inches)1 2 SAMPLE NO.2 3 — —DEPTHCfeet)ELEVATION ~12.0 feet BORING B- 5 % 1 ;•_'/.•' 1V 1 MATERIAL1 SYMBOLSM SC SP • QU)uj<r H_JLLUH IDHO FILL: Brown fine to coarse SILTY SAND, medium dense. moist Light brown to yellow-brown fine to coarse CLAYEY SAND, medium dense, wet Green-brown fine to coarse SAND, medium dense, wet, with minor amounts of GRAVEL NOTES: 1. Total depth of boring = 4 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY UMC DATE 6-11-98 Job No. 8-252-102100 - July 7, 1998 A-6 AG RA EARTH & ENVIRONMENTAL, INC. TEST BORING LOG TYPE 4" Hand Auger STRIKE/DIPand otherDEPTH-SPECIFICNOTESDRY DENSITY(pcf)5.1 16.2 MOISTURE(X)BLOWS/FOOTbag bag SAMPLE SIZE( i nches)1 2 SAMPLE NO.1 2 3 4 — — — —DEPTH(feet)ELEVATION "2.0 feet BORING B- 6 ^ ^ M H if i|§£ %1 MATERIAL| SYMBOLSC SM SC <nocnLUCCH_lh°Z-JIDHO(rt FILL: Brown fine to coarse CLAYEY SAND, medium dense, moist, with some GRAVEL Red-brown SILTY SAND, medium dense, wet Yellow brown fine to coarse CLAYEY SAND, medium dense, saturated ...color change to gray-brown NOTES: 1. Total depth of boring = 5 feet. 2. No free groundwater encountered. 3. Boring backfilled with cuttings on 06/11/98. 4. Elevation from plan provided by Dudek & Associates, undated. THIS BORING LOG SUMMARY APPLIES ONLY AT TIME AND LOCATION INDICATED. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND TIMES. LOGGED BY UMC DATE 6-11-98 Job No. 8-252-102100 - July 7, 1998 A-7 APPENDIX B Ms. Meleah Ashford Dudek & Associates Agua Hedionda Sewer Access Road Job No. 8-252-102100 July 14, 1998 Page B-1 APPENDIX B LABORATORY TESTING The laboratory test program for the geotechnical investigation was designed to fit the specific needs of this project. Testing was limited to on-site materials obtained during subsurface exploration activities. A brief description of each type of test performed is presented below. Results of the laboratory program are provided on the following page and on the test boring logs in Appendix A. In-situ moisture contents were determined for most samples. Data obtained are listed on the boring logs in Appendix A. Strength characteristics were determined in the laboratory by a direct shear test performed on one sample in accordance with ASTM D 3080 procedures. The sample was remolded to an estimated 90% relative compaction and tested at three confining pressures in a 2.5-inch diameter circular shear box using a controlled displacement rate. Resultant data are listed in Table 1. The grain size distribution of one sample was determined in accordance with ASTM D 422. Results are presented graphically on Page B-2. Remaining samples collected during the field exploration program are stored in the laboratory for future reference and analysis, if needed. Unless a request is received to the contrary, all samples will be discarded 30 days from the date of this report. TABLE 1 SUMMARY OF DIRECT SHEAR TEST RESULTS (ASTM D 3080) Boring No./ Sample No. 2/1 Normal Stress (psf) 1125 2160 3195 Peak Shear Stress (psf) 794 1506 2236 Shear Stress at 0.25 inch displacement (psf) 794 1506 2236 AGRA Earth & Environmental I Recycled Paper 100 90 PERCENT PASSING (BY WEIGHT)) A. Ol O) ~J 0> o o o o cJU 20 10 °5 US STANDARD SIEVE SIZE 3,, 2" r/S" 1" %" 1/2"34: No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 00 BOULDERS 1 ii i iii 100 50 COBBLES Sample No. or Location 6/1 I | I I "*"t •^* S 1 \ \ ^S>'\,k%k N |^ \\ \t\ \\ t V\ y \ l s '1 1 10 5 1.0 0.5 0.1 0.05 0.01 0.005 0.001 GRAIN SIZE IN MILLIMETERS GRAVEL Coarse Fine SAND Coarse Medium Fine TestDate USCS 6/22/98 SC Description Clayey Sand Natura Water 5.1 LL PL PI SE Max. Dry Density Optimum Water Fines (Silt and Clay) GRAIN SIZE DISTRIBUTION 4-^ AGRA Earth & Environmental Project: Agua Hedionda Sewer Access Road By: WMC Date: 07/07/98