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HomeMy WebLinkAboutCT 79-11; La Costa Avenue Lot 405; Soils Report Preliminary; 1980-05-29- - - - - - -~ - - -. - - - - - - - PRELIMINARY SOIL INVESTIGATION AND GEOLOGIC RECONNAISSANCE for LOT 405 CARLSBAD TRACT 79-11 Carlsbad, California For HCH AND ASSOCIATES San Diego, California BY GEOCON, INCORPORATED San Diego, California May, 1980 - GEOCON ENGINEERSANDGEOLOGISTS . CONSULTANTSINTHEAPPLIEDEARTHSCIENCES INCORPORATED - File No. D-2234-MO1 May 29, 1980 - HCH and Associates 8963 Complex Drive, Suite A San Diego, California 92123 Attention: Mr. Mike Bingham Subject: Lot 405 Carlsbad Tract 79-11 La Costa Avenue Carlsbad, California PRELIMINARY SOIL INVESTIGATION AND GEOLOGIC RECONNAISSANCE Gentlemen: In accordance with your request, we have performed a preliminary soil investigation and geologic reconnaissance for the subject project. - - - The entire site is overlain by fill placed in conjunction with grading of the surrounding development as documented in a report by Benton Engineering, Incorporated dated October 19, 1970. Sur- ficial failures have occurred in the fill slope along the north- ern portion of the site, and remedial grading will be necessary as recommended herein. In addition, the fill is underlain by a relatively thick topsoil horizon, and the remedial grading will encompass treatment of that condition as well. It is our opinion that the site is suitable ,for development of the proposed five-unit condominium complex subject to certain stipulations and conditions presented herein. - If you have any questions regarding this report, or if we may be of further service, please do not hesitate to contact our office. -. -. Very truly yours, GEOCO INC RPORATED A%$$?gb Mic ae' W. art CEG 706 MSC:MWH:lm copies: (4) addressee /P.$!@* cl+. Michael S. Cha in Staff Geologist n 8645 CONVOY COURT . SAN DIEGO. CALIFORNIA 92111 . PHONE (714) 292-5100 -. - TABLE OF CONTENTS Page - - - - - PRELIMINARY SOIL INVESTIGATION AND GEOLOGIC RECONNAISSANCE Purpose and Scope. .................. Site and Project Description ............. Field Investigation. ................. Figure 1, Site Plan. ................. Laboratory Tests ................... Soil Conditions. ................... Fill ......................... Topsoil ........................ Delmar Formation ................... Geologic Hazards ................... Seismicity ...................... Groundwater. ..................... CONCLUSIONS AND RECOMMENDATIONS Genera 1.. ..................... Grading ........................ Figure 2, Cross-Section. ............... Figure 3, Drain Detail ................ Foundations and Floors ................ Drainage ....................... LIMITATIONS AND UNIFORMITY OF CONDITIONS APPENDIX A Table I, Moisture-Density & Direct Shear Tests .... Table II, Compaction Test Results. Figure 4, Log of Test Boring 1 . 1 : 1 : : : : : : : Figure 5, Log of Test Boring 1 Continued ....... Figure 6, Log of Test Boring 2 ............ Figure 7, Log of Test Boring 2 Continued ....... Figure 8, Log of Test Trenches 1 & 2 ......... Figure 9, Consolidation Curve. ............ APPENDIX B 9 10 :: 12 12 A-l A-2 A-3 A-4 A-5 A-6 A-7 A-8 RECOMMENDED GRADING SPECIFICATIONS . . . . . . . . . B-l - GEDCON - - - - - - - File No. D-2234-MO1 May 29, 1980 PRELIMINARY SOIL INVESTIGATION AND GEOLOGIC RECONNAISSANCE Purpose and Scope The purpose of our investigation was to evaluate the surface and subsurface soil and geologic conditions at the site and, based on conditions encountered, to provide recommendations for development of the site to receive the proposed five unit condominium complex. The investigation consisted of a site geologic reconnaissance, the drilling of two large-diameter exploratory borings and the excavation of two test trenches. Laboratory tests were perform- ed on selected representative soil samples obtained at various depths in the test borings to evaluate pertinent physical prop- erties of the soil types encountered. The conclusions and rec- ommendations that follow are based on an analysis of the data obtained from our field exploration and laboratory tests and on our experience with similar soil and geologic conditions. The locations and descriptions contained herein are based upon a site reconnaissance and upon preliminary site and development plans provided to us by HCH and Associates. If project details 'vary significantly from those outlined, this firm should be no- tified for review and possible revision of recommendations presented herein prior to final design submittal. Site and Project Description The rectangular .37? acre site is located on the north side of La Costa Avenue approximately 300 feet east of its intersection with Gibraltar Street in the La Costa area of~carlsbad, Cali- fornia. -l- GEOCON - - - - - - - - - - .- - - - File No. D-2234-MO1 May 29, 1980 The southern two-thirds of the lot is flat-lying, having been graded to that configuration during mass grading of La Costa South, Unit No. 5. A 1.5 horizontal to 1.0 vertical fill slope occupies the northern third of the site. Considerable surficial sloughing has occurred in the fill slope on the subject proper- ty and adjoining lots. Recorrunendations have been provided herein for reconstruction of the damaged slope. Vegetation on the flat-lying portion of the site consists of sparse growths of native weeds and grasses. Localized dense growths of a phreatophyte (water-loving plant) are present on the face of the fill slope at the north end of the lot. It is proposed to construct a five-unit, wood-frame condominium complex at the site. Grading will consist predominantly of re- medial work in the vicinity of the existing fill slope as rec- ommended hereinafter. No significant changes will be made to the overall existing grades at the project. Field Investigation The field investigation was-performed on May 5 and 13, 1980 and consisted of a site reconnaissancebyourengineeringgeo- logist, the excavation of two exploratory borings, and the excavation of two exploratory test trenches at the approximate locations shown on the attached Site Plan, Figure 1. The exploratory trenches were advanced to depths ranging from 8 to 10 feet below existing grade utilizing a rubber-tired backhoe equipped with a 12-inch wide bucket. -2- GEOCON - - - - -. - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 I T-l I T-2 PROPOSED STRUCTURE E _ LA COSTA _ AVENUE _- 8 LOCATION OF TEST BORING W LOCATION OF TEST TRENCH SITE PLAN AND LOCATION OF TEST BORINGS & TRENCHES LOT 405 CARLSBAD TRACT 79-11 Carlsbad, California XURE GEOCON, INCORPORATED 1 PAGE 1 3 GEOCON - - - - - - File No. D-2234-MO1 May 29, 1980 Drilling was performed by a truck-mounted drill rig equipped with a 30-inch diameter bucket bit. As drilling proceeded, undisturbed soil samples were obtained by driving a three-inch O.D. split-tube sampler 12 inches into the soil mass with blows from a 800 to 2400 pound telescoping Kelly bar falling 12 inch- es. The sampler was equipped internally with one-inch-high by 2-3/8-inch diameter brass sample rings to facilitate sample re- moval and testing. Disturbed bulk samples were also obtained. Each boring was drilled to a depth of approximately 50 feet be- low the existing ground surface. During the investigation, the soils encountered were continu- ously examined, visually classified, and logged. Logs of the test borings and trenches are presented on Figures 4 through 8 of Appendix A. The logs depict the depth and description of the various soil types encountered and include the depths at which samples were taken. Laboratory Tests Laboratory tests were performed in accordance with generally accepted test methods of the American Society for Testing and Materials (ASTM) and other suggested procedures. Selected rel- atively undisturbed drive samples were tested for their in- place dry density, moisture content, shear strength, and consolidation characteristics. The maximum dry density and optimum moisture content of dis- turbed bulk samples were determined in accordance with ASTM Test Method D155?-78. - -4- - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 The results of our laboratory tests are summarized in Appendix A. In-place moisture-density relationships are also presented on the Logs of Test Borings. Soil Conditions The majority of the site is overlain by fill soils to a maximum depth of approximately 27 feet. A small area of cut exists at the southwest corner of the lot. Natural soils of the Eocene Delmar Formation are exposed in the cut area. Varying thick- nesses of clayey topsoils are present at the contact between the fill and underlying formational soils. Fill. The fill soils were found to consist of intermixed sandy clays and clayey and silty sands. In general, the fill material is relatively firm, and no exceptionally loose zones of soil were encountered. The fill is immediately underlain by clayey topsoils which are discussed below. The fill was placed during mass grading of La Costa South, Unit No. 5 in conjunction with testing and observation services provided by Benton Engineering, Incorporated, as documented in their report dated October 19, 1970 entitled "Project No. JO-l- 5D, County Permit No. L5548, Final Report on Compacted Filled Ground, Lots 330 to 382, inclusive, Lots 389 to 394, inclusive, Lots 400 to 410, inclusive, and Certain Street Areas of La Costa South Unit No. 5, Also certain offsite areas adjacent to Lots 368 to 370, inclusive and Lots 377 to 379, inclusive, San Diego County, California". The results of-density tests 277, 282, 286, 292, 388, 402, 408, 428, 466, 472, 474, 476, 478 and 510 - - -5- GEOCON -. - - - - - - -. - - -_ - - - - - - - File No. D-2234-MO1 May 29, 1980 recorded in the above referenced report indicate that fill placed at the site was compacted to at least 90 percent of maximum dry density. The moisture-density test results of undisturbed samples of the fill taken from our exploratory borings tend to support the above indication. It should be noted that fill depths of up to 40 feet are in- dicated in the referenced report, whereas grading plans for the site and the results of our exploratory borings indicate maximum fill depths to be more on the order to 27 feet. Examination of soil conditions encountered in our exploratory borings and trenches further indicates that the fill mass is immediately underlain by a thick layer of clay topsoil. No evidence of benching of the fill into formational soils was observed in our excavations. For this reason, recommendations have been included herein to provide for reconstruction of the fill slope at the north end of the site to reduce the likeli- hood of deep-seated failure of the fill mass near its contact with the topsoil. Reconstruction of the slope will also en- compass repair of the existing near-surface sloughage. Topsoil. Topsoils consisting of stiff clays and sandy clays were encountered immediately below the fill. The top- soil layer was in excess of five feet thick in both of our exploratory borings. Delmar Formation. The Delmar Formation is exposed in the cut portions of the building pad at the southwest portion -6- GEOCON - - -. - - - - - File No. D-2234-MO1 May 29, 1980 of the lot and is present below the existing fill and topsoil and nearthebase of slopeinthe northerly portion of the site. The formational soils typically consist of dense to very dense silty sands with varying clay content. Occasional thin beds of very dense sandy silt were also encountered. Free water seep- age was noted in localized zones on the walls of Boring 2 within the formational materials. Geologic Hazards Some of the formational materials in the vicinity of the site are characteristically weak and are subject to failure as near- surface slumps or more deeply seated landslides. At the time of this investigation, an active landslide was present along the south side of La Costa Avenue, immediately opposite the subject site. In addition, several other very recent as well as ancient slides were observed in the general vicinityofthe site. Although no evidence of ancient landsliding was observed in any of our exploratory excavations, an offsite boring imme- diately north of the property is presently planned to further explore the possibility of the presence of a deep-seated slip surface underlying the site. The results of the additional test boring will be presented as an addendum to this report. It is our opinion, based on our site reconnaissance, evidence obtained in the exploratory excavations and a review of pub- lished and unpublished geologic maps and reports, that the site is not located on any known fault trace. In addition, no landslides or other unstable geologic conditions were ob- served on the property. - - -J- - - - - - -. - - - - - - - - File No. D-2234-MO1 May 29, 1980 Seismicity No active faults are known to exist at or in the immediate vi- cinity of the site, and none were encountered in the course of our investigation. The nearest known active fault is the Elsin- ore Fault which lies approximately 24 miles to the northeast. It is our opinion that the site could be subjected to moderate to severe ground shaking in the event of a major earthquake along the Elsinore Fault or one of a number of other active and potentially active faults in the Southern California re- gion, however, the seismic risk at the site is not signifi- cantly greater than that of the surrounding developments. Groundwater As discussed earlier in this report, localized water seeps were observed in Boring 2 within the Delmar Formation at a depth of about 26 feet below the existing ground surface. Al- though the depth of the free water is such that it probably does not represent a significant geologic hazard in itself, provisions have been made in the slope reconstruction details presented herein to intercept free water which may migrate to the face of the slope at then north end of the site. The pre- sence of phreatophytes on the face of the slope is an indica- tion that the above condition may be at least partially responsible for existing near-surface sloughage in the slope. - - -8- File No. D-2234-MO1 May 29, 1980 - - - - CONCLUSIONS AND RECOMMENDATIONS General 1. It is our opinion that the site is suitable for the pro- posed development of a five-unit condominium complex provided that: a. the existing fill has been properly compacted as documented in the report of October 19, 1970 by Benton Engineering; and b. the recommendations of this report are carefully followed. 2. Geocon, Incorporated assumes no responsibility for the performance of fill placed in conjunction with testing and ob- servation services provided by others. We recommend that Benton Engineering be retained to review the above referenced report to determine whether soil conditions at the site remain suit- able for construction of the proposed project. 3. Depending on the condition of existing fills at the site, some postconstruction settlement may be experienced in struc- tural areas. The grading recommendations provided herein are intended only to reduce the possibility of deep-seated failure near the contact of the existing fill with underlying topsoils and to repair existing near-surface sloughage. A gravel blanket drain is also reconnrended to intercept water which may migrate through the fill and eventually exitthrough the face of the slope. -9- GEOCON - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 Grading 4. We recommend that the face of the existing fill slope be reconstructed as diagrammed on Figures 2 and 3. The site should first be cleared of vegetation. After the vegetation has been exported, the face of the slope should be overexcavated to an inclination of 1.0 horizontal to 1.0 vertical beginning at a point 15 feet south of the existing top of slope (see Figure 2). The excavation should extend at least two feet below the con- tact of the topsoil and the underlying formational material. A representative of our office should observe the excavation to ascertain that the proper depth has been reached. 5. After the excavation is complete, a gravel blanket drain should be placedas shown in Figure 3. The gravel should be wrapped in Mirafi 140 filter fabric to prevent clogging of the gravel by infiltration of fine material. A four-inch-diameter perforated A.B.S. pipe should be placed in the gravel blanket approximately three inches above the bottom of the excavation. The pipe should have a fall of at least one percent over the entire length of the drain. A nonperforated pipe should carry the water through the reconstructed slope to an appropriate controlled drainage. A gunite bench drain would be suitable for this purpose. A representative of our firm is able to assist in obtaining the filter fabric for drain construction. 6. The drain system would probably be most easily constructed concurrently with replacement of the slope material. -lO- GEOCON I I I I I I I I I I I I I I I I I 1 I NATURAL GROUNDSURFACE t PROPOSED SLOPE RECONSTRUCTION EXISTING GRADE loo’- -------1’ SEE DRAIN DETAIL BELOW IC CROSS -SECTION SCALE: I”= 40’ FIGURE: 2 DRAIN DETAIL FIGURE : 3 NO SCALE -- - - -. - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 7. Fill should be replaced in the excavation in layers no thicker than will allow for adequate bonding and compaction. A layer thickness of six to eight inches may be assumed to be satisfactory for this project. The fill material should not be more than two percent above optimum moisture content when being replaced and recompacted. It may be necessary to allow the overexcavated material to aerate for a period of time to reduce the moisture content to an acceptible level. An alter- native to such aeration would be to import and mix dryer material into the existing material. 8. A small vibratory sheepsfoot such as a Raygo Rumbler would provide the most satisfactory means of compacting the material used to reconstruct the slopes. 9. The finished slope should be planted with a light ground cover to reduce the potential for erosion by surface water. Iceplant is not suitable for this purpose. Foundations and Floors 10. Foundations and floors should conform to the recommenda- tions in the Benton Engineering report of October 19, 1970 for "'Type A Lots". Drainage 11. Adequate site drainage is imperative.' Under no circum- stances should water be allowed to pond adjacent to footings. -12- GEOCON - - - - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 12. Water should not be allowed to discharge over slopes. Surface runoff should be directed into swales or other con- trolled drainages. 13. Roof downdrains should discharge into splashblocks and runoff should be directed to controlled drainages. 14. The above recommendations are subject to revision based on results of additional field investigations or a change in development plans. Our office should be notified in the event of any significant changes in development plans. -13- GEOCON _ ^ _ _ ^ _ _ _ _ - - - - - - - - File No. D-2234-MO1 May 29, 1980 LIMITATIONS AND UNIFORMITY OF CONDITIONS 1. The recommendations of this report pertain only to the site investigated and are based upon the assumption that the soil conditions do not deviate from those disclosed in the investigation. If any variations or undesirable conditions are encountered during construction, or if the proposed con- struction will differ from that planned at the present time, Geocon, Incorporated should be notified so that supplemental recommendations can be given. 2. This report is issued with the understanding that it is the responsibility of the owner, or of his representative, to ensure that the information and recommendations contained herein are brought to the attention of the architect and en- gineer for the project and incorporated into the plans, and the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field. 3. The findings of this report are valid ads of the present date. However, changes in the conditions of a property can -14- GEOCON . ^ ^ _ _ ^ - - - - _,_ __ - - - - - - - - - - - - _- - - File No. D-2234-MO1 May 29, 1980 occur with the passage of time, whether they be due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards may occur, whether they result from legislation or the broad- ening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control. Therefore, this report is subject to review and should not be relied upon after a period of three years. -15- GEOCON .__^ ^_-^_ .___ - - - - - - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 TABLE I Summary of In-Place Moisture-Density and Direct Shear Test Results Sample No. l-l l-3 l-5 l-6 l-7 l-8 l-9 l-10 l-11 l-12 2-l 2-2 Depth ft. -- 5 10 15 20 21 25 30 35 46 51 10 16 Dry Moisture Unit Density Content Cohesion pcf % psf 103.5 20.6 101.7 22.5 103.3 22.0 104.1 18.5 103.4 23.0 104.0 9.8 113.8 17.3 104.6 20.6 109.8 19.2 156.9 2.2 112.4 14.8 121.1 12.2 -- 902 -- -- -- -- 450 -- A-l Angle of Shear Resistance degrees 28 -- 24 -- GEOCON ..,^^Do^D.-D~ - - - - - - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 TABLE II Summary of Laboratory Compaction Test Results A.S.T.M. D1557-70 Max.Dry Optimum Sample Depth Density Moisture No. ft. Description pcf % dry wt. l-2 6 Light green-gray, Silty, 114.2 14.6 fine fine to fine SAND 1-4 11 Brown, Sandy CLAY 121.8 12.2 A-2 - - File No. D-2234-MO1 May 29, 1980 dium dense, moist, light green- gray, Silty, very fine to fine -- ---- --__~ Medium dense, very moist, orange- brown, Clayey medium SAND EDPSOIL/FILL--- Medium stiff, very moist, green/ brown/black, Sandy CLAY with larg root fragments, wood chips, stron organic odor Medium stiff, very moist, dark brown, Sandy CLAY, highly organic Figure 4, Log of Test Boring 1 Continued next page A-3 GEOCON - - - 7 - - - 7 - -, -. - - - - - - - - - - - - - - - - - - - - - File No. D-2234-MO1 Mnv 39 lQ,Qfl -- __- Medium hard, moist, brown, Sandy CLAY/Clayey SAND ( 38- "':" a:.'; L- becomes light green layer of very dense, moist, gray, Sandy SILT --__~--- ,. .'.I:I: I.. Very dense, moist, orange-brown, Silty, medium to very coarse SAND, 44.. .:I..: I : I .'. highly micaceous :~;I:i~I:: ------- free water on wall of hole 46-l-11 ti.;':.J: 32/ 109.8 19.2 :..'I;;1 : !,: 8" 48- ::I:,I;II( Cj:iIi’: 50- 1-12 +j:.‘,j’;!, i 8 I Very dense, moist, gray, Silty 156.9 2.2 52.. SAND, micaceous, cemented BORING TERMINATED AT 51.0 FEET h'igure 5, Log of Test Boring 1 Continued A-4 - - File No. D-2234-MO1 \I___ In ,non - - - -- - - - - - - - - - - - Medium dense, moist, green-gray, Silty, very finr to fine SAND -_ chunks of brown CLAY ----- ium dense, moist, green/brown, Clayey SAND/SILT to stiff Sandy m hard, moist, dark brown, ---- -- Medium dense, moist, gray/brown, orange nodules becomes orangelgray free water entering hole - minor remolded clay encountered l/S" thick, at bndry of several 3"-4" thick or clayey sand lenses A-5 - - - - - - - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 .30.- -32- -34.. -36- -38- -4o- -42.. -44- -46- -48- -5o-- Figure LOG 1 X47,*, OF TTi +a& i ;, .! , :;:, I,’ i.j:i /:/:I ,I,.‘! 11: I’:/ :; G . . I:l.‘l: i.il.1 . ..” i:t:1 i;ii,l ,;I’[: I:!:/: I:.1 :/: I .I: 1, I :I: I: /,:;.j: - h&C-,. Rcr,r,o, *,orr” - - Log or BORING NO. 2 CONTINUED ~--- Dense, moist, light green, Silty, medium to coarse SAND _-~-~-- Dense, moist, orange-brown. Silty medium to coarse SAND, highly ' micaceous, locally gypsiferous fissile along micaceous zones Very dense, very moist, pray, Silty, fine to medium SAND, highly micaceous, fissile laminae BORING TERMINATED AT 50.0 FEET :st Boring, 2 Continued A-b DR” DENS/TI P.C.! uo,*,um CovIEN7 % a,/ r, - - - - - - - - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 Soft, wet, black-brown, Sandy Medium dense, very moist, orange/ gray mottled, Clayey SAND TRENCH TERMINATED AT 8.0 FEET 0.. 2.. TRENCH NO. 2 : .'~ TOPSOIL . . .: '. '. '. Soft, wet, black-brown, Sandy .'.1.., CLAY __ .;:.,,: 1 \-- becomes dark olive-brown 4. 6- 8- LO. :.: . . ,. . . . ..,I : . . . ..c.. ; <, .'~' '. .>; ,;z:. /. ', :: /. 'i., '7... ..)/: ..;; L'. :,,/ DELMAR FORMATION Medium dense, very moist, gray- brown/orange mottled, very Clayey SAND TRENCH TERMINATED AT 10.0 FEET Figure 8, Log of Test Trenches 1 & 2 A-7 GEOCON . .._^__^_ ._-- - - - - - - - .- - - - File No. D-2234-MO1 Mzlv 79 lOan IALL” -2. I,“\, CONSOLIDATION CURVE APPLIED PRESSURE (in KIPS /ft* ) - - - - - - .- - - -. - File No. D-2234-MO1 May 29, 1980 RECOMMENDED GRADING SPECIFICATIONS for LOT 405 CARLSBAD TRACT 79-11 Carlsbad, California 1.1 1.11 1.12 1.13 2.1 2.11 General Description These specifications have been prepared for grading and site development of Lot 405 Carlsbad Tract 79-11 located in the La Costa area of Carlsbad, California. Geocon, Incorporated, hereinafter described as the soil engineer, should be consulted prior to any site work connected with these specifications. These spec- ifications shall only be used in conjunction with the soil report of which they are a part. This item shall consist of all clearing and grubbing, preparation of land to be filled, filling of the land, spreading, compaction and control of the fill, and all subsidiary work necessary to complete the grading of the filled areas to conform with the lines, grades and slopes as shown on the accepted plans. The soil engineer shall test and observe all grading operations. In the event that any unusual conditions not covered by the special provisions are encountered during the grading operations, the soil engineer shall be contacted for further information. Tests The standard test used to define maximum density of all compaction work shall be the ASTM Test Procedure D1557-78. All densities shall be expressed as a relative compaction in terms of the maximum density obtained in the laboratory by the foregoing standard procedure. - - B-l - - - - - - - - - File No. D-2234-MO1 May 29, 1980 3.1 3.11 3.12 3.13 3.14 3.15 3.16 Clearing, Grubbing, and Preparing Areas to be Filled Any trees not utilized in landscaping,, structures, weeds, and other rubbish shall be removed, piled, or otherwise disposed of so as to leave the areas that have been dis- turbed with a neat and finished appearance, free from unsightly debris. Any septic tanks, if encountered, and debris must be removed from the site prior to any building, grading or fill operations. Septic tanks, including all connecting drain fields and other lines, must be totally removed and the resulting depressions properly reconstructed and filled to the complete satisfaction of the super- vising soil engineer. All water wells on the site shall be capped according to the requirements of the San Diego County Health De- partment. The strength of the cap shall be at least equal to the adjacent soil. The final elevation of the top of the well casing must be a minimum of 36 inches below any adjacent grade prior to any grading of fill operations. All buried tanks, if encountered, must be totally removed and the resulting depressions properly recon- structed and filled to the complete satisfaction of the supervising soil engineer. All vegetable matter and soil designated as unsuitable by the soil engineer-shall be removed under the direc- tion of the soil engineer. The then exposed surface shall then be plowed or scarified to a depth of at least eight inches and until the surface is free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. The original ground upon which the fill is to be placed shall be plowed or scarified deeply, and where the slope ratio of the original ground is steeper than 6.0 hori- zontal to 1.0 vertical, the bank shall be stepped or benched, At the toes of the major fills and on the side- slope fills, the base key shall be, as described else- where in this report, at least 10 feet in width, cut at B-2 - - GEOCON . ..^^ ""^" ._-- - - - - - - - - - - - File No. D-2234-MO1 May 29, 1980 3.17 4.1 4.11 4.12 5.1 5.11 5.12 least three feet into the undisturbed or native soil, and sloped back into the hillside at a gradient of not less than two percent. Subsequent keys should be cut into the hillside as the fill is brought up the slope. The construction of subsequent keying operations shall be determined by the soil engineer during grading oper- ations. Ground slopes which are flatter than 6 to 1 shall be benched when considered necessary by the soil engineer. After the foundation for the fill has been cleared, plowed, or scarified, it shall be disced or bladed un- til it is uniform and free from large clods; brought to the proper moisture content by adding water or aer- ating; and compacted to relative density of not less than 90 percent. Materials Native soil, free of organic material and undesirable deleterious material, may be used as fill. Native soil which is expansive shall not be placed on the top two feet of building pads without the approval of the soil engineer. The materials for fill shall be approved by the soil engineer before commencement of grading operations. Any imported material must be approved for use before being brought to the site. The materials used shall be free from vegetable matter and other deleterious material, and be nonexpansive. Expansive soil is defined as soil which expands more than 3.0 percent when saturated at 90 percent relative compaction and optimum moisture content under a surcharge of 150 psf. Placing, Spreading, and Compacting Fill Haterial The selected fill material shall be placed in layers which when compacted shall allow-adequate bonding and compaction. Each layer shall be spread evenly and shall be thoroughly blade mixed during the spreading to ensure uniformity of material in each layer. When the moisture content of the fill material is be- low that specified by the soil engineer, water shall B-3 GEOCON ...^^n..^n.m”n - - - - - - - - - - - - - -, - File No. D-2234-MO1 May 29, 1980 5.13 5.14 5.15 5.16 5.17 5.18 be added until the moisture content is as specified to assure thorough bonding during the compaction process. When the moisture content of the fill material is above that specified by the soil engineer, the fill material shall be aerated by blading or other satisfactory methods until the moisture content is as specified. After each layer has been placed, mixed, and spread evenly, it shall be thoroughly compacted to a relative compaction of not less than 90 percent. When fill material includes rock, no rocks will be allowed to nest, and all voids must be carefully filled with small stones or earth and properly compacted. No rocks larger than six inches in diameter will be permitted in the fill. Compaction shall be by sheepsfoot rollers, multiple- wheel pneumatic-tired rollers, or other types of acceptable compacting rollers. Rollers shall be of such design that they,will be able to compact the fill to the specified moisture content range. Rolling of each layer shall be continuous over its entire area and until the required density has been obtained. Field density tests shall be made by the soil engineer. Lhere sheepsfoot rollers are used, the soil may be disturbed to a depth of several inches. Density tests s-hall be taken in compacted material below the disturbed surface. When these tests indicate that the density of any layer of fill or-portion thereof is below the required 90 percent density, the particular layer or portion shall be reworked until the required density has been obtained. The fill operation shall be continued in compacted layers, as specified above, until the fill has been brought to the finished slopes and graded as shown on the accepted plans. Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction opera- tions shall be continued until the slopes are stable. B-4 - - GEOCON 1UrnlPnl.Te” - - - - - - - - -. - - - - - - - File No. D-2234-MO1 May 29, 1980 5.19 All earthmoving and working operations shall be con- trolled to prevent water from running into excavated areas. All water shall be promptly removed and the site kept dry. 6.1 6.11 Disposal of Oversize Rock Oversize rock shall be either exported from the site, used for landscaping purposes, or placed in designated nonstructural fill areas. 6.12 Prior to grading, the soil engineer shall be consulted to approve any proposed nonstructural fill areas. In general, nonstructural fill areas will be acceptable if located outside of the "zone of influence" of proposed structures; e.g. rear yard fills at least 15 feet from structures and beneath street areas (deeper than pro- posed utility lines). 6.13 Oversize rock shall not exceed four feet in greatest dimension, shall be placed in lifts not exceeding four, and shall be placed in a manner that will not produce "nesting" of the rock. The voids between the rocks shall be completely filled with fine granular material. 6.14 7.1 7.11 No oversize rock shall be placed within four feet of finish lot grade nor within the anticipated depth of utility lines, whichever is deeper. Engineering Observation Field observations by the soil engineer shall be made during the fill and compaction operations so that he can express his opinion regarding the conformance of the grading with the accepted specifications. 8.1 Seasonal Limits 8.11 No fill material shall be placed; spread, or rolled while it is at an unsuitable high moisture content, nor during unfavorable weather conditions. When the work is interrupted by heavy rain, fill operations shall not be resumed until field tests by the soil engineer indicate that the moisture content and den- sity of fill are as previously specified. B-5 GEOCON . ..I^_“^~.__.. . CONSULTANTS IN THE APPLIED EARTH SCIENCES File No. D-2234-MO1 June 11, 1980 HCH and Associates 8963 Complex Drive, Suite A San Diego, California 92123 Attention: Mr. Mike Bingham Subject: Carlsbad Tract 79-11 La Costa Avenue Carlsbad, Califol ADDENDUM : rnia TO PRELIMINARY SOIL INVESTIGATION AND GEOLOGIC RECONNAISSANCE Gentlemen: This addendum is to provide the results of an offsite test boring which was excavated at a location approximately 50 feet north of the subject site's north property line. The offsite drilling was performed to further investigate whether deep-seated ancient landsliding has occurred at the site. The 30 inch diameter boring was drilled to a depth of 20 feet The approximate location of the additional boring is shown on the attached Site Plan, Figure 1. Also shown on Figure 1 is the approximate limits of areas to be excavated for the proposed buttress. A log of the boring is presented on Fig- ure 2. The log depicts the depth and description of the various soil types encountered. In general, the soils encountered in the boring consisted of massive, dense, silty, fine- to medium-grained micaceous sands with slightly clayey zones and cemented layers. Mea- surements of iron-stained zones in the sand indicate a gen- eral northeasterly strike and a southerly dip of 10 to 15 degrees within the formation. No evidence of ancient landsliding was observed in the bor- ing. At a depth of approximately 20 feet below the pad grade of Lot 400, extremely dense cemented sandstone was encounter- ed, and the boring was terminated. n 6645 CONVOY COURT . SAN DIEGO, CA LIFORN ‘IA 92111 . PHONE 1714) 292-5100 File No. D-2234-MO1 June 11, 1980 A reconnaissance of exposures of formational soils in cut slopes in the general vicinity of the site indicates that the attitudes observed in our boring are representative of the regional strike and dip in the La Costa area. If you have any questions, or if we may be of further ser- vice, please do not hesitate to contact our office. Very truly yours, GEOCON. INCORPORATED MSC:MWH:lm copies: (4) addressee -2- File No. D-22344 1 June 11, 1980 @..-LOCATION 0~ TEST GORING ~...A~PRox. LOCATION OF PROPOSED SLOPE RECONSTRUCTION ( BUTTRESS) SITE PLAN AND LOCATION OF TEST BORINGS CARLSBAD TRACT 79-11 Carlsbad, California ‘IGURE 1 I GEOCON, INCORPORATED [ PAGE 3 GEOCON - - - File No. D-2234-MO1 June 11, 1980 tern SAUPLE LOG .4 A"*rofim DESCRIPmJN /N N"w9ER IDo(T,ON Rmr/om DRY uo,*Tu*, P-ET OF *,o.lm oEN*lrl CovrfN~ SAW-M 0. c. I % c+w n 0. BORING NO. 3 ,, 2- 4.. 6- 8- lo- Dense, moist, light yellow-brown, Silty, fine to medium SAND, micaceous, cemented zones, slightly Clayey zones ,i:;: i;l :>,';,'; / :I, $,$; ";i;l: j+?:i:: :x7 -- metavolcanic rock fragments / ::I &ii: ---.-- becomes light brown 12- :,, ., '-I:/~~' ; '. >r,. : 14. 16- 18s 20-' $1. 1:; : .;L :$f.:y . . .,.. ;,:/fq~--- highly cemented nodule i'i';,;l;;' ).-- light pay-brown /' $g,'/ / i:i:.$j.;j: r- becomes highly cemented ---. ,... BORING REFUSAL AT 20.0 FEET ON CEMENTED MATERIAL ‘igure 1, Log of Test Boring 3 -4- GEOCON .._. -