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HomeMy WebLinkAbout3593; Faraday Avenue Extension; Engineering Geology Report; 1999-11-05&L== Leighton and Associates A GTG Company GEOTECHNICAL CONSULTANTS ENGINEERING GEOLOGY REPORT OF ROUGH-GRADING, FARADAY AVENUE EXTENSION, STATION 10+00 TO STATION 62+00, CARLSBAD, CALIFORNIA PROJECT NO. 3593 Project No. 980118-003 November 5, 1999 Prepared For CITY OF CARLSBAD Engineering Department 2075 Palmas Drive Carlsbad, California 92009-1576 3934 Murphy Canyon Road, #6205, San Diego, CA 9213-4425 (619) 292-8030 • FAX (619) 292-0771 • www.leightongeo.com ^HBHfS Leighton and Associates A GTG Company GEOTECHNICAL CONSULTANTS Novembers, 1999 Project No. 980118-003 To: City of Carlsbad, Engineering Department 2075 Palmas Drive Carlsbad, California 92009-1576 Attention: Ms. Sheri Howard Subject Engineering Geology Report of Rough Grading, Faraday Avenue Extension, Station 10+00 to Station 62+00, Carlsbad, California, Project No. 3593 In accordance with your request and authorization, Leighton and Associates, Inc. has provided limited geotechnical observation services during rough-grading operations for the Faraday Avenue Extension project, Station 10+00 to Station 62+00 in Carlsbad, California. The accompanying report summarizes our observations of the geotechnical conditions encountered during rough-grading of the subject site. If you have any questions regarding this report, please do not hesitate to contact this office. We appreciate this opportunity to be of service. "^^ Respectfully submitted, LEIGHJON AND ASSOCIATES, INC. CERTIFIED ENGINEERING GEOLOGIST JD/SAC/MRS Distribution: (4) Addressee Michael R. Stewarr>££G 1349 (Exp. 12/31/99) Vice President/PrincipalGeologist S Senior 3934 Murphy Canyon Road, #B205, San Diego, CA 9213-4425 (619) 292-8030 • FAX (619) 292-0771 • www.leightongeo.com 980118-003 TABLE OF CONTENTS Section Page 1.0 INTRODUCTION 1 2.0 SUMMARY OF ROUGH-GRADING OPERATIONS 3 2.1 SITE PREPARATIONS AND REMOVALS 3 2.2 SUBDRAINS AND PANEL DRAINS 4 3.0 ENGINEERING GEOLOGY SUMMARY 6 3.1 GENERAL 6 3.2 GEOLOGIC UNITS 6 3.2.1 Artificial Fill (by others, Map Symbol-AJ) 6 3.2.2 Older Artificial Fill (by others, Map Symbol-Afc) 6 3.2.3 Topsail (Unmapped) 7 3.2.4 Quaternary Alluvium (Map Symbol-Qal) 7 5.2.5 Quaternary Colluvium (Map Symbol ~ Qcol) 7 3.2.6 Quaternary Landslide Deposits (Map Symbol-Qls) 7 3.2.7 Quaternary Marine Sediments (Map Symbol - Qm) 8 3.2.8 Tertiary Santiago Formation (Map Symbols - Ts (ss), Ts(cs) andTs. 8 3.2.9 Cretaceous/Jurassic Santiago Peak Volcanics (Map Symbol - KJsp 8 3.3 GEOLOGIC STRUCTURE 8 3.4 LANDSLIDES AND SURFICIALFAILURES 9 3.5 FAULTING 9 3.6 GROUND WATER 9 4.0 CONCLUSIONS AND RECOMMENDATIONS 10 4.1 REMOVALS 10 4.2 SLOPE STABILITY 10 4.3 CONSTRUCTION DELAY 10 4.4 SUPPLEMENTAL DESIGN RECOMMENDATIONS 10 4.5 SUBDRAIN OUTLETS 11 5.0 LIMITATIONS 12 FIGURES FIGURE 1 - SITE LOCATION MAP - PAGE 2 PLATES PLATES 1 THROUGH 7 - AS-GRADED GEOTECHNICAL MAPS - IN POCKETS APPENDICES APPENDIX A - REFERENCES 980118-003 1.0 INTRODUCTION In accordance with your request and authorization, Leighton and Associates, Inc. (Leighton) has provided limited geotechnical services during rough grading for the extension of Faraday Avenue, Station 10+00 to Station 62+00 in Carlsbad, California (Figure 1). Rough grading for the project was conducted from July 1999 to September 1999. This report summarizes our observations of the geologic conditions encountered during mapping of the rough-grading operations. -1- CITY OFOCEANSIDE PACIFICOCEAN CITYOF SAN MARCOS V I CITY OF ENCINITAS SITE LOCATION MAP Faraday Avenue Extension Carlsbad, California PROJECT No. 980118-003 SCALE Not to scale ENGR./GEOL. SAC/MRS DRAFTED By KAM DATE October 1999 — I n D~l n Leighton and Associates, Inc. FIGURE No.L 980118-003 2.0 SUMMARY OF ROUGH-GRADING OPERATIONS Rough grading for the extension of Faraday Avenue was conducted from July 1999 through September 1999. Rough grading operations were performed by W.R. Connelly, Inc. Geologic mapping, evaluation of removals, recommendations for subdrain installation, and slope stability analysis were performed by Leighton and Associates. Geotechnical observation of placement and testing of compacted fills was provided by Kleinfelder under separate contract with the City of Carlsbad. A geologist from Leighton was on site on an as-needed basis during the excavation activities of rough grading. 2.1 Site Preparations and Removals Prior to grading, the areas of proposed development were stripped of surface vegetation and debris. Removals of unsuitable and potentially compressible soil, including undocumented fill, topsoil, colluvium, alluvium, and highly weathered formational material, were generally made to competent material. In areas, where ground water and saturated materials impeded further excavation in alluvial materials, removals were made to approximately 2 feet above the existing groundwater elevation. Removals of the unsuitable and potentially compressible soil were performed in general accordance with recommendations made in the project geotechnical report (Leighton, 1998) and field recommendations made during the course of grading. Approximate bottom elevations in the removal areas are shown on the As-Graded Geologic Maps (Plates 1 through 7). In fill slope areas (including stability and buttress fills), remedial removals were made to allow for placement of compacted fill within a 1:1 projection downward from the toe of slope. Except where limited by biological constraints, these removals were completed to competent formational materials or, where encountered, to approximately 2 feet above ground water. The limits of fill placement mapped along the margins of the work alignment identify the top of the temporary backcuts that were made during rough grading. For this reason, compressible soils may underlie some fills placed during rough grading along the limits of work. Any future construction or grading adjacent to the limit of work should include removal of unsuitable material beneath fill along the margins of the project. To create sufficient fall on subdrains, some excavations were made outside the limits of work. For these excavations, complete removal of compressible soils was not performed. The locations of these partial removals are shown on the As-Graded Geologic Maps (Plates 1 through 7). Fill was placed over installed subdrains in these areas only to restore original topography and should not be considered competent, engineered fill. Before placement of additional fills or structural improvements in these areas, complete removals should be made. In areas where clay seams, landslide failure surfaces, or potential landslide failure surface were encountered, removals were made to allow for buttressing of these surfaces to mitigate instability. The limits of the keyways for stability and buttress fills are shown on the As-Graded Geologic Maps (Plates 1 through 7). -3- 980118-003 2.2 Subdrains and Panel Drains Subdrains were installed along the heel of stability and buttress fills and along canyon fills. The approximate locations of these drains are shown on the accompanying As-Graded Geologic Maps (Plates 1 through 7). Buttress and canyon subdrains consisted of 4-inch and 6-inch diameter perforated pipe surrounded by % inch gravel wrapped with filter fabric. The following table contains a summary of the locations where subdrains were extended from below the roadway and into the area of the proposed golf course. Preliminary grading plans were reviewed and the subdrain outlets located such that they could be extended during the golf course grading. In several areas, the subdrain outlet was left below grade and a temporary vertical outlet was installed. These temporary outlets should be removed and the drain extended as part of future grading. ^Station 25+45 30+50 35+50 37+00 41+00 44+40 50+40 ^ 36.5 55 52.5 60.5 90 65 80 In addition to the subdrain pipes, vertical panel drains were installed at regular intervals along the backcut of selected slope buttress fills. Backdrains consisted of 4-foot wide panels of J-Drain 302 placed on approximate 20-foot centers. Vertical panel drains were spaced along the backcuts at the following stability and buttress fill locations on the north side (uphill) of the roadway alignment. Vertical Panel Drain Locations Station 24+50 to Station 30+20 Station 30+60 to Station 33+70 Station 38+60 to Station 41+70 Station 41+30 to Station 43+40 -4- 980118-003 Several subdrains were installed and extended to proposed storm drain structures. Subdrains should be connected to the drain structures as part of the continuing roadway construction. These subdrain outlets are located as follows: Subdrain Location Station 2 1+30 Station 50+80 Station 55+03 Station 56+00 Proposed Outlet Point Brow Ditch Storm Drain Box Storm Drain Box (2 drains) Storm Drain Box -5- 980118-003 3.0 ENGINEERING GEOLOGY SUMMARY 3.1 General A summary of the geologic conditions including geologic units, geologic structure, and faulting is presented below. The as-graded geologic conditions of the site are presented on the As-Graded Geologic Maps (Plates 1 through 7). 3.2 Geologic Units The geologic units encountered during the rough grading of Faraday Avenue project consisted of the following: recent and previously placed artificial fill, topsoil, alluvium, colluvium, Quaternary Landslide Deposits, Tertiary Santiago Formation, and Cretaceous/Jurassic Santiago Peak Volcmics. The approximate limits of the geologic units encountered during rough-grading are presented on the As-Graded Geologic Maps (Plates 1 through 7), and are briefly described below. 3.2.1! Artificial Fill (bv others. Map Svmbol-Af) Soils derived from on site excavations were used as fill material to achieve design grades, and to construct stability and buttress fills. These soils were placed by W.R. Connelly, Inc., under the observation and testing services of Kleinfelder. As encountered during grading these soils generally consisted of light brown to dark brown, gray and greenish gray, sands, silts and clays. These fill soils are differentiated on the geotechnical maps from the existing fill soils from the previous phases of adjacent grading. 3.2.2 Older Artificial Fill (bv others. Map Symbol-Afc) Older artificial fill soils were encountered at the intersection of Faraday and Cannon Road at Station 10+00 and at the end of the existing Faraday Avenue near Station 62+00. According to review of previous reports, the soils at Cannon Road were placed under the observation and testing services of Geopacifica, (1996). Desiccated, loose and disturbed portions of existing fills were removed before placement of additional fill material. These fill soils are differentiated on the geologic maps from the fill soils place during the current phase of grading. -6- 980118-003 3.2.3 Topsoil (Unmapped) Topsoil consisting of dry, loose, silty and clayey sands and clays, generally on the order of 2 to 4 feet in thickness and locally up to 6 feet in thickness, was encountered on portions of the site where no grading had previously been completed. These soils were considered potentially compressible and unsuitable to receive improvements in their existing condition. Where situated within the limits of work, these soils were removed and recompacted during rough grading operations, except at the margins where temporary backcuts blend to the existing grade. 3.2.4 Quaternary Alluvium (Map Svmbol-Oal) Quaternary alluvium was encountered in the lower portions of all the drainages at the site. As encountered, this material generally consisted of light to dark brown, moist, loose to medium dense, porous, clayey to silty, fine to coarse sand. Abundant roots and rootcasts were also visible within this unit. Where possible within the limits of work, this material was completely removed during grading to competent formational material. Where saturated conditions were encountered, removals were made to approximately 2 feet above the groundwater table. Saturated alluvial soils that were left in place beneath the roadway prism are mapped from Station 16+25 to Station 19+50 (approximate) and Station 35+50 and Station 36+00 (approximate). Due to the potential for consolidation settlements, we have recommended installation of settlement monuments and monument surveying in these areas. 3.2.5 Quaternary Colluvium (Map Symbol - Qcol) Quaternary colluvium was encountered throughout the site in areas situated at elevations above the alluvial drainages. Colluvial soils generally consisted of light to dark brown, damp to moist, loose to medium dense, silty to clayey sand and soft to firm, silts and clays. The colluvial soils were typically porous and potentially compressible. These soils were removed and recompacted where encountered within the limits of work. 3.2.6 Quaternary Landslide Deposits (Map Symbol-Pis) Quaternary landslide deposits were encountered across the alignment of the road from Station 23+00 to 27+00 (approximate). This unit consisted of soils derived from topsoil, alluvium, colluvium, and Santiago Formation materials. A landslide failure surface that consists of remolded or highly sheared plastic clay seam generally underlies this unit. Highly weathered and disturbed portions of the landslide were removed during the grading operations. Stabilization of the landslide included the construction of buttress keys as shown on the geotechnical map. A portion of unexcavated slide material that was left in place underlies the roadway from Station 23+00 to 27+00. Based upon our analysis of the as-graded conditions in this area, a factor of safety of at least 1.5 was attained for this material and the as-graded slopes. -7- 980118-003 3.2.7 Quaternary Marine Sediments (Map Symbol - Qm) The Pleistocene-aged marine and lagoonal sediments were observed to be of limited areal extent overlying Santiago Formation materials near the intersection with Cannon Road. As encountered during grading, this unit generally consists of finely bedded, sandy clays and silts, interbedded with fine-grained sands. 3.2.8 Tertiary Santiago Formation (Map Symbols - Ts (ss). Ts(cs) and Ts The Eocene-aged Santiago Formation, as encountered during grading, generally consists of three distinct divisions: a massive, fine to medium grained, white to light gray sandstone; a massive, randomly fissured, sandy siltstone and claystone; and a fine to medium grained sandstone, interbedded with sandy silts and clays. The dominant locally observed type has been mapped on the As-Graded Geologic Maps (Plates 1 through 7). Clay seams or potential landslide surfaces observed within this unit commonly divide differing sub-units or are found near changes in lithology. 3.2.9 Cretaceous/Jurassic Santiago Peak Volcanics (Map Symbol - KJsp The basement geologic unit observed on the project is the Cretaceous and Jurassic-aged Santiago Peak Volcanics. This volcanic rock varies somewhat in composition, but is primarily dacites and andesite. The weathered rock encountered during grading was typically light to dark red-brown in color. Weathering of this unit is generally controlled by fractures and jointing, which are typically at right angles. We observed that the uppermost metavolcanic rock is generally moderately to highly fractured (fracture spacing on the order of 2 to 6 inches) with a moderate to high amount of fines generated during the removals. Below these depths, fracturing is believed to be more widely spaced. 3.3 Geologic Structure Based on our geologic mapping during the rough-grading operations, bedding on site varies considerably along the alignment. Generalized mapped bedding plane strike and dip attitudes are presented in the As-Graded Gee-technical Maps. It should be noted that due to the undulatory nature of the bedding contract, significant local variation can exist. 3.4 Landslides and Surficial Failures Based on our review of the preliminary geotechnical report (Leighton, 1998), and our mapping during rough grading operations, there were no additional indication of landslides or other surficial failures within the site other than those landslides that were previously discussed. However, during a review of pertinent aerial photographs, several features, which may be related to mass movement, can be seen in the immediate vicinity. Therefore, we recommend that prior to any development -8- 980118-003 outside the limits of this phase of grading, a thorough evaluation with regard to landslides or other mass movement be completed by a qualified geotechnical engineer and engineering geologist. 3.5 Faulting Inactive Miocene-aged normal faults that offset the Santiago Formation were identified during site grading and our previous investigation. These faults are attributed to Miocene extension and are not believed to present a significant constraint to the project. No evidence of active faulting was encountered nor anticipated during rough-grading operations at the site. No evidence of surface faulting was observed during grading operations on site or during a review of pertinent aerial photographs. 3.6 Ground Water Ground water was encountered during rough grading operations of the site and symbols identifying observed locations and elevations are presented on the As-Graded Geotechnical Map. It should be noted that the majority of this phase of grading lacks a shallow ground water or widespread perched ground water condition. Subdrains and/or panel drains were installed in areas of observed seepage and in areas where future seepage is anticipated. Groundwater does not appear to be a significant constraint to proposed improvements provided the improvements are constructed with appropriate consideration to address surface and subsurface infiltration. Areas of additional localized seepage may occur after period of heavy rainfall or irrigation of upslope properties. If areas of additional seepage are noted, this office should be notified in a timely manner so that additional recommendations can be provided. -9- 980118-003 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 Removals Removal of compressible soils during rough grading for Faraday Avenue was performed in general accordance with the project geotechnical reports, geotechnical recommendations made during the course of grading, and the City of Carlsbad requirements. 4.2 Slope Stability Based on our geologic observation, engineering analysis and testing, it is our opinion that the slopes constructed of properly mixed and compacted fills (Leighton, 1998) at inclinations of 2:1 (horizontal to vertical) or flatter possess a factor of safety of 1.5 or greater to resist deep-seated and surficial instability. We recommend that all graded slopes be landscaped with drought- tolerant, slope stabilizing vegetation as soon as possible to minimize the potential for erosion. Erosion control fabric/measures should be considered while vegetation becomes established. Design of surface drainage provisions are within the purview of the project civil engineer. 4.3 Construction Delay We have recommended that settlement monitoring be performed for the two areas where saturated alluvium was left-in-place beneath the roadway fill prism from Station 16+25 to Station 19+50 and from Station 35+50 to Station 36+00. We recommend this office be provided with settlement monitoring data for review prior to construction of improvements in these areas. 4.4 Supplemental Design Recommendations It is our understanding that the City's testing laboratory will be performing additional tests throughout the remainder of the project to confirm that design assumptions agree with as-graded conditions. Supplemental design recommendations may be warranted based on observations and test results. This office should be contacted to provide additional recommendations where conditions differ from those assumed during the preliminary design phase. -10- 980118-003 4.5 Subdrain Outlets The site grading included the construction of several subdrain systems that will require the construction of outlets. These outlets should be constructed and the drains connected as part of the installation of the storm drain system. Care should be taken to not damage the outlets during future construction. In addition, several drains were extended to the proposed golf course area and temporary outlets constructed. These drains should be extended during future construction or be allowed to drain freely. -11- 980118-003 5.0 LIMITATIONS The presence of our field representative at the site was intended to provide the owner with professional advice, opinions, and recommendations based on observations of the exposed geologic conditions. We do not guarantee the contractor's work or services provided by other consultants, nor do our services relieve the contractor or his subcontractors of their responsibility if defects are subsequently discovered in their work. Our responsibilities did not include any supervision or direction of the actual work procedures of the contractor, his subcontractors, or the City of Carlsbad's designated testing laboratory. -12- 980118-003 APPENDIX A REFERENCES City of Carlsbad, Contract Documents and Special Provisions for Faraday Avenue Extension, Contract No. 3593, dated January 5, 1999. Geopacifica, 1990, As-Graded Geotechnical Report, Kelly Ranch Phase 1, Carlsbad Tract No. 83-30, Carlsbad, California, Project No. 160.1.4, dated January 10, 1990. Leighton and Associates, Inc., 1998, Geotechnical Investigation for the Proposed Faraday Avenue Extension, Alternate 8 Split, Carlsbad, California, Project No. 980118-003, dated July 1, 1998. , 1999a, Summary of Settlement Monitoring at Surcharge No. 1, Faraday Avenue Extension, Carlsbad, California, Project No. 980118-003, dated September 2, 1999. , 1999b, Geotechnical Review of Improvement Plans for Faraday Avenue Extension, Carlsbad, California, Project No. 980118-003, dated September 13, 1999. , 1999c, Method of Documenting Stability Fill Geometries and Keyway Elevations, Faraday Avenue Extension, Carlsbad, California, Project No. 980118-003, dated September 13, 1999. PLANS O'Day Consultants, 1999, Grading and Drainage Plans for Faraday Avenue, Project No. 3593, Sheet 1-15, dated June 10, 1999. A-l