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HomeMy WebLinkAbout8850373-07; Calavera Hills Park Site; Calavera Hills Park Site; 1986-11-24LEIGHTON and ASSOCIATES INCORPORATED SOIL ENGINEERING GEOLOGY GEOPHYSICS GROUND WATER HAZARDOUS WASTES November 24, 1986 Project No. 8850373-07 TO: ATTENTION: SUBJECT: City of Carlsbad Parks and Recreation Department 1166 Elm Avenue Carlsbad, California 92008-1989 Mr. Mark Steyaert, Park Planner Geotechnical Evaluation of Fill Soils Along Elm Avenue, Calavera Hills Park Site, Carlsbad, California References: (1) "Geotechnical Investigation, Calavera Hills Park Site, Carlsbad, California," Project No. 4850373-02, dated July 24, 1985, by Leighton and Associates, Inc. (2) "Supplemental Seismic Refraction Survey, Calavera Hills Park Site, Carlsbad, California," Project No. 4850373-05, dated May 16, 1986, by Leighton and Associates, Inc. (3) "Supplemental Geotechnical Reconnaissance and Grading Plan Review, Calavera Hills Park Site, Carlsbad, California," Project No. 8850373-06, dated October 21, 1986, by Leighton and Associates, Inc. , (4) "Grading Plans For: Calavera Park Site (CUP-266)," Project No. PE 2.86.16, Drawing No. 269-6, Prepared at a Scale of 1"=40', dated September 25, 1986, by Rick Engineering Company Introduction In accordance with your request and authorization, we have performed a geotechni- cal evaluation of the existing fill soils along Elm Avenue within the project park site. The purpose of this study was to evaluate the fill on the site and its suitability for structural support. The accompanying report presents a summary of our investigation and provides conclusions and recommendations relative to the proposed site development. 5421 AVENIDA ENCINAS, SUITE C, CARLSBAD, CALIFORNIA 92008 IRVINE WESTLAKE/VENTURA o DIAMOND BAR/WALNUT ° SAN BERNARDINO/RIVERSIDE o PALM DESERT o SANTA CLARITA/VALENCIA ° CARLSBAD o TEMECULA/RANCHO CALIFORNIA (619) 931-9953 SAN DIEGO 8850373-07 Since this is a supplemental investigation, this report incorporates and supple- ments the findings, conclusions, and recommendations presented in the referenced geotechnical reports (References 1, 2, and 3, above). Background A preliminary geotechnical report of the subject site was issued on July 24, 1985 (Reference 1). This report outlined the geotechnical conditions at the site at the time of preparation of the report. Subsequently, Leighton and Associates, Inc. was requested to perform a geotechnical review of the project grading plans (Reference 3). During the geotechnical reconnaissance of the site associated with the review of the grading plans, it was observed that the northern portion of the site has been graded since the preparation of Reference 1. This grading appeared to predominantly consist of the placement of a daylight fill area along the southern edge of the existing Elm Avenue. Communications with Mr. Mark Steyaert, Park Planner (City of Carlsbad), indicated that this fill was associated with the construction of Elm Avenue along the northern subject property boundary. As discussed in Reference 3, Leighton and Associates, Inc. recommended that this fill be evaluated by an appropriate geotechnical investigation. In accordance with your written authorization dated November 3, 1986, we have conducted a geotechnical evaluation of this recent fill on the site. Presented herewith is the results of our investigation and recommendations to mitigate the presence of these fill areas. Scope Our scope of services for this investigation included: • Review of the previous geotechnical reports issued for the subject site. • A subsurface exploration program consisting of the excavation, logging, and sampling of three large-diameter borings in the existing fill on the site. The purpose of this program was to evaluate the engineering characteristics of the fill soils. • Geotechnical analysis of data to evaluate the engineering characteristics of the existing fill as it pertains to the proposed development of the site. • Preparation of this report presenting our findings, conclusions, and recommendations. - 2 - ULJ LEIGHTON and ASSOCIATES INCORPORATED 8850373-07 Findings and Conclusions As discussed in Reference 3, approximately 17 feet to 31 feet of roadside fill was placed along the southern edge of the existing Elm Avenue, corresponding to the approximate Stations 71+76 and 70+00 (Reference 4), respectively. Please refer to Plate I, Geotechnical Map, contained in Reference 3 for the approximate aerial limits of the roadside fill. Our findings and conclusions of this investigation are presented below. • The borings were drilled to a maximum depth of approximately 5 feet due to excessive rock and difficult drilling conditions. As a result of the rocky nature of the fill, it was not possible to obtain undisturbed samples or evaluate the relative compaction of the fill. • The fill observed in our subsurface exploration predominantly consisted of subangular cobbles and boulders typically ranging in size from 6 to 14 inches in diameter within a loose to medium dense, clayey sand matrix. Several rocks within the fill were noted as nested on top of each other with abundant void spaces between the rock to rock contacts. Void spaces measured in the borings ranged from less than 0.5 inches to approximately 8 inches in maximum width. Based on observation of the roadside fill slope, we anticipate that the entire fill has been used as a rockfill. • Because it was not possible to penetrate the fill soils, it was not possible to evaluate the fill to natural soil contact. Due to safety considerations, the use of a larger drilling rig to penetrate through the fill and downhole log the excavation was not attempted. • Based on communications with representatives of the City of Carlsbad, we understand that no as-graded report associated with the placement of the existing fill was available for our review. Therefore, it is uncertain whether appropriate subdrainage, as recommended in Section 7.3.10 of Reference 1, was installed prior to fill placement. • Based on the findings mentioned above, it is our opinion that there is a potential for fill settlement. The potential settlement may be caused by the migration of fine soils into the void spaces. This is based on our limited observation of fill and anticipation of the presence of similar conditions throughout the fill. The rate and amount of potential settlement cannot be estimated. However, the infiltration of water will ease the migration of fine soils into the voids and accelerate the associated settlement. t It is our opinion that the shear strength of the existing fill soils is adequate to support the proposed fill slope as depicted on the project grading plans (Reference 4). Accordingly, the proposed fill slope to be constructed over the existing fill is considered to be grossly stable. - 3 -\s>y JLJ LEIGHTON and ASSOCIATES INCORPORATED 8850373-07 Recommendations • Fire Station Building Based on a review of the project grading plans (Reference 4), a fire station building is proposed in the northwest corner of the site. The grading plans indicate the thickness of the existing fill in this area is generally less than 12 feet. If relocation of this structure beyond the limits of the existing fill is not feasible or desirable, we recommend that the existing fill in this area be removed and replaced with compacted fill. We recommend that the existing fill be removed to dense formational soils. This removal should extend a minimum of 5 feet beyond the settlement sensitive structures and improvements. The excavation should not be steeper than 1:1 (horizontal to vertical) and should be in conformance with OSHA safety regulations. The replacement fill should be compacted to at least 90 percent relative compaction (based on ASTM D1557-78). In general, placement of fill should be performed in accordance with local grading ordinances, sound construction practice, the General Earthwork and Grading Specifications, and recommendations outlined in Reference 1. The alternative of supporting the building on a drilled pier and grade beam system supported in formational materials was also considered. However, due to the high potential of caving during construction, this alternative is not . considered practical. • Other Areas Based on a review of the grading plans (Reference 4), no structures are planned in the remaining existing fill areas. Accordingly, these areas may be desig- nated as nonstructural areas. However, should any future structures be constructed, we recommend that these structures be located on the shallow portions of the existing fill such that removal and replacement of the existing fill could be performed prior to placement of the proposed fill. Construction Observation All removals, fill placements, trench excavations, pier excavations, and concrete placement in pier excavations, should be performed in accordance with the recom- mendations and general earthwork and Grading Specifications presented in the referenced reports. _ 4 .va» LJLJ LE1GHTON and ASSOCIATES INCORPORATED 8850373-07 If you have any questions regarding our report, please do not hesitate to contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. Ahmad Ghazinoor, RCE 34692 Project Geotechnical Engineer Rodney xT/Weick, CEG 1094 Chief Engineering Geologist RLW/AG/RW/lj Distribution:(3) Addressee (1) Rick Engineering Company Attention: Mr. Barry Bender (1) Recreation Systems, Inc. Attention: Mr. Rod Barrette - 5 -N£>y LJU LEIGHTON and ASSOCIATES INCORPORATED