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HomeMy WebLinkAbout; James Drive Extension; James Drive; 1985-09-01GEOTECHNICAL CONSULTANTS STUDIES IN APPLIED EARTH SCIENCES Project No. 183.1.1 September 1, 1985 Berryman & Stephenson, Inc. 16880 West Bernardo Drive San Diego, California 92127 Attention: Mr. Ivan Fox Subject: GEOTECHNICAL INVESTIGATION James Drive Extension James Drive & Basswood City of Carlsbad, California Gentlemen: INTRODUCTION This report presents the results of my soil and geological investigation for an extension of James Drive from Basswood to approximately 1,000 feet to the northwest. The purpose of this investigation was to evaluate the geotechnical conditions along the proposed alignment and to provide recommendations concern- ing the soil and geological engineering aspects of the proposed road development. Based on my review of an undated plan entitled "James Drive Assessment District No. 83-2," by Berryman & Stephenson, Inc., the proposed street will be almost entirely in cut resulting in cut-slope heights of up to approximately 3 feet at a 2:1 (horizontal to vertical) inclination. SCOPE The scope of work performed in this investigation included a geologic site reconnaissance, subsurface exploration, labora- tory testing, engineering analysis of the field and laboratory data and the preparation of this report. The data obtained and the analyses performed were for the purpose of providing design and construction criteria for site earthwork. In addition, samples of the materials encountered at proposed finish grade were tested to provide a street section. 2255 Fire Mountain Drive, Oceanside, CA 92054 • (619) 439-2497 o Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Two GEQPACIFICA GEOTECHNICAL CONSULTANTS SITE CONDITIONS •O A. Surface The proposed road alignment extends from the intersection of Basswood and James Drive to approximately 1,000 feet to the northwest. Ground surface elevations along the align- ment vary from a high of approximately el. 159 at the intersection of Basswood and James Drive to a low of approximately el. 155 at the proposed terminus of James Drive. The ground surface is dominated by flat, gently-sloping terrain. The natural slope along the alignment is essentially flat. A moderate to heavy growth of grass and low brush covers the road alignment. B. Site Geology The site bedrock is composed of nearly flat-lying sedimen- tary rock units of the Lindavista Formation. These materials consist of interbedded fine-grained sandstones and siltstones. The sedimentary rocks are massive. No faults were observed in the exploratory excavations made for this investigation nor are any mapped in the area. No landsliding is present or anticipated on the site. C. Subsurface A geologic reconnaissance and subsurface investigation was performed by hand excavating three test pits to a maximum depth of three feet. The test pit locations are indicated on the site plan. Logs of the test pits are presented in Appendix A. Details of the laboratory testing and the laboratory test results are presented in Appendix B. The materials encountered in the exploratory test pits consisted predominantly of dense formational silty and clayey sands to the depths explored. Based on past experience with similar materials, the sandy formational materials of the Lindavista Formation possess only a negligible potential for expansion. o o Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Three GEOTECHNICAL CONSULTANTS O o The test pit logs and related information depict subsurface conditions at the specific locations shown on the site plan and on the particular dates designated on the logs. Sub- surface conditions at other locations may differ from conditions occurring at these test pit locations. Also, the passage of time may result in changes in the subsurface conditions due to environmental changes. D. Groundwater Groundwater was not encountered in any of the exploratory excavations made for this investigation and no surface seeps were observed. It must be noted, however, that fluctuations in the level of groundwater may occur due to variations in surface topography, subsurface stratifica- tion, rainfall and other possible factors which may not have been evident at the time of my field investigation. In addition, experience has shown that a groundwater con- dition can and may develop in areas where no groundwater condition existed prior to site development. Irrigation from adjacent nurseries and poor drainage have created some wet areas. E. Seismic Considerations Based on my site reconnaissance and a review of some available published information including the City of San Diego Seismic Safety Study Fault Location Map and the County of San Diego Faults and Epicenters Map, there are no active or potentially active faults known to pass through the site. The faults generally considered to have the most potential for earthquake damage in the vicinity of the site are within the active Elsinore and San Jacinto Fault Zones located approximately 22 and 45 miles northeast of the site, respectively. The Rose Canyon Fault is located approximately 12 miles southwest of the site. No earth- quake epicenter clusters are associated with this system and no faults associated with the Rose Canyon Fault Set are classified as active under current criteria. Although research on earthquake prediction has greatly increased in recent years, seismologists have not yet reached the point where they can predict when and where an earthquake will occur. Nevertheless, on the basis of Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Four GEQFACIFICA GEOTECHNICAL CONSULTANTS current technology, it is reasonable to assume that the proposed road improvements will be subject to the effects of at least one moderate earthquake during their design life. During such an earthquake, the danger from fault offset through the site is remote, but strong ground shaking is likely to occur. CONCLUSIONS AND RECOMMENDATIONS From a soil and geological engineering standpoint, it is my opinion that the site is suitable for construction of the proposed road improvements provided the conclusions and recommendations presented in this report are incorporated into the design and construction of the project. Detailed recommen- dations for the earthwork are presented in the following paragraphs. O A. Clearing and Stripping The area of the road alignment should be stripped of all surface vegetation and cleared of all obstructions including any miscellaneous trash or debris that may be present at the time of construction. The stripping depths required to satisfactorily remove surface vegetation should be determined in the field by the soil engineer's repre- sentative at the time of construction. The cleared and stripped materials should be disposed of off-site. B. Preparation for Filling After the alignment has been cleared and stripped, the exposed subgrade soils in areas to receive fill should be scarified to a depth of 6 inches, moisture-conditioned, and compacted to the requirements presented in Item E, "Compac- tion." In general, the natural surface soils are loose to only shallow depths and as a result, the normal scarifica- tion and recompaction process should be adequate to effec- tively stabilize these soils. o o Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Five GEQFACIFICA GEOTECHNICAL CONSULTANTS O C. Excavation Based on the results of my exploratory excavations and my experiences with formational soils similar to those present on this site, it is my opinion that the on-site natural formational soils can be excavated utilizing ordinary heavy earthmoving equipment. The bidding contractors should not, however, be relieved of making their own independent evalu- ation of the excavatability of the on-site materials prior to submitting their bids. D. Materials for Fill All existing on-site soils with an organic content of less than 3 percent by volume are in general suitable for reuse as fill. Fill material should in general, however, not contain rocks or lumps over 12 inches in greatest dimension and not more than 25 percent larger than 2-1/2 inches. E. Compaction All structural fill should be compacted to a minimum degree of compaction of 90 percent based upon ASTM Test Designa- tion D 1557-78. Any fill material should be spread and compacted in uniform horizontal lifts not exceeding 8 inches in uncompacted thickness. Before compaction begins, the fill should be brought to a water content that will permit proper compaction by either: 1) aerating the fill if it is too wet, or 2) moistening the fill with water if it is too dry. Each lift should be thoroughly mixed before compaction to ensure a uniform distribution of moisture. F. Slopes Based on the results of my soil and geological engineering reconnaissance of the site, my past experience with similar materials, and my engineering analysis, it is my opinion that proposed 2:1 (horizontal to vertical) cut slopes will mass instability (minimum static factor of The cut slopes, however, should be qualified engineering geologist at the time to assure that no adverse geologic which may not have been discovered in be safe against safety of 1.5). inspected by a of construction conditions exist connection with the work performed for this investigation. o Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Six _ GEQPACIFICA GEOTECHNICAL CONSULTANTS O The on-site soils will be moderately susceptible to erosion. Therefore, the project plans and specifications should contain all necessary design features and construc- tion requirements to prevent erosion of the on-site soils both during and after construction. Slopes and other exposed ground surfaces should be appropriately planted with a protective ground cover. It should be the grading contractor's obligation to take all measures deemed necessary during grading to provide erosion control devices in order to protect slope areas and adjacent properties from storm damage and flood hazard originating on this project. It should be made the contractor's responsibility to maintain slopes in their as-graded form until all slopes, berms, and associated drainage devices are in satisfactory compliance with the project plans and specifications. G. Trench Backfill Pipeline trenches should be backfilled with compacted fill. Backfill materials should be placed in lift thick- nesses appropriate to the type of compaction equipment utilized and compacted to a minimum degree of compaction of 90 percent by mechanical means. In pavement areas, that portion of the trench backfill within the pavement section should conform to the material and compaction requirements of the adjacent pavement section. H. Drainage With regard to the need for subsurface drainage provisions, no conditions were encountered during the field investiga- tion phase of my geotechnical investigation work which would suggest the need for subsurface drains for intercept- ing and disposing of free groundwater. However, the need for such drainage provisions can normally best be determined during the site preparation and earthwork opera- tions based on a close examination of the soil, geological, and groundwater seepage conditions being exposed. If con- ditions are encountered during construction that suggest the need for subsurface drains, I can at that time provide specific recommendations for their installation. o GEOPACIFICA Geotechnical Investigation James Drive Extension Project No. 183.1.1 September 1, 1985 Page Seven GEOTECHNICAL CONSULTANTS O o o I. Construction Observation Variations in soil conditions are possible and may be encountered during construction. In order to permit correlation between the preliminary soil data and the actual soil conditions encountered during construction and so as to assure conformance with the plans and specifica- tions as originally contemplated, it is essential that the soil engineer be retained to perform on-site review during the course of construction. All earthwork should be per- formed under the direction of the soil engineer's repre- sentative to assure proper site preparation, selection of satisfactory fill materials, as well as placement and compaction of the fills. J. Street Section Based upon the R-Value obtained, I recommend that the pro- posed street section be 3 inches of AC on 8 inches Class II aggregate base. If you have any questions, please call. Very truly yours, GEOPACIFICA o JAMES F. KNOWLTON C.E.G. 1045 o o o o o APPENDIX A BACKHOE COMPANY: BUCKET SIZE: Hati d Excavated DATE: 8-8-85 I p UJ U-* Q ib 0 - - 10 1 e; UJ 05: CO ^ CO >; to co2 tu Q rr ^o cjo H Q- Q HI . ^ z t-iH. ^ CO C S005 o COCO — _l Jj CO 52o SOIL DESCRIPTION TEST PIT NO. ! ELEVATION TOPSOIL: Light Brown Silty Sand, dry, loose BEDROCK: Lindavista Formation, Light brown and reddish brown sandstone, slightly moist, T.D. 3' No Water No Caving TEST PIT NO. 2 ELEVATION — 5 — 10 — 15 — TOPSOIL: Brown silt, dry, loose BEDROCK: Lindavista Formation, Light brown and brown silty sandstone, slightly moist, dense T.D. 3' No Water No Caving LOG OF TEST PITS PROJECT NO. 183.1.1 JAMES DRIVE EXTENSION FIGURE NO A-l o o o RACKHOE COMPANY: BUCKET SIZE : Han d Excavated DATE: 8-8-85 isOii 0 — 5 10 is .. Ul^,-J CO CO CO2 "JLil HQ (£ CO t) Q UJ fe^5 005 0 CO <«dq_j CO 5200 SOIL DESCRIPTION TEST PIT NO. ELEVATION TOPSOIL: Brown sandy silt, dry, loose BEDROCK: Lindavista Formation, Brown to reddish brown, sandstone, slightly moist, dense T.D. 3' No Water No Caving TEST PIT NO.ELEVATION 10 15 LOG OF TEST PITS PROJECT NO. 183.1.1 JAMES DRIVE EXTENSION FIGURE NO.A-2 o -o APPENDIX B Sample No. Tl-2 Sample No. Tl-2 Sample No. *Tl-2 Summary of Laboratory Compaction Test Results ASTM D1557-70 Description Brown, Silty SAND Maximum Dry Density pcf 117.1 Optimum Moisture % Dry Wt, 11.2 Summary of Laboratory Expansion Index Test Results Moisture Content Before Test 9.3 After Test 17.3 Dry Density pcf 112.8 Expansion Index 0 Summary of Direct Shear Test Results Dry Density pcf 105.0 Moisture Content 11.7 Unit Cohesion psf 270 Angle of Shear Resistance Degrees 31 *Sample remolded to approximately 90 percent of maximum dry density at near optimum moisture content. JAMES DRIVE EXTENSION JOB NO.:183.1.1 DAT E.-September 1,1985 FIGURE:B-l