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HomeMy WebLinkAbout7078; Calavera Hills Sewage Treatment Plant; Calavera Hills Sewage Treatment Plant; 1987-01-15LIMITED GEOTECHNICAL CONSULTING CALAVERA HILLS SEWAGE TREATMENT PLANT EL CAMINO REAL CARLSBAD, CALIFORNIA FOR CITY OF CARLSBAD 2075 LAS PALMAS DRIVE CARLSBAD, CALIFORNIA 92008 JOB NO. 7078 JANUARY 15, 1987 Testing Engineers—San Diego A Division of United States Testing Company, Inc. 3467 Kurtz St., P.O. Box 80985, San Diego, Ca. 92138(619)225-9641 I Jf J 2956 Industry Street, Oceanside, California 92054 (619) 757-0248 January 15, 1987 Job No. 7078 City of Carlsbad 2075 Las Palmas Drive Carlsbad, California 92008 Attention: Mr. Al Virgilio Subject: Limited Geotechnical Consulting Services Calavera Hills Sewage Treatment Plant Approximately Two Miles Northeast of El Camino Real and Tamarack Avenue, Carlsbad, California Gentlemen: In accordance with your request, we are pleased to present the results of our soil and foundation investigation for the proposed pump station improvement. Recommendations for development of this site are presented in the following report and should be incorporated into the design and construction of the proposed structure. Calavera Hills Treatment Plant Carlsbad, California January 15, 1987 Job No. 7078 We have appreciated the opportunity to be of service to you on this interesting project and look forward to a continued association on this and future projects. If you should have any questions regarding this report, please do not hesitate to contact us. Steven C. Geyer Project Engineer Respectfully submitted, TESTING ENGINEERS-SAN DIEGO Stephen M. Poole, RCE 40219 Geotechnical Department Manager SMP/SCG/eh Addressee (3) cc: Eraser & Associates - Clarence Magnusen (1) o o O TABLE OF CONTENTS INTRODUCTION 1 PROJECT DESCRIPTION 1 PROJECT SCOPE 1 FIELD EXPLORATION 2 LABORATORY TESTING 3 CLASSIFICATION 3 MOISTURE/DENSITY 3 SHEAR TESTS 4 U.B.C. SWELL TESTS 4 CONCLUSIONS 6 RECOMMENDATIONS 7 GENERAL 7 DEWATERING AND EXCAVATION 8 UPLIFT RESISTANCE 8 FOUNDATION DESIGN AND CONSTRUCTION 9 FOOTINGS 10 ALLOWABLE BEARING CAPACITY 10 SETTLEMENT 11 CONCRETE TANK WALLS 11 DRAINS 13 REVIEW 13 LIMITATIONS 14 ENCLOSURES; Boring Log Plate 1 Symbols and Terms Used Plate 2 Unified Soil Classification Plate 3 Shear Test Plate 4 O O Calavera Hills Treatment Plant Page No. 1 Carlsbad, California January 15, 1987 Job No. 7078 INTRODUCTION PROJECT DESCRIPTION The site is located approximately 2 miles northeast of the intersection of El Camino Real and Tamarack Avenue in Carlsbad, California. We understand that the site is to be developed by the construction of a new pump station. This six-sided concrete structure has an approximate base dimensional of 14 feet by 12 feet and a wall height of 13 feet with a significant depth below ground surface. No plans were available for our review at the time of this writing. PROJECT SCOPE The purpose of our investigation was to determine the following soil parameters for the proposed development. o allowable bearing capacity o expansive potential o influence of groundwater table Calavera Hills Treatment Plan Page No. 2 Carlsbad, California January 13, 1987 Job No. 7078 FIELD EXPLORATION Subsurface conditions were explored by drilling one 8-inch diameter boring with a Mobile B-53 drill rig. Boring No. 1 was located approximately 15 feet south of the present chlorination contact tank and was completed to a depth of 26.5 feet. No groundwater was encountered in this boring. Please refer to the boring log presented on Plate 1. A civil engineer from our office was present during the drilling of the boring to log materials encountered and to obtain representative samples at selected depths for transportation to our laboratory. Samples consisted of relatively undisturbed samples collected in one-inch-high, 2.37-inch-inside-diameter rings, bag, and bulk samples. The ring samples were collected by driving the sampler eighteen inches into the soil by consecutive thirty-inch drops with a one-hundred-forty-pound hammer. In the case of the standard two-inch diameter sampler, the number of blows required to achieve the final twelve inches of penetrations is referred to as the "N-value" of the Standard Penetration Test (SPT). This value provides a measure of soil strength and bearing capacity, as it relates to the soil consistency or condition as it is defined on the symbols and terms used on the boring log, and presented on Plate 2. Calavera Hills Treatment Plan Page No. 3 Carlsbad, California January 13, 1987 Job No. 7078 LABORATORY TESTING CLASSIFICATION Soils were visually classified according to the Unified Soil Classification System as presented on Plate 3. Soil classifications are shown on the Boring Log. MOISTURE/DENSITY The field moisture content and dry unit weight were determined for selected undisturbed soil samples obtained from the test borings. When disturbed samples were obtained, only the field moisture contents were determined for these samples. The dry unit weight was determined in pounds per cubic foot, and the field moisture content was determined as a percentage of the dry unit weight. The results of these tests are shown on the attached boring log. Calavera Hills Treatment Plan Page No. 4 Carlsbad, California January 13, 1987 Job No. 7078 SHEAR TEST A shear test was performed on an undisturbed sample of representative site soil. The sample was tested utilizing direct shear machine of the strain control type. The rate of deformation was approximately 0.05 inches per minute. The sample was sheared under varying confining loads to determine the Coulomb Shear parameters: angle of internal friction and cohesion. The shear test result is presented on Plate 4. U.B.C. SWELL TEST The expansion potential of a selected sample was evaluated using a swell test (U.B.C. Test Standard No. 29-2). A sample of soil was remolded to a saturation content of approximately 50 percent. A surcharge load of 144 pounds per square foot was applied to the sample, which was then inundated. The expansion index (E.I.) was recorded as the increase in the thickness of the soil sample relative to the original 1-inch sample. The sample was allowed to swell for at least 24 hours. Calavera Hills Treatment Plan Page No. 5 Carlsbad, California January 13, 1987 Job No. 7078 Results were as follows: Material Expansion Location Depth, Ft Type E.I. Potential 1 10.0 dark gray 53 low organic clay Calavera Hills Treatment Plan Page No. 6 Carlsbad, California January 13, 1987 Job No. 7078 CONCLUSIONS Based on our field investigation, laboratory testing, and engineering analyses, it is our opinion that the subject site is suited for the proposed construction of new facilities from a geotechnical engineering viewpoint. The recommendations presented in the following section should be incorporated into the design, grading, and construction considerations. 1. Site materials consist of fill underlain by silty/sandy clays in a stiff to very stiff condition. These materials are adequate for the proposed structures. 2. These silty/sandy clays were found to have a low expansive potential. 3. Groundwater is not expected to be a factor in the development of the site. Calavera Hills Treatment Plan Page No. 7 Carlsbad, California January 13, 1987 Job No. 7078 GENERAL RECOMMENDATIONS 1. The site for the propsoed development should be excavated and adequately shored if necessary or as required by OSHA standards. The resulting excavations should be viewed by a qualified Geotechnical Engineer or Engineering Geologist to evaluate whether all deleterious materials have been removed. 2. Below grade walls or other structures that will be backfilled, should be braced during backfilling operations to prevent excessive movement or deflection. Backfilling within three feet of below grade walls should be performed with hand operated equipment. Calavera Hills Treatment Plan Page No. 8 Carlsbad, California January 13, 1987 Job No. 7078 3. A qualified soils technician under the supervision of a geotechnical engineer should be present for all fill or backfilling placement operations. The soils technician should evaluate all materials to be placed, and should perform in-place density tests at appropriate intervals to evaluate the compaction effort relative to 90 percent of the maximum dry density as determined by ASTM D-1557. DEWATERING AND EXCAVATION No groundwater was encountered in our field investigation, however we suggest that the contractor evaluate the groundwater at the time of construction. UPLIFT RESISTANCE Because hydrostatic uplift pressures resulting from fluctuating ground water levels are expected, such design factors as footing flange size should be taken into consideration. Calavera Hills Treatment Plan Page No. 9 Carlsbad, California January 13, 1987 Job No. 7078 FOUNDATION DESIGN AND CONSTRUCTION Soil expansion test results indicate a low expansive soil condition. Thus, the following recommendations are offered: FOOTINGS 1. All footings for individual structures should be founded either on in-situ soil or structural fill to minimize possible differential settlement. 2. Concrete slabs should be underlain with four inches of clean sand or crushed rock. In addition, a vapor barrier consisting of a minimum six mil polyvinyl chloride membrane, with all laps sealed, should be provided in areas that may adversely be affected by moisture. One inch of sand should be placed over the membrane to aid in the uniform curing of the concrete. Calavera Hills Treatment Plan Page No. 10 Carlsbad, California January 13, 1987 Job No. 7078 3. Concrete slabs should be reinforced with steel bar or mesh as advised by a structural engineer. All slab reinforcement should be supported to ensure proper positioning in the upper third of the slab during placement of concrete. 4. Concrete slabs should be scored, or fitted, with expansion and construction joints at appropriate intervals. ALLOWABLE BEARING CAPACITY An allowable bearing capacity of 4,000 pounds per square foot is recommended for the proposed pump station founded at least 10 feet below the ground surface. The allowable bearing capacity assume uniform loading conditions and is the maximum long term soil contact pressure and may be increased by 1/3 for earthquake or other temporary loading. SETTLEMENT Because of the composition of the soil at the site, settlement of the proposed structures should occur during the construction phase and should be within limits acceptable. We believe that the settlement should be less than one inch. Calavera Hills Treatment Plan Page No. 11 Carlsbad, California January 13, 1987 Job No. 7078 CONCRETE TANK WALLS All concrete structures should be adequately reinforced with steel bar or mesh as designed by a registered structural engineer. Further, providing that the concrete walls are free to move away from the backfill slightly, the lateral soil pressure exerted on the walls may be considered to be the "active" earth pressure. Most unrestrained walls can move sufficiently to permit development of "active" earth pressures. The planned walls, as outlined above and with level backfills, may be designed for an "active" earth pressure using an equivalent fluid unit weight of 50 pounds per cubic foot. Should sloping backfill up to 2 horizontal to 1 vertical be used, the equivalent fluid unit weight should be increased to 70 pounds . per cubic foot. Walls that do not permit movement and are non-yielding, such as basement walls, should be designed for an equivalent fluid unit weight 25 percent greater than the above noted values. Calavera Hills Treatment Plan Page No. 12 Carlsbad, California January 13, 1987 Job No. 7078 Utilizing an imported non-expansive soil to backfill behind the tank walls would enable used desxign fluid unit weights approaching 30 to 45 pounds per cubhic feet, for level and sloping backfills, respectively with 25 percent increases for non-yielding conditions. Acceptable granular soil should be placed within a distance extending behind the walls a distance approximately equivalent to the wall height. Lateral resistance to sliding may be developed using passive soil pressure approximated with an equivalent fluid unit weight of 250 pounds per cubic foot. In addition, frictional resistance may be estimated between soil and concrete using a coefficient of friction of 0.40. Drainage behind all walls should be sufficient to ensure that no free moisture accumulates against the wall. A 12 inch width of granular backfill in conjunction with a system of perforated drain pipe should be detailed and constructed for this purpose. Calavera Hills Treatment Plan Page No. 13 Carlsbad, California January 13, 1987 Job No. 7078 O DRAINS Positive drainage away from the proposed structures should be maintained for at least ten feet. Steps should be taken to avoid ponding near the footing for the same distance. Drainage requirements should be in keeping with Unified Building Code and any local regulations. REVIEW O The final foundation and grading plans should be reviewed by this office to minimize any misunderstandings between the plans and recommendations presented herein. In addition, foundation excavations and earthwork performed on-site should be evaluated by a qualified Engineering Geologists or Geotechnical Engineer. If conditions are found to vary substantially from those stated herein, appropriate recommendations should be requested. Calavera Hills Treatment Plan Page No. 14 Carlsbad, California January 13, 1987 Job No. 7078 INVESTIGATION LIMITATIONS The materials encountered on the project site and utilized in our laboratory investigation are believed representative of the total area; however, soil and bedrock materials vary in characteristics between excavations and natural outcrops. Since our investigation is based on the site materials observed, selective laboratory testing and engineering analyses, the conclustions and recommendations are professional opinions. These opinions have been derived and no warranty is expressed nor implied. Testing Engineers-San Diego COr^or^ 6 -O -3 BORING LOG Project: Type of Hammei ^u_ X1—a. LUO - 2 . 4 _ 6 -8 _ 10 . 12 14 " 16 - 18 . 20 - 22 -24 . 26 . 28 SYMBOLSM/SP CL CL CL CL/OH Pump Sta. /Carlsbad r)n|p. 12/22/86 Rig. B-61 HnlP Dinmeter- 8" H.S.A. Boring ' Weight ^ Fill' 140 Ih/^n" RrnnnH Wnfpr None Nn- 1 Elevat Loaa FIELD DESCRIPTION 0-9.0' FILL, olive-gray silt with dark grey/black clay nodules; poorly sorted with decomposed gravelly material 1" diameter 9.0-19.0' CLAY, dark/gray/black very stiff - organic clay 14.0-19.0 CLAY, gray, plastic, moderately stiff with minor medium grain sand - sand layer 16 0 16 5' 19.0 '-23.0' CLAY, dark brown, very stiff 23.0-26.5' FINE /MED. SANDY CLAY - gray . moderately plastic; sandy with calcite carbonate nodules BORING TERMINATED 26.5' No groundwater encountered BLOWS/FTii 19 26 45 4 SAMPLEDR DR DR DR DR nn- 1S6' ed By: £ CO . —z u-UJ O 0 Q- >-cra 89 91 89 72 SCG MOISTURECONTENT (%)18 15 12 10 55 ooOJ 1 PLATE Testing Engineers-Son Diego SYMBOLS AND TERMS USED ON BORING LOGS SAMPLER TYPES (Shown in SAMPLE column) DRI S DR B BK /EN RING DRIVEN BULK AMPLE BAG SAMPLE SAMPLE DISTURBED H SHELBY TUBE ROCK CORE K SPLIT SPOON n \ NO ECOVERY TERMS DESCRIBING CONSISTENCY OR CONDITION COARSE GRAINED SOILS (major portion retained on No. 200 sieve): Includes (1) clean gravels and sands, and (2) silty or clayey gravels and sands. Condition in the following table is based on our interpretation of blow counts using a hammer as noted on the boring log. DESCRIPTIVE TERM Very loose Loose Medium-dense Dense Very dense SPT VALUES,N blows per 12 in. (After Terzaghi a Peck, 1968) 0 to 4 4 to 10 10 to 30 30 to 50 >50 FINE GRAINED SOILS (major portion passing No. 200 sieve): Includes (1) inorganic and organic silts and clays, (2) gravelly, sandy, or silty clays, and (3) clayey silts. Consistency is rated according to shearing strength, as indicated by penetromeler readings or by unconfined compression tests. DESCRIPTIVE TERM Very soft Soft Firm Stiff Very stiff Hard UNDRAINED SHEAR STRENGTH KIPS/SO FT less than 0.25 0.25 to 0.50 0.50 to 1.00 1.00 to 2.00 2.00 to 4.00 4.00 and higher NOTE: Fissured clays may have lower unconfined compressive strengths than shown above, because of planes of weakness or cracks in the soil. The consistency ratings of such soils are based on penetrometer readings. TERMS CHARACTERIZING SOIL STRUCTURE Fissured — containing shrinkage cracks, frequently filled with fine sand or silt, usually more or less vertical Interbedded — composed of alternate layers of different soil types Calcareous — containing 12 to 50 percent calcium carbonate Carbonate — containing more than 50 percent calcium carbonate Well graded — having wide range in grain sizes and substantial amounts of all intermediate particle sizes Poorly graded — predominately of one grain size, or having a range of sizes with some intermediate size missing Terms used in this report for describing soils according to their texture or grain size distribution are in accordance with the UNIFIED SOIL CLASSIFICATION SYSTEM, as described in Technical Memorandum No. 3-35? Waterways Exp.Sta.J/53 PI ATF 2 Testing Engineers-San Diego UNIFIED SOIL CLASSIFICATION 60 50 40 MV•vC = 30 «J 0 Q. 20 10 0 PLASTICITY CHART CL feLrJJU.^' ly // ML , ^ * V/ jnd 0 \ >? L CH ;< / OH $/ "/ and 1 / / AH / 0 10 20 30 40 SO 60 70 80 90 100 Liquid Limit 0) *tn O 8 0 (/I Z d cs I Q S Z o B »(K O< e O M_o o "5 co.c V o 2 GROUP SYMBOL GW GP GM GC SW SP SM SC TYPICAL NAMES Well-graded grovels, gravel-sand mixtures, little or no fines Poorly graded gravels, grovel -sand mixtures, little or no fines Silty. gravels, gravel- sond-silt mixtures Clayey gravels, gravel sand-clay mixtures Well-graded sands, gravelly sands, little or no fines Poorly graded sands, gravelly sands, little or no fines Silty sands, sand-silt mixture Clayey sands, sand- clay mixtures It/» O0CJ 6 _j t! O — <" 0a EUJ to Z „, < _tr o ? 'I % 1 u. •—o "oJC co-C O) o GROUP SYMBOL ML CL OL. MH CH OH PI TYPICAL NAMES Inorganic silts and very fine sands, rock flour silty or clayey fine sands, or clayey silts with slight plasticity Inorganic cloys of low to medium plasticity, gravelly clays, sandy clays, silty cloys, lean clays Organic silts and organic silty clays of low plasticity Inorganic silts, micaceous or diotomaceous fine sandy or silty soils, elastic silts Inorganic clays of high plasticity, fat clays Organic clays of medium to high plasticity, organic silts Peat and other highly organic soils NOTE: DGroup symbol presented in SYMBOL column on BORING LOG. 2) The A line is an empirical relationship established by A. Casagrande. PLATE Tes ting Engineers - San Diego SHEAR TEST RESULTS SHEAR STRENGTH (ksf)— • ro OJ .pkX ^/X x X X (^ X1 ^ X x ^ (X* x X /*X ^ 0= 37" C/ ~ 98 psf <*X1X / X X s/ x x ^' f J 1 2 34 NORMAL PRESSURE (ksf) SOIL DESCRIPTION-.dark gray^ dense sand .IDR NO- 7078 BORING NO: . - • . 1 DEPTH: \ 16.5' PI ATF 4