Geotechnical Investigation Report

Transcription

1 Geotechnical Investigation Report Proposed,000-Gallon Water Storage Tank Fagasa Pass Tank Upper Pago Pago, American Samoa Prepared for: ASPA Water Engineering Division Tafuna, American Samoa PO Box PPB Pago Pago AM Samoa December 29, Waihona Street, Unit B-7, Pearl City, Hawaii Phone: Fax:

2 TABLE OF CONTENTS INTRODUCTION 1 FIELD INVESTIGATION 1 RECOMMENDATIONS 2 LIMITATIONS AND REVIEW 5 Site Location Site Plan Test Pit Locations and Logs Laboratory Test Reports ASPA Fangasa Pass Tank Geotechnical Investigation

3 INTRODUCTION Presented in this report are the results and recommendations of a geotechnical investigation completed at the proposed,000-gallon Water Storage Tank, located at Fagasa Pass, Pago Pago Village, American Samoa. Construction Engineering Labs, Inc. was contracted by ASPA Water Engineering Division to evaluate current site conditions for the determination of the soil bearing capacity for the entire proposed area footprint of Water Storage Tank, and minimum depth of foundation. The field investigation was comprised of the construction of four (4) test pits, collection of samples, field testing and laboratory analysis. A. Geotechnical Investigation 1. Site visit by soils engineer field evaluation and testing 2. Monitoring and logging of the construction of 3 Test Pits 3. Review and correlate any available soil information on the site. 4. Review available site mapping and aerial photographs B. Field Testing 1. Field analysis of the soil for ph content C. Laboratory Testing 1. Grain Size Analysis TP 1, 2, 3 2. Atterberg Limits TP 1, 2 3. Expansion TP 1, 3 4. Modified Proctor Analysis TP 1, 2, 3 D. Evaluation and Report 1. Correlate and analyze the laboratory and field results. 2. Develop geotechnical recommendations for soil bearing capacity and minimum depth of foundation 3. Submit a written report summarizing the findings and recommendations. PROJECT AND SITE DESCRIPTION The site is located in west of the Fagasa Pass trail, formed by pyroclastic deposits in the vicinity of Fatifati Mountain on the island of Tutuila, American Samoa. The site is located uphill of the Vaipito Reservoir in Upper Pago Pago Village. The site is bounded by mountain slopes, wooded areas, and a Federal Park Reserve trail. FIELD INVESTIGATION CEL was present at the site on February 27, 2015 to perform site reconnaissance. CEL returned to the site on March 19, 2015 to complete the field investigation and testing. Findings from our site reconnaissance and field testing indicate the following: 1) Terrain surrounding the proposed tank location is generally rugged, well forested, and steeply sloped. ASPA Fagasa Pass Tank Geotechnical Investigation Page 1

4 2) The project area is well vegetated (with grass, perimeter trees, and potted plants for landscaping purposes). The potted plants removed prior to initiation of field investigation. 3) The soil exhibited properties consistent with pyroclastic silt and sand, mixed with roots, other organic debris, and some ash. The subsurface soil is comprised of topsoil and organics (dark gray clayey silt with sand sandy loam ). The thickness of the topsoil ranged from 1 to 1.5 meter (m). The topsoil is underlain by moderately expansive, light brown and tan elastic silt with some sand and clay extending to depths of 3 to 3.4 m. Gravel, cobbles and boulders, as well as the strata beneath the 3 meter level are comprised of sandstone, grading from weakly to well cemented with depth. The soil is slightly acidic, with ph values ranging from 5.8 to ) The topsoil contained a significant amount of organic material comprised mostly of decomposing rainforest debris and is generally deemed unsuitable for structural fill purposes. 5) Unit weights of the subsurface soil are on the lighter side, possible due to the ash content and the nature of deposition from nearby pyroclastic activity. In-situ soil density values of 70 to 80 pounds per cubic foot are anticipated from laboratory proctor and in situ soil moisture content test results. RECOMMENDATIONS Site Grading Surface soils are not suitable for use as structural fill due to their high organic content and potentially expansive characteristics. Soil should be removed to minimum depth of 3 feet below the bottom and 10 feet beyond the exterior edge of Tank foundation or structural slab. The subgrade shall be proof rolled prior to placement of structural fill. Our geotechnical engineer shall observe the proof rolling operations and direct the contractor when the pad is ready to receive structural fill. CEL anticipates that the majority of the cut on the site may be excavated using an Excavator or Caterpillar D-10 bulldozer (or equivalent) equipped with a single-tooth ripper. Fangasa Pass Tank Footprint Preparation Prior to placement of any fill, the floor of the excavation shall extend to 10 feet laterally beyond the exterior edge of the tank foundation and be compacted to firm conditions as directed by the geotechnical engineer. Stabilization of the subgrade may be required to minimize potential impacts from moderately expansive soils. Stabilization may be comprised of either compaction of 2 to 4 inch sized drain rock into the subgrade using a vibratory roller or the use of geofabric/geogrid, whichever is more readily available and cost efficient. Any detected voids, soft soils, or tree debris in excess of ½ inch in diameter shall be excavated/removed and backfilled with structural fill, compacted to at least 95% relative density. Proof roll and void remediation operations shall be monitored by our geotechnical engineer. The proof rolled/stabilized area shall then be brought back to design grades (24-inches minimum) using structural fill comprised of minus 3-inch structural fill or alternative material that has been reviewed and approved by the geotechnical engineer, overlain by 6- ASPA Fagasa Pass Tank Geotechnical Investigation Page 2

5 inches minimum of base course. The imported structural fill shall meet the following criteria: 1. Between 8 to 20 percent of soil by weight shall pass the #200 sieve 2. The Plasiticity Index (P.I.) of the portion of soil passing the $40 sieve shall not be greater than The material shall have a minimum CBR value of 25 and a CBR expansion value of less than 1 percent when tested in accordance with ASTM D The structural fill shall be placed in maximum 8-inch thick loose lifts, compacted to 95% percent of the maximum dry density as determined in the laboratory in accordance with ASTM D Fill placed in areas which slope steeper than 5H:1V shall be continually benched as the fill is brought up in lifts. The structural fill shall extend at least 10 feet beyond the structural footprint and slope away from the structure at a minimum slope of 5%. Bottom of tank foundations shall be embedded at least 18 inches below the lowest adjacent surface grade. Soil Bearing Capacity Soil bearing capacity the Tank footprint shall be as follows: Dead plus live loads 2,000 psf. Increase for wind and seismic loads 600 psf Total for all loads 2,600 psf Resistance to Lateral Loads Imported Granular Fill Friction Factor 0.45 Passive Soil Pressure 300 pcf with max of 1,500 pcf Active Earth Pressure (equivalent fluid pressures) 45 pcf for free standing 65 pcf for restrained. Estimated Settlements Foundations constructed as recommended herein should experience minimal settlements. Total settlements of foundations should be less than one inch, and differential settlements should be less than half of the total settlements. Concrete Pavement Access Drives and Parking Areas Access drives and parking areas should be over-excavated a minimum of one foot below the finished subgrade. The surface of this layer should be ripped to a minimum depth of two feet and the ripped material should be hoe rammed or crushed to a maximum particle size of 6 inches and should be re-compacted to at least 95% relative density. Any voids encountered should be collapsed, over-excavated, and backfilled with structural fill compacted to at least 95% relative density. The areas should then be brought back to design grades as follows: Light Traffic Loads (Axil-Load Category 1): Based on moderate subgrade or sub-base support, a 4 inch thick concrete pavement section (aggregate-interlock joints) underlain by 4 inches of base course and 6 inches of 3-inch minus structural fill (sub-base), compacted to 95% maximum dry density as determined by laboratory Proctor Analysis. CBR values for selected base course should ASPA Fagasa Pass Tank Geotechnical Investigation Page 3

6 be at least. CBR values for sub-base should be at least 25. Any fill requirements below the sub-base course may be comprised of 3-inch minus structural fill. Heavy Traffic Loads (Axil-Load Category 2): Based on very high subgrade or sub-base support, a 7-inch thick concrete pavement section (aggregate-interlock joints) underlain by 18 inches of base course compacted to % maximum dry density as determined by laboratory Proctor Analysis. CBR values for selected base course should be at least. Any fill requirements below the base course may be comprised of 3-inch minus structural fill. CBR values for sub-base shall be at least 25. Fills Over Natural Slopes Where fill is planned to be placed over slopes that are greater than or equal to 5% gradient, the area to receive fill should be benched prior to fill placement. CEL recommends that benches into the native volcanic material be a minimum of 8 feet wide and a maximum height of 5 feet. Materials, Placement, and Compaction of Fill-Footings and Trenches Where fill is to be placed in confined areas such as under footings, behind retaining walls, or in utility trenches, the material should consist of structural fill as previously described in this report. The structural fill should be placed in 8 loose lifts and compacted to at least 95% of the material s maximum dry density. Any area of fill that appears soft, loose, or unstable should be removed and replaced with suitable material. All trenching activities should comply with American Samoa Power Authority and Department of Public Works, American Samoa, guidelines and specifications. If trenches are to be greater than 4 feet in depth, sloping and/or benching may be required to provide safe access to/from the trench. Compaction Standard and Testing The maximum relative density of fill materials (1-inch minus material) should be determined in the laboratory using ASTM D1557 (Modified Proctor). In addition, roller test patterns to determine the maximum relative density of the 6-inch minus and 3-inch minus fill materials should be accomplished in the field for each compaction device proposed to be used by the contractor on the project. The roller test pattern consists of measuring the in-place relative moist density of fill after 2, 4, 6, 8, and 10 passes on a lift of fill with the compaction equipment. The density after each set of passes is measured and plotted versus the number of passes, this forming a relative density curve. The 95% relative density specified herein refers to 95% of the maximum density developed by the roller test pattern using a 10-ton vibratory roller. Should any piece of compaction equipment be inadequate to achieve the specified compaction, the equipment should be replaced or the lift thickness should be decreased so that the specified degree of compaction may be achieved. Soil Sulphate Content Soil ph reading taken in the field were used as the basis evaluating the corrosive properties of the soil, including sulfate content. Generally, the ph values measured at random locations within the Tank # 2 footprint area ranged from 5.5 to 6.3. Though the soil had a high organic content (mostly decomposing rainforest debris), significant sulfate concentrations usually ASPA Fagasa Pass Tank Geotechnical Investigation Page 4

7 generate soil ph levels on the order of 4 or less. Chloride contents for the subject site soils are in excess of 20 parts per million. Project Monitoring Operations to be monitored by our geotechnical engineer include the following: 1. Excavation and backfill operations completed within the Tank # 2 footprint plus 10 feet laterally from the lower outside edge of the Tank # 2 foundation. 2. Excavation and backfill operations associated with retaining wall construction. 3. Removal of unsuitable surface soils from project site. 4. Subgrade proof rolling, stabilization, and void remediation. Subgrade quality will be evaluated within the excavation as it relates to the soil bearing capacity reported above. LIMITATIONS AND REVIEW This report has been prepared in general accordance with accepted local engineering practice for the exclusive use of ASPA Water Engineering Division for the subject Water Tank site, detailed in the report above. The conclusions and recommendations of this report are based upon data obtained from the observations made during site reconnaissance and test pit construction, along with field and laboratory analysis of select soil samples. CEL assumed that the subsurface conditions do not deviate from those observed. If any variations or undesirable conditions are encountered or there is a significant change in the surface and cut face conditions, CEL should be notified so that the changes can be reviewed, and conclusions and recommendations of this report modified or verified in writing. Excluded from CEL's scope of work was the identification and classification of contaminated soils concerning environmental conditions; therefore, no attempt was made nor should one be construed, that this report addresses environmental concerns with regard to contaminated soil material and water. Should you have any questions regarding this report, or if we can be of further assistance, please contact us at your convenience. We appreciate the opportunity to have been of service to you on this project. Sincerely, CONSTRUCTION ENGINEERING LABS, INC. Robert J Thomas, Jr., P.E. Geotechnical Engineer THIS WORK WAS PERFORMED BY ME OR UNDER MY SUPERVISION (License expires April 30, 2016) ASPA Fagasa Pass Tank Geotechnical Investigation Page 5

8 SITE LOCATION

9 SITE PLAN

10 Approximate Test Pit Locations TP-4 TP-3 TP-2 TP-1 Depth Below Adjacent Surface Grade TP-1 TP-2 TP-3 TP-4 Topsoil, Dark Gray Clayey Silt with Sand, Some Organic Sandy Loam 0-1 m 0-1 m 0-1 m m Light Brown Sandy Elastic Silt Moderately Expansive (3.6%) 1-3 m m m Tan Clayey Silt with Some Sand Moderately Expansive (2.2%) Mottled Purple Sandy Silt with Gravel/Cobbles/Boulders & Red Ash m m Mottled Brown Sand Stone 3 m m m m + Note: Gravels, Cobbles, and Boulders comprised of Sandstone, weakly to well cemented

11 LABORATORY TEST REPORTS

12 Particle Size Distribution Report 6 in. 3 in. 2 in. 1½ in. 1 in. ¾ in. ½ in. 3/8 in. #4 #10 #20 #30 #40 #60 # #140 # PERCENT FINER GRAIN SIZE - mm. % Gravel % Sand % Fines % +3" Coarse Fine Coarse Medium Fine Silt Clay SIEVE PERCENT SPEC.* PASS? SIZE FINER PERCENT (X=NO) #4 #8 #16 #30 #50 # # Material Description Light Brown sandy elastic silt Atterberg Limits PL= 62 LL= 68 PI= 6 Coefficients D 90 = D 85 = D 60 = D 50 = D 30 = D 15 = D 10 = C u = C c = USCS= MH Moisture-75.8% Expansion-3.6% Classification AASHTO= Remarks A-5(5) * (no specification provided) Source of Sample: Tank #1 Sample Number: TP-1 #1 Date: 4/9/15 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Client: Project: Project No: American Samoa Power Authority (ASPA) Upper Pago pago National Park ASPA Figure

13 Particle Size Distribution Report 6 in. 3 in. 2 in. 1½ in. 1 in. ¾ in. ½ in. 3/8 in. #4 #10 #20 #30 #40 #60 # #140 # PERCENT FINER GRAIN SIZE - mm. % Gravel % Sand % Fines % +3" Coarse Fine Coarse Medium Fine Silt Clay SIEVE PERCENT SPEC.* PASS? SIZE FINER PERCENT (X=NO) 1 1/2" 1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 # # Material Description Purple sandy silt with gravel Atterberg Limits PL= 35 LL= 40 PI= 5 Coefficients D 90 = D 85 = D 60 = D 50 = D 30 = D 15 = D 10 = C u = C c = USCS= ML Moisture-54.2% Classification AASHTO= Remarks A-4(2) * (no specification provided) Source of Sample: Tank #1 Sample Number: TP-2 #2 Date: 4/9/15 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Client: Project: Project No: American Samoa Power Authority (ASPA) Upper Pago pago National Park ASPA Figure

14 Particle Size Distribution Report 6 in. 3 in. 2 in. 1½ in. 1 in. ¾ in. ½ in. 3/8 in. #4 #10 #20 #30 #40 #60 # #140 # PERCENT FINER GRAIN SIZE - mm. % Gravel % Sand % Fines % +3" Coarse Fine Coarse Medium Fine Silt Clay SIEVE PERCENT SPEC.* PASS? SIZE FINER PERCENT (X=NO) #4 #8 #16 #30 #50 # # Material Description Tan Clayey Silt Atterberg Limits PL= LL= PI= Coefficients 67 D 90 = D 85 = D 60 = D 50 = D 30 = D 15 = D 10 = C u = C c = USCS= Classification AASHTO= Remarks Natural Moisture-56.8% Expansion-2.2% * (no specification provided) Source of Sample: Tank #1 Sample Number: Tp-3-4 #3 Date: 4/8/15 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Client: Project: Project No: American Samoa Power Authority (ASPA) Upper Pago pago National Park ASPA Figure

15 COMPACTION TEST REPORT %, 81.6 pcf 81 Dry density, pcf ZAV for Sp.G. = Water content, % Test specification: ASTM D Method C Modified Elev/ Classification Nat. % > % < Sp.G. LL PI Depth USCS AASHTO Moist. 3/4 in. No.200 MH A-5(5) TEST RESULTS MATERIAL DESCRIPTION Maximum dry density = 81.6 pcf Light Brown sandy elastic silt Optimum moisture = 24.0 % Project No. ASPA Client: American Samoa Power Authority (ASPA) Remarks: Project: Upper Pago pago National Park Source of Sample: Tank #1 Sample Number: TP-1 #1 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Figure

16 COMPACTION TEST REPORT %, 78.1 pcf Dry density, pcf ZAV for Sp.G. = Water content, % Test specification: ASTM D Method A Modified Elev/ Classification Nat. % > % < Sp.G. LL PI Depth USCS AASHTO Moist. #4 No.200 ML A-4(2) TEST RESULTS MATERIAL DESCRIPTION Maximum dry density = 78.1 pcf Purple sandy silt with gravel Optimum moisture = 30.1 % Project No. ASPA Client: American Samoa Power Authority (ASPA) Remarks: Project: Upper Pago pago National Park Source of Sample: Tank #1 Sample Number: TP-2 #2 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Figure

17 78 COMPACTION TEST REPORT ZAV for Sp.G. = %, 76.9 pcf Dry density, pcf Water content, % Test specification: ASTM D Method C Modified Elev/ Classification Nat. % > % < Sp.G. LL PI Depth USCS AASHTO Moist. 3/4 in. No TEST RESULTS MATERIAL DESCRIPTION Maximum dry density = 76.9 pcf Tan Clayey Silt Optimum moisture = 34.4 % Project No. ASPA Client: American Samoa Power Authority (ASPA) Remarks: Project: Upper Pago pago National Park Source of Sample: Tank #1 Sample Number: Tp-3-4 #3 CONSTRUCTION ENGINEERING LABS, INC. Pearl City, Hawaii Figure