Geotechnical Engineering Report

Transcription

1 BIG CYPRESS SEMINOLE INDIAN RESERVATION WATER TREATMENT FACILITY October 29, 2015 Terracon Project No. HD Prepared for: REISS ENGINEERING, INC Spring Villas Pt. Winter Springs, FL Prepared by: Terracon Consultants, Inc. West Palm Beach, Florida

2 October 29, 2015 Reiss Engineering, Inc Spring Villas Pt. Winter Springs, Florida Attn: Ms. E. Devan Henderson, P.E. Re: Geotechnical Engineering Report Big Cypress Seminole Indian Reservation Water Treatment Facility Project Number: HD Dear Ms. Henderson: Terracon Consultants, Inc. (Terracon) has completed geotechnical engineering services for the above referenced project. This study was performed in accordance with the Consultant Agreement between REISS ENGINEERING, INC. (REISS) and Terracon dated June 9, This report presents the findings of the subsurface exploration and provides geotechnical engineering recommendations concerning the proposed construction. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Terracon Consultants, Inc. Jaime Velez, P.E. Kevin E. Aubry, P.E. Senior Project Engineer Geotechnical Services Manager FL Registration No FL Registration No Responsive Resourceful Reliable

3 TABLE OF CONTENTS EXECUTIVE SUMMARY... i 1.0 INTRODUCTION PROJECT INFORMATION SUBSURFACE CONDITIONS Field Exploration Stratigraphy Groundwater LABORATORY TEST RESULTS Index Properties RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION Geotechnical Overview Soil Exchange In-situ Densification Fill Composition, Placement and Compaction Foundation Design GENERAL COMMENTS... 7 APPENDIX A FIELD EXPLORATION Exhibit 1 Boring Location Plan Exhibit 2 Subsurface Profiles Responsive Resourceful Reliable

4 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD EXECUTIVE SUMMARY This Geotechnical Engineering Report was performed in accordance with our Proposal dated February 14, 2014 and the Consultant Agreement between REISS ENGINEERING, INC. (REISS) and Terracon dated June 9, Terracon previously provided a geotechnical study for the project and the results were provided in a report dated July 24, We understand that the locations of the proposed project components (a Chemical Containment Canopy Slab, a Clearwell and two single story structures) have changed and therefore additional geotechnical work was required. The attached report includes the results of three engineering borings drilled at the site on October 7, The borings disclosed the site soils to consist of mostly loose to medium dense clean to silty sands and shelly sands to about 17 to 22 feet below grade, followed by mostly weakly cemented sand and shell. A major exception to this general profile exists at the location of Boring B-1 where very loose, very clayey sand (with trace root fibers) was present from 6 to 8.5 feet below grade. Very loose clayey, silty sand is also present at the site at greater depth from about 37 to 47 feet below grade where it is underlain by more cemented sand and shell (which extends to the maximum exploration depth of 50 feet). Based upon topographic information provided to us, and measured depths to groundwater, we estimate that the surface of the groundwater was approximately elevation feet with respect to the North American Vertical Datum of 1988 (NAVD) at the time of our exploration. The results of this study indicate that the subject site is mostly suitable for the planned construction from a geotechnical viewpoint. However, the very loose, very clayey sand layer that begins at 6 feet below grade at the location of Boring B-1 is too weak for support of the proposed structures. As such, it should be excavated and replaced from within the footprint of the proposed structures, where present, including 5 feet beyond the plan limits of the structures. Although these weak soils were only found within the boring located beneath the clearwell, these soils may potentially extend beneath the footprints of the single story buildings and the Chemical Containment Canopy Slab as well. Once site preparation and soil exchange is completed as described herein, the site will be suitable for support of the proposed structures when employing shallow foundation systems, as is currently planned. This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled GENERAL COMMENTS should be read for an understanding of the report limitations. Responsive Resourceful Reliable i

5 GEOTECHNICAL ENGINEERING REPORT BIG CYPRESS SEMINOLE INDIAN RESERVATION WATER TREATMENT FACILITY HENDRY COUNTY, FLORIDA Terracon Project No. HD October 29, INTRODUCTION This geotechnical engineering report has been prepared for the proposed improvements to the existing Water Treatment Facility located within the Big Cypress Seminole Indian Reservation in. This report describes the methods of study and key findings from the subsurface exploration and provides geotechnical engineering recommendations for the proposed construction. 2.0 PROJECT INFORMATION Terracon previously provided a geotechnical study for the project and the results were provided in a report dated July 24, We understand that the locations of the proposed project components have changed and therefore additional geotechnical work was required. Based upon the information provided to us, we understand that the current project will consist of the design and construction of the following: 1. A Chemical Containment Canopy Slab. The slab will be reinforced concrete that is about 135 ft by 30 ft in plan size and supports chemical storage tanks and the columns of a pre-engineered metal canopy roof. According to the plans provided to us the tanks will range in diameter from about 2 feet to 12 feet and will be as tall as about 17 feet. Using an assumed fluid density of 75 pounds per cubic feet, we estimate that the larger tanks (8 to 12 ft diameter) will weigh between about 50 and 130 kips when full. We anticipate that the average bearing pressure of the 135 ft by 30 ft canopy slab under the weight of the tanks and other features above it will not exceed about 500 pounds per square foot (psf). Currently the slab is designed to be mostly 16 inches thick except at the canopy column locations where it will be 26 inches thick. The slab will bear at elevation feet with respect to the North American Vertical Datum of 1988 (NAVD). 2. A Clearwell structure. The clearwell structure will be an enclosed concrete structure that is about 20 ft by 25 feet in plan. The bottom slab will bear about 3 feet below existing grade (bear at about elevation feet NAVD). We understand that the slab will impose a bearing pressure of about 900 psf on the underlying soils. Responsive Resourceful Reliable 1

6 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD Two single story precast concrete buildings. One building will be 18 ft by 10 ft in plan size (Monitoring Building) while the other will be 21 ft by 10 ft in plan (Electrical Building). We have assumed that the walls of the buildings will transmit loads of not more than 2 kips per foot to their foundations. Current plans are to support the walls and buildings on an 8-inch (uniformly) thick precast concrete slab. The new structures are to be located just north of the existing water treatment facility (see Exhibit 1), in an area that is currently covered with maintained grass. Based on review of a Topographic Survey (by Miller Legg) that was provided to us, the existing ground surface elevation within the area of the proposed structures ranges from about +15 to +17 feet NAVD with a slight downward slope from south to north. 3.0 SUBSURFACE CONDITIONS 3.1 Field Exploration Subsurface conditions at the project site were explored using three Standard Penetration Test (SPT) borings. The SPT borings were located within the proposed structure footprints and were drilled to depths of 30 to 50 feet below the ground surface. The SPT borings were completed using mud rotary methods and samples of the subsurface components were obtained using a standard split barrel (the Standard Penetration Test after ASTM D 1586). The boring locations are shown on the attached Exhibit 1. The boreholes were backfilled with grout upon their completion. Samples recovered from the borings were placed in moisture-proof containers and returned to our laboratory for visual examination and classification in accordance with the Unified Soil Classification System (ASTM D 2487). 3.2 Stratigraphy The borings disclosed about 6 inches of topsoil overlying very loose to loose relatively clean sands to about 5 to 6 feet below grade. At the locations of Borings B-2 and B-3 the clean sands are underlain by about 6 inches to 1 foot of clayey sand followed by medium dense silty sand sized to gravel sized shell fragments. At the location of Boring B-1 the clean sands are underlain by 2.5 feet of very loose, very clayey sand (with trace root fibers) followed by the silty sand size to gravel size shell fragments. Loose to medium dense, slightly silty to silty sand enters the profile at about 12 feet below grade and continues to about 17 to 22 feet below grade where weakly cemented sand and shell exists. A 10 ft (approximately) thick layer of very loose clayey, silty sand enters the profile at about 37 feet below grade and is followed by cemented sand and shell, which extends to the maximum exploration depth of 50 feet. Responsive Resourceful Reliable 2

7 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD The subsurface conditions found are relatively consistent with those disclosed in the 2014 subsurface exploration with the major exceptions of very loose clayey and clayey, silty sands being present at 6 feet below grade (at the location of Boring B-1) and at 37 to 47 feet below grade, respectively. 3.3 Groundwater Groundwater levels were measured in the borings on the date of drilling (October 7, 2015). The depth to groundwater ranged between 1.8 and 2.3 feet below surface grade. Based upon review of a topographical survey (by Miller Legg) that was provided to us, and the measured depths to the groundwater level, we estimate that the groundwater elevation at the time of the exploration was approximately feet NAVD. The borings were drilled during what is commonly referred to as the wet season. It should be recognized that the groundwater levels reported herein are representative of conditions at the time of drilling and will fluctuate above and below these levels in response to changes in rainfall, drainage and other such conditions. It should be noted that the groundwater level measured at the site during the prior July 15, 2014 field exploration was about +15 feet NAVD. 4.0 LABORATORY TEST RESULTS 4.1 Index Properties Soil samples collected from the borings were reviewed in our laboratory by a geotechnical engineer and assigned a visual-manual classification using the Unified Soil Classification System (ASTM D 2487; U.S.C.S.). Also, two (2) samples of the clayey sand strata were selected for index property testing to aid in their classification. These samples were tested for moisture content (ASTM D 2216), organic content (ASTM D 2974), fines content (ASTM D 1140), and Atterberg Limits tests (ASTM D 4318). The results of the laboratory testing are shown as part of the Subsurface Profiles on the attached Exhibit 2 in Appendix A and are summarized in the table below. Boring Stratum No. Depth Below Grade (feet) USCS Classification Moisture Content (%) Organic Content (%) Amount Passing No. 200 Sieve (%) Atterberg Limits (%) LL PI B SC B SM-SC Notes: LL Liquid Limit (%) PI Plasticity Index (%) Responsive Resourceful Reliable 3

8 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION 5.1 Geotechnical Overview The results of this study indicate that the subject site is mostly suitable for the planned construction from a geotechnical viewpoint. However, the very loose, very clayey sand layer that begins at 6 feet below grade at the location of Boring B-1 is too weak for support of the proposed structures. As such, it should be excavated and replaced from within the footprint of the proposed structures, where present, including 5 feet beyond the plan limits of the structures. Although these weak soils were only found within the boring located beneath the clearwell, these soils may potentially extend beneath the footprints of the single story buildings and the Chemical Containment Canopy Slab as well. Once site preparation and soil exchange is completed as described herein, the site will be suitable for support of the proposed structures when employing shallow foundation systems, as is currently planned. Based on our prior subsurface explorations at the site, the groundwater level has reached about +15 feet NAVD in the past, during the wet season. This is higher than the proposed top of slab elevation for the clear well. We therefore recommend that the lower portion of the clear well walls be waterproofed. More detailed recommendations for site preparation and foundation design and construction follow. 5.2 Soil Exchange The very loose, very clayey sand (i.e. Stratum 7) at the location of Boring B-1 should be removed and replaced with engineered fill. The excavation/removal should extend throughout the full lateral extent of this soil layer where it underlies the proposed structures including a 5 foot horizontal extension beyond the plan limits of the structures. The limits of the Stratum 7 soil removal and replacement can only be accurately determined as excavations are made to remove them. The excavation for soil exchange should be made in accordance with all applicable State and Federal requirements. OSHA 29 CFR Part 1926 (Subpart P, Excavations) defines the subsurface profile within the planned depths of excavation as Type C soil. Temporary sideslopes in a fully dewatered excavation made in these soils can be inclined at 1-1/2:1 (horizontal: vertical) or somewhat flatter provided seepage forces do not act on the sideslopes. If the prescribed minimum sloping requirements cannot be met because of space limitations or other restrictions, then a sheeting or shoring system will become necessary. Responsive Resourceful Reliable 4

9 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD The excavated volume should be backfilled with clean, granular materials that are free of debris, cinders, combustibles, roots, sod, wood, cellulose and organic material. The fill should have not more than 12 percent passing the U.S. Standard No. 200 Sieve (dry weight basis), have no particle size larger than 1 inch, and have not more than 2 percent organics (by weight). The Stratum 2 materials should meet these criteria and may be stockpiled and re-used as backfill provided the surficial topsoil layer is stripped first and not intermixed with it. The fill should be placed in 12-inch thick (maximum) loose lifts with each lift compacted to at least 95 percent of the ASTM D 1557 maximum dry density. The very clayey sand removal and subsequent replacement filling should be accomplished in a dry condition in conjunction with an appropriately designed and implemented dewatering operation. The dewatering system should be one that lowers the phreatic surface to not less than 2 feet below the excavation bottom. The purpose of the dewatering is to allow compaction of the granular backfill and visual confirmation that the very loose clayey sand was removed. 5.3 In-situ Densification Outside of the soil exchange zones, surface vegetation and topsoil should be removed from the planned structure areas and wasted or used in landscaping areas. These areas should be compacted to increase the shear strength and reduce compressibility of the underlying soils. Densification should be performed along the stripped grade or at the bearing level of the slabs, whichever is lower. At this level the soils should be densified using a self-propelled vibratory compactor that imparts a dynamic drum force of not less than 44,000 pounds. The compactor should be operated at a travel speed of no more than 1.5 miles per hour (normal walking speed). Rolling should continue until no further settlement can be visually discerned at the rolled surface. In no case should any section of subgrade receive less than ten (10) roller passes. Density control should be exercised in the upper 12 inches of the subgrade materials. Soils in this interval should be compacted to not less than 95 percent of the maximum dry density determined by the Modified Proctor Test (ASTM D 1557). To facilitate compaction, the groundwater level within the structure footprint may need to be artificially lowered (i.e. dewatering) to not less than 24 inches below the grade at which compaction is occurring. Ground vibrations induced by the vibratory roller compaction should be monitored to assure that they do not reach levels which prove damaging to neighboring structures. Responsive Resourceful Reliable 5

10 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD Fill Composition, Placement and Compaction Fill required for raising the structure pads to final grades, if any, should consist of clean, granular materials that are free of debris, cinders, combustibles, roots, sod, wood, cellulose and organic material. The fill should have not more than 12 percent passing the U.S. Standard No. 200 Sieve (dry weight basis), have no particle size larger than 1 inch, and have not more than 2 percent organics (by weight). The fill should be placed in 12-inch thick (maximum) loose lifts with each lift compacted to at least 95 percent of the ASTM D 1557 maximum dry density. 5.5 Foundation Design Upon completion of site preparation as described herein, the proposed structures may rest on reinforced concrete slabs as planned. The slabs should be reinforced for the loads that they will sustain and should also be appropriately jointed to control shrinkage cracking. The thickened edge portions of the Chemical Containment Canopy Slab should be designed for an allowable bearing pressure of 2,000 psf. The bottom of the slabs should be not less than 12 inches below the lowest adjacent grade. Thickened edges for the slab areas should be excavated, formed and have their structural concrete cast in the dry. The excavation bottoms should be tamped with a hand held or walk behind compactor prior to placement of reinforcement steel. The compaction efforts need to achieve at least 95 percent of the maximum dry density (ASTM D 1557) for a minimum depth of 12 inches below the slab footing excavation bottoms. The foundation slabs that are planned for the Chemical Containment Area, Clearwell and single story structures are estimated to sustain settlement of less than 1 inch provided that they are constructed in accordance with the geotechnical recommendations provided herein and their loads do not exceed what was described earlier in Section 2.0 of this report. Because the soils at the site are mostly granular in nature, foundation settlement should occur as rapidly as the loads are applied and should be nearly complete once the tanks and clearwell structures are filled. If moisture vapor intrusion is a concern, we recommend that an impervious membrane be inserted between the underside of the slabs and the soil subgrade to reduce the potential for moisture rise. Ordinarily, a 6-mil thick film of polyethylene is sufficient for floor slab construction of the type expected for this project. Based on our prior subsurface explorations at the site, the site groundwater level has reached about +15 feet NAVD in the past, during the wet season. This is higher than the proposed top of slab elevation for the clear well. We therefore recommend that the lower portion of the clear well walls be waterproofed. Responsive Resourceful Reliable 6

11 Big Cypress Seminole Indian Reservation Water Treatment Facility October 29, 2015 Terracon Project No. HD GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between borings, across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either expressed or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing. The project plans and specifications should be provided to us for review and verification of the implementation of the recommendations described herein. Further, a representative of Terracon should be on-site during the earthwork phase of the project to verify and document that construction activities were consistent with the recommendations described herein. This is especially important for the recommendations for soil exchange beneath the proposed Clearwell structure footprint and adjacent structures. Responsive Resourceful Reliable 7

12 APPENDIX A EXHIBIT 1 BORING LOCATION PLAN EXHIBIT 2 SUBSURFACE PROFILES

13 N B-1 B-2 B-3 B-1 LEGEND APPROXIMATE LOCATION OF STANDARD PENETRATION TEST BORING SCALE IN FEET Project Mngr: Drawn By: Checked By: Approved By: JV DV JV KA Project No. Scale: File No. Date: HD BORING LOCATION PLAN GEOTECHNICAL ENGINEERING REPORT AS-SHOWN Consulting Engineers and Scientists HD BIG CYPRESS WATER TREATMENT PLANT 1225 OMAR ROAD WEST PALM BEACH, FL PH. (561) FAX. (561) HENDRY COUNTY, FLORIDA EXHIBIT

14 BORING NO. B-1 B-2 B-3 MC= =29.9 OC=3.2 LL=28.5 PI=12 DEPTH IN FEET DEPTH IN FEET MC= =24.2 LEGEND Brown fine SAND, grass roots (TOPSOIL) (PT) Brown fine to medium SAND (SP) Gray to brown SAND with clay (SC) Light gray silty SAND size to GRAVEL size shell fragments (SM, GM) Gray fine SAND, slightly silty to silty (SP-SM, SM) Gray cemented sand and shell (SHELLROCK) Gray very clayey SAND with trace root fibers (SC) Gray clayey, silty SAND (SM-SC) SP N Unified Soil Classification System Group Symbol (ASTM D 2487) Indicates the number of blows of a 140 pound hammer, freely falling a distance of 30 inches, required to drive a 2-inch diameter sampler 12 inches (ASTM D 1586) Standard Penetration Test (SPT) B-1 boring and number WOH/30 Depth of groundwater (feet) & date measured Indicates sampler advanced due to weight of hammer a total of 30 inches (1) (2) (3) OC MC -200 LL PI NOTES Organic Content (%) Moisture Content (%) Amount Finer Than The U.S. Standard No. 200 Sieve (%) Liquid Limit (%) Plasticity Index (%) Borings were drilled on October 7, 2015 using a Central Mine Equipment Model 45B (CME 45B) drilling rig and were backfilled with grout. Strata boundaries are approximate and represent soil strata at each test hole location only. Soil transitions may be more gradual than implied. Groundwater depths shown on the subsurface profiles represent groundwater surfaces on the dates shown. Groundwater level fluctuations should be anticipated throughout the year. Project Mngr: Drawn By: Checked By: Approved By: JV DV JV KA Project No. Scale: File No. Date: HD AS-SHOWN HD Consulting Engineers and Scientists 1225 OMAR ROAD WEST PALM BEACH, FL PH. (561) FAX. (561) SUBSURFACE PROFILES GEOTECHNICAL ENGINEERING REPORT BIG CYPRESS WATER TREATMENT PLANT HENDRY COUNTY, FLORIDA EXHIBIT 2