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Home My WebLink AboutREPORT OF GEOTECHNICAL EXPLORATIONV i� �F INTERNATIONAL FLORIDA'S LEADING ENGINEERING SOURCE Report of Geotechnical Exploration figr � g p M m ; MONSOON 111 % MEN "Alm — - AN= Proposed 2-Story Residence Lot 4,13 Nettles Island St. Lucie County, Florida I June 15, 2015 GFA Project No.: 15-0843.00 For: Manny Gulino ' I Florida's Leading Engineering Source Environmental - Geotechnical - Construction Materials Testing • Threshold and Special Inspections - Plan Review & Code Compliance ''�"ERNATIO Manny Gulino 193 Vineyard Meadow Farms Road Vineyard Haven, MA 02568 Site: Proposed 2-Story Residence Lot 413 Nettles Island St. Lucie County, Florida GFA Project # 15-0843.00 Dear Mr. Gulino: June 15, 2015 GFA International, Inc. (GFA) has completed the subsurface exploration and geotechnical engineering evaluation for the above -referenced project in accordance with the geotechnical and engineering service agreement for this project. The scope of services was completed in accordance with our Geotechnical Engineering Proposal (15-0843.00) dated May 29, 2015, planned in conjunction with and authorized by you. EXECUTIVE SUMMARY The purpose of our subsurface explo ation was to classify the nature of the subsurface soils and general geomorphic conditions and evaluate their impact upon the proposed construction. This report contains the results of our ssubsurface exploration at the site and our engineering interpretations of these, with respect to the project characteristics described to us including providing recommendations for site preparation and the design of the foundation system. Based on conversations with the client, the project -consists of removing an existing modular home structure and then constructing a 2-story residence. GFA was informed that the site did not require a pile foundation due to flood zone or other requirements. We have not received any information regarding structural loads. For the foundation recommendations presented in this report we assumed the maximum column load will be 50 kips and the maximum wall loading will be 4 kips per linear foot. GFA estimates the site is at or near final grade. The recommendations provided herein are based .upon the above considerations. If the project description has been revised, please inform GFA International so that we may review our recommendations with respect to any modifications. A total of one (1) standard penetration test (SPT) boring to depths of approximately forty-five (45) feet, and one (1) Auger Boring (AB) to approximately ten (10) feet, below ground surface (BGS) were completed for this study. The subsurface soil conditions encountered at this site generally consist of medium dense sand or slightly silty sand (SP,SP-SM,SM) to a depth of 4 feet, medium dense sand with occasional loose layers to from 4 to 11 feet,, very loose/soft silt and clay (CL,ML) from 11 to 18 feet, gray sand or silt and clay (SP,CL,ML) from 18 to 331/z feet, and then medium dense sand with some 521 NW Enterprise Drive - Port St. Lucie, Florida 34986 • (772) 924.3575 - (772) 924.3580 (fax) • www OFFICES THROUGHOUT FLORIDA Proposed 2-Story Residence Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 2 of 9 cemented sand (SP) to the boring termination depths. Please refer to Appendix D - Record of Test Borings for a detailed account of each boring and sounding. Silty and clayey soils were encountered in the borings that could cause possible long term differential settlement with some potential settlement problems. For that reason to reduce settlement problems, GFA recommends the residence be supported on a shallow foundation system consisting of a modified monolithic slab (reinforced mat foundation). i A typical modified monolithic slab has load bearing footings that are a minimum of 18 inches deep and 24 inches wide with three No.!5 reinforcing bars on top and bottom. Though footing dimensions may be different for the allowable bearing pressure given above, we recommend the minimum 24 inches width. The slab should be at least 5 inches thick reinforced with No. 4 reinforcing bars at 12" centers both ways. Final design will be determined by the structural engineer or others. The subgrade soils should be improved with compaction from existing grade prior to constructing the foundation pads. The top 2 feet below existing grade should be compacted to a minimum of 95% density prior to placing fill to achieve final grade. Fill should be placed in 12- inch lifts and compacted to achieve a minimum 95% density. After excavation for mat/footings, the subgrade to a depth of 2 feet below bottom of mat/footings should be compacted to achieve a minimum 95% density. Analysis of the foundation performance under hurricane conditions or other storm events, including the effects of loss of soil support due to scour or other forces, is not within the scope of this report, and the recommendations are valid only for normal conditions. Additional analysis and options for foundation systems with scour conditions or other scenarios can be performed if requested. For the existing seawall and/or retaining wall, they must have the structural integrity to withstand the loadings imposed by the new residence or other structures and construction methods. Evaluation and design of the walls are the responsibility of the structural engineer, specialty engineer, contractor, or others. Evaluation of the walls are not within our scope of work. We appreciate the opportunity to be of service to you on this project and look forward to a continued association. Please do :not hesitate to contact us if you have any questions or comments, or if we may further assist you as your plans proceed. 111 Res a � 1 b ii dr, GFA��h Q i • ��ip Flodclb� rtif f��u�la'�r'gation Number 4930 6�g Id V%,Mol4, P.E. ; Sep �oftniial Engfneq- Flo `Sgj%tratiff Nq:' 5 i� Q ' .. ' •� �o Copies��i � dHig David Alker Project Manager C,FA OL and OH GROUPS. The soil in the OL and OH groups are characterized by the presence of organic odor or color, hence the symbol O. Organic silts and clays are classified in these groups. The materials have a plasticity range that corresponds with the ML and MH groups. HIGHLY ORGANIC SOILS The highly organic soils are usually very soft and compressible and have undesirable construction characteristics. Particles of leaves, grasses, branches, or other fibrous vegetable matter are common components of these soils. They are not subdivided and are classified into one group with the symbol PT. Peat humus and swamp soils with a highly organic texture are typical soils of the group. GF DISCUSSION OF SOIL GROUPS COARSE GRAINED SOILS GW and SW GROUPS. These groups comprise well -graded gravelly and sandy soils having little or no plastic fines (less than percent passing the No. 200 sieve). The presence of the fines must not noticeably change the strength characteristics of the coarse -grained friction and must not interface with it's free -draining characteristics. i GP and SP GROUPS. Poorly graded gravels and sands containing little of no plastic fines (less than 5 percent passing the No. 200 sieve) are classed in GP and SP groups. The materials may be called uniform gravels, uniform sands or non -uniform mixtures of very, coarse materials and very fine sand, with intermediate sizes lacking (sometimes called skip -graded, gap graded or step - graded). This last group often results from borrow pit excavation in which gravel and sand layers are mixed. GM and SM GROUPS.-. In general, the GM and SM groups comprise gravels or sands with fines (more than 12 percent the No. 200 sieve) having low or no plasticity. The plasticity index and liquid limit of soils in the group .should plot below the "A" line on the plasticity chart. The gradation of the material is not considered significant and both 'well and poorly graded materials are included. I GC and SC GROUPS. In general, the GC and SC groups comprise gravelly or sandy soils with fines (more than 12 percent passing the No, 200 sieve) which. have a fairly high plasticity. The liquid limit and plasticity index should plat above the "A" line on the plasticity chart. FINE GRAINED SOILS ML and MH GROUPS: In these groups, the symbol M has been used to designate predominantly -silty ,material. The symbols L and H represent low and high liquid limits, respectively, and an arbitrary dividing line between the two set at a liquid limit of 50. The soils in the MIL and MH groups are sandy silts, clayey silts or inorganic silts with relatively low plasticity. Also included are loose type soils and rock flours. CL and CH GROUPS. In these groups the symbol C stands for clay, with L and H denoting low or high -liquid limits, with the dividing line again set at a liquid of 50. The soils are primarily organic clays. Low plasticity clays are classified as CL and are usually lean clays, sandy clays or silty clays. The medium and high plasticity clays are classified as CH. These include the fat clays, gumbo clays and some volcanic clays. 6[P Appendix E - Discussion of Soil Groups 60- ." r. Since 198844 -- AUGER BORING LOGS WITH HAND CONE PENETROMETER (HCP) TESTS Client: Manny Gulino Project: Proposed 2-Story Residence Lot 413 Nettles Island, St. Lucie County, FL Elevation: Existing Grade Project No: Lab No: Test Date: Technician: 15-0843.00 6/11 /2015 WN/JB . TEST LOCATION: AB —1 N27.28671 °; W80.219900 HCP Depth (feet) Description (color, texture, consistency, remarks) Depth Reading 0-4 Brown fine sand, some shell SP 1 30 4-7 Gray fine sand, some shell SP 2 60 7 - 10 Gray fine sand, trace silt and shell SP 3 80+ 4 60 5 80+ 6 80+ 7 70 - 8 80+ 9 60 10 40 Water table at 4 feet below ground surface GFA INTERNATIONAL 521 N.W. ENTERPRISE DRIVE, PORT ST. LUCIE, FLORIDA 34986 PHONE: (772) 924-3575 - FAx: (772) 924-3580 STANDARD PENETRATION TEST BORING (ASTM D-1586) Client: Manny Gulino Project No.:15-0843.00 Lab No.: Project: Proposed 2-Story Residence I Page: 3 of 3 Lot 413 Nettles Island, St. Lucie County, FL Date: 6/11/2015 Elevation: Existing Grade Drill Rig: Simco-24 Water Level: 4 feet after 0 hours Drilling Fluid commenced at depth of 10 feet Field Party: WN/JB TEST LOCATION: SPT -1 N27.286740 W80.220030 Laboratory Tests Depth Blows/ N Sample Layer: USCS Description Passing Moisture Organic (feet) 6 in. Value No. From/to No. 200 Content Content 40 -------------- Drilled dense 40 to 43%2 feet 42 ------ ------ 43 ------- ------ 6 43'/2 - 48%2 SP Light gray fine sand, trace silt, 44 -- 5 ------ little cemented sand _ 45 5 10 12 Terminated boring at 45 feet 46 ---- --- 47 ------ ------ 48 ------- ------ 49 ------ ------ 50 ------ ------ 51 ---- --- 52 ------- ------ 53 ------- ------ 54 ------ ------ 55 ------- ------ 56 ------- ------ 57 ------- ------ 58 ------ ------ 59 ------- ------ GFA INTERNATIONAL J 521 N.W. ENTERPRISE DRIVE, PORT ST. LucLE, FLORIDA 34986 PHONE: (772) 924-3575 - FAx: (772) 924-3580 STANDARD PENETRATION TEST BORING (ASTM D-1586) Client: Manny Gulino Project No.:15-0843.00 Lab No.: Project: Proposed 2-Story Residence Page: 2 of 3 Lot 413 Nettles Island, St. Lucie County, FL Date: 6/11/2015 Elevation: Existing Grade Drill Rig: Simco-24 Water Level: 4 feet after 0 hours Drilling Fluid commenced at depth of 10 feet Field Party: WN/JB TEST LOCATION: SPT - 1 N27.28674° W80.22003° Laboratory Tests Depth Blows/ N Sample Layer: USCS Description Passing Moisture Organic (feet) 6 in. Value No. From/to No. 200 Content Content 20 -------------- 21 ------- ------ 22 ------ ------ 23 ------- ------ 23Y2 - 25 CL,ML Gray silt and clay, little sand 24 ---1 -- ------ 2 25 2 4 11 26 ------ ------ 27 ------- ------ 28 ------- ------ 4 28% - 30 CL,ML Gray silt and clay, little shell 29 -- 6 6 12 12 —30 31 ------- ------ 32 ------ ------ 33 ------- ------ 34 -- 7--- ------ 33%2 - 35 SP Light gray fine sand, trace shell 7 —35 7 14 13 Drilled dense 36%2 to 38%2 feet —36 ----- 37 ------- ------ 38 ------ ------ 40 SP Light gray fine sand, some cemented sand 39 2 --- ------ 6 [12 6 12 14 GFA INTERNATIONAL 521 N.W. ENTERPRISE DRIVE, PoRT ST. Luc1E, FLORIDA 34986 PHONE: (772) 924-3575 - FAx: (772) 924-3580 STANDARD PENETRATION TEST BORING (ASTM D-1586) Client: Manny Gulino Project No.:15-0843.00 Lab No.. Project: Proposed 2-Story Residence Page: 1 of 2 Lot 413 Nettles Island, St. Lucie County, FL Date: 6/11/2015 Elevation: Existing Grade Drill Rig: Simco-24 Water Level: 4 feet after 0 hours Drilling Fluid commenced at depth of 10 feet Field Party: WNUB Hand Au:rer with Hand Cone Pentrometer Test (HCP in ksf) performed in top 4 feet TEST LOCATION: SPT - 1 N27.286740 W80.220030 Laboratory Tests Depth Blows/ N Sample Layer: USCS Description Passing Moisture Organic (feet) - 6 in. Value No. From/to ' No.200 Content Content 0 0-2 SP Brown fine sand, some shell HCP= 80+ HCP= 80+ 2-4 SM Brown fine sand, some silt, trace shell ---_ 3 HCP= --- ......... 80+ --- 4 HCP= 80+ 4 4-6 SP-SM Brown fine sand, little silt, little shell --- 5 ---- 3 --- ------ 3 7 3 6 ___5___ ______ 6 - 11 SP Gray fine sand, occasional some shell 5 ---- 7 8 11 19 4 8 --14- ------ 6 5 9 --- ---- 5 ------ 10 5 -- -- 10 - 4 --- _ 1 2 6 11-17 CL,ML Gray silt and clay, little sand 12 - 1 ------ ------ WOH ---- 13 WOH ---- ____ WOH WOB 7 WOH=Weight of Hammer 14 WOH ----15 1 -- - ---- 1 2 8 16 1 --- ---- 1 17 1 --• ---- ------ 17 - 18 CL,SC Gray fine sand and silt and clay, trace shell 1 2 9 ---- 18 5 --- -.......... 18 - 20 SP Gray fine sand 5 --- 19 - 8 L 7 15 10 6 1 1 1 1 1 1 1 NOTES RELATED TO RECORDS OF TEST BORING AND GENERALIZED SUBSURFACE PROFILE 1. Groundwater level was encountered and recorded (if shown) following the completion of the soil test boring on the date indicated. Fluctuations in groundwater levels are common; consult report text for a discussion. 2. The boring location was identified in the field by offsetting from existing reference marks and using a cloth tape and survey wheel. 3. The borehole was backfilled to site grade following boring completion, and patched with asphalt cold patch mix when pavement was encountered. 4. The Record of Test Boring represents our interpretation of field conditions based on engineering examination of the soil samples. 5. The Record of Test Boring is subject to the limitations, conclusions and recommendations presented in the Report text. 6. "Field Test Data" shown on the Record of Test Boring indicated as 11/6 refers to the Standard Penetration Test (SPT) and means 11 hammer blows drove the sampler 6 inches. SPT uses a 140-pound hammer falling 30 inches. 7. The N-value from the SPT is the sum of the hammer blows required to drive the sampler the second and third 6- inch increments. 8. The soil/rock strata interfaces shown on the Records of Test Boring are approximate and may vary from those shown. The soil/rock conditions shown on the Records of Test Boring refer to conditions at the specific location tested; soil/rock conditions may vary between test locations. 9. Relative density for sands/gravels and consistency for silts/clays are described as follows: SPT CPT SANDS/GRAVELS SPT CPT SILTS/CLAYS BLOWS/FOOT KG/CM RELATIVE DENSITY BLOWS/FOOT KG/CM2 CONSISTENCY 0-4 0-16 Very loose 0-1 0-3 Very soft 5-10 17-40 Loose 2-4 4-6 Soft 11-30 41-120 Medium Dense 5-8 7-12 Firm 31-50 121-200 Dense 9-15 13-25 Stiff over 200 Very Dense 16-30 25-50 Verystiff r9+7 >30 >50 Hard 10. Grain size descriptions areas follows: NAME SIZE LIMITS Boulder 12 Inches or more Cobbles 3 to 12Inches Coarse Gravel '/4 to 3 Inches Fine Gravel No. 4 sieve to % inch Coarse Sand No. 10 to No. 4 sieve Medium Sand No. 40 to No. 10 sieve Fine Sand No. 200 to No. 40 sieve Fines Smaller than No. 200 sieve 11. Definitions related to adjectives used in soil/rock descriptions: PROPORTION ADJECTIVE APPROXIMATE ROOT DIAMETER ADJECTIVE <5% Trace Less than 1/32" Fine roots 5% to 12% Little 1/32" to '/<" Small roots 12% to 30% Some '/4" to 1" Medium roots 30% to 50% And Greater than V Large roots Organic Soils: Soils containing vegetable tissue in various stages of decomposition that has a fibrous to amorphous texture, usually a dark brown to black color, and an organic odor. Organic Content <25%: Slightly to Highly Organic; 25% to 75%: Muck; >75%: Peat 19 �1w e�hr y yh Test 'Location Plan Proposed 2-Story Residence Lot 413 Nettles Island St. Lucie County, FL GFA Project No. 15-0843.00 Legend + Approximate Standard Penetration Test (SPT) Boring & Auger Boring (AB) Locations Vicinity Map Proposed 2-Story Residence Lot 413 Nettles Island St. Lucie County, FL GFA Project No. 15-0843.00 Aa Ica '�1 ��ti.'Netles.B1 ti �.• 5 fib , Imagery>Date 1 9951 lath' 27.28bU72° Ian-80.218981° eleu Oft eye alt 1278 ft 1 4 J �K^ Proposed 2-Story Residence Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 9 of 9 structures. A proposal for vibration monitoring during compaction operations can be supplied upon request. 4.0 REPORT LIMITATIONS This consulting report has been prepared 'for the exclusive use of the current project owners and other members of the design team for the Proposed 2-Story Residence, Lot 413 Nettles Island, St. Lucie County, Florida. This report has been prepared in accordance with generally accepted local geotechnical engineering practices; .no other warranty is expressed or implied. The evaluation submitted in this report, is based in part upon the data collected during a field exploration, however, the nature and extent of variations throughout the subsurface profile may not become evident until the time of construction. If variations then appear evident, it may be necessary to reevaluate information and professional opinions as provided in this report. In the event changes are made in the nature,, design, or locations of the proposed structure, the evaluation and opinions contained in this report shall not be considered valid, unless the changes are reviewed and conclusions modified or verified in writing by GFA International. Please also find in Appendix F a supplement by the American Society of Foundation Engineers (ASFE) that is entitled "Important Information About Your Geotechnical Engineering Report". The supplement will help explain further limitations of geotechnical reports, the nature -of geotechnical issues and information' concerning the management of your geotechnical risks. 5.0 BASIS FOR RECOMMENDATIONS The analysis and recommendations submitted in this report are based on the data obtained from the tests performed at the locations indicated on the attached figure in Appendix B. This report does not reflect any variations, which may occur between borings. While the borings are representative of the subsurface conditions at their respective locations and for their vertical reaches, local variations characteristic of the subsurface soils of the region are anticipated and may be encountered. The delineation between soil types shown on the soil logs is approximate and the description represents our. interpretation of the subsurface conditions at the designated boring locations on the particular date drilled. Any third party reliance of our geotechnical report or parts thereof is strictly prohibited without the expressed written consent of GFA International. The applicable SPT methodology (ASTM D-1586), CPT methodology (ASTM D-3441), and Auger Boring methodology (ASTM D-1452) used in performing our borings and sounding, and for determining penetration and cone resistance is specific to the sampling tools utilized and does not reflect the ease or difficulty to advance other tools or materials. 6fA Proposed 2-Story Residence--- Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 8 of 9 Initial site preparation should consist of performing stripping (removing surface vegetation, near surface roots, and other deleterious matter) and clearing operations. This should be done within, and to a distance of five (5) feet beyond, the perimeter of the proposed building footprint (including exterior isolated columns). Foundations and any below grade remains of any structures that are within the footprint of the new construction should be removed, and utility lines should be removed or properly abandoned so as to not affect structures. 2. Following site stripping and prior the placement of any fill, areas of surficial sand (not exposed limestone) should be compacted ("proof rolled") and tested. We recommend using a steel drum vibratory roller with sufficient static weight and vibratory impact energy to achieve the required compaction. Density tests should be performed on the proof rolled surface at a frequency of not less than one test per 2,500 square feet, or a minimum of three (3) tests, whichever is greater. Areas of exposed intact limestone shall be visually confirmed by the project geotechnical engineer prior to fill placement, in lieu of proof rolling. 3. Fill material may then be placed in the building pad as required. The fill material should be inorganic (classified as SP, SW, GP, GW, SP-SM, SW-SM, GW-GP, GP -GM) containing not more than 5 percent (by weight) organic materials. Fill materials with silt/clay-size soil fines in excess of 12% should not be used. It should be placed in lifts with a maximum lift thickness not exceeding 12-inches: Each lift should be compacted and tested prior to the placement of the next lift. Density tests should be performed within the fill at a frequency of not less than one test per 2,500 square feet per lift in the building areas, or a minimum of three (3) tests per lift, whichever is greater. 4. For any footings bearing on a limestone formation, the bottom of all footing excavation shall be examined by the engineer / geologist or his representative to determine the condition .of the limestone. The limestone shall be probed for voids and loose pockets of sand. Such areas shall be cleaned to depth of 3 times the greatest horizontal dimension and backfilled with lean concrete. 5. For footings placed on structural fill or compacted native granular soils, the bottom of all footings shall be tested for compaction and examined by the engineer / geologist or his representative to determine if the soil is free of organic and/or deleterious material. Density tests should be performed at a frequency of not less than one (1) density test per each isolated column footing and one (1) test per each seventy five (75) lineal feet of wall footings. If compaction cannot be attained due to persistent wetness or the water table near the bottom of the footing excavation, or due to silty/clayey soil `pumping' during compaction, GFA recommends undercutting below bottom of footing and replacement with No. 57 stone, or rock/sand fill for subgrade that cannot be compacted. The rock/sand fill should be compacted and tamped into the excavation and inspected and verified by a representative from GFA, and tested with hand cone penetrometers, probe rods, or density tests. 6. The contractor should take into account the final contours and grades as established by the plan when executing his backfilling and compaction operations. Using vibratory compaction equipment at this site may disturb adjacent structures. We recommend that you monitor nearby structures before and during proof -compaction operations. A representative of GFA International can monitor the vibration disturbance of adjacent 6 FA ? Proposed 2-Story Residence"} I; - Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL ! June 15, 2015 GFA Project No. 15-0843.00 Page 7 of 9 Silty and clayey soils were encountered in the borings that could cause possible long term differential settlement with some potential settlement problems. For that reason to reduce settlement problems, GFA recommends the residence be supported on a shallow foundation system consisting of a modified monolithic slab (reinforced mat foundation). A typical modified monolithic slab has load bearing footings that are a minimum of 18 inches deep and 24 inches wide with three No. 5 reinforcing bars on top and bottom. Though footing dimensions may be different for the allowable bearing pressure given above, we recommend the minimum 24 inches width. The slab should be at least 5 inches thick reinforced with No. 4 reinforcing bars at 12" centers both ways. Final design will be determined by the structural engineer or others. A moisture barrier is recommended beneath the floor slab to reduce moisture migration from the underlying soil resulting in dampness of the slab. For design purposes, the stiffened mat with thickened edge footing foundation may be designed with a contact pressure of 400 psf, a modulus of subgrade reaction (k) value of 70 pci., and an allowable bearing capacity of 2,500 psf may', be used for foundation design of the mat thickened edge footings. Expected settlement of the structure is up to 1'/z inches total and less than inch differential. The floor slab with thickened edge footings should be designed as a rigid mat with sufficient thickness and rigidity to distribute loading conditions and limit potential cracking due to localized subgrade settlement affects. Flexible or adjustable utility and other connections should be considered to accommodate the settlement. The footprint of the mat should be prepared per Site Preparation below. Excessive moisture vapor transmission through floor slabs -on -grade can result in damage to floor coverings as well as cause other deleterious affects. An appropriate moisture vapor retarder should be placed beneath the floor slab to reduce moisture vapor from entering the building through the slab. The retarder should be installed in general accordance with applicable ASTM procedures including sealing around pipe penetrations and at the edges of foundations. 3.2 Site Preparation (Mat Foundation) GFA recommends the following compaction requirements for this project: ➢ Proof Roll ............................................ .......................... 95% of a Modified Proctor ➢ Building Pad Fill.............................................................95% of a Modified Proctor ➢ Footings.........................................................................95% of a Modified Proctor The compaction percentages presented above are based upon the maximum dry density as determined by a "modified proctor' test (ASTM D-1557). All density tests should be performed to a depth of 2 feet below bottom of excavation and 2 feet below bottom of mat/footings. All density tests should be performed using the nuclear method (ASTM D-2922), the sand cone method (ASTM D-1556), or Hand Cone Penetrometer (HCP) tests. Our recommendations for preparation of the site for use of shallow foundation systems are presented below. This approach to improving and maintaining the site soils has been found to be successful on projects with similar soil conditions. GFA Proposed 2-Story Residenc& L Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 6 of 9 Boring logs derived from our field exploration are presented in Appendix D: "Record of Test Borings". The boring logs depict the observed soils in graphic detail. The Standard Penetration Test borings indicate the penetration resistance, or N-values, and the auger borings the HCP values logged, during the drilling and sampling activities. The classifications and descriptions shown on the logs are generally based upon visual characterizations of the recovered soil samples. All soil samples reviewed have been depicted and classified in general accordance with the Unified Soil Classification System, modified as necessary to describe typical Florida conditions. See Appendix E: "Discussion of Soil Groups", for a detailed description of various soil groups. The subsurface soil conditions encountered at this site generally consist of medium dense sand or slightly silty sand (SP,SP-SM,SM) to a depth of 4 feet, medium dense sand with occasional loose layers to from 4 to 11 feet, very loose/soft silt and clay (CL,ML) from 11 to 18 feet, gray sand or silt and clay (SP,CL,ML) from 18 to 33'/2 feet, and then medium dense sand with some cemented sand (SP) to the boring termination depths. Please refer to Appendix D - Record of Test Borings for a detailed account of each boring and sounding. 2.5 Hydrogeological Conditions On the dates of our field exploration, the groundwater table was encountered at a depth of approximately 4 feet below the existing ground surface. The groundwater table will fluctuate seasonally depending upon. local rainfall and other site specific and/or local influences including the water levels in the nearby Intracoastal Waterway (Indian River) with tidal influences. Brief ponding of stormwater may occur across the site after heavy rains. No additional investigation was included in our scope of work in relation to the wet seasonal high groundwater table or any existing well fields in the vicinity. Well fields may influence water table levels and cause significant fluctuations. If a more comprehensive water table analysis is necessary, please contact our office for additional guidance. _ 3.0 ENGINEERING EVALUATION AND RECOMMENDATIONS 3.1 General A foundation system for any structure must be designed to resist bearing capacity failures, have settlements that are tolerable, and resist the ,environmental forces that the foundation may be subjected to over the life of the structure. The soil bearing capacity is the soil's ability to support loads without plunging into the soil profile. Bearing capacity failures are analogous to shear failures in structural design and are usually sudden and catastrophic. The amount of settlement that a structure may tolerate is dependent on several factors including: uniformity of settlement, time rate of settlement, structural dimensions and properties of the materials. Generally, total or uniform settlement does not damage a structure but may affect drainage and utility connections. These can generally tolerate movements of several inches for building construction. In contrast, differential settlement affects a structure's frame and is limited by the structural flexibility. C,FA Proposed 2-Story Residence---`'4 Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 5 of 9 2.2 Field Exploration A total of one (1) standard penetration test (SPT) boring to depths of approximately forty-five (45) feet, and one (1) Auger Boring (AB) to approximately ten (10) feet, below ground surface (BGS) were completed for this study. The upper 4 feet of the SPT borings were drilled with a hand auger in order to avoid damaging utilities. Hand Cone Penetrometer (HCP) tests were conducted at one -foot intervals in the auger boring. The HCP test, in conjunction with information about the soil type, is empirically correlated to the relative density of subsurface soils. The locations of the borings performed are illustrated in Appendix B: "Test. Location Plan". The Standard Penetration Test (SPT) and 'HCP methods were used as the investigative tools within the borings. SPT tests were performed in substantial accordance with ASTM Procedure D-1586, "Penetration Test and Split -Barrel Sampling of Soils" and the auger borings in substantial accordance with ASTM Procedure D-1452, "Practice for Soil Investigation and Sampling by Auger Borings". The SPT test procedure consists of driving a 1.4-inch I.D. split - tube sampler into the soil profile using a 140-pound hammer falling 30 inches. The number of blows per foot, for the second and third 6-inch increment, is an indication of soil strength. The soil samples recovered from the soil borings were visually classified and their stratification is illustrated in Appendix D: "Record of Test Borings". It should be noted that soil conditions might vary between the strata interfaces, which are shown. The soil boring data reflect information from a 'specific test location only. Site specific survey staking for the test locations was not provided for our field exploration'. The indicated depth and location of each test was approximated based upon existing grade and estimated distances and relationships to obvious landmarks. The boring depths were confined to the zone of soil likely to be stressed by the proposed construction and knowledge of vicinity soils. 2.3 Laboratory Analysis Soil samples recovered from our field exploration were returned to our laboratory where they were visually examined in general accordance with ASTM D-2488. Samples were evaluated to obtain an accurate understanding of the soil properties and site geomorphic conditions. After a thorough visual examination of the recovered site soils, no laboratory testing was deemed necessary. Bag samples of the soil encountered during our field exploration will be held in our laboratory for your inspection for 30 days and then discarded unless we are notified otherwise in writing. The recovered samples were not examined, either visually or analytically, for chemical composition or environmental hazards. GFA would be pleased to perform these services for an additional fee, if required. 2.4 Geomorphic Conditions The geology of the site as mapped on the USDA Soil Survey website consists of Arents, 0 to 5 percent slopes (4). These are sandy soils and organic soils are not indicated. However, these are areas in which the soils have been generally altered by grading, shaping, and covered with fill and therefore the soils can be variable. It should be noted that the Soil Survey generally extends to a maximum depth of 80 inches (approximately 63/ feet) below ground surface and is not indicative of deeper soil conditions. GfA Proposed 2-Story ResidencE - Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 4 of 9 1.0 INTRODUCTION 1.1 Scope of Services The objective of our geotechnical services was to collect subsurface data for the subject project, summarize the test results, and discuss any apparent site conditions that may have geotechnical significance for building construction. The following scope of services is provided within this report: Prepare records of the soil boring logs depicting the subsurface soil conditions encountered during our field exploration. 2. Conduct a review of each soil sample obtained during our field exploration for classification and additional testing if necessary. 3. Analyze the existing soil conditions found during our exploration with respect to foundation support for the proposed structure. 4. Provide recommendations with respect to foundation support of the structure, including allowable soil -bearing capacity, bearing elevations, and foundation design parameters. 5. Provide criteria and site preparation procedures to prepare the site for the proposed construction. 1.2 Project Description Based on conversations with the client, the project consists of removing an existing modular home structure and then constructing a 2-story residence. GFA was informed that the site did not require a pile foundation due to flood zone or other requirements. We have not received any information regarding structural loads. For the foundation recommendations presented in this report we assumed the maximum column load will be 50 kips and the maximum wall loading will be 4 kips per linear foot. GFA estimates the site is at or near final grade. The recommendations provided herein are based upon the above considerations. If the project description has been revised, please inform GFA International so that we may review our recommendations with respect to any modifications. 2.0 OBSERVATIONS 2.1 Site Inspection The project site was generally flat. The grade at the site was estimated to be even with the adjacent road at the time of drilling. A one-story modular residential structure occupied the property. Residential structures were adjacent to the property. The Intracoastal Waterway (Indian River) bordered the east side of the property. A seawall was on the east side of the property. C,FA Proposed 2-Story Residence Geotechnical Report Lot 413 Nettles Island, St. Lucie County, FL June 15, 2015 GFA Project No. 15-0843.00 Page 3 of 9 TABLE OF CONTENTS 1.0 INTRODUCTION.................................................................................................................4 1.1 Scope of Services............................................................................................................4 1.2 Project Description...........................................................................................................4 2.0 OBSERVATIONS.................................................................................................................4 2.1 Site Inspection.................................................................................................................4 2.2 Field Exploration...............................................................................................................5 2.3 Laboratory Analysis..........................................................................................................5 2.4 Geomorphic Conditions....................................................................................................5 2.5 Hydrogeological Conditions..............................................................................................6 3.0 ENGINEERING EVALUATION AND RECOMMENDATIONS..............................................6 3.1 General............................................................................................................................6 3.2 Site Preparation (Mat Foundation)...................................................................................7 4.0 REPORT LIMITATIONS ....................... '?............................................................................... 9 5.0 BASIS FOR RECOMMENDATIONS....................................................................................9 Appendix A - Vicinity Map Appendix B - Test Location Plan Appendix C - Notes Related to Borings Appendix D - Record of Test Borings Appendix E - Discussion of Soil Groups GFA