Aspring_Final_Geotechnical_Report_Part1.pdf

To: Mr. Scott Turgeon and Ms. Jessica Robbins

USDA - NRCS

Date: June 30, 2016

From: James A. Baiges, P.E.

Amec Foster Wheeler Environment & Infrastructure, Inc.

To: Mr. Jorge Munoz

NRCS

Date: March 31, 2016

From: James A. Baiges, P.E.

Geotechnical Exploration and Evaluation Report

NRCS Aspring WRP Project

Hendry County, Florida Project Number: 1411770010

Mr. Scott Turgeon and Ms. Jessica Robbins

USDA-NRCS

452 HWY 98 North

Okeechobee, FL 34972-4168

NRCS ASPRING WRP Project June 30, 2016 Amec Foster Wheeler Environment & Infrastructure, Inc. Project No. 1411770010

2580 Metrocentre Blvd. Suite #6 ● West Palm Beach, FL, 33407● Phone: 561-242-7713 ● Fax 561-242-5591 ii

C O N T E N T S

1.0 Project Information

2.0 Field Exploration

3.0 Laboratory Testing

4.0 Site and Subsurface Conditions

4.1 Soil Survey

4.2 Subsurface Conditions

4.3 Groundwater Conditions

5.0 Engineering Analyses

5.1 Seepage Analysis

5.1.1 Introduction

5.1.2 Steady-State Seepage Model Set-up

5.1.3 Seepage Cases

5.1.4 Boundary Condition

5.1.5 Steady-State Seepage Analysis Results

5.2 Slope Stability Analysis

5.2.1 Slope Stability Model Set Up

5.2.2 Design Criteria for Slope Stability

5.2.3 Slope Stability Analyses Results

5.3 Settlement Potential

6.0 Recommendations For Site Preparation

6.1 General Recommendations

6.2 Site Preparation Recommendations

6.2.1 Clearing

6.2.2 Proof-rolling and Removal of Unsuitable Soils

6.2.3 Subgrade Preparation

6.2.4 Structural Filling and Backfilling

6.2.5 Trench Backfilling

6.2.6 Suitability of Borrow Area Soils

6.2.7 Erosion Control

6.3 General Construction Monitoring and Testing Guidelines

7.0 Basis For Recommendations and Limitations

A T T A C H M E N T S

Site Vicinity Map Field Exploration Plan USDA NRCS Soil Survey

Generalized Subsurface Profile Soil Test Boring Records Summary of Laboratory Test Results Particle Size Analysis Reports Field and Laboratory Test Procedures Photographic Documentation Results of Seepage and Slope Stability Analyses

1.0 Project Information

The subject property is located on the east side of County Road 835, just southwest of the intersection of Hill Grade Road, in Hendry County, Florida. A Site Vicinity Map is presented as

Figure 1. The project site encompasses approximately 1,131 acres, within Sections 7, 8, 17, and

18, Township 45 South, Range 34 East.

We understand that this phase of the project involves the preparation of engineering plans and specifications for various improvements aimed at restoring, to the extent possible, the ecological functions and wildlife habitats which existed at this site prior to agricultural manipulation. Details of the Aspring Wetland Restoration Project Plans prepared by Amec Foster Wheeler and dated

March 4, 2016 have been reproduced as our Field Exploration Plan, Figure 2. It shows the approximate project extent and the location of the proposed improvements. In summary, the planned improvements include the removal of 9 existing structures and land smoothing of 14 areas to restore surface runoff, as well as the construction of 5 water control structures, 7 ditch blocks, one channel, and an earthen dike extending 18,000 feet.

2.0 Field Exploration

Our field exploration included 17 Standard Penetration Test (SPT) borings at selected locations across the project site and an additional 10 borings were performed at the location of the two planned borrow areas. The borings were terminated at depths between 10 and 25 feet (17 borings) and 6 feet (10 borings at the borrow areas) below the existing ground surface. The borings were performed near the approximate location of the proposed water control structures, ditch blocks, land smoothing areas and new earthen dikes. The boring locations were laid out in the field by Amec Foster

Wheeler personnel using a handheld GPS device; the geographical coordinates for each boring location are listed in the attached Soil Test Boring Records. Table 1 includes general information regarding the subject site improvements, latitude and longitudinal coordinates, drilled depth, and groundwater level depth at each boring. The approximate boring locations in reference to the proposed improvements are shown in Figure 2.

The attached Soil Test Boring Records graphically show the SPT penetration resistance (N-Values), subsurface stratification and observed groundwater levels. The stratification lines and the depth designations presented in the boring records represent the approximate boundaries between soil types. In some instances, the transition between soil types may be gradual. Brief descriptions of the field sampling and testing procedures are attached.

3.0 Laboratory Testing

Soil samples collected during our field exploration were placed in moisture proof containers and transported to our West Palm Beach soils laboratory. All samples were visually classified by a

Geotechnical Engineer and described using nomenclature consistent with the Unified Soil

Classification System (USCS). In addition, select samples were subjected to laboratory testing to aid in their classification. The laboratory testing program included the following:

21 Natural moisture content determinations (ASTM D-2216)

2 Atterberg Limits determinations (ASTM D-4318)

5 Particle size analyses (ASTM D-6913)

16 Fines content (% finer than No. 200 sieve) determinations (ASTM D-1140)

4 Organic content determinations (ASTM D-2974)

Results of these tests are presented on the attached Summary of Laboratory Test Results, Table 2. Brief descriptions of the laboratory test procedures are also attached.

The soil samples collected during our field exploration will be kept at our office for a period of three months from the date of this report. The samples will then be discarded unless you request otherwise.

4.0 Site and Subsurface Conditions

The existing site conditions were observed by personnel from our offices during site reconnaissance and boring layout operations performed on April 11, 2016, and again during the field exploration services performed between April 27 and April 29, 2016. Currently, the subject property is being used for cattle grazing. The property has extensive improved pasturelands with numerous drainage improvements.

Soil Survey

We reviewed the United States Department of Agriculture (USDA) / Natural Resources

Conservation Service (NRCS) Web Soil Survey. The Soil Survey is presented in the attachments identifies the approximate boundaries of the different soil map units throughout the subject site. The

USDA/NRCS Soil Survey Report for the site property indicates there are 12 soil types mapped.

A list of the soil map units identified in the survey and complete descriptions of each of those units are also attached. The Soil Survey identifies numerous soil map units covering small extents throughout the site and provides soil information to a depths of 80 inches or less.

The USDA / NRCS soil classifications are based on an interpretation of aerial photographs and widely spaced hand auger borings. Borders between mapping units are considered approximate, and the transition between soil types may be very gradual. Areas of dissimilar soils can occur within a mapped unit. However, the soil survey provides a good basis for an initial evaluation of shallow soil conditions in the area, and can provide an indication of changes that may have occurred due to land filling, excavation, and other activities at the site. Based on the Soil Survey, the site is mostly mantled by sand deposits with small areas of loamy sand and muck.

Subsurface Conditions

A pictorial representation of the subsurface conditions encountered at the explored locations is shown on the attached Generalized Subsurface Profile. The attached Soil Test Boring Records should be referred to for detailed descriptions of the subsurface conditions encountered at each explored location. When reviewing the boring records and generalized subsurface profile, it should be understood that actual soil conditions may vary between and away from the boring locations.

The profile and the soil conditions outlined below highlight the major subsurface stratification encountered during our field exploration.

The soils encountered at the explored locations and depths consist generally of fine to medium grained sands with varying amounts of silt (USCS soil types SP, SP-SM, and SM). Erratic layers of sandy silt and lean clay (USCS Soil types ML and CL) were encountered at a few locations.

Groundwater Conditions

Groundwater in the boreholes was observed at depths ranging from approximately 0.8 to 4.3 feet below the existing ground surface. Fluctuations in groundwater level at this site should be anticipated throughout the year due to a variety of factors, the most important of which is recharge from rainfall. Thus, we expect groundwater levels will rise above the levels encountered during our field exploration (April 27 to 29, 2016) after periods of heavy rains. Fluctuations in groundwater levels throughout the site are also anticipated, influenced by variations in the infiltration and drainage characteristics of the near surface soils, the topography of the site, and the distance to artificial drainage features and other relief points.

5.0 Engineering Analyses

As previously mentioned, the planned improvements include the removal of 9 existing structures and land smoothing of 14 areas to restore surface runoff, as well as the construction of 5 water control structures, 7 ditch blocks, one channel, and an earthen dike extending 18,000 feet.

Three of the proposed water control structures (SWC-1 to SWC-3) consist of installing an 18-inch diameter reinforced concrete culvert under the existing access roads within the project site. Water control structure SWC-4 consists of a 100 foot long by 12 feet wide geoweb stabilized emergency overflow weir. Water control structure SWC-5 consists of a 24 feet long by 15 feet wide concrete overflow weir The proposed dike (Dike 1) consists of an earth embankment that generally is up to about 3 feet in height, with 12-foot wide crests and 3:1 (horizontal:vertical) slopes and extends approximately 18,000 feet along the northwest, north, and east easement boundary of the project.

If additional water control structures are anticipated or the proposed locations are changed, we should be given an opportunity to evaluate the changes/additions in order to determine whether additional explorations and/or analyses would be necessary.

Seepage Analysis

5.1.1 Introduction

As part of the design of the Aspring Wetland Restoration Project, seepage and stability analysis were performed to evaluate the potential seepage across the embankment and foundation materials and stability of the proposed embankment. A representative geometric section was modeled that represents the typical conditions at and downstream of the dike. The upstream and downstream slope of the embankments are 3H:1V (3 ft horizontal to 1 ft vertical), with a 12 wide crest at elevation 20 ft, NAVD.

The new dike, Dike 1, is approximately 18,000 lineal feet of length and commences on the north-west border extending along the project’s north and east easement. The ground surface along the profile of the embankment commonly varies from approximately 17 to 18 feet with localized sections of ground surface at 15 to 16 ft, NAVD. A ground surface of 17 ft, NAVD was utilized for seepage and slope stability analysis. The stratigraphy of the site was evaluated and determined to consist of two general conditions, summarized in Table 3.

Table 3: Summary of Design Cross Section Stratigraphy

Stratigraphy A Stratigraphy B

Embankment Fill Compacted Sand 20 to 17 20 to 17

Stratum 1 Surficial Sand 17 to 15 17 to 2

Stratum 2 Sand with Silt to Silty Sand 15 to 2 -

Stratum 3 Silty Sand 2 to -8 2 to -8

Material Description Elevation (ft, NAVD88)

An existing agricultural canal is observed bordering beyond the projects’ north easement from

Sta. 25+50 to 90+50 of the Dike 1 alignment. Similarly, an additional agricultural canal extends along the southeast easement from Sta. 167+00 to 180+00. Thus, approximately 6,500 lineal feet of the embankment is to be constructed adjacent to existing north agricultural canal which has an approximate invert elevation of 12.5ft, NAVD88. The cross section profile along the north easement is consider the most critical based on the proposed dike section and the proximity of the existing agricultural canal and the anticipated groundwater conditions (normal pool level and

25 year 72-hr event level). Topographic review of the ditch cross section indicate side slopes of the agricultural ditch range from 1.7H:1V to 2.0H:1V. The design cross section incorporates the agricultural ditch with 1.7H:1V side slopes. Design cross sections and stratigraphies are shown in the figures included in the attachment.

5.1.2 Steady-State Seepage Model Set-up

Seepage analyses were performed on the two (2) design cross sections based on the soil statigraphy profile (A and B) described above. The seepage analyses were performed using the

“SEEP/W” computer program of the in GeoStudio 2012 Version 8.15.5.11777 software suite.

SEEP/W is a two-dimensional finite element program that performs seepage analyses for hydrogeologic models and determines seepage paths, seepage flow rates, phreatic surfaces, pore water pressures, and exit gradients for steady state seepage problems.

The SEEP/W model requires the user to input the geologic strata, soil/water physical properties, water levels, topography, and boundary conditions. It then solves the flow equations iteratively by satisfying LaPlace’s equation for fluid flow, generating flow paths and lines of equipotential pressure. The flow paths and lines of equipotential pressure are a pictorial presentation that shows the total head and flow within the 2-D finite element mesh used to depict the cross-section being analyzed. Because the flow lines and equipotential (head) lines cross at right angles, the solution has the appearance of a net, called flow nets.

The relevant physical property required for seepage analysis is hydraulic conductivity, which defines the rate at which water can move through a porous medium. The hydraulic conductivity of embankment fill sections and the subsurface geology are presented in Table 4.

Table 4: Summary of Estimated Hydraulic Conductivity

5.1.3 Seepage Cases

The design sections were each analyzed for two seepage cases that are described below. Each case assumed steady-state seepage through the embankment and foundation strata. The seepage cases were selected from several combinations of water levels taking into account the typical and 25 year storm operating water levels for the wetland and agricultural ditch. The descriptions of two cases are discussed below:

Case 1 – Normal Operating Pool: This case analyzes the long-term steady-state seepage with the pool level in the wetland and normal operational conditions downstream of the wetland;

Case 2 – 25 Year Storm Operating Pool: It simulates the conditions during the Design

Storm with an elevated water level in wetland, and storm conditions downstream of the wetland.

5.1.4 Boundary Condition

The boundary conditions were established based on conditions encountered in the borings, anticipated conditions during operation of the project area and the downstream agricultural canal and are summarized in Table 5.

Table 2: Summary of Estimated Hydraulic Conductivity

Embankment Fill Compacted Sand 9E-03

Stratum 1 Surficial Sand 2E-02

Stratum 2 Sand with Silt to Silty Sand 4E-03

Stratum 3 Silty Sand 1E-03

Estimated Hydraulic

Conductivity (cm/sec) Material Description

Table 5: Summary of Boundary Conditions for Design Sections A and B

Location

Case 1

Normal Operational

Condition

Case 2

25 Year Storm Operational

Condition

Wetland Pool 17.2 18.2

Downstream Agricultural Canal 14.4 15.1

Far-field Groundwater Table 14.0 14.0

Boundary Condition Water Level Elevation (ft, NAVD)

5.1.5 Steady-State Seepage Analysis Results

Results of the seepage analysis is summarized in Table 6. The results show that the seepage through the embankment and foundation strata is expected to range between 1.4 x10-4 and 3.8 x10-3 ft3/sec/lineal foot of embankment.

According to EM1110-2-1901 (USACE, 1993), Factors of Safety (FS) against piping in the range of 2.5 to 5.0 are recommended. For this study, a minimum factor of safety equal to 3 was used.

It should be noted that, based on the seepage analyses, the potential seepage outbreak occurs within the Strata 2 (SP) along the upstream agricultural ditch side slope surface. Strata 2 has a saturated unit weight (γsat) of 115 lb/ft3 and internal friction angle (γ’) of 29 degrees, the critical gradients for vertically upward and horizontal seepage are approximately 0.84 and 0.46, respectively. Applying the factor of safety yields the maximum allowable vertical and horizontal exit gradients of approximately 0.28 and 0.15, respectively.

Based on the results of seepage analysis, the computed maximum vertical and horizontal exit gradients for all design sections are above a FS of 3, as recommended by USACE EM 1110-2-

1901. Results of the seepage analysis for each section evaluated are included in the attachment.

Table 6: Summary of Seepage Through Embankment and Foundation Strata

Total Flow

Through

Dike

(ft3/sec/lf)

Total Flow

Into Ag.

Canal

(ft3/sec/lf)

Vertical

Exit

Gradient

(iy)

Horizontal

Exit

Gradient

(ix)

Total Flow

Through

Dike

(ft3/sec/lf)

Total Flow

Into Ag.

Canal

(ft3/sec/lf)

Vertical

Exit

Gradient

(iy)

Horizontal

Exit

Gradient

(ix)

Stratigraphy A 1.4E-04 1.4E-04 0.07 0.13 1.9E-04 1.8E-04 0.08 0.12

Stratigraphy B 3.8E-03 3.7E-04 0.06 0.08 4.7E-04 4.5E-04 0.09 0.12

Case 1: Normal Pool Case 2: 25 Year Storm

Model

Slope Stability Analysis

5.2.1 Slope Stability Model Set Up

The slope stability analysis was completed using the SLOPE/W software package in GeoStudio

2012 Version 8.12.3.7901 software suite. “SLOPE/W” performs a finite difference limit-equilibrium analysis using a method-of-slices search routine to look for the critical failure surface with the minimum factor of safety. The failure surface used in the search routine can be either circular or wedge-shaped. For our analyses, we completed circular failure surface searches since this is considered to be the most critical failure surface for the site conditions.

Input to SLOPE/W includes pore water pressures calculated from a phreatic surface that is defined by the user or pore water pressures generated by SEEP/W. For this report, the phreatic surface and pore pressures were generated using SEEP/W. The circular and block failure surfaces search routine used several methods, including Bishop, Janbu, Spencer, and

Morgenstern-Price, to find the minimum factor of safety for the embankments slopes.

The two loading conditions were analyzed. These loading conditions included steady state seepage for the normal operating pool and 25 year storm operating pool, as discussed in Section

5.1.4. Analyses for the stability of embankment slopes under steady state seepage were completed using an effective stress analysis with pore pressures estimated using the SEEP/W output from the seepage analyses completed on the two design sections.

Effective stress strength properties were used for all of the embankment and foundation soils due to the relatively permeable nature of the soils, and based on the results of our recent SPT Borings, laboratory classification testing and published correlations, and our experience with similar soils.

The effective strength parameters of each soil strata described in Table 7 were used to model the embankment fill and foundation materials for the stability analyses. Strength and unit weight properties for each stratum were estimated using empirical correlations with field and laboratory test results both from this study and previous geotechnical reports. As part of the soil strength properties selection, consideration was given to literature and laboratory values as well as experience with similar projects.

Table 7: Summary of Unit Weight and Shear Strength Parameters

Effective Friction

Angle (φ', degrees)

Cohesion

(c', psf)

Embankment

Fill Compacted Sand 30 0 105 115

Stratum 1 Surficial Sand 29 0 105 115

Stratum 2 Sand with Silt to

Silty Sand 30 0 95 110

Dry Unit

Weight

(γd, pcf)

Material Description

Saturated

Unit Weight

(γ, pcf)

Effective Stress Parameters

5.2.2 Design Criteria for Slope Stability

The required minimum Factors of Safety (FOS) for dikes is presented in EM 1110-2-1902 (USACE

2003). According to EM 1110-2-1902, the required minimum factor of safety of 1.5 and 1.4 is required for normal operating pool and maximum operating pool under steady-state seepage, summarized in Table 8.

Table 8: Slope Stability Criteria

Normal Operating Pool 1.5

Maximum Operating Pool 1.4

Analysis Condition Required Minimum Factor of Safety

5.2.3 Slope Stability Analyses Results

Tables 9 summarizes the results of the static stability analysis of the upstream and downstream embankment slopes and the upstream slopes of the agricultural canal. All factors of safety (FS) for the dike embankment slopes, as shown in Table 9, are greater than the minimum factor of safety required by USACE Manual EM 1110-2-1902. Slope stability analysis results indicate that the embankment slopes and downstream slopes of the dike embankment design section meet the required minimum factors of safety for all loading cases.

Table 9: Slope Stability Results

Upstream

Embankment

Downstream

Embankment

Agricultural

Canal

Upstream

Embankment

Downstream

Embankment

Agricultural

Canal

Stratigraphy A 1.9 2.1 0.9 1.9 2.0 0.9

Stratigraphy B 1.9 2.1 1.0 1.9 2.1 0.9

Case 2: 25 Year StormCase 1: Normal Pool

Factor of Safety (FS)

Model

The agricultural canal was analyzed to be at a FS of 1.1 in the pre-construction condition suggesting that canal slope are marginally stable but are below the FS minimum values for an engineered stable slopes. These canals are usually maintained by periodically removing accumulated sediment and vegetation which may result in steep side slopes that gradually fail with time until achieving an inclination resembling the response angle of the sandy deposit (FS~1).

Additional slope stability analysis performed considering the pore water pressure increase due to steady-state seepage for the expected normal operational pool and the 25 year storm pool levels show that the new loading regime impacts the stability of the agricultural canal, resulting in a lower

FS.

In conclusion, the expected seepage regime would marginally reduce the stability of the existing agricultural canal that would lead to the eventual localized slope failures reducing the offset distance between the new dike and the existing agricultural canal. The progressive slope failures would eventually stabilize as the failed slope inclination decreases and the FS approaches to 1, similar to the existing conditions. As a result of these localized failures the offset distance between the new dike and the agricultural canal will most likely be reduced. Based on the anticipated failure surfaces, we may expect that this offset distance would not be reduced to less than 8 to 10 feet and may be adequate to assure the global stability of the dike. The offset distance could be utilized as an access route for maintenance purposes. Results of the slope stability analysis for each section and loading condition evaluated are included in the attachment.

Settlement Potential

Our analysis included an estimate of total and differential settlements expected beneath the water control structures and earthen embankments. Soil strength and compressibility parameters were estimated based on correlations with SPT N-values along with the results of our laboratory tests and our engineering judgement. Settlements of the water control structures were estimated considering elastic settlement for a mostly granular material (sand) profile. Based on our analyses, we estimate total settlements should not exceed one inch. Due to the granular nature of the soil profile observed, we anticipate that the settlement would likely occur during the construction phase of the project due to the linear elastic compression of the underling sandy soils. As an additional measure, we recommend that individual joints of the RCP culverts be wrapped with a layer of geotextile filter fabric to reduce the potential of soil migration through openings that may develop at the joints as a result of differential settlement between the pipe segments. The geotextile material should extend a minimum of 18 inches in either direction from the joint, and should consist of FDOT

Type D-3 for Filter Fabric Jacket (Culvert) consistent with the actual soil type being used as embankment fill.

6.0 Recommendations For Site Preparation

General Recommendations

Based on our evaluation of the subsurface information obtained from field exploration and laboratory testing program, we conclude that the subsurface soils within the explored locations and depths are generally suitable for the construction of the proposed improvements using conventional earthwork and construction methods.

The removal of existing structures and land smoothing operations will involve earthmoving operations, excavating and grading. Consideration could be given to hauling any excess materials to the location of new structures and dikes where they can be used as fill. The construction of new water control structures will involve controlled excavation, possibly requiring dewatering measures, the conditioning of the exposed soils at the bottom of the excavation for the support of the new structures, and the controlled placement and compaction of fill material around and above the structures to reach the design finish grades. The construction of ditch blocks and earthen dikes will involve clearing and grubbing of surface vegetation and topsoil, conditioning/proof-rolling of the exposed surface and removal of near surface yielding or otherwise unsuitable soils where present, and controlled placement and compaction of fill to reach the design finish grades.

Generic recommendations for the geotechnical aspects of the proposed improvements are presented in the following sections of this report.

Site Preparation Recommendations

6.2.1 Clearing

The proposed construction areas extending 5 feet beyond the limits of the proposed structures and embankments shall be cleared, grubbed and stripped of all vegetation and topsoil. All tree stumps and root concentrations should be removed from the cleared areas. Care should be exercised to minimize disturbance to any vegetation that is designated to remain.

6.2.2 Proof-rolling and Removal of Unsuitable Soils

Following the clearing operations and documentation of the acceptability of the exposed surface soils by the geotechnical engineer, the proposed embankment areas shall be proof-rolled using a heavy (10 to 12 ton) vibratory roller. The purpose of the proof-rolling procedure is to identify near-surface soft/yielding soils. Any areas that rut or deflect excessively during the proof-rolling process or areas where the presence of unsuitable soils has been determined through further exploratory efforts should be excavated as needed to remove the yielding/unsuitable soils, and subsequently backfilled with approved fill material, placed and compacted in lifts as specified below. The excavation of yielding or otherwise unsuitable soils shall extend at least five feet beyond the footprint of the proposed embankment or structure. The proof-rolling operations and the replacement of unsuitable soils, if any, shall be witnessed by a qualified individual working under the direction of a geotechnical engineer. The depth of excavation may vary across the site.

If the excavation extends below the ambient groundwater level, dewatering measures may be necessary.

6.2.3 Subgrade Preparation

The subgrade at the base of the proposed earthen dikes and at the bottom of the excavations for the construction of the proposed water control structures should be inspected to detect the presence of highly compressible or otherwise unsuitable soils. Any unsuitable soils should be excavated and replaced as recommended herein. The subgrade soils within 12 inches of the surface should be compacted with a vibratory roller or walk-behind vibratory plate compactor so as to produce in-situ dry densities equivalent to at least 95 percent of the Modified Proctor (ASTM

D-1557) maximum dry density value of the compacted material.

The water control structures should bear on level granular subgrade free of any vegetation, muck or organic material within five feet (laterally) from the limits of the structures’ foot-print. The depth of excavation may vary across the site. If the excavation extends below the ambient groundwater level, dewatering measures may be necessary. We recommend that the water control structures be constructed in the “dry” in order to evaluate the acceptability of the subsurface soils and to construct a level and compacted bearing surface. In the event that undesirable materials

(organics or soft and yielding materials) are encountered at the bearing elevation, we recommend that this material be removed and replaced with compacted structural fill. The upper 12 inches of the planned bearing surface supporting the proposed structures should consist of cohesionless

(granular) soils compacted to a density equivalent to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557).

Soil compaction may be achieved with the use of a vibratory plate compactor or impact rammer.

In order to achieve the desired maximum dry density, fill placement may need to be placed in controlled lifts not exceeding 6-inches in loose measure. If backfill material is to be placed below the groundwater table it should consist of bedding stone or gravel (e.g. ASTM C-33 No. 89 stone, AASHTO No. 57, 67, 7 or 8 stone wrapped around with geotextile filter fabric).

6.2.4 Structural Filling and Backfilling

Structural fill, as required, should be placed and compacted in accordance with the project’s construction specifications and to the lines and grades presented in the project documents. All fill material shall be placed in controlled manner where required; particularly the material forming water bearing earthen embankments and around water control structures. Controlled fill material should be placed in lifts, not exceeding 12 inches in thickness unless otherwise indicated, individually compacted with a heavy (10 to 12 ton) vibratory roller. Sufficient passes of the vibratory compactor should be provided to produce in-situ dry densities of at least 95 percent of the Modified Proctor

(ASTM D-1557) maximum dry density value of the fill material, unless otherwise specified in the contract documents. Fill material placed within 5 feet of structures should be compacted using light compaction equipment such as plate tampers or vibratory rammers. Fill to be compacted with light equipment should be placed in thin controlled lifts, not exceeding 6 inches in loose thickness.

In general, structural fill material should consist of sandy soils, free of organics or other deleterious components, with less than 15 percent of fines (USCS soil types SP, SW, SP-SM, SW-SM, SP-SC, SW-SC, SM and SC). Although it would be acceptable to utilize sandy soils with fines contents greater than 12 percent (USCS soil types SM and SC) as fill material, these soils have a tendency to retain moisture, which renders them difficult to compact unless strict moisture control is exercised, particularly when placed in close proximity to the groundwater level. SP & SW soils should have a coefficient of curvature of 2.5 or greater.

6.2.5 Trench Backfilling

Structural fill, as required, should be placed and compacted based on construction specifications.

It is recommended that pipe trench backfill material be placed in lifts not exceeding 6 inches in loose thickness and compacted by utilizing a vibratory compactor. Each lift should be compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557). Care must be exercised to ensure proper placement and compaction of the structural fill material in the haunches. We recommend that structural fill materials be worked under the haunches and compacted by a hand tamper, a pole, or 2-inch timber. Hand tampers should weigh no less than

20 pounds and should have a tamping face no larger than 6 inches square. Care should be taken to avoid damaging the crown of the proposed pipe during compaction operations.

6.2.6 Suitability of Borrow Area Soils

In general, the soils encountered at the explored locations appear to be generally suitable for reuse as controlled fill material. However, the soils have relatively high fines content, particularly at depths below 2 to 5 feet. The Contractor should consider mixing the lower sands with higher fines content with the near surface cleaner sands to facilitate their handling and compaction. Soils with appreciable amounts of organics, more than 4 percent, should not be used as controlled fill. All soils excavated from below the groundwater table will require drying prior to placement and compaction.

Surface Water Control and Dewatering - The Contractor should be responsible for controlling surface water runoff during site preparation and construction procedures. Construction areas should be graded to drain stormwater runoff away from the work areas. The Contractor should be responsible for implementing temporary dewatering measures which may be necessary to facilitate the excavation process and allow the proper placement and compaction of fill material. In general, groundwater levels should be maintained a minimum of 24 inches below any compaction surface.

The Contractor shall take the necessary precautions so that dewatering activities do not adversely affect hydro periods of existing wetlands or the integrity/serviceability of nearby facilities and buried utilities or other features.

6.2.7 Erosion Control

Erosion control measures will be required on the earthen embankment side slopes. The sandy soils which will form the slopes are particularly susceptible to surface erosion as a result of short-duration intense rainstorms and wind driven waves from surface water. Consideration can be given to the use of biodegradable mesh or fabric on the embankment slopes to minimize surface erosion while a permanent vegetative cover can be established. Alternatively, sodding of the slopes or the application of relatively heavy, highly viscous, hydraulically-applied mulches could be used to minimize erosion. Regardless of the type or method of erosion control measures employed, some maintenance of the slopes should be anticipated, particularly in their early life. Any erosion rills that develop should be fixed so that a permanent vegetative cover can become established. Armoring may be necessary to prevent erosion of the embankment slopes in areas subject to long term saturation.

General Construction Monitoring and Testing Guidelines

Prior to initiating compaction operations, representative samples of the structural fill and on-site excavated soils should be collected and tested to determine their index properties and compaction characteristics. The maximum dry density, optimum moisture content, gradation and plasticity characteristics should be determined. These tests are needed for compaction quality control during the construction.

During compaction operations, a representative number of in-place field density tests should be performed to confirm that the specify compaction levels are attained. We recommend the following minimum density testing frequencies:

Recommended Field Density Test Frequencies

Feature Recommended Minimum Density Test Frequency

Water Control Structures 1 test per 30 lf of pipe 1 test at each bottom inlet structure

Earthen Embankments 1 test per 2,500 ft2 of area.

Test proof-rolled subgrade and each fill lift

7.0 Basis For Recommendations and Limitations

Our professional services have been performed, our findings obtained and our recommendations prepared in accordance with generally accepted geotechnical engineering practices. This company is not responsible for the conclusions, opinions or recommendations made by others based on the data presented in this report.

The preliminary recommendations submitted in this report are based upon the data obtained from the borings performed at the locations indicated herein. Regardless of the thoroughness of a geotechnical exploration, there is always a possibility that subsurface conditions will be different from those at specific boring locations and that conditions will not be as anticipated by the designers or contractors. In addition, the construction process itself may alter soil conditions.

If any subsurface soil variations become evident during the course of this project, a re-evaluation of the recommendations contained in this report will be necessary after we have had an opportunity to observe the characteristics of the conditions encountered. The applicability of the report should also be reviewed in the event significant changes occur in the design, nature or location of the proposed facilities.

Experienced geotechnical personnel should observe and document the construction procedures used and the conditions encountered. Unanticipated conditions and inadequate procedures should be reported to the design team.

The assessment of site environmental conditions or the presence of pollutants in the soil or groundwater throughout the subject site is beyond the scope of this geotechnical exploration.

ATTACHMENTS

SITE VICINITY MAP

SR 80

CR 832

CR 833

CR 835

US 27

HILL GRADE RD

COLLIER COUNTY

PALM BEACH

COUNTY

HENDRY COUNTY

BROWARD

COUNTY

Legend Project Boundary County Boundary

Site Vicinity Map Drawn Date

Checked Date

KJS

TSK

Gainesville Florida

Project No.

1411770010

USDA NRCS - Aspring

Figure

Source: ESRI 2010; DeLorme 2013; NRCS 2014

Path: P:\EAT\2014\Projects\NRCS\NRCS ASPRING\DISCIPLINES\GIS\MXD\Submitted Figure Phase III\Figure 1 Location Map.mxd justin.tagle Date Saved: 3/26/2015 3:51:04 PM

5/23/2016

5/23/2016

0 6 123 Miles 1 in = 6 miles

FIELD EXPLORATION PLAN