B08_Solicit_Geo_Report-Other_ATTCH_5.pdf

ECS Florida, LLC Geotechnical Engineering Report, Addendum No. 1 Guy Bradley Flamingo Visitor Center - Proposed Elevator and Other Improvements

1 Flamingo Lodge Highway Homestead, Miami-Dade County, Florida 33034

ECS Project Number 25:3404

January 8, 2019

Guy Bradley Flamingo Visitor Center – Proposed Elevator January 8, 2019 ECS Project No. 25:3404-Addendum No. 1 Page 2

January 8, 2019

Mr. Bobby L. Baker, P.E.

Vice President Baker Design Build 219 North Newman Street, 2nd Floor Jacksonville, Florida 32202

ECS Project No. 25:3404

Reference: Geotechnical Engineering Report, Addendum No. 1

Guy Bradley Flamingo Visitor Center – Proposed Elevator and Other Improvements 1 Flamingo Lodge Highway Homestead, Florida 33034

Dear Mr. Baker:

ECS Florida, LLC (ECS) previously performed a subsurface exploration, laboratory testing, and geotechnical engineering analyses for the above-referenced project located in Homestead, Florida (ECS Project No. 25:3404 dated November 20, 2018). Since the referenced geotechnical report was completed, the project structural engineer requested geotechnical recommendations to support the following structural features: a two-story exterior stairway, a concrete masonry unit (CMU) screen wall, and new columns, walls and slabs-on-grade. According to information provided by the project structural engineer, maximum column and wall loads are assumed be about 5 kips and 1.5 kips per lineal foot, respectively.

The following design recommendations given in this supplemental report were developed using information from the referenced geotechnical report. A soft clay layer was encountered during our field exploration at depths of approximately two to ten feet below existing ground surface. This subsurface condition within the site warrants special foundation recommendations. Our recommendations are discussed below and presented in order of preference. This letter should be considered an addendum to the referenced geotechnical report and should not be considered separately from that report. This report presents our understanding of the geotechnical aspects of the project, field exploration, laboratory testing, and our design and construction recommendations.

ECS Project No. 25:3404-Addendum No. 1 Page 3

Helical Piles

The staircase, columns and property screen wall can be supported by a system of deep foundations.

Helical piles can penetrate the soft, wet clay soils observed at the site, reaching the underlying dense sand layer. Helical pile foundations will reduce the need for extensive subgrade improvement if shallow foundations are selected to support the project components described above. Refer to Section

5.1.1 of our original report (referenced above) for helical pile recommendations.

Shallow, Spread Footing Foundations

As an alternative to helical piles, the structural frame and walls for the planned exterior stairwell structure, columns and property screen wall may be supported using a shallow, spread footing foundation system. Due to the potential for excessive consolidation settlements of the soft, wet clay soils and bearing capacity failures, it is recommended that footings bear on improved subgrade soils.

A net allowable bearing pressure of 2,000 psf can be considered for foundations bearing on improved subgrade consisting of limerock as described below. The above bearing pressure is applicable for footings bearing a minimum of two feet below existing grade or finished grade, whichever is deeper.

The allowable bearing capacity value is based on a factor of safety of at least three against a bearing capacity failure.

In order to utilize the above bearing capacity the subgrade should be improved by removing the soft, wet clay soils below the foundations and replacing with compacted limerock fill. Based on our soil borings, the clay soils were encountered to a depth of ten feet below existing site grades. The limerock should extend at least two feet beyond the perimeter edge of the footings. See below for guidelines on soil stabilization with limerock.

Continuous strip footings should have a least dimension of 12 inches in width and column footings should have a least dimension of 18 inches for bearing capacity considerations. Foundations subject to moments or overturning forces should be proportioned such that the resultant soil reaction force on the bottom of the foundation lies within the middle one-third of the foundation.

Stabilization with Limerock

Subgrade material should be stabilized with limerock to a minimum Limerock Bearing Ratio (LBR) of 40 percent, as specified by FDOT requirements for Type B or Type C Stabilized Subgrade. All stabilized subgrade materials should be compacted to 98 percent of the Modified Proctor (ASTM D1557) maximum dry density. Furthermore, the stabilized subgrade may be imported material or a blend of on-site soils and imported materials. If a blend is proposed, we recommend that the contractor perform a mix design to find the optimum mix proportions. It should be noted that a minimum of 97 percent of the stabilized material should pass a 3½ inch sieve.

ECS Project No. 25:3404-Addendum No. 1 Page 4

Settlements

The resulting total foundation movements due to elastic and consolidation settlements are estimated to not exceed about one inch for the maximum foundation loads described above if our recommendations provided herein are met. Lesser settlement would be expected for smaller foundation loads. Differential movements between foundation elements should not exceed about 75 percent of the predicted total movement. Careful field inspection of footing excavations will contribute substantially to reducing foundation movements.

Resistance to sliding will be developed by friction along the base of the footing and passive earth pressure acting on the vertical face of the footing. A coefficient of friction of 0.35 can be used along the bottom of the limerock base layer bearing in native clay soils. Refer to Section 5.1.2 of our original report (referenced above) for active and passive earth pressure parameters.

Floor Slabs

The on-site natural soils are considered suitable for support of the lowest floor slabs, although moisture control during earthwork operations, including the use of disking or appropriate drying equipment, may be necessary. Based on our subsurface exploration, it appears that the slabs for the structures will bear on natural soils and/or compacted structural fill. This material is likely suitable for the support of a slab-on-grade or monolithic slab with turn down edge after the subgrade has been properly prepared and compacted; however, there may be areas of loose or yielding soils that should be removed and replaced with compacted structural fill in accordance with the recommendations included in this report. The following graphic depicts our soil-supported slab recommendations:

Figure 1: Soil supported slab recommendations

1. Drainage Layer Thickness: four inches

2. Drainage Layer Material: GRAVEL (GP, GW), SAND (SP, SW)

3. Subgrade compacted to 98% maximum dry density per ASTM D698

Subgrade Modulus: Provided the placement of Structural Fill and Granular Drainage Layer per the recommendations discussed herein, the slab may be designed assuming a modulus of subgrade reaction, k of 150 pci (lbs/cu. inch). The modulus of subgrade reaction value is based on a one foot by one foot plate load test basis and assuming that the subgrade is properly compacted.

Slab Isolation: Ground-supported slabs should be isolated from the foundations and foundation-supported elements of the structure so that differential movement between the foundations and slab will not induce excessive shear and bending stresses in the floor slab. Where the structural configuration prevents the use of a free-floating slab, the slab should be designed with suitable

Concrete Slab Vapor Barrier

Granular Capillary Break/Drainage Layer

Compacted Subgrade

Floor Slabs