B08_Solicitation_Attachment_3_-_Geotechnical_Report.pdf

GEOTECHNICAL INVESTIGATION REPORT

Empire Water System Renovations Sleeping Bear Dunes National Lakeshore, Michigan

January 2020

Prepared For:

HDR

703 Main Street, Suite 200

Rapid City, South Dakota 57701

Prepared By:

Otwell Mawby Geotechnical, P.C.

Consulting Engineers

309 East Front St.

Traverse City, Michigan 49684

PN: G19-179

TABLE OF CONTENTS

Page No.

1.0 INTRODUCTION

2.0 TYPE OF CONSTRUCTION

3.0 FIELD INVESTIGATION

4.0 SITE AND SUBSURFACE CONDITIONS

5.0 ENGINEERING ANALYSIS

5.1 Pump House

5.2 Water Tank

5.3 Site and Subgrade Preparation

5.4 Groundwater

6.0 LIMITATIONS

7.0 CLOSURE

APPENDICES

Appendix A Site Plan Appendix B Boring Logs

Geotechnical Investigation Report Empire Water System Renovations

Sleeping Bear Dunes National Lakeshore, Michigan

January 2020

1.0 INTRODUCTION

A geotechnical investigation has been completed for the Empire Water System Renovations in

Sleeping Bear Dunes National Lakeshore, Michigan. The investigation included site reconnaissance, subsurface exploration consisting of test drilling, evaluation of the encountered conditions, engineering analysis, and preparation of this report. The investigation results are reported herein. The investigation was performed for HDR in accordance with our proposal dated August 28, 2019.

2.0 TYPE OF CONSTRUCTION

We have been provided preliminary plans for the project prepared by HDR. The project generally includes 5,050 l.f. of 4 to 8-inch water main and appurtenances, a new water tank, and a new well house. The water main will connect existing wells to the water tank and pump house, throughout the maintenance complex, and to housing units along Barrack Drive to the north.

Barrack Drive is substantially lower than the maintenance complex and the design includes a

PRV station near approximate Station 8+00. The water main will have minimum cover of 6 ft with bedding extending from 6 inches below to 6 inches above the pipe.

The pump house will be approximately 25 ft by 25 ft in plan. We have considered that it will be a single-story, slab-on-grade structure with conventional cast-in-place concrete foundations. Our recommendations are based on either a masonry or light-frame structure with maximum wall loads of up to 3 kips per foot. We have considered that the building’s finish floor elevation will be within 2 ft of existing grades.

The water tank will have a capacity of approximately 50,000 gallons with a diameter on the order of 15 to 20 ft. We have considered that the tank will be of at-grade, steel construction.

We should be informed of any changes from these design considerations as they may affect our recommendations.

3.0 FIELD INVESTIGATION

The field investigation was completed in December 2019 and consisted of the advancement of a series of four soil borings. The boring was performed at the location indicated on Figure No. 1, Site Location Map, attached in Appendix A. The approximate boring locations were staked in the field by our personnel and the ground surface elevation was estimated by interpolation from the elevation contours on the provided topographic plan. Ground elevations herein are given in feet. The project Land Surveyor should be retained if more precise location or elevation information is desired.

The borings were advanced with a truck mounted Acker Renegade drill rig equipped with 3 ¼” inner diameter hollow stem augers. Split spoon sampling was completed with an automatic hammer to produce Standard Penetration Test “N-values”. The “N-value” provides an indication of the relative density of granular soils. Samples were retained and returned to our laboratory. A continuous log of the boring was recorded based on the recovered samples, soil cuttings, and drilling observations.

Soil samples were classified and the boring logs were prepared which graphically depict the subsurface soils. The details of the soils encountered in the investigation can be found on the boring logs attached in Appendix B.

The soil borings were performed solely for the purpose of a geotechnical investigation.

Environmental services are not included in the geotechnical scope of service.

4.0 SITE AND SUBSURFACE CONDITIONS

The site is developed as the Sleeping Bear Dunes maintenance complex with several drives and numerous small buildings. The site is located on high ground south of Empire, Michigan, with

Lake Michigan present to the west. Buildings present along Barrack Drive to the north are approximately 250 ft lower than the maintenance complex. The inclination of the slope was generally as steep as 1.5H:1V to 2H:1V based on the provided topographic plan. The site was wooded with mature deciduous trees with the exception of cleared areas for the maintenance area and lower structures. The site was significantly higher than any local surface water or wetlands.

Borings generally encountered granular (sand) soil. Boring B-1, at the lower portion of the site, found brown poorly graded sand (Unified Soil Classification System group symbol SP) beneath two inches of topsoil. The sand in the upper 5.5 ft was described as possible fill based on the color of the material and loose to very loose relative density. The lower sand was brown to light brown, though also very loose in relative density. Boring B-2, north of the carpentry shop, found two inches of gravel and six inches of topsoil above light brown to tan sand. The sand graded occasionally with trace gravel and was loose becoming medium dense in relative density.

Borings B-3 and B-4 found dark brown poorly graded sand with silt (SP-SM) in the upper approximately 10 ft beneath topsoil and gravel. The upper sand was described as possible fill based on the dark color; however, the relative density was loose to medium dense and there were no definitive indications of fill such as buried topsoil, debris, etc. Brown to tan sand extended below the upper sand to the explored depth of 15 ft in Boring B-3 and was underlain from a depth of approximately 22.5 ft in Boring B-4 by poorly graded sand with gravel.

Groundwater was present at a depth of approximately 14 ft in Boring B-1.

This section has included a general description of the subsurface and groundwater conditions for the site. The boring logs attached in Appendix B should be reviewed for additional detail. The described conditions are based on a limited number of test borings and samples. Variations from these locations should be expected.

5.0 ENGINEERING ANALYSIS

5.1 Pump House

A conventional continuous shallow foundation system is recommended for support of the proposed pump house. Due to possible variation in subsurface conditions and possible fill, it is important that the construction be completed in accordance with the recommendations presented herein.

The following parameters are recommended for foundation design:

Table 5.1.1 – Foundation Design Parameters

Minimum Width of Continuous Foundations, inches 12

Maximum Net Allowable Foundation Bearing Capacity, psf 2000

Minimum Embedment Depth for Frost Protection, inches 42

We have considered that the foundations will bear in the encountered poorly graded sand with silt or on engineered fill. The recommended maximum net allowable bearing capacity is based on a factor of safety greater than 3.0 and predicted settlement of less than 1 inch.

Subgrade preparation for floor slabs should be completed as described in the Site and Subgrade

Preparation section of this report. A minimum of 6 inches of MDOT Class II sand should be placed beneath the floor slab. A modulus of subgrade reaction, k30, of 100 pci is recommended for design of floor slabs. If the floor slab will have a moisture sensitive covering or be within a moisture-controlled area, a vapor barrier should be provided as recommended in ACI 302.1R

Guide for Concrete Floor and Slab Construction.

5.2 Storage Tank

The storage tank is expected to have a cast-in-place concrete slab with walls supported by a continuous reinforced concrete ringwall foundation. A net allowable bearing pressure of 2,500 psf is recommended for foundation design. The foundation should bear a minimum of 3.5 ft below grade for frost protection. It is recommended that lateral loads be resisted internally within the ringwall concrete and reinforcement and not by passive pressure from foundation backfill material.

We have completed preliminary analysis on anticipated tank configurations of 18 ft diameter with a distributed pressure of 2,000 psf. We estimate settlement on the order of 1 inch at the center of the tank and 0.5 inch at the edge, corresponding to differential settlement on the order of 0.5 inch. This estimate assumes a flexible base and differential settlement could be reduced by increasing the rigidity of the structure.

Subgrade preparation for the tank should be completed as described in the following section.

5.3 Site and Subgrade Preparation

Site preparation should include the removal of all vegetation and topsoil within the construction area. Prior to placement of any structures or engineered fill, the granular subgrade should be compacted by the contractor using suitable compaction equipment to a minimum of 95 percent of the material’s Michigan Cone maximum density within the upper 12 inches.

The foundation subgrade should be verified to be consistent with the described conditions and acceptable for the recommended net allowable bearing capacity. We recommend that a foundation subgrade evaluation be conducted after excavation for the foundations has occurred and the foundation subgrade is exposed. This evaluation should include the use of a dynamic cone penetrometer (ASTM STP 399) to confirm anticipated subgrade conditions and nuclear density testing (ASTM D 6938) to confirm that compaction requirements have been achieved.

Although indications of previous development were not observed within the pump house or water tank footprint, any encountered structures or abandoned utilities should be removed from the construction area and replaced with engineered fill. Soil within the upper 10 ft was identified as “possible fill” based on its dark brown color. If this material is found to be unsuitable due to loose relative density, deleterious material, etc. it should be removed and replaced with engineered fill. Construction with frozen soil should not occur.

Engineered fill is controlled material placed in lifts under the observation of the geotechnical engineer. On-site granular material or imported MDOT Class II sand is generally recommended for engineered fill. The upper granular material classified as poorly graded sand (present in

Borings B-1 and B-2) is expected to be suitable as engineered fill provided it is free of topsoil, debris, or other deleterious material. If additional engineered fill is required, it should consist of imported material meeting the requirements for MDOT Class II sand. Engineered fill should be compacted in lifts of 9 inches or less and a program of inspection, testing, and documentation of the engineered fill should be implemented. The granular soil should be compacted to a minimum of 95 percent of its MDOT Michigan Cone maximum dry density.

Bedding for PVC water main should consist of imported MDOT Class II sand except that maximum particle size should not exceed ¾ inch for angular rock and 1 ½ inch for round rock.

Due to the frequent presence of gravel, the on-site soil is not expected to be suitable for bedding.

Installation for PVC water main should be in accordance with AWWA C605.

The slope down to Barracks Drive is relatively steep. Appropriate erosion protection will be needed for the project but especially at this location. Further, the slope is expected to be marginally stable and creep or instability could affect the water main installation over time. Our scope of service has not included a slope stability analysis.

5.4 Groundwater

Groundwater was not present in the upper Borings B-2 to B-4. Groundwater was encountered at a depth of approximately 14 ft within Boring B-1. Groundwater at the boring locations is expected to be below the depth of construction and not a concern for construction. However, it is possible that groundwater elevations may vary beyond the boring locations.

The pump house slab should be located above the surrounding grade and site grades should be selected to provide drainage away from the structure.

6.0 LIMITATIONS

The evaluations and recommendations presented in this report have been developed on the basis of available data relating to the location, type, and finished elevation for the proposed development. Any changes in this data, deviations from encountered conditions, or the final design plans should be brought to our attention for review and evaluation with respect to our geotechnical recommendations. Variations in the soil conditions from the existing borings is possible and such variations may not become evident until construction occurs and we recommend that we be retained during construction to provide subgrade verification. If changes occur to the location or structural design or if construction reveals differences in the soil conditions from those observed in our investigation and utilized in our analyses, we request the opportunity to review and if necessary, revise our recommendations.

7.0 CLOSURE

We appreciate the opportunity to have provided geotechnical services for the Empire Water

System Renovations and express our interest in providing subgrade verification and materials testing services during construction. We should be contacted if any questions arise regarding the recommendations provided herein.

Very truly yours, OTWELL MAWBY GEOTECHNICAL, P.C.

Melzar L. Coulter, P.E.

Sr. Geotechnical Engineer

Roger L. Mawby, P.E.

President

MLC/RLM/mc

APPENDICES

Appendix A - Site Plan

Appendix B - Boring Logs

Appendix A

Site Plan

Empire Utility Improvements Empire Township, Michigan Figure 1: Site Location Map

Otwell Mawby Geotechnical, PC Traverse City, Michigan

Project No:

G19-179

Date:

12/10/19

Source:

Gourdie-Fraser, Inc.

- Approximate Soil Boring Location (Typical)

B-2

N

B-1

B-3

B-4

Appendix B

Boring Logs