Attachment 3-GeotechStudyReport.SilverLake.Final.07.28.2014.pdf

REPORT

GEOTECHNICAL STUDY

PROPOSED SILVER LAKE BOARDWALK

REPLACEMENT

UINTA-WASATCH-CACHE NATIONAL FOREST

BIG COTTONWOOD CANYON NEAR

COTTONWOOD HEIGHTS, UTAH

Submitted To:

Case, Lowe and Hart, Inc.

2484 Washington Boulevard, Suite 510

Ogden, Utah 84401

Submitted By:

GSH Geotechnical, Inc.

473 West 4800 South

Salt Lake City, Utah 84123

July 28, 2014

Job No. 1019-010-14

GSH Geotechnical, Inc. GSH Geotechnical, Inc.

473 West 4800 South 1596 West 2650 South, Suite 107 Salt Lake City, Utah 84123 Ogden, Utah 84401 Tel: (801) 685-9190 Tel: (801) 393-2012 www.gshgeo.com www.gshgeo.com

Mr. Kevin Lewis Case, Lowe and Hart, Inc.

2484 Washington Boulevard, Suite 510 Ogden, Utah 84401

Mr. Lewis:

Re: Report

Geotechnical Study Proposed Silver Lake Boardwalk Replacement Uinta-Wasatch-Cache National Forest Big Cottonwood Canyon Near Cottonwood Heights, Utah (40.604105º North: 111.588077º West)

1. INTRODUCTION

1.1 GENERAL

This report presents the results of our geotechnical study performed along the east half of the existing boardwalk, including bridges and dock surrounding Silver Lake located in Big Cottonwood Canyon near Cottonwood Heights, Utah. The general location of the site with respect to major topographic features, as of 1998, is presented on Figure 1, Vicinity Map. A more detailed layout of the site on an aerial based map (Figure 2, Site Plan) shows the existing boardwalk, bridges, and dock. The locations of the borings drilled/hand augured in conjunction with this study are also presented on Figure 2.

1.2 OBJECTIVES AND SCOPE

The objectives and scope of this study are based on the “Architect-Engineer Statement of Work” provided by the USDA Forest Service, as well as discussions between Mr. Kevin Lewis of Case, Lowe and Hart, Inc.; Mr. Todd Touchard of the U.S. Forest Service; and Mr. Alan Spilker of GSH Geotechnical, Inc. (GSH).

In general, the objectives of this study were to:

1. Define and evaluate the subsurface soil conditions along the existing boardwalk at the north bridge abutment.

2. Provide foundation support recommendations

Geotechnical Study

In accomplishing these objectives, our scope has included the following:

1. A field program consisting of the drilling, logging, and sampling of 8 borings with a track mounted drill rig and 10 hand auger borings along the east portion of the existing boardwalk.

2. A laboratory testing program.

3. An office program consisting of the correlation of available data, engineering analyses, and the preparation of this summary report.

1.3 AUTHORIZATION

Authorization was provided by a signed Work Order Number 914 dated May 8, 2014.

1.4 PROFESSIONAL STATEMENTS

Supporting data upon which our recommendations are based are presented in subsequent sections of this report. Recommendations presented herein are governed by the physical properties of the soils encountered in the exploration borings and the layout and design data discussed in Section 2, Proposed Construction, of this report. If subsurface conditions other than those described in this report are encountered and/or if design and layout changes are implemented, GSH must be informed so that our recommendations can be reviewed and amended, if necessary.

Our professional services have been performed, our findings developed, and our recommendations prepared in accordance with generally accepted engineering principles and practices in this area at this time.

2. EXISTING AND PROPOSED CONSTRUCTION

2.1 EXISTING BOARDWALK /BRIDGES AND DOCK

The existing boardwalk is 6 feet wide constructed of wood with multiple bridges and a dock extending out to the lake. The majority of the boardwalk spans across existing wetlands and we understand is supported on wood blocks (see Photo 1 on the following page).

Photo 1

2.2 PROPOSE BOARDWALK /BRIDGES AND DOCK REPLACEMENT

Plans are to reconstruct portions, if not all, of the existing boardwalk, bridges, and dock. The new structures would be 8 feet wide and of wood or composite. Anticipated maximum loading would be on the order of 15 pounds per square foot (psf) dead load and up to 350 psf live-snow load. For an 8-foot wide boardwalk, this translates to maximum lineal loading on the order of 2,920 pounds per lineal foot.

3. SITE INVESTIGATIONS

3.1 FIELD PROGRAM

In order to define and evaluate the subsurface soil and groundwater conditions, 8 boring were completed with a track-mounted hollow stem auger drill rig to depths of 12 to 27 feet. Also, 10 supplemental hand auger borings were completed to depths of 3 to 6 feet. The locations of the borings are presented on Figure 2.

The field portion of our study was under the direct control and continual supervision of an experienced member of our geotechnical staff. During the course of the drilling operations, a continuous log of the subsurface conditions encountered was maintained. In addition, samples of the typical soils encountered were obtained for subsequent laboratory testing and examination.

The soils were classified in the field based upon visual and textural examination. These classifications have been supplemented by subsequent inspection and testing in our laboratory.

Detailed graphical representation of the subsurface conditions encountered is presented on Figures 3A through 3H, Boring Logs, and Figures 4A through 4J, Hand Auger Logs. Soils were classified in accordance with the nomenclature described on Figure 5, Key to Boring Log

(USCS).

Samples were taken with the drill rig utilizing a 2.0-inch outside diameter, 1.38-inch inside diameter drive sampler (SPT), and a 1.54-inch inside diameter drive sampler (California). The blow counts recorded on the boring logs were those required to drive the sampler 12 inches with a 140-pound hammer dropping 30 inches. Additionally, hand samples were taken and during hand augering and placed in sealed plastic bags.

The approximately GPS coordinates at each boring location are presented in the table below:

Boring Number Boring Type Latitude Longitude

B-1 Track Mounted Drill 40.60390 -111.58493 B-2 Track Mounted Drill 40.60411 -111.58560 B-3 Track Mounted Drill 40.60441 -111.58592 B-4 Track Mounted Drill 40.60461 -111.58628 B-5 Track Mounted Drill 40.60344 -111.58554 B-6 Track Mounted Drill 40.60346 -111.58651 B-7 Track Mounted Drill 40.60333 -111.58787 B-8 Track Mounted Drill 40.60284 -111.58814

B-1A Hand Auger 40.60502 -111.58635 B-2A Hand Auger 40.60489 -111.58629 B-3A Hand Auger 40.60409 -111.58531 B-4A Hand Auger 40.60360 -111.58498 B-5A Hand Auger 40.60330 -111.58587 B-6A Hand Auger 40.60346 -111.58685 B-7A Hand Auger 40.60354 -111.58756 B-8A Hand Auger 40.60318 -111.58506 B-9A Hand Auger 40.60346 -111.58844 B-10A Hand Auger 40.60267 -111.58816

3.2 LABORATORY TESTING

3.2.1 General

In order to provide data necessary for our engineering analyses, a laboratory testing program was performed. The program included moisture, density, partial gradation, and chemical tests. The following paragraphs describe the tests and summarize the test data.

3.2.2 Moisture and Density Tests

To aid in classifying the soils and to help correlate other test data, moisture and density tests were performed on selected samples. The results of these tests are presented on the boring logs, Figures 3A through 3H.

3.2.3 Partial Gradation Tests

To aid in classifying the granular soils, partial gradation tests were performed. Results of the tests are tabulated below:

Boring No.

Depth (feet)

Percent Passing No. 200 Sieve

Soil Classification

B-1 11.0 8.8 SP-SC

B-2 16.0 31.4 SM

B-3 6.0 3.1 SP

B-4 11.0 16.3 GM

B-5 9.5 4.0 SP

B-5 21.0 51.2 ML-SM

B-6 21.0 13.9 SM

B-8 16.0 12.5 SC-OH

B-8 21.0 9.1 SC-OH

3.2.4 Chemical Tests

Chemical tests were performed on representative samples of the typical organic clay soils, as well as the silty sand soils encountered in the borings along the boardwalk alignment. The results of the chemical tests are tabulated on the following page.

Boring No.

Depth (feet)

Soil Classification pH

Total Water Soluble Sulfate

(mg/kg-dry) Resistivity (ohm-cm)

B-6 26 SM 8.25 <6.2 10,200

B-8 16 SC-OH 6.96 314 4,290

4. SITE CONDITIONS

4.1 SURFACE

The existing boardwalk, bridges and dock span wetlands, streams, and the lake. All sampling was below or at the existing water surface.

4.2 SUBSURFACE SOIL AND GROUNDWATER

Due to the soil depositional history (delta/marsh type deposits) high variability was encountered within the soils at the site. Various soil types including silty clay, sandy clay, clayey sand, silty sand, fine and coarse sand, and fine and coarse gravel were encountered at different depths.

Soils ranged from very soft/very loose to stiff/dense, were generally dark brown to brown, and were saturated.

For a more detailed description, please refer to the boring logs, Figures 3A through 3H and Figures 4A through 4J. The lines designating the interface between soil types on the boring logs generally represent approximate boundaries. In-situ, the transition between soil types may be gradual.

5. DISCUSSIONS AND RECOMMENDATIONS

5.1 SUMMARY OF FINDINGS

Preliminarily design incorporates Shallow foundations, Diamond Pier Foundations, helical piers, and driven wood piles. Initial design recommendations are provided for each system. However, at the south portion of the site, Borings B-7 and B-8 (see Figure 2, Site Plan), the soils were very soft/very loose over the boring depths, 12 to 22 feet, and helical piers or wood piles would extend below these depths.

Settlements of either properly installed helical piers or wood pile foundation are expected to be minimal. In the following sections, discussions pertaining to each option are provided.

5.2 FOUNDATIONS

5.2.1 General

The soils are moderately good along the east portion of the boardwalk, as shown on Figure 2, Site Plan, from Borings B-1A through B-5A (Stations 1+00 to 8+00 and roughly 43+00 through 46+00). Along this portion of the alignment, a shallow spread foundation may be utilized.

However, the groundwater encountered is at or near the surface, making it difficult to install spread foundations below existing grades.

Deep foundation systems considered herein are Diamond Pier foundations, helical piers, and driven wood piles. Neither of these systems create spoils or require structural fills. The installation equipment for both Diamond Pier and helical piers may be more economical as they do not require a significantly large floating platform or heavy machinery. At some of the boring locations (Borings B-3 and B-4, see Figure 2 Site Plan), a bearing soil strata comprised of dense sands/gravels/cobbles was encountered. However, the majority of the borings did not encounter a suitably dense/hard end-bearing strata within the depths penetrated, 12 to 27 feet, and, more particularly, Borings B-7 and B-8 along the southern portion of the boardwalk (see Figure 2, Site Plan) encountered very soft soils within the full depths penetrated, 12 to 22 feet.

Areas where each foundation system is most likely to be utilized is shown on Figure 2, Site Plan.

5.2.2 Shallow Foundations

As discussed previously, shallow foundation may be utilized to support the boardwalk and bridge between Stations 1+00 to 8+00 and roughly 43+00 through 46+00. The upper 1.5 feet are generally loose/disturbed. Additionally, at Borings B-1A and B-4 A, there is a surficial layer of unsuitable silty clay extending 1.5 to 2.0 feet below the surface.

Spread foundations must be supported on natural granular soils or a minimum 24 inches of granular replacement fill extending to the bottom of the upper disturbed/unsuitable soil zone.

With either surface water and/or high groundwater near the surface, in most instances, the installation of spread foundation may become quite difficult if not constructed above the water level. This will require installing structural fill.

For design, the following parameters are provided with respect to the projected loading discussed in Section 2, Proposed Construction of this report:

Minimum Recommended Depth of Embedment for Frost Protection - 36 inches

Recommended Minimum Width for Continuous Wall Footings - 20 inches

Minimum Recommended Width for Isolated Spread

Footings - 36 inches

Recommended Net Bearing Pressure for Real Load Conditions - 1,500 pounds per square foot

Bearing Pressure Increase for Seismic Loading - 50 percent

The term “net bearing pressure” refers to the pressure imposed by the portion of the structure located above lowest adjacent final grade. Therefore, the weight of the footing and backfill to lowest adjacent final grade need not be considered. Real loads are defined as the total of all dead plus frequently applied live loads. Total load includes all dead and live loads, including seismic and wind.

Under no circumstances should the footings be established upon soft, loose or disturbed soils, non-engineered fills, sod, rubbish, frozen soils, debris, or installed within ponded water. If the natural soils upon which the footings are to be established become loose or disturbed, they must be removed and replaced with granular structural fill. If granular structural fill upon which the footings are to be established become disturbed, they should be recompacted to the requirements for structural fill.

The width of replacement fill below footings should be equal to the width of the footing plus one additional foot for each foot of fill thickness placed. For example, if the width of the footing is 2 feet and the thickness of the structural fill beneath the footing is 1 foot, the width of the structural fill at the base of the footing excavation would be a total of 3 feet. We recommend that footing excavations be completed with a smooth-lip bucket to reduce disturbance of the bearing subgrade soils.

5.2.3 Diamond Pier Foundations

Diamond Pier foundations consist of a precast concrete head installed at or just above the ground surface and steal bearing pins are driven through the head and into the ground using simple hand-held tools. The pins generally extend 3 to 8 feet below the ground surface. Design, drawing details, specifications, and installation instructions for this foundation system are provided by Diamond Pier Foundation System Inc. and generally contracted as design-build.

Phone: 253-858-8809;866-255-9478 Website: www.diamondpier.com

5.2.4 Helical Piers

Helical piers can be configured with various numbers and sizes of helices by which the capacity and required depth of embedment may be optimized for particular subsurface conditions. The optimum lead helix configuration and final bearing depths are best determined by a test installation after the design loads have been determined prior to preparing the final bid package.

A test installation is relatively inexpensive and the materials are able to be re-used and, typically, not included in the cost of the test.

Helical pier capacity can be verified in the field by measuring the installation torque. The relationship between the 2 quantities is empirical and may be expressed by the following equation:

ultimate capacity (lbs) = 10 x installation torque (ft-lbs)

A bearing depth for helical piers is not readily apparent at each of the boring locations and is likely to vary significantly across the site. Based on the soils encountered within our borings and the anticipated light loading and moderate pier spacing, we project that a helical pier system with a double helix would reach adequate torque to support the boardwalk. Anticipated depths for the helical piers in general is on the order of 15 to 25 feet below the surface. Again, test installation(s) should be used to determine the bearing elevation.

Lateral Loads

Lateral forces may be taken up in tension or compression using helical piers placed at an opposing angle to the direction of the lateral force.

Pier Spacing

Pier spacing is recommended to be not less than 3 times the diameter of the largest helix. No reduction in load carrying capacity, due to group action, should be necessary with this spacing.

Settlements

If the helical piers are installed as described above, we anticipate the total movement to be less than one-half inch and differential movement less than one-quarter inch.

Corrosion

Piers will likely need to be installed to a higher factor of safety to prolong the functional life of a helical pier installed.

Apparent Advantages

1. Bearing elevation and capacities can be immediately determined upon installation.

2. They can be quickly installed and do not require any cure time, allowing for subsequent work to continue almost immediately after installation.

3. They can be quickly removed and reinstalled should location discrepancies occur during construction.

4. The piers shaft area is negligibly small and, therefore, down drag side friction would have negligible effect on the pier.

There are various contractors in this area which could perform this type of work, including:

Intermountain Helical Piers Contact: Mr. Bill Boulter (801-420-4385)

Alpine Foundation Solutions 223 West 1230 North, Suite 131 Provo, Utah 84604 Contact: Mr. Boyd Riding (801-857-4777)

Hayward Baker, Inc.

4001 S. 700 E # 539 Salt Lake City, Utah 84107 Contact: Mr. Todd Ross (801-363-0546)

With the resistivity and pH differences shown between soil types, corrosion potential is likely.

Corrosion potential will need to be addressed by a corrosion expert for the applied system.

5.2.5 Driven Wood Piles

Ninety percent of wood piles installed in the United States are comprised of southern pine treated with Chromated Copper Arsenate (CCA) and meeting the requirements under ASTM D25.

If wood piles are utilized for foundations, they will generally be designed as friction piles.

However, at Borings B-3 and B-4 located at the north end of the lake (see Figure 2, Site Plan), an end bearing strata was encountered at depths of 12 and 16 feet. At such bearing strata, the design capacity will be dictated by the strength of the pile.

The table on the following page provided estimated nominal side resistance of wood pile per square foot based on the soils encountered at the site.

Soil Type Depth (Feet) Side resistance (PSF)

Sand 0-3 50

Sand 3-10 400

Sand 10-20 500

Peat/Organic soils 0-10 0

Peat/Organic soils 10-20 5

Clays 0-4 0

Clays 4-20 200

Additional general soil parameters, excluding the upper 2 feet, are provided in the following table:

Soil Type

Estimated Dry Unit Weight

(PCF)

Estimated Friction Angle

Estimated Cohesion

(PSF)

Sand 100-110 31 --

Peat/Organic soils 40 10 25

*Clays 90 --- 400

* Highly organic clay soils must assume values closer to that provide for peat/organic soils.

5.2.6 Installation

Installation may be difficult as driven piles will require moderate to heavy equipment, which will most likely not be readily accessible to the site location across the wetlands. Equipment and final design would require communications between the structural engineer, GSH, and the contractor.

5.2.7 Settlements

Maximum settlements of the individual piles (excluding elastic settlement within the pile) are expected to be minimal.

5.2.8 Lateral Capacity

A lateral pile capacity analysis was not completed at this time. Many factors, including pile/pier size, confinement conditions, spacing, head conditions (i.e. fixed or free), and loading will need to be better defined prior to completing a lateral capacity analysis. As these design factors become available, GSH may complete a lateral capacity analysis.

Additionally, it is projected that much of the lateral forces will be taken up by the pile cap and bedrock at the abutments.

5.3 STRUCTURAL FILL

Structural fill is defined as all fill which will ultimately be subjected to structural loadings.

Structural fill may be required as site grading fill and possibly as replacement fill below footings.

All structural fill must be free of sod, rubbish, topsoil, frozen soil, and other deleterious materials.

Structural site grading fill is defined as structural fill placed over relatively large open areas to raise the overall grade. For structural site grading fill, the maximum particle size shall not exceed 4 inches; although, occasional larger particles, not exceeding 8 inches in diameter, may be incorporated if placed randomly in a manner such that “honeycombing” does not occur and the desired degree of compaction can be achieved. The maximum particle size within structural fill placed within confined areas shall be restricted to 2 inches.

To stabilize soft subgrade conditions and/or where the grade is within 1 foot of groundwater, a mixture of coarse gravels and cobbles and/or 1.5- to 2.0-inch gravel (stabilizing fill) should be utilized.

Only granular soils are recommended as structural fill in confined areas, such as below foundations.

Import structural replacement fill below foundations and floor slabs shall consist of a well graded sand and gravel mixture with less than 30 percent retained on the 0.75-inch sieve and less than 20 percent passing the No. 200 Sieve (clays and silts).

Non-structural site grading fill is defined as all fill material not designated as structural fill and may consist of any cohesive or granular soils not containing excessive amounts of degradable material.

Structural fill (other than stabilizing fill) shall be placed in lifts not exceeding 8 inches in loose thickness. Structural fills shall be compacted in accordance with the percent of the maximum dry density as determined by the AASHTO1 T-180 (ASTM2 D-1557) compaction to 95 percent.

Coarse gravel and cobble mixtures (stabilizing fill), if utilized, should be end-dumped, spread to a maximum loose lift thickness of 15 inches, and compacted by dropping a backhoe bucket onto the surface continuously at least twice. As an alternative, the stabilizing fill may be compacted

1 American Association of State Highway and Transportation Officials 2 American Society for Testing and Materials by passing moderately heavy construction equipment or large self-propelled compaction equipment at least twice. Subsequent fill material placed over the coarse gravels and cobbles should be adequately compacted so that the “fines” are “worked into” the voids in the underlying coarser gravels and cobbles or when necessary, separated by a filter fabric.

5.4 SITE OBSERVATIONS

Observation and documentation during pile driving, as well as other critical facets of construction, will need to be conducted by qualified personnel to ensure quality control and compliance with construction documents.

If you have any questions or would like to discuss these items further, please feel free to contact us at (801) 685-9190.

Respectfully submitted, GSH Geotechnical, Inc. Reviewed by:

Bryan N. Roberts, P.E. Alan D Spilker, P.E.

State of Utah No. 276476 State of Utah No. 334228 Project Geotechnical Engineer President/Senior Geotechnical Engineer

BNR/ADS:jlh

Encl. Figure 1, Vicinity Map

Figure 2, Site Plan Figures 3A through 3H, Boring Logs Figures 4A through 4J, Hand Auger Logs Figure 4, Key to Log Boring (USCS)

Addressee (email) cc: Mr. Todd Touchard (email) U.S. Forest Service

324 25th Street Ogden, Utah 84401

CASE, LOWE, AND HART, INC.

JOB NO. 1019-010-14

REFERENCE:

USGS 7.5 MINUTE TOPOGRAPHIC QUADRANGLE MAP(S)

ENTITLED “BRIGHTON, UTAH” AND “PARK CITY WEST, UTAH”

BOTH DATED 1998

1000 10000 2000

SCALE IN FEET

FIGURE 1

VICINITY MAP

GSHo

SITE

60 600 120

APPROXIMATE SCALE IN FEET

CASE, LOWE, AND HART, INC.

JOB NO. 1019-010-14

REFERENCE:

ADAPTED FROM DRAWING ENTITLED

“SILVER LAKE BOARDWALK RECONSTRUCTION”

BY US DEPARTMENT OF AGRICULTURE, NOT DATED

FIGURE 2

SITE PLAN

GSHo

B-1

B-2

B-3

B-4

B-5B-6

B-8

B-7

B-1A

B-2A

B-3A

B-4A

B-5A

B-6A

B-10A

B-8A

B-7A

B-9A

BOREHOLE LOCATIONS

HAND AUGER LOCATIONS

Potential Shallow Foundation or Deep Foundation (Diamond Piers, Helical Piers, Driven Wood Piles)

Deep Foundation (Helical Piers, Driven Wood Piles)

KEY: