2011_South_Manitou_Island_Geotechnical_Report_0006.pdf

REPORT OF SUBSURFACE EXPLORATION

FOR

PROPOSED DOCK IMPROVEMENTS SOUTH MANITOU ISLAND,

LAKE MICHIGAN

JULY, 2011

CEC PROJECT #GD-11093

Prepared By:

Coleman Engineering Company 635 Circle Drive Iron Mountain, Michigan 49801

TABLE OF CONTENTS

PAGE #

I. INTRODUCTION

II. FIELD PROCEDURES

III. LABORATORY PROCEDURES

IV. SITE CONDITIONS

V. ANALYSIS AND RECOMMENDATIONS

Pile Foundations

VI. LIMITATIONS OF SUBSURFACE EXPLORATION

APPENDICES

APPENDIX A PROJECT LOCATION DRAWING

APPENDIX B BORING LOCATION DRAWING

APPENDIX C CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

(UNIFIED SOIL CLASSIFICATION SYSTEM – USCS)

APPENDIX D SOIL EXPLORATION-GENERAL NOTES AND LEGEND

APPENDIX E BORING LOGS

Coleman Engineering Company 1 Dock Expansion South Manitou Island, Michigan July, 2011

I. INTRODUCTION

It has been proposed to add an extension to an existing dock on the south side of Manitou Island, on Lake Michigan near Leland, Michigan. The proposed extension will extend approximately 90 feet west of the existing dock. The existing dock is a timber framed structure supported on timber piles.

The elevation of the existing dock deck is approximately 583 +/-. Water depths ranged from 6 feet to 21 ½ feet at the boring locations for the current study.

A soils analysis for the existing dock was prepared by McDowell & Associates (McDowell & Associates Report – MAR1982) dated May 29, 1982 (Job No. 82-78) for McNamee, Porter & Seeley. This report recommended that the dock be supported on timber piles with a 12/10 inch butt/tip diameter. Because of some apparent dense/very dense subsurface conditions identified in the borings, the piles were recommended to be installed by jetting to avoid/minimize damage that could occur from conventional full embedment depth driving. Within 1 to 2 feet of the final embedment depth, it was further recommended that piles be seated by conventional pile hammer driving into a medium dense to dense poorly graded sand (SP) layer observed in the borings at about 30 feet below the lake surface at the time of drilling (+ 578.6). The design capacity for piles installed by the recommended jetting method was calculated to be 25 tons/50 kips. The factor of safety for these piles and the actual installed depths was not provided to Coleman Engineering Company (CEC).

II. FIELD PROCEDURES

The site of the proposed dock expansion was evaluated with four (4) test borings, designated as B-1 through B-4. Borings were performed about 2 feet above the current lake surface on a barge. Lake surface elevation at the time of drilling was + 578.2. Borings terminated at depths ranging from about 42 feet to about 68 ½ feet below the lake surface, corresponding to completion elevations of about +536.4 to +509.9.

Borings were advanced with a CME 55 drill unit mounted on a skid rig present on the site June 11 and 12, 2011. To perform the borings the skid rig was placed on an 18 by 50 foot spud barge provided by Grand Traverse Systems, LLC of Traverse City, Michigan. The barge was provided to the project under a separate contract with Mactec, the prime consultant for the project. Subsurface drilling was completed primarily with mud rotary drilling techniques using a 2 7/8-inch roller bit.

Mud rotary drilling consists of advancing soil borings using a rotary bit designed to allow drilling fluid to flow through the bit. Bentonite based drilling mud is pumped through the bit to flush soil cuttings to the surface as the bit advances. At each sampling interval, the roller bit was removed and sampling tools were lowered to the undisturbed soils. Soil sampling was performed in accordance with ASTM D-1586, "Penetration Test and Split Barrel Sampling of Soils" with a 2-inch O.D. split spoon. Thirty-two (32) such samples were obtained.

A field log was prepared for each boring during exploration which contained the work method, standard penetration test (SPT – N-Values) data, samples recovered and the indication of the presence of various soil types. The field logs were submitted to Coleman Engineering Company’s (CEC) Iron Mountain Laboratory along with the soil samples for evaluation of the subsurface information and preparation of the final boring logs.

Coleman Engineering Company 2 Dock Expansion

The boring locations were selected and established in the field by CEC based on drawings provided by Krech Ojard & Associates. Appendix A indicates the general site location. Appendix B indicates the location of the borings/probes on the site.

III. LABORATORY PROCEDURES

All field soil samples collected were visually classified in accordance with ASTM D-2488, “Description and Identification of Soils (Visual-Manual Procedure).” Because of our extensive past experience with the type of subsurface conditions encountered, additional laboratory testing was deemed unnecessary.

The final logs contain both factual and interpretive information. It should be emphasized that the recommendations are based only on the final boring logs. On the final logs, horizontal lines designating the interface between differing materials encountered represent approximate boundaries.

The transition between soil layers is typically gradual.

IV. SITE CONDITIONS

The lake depth in the area of the proposed dock extension varies from about 6 feet at boring location B-4 to about 22 ½ feet at boring location B-3, getting deeper northward from shore. Water surface elevation at the time of drilling was +578.2.

In general, the borings disclosed native, fine to medium grained poorly graded sand (SP) to boring termination depths. The upper 15 to 18 ½ of the native sand was generally loose transitioning to medium dense at the termination depths. Trace amounts of gravel were noted in the lower half of the borings.

The subsurface conditions in the area of the dock expansion are generally less dense with depth than those observed in MAR1982 for the existing structure. In particular, the dense to very dense layer encountered in MAR1982 at a depth of about 20 to 25 feet below the lakebed was not encountered in the four borings completed for the current project. Specifically, the N-Values in MAR1982 averaged 27 (N-Values greater than 50 counted as 50) in a range of 3 to 29 while the N-Values for the current study averaged 12 within a range of 3 to 29. We can discern no obvious explanation for the difference in N-Values between the two studies.

V. ANALYSIS AND RECOMMENDATIONS

Coleman Engineering Company 3 Dock Expansion

Pile Foundations

Our recommended timber pile capacities assume that timber piles will be installed to a minimum embedment depth of 30 feet below the lake bottom at the dock site. The borings for this study did not clearly define an end bearing stratum, such as bedrock, that had the potential for driving refusal at depth. Thus, the piles at this site are expected to develop their total capacities based upon a combination of end bearing and skin friction. Loose to medium dense sands are generally ideal diving conditions for timber piles and commonly provide compressive and uplift design capacities in the range of 20 to 100 kips. However, the use of jetting to install the piles limits the end bearing and frictional capacities that can be calculated relative to the capacities that can be calculated for piles driven full depth.

Design pile capacities for this project were calculated utilizing methods presented in Department of the Navy Facilities Engineering Command (NAVFAC) Design Manual DM- 7.2, 1982, pgs. 192-196. The calculations were based upon assumed tip/butt diameters of 10/12 inches.

Capacities for other pile types and geometries can be provided upon request. Our calculated ultimate capacities for this project are summarized below:

End Bearing, Qe (Kips) Side Friction, Qf (Kips Total Ultimate

Compressive Capacity, Qt (Kips)

Total Ultimate Uplift Capacity, Qt (Kips)

16 32 48 24

A factor of safety of 3.0 is the industry accepted standard in determining an appropriate design capacity. A lower factor of safety can be considered based upon past local experience with similar foundation support, the potential non-critical nature of the consequences of structure failure to life and property and the results of pile load tests and/or wave equation analysis. The recommended design capacities can be increased by one-third for short-term transient type live loadings.

Lateral loads on piles can be evaluated using f = 20 tons per cubic foot (tcf) where f is the Coefficient of Variation of Lateral Subgrade Reaction. The soil value f* is used to determine the coefficient of lateral subgrade reaction (KH) where KH = (f*z)/D; z is the depth below ground surface and D is the width/diameter of the foundation element (see NAVFAC DM-7.2, 1982, pgs. 235-241).

If lateral pile loads are to be evaluated using the software program L-PILE, the appropriate soil model is sand with recommended program required values that include a friction angle of 28 degrees, total unit weight of 120 pcf, a submerged unit weight of 60 pcf, a soil modulus “k” parameter of 40 pounds per cubic inch (pci).

If a pile load test is to be performed for this project, we recommend it be done in accordance with the requirements of ASTM D-1143.

Pile center-to-center spacing is recommended to be not less than two (2) pile widths/diameters and preferably seven (7). Further, we recommend that an experienced geotechnical engineer or his

Coleman Engineering Company 4 Dock Expansion representative observe the installation of production piles. These observations are to check that the installation criteria are properly implemented. If the project had various sections and lengths of piles, the engineer/representative can check dimensions and the condition of the pile prior to installation.

The engineer can provide alternative recommendations as deemed appropriate should anomalous or unforeseen conditions occur.

We understand that in the past the piles have been jetted to just above the design tip depth then driven 1 to 2 feet to termination to “seat” the piles. This seems appropriate when dense subsurface conditions are encountered to avoid pile damage. However, the subsurface conditions encountered by this study indicate loose sands increasing to medium dense in the last 10 feet or so. Thus, it might be more appropriate to consider driving the last 5 to 10 feet to “seat” the piles with the actual depth of the “seat” limited to the penetration where damage to the pile is expected as the result of further driving.

For driven piles, it is recommended that the pile driving hammer selected by the piling contractor be matched to the pile to be driven. As a guide, the pile hammer selected should have a hammer weight in the range of 0.5 to 3.0 times the weight of the pile.

Jetting, to be effective, necessarily disrupts the local subsurface conditions and can negatively impact previously installed piles for this and previous projects at this site. Thus, all piles located within about 25 lateral feet of the piles jetted into place for this project need to be seated/reseated after all jetting operations are complete.

APPENDIX A

PROJECT LOCATION DRAWING

APPENDIX B

BORING LOCATION DRAWING

APPENDIX C

CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

(UNIFIED SOIL CLASSIFICATION SYSTEM - USCS)

COLEMAN ENGINEERING COMPANY

635 Circle Drive

Iron Mountain, Michigan 49801

CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

ASTM Designation: D-2487 – 83

(Based on Unified Soil Classification System)

Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification

Group Group NameB Symbol

Coarse-Grained Soils More than 50 % retained on No. 200 sieve

Gravels More than 50 % of coarse fraction retained on No. 4 sieve

Clean Gravels Less than 5 % finesC

Cu > 4 and 1 < Cc < 3 E GW Well-graded gravel F

Cu < 4 and/or 1 > Cc > 3E GP Poorly graded gravelF

Gravels with Fines more than 12 % finesC

Fines classify as ML or MH GM Silty gravelF.G.H.

Fines classify as CL or CH GC Clayey gravelF.G.H.

Sands 50 % or more of coarse fraction passes No. 4 sieve

Clean Sands Less than 5 % finesD

Cu > 6 and 1 < Cc < 3E SW Well-graded sand

Cu < 6 and/or 1 > Cc > 3E SP Poorly graded sand l

Sands with Fines More than 12 % finesD

Fines classify as ML or MH SM Silty sandG.H.J.

Fines classify as CL or CH SC Clayey sandG.H.I.

Fine-Grained Soils 50 % or more passes the No. 200 sieve

Silts and Clays Liquid limit less than 50 inorganic Pl > 7 and plots on or above “A” lineJ CL Lean clayK.L.M.

Pl < 4 or plots below “A” lineJ ML SiltK.L.M.

organic Liquid limit – oven dried < 0.75 OL Organic clayK.L.M.N.

Liquid limit – not dried Organic siltK.L.M.O.

Silts and Clays Liquid limit 50 or more inorganic Pl plots on or above “A” line CH Fat clayK.L.M.

Pl plots below “A” line MH Elastic siltK.L.M.

organic Liquid limit – oven dried < 0.75 OH Organic clayK.L.M.P.

Liquid limit – not dried

Organic siltK.L.M.Q.

Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-in. (75-mm) sieve.

B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12 % fines require dual symbols:

GW-GM well-graded gravel with silt GW-GC well-graded gravel with clay GP-GM poorly graded gravel with silt GP-GC poorly graded gravel with clay D Sands with 5 to 12 % fines require dual symbols:

SW-SM well-graded sand with silt SW-SC well-graded sand with clay SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay

E Cu = D60/D10 (D30)

2 L If soil contains > 30 % plus No. 200, predominantly sand, add “sandy” to group name.

M If soil contains > 30 % plus No. 200, predominately gravel, add “gravelly” to group name.

N Pl > 4 and plots on or above “A” line.

O Pl < 4 or plots below “A” line.

P Pl plots on or above “A” line.

Q Pl plots below “A” line.

D10 x D60 F If soils contains > 15 % sand, add “with sand” to group name.

G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

H If fines are organic, add “with organic fines” to group name.

I If soil contains > 15 % gravel, add “with gravel” to group name.

J If Atterberg limits plot in hatched area, soil is a CL-ML, silty clay.

K If soil contains 15 to 29 % plus No. 200, add “with sand” or “with gravel”, whichever is predominant.

APPENDIX D

SOIL EXPLORATION-GENERAL NOTES AND LEGEND

APPENDIX E

BORING LOGS