C8388_Geotechnical_Memo.pdf

K:\Projects\U\Uscg\60515933_Cgreedyis\400-Technical\440-Field And Laboratory Data\Geotechnical\Report\Uscg Reedy Island 30pct Geotech Memo Draft.Docx

COMMERCIAL IN CONFIDENCE

1/2

To:

Commanding Officer Civil Engineering Unit Cleveland United States Coast Guard 1240 East 9th Street Room 2179 Cleveland, OH 44199-2060

CC:

Brendan Grady, RA, NCARB – AECOM PM Beth Kalapos, AIA – AECOM Deputy PM Tim Lauth,P.E. – AECOM Senior Structural Engineer

AECOM

1300 East 9th Street Suite 500 Cleveland, OH 44114-1503

Project name:

Reedy Island Rear Range Light

Project ref:

60515933, Task 00004

From:

Erik J. Bogen, E.I.

Makarand S. Jakate, P.E.

Date:

October 26, 2016

DRAFT

Geotechnical Memorandum Subject: Subsurface Exploration and Preliminary Foundation Recommendations (30% Submittal)

The following draft memorandum presents a summary of the subsurface exploration performed on October 4 and 5, 2016 and preliminary foundation recommendations for the Reedy Island Rear Range Light project in New Castle County, Delaware.

Field Exploration Subsurface conditions were evaluated by drilling one (1) exploratory boring at the existing Reedy Island Rear Range Lighthouse site, as shown in Figure 2. The boring was drilled at the site on October 4 and 5, 2016 by AECOM’s subcontractor, CGC Geoservices, LLC. The boring (B-01) was drilled adjacent to the south side of the existing lighthouse. Miss Utility of Delmarva was notified, and boring locations were verified as clear of utility conflicts prior to the start of drilling activities. AECOM established the boring locations in the field using a hand-held GPS unit and field measurements with a measuring tape.

A Diedrich D-50 truck-mounted drill rig was used to drill the boring. The drill rig was used in conjunction with 3-1/4 inch inner diameter, continuous flight, hollow-stem augers to a depth of 18.5 feet below ground surface (ft bgs). Drilling with hollow-stem augers was completed on October 4, 2016. Drilling was resumed at 18.5 ft bgs on October 5 using a 2- 15/16 inch outer diameter tricone bit with bentonite drilling mud to borehole termination at 80.0 ft bgs. An AECOM engineer was on-site during all drilling operations to monitor and direct the drilling subcontractor, and to visually classify and log soil and formations encountered during the investigation.

Soil samples were collected from the borings for visual classification and testing. Samples were obtained by Standard Penetration Testing (SPT) with a split-spoon sampler at intervals of 2.5 ft from 0.0 to 20.0 ft bgs and intervals of 5.0 ft to a depth of 80.0 ft bgs, in general accordance with ASTM D 1586. Samples were placed in sealed glass jars upon recovery for additional analysis. Soil samples were delivered to the AECOM geotechnical laboratory in Conshohocken, Pennsylvania, for additional testing. Groundwater was logged when encountered and the water level inside the augers was measured at the conclusion of drilling. Upon completion, borings were backfilled with cement and bentonite grout.

The boring locations were not surveyed and the elevations reported on the boring logs should be considered approximate. A log of the exploratory boring, including soil descriptions and types of sampling, is provided in Appendix A.

Subsurface Conditions The following section summarizes the subsurface conditions encountered during the field exploration described in the previous section.

Geotechnical Memorandum Reedy Island Rear Range Light<HeaderText1> DRAFT

AECOM

K:\Projects\U\Uscg\60515933_Cgreedyis\400-Technical\440-Field And Laboratory Data\Geotechnical\Report\Uscg Reedy Island 30pct Geotech Memo Draft.Docx

COMMERCIAL IN CONFIDENCE

2/2

A layer of topsoil, 5 inches in thickness, was encountered at the surface. Three primary subsurface strata were identified. A stratum, consisting of silt and clay soils was encountered below the topsoil and extended to a depth of 10.5 ft bgs. This stratum was found to have a generally stiff to hard consistency.

A stratum of clay with sand interlayers was encountered at 10.5 ft bgs and extended to 36 ft bgs. The sand interlayers within the clay were encountered at depths of 10.5 ft and 18.0 ft, and ranged in thickness from around 2.5 to 3.5 feet.

Clay soils within this stratum were generally very soft to soft from 13.0 ft to approximately 28 ft bgs and became stiff to very stiff between 28 and 36 ft bgs. The sand interlayers had a generally loose to dense compactness.

A formation of dark gray to greenish gray fine to coarse sand was encountered at approximately 36 ft bgs and extended to boring termination at 80.0 ft bgs. This sand formation was found to have a generally loose to medium dense compactness.

Groundwater was encountered at 9 ft bgs during drilling, and subsequent measurements of the groundwater level ranged from 3.8 to 5.4 ft bgs.

Preliminary Recommendations Based on the subsurface exploration and the information provided by USCG, the existing foundations appear to be shallow foundations bearing at a depth of 3 feet 4 inches below existing grade. Based on our subsurface investigation, the soil layer present at the bearing depth consists of stiff to hard silt and clay unit described above. For foundations bearing in the stiff to hard silt and clay at the depth of 3 feet, 4 inches, an allowable bearing pressure of 3000 pounds per square foot (psf) may be used for design.

Because there is no evidence of significant differential settlement of the existing tower foundations and little to no evidence of geotechnical failure of the foundation over the 106-year life of the structure, no major structural changes to the existing foundation configuration are recommended.

Attachments Figure 1 – General Location Map

Figure 2 – Soil Boring Location Plan

Appendix A – Log of Soil Boring

GENERAL LOCATION MAP

SITE

LOCATION

Map Data ©2016 Google

PROPERTY LOCATION

(NEW CASTLE COUNTY)

NEW CASTLE COUNTY, DELAWARE

USCG REEDY ISLAND REAR RANGE LIGHT

NEW CASTLE COUNTY, DELAWARE

USCG REEDY ISLAND REAR RANGE LIGHT

SOIL BORING LOCATION PLAN

5" TOPSOIL

Stiff to very stiff, moist, brown, sandy SILT (ML), trace organics

Hard, moist, gray with brown mottling, lean CLAY (CL) with sand, trace rock fragments becomes very stiff

Very stiff to hard, moist, grayish brown, silty CLAY (CL-ML) with sand, oxidation staining

Very stiff to hard, moist to wet, grayish brown, SILT (ML), trace sand

Loose, wet, gray, silty fine to medium SAND (SM)

Loose, wet, gray, medium SAND (SP), oxidation staining

Very soft, wet, gray lean CLAY (CL) with sand

No recovery

Medium dense, wet, brown silty fine to coarse SAND (SM), trace gravel, oxidation staining

Very soft, wet, gray with brown mottling, lean CLAY (CL), trace sand, gravel

Soft to medium stiff, moist, brownish gray, lean CLAY (CL), trace sand, gravel, rock fragments, oxidation staining

WOH

Shelby Tube sample attempted; No recovery.

End HSA drilling at 18.5';

stop on 10/4. Resume drilling 10/5 using rotary mud method with tricone bit.

0.4

1.5

5.5

8.0

10.5

12.0

13.0

16.0

18.0

21.5

27.3

0.0

SS-1

SS-2

SS-3

SS-4

SS-5

SS-6

ST-1

SS-7

SS-8

ST-2

SS-9

3.0 1.5

4.5+ 4.5+

2.25 2.0 2.25

2.0 2.5 4.0

2.0 2.0 4.0

0.25 0.25 0.25

0.25 0.25

<0.25

0.75 0.5 0.25

N um b er

T yp e

P oc ke t P en e-tr om et er

, t sf

Sa m pl in g R es is t.

Bl ow s/

6" O

R C

O R

E% R

Q D

R ec ov er y, W at er C on te nt

R ec ov er y, SAMPLES

D ep th fe et

G ra p hi c Lo g

REMARKS AND

OTHER DETAILS

MATERIAL DESCRIPTION

Groundwater Level(s)

3.25" I.D. HSA, 2-15/16" Tricone

Hammer Data

CGC Geoservices

Split-spoon, Shelby Tune

Boring Location Lat./Long.: 39.40646,-75.59016

Hollow-Stem Auger / Rotary Mud

E. Bogen

Enc. @9'; WL @5.4' prior to start of mud drilling; Overnight WL @3.8'

Borehole Backfill

Logged By

Date(s) Drilled

Sampling Method(s) 140 lb./30 in. Manual w/Cathead

Drill Rig Type

Drilling ContractorDiedrich D-50 Truck

Drilling Method

Total Depth of Borehole

Drill Bit Size/Type

Checked By

Surface Elevation

10/4-5/2016

80.0´ bgs

Cement-Bentonite Grout

Project Location: New Castle County, DE Sheet 1 of 3

Log of Boring B-01

R ep or t:

G E

O _C

R ; F ile K

:\P R

O

JE

C T

S \U

\U S

C G

\6

C G

R E

E D

Y

IS

\4

-T E

C H

N

IC

A L\

0-

F

IE

LD

A

N D

L A

B O

R A

T O

R Y

D A

T A

\G E

O T

E C

H N

IC

A

L\ R

E E

D Y

_I S

LA

N

D _R

A N

G E

_R E

A R

_L

IG

H T

LO

G S

.G P

J;

0/ 6/

:2

6:

P M

Project Number: 60515933

Project: Reedy Island Range Rear Light becomes stiff to very stiff, dark gray, no oxidation staining

Loose, wet, dark bluish gray, medium SAND (SP), trace clay, gravel becomes very loose, trace gravel becomes medium dense, trace fine rounded quartz gravel becomes bluish gray, fine to medium grained, trace silt becomes loose, mottled bluish gray and white becomes dense, greenish-gray, trace white calcareous cemented sand fragments

36.3

SS-10

SS-11

SS-12

SS-13

SS-14

SS-15

SS-16

2.25 1.5 2.5

N um b er

T yp e

P oc ke t P en e-tr om et er

, t sf

Sa m pl in g R es is t.

Bl ow s/

6" O

R C

O R

E% R

Q D

R ec ov er y, W at er C on te nt

R ec ov er y, SAMPLES

D ep th fe et

G ra p hi c Lo g

REMARKS AND

OTHER DETAILS

MATERIAL DESCRIPTION

Project Location: New Castle County, DE Sheet 2 of 3

Log of Boring B-01

R ep or t:

G E

O _C

R ; F ile K

:\P R

O

JE

C T

S \U

\U S

C G

\6

C G

R E

E D

Y

IS

\4

-T E

C H

N

IC

A L\

0-

F

IE

LD

A

N D

L A

B O

R A

T O

R Y

D A

T A

\G E

O T

E C

H N

IC

A

L\ R

E E

D Y

_I S

LA

N

D _R

A N

G E

_R E

A R

_L

IG

H T

LO

G S

.G P

J;

0/ 6/

:2

6:

P M becomes medium dense

End of Boring at 80´ bgs

17 80.0

SS-17

SS-18

SS-19

N um b er

T yp e

P oc ke t P en e-tr om et er

, t sf

Sa m pl in g R es is t.

Bl ow s/

6" O

R C

O R

E% R

Q D

R ec ov er y, W at er C on te nt

R ec ov er y, SAMPLES

D ep th fe et

G ra p hi c Lo g

REMARKS AND

OTHER DETAILS

MATERIAL DESCRIPTION

Project Location: New Castle County, DE Sheet 3 of 3

Log of Boring B-01

R ep or t:

G E

O _C

R ; F ile K

:\P R

O

JE

C T

S \U

\U S

C G

\6

C G

R E

E D

Y

IS

\4

-T E

C H

N

IC

A L\

0-

F

IE

LD

A

N D

L A

B O

R A

T O

R Y

D A

T A

\G E

O T

E C

H N

IC

A

L\ R

E E

D Y

_I S

LA

N

D _R

A N

G E

_R E

A R

_L

IG

H T

LO

G S

.G P

J;

0/ 6/

:2

6:

P M