Attachment_2_-_Four_Locks_Geotechnical_Report.pdf

19955 Highland Vista Dr., Suite 170 Ashburn, Virginia 20147

(703) 726-8030 www.geoconcepts-eng.com

LETTER OF TRANSMITTAL

TO: Mr. James Colfelt, PE, BSCP

Alpha Corporation 21351 Ridgetop Circle, Suite 200 Dulles, Virginia 20166

FROM: Rebecca Smith-Zakowicz, PG Paul E. Burkart, PE DATE: May 11, 2017

RE: Preliminary Foundation Recommendations, 4 Locks Boat Ramp, Clear Spring, Maryland

OUR CONTRACT NUMBER:

15406.01

AS REQUESTED FOR REVIEW AND COMMENT FOR APPROVAL PLEASE RECYCLE

COPIES NO. DESCRIPTION

Boring Location Plan, Figure 1 Test Boring Logs

NOTES/COMMENTS:

GeoConcepts is pleased to provide preliminary foundation recommendations for the 4 Locks Boat Ramp project. The site is located just south of the intersection of Four Locks Road and Starliper Road in Clear Spring, Maryland. Based on information provided to us, an 18-foot long concrete pedestrian access ramp was originally constructed on the upstream side of the boat ramp. It has since deteriorated and the existing concrete is unstable and unsafe for public use. The downstream concrete access walkway of the boat ramp remains intact but shows signs of wear and the concrete reinforcement is now visible. Other problems include launching and retrieving watercraft during low water conditions and Architectural Barriers Act Accessibility Standards (ABAAS) are currently not being met by the 4 Locks Boat Ramp.

It is our understanding that improvements will include the restoration of the existing boat ramp, and the addition of a floating dock and pedestrian walkway in accordance with ABAAS standards.

On December 13, 2016, we drilled two test borings in the proposed site improvement areas to evaluate the subsurface conditions. Test boring logs and a boring location plan are included in this transmittal.

Existing fill was encountered in each test boring to depths of about 8 feet and 13.5 feet. The depth to groundwater appeared to be consistent with the shoreline water elevation provided to us on the plans dated December 7, 2016 by Alpha Corporation. Bedrock in test borings B-1 and B-2 was encountered at about elevation EL 340.5.

Based on the results of our field investigation and the information provided to us, we recommend shallow foundations for support of any structures/slabs including the proposed concrete bulkhead and retaining wall. Spread footings founded in the relatively firm existing materials may be designed with a net allowable soil bearing pressure of 1,000 psf. In order to achieve the design bearing pressure, lowering or undercutting of specific footings may be required. It is critical that all footing subgrades be observed and approved for the appropriate bearing pressure by the geotechnical engineer, prior to placement of steel reinforcement or concrete. Footing subgrades should be located at least 2.5 feet below final exterior grades for frost considerations.

Footing subgrades should be observed and approved by the Geotechnical Engineer of Record or his/her representative prior to placement of concrete, to ascertain that footings are placed on suitable bearing soils as recommended herein. Footings should be excavated and concrete placed the same day in order to avoid disturbance from water or weather. Disturbance of footing subgrades by exposure to water seepage or weather conditions should be avoided. Any existing fill, disturbed, frozen, or soft subgrade soils should be removed prior to placing footing concrete. It may be desirable to place a 3 to 4-inch thick “mud mat” of lean concrete immediately on the approved footing subgrade to avoid softening of the exposed subgrade. Forms may be used if necessary, but less subgrade disturbance is anticipated if excavations are made to the required dimensions and concrete placed against the soil. If footings are formed, the forms should be removed and the excavation backfilled as soon as possible. Water should not be allowed to pond along the outside of footings for long periods of time. In addition, a dewatering program is recommended for installation of foundations which may include construction of a cofferdam/cut off trench, with localized sumps and pumps.

For the ramp repair, we recommend a rigid pavement section be used. Please see the following table for a preliminary pavement section.

Jointed Reinforced Concrete Pavement (JRCP)

Concrete Flexural Strength (psi) 4,500

Concrete Thickness, T (inches) 8.0

Minimum Percent Steel Reinforcement Required 0.1 (WWF placed at mid-depth of the concrete)

Dowel Requirements 1-inch diameter smooth dowel along transverse joints, 18-inch length, 12-inch O.C., placed at mid-height of concrete

Graded Aggregate Subbase (inches) 6.0

Fill may be required for site grading. Fill material should be placed in lifts not exceeding 8 inches loose thickness, with fill materials compacted by hand operated tampers or light compaction equipment placed in maximum 4-inch thick loose lifts. Fill should be compacted at +/- 2% of the optimum moisture content to at least 95 percent of the maximum dry density per ASTM D-698.

Materials used for compacted fill for support of footings, floor slabs, and pavements should consist of soils classifying SC, SM, SP, SW, GC, GM, GP, or GW per ASTM D-2487, with a maximum dry density greater than 105 pcf. It is expected that portions of soils excavated at the site will be suitable for re-use as fill based on classification. However, the Stratum A existing fill may not be suitable for re-use as new compacted fill due to deleterious man-made materials in the fill. In addition, drying of excavated soils by spreading and aerating may be necessary to obtain proper compaction. This may not be practical during the wet period of the year. Accordingly, earthwork operations should be planned for early Spring through late Fall, when drier weather conditions can be expected. Individual borrow areas, both from on-site and off-site sources, should be sampled and tested to verify classification of materials prior to their use as fill.

This preliminary letter of transmittal was prepared in accordance with generally accepted geotechnical engineering practices. No warranties, expressed or implied, are made as to the professional services included in this report.

RSZ/PEB

\\GeoData\Geoconcepts\PROJECTS\Active 15 Projects\15406.03, 4 Locks Boat Ramp\Documents\Preliminary Results\Updated\LOT, 5.11.17.doc

1+1+1+2

2+2+2+3

1+2+2+3

3+3+4+4

2+2+2+2

1+2+3+3

0+0+0

2+2+3

1+2+1

50/0

367.5 367.0

359.5

354.0

344.0

340.4

335.5

A

B2

B1

B3

Topsoil = 0.5ft.

Fill, dark brown, fine, SILTY SAND, loose, moist, SM

Residual, dark gray, fine to medium, SILTY SAND, loose, wet, SM

Very loose

Residual, dark gray, fine, SANDY SILT, soft, moist, ML

Unweathered, very hard, dark gray white, LIMESTONE, very widely fractured

Bottom of Boring at 32.0 ft

OFFSET NOTES:

Automatic hammer 3.25", CME 55

PROJECT NUMBER:

12/13/16 - 12/13/16

DRILLING METHOD:

Alpha Corporation

15206.03

K. Kersh

367.5

DATES DRILLED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft):

DRILLER:

4 Locks Boat Ramp

Clear Spring, Maryland

THE STRATIFICATION LINES REPRESENT APPROXIMATE BOUNDARIES. THE TRANSITION MAY BE GRADUAL.

SAMPLE TYPES:

Split Spoon

Rock Core

REMARKS:

SOIL

MATERIAL DESCRIPTION

ft ft ft

12.0

25.0

8.0

UPON COMPLETION:

ENCOUNTERED:

19955 Highland Vista Dr., #170 Ashburn, Virginia 20147

703-726-8030 703-726-8032 fax

12/13/2016

Connelly & Associates

J. Valentino

B-1DRILLING CONTRACTOR:

BORING NUMBER:

SHEET 1 OF 1

LOCATION:

LOGGED BY:

GROUND WATER LEVELS:

LOCATION:

PROJECT:

B O

R E

H O

LE

/T

E S

T P

IT

L

O G

S .G

P J

G E

O C

O N

C E

P T

S T

E M

P

LA

T E

2-

-2

5.

G D

T

/1

/1

20 40 60 80

STANDARD

PENETRATION

TEST RESISTANCE

(BPF)

16.0 ftCAVED:

R E

C

R Q

D

ROCK

R E

C (i n)

SPT

BLOW

COUNTS

ELEV.

355.5

342.5

359.5

ELEV.

ELEV.

ELEV. 351.5

ELEV.

(ft)

DEPTH

(ft)

S T

R A

T U

M

S A

M P

LE

T

Y P

E

G R

A P

H

IC

1+1+2+1

1+1+1+1

1+1+1+1

4+2+1+1

2+2+2+3

1+1+2

1+1+2

2+4+6

50/0

368.2 367.7 366.2

364.2

362.2

360.2

354.7

344.7

340.7

21.3

29.1

22.9

21.3

34.6

22.9

A

B1

B2

Topsoil = 0.5ft.

Fill, dark gray, fine to medium, silty clayey SAND, roots, very loose, moist, SC-SM Fill, dark brown, fine, sandy LEAN CLAY, roots, soft, moist, CL Fill, dark brown, fine, silty clayey SAND, very loose, moist, SC-SM

Fill, dark brown, medium to coarse, clayey SAND, very loose, moist, SC Loose

Residual, dark brown, medium to coarse, sandy LEAN CLAY, soft, moist, Pp=1.25, CL

Residual, dark gray, medium to coarse, SILTY SAND, medium dense, moist, SM

Auger Refusal at 27.5 ft

OFFSET NOTES:

Automatic hammer 3.25", CME 55

PROJECT NUMBER:

12/13/16 - 12/13/16

DRILLING METHOD:

Alpha Corporation

15206.03

K. Kersh

368.2

DATES DRILLED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft):

DRILLER:

4 Locks Boat Ramp

Clear Spring, Maryland

THE STRATIFICATION LINES REPRESENT APPROXIMATE BOUNDARIES. THE TRANSITION MAY BE GRADUAL.

SAMPLE TYPES:

Split Spoon

REMARKS:

SOIL

MATERIAL DESCRIPTION

ft ft

13.5

24.0UPON COMPLETION:

ENCOUNTERED:

19955 Highland Vista Dr., #170 Ashburn, Virginia 20147

703-726-8030 703-726-8032 fax

12/13/2016: NOT ENCOUNTERED

Connelly & Associates

J. Valentino

B-2DRILLING CONTRACTOR:

BORING NUMBER:

SHEET 1 OF 1

LOCATION:

LOGGED BY:

GROUND WATER LEVELS:

LOCATION:

PROJECT:

B O

R E

H O

LE

/T

E S

T P

IT

L

O G

S .G

P J

G E

O C

O N

C E

P T

S T

E M

P

LA

T E

2-

-2

5.

G D

T

/1

/1

20 40 60 80

STANDARD

PENETRATION

TEST RESISTANCE

(BPF)

6.0 ftCAVED:

R E

C (i n)

SPT

BLOW

COUNTS

ELEV.

354.7

344.2

ELEV.

ELEV.

362.2

ELEV.

(ft)

M C

DEPTH

(ft)

S T

R A

T U

M

S A

M P

LE

T

Y P

E

G R

A P

H

IC