Stony_Brook_Geotech_Report_REVISED_07-03-15.pdf

HEB Engineers, Inc. • www.hebengineers.com • Office (603) 356-6936 • Fax (603) 356-7715 Post Office Box 440 • 2605 White Mountain Highway • North Conway, NH 03860

GEOTECHNICAL ASSESSMENT REPORT

BOG LOOP AOP CULVERT REPLACEMENT

over STONY BROOK located in the

WHITE MOUNTAIN NATIONAL FOREST

NEW HAMPSHIRE

Work Order #AG-28H8-D13-0052

Prepared for:

USDA Forest Service

October 31, 2013 Revised: July 3, 2015

Prepared by:

HEB Engineers, Inc.

HEB Project #2013-059

GEOTECHNICAL ASSESSMENT REPORT

for the

BOG LOOP AOP CULVERT REPLACEMENT

over STONY BROOK located in the

WHITE MOUNTAIN NATIONAL FOREST

NEW HAMPSHIRE

October 31, 2013 Revised: July 3, 2015

TABLE OF CONTENTS

Page

I. INTRODUCTION

A. Scope of Work B. Existing Site Conditions C. Proposed Construction

II. SUBSURFACE INVESTIGATION

A. Exploration B. Laboratory Testing

III. SUBSURFACE CONDITIONS

A. Soil Conditions B. Groundwater C. Refusal

IV. ENGINEERING ANALYSIS AND RECOMMENDATIONS

A. Analysis B. Refusal

V. LIMITATIONS

APPENDIX A: Existing-Features Plan & Profile

APPENDIX B: Boring Logs http://www.hebengineers.com/

USDA Forest Service Revised: July 3, 2015 Bog Loop AOP Culvert Replacements, WMNF, NH Page 2 of 4 Stony Brook Geotechnical Assessment Report

I. INTRODUCTION

A. Scope of Work The purpose of the geotechnical assessment was to:

1. Assess the nature, consistency, and relative density of the soils encountered at the site, retrieve samples for visual classification, and perform standard penetration tests in the overburdened soil.

2. Assess the elevation of the groundwater table and the depth of any bedrock encountered.

3. Assess the implications of the subsurface conditions on the proposed bridge substructure design and provide parameters for design.

Presented herein are descriptions of the subsurface exploration program, conditions encountered, and geotechnical evaluation and recommendations. The geotechnical assessment is subject to the limitations presented in Section V.

B. Existing Site Conditions A 103-inch by 71-inch arch corrugated metal pipe (CMP) culvert is currently used to allow Stony Brook to pass under Bog Dam Loop Road. The culvert has no headwall, but is mitered to conform to the road embankment side slopes on the upstream and downstream side of the crossing.

The soils in the White Mountain National Forest have not been mapped by the US Department of Agriculture (USDA), Natural Resources Conservation Service. Soil data is not available through the Natural Resources Conservation Service for this site.

C. Proposed Construction The goal of the replacement of the existing culvert is to create a crossing that meets the hydraulic needs of Stony Brook, as well as providing a crossing that promotes aquatic wildlife passage. The proposed design may include a pipe-style crossing or a small-span bridge. The proposed design will likely need to meet the New Hampshire Department of Environmental Services (NHDES) Stream Crossing Rules for a Tier 2 stream crossing.

II. SUBSURFACE INVESTIGATION

A. Exploration The subsurface exploration program consisted of two borings conducted on September 25, 2013 by New Hampshire Boring, Inc. of Londonderry, NH. Joe Klementovich, EIT, of HEB Engineers, Inc. (HEB) observed the work. An existing-features plan depicting the general location of the site and borings is included in Appendix A. Borings were conducted utilizing a truck mounted drilling rig. Standard penetration test (SPT) borings were completed in accordance with ASTM D-1586 utilizing a 2¼-inch diameter hollow stem flight auger and a 13/8-inch ID split spoon sampler driven with a 140 lb. hammer. HEB recorded independent field notes to compare with the driller’s logs.

Soil samples were taken and classified according to the Unified Soil Classification System, ASTM D 2488, at 5-foot intervals. NH Boring obtained the samples. The number of hammer blows (N) per 6 inches was recorded. A copy of the boring logs is included in Appendix B.

B. Laboratory Testing No laboratory testing was performed as part of this project.

Bog Loop AOP Culvert Replacements, WMNF, NH Page 3 of 4

III. SUBSURFACE CONDITIONS

A. Soil Conditions Boring B-1 was located on the southern side of Stony Brook along Bog Dam Loop Road, approximately 17 feet from the Stony Brook signpost and 4 feet from the western edge of the road.

The ground surface elevation at this boring location is approximately 1,750.5 feet. The following table show results from Boring B-1:

B-1 Boring Summary Depth Description

5-7’ Brown, fine to coarse sand with some clay and gravel 10-12’ Gray silt and fine sand with gravel.

15-17’ Gray, fine to coarse sand with some clay and gravel 18-20’ Attempted rock core was identified as a boulder 20-22’ Gray, fine to coarse sand with some clay

Boring B-2 was located near the northern side of Stony Brook along Bog Dam Loop Road, approximately 42 feet from the Stony Brook signpost and 4 feet from the eastern edge of the road.

The ground surface elevation at this boring location is approximately 1,750.6 feet. The following table show results from Boring B-2:

B-2 Boring Summary Depth Description

5-7’ Brown, medium to coarse sand with gravel 10-12' Brown, medium to coarse sand with gravel

15-17’ Grayish, brown fine to coarse sand 20-22’ Grayish, brown fine to coarse sand

B. Groundwater Exact groundwater determination was not possible due to the use of casing to support the boring.

However, due to the proximity of Stony Brook, groundwater is most likely at the same elevation of approximately 1,739.8 feet. Groundwater levels may fluctuate, with soil density, precipitation, time of year, and short time of observation all being factors. Installation of piezometers, or monitoring wells, and monitoring over a period of several months to a year is the only practical way of determining the variability of the ground water level. HEB does not believe the installation of piezometers or monitoring wells is necessary for this project.

C. Refusal Refusal was encountered at elevations 1,728.5 and 1,728.9 feet in Boring B-1 and B-2 respectively.

Bog Loop AOP Culvert Replacements, WMNF, NH Page 4 of 4

IV. ENGINEERING ANALYSIS AND RECOMMENDATIONS

A. Analysis The soils encountered at this elevation can be characterized as medium to coarse sand with gravel.

The overall soil classification was determined to be SW (well-graded sands, gravelly sands, little or no fines) based on the Unified Soil Classification System.

The average penetration resistance was 40 blows per foot at the proposed footing elevation.

B. Recommendations The recommended foundation is spread footings located approximately 5 feet below the bottom of the channel at an elevation of approximately 1,737 feet.

The bearing resistance factor, øb, is taken as 0.45 from Section 10.5.5.2.2 of the AASHTO LRFD Bridge Design Specifications. The nominal bearing resistance, qn, was calculated to be 68 ksf according to Section 10.6.3.1 of the AASHTO LRFD Bridge Design Specifications. The factored bearing resistance at the strength limit state shall not exceed 30 ksf.

Groundwater can be assumed to remain near the level of the brook surface, approximately 13 feet below the existing road surface. It is assumed that pumping and/or dewatering wells and cofferdams will be required to keep excavations dry in order to install the bridge footings.

V. LIMITATIONS

The evaluation and recommendations described in this geotechnical assessment are based in part on the data obtained from a limited number of soil and/or bedrock samples from widely spaced subsurface borings. The explorations indicate subsurface conditions only at the specific locations and times, and only to the depths penetrated. The nature and extent of variations between these explorations or at other site locations may not become evident until, and if, further investigation is performed. The recommendations are based in part on assumptions made about conditions at the site. If variations or other latent conditions are evident, it will be necessary to re-evaluate the recommendations of this report.

The generalized soil profile described in the text is intended to convey trends in subsurface conditions.

The boundaries between strata are approximate and idealized and have been developed by interpretations of widely spaced explorations and samples. Actual soil transitions are probably more gradual. For specific information, refer to the boring logs in Appendix B. No laboratory testing of soil samples was performed.

This report has been prepared for the exclusive use of the USDA Forest Service for specific application of the proposed Bog Dam Loop Road Culvert Replacement over Stony Brook, in accordance with generally accepted geotechnical practices. No other warranty, express or implied, is made.

P:\Jobs\2013\2013-059 USFS - Bog Loop AOP Culvert Replacements, Berlin, NH\Reports\Geotech Report\Stony\Stony Brook Geotech Report REVISED 07-03-15.doc

APPENDIX A

Existing-Features Plan & Profile

Scale

Date

CAD File No.

Checked

Drawn

Drawing No.

Project

Project Name

Drawing Title

No.

Revision/Issue Date

HEB Engineers, Inc.

PO Box 440, 2605 White Mountain Hwy.

North Conway, NH 03860 www.hebengineers.com

P J o b s

U

S F

S

B o g

L o o p

A

O P

C u l v e r t

R e p l a c e m e n t s

B e r l i n

N

H D w g

S t o n y

B r o o k X r e f s S t o n y

B r o o k

S u r v e y d w g

V

A

M t c h i n g a s

APPENDIX B

Boring Logs

HEB Engineers, Inc.

Post Office Box 440

2605 White Mountain Hwy.

North Conway, NH 03860 www.hebengineers.com

Office (603) 356-6936

Fax (603) 356-7715

P J o b s

U

S F

S

B o g

L o o p

A

O P

C u l v e r t

R e p l a c e m e n t s

B e r l i n

N

H D w g

T e m p B o r i n g

L o g s S t o n y

B r o o k

B o r i n g

L o g d w g

L a y o u t

P

M e g r e n i e r

V. LIMITATIONS