EBUAmmo_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 the

EAST BRANCH OF THE UPPER AMMONOOSUC RIVER

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 the EAST BRANCH OF THE UPPER AMMONOOSUC RIVER 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. Recommendations

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 East Branch of the Upper Ammonoosuc River 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 56-inch circular corrugated metal pipe (CMP) culvert is currently used to allow the East Branch of the Upper Ammonoosuc River to pass under Bog Dam Loop Road. The bottom third of the culvert is embedded in the streambed and a cobble stream bottom extends the length of the culvert. The culvert has a boulder headwall on the upstream and downstream side of the crossing from which the culvert projects.

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 the East Branch of the Upper Ammonoosuc River, 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 one boring 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. 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-5 was located on the northeastern side of the East Branch of the Upper Ammonoosuc River along Bog Dam Loop Road approximately 3 feet from the southeastern edge of the road and 50 feet from TBM #601. The ground surface elevation at this boring location is approximately 1,777.4 feet. The following table show results from Boring B-5:

B-5 Boring Summary Depth Description 5-10’ Brown, fine to coarse sand with some gravel 10’ 10”-12” diameter boulders, bedrock not encountered 16’ 10”-12” diameter boulders, bedrock not encountered

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

However due to the proximity of the East Branch of the Upper Ammonoosuc River, groundwater is most likely at the same elevation of approximately 1,766.3 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 groundwater level. HEB does not believe the installation of piezometers or monitoring wells is necessary for this project.

C. Refusal Refusal was encountered at an elevation of 1,761.4 feet in Boring B-5.

IV. ENGINEERING ANALYSIS AND RECOMMENDATIONS

A. Analysis The soils encountered at this elevation can be characterized as sandy 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.

Since boulders were encountered, the average penetration resistance was 100+ blows per foot at the proposed footing elevation. Based on borings taken at nearby sites, we recommend using an average penetration resistance of 40 blows per foot for design purposes.

B. Recommendations The recommended foundation type is spread footings located approximately 5 feet below the bottom of the channel at an elevation of approximately 1,764 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 shall not exceed 30 ksf.

Groundwater can be assumed to remain near the level of the brook surface, approximately 11 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.

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

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 of the East Branch of the Upper Ammonoosuc River, 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\EBUAmmo\EBUAmmo 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 E

B U

A m m o X r e f s E

B U

A m m o

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 E

B U

A m m o

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