Ida-clear4783-1 GR 0226 Dent Bridge Road Geotechnical Report

Dent Bridge Road Improvements

January 2026

Geotechnical Report No. 02-26

Dent Bridge Road Improvements

FINAL GEOTECHNICAL ENGINEERING

REPORT

ID FLAP CLEAR 4783(1)

Clearwater County, Idaho
January 2026

1-i

This page intentionally left blank

Dent Bridge Road Improvements

January 2026

1.1

1.2

1.3

2.1

2.1.1
2.1.2
2.1.3

4.1

4.2

4.3

5.1

5.2

6.1

6.2

6.3

6.4

6.5

6.5.1

6.6

i

Dent Bridge Road Improvements

January 2026

LIST OF TABLES

FIGURES

Figure 1

Project Overview Map

Figures 2 through 12

Exploration Location Maps

APPENDICES

Appendix A

Boring Logs

Appendix B

Laboratory Test Results

Appendix C

Vibrating Wire Piezometer and Slope Inclinometer Graphs

ii

Dent Bridge Road Improvements

January 2026

1 INTRODUCTION

This report provides the geotechnical investigation results, analysis, and final recommendations for the ID FLAP CLEAR 4783(1) – Dent Bridge Road Improvements Project. The project is located along the two-lane paved (rural) Dent Bridge Road that begins in Orofino, Idaho at Milepost (MP) 0.0 and ends at MP 15.0 at the southern approach of the Dent Bridge (Figure 1, Project Overview Map.

1.1

PROJECT OVERVIEW

Dent Bridge Road serves as a connecting road from Orofino, Idaho to Dent Bridge and the city of Elk River, Idaho. It provides access to the Dworshak Reservoir, campgrounds, recreational trails (such as Dent acres), Canyon Creek, and the Clearwater National Forest. The road serves a variety of users including tourists, adjacent communities, truckers, hikers, snowmobile riders, bikers, hunters, campers, ATV riders, fishermen, and equestrian enthusiasts.

1.2

EXISTING CONDITIONS

Dent Bridge Road currently has a worn, cracked, and rough asphalt surface caused by an insufficient roadway base. Some areas have experienced severe damage such as surface cracks, potholes, road narrowing and soft spots. Poor roadway surface conditions reduce traction and stability for vehicles and will make the road more difficult for the county to maintain. Additional notable safety and structure concerns include:
•

Sections of existing guardrail which are structurally deficient and improperly placed. The guardrails are frequently too low, even contacting the gravel shoulder in some areas, and are only supported at every other length of railing. The guard rail has been visibly struck many times. Low rail height has allowed trucks to collide with the rail, roll over it, and leave the roadway.

•

An 18’ bridge is in danger of collapse which will result in closure of the road to all public and emergency traffic.

•

At MP 6.2 there is an unsafe 90° curve where data shows that 3 accidents have occurred