Attach 2 - Geo-Technical 2023.pdf

Mendocino National Forest

M10 Road Repair Contract – Solicitation # XXXX

Attachment 01, Notes. (See drawing on page 2)

1. The FS Drawing, C1.1 (page 2 of this attachment) represents the results and evaluation of a preliminary surface survey conducted by Forest Service Region 5 geotechnical staff in the spring of 2023. The findings are consistent with further visual surface surveys conducted by engineering staff from the Mendocino NF.

2. For the geo-technical survey included in the design phase if the Contractor’s work, the objective is to confirm or correct the apparent conditions as shown on drawing C1.1. and as noted here:

a) The measurements shown in the drawings are in meters. Elevations and distances included here are also in meters so as to remain consistent.

b) The old Dormant Landslide (labeled “Inactive” on the drawing) created a bowl-shaped scar which has grown over with brush. No significant number of large trees have grown within the excavated area which runs from the current top of the ridge down about 45-50 meters.

This slide exposed numerous sub-surface seepage paths which now appear as springs near the top of the slide mass at 1,020 – 1,040 M elevations. Dormant Landslide is a relative term. It appears as though some significant time has elapsed since this slide moved. Perhaps hundred years or more although trees in the scar appear to be less than forty years old. Stabilization measures of the Dormant Landslide is not considered to be part of the contract scope. If during further investigation, the Dormant landslide is found to be active, a proposal shall be submitted to the CO for review which will include a cost adjustment and changes in schedule.

c) Activity in the more current slide ( labeled “Active Landslide”) has occurred on the face and below the Dormant Landslide. This appears to be mostly surface debris slides shedding off the dormant slide mass.

d) Drainage from the exposed springs has occurred down the face of both the Dormant and Active Landslides as well as off the sides, mostly to the west.

e) The average slope from the top of the ridge to the road is about 60%. The slope immediately above and below the road varies from 70 -90%. The road-cut wall on the uphill side of the road has remained fairly intact with the debris flows going over it. This suggests that no significant slip-surface may exist at, or immediately beneath the road within the project area.

3. Additional objectives for the geotechnical survey are:

a) Determine the extent of any discovered slip-surface under or adjacent to the road within the project area.

b) Determine the best location (in consultation with FS-MNF Engineering and FS-R5 Geotechnical staff) for a inclinometer and piezometer(s) to monitor any future slippage or other down-slope movement and groundwater movement/elevations.

4. The Contractor is free to utilize any information contained on FS Drawing C1.1 either for the survey or in their design. The information contained in this appendix is provided for the Contractors convenience and the Contractor is fully responsible for any utilization into the projects design or construction.

Inactive Landslide?

Active Landslide

Uncontrolled drainage onto active landslide

Scarp Pnt 1

Pnt 2

Pnt 3

Pnt 4

Rock Outcrop

Pnt 5

Debris Chute

Debris Chute

Current debris source Stabilization could occur here - Tieback reaction pads potentially

Lined ditch to pickup surface runoff

Install H beam stabilized reinforced rock buttress debris bench. Harden road prism. Clean as required.

Access ramp

Cleanout access ramp

Spring and/or sink hole

Horizontal drain arrayHorizontal drain array

Pnt 1

Pnt 2

Pnt 3

Pnt 4

Pnt 5

M

L A

N D

S

LI

D E

M A

Y

S

IT

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C O

N D

IT

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C1.1

AS NOTED

5/1/2023

Romero

M E

N D

O C

IN

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N F

3SHEET OF

DRAWING

PROJECT NUMBER

CHECKED BY

SCALE

DATE

CHECKED BY

DESIGNED BY

DRAWN BY

F O

R E

S T

D R

A W

IN

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P R

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JE

C T

N A

M E

N A

M E

FOREST

REGION

SOUTHWEST

PACIFIC

DATENO. REVISIONS

R5

SERVICE

U S D A

All units in meters

Pnt 1 39.337808, -122.70035

Pnt 2 39.337936, -122.69911111

Pnt 3 39.339036111, -122.700638888

Pnt 4 39.338799, -122.699577

Pnt 5 39.338467, -122. 699836