GM 38-20 Big Bend Toilet.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: August 5, 2020

TO: Michael Traffalis Project Manager

FROM: Evan Garich Geotechnical Engineer

SUBJECT: Geotechnical Memo 38-20 Geotechnical Recommendations GTSR Big Bend Vault Toilet Construction

MT PRA GLAC 10(46)

Glacier National Park, MT

INTRODUCTION/ PROJECT DESCRIPTION

This memorandum has been developed to support the design and construction of a new double vault toilet in Glacier National Park (GNP). The project location is at the Big Bend pullout area on Going-to-the-Sun Road. The project includes design and construction of two new double vault toilets consistent with other CXT type toilets used on the Going-to-the-Sun Road (GTSR).

SITE CONDITIONS

The project site is located at the Big Bend pullout along Going-to-the-Sun Road, approximately 2.8 miles below Logan Pass. The project site is located at an elevation of approximately 5,800 feet. A talus/colluvium slope extends from the edge of the existing pavement approximately 60 feet horizontally and 35 feet vertically to the base of a near vertical cliff. The cliff is mapped as dolomitic quartzite and siltite rock of the Wallace Formation. The exposed cliff height is estimated to be approximately 40 feet.

The slope below the rock face is mostly vegetated, although rocks are visible through vegetation. Rock blocks that are presumed to have originated as rockfall from the cliff are present on the slope in block sizes/boulders as large as 11’x11’x5’. It is understood that GNP maintenance and WFL construction have not noted significant rockfall impacting the pavement at the project site. It is understood that the structure roof will not consider a rockfall impact design load case.

SUBSURFACE CONDITIONS

A limited subsurface investigation was performed at the site on June 18th, 2020. The purpose of the investigation was to excavate material near the proposed building to determine the type of subsurface materials present and if bedrock was present. The NPS provided a John Deere 310 SJTC backhoe and operator. Three test pits were excavated; the approximate locations are shown on Figure 1. The front edges of the test pits were located approximately 6 to 8 feet from the edge of existing pavement and the back walls of the test pits were located approximately 21 to 28 feet from the edge of existing pavement.

Figure 1. Project site and approximate locations of test pit excavations.

Generally, the following subsurface conditions were encountered, starting at the ground surface:

• a soil-like layer of silty cobbles and boulders with gravel and sand. This layer ranged from approximately 1 to 6 feet in thickness and graded rockier with depth. Below which was:

BB20-03TP

BB20-02TP

BB20-01TP

• boulders and cobbles in a soil matrix. Similar to the above layers, but higher percentage of rock. This layer ranged from approximately 1 to 7 feet in thickness.

Below which was:

• rock – either bedrock or large displaced blocks of rock. The rock was encountered as deep as 10 feet below the ground surface at the back wall of the test pits and as shallow as 3 feet below the existing ground surface at the front of the test pits. In test pit BB20-03TP the rock was encountered at approximately the elevation of the adjacent pavement.

Boulders up to 2.5’x3’x1’ were encountered in the test pits. Groundwater was not observed in the test pits. The sidewalls remained stable while the test pits were excavated and backfilled.

It was difficult, but possible to excavate the rock layer with the backhoe that was onsite.

Photos of the field investigation are provided in Attachment 1. Logs of the test pits are provided in Attachment 2.

DESIGN RECOMMENDATIONS

The following recommendations are applicable to the proposed pre-cast concrete vault toilet at the project site.

• Recommended allowable/service limit state bearing pressure: 8.0 ksf

• Recommended allowable/factored coefficient of friction against sliding: 0.49

• Recommended allowable/factored static at rest equivalent fluid unit weight: 55 pcf

• Recommended allowable/factored static passive equivalent fluid unit weight: 220 pcf o Passive earth pressure should be neglected within 2 feet of the final ground surface.)

• Recommended allowable/factored seismic active equivalent fluid unit weight: 60 pcf (this is a total pressure, not a delta to the at rest equivalent fluid unit weight.)

It is recommended to use standard rockery retaining wall details that have been used along GTSR and within Glacier National Park on previous contracts.

CONSTRUCTION CONSIDERATIONS

The contractor should be prepared to encounter large boulders and rock while excavating for the structure and wall placement. Boulders up to 2.5’x3’x1’ were encountered while excavating. The contractor should anticipate encountering boulders larger than this as boulders up to 11 feet in maximum dimension are present on the slope. These large boulders may need to be broken up prior to transport, which may require a hoe ram or boulder reduction methods.

The rock encountered while digging the test pits was excavatable with the backhoe on site.

However, the backhoe did experience difficulty excavating the rock and likely could not have excavated much deeper. A larger excavator will likely experience less difficulty excavating the rock, however a hoe ram or similar equipment may still be required to perform the required excavations for the project.

The test pit side walls were stable during the field investigation. Excavations may experience instability in larger excavations or if any seepage into the excavation face is encountered.

CLOSING

Please contact Evan Garich at (360) 619-7824 or Evan.Garich@dot.gov with any questions regarding this memorandum.

ATTACHMENTS:

Attachment 1 – Investigation Photos Attachment 2 – Test Pit Logs mailto:Evan.Garich@dot.gov

Attachment 1 – Investigation Photographs

Figure A1. View of field investigation excavation.

Figure A2. View of field investigation excavation.

Figure A3. View of field investigation excavation.

Figure A4. View of field investigation excavation.

Figure A5. View of field investigation excavation.

Figure A6. View of field investigation excavation.

Attachment 2 – Test Pit Logs silty Cobbles and Boulders with gravel and sand;

medium dense to very dense, brown, moist, angular/blocky clasts, low plasticity silt decreasing soil content, increasing cobbles and boulders

Boulder. Max boulder size excavated approximately 2.5'X3'X1'

10 ft Apparent bedrock, rock surface and bedding slopes toward the roadway. Difficult to excavate.

Rock surface at 10 feet b.g.s at back wall of test pit, 28 feet from edge of pavement.

Rock surface at 5 feet b.g.s. at front wall of test pit, 8 feet from the edge of pavement.

Sidewalls stable for the duration of excavation.

Bottom of borehole at 10.1 ft.

Groundwater Depth:

While Drilling: --- Not encountered.

At Completion: --- Not encountered.

After Drilling: --- Not encountered.

Notes:

Depth taken at back of test pit. Back wall located 28 feet from edge of pavement.

Latitude: 48.72701° Longitude: -113.724° Date Started: 6/18/20 Date Completed: 6/18/20 Driller/Company: NPS/NPS Hammer Type: 140 lbs Automatic

Drill: 310 SJTC Backhoe

Logger/Company: E. Garich/WFL

BB20-01TPBORING LOG

Sheet: 1 of 1

Project Location: Going-to-the-Sun Road, Big Bend

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: GTSR - Big Bend Toilet D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

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L og angular/blocky clasts, low plasticity silt

5 ft highly fractured rock with soil matrix, platey, easy to excavate

8 ft Apparent bedrock, rock surface and bedding slopes toward the roadway. Difficult to excavate.

Difficult to excavate rock encountered at 8 feet b.g.s at back wall of test pit (approximately pavement elevation).

Difficult to excavate rock encountered at 6 feet below pavement elevation at front of test pit.

Sidewalls stable for the duration of excavation.

Bottom of borehole at 11.1 ft.

Groundwater Depth:

While Drilling: --- Not encountered.

At Completion: --- Not encountered.

After Drilling: --- Not encountered.

Notes:

Depth taken at back of test pit. Back wall located 23' from edge of pavement.

Latitude: 48.72695° Longitude: -113.724° Date Started: 6/18/20 Date Completed: 6/18/20 Driller/Company: NPS/NPS Hammer Type: 140 lbs Automatic

Drill: 310 SJTC Backhoe

Logger/Company: E. Garich/WFL

BB20-02TPBORING LOG

Sheet: 1 of 1

Project Location: Going-to-the-Sun Road, Big Bend

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: GTSR - Big Bend Toilet D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

IN

G L

O G

F

H W

A _D

A T

A T

E M

P

LA

T E

_2

3.

G

D T

/4 /2

5:

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W -W

O R

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G ra ph ic angular/blocky clasts, low plasticity silt

6 ft decreasing soil content, increasing cobbles and boulders

9 ft Apparent bedrock, rock surface and bedding slopes toward the roadway. Difficult to excavate.

10 ft

Difficult to excavate rock encountered at 9 feet b.g.s at back wall of test pit (approximately pavement elevation).

Difficult to excavate rock encountered at pavement elevation at front of test pit.

Sidewalls stable for the duration of excavation.

Bottom of borehole at 10 ft.

Groundwater Depth:

While Drilling: --- Not encountered.

At Completion: --- Not encountered.

After Drilling: --- Not encountered.

Notes:

Depth taken at back of test pit. Back wall located 21' from edge of pavement.

Latitude: 48.72705° Longitude: -113.724° Date Started: 6/18/20 Date Completed: 6/18/20 Driller/Company: NPS/NPS Hammer Type: 140 lbs Automatic

Drill: 310 SJTC Backhoe

Logger/Company: E. Garich/WFL

BB20-03TPBORING LOG

Sheet: 1 of 1

Project Location: Going-to-the-Sun Road, Big Bend

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: GTSR - Big Bend Toilet D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

IN

G L

O G

F

H W

A _D

A T

A T

E M

P

LA

T E

_2

3.

G

D T

/4 /2

5:

C :\P

W -W

O R

K \D

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