B08_Attach_3_Sperry_Geotech_Report.pdf

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August 10, 2018 Project No. 218-041

Ms. Elizabeth Hallas Anderson Hallas Architects 715 14th Street Golden, CO 80401

Subject: Geotechnical Engineering Investigation

Sperry Chalet Glacier National Park

Dear Ms. Hallas, Yeh and Associates, Inc. have completed the geotechnical engineering investigation for the proposed reconstruction and restoration of the Sperry Chalet in Glacier National Park, near West Glacier, Montana. This study was performed in general accordance with our proposal dated February 14, 2018. Our work consisted of site reconnaissance, engineering analyses and preparation of this report.

Project Description: The Sperry Chalet was severely damaged in the Sprague Fire of 2017.

The project includes reconstruction and restoration of the Chalet, while retaining as much of the historic structure as possible. New foundations will be constructed to replace damaged, unserviceable foundations and fully support the roof loads.

Purpose and Scope: The purpose of our investigation was to explore and evaluate site conditions at the structure location and, based on the conditions found, develop recommendations for allowable bearing capacity for new foundations and provide seismic site class information. The conclusions and recommendations in this report are based on analysis of the data from our field exploration/reconnaissance, and on our experience with similar soil and geologic conditions.

Geology: The project area is located in the Lewis Range of the northern Rocky Mountains, in Glacier National Park. The United States Geological Survey (USGS) has mapped the site as outcropped bedrock of the Grinnell Formation. The Grinnell formation largely consists of red and green argillite and siltite with interlayered quartz arenite. A geologic map of the site is presented in Figure 1. Relevant portions of the map legend are attached at the end of this report.

Sperry Chalet August 10, 2018 Geotechnical Investigation YA Project 218-041

Figure 1 -Site Geology

Surface Conditions: In the northern portion of the building, the outcropped bedrock ledge was covered by a thin layer of ash, debris and soil (Figure 3). In the crawl space area of the structure (southern portion of the building), two test holes were hand excavated adjacent to interior column pads to determine the bedrock surface elevation. Bedrock was encountered beneath approximately 18-inches of clayey sand soil mixed with ash and debris (Figure 4). We anticipate the soil and debris cover over the bedrock in the crawl space portion the building will vary from several inches to up to about 2 feet.

SITE

Figure 2 - Exterior Bedrock Ledge – Argillite and Quartz Arenite

Figure 3 - Interior Bedrock Ledge with Ash/Debris Cover

Figure 4 - Interior Column Test Hole Excavation TH-1

Bearing Capacity: The Chalet foundations are constructed with stacked stone and mortar bearing on the bedrock. The bedrock consists of hard to very hard interlayered argillite and arenite. Based on the surface and subsurface conditions encountered, we recommend new foundations bear directly upon the bedrock. Existing soil, ash or debris should be cleared from the foundation footprint. We anticipate the soil and debris cover in the south portion the building will vary from several inches to up to about 2 feet. Loose or spalling rock should also be removed.

The footings bearing on the bedrock may be designed for a maximum allowable bearing pressure of 6,000 psf. Total movement of the foundation resulting from structural loads and bedrock conditions is estimated to be less than one-half inch. Differential movement should be about ½ to ¾ of the total movement. Foundations should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement.

It is recommended that the foundation excavations be observed by a representative of the geotechnical engineer. If the rock conditions encountered differ significantly from those presented in this report, supplemental recommendations may be required.

Seismic Site Class: Based upon the nature of the bedrock, a Site Class B may be used for the design of the structure for the proposed project (IBC 2012/2015). The project site (site coordinates 48.6050 N, 113.7860 W) is located in a seismic area with a mapped maximum short period (SS) and 1-second period (S1) ground motion, respectively, of 0.479 g and 0.141g. The site coefficients, Fa and Fv, for the same periods are 1.0 and 1.0, respectively.

Limitations: This report includes our recommendations relating to the geotechnical aspects of project design and construction. The conclusions and recommendations stated in this report are based on the conditions found at during our site reconnaissance. Our findings, conclusions, and recommendations should not be extrapolated to other areas or used for other projects without our prior review. Furthermore, they should not be used if the site has been altered without Yeh and Associates’ prior review to determine if these recommendations remain valid.

Yeh and Associates has prepared this report for the exclusive use of Anderson Hallas and the National Park Service for the proposed reconstruction of the Sperry Chalet in Glacier National Park. This report was prepared in substantial accordance with the generally accepted standards of practice for geotechnical engineering as exist in the site area at the time of our investigation. No warranty is expressed or implied. The recommendations in this report are based on the assumption that Yeh and Associates will conduct an adequate program of construction testing and observation to evaluate compliance with our recommendations.

Respectfully submitted, YEH AND ASSOCIATES, INC. Reviewed by:

Samantha C. Sherwood, P.E. T. Samuel Holder, P.E.

Project Manager Senior Project Manager

Attachments:

Test Hole Location Plan Geologic Map Legend

Excerpts from USGS Geologic Map of Glacier National Park (Whipple, 1972)

Consulting Engineers & Scientists

Yeh and Associates, Inc. PROJECT NUMBER:

SCALE

SHEET REVISION DATEBY

OF

SHEET

& Associates, Inc.

project without written authorization from Yeh service and shall not be used for any other document are instruments of professional

Associates, Inc. The ideas incorporated on this

This document is the property of Yeh &

REUSE OF DOCUMENT

DRAWN BY:

CHECKED BY:

DATE:

DATE:

HORIZ: VERT:

NO.

DESIGNED FOR:

1:1

8/7/2018

8/7/2018

MJW

SCS

218-041

ANDERSON HALLAS ARCHITECTS

SPERRY CHALET

GLACIER NATIONAL PARK

TEST HOLE LOCATION PLAN 1

TEST HOLE/HAND EXCAVATION LOCATION

TH-1 TH-2

Dear Ms. Hallas,