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HomeMy WebLinkAboutHersey and Bean Planing Mill - Wall Stabilization Report 2011HERSEY & BEAN PLANING MILL STILLWATER, MN WALL STABILIZATION REPORT February 4, 2011 PREPARED FOR City of Stillwater 216 North Fourth Street Stillwater, MN 55082 MINNESOTA HISTORICAL & CULTURAL GRANTS This project has been financed in part with funds provided by the State of Minnesota through the Minnesota Historical Society from the Arts and Cultural Heritage Fund. tili COLLABORATIVE DesignGroup, iiic. 100 Portland Avenue South, Suite 100 Minneapolis, MN 55401 Phone: 612.332.3654 Fax: 612.332.3626 Contact: Craig Milkert, PE CDG Project Number 10018.00 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4, 2011 TABLE OF CONTENTS EXECUTIVE SUMMARY 1 INTRODUCTION 2 SCOPE OF WORK 2 REVIEW OF DOCUMENTS 2 OBSERVATIONS 3 DISCUSSION 4 RECOMMENDATIONS 5 APPENDIX A - PHOTOGRAPHS APPENDIX B - SITE DRAWING APPENDIX C - ARCHIVAL PHOTOGRAPHS &COLLABORATIVE ❑esignGroup,... HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 EXECUTIVE SUMMARY The ruins of the Hersey & Bean planing mill are located at the base of the bluff that extends adjacent to the east side of current TH36 and just to the west of a dirt access trail that parallels the St. Croix River in Stillwater, MN. The Hersey & Bean Planing Mill ruins have been Determined Eligible for the National Register of Historic Places as part of the Stillwater South Main Street Archaeological District. The walls are part of archeological site 21WA92. The ruins of the planing mill include an approximately 20 foot tall limestone wall constructed against the bluff, which has become unstable. Despite the collapse of portions of the rear retaining wall, the structural foundations of the ruins of the planing mill exhibit excellent integrity of location, materials, and association. The original construction of the stone walls for the Hersey & Bean Planing Mill used irregular shaped limestone with thin mortar joints. While much of the deterioration of the stone wall has occurred over the past 137 years, it is evident from the photo documentation that the tall west wall has significantly deteriorated within the past 4 years. The loss of stone is originating at the bottom of the wall, causing instability and collapse of the wall from the bottom towards the top of the wall. The face stones are literally falling in towards the bluff due to lack of support from the backup stone. The one factor that has been introduced to the building in recent years is the construction of the drainage ditch to the north and the culverts under the trail. This ditch drains water from the north and uses culverts under the trail to discharge water to the river. We believe that the water that is backing up at the base of the wall has softened or possibly eroded the soil from beneath the wall. Weakening of the soils beneath the wall and the corresponding progressive collapse has likely been occurring for a number of years. The wall at the south end of the site is also becoming unstable due to the erosion of soil from behind the wall. Due to safety reasons, restoration and stabilization of the tall west wall will require a large amount of deconstruction first. Reconstruction of the wall will be very expensive, impractical, and ultimately lose the historic character of the wall. Very little of the actual historic construction will remain, and the end result will be a re -constructed duplicate of the original. Our recommendation is to carefully de -construct the tall west wall down to a level approximately four feet above its base. The stones should be removed individually, starting at the top, to avoid collapse of the remainder of the wall and damage to the bottom of the wall. Although this method will result in the loss of a large portion of the historic building, it will result in a safe site for the public to experience this important piece of Minnesota history. Retaining the base of the walls will still show the footprint of the buildings. The other wall that should be considered for deconstruction is the south wall. Continued erosion of the soil and rock behind the wall are causing instability. This wall should also be deconstructed and stabilized to within approximately four feet of its base. The drainage ditch and culverts should be reconfigured to drain water away from the base of the wall and ruins. COLLABORATIVE DesignGroup,,.., 1 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 INTRODUCTION The ruins of the Hersey & Bean planing mill are located at the base of the bluff that extends adjacent to the east side of current TH36 and just to the west of a dirt access trail that parallels the St. Croix River in Stillwater, MN. The Hersey & Bean Planing Mill ruins have been Determined Eligible for the National Register of Historic Places as part of the Stillwater South Main Street Archaeological District. The walls are part of archeological site 21WA92. The City of Stillwater requested that Collaborative Design Group provide Structural Engineering and Historic Preservation services to investigate the collapse of the historic limestone wall of the historic Hersey & Bean planing mill on the southern end of the Aiple property adjacent to the St. Croix River and provide recommendations for its stabilization and/or repair. Following the localized flooding in the spring of 2010, a significant portion of the wall collapsed over a period of 8 weeks. After review of the situation with the City and a representative from the State Historic Preservation Office, it was decided that a modified scope of work would be pursued. SCOPE OF WORK The following is the scope of work performed: o Review existing documents for information regarding wall history and construction to determine requirements for restoration. o Perform site investigation of the limestone wall, including photo -documentation and measured drawings. o Provide Condition Assessment Report outlining the cause of the collapse and develop recommendations for both immediate stabilization and long term preservation. Review of documents The "Intensive Literature Search and Phase I/II Archeological Investigations for the St. Croix River Crossing Project" report prepared by Two Pines Resources Group, LLC dated May 2005 was reviewed and summarized as follows: The site encompasses the remains of the Hersey & Bean Lumber Company's steam - powered planing mill (1873-1906). This remains consist of the limestone ruins of the planing mill, including a wall with a window/door opening and two arched openings constructed of brick that marked a possible "water outlet" in the partially extant wall, and another that marked the opening of the flue that was excavated into the bluff. The site was recommended as a single contributing property to the NRHP-eligible Stillwater Cultural Landscape District. The planing mill was added to the Hersey & Bean Lumber Company complex in 1873. This mill, which was referred to as the "Little Mill," was constructed to the south of the main mill and was designed to cut the long pieces of lumber that were necessary for the construction of railroad bridges. In order to accommodate the length of these timbers, the cutting saw was actually constructed on a raised platform that extended out into the COLLABORATIVE DesignGroup,;,« 2 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 river. The planing mill was damaged by fire in 1887 and rebuilt on the same location. The planing mill was abandoned in 1906, when the Hersey & Bean Lumber Company ceased operation. The ruins of the planing mill consist of a 23-ft (7-m)-high limestone retaining wall constructed against the bluff, the remains of the limestone walls of the boiler room that were partially cut into the bedrock, and the underground brick -lined flue that extends 82 ft. to the west. Portions of the wall along the west side of the ruin have slumped creating large debris piles that obscure any interior features within the ruins. Despite the collapse of portions of the rear retaining wall, the structural foundations of the ruins of the planing mill exhibit excellent integrity of location, materials, and association. Observations Visual observations of the site and wall are recorded below. Photos are shown in Appendix A at the end of this report. The following rating system was used in assessing the building condition: • Good: The building component is new, with no apparent defects. • Average: The building component is able to perform its originally intended function in its current condition. Any defects are minor and do not affect the performance of the building component. • Poor: The building component is unable to perform its originally intended function in its current condition. The component has major defects, but is repairable. • Unacceptable: The building component is unable to perform its originally intended function in its current condition, and cannot be economically repaired. Replacement of the building component is required. OBSERVATIONS REFERENCE PHOTO RUINS WALLS • The planing mill ruins lay at the base of the bluff and west of the dirt access trail. The river is east of the trail • The condition of the limestone walls of the planing mill varies from poor to unacceptable across the site. • The center portion of the tall west wall has progressively collapsed from July of 2004 to April 2010 COLLABORATIVE DesignGroup,- Photos 1 & 2 Photos 3 - 8 Photos 9 - 17 3 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 OBSERVATIONS REFERENCE PHOTO • The wing wall perpendicular to the tall wall on Photos 18 & 19 the north end is unstable and in unacceptable condition. This wall was originally constructed with two wythes of stone. Only the outer wythe is still extant. • The wall at the far southern end of the site is Photos 3, 5, & 20 unstable due to erosion behind the wall, ands is in unacceptable condition. • Large stone have been placed at the top of the Photo 21 tall west wall. The instability of the wall makes support of these stones questionable. • The tall west wall was constructed by laying up Photos 22 & 23 the outer wythe of stone and filling the void between the outer wythe and bluff with stone • The wall appears to have collapsed due to lack of support at the bottom of the wall. • A weak and deteriorated mortar is present in Photos 24 & 25 many of the stone joints. • A drainage ditch is present extending from the Photo 26 north. • The spring flooding of the river extends over the Photo 27 trail, causing the water to back up in the culverts and the ditch. Standing water was present at the base of the wall. • The ditch ends at the base of the tall west wall, Photos 28 — 30 and drains to the river with a steel culvert and a PVC culvert under the trail. • The steel culvert appears to be clogged with debris Photo 29 DISCUSSION The original construction of the stone walls for the Hersey & Bean Planing Mill used irregular shaped limestone with thin mortar joints. The mortar throughout is in poor to unacceptable condition. The west walls of the building were constructed against the bluff. While these walls may appear to be retaining walls, they were actually relying on the bluff for support. No footings were observed beneath the walls during this investigation, but it is unlikely that any exist. Typical construction from this era would have the stone walls constructed directly on the ground surface. (COLLABORATIVE DesignGroup,;,„ 4 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 While much of the deterioration of the stone wall has occurred over the past 137 years, it is evident from the photo documentation that the tall west wall has significantly deteriorated within the past 4 years. In fact, the majority of the collapse occurred in March and April of this year. So, the question that needs to be answered is what has changed in recent years to create the instability of the wall? The original wall construction battered, or leaned the stone wall against the bluff. As the face stone was laid up to create the finished interior face of the building foundation wall, random and sometimes loose stones were placed as a backup between the face stone and the bluff to provide structural integrity. From our observations, it is apparent that the current instability is caused from the loss of the backup stone between the face of the wall and the bluff. The loss of stone is originating at the bottom of the wall, causing instability and collapse of the wall from the bottom towards the top of the wall. The face stones are literally falling in towards the bluff due to lack of support from the backup stone. The one factor that has been introduced to the building in recent years is the construction of the drainage ditch to the north and the culverts under the trail (see Site Plan drawing in Appendix B at the end of this report). This ditch drains water from the north and uses culverts under the trail to discharge water to the river. It is likely that the steel culvert was installed initially, and the PVC culvert was added when the steel culvert became clogged. The culvert location is at the base of the tall west wall. During our site visit on March 24, 2020, the river had risen to the point of covering the trail and backing water up through the culverts and into the ditch. A large pool of water had formed at the base of the wall. The water had receded before our site visit on April 5, 2010, draining the pool and exposing the culverts. We believe that the water that is backing up at the base of the wall has softened or possibly eroded the soil from beneath the wall. A compromised foundation for the wall would cause a progressive collapse as has occurred. When the stones at the base of the wall fall away, the back up stone behind the face stone will eventually fall out also. As the back up stone continue to drop, the integrity of the face stone is compromised, causing the face stone to fall into the wall. It is easy to understand that the wall will continue to collapse in on itself. This weakening of the soils beneath the wall and the corresponding progressive collapse has likely been occurring for a number of years. It is evident that many of the other stone walls have collapsed over the years. The two main areas of apparent wall instability are the small wing wall at the far north end of the tall west wall (photos 18 & 19), and the wall at the far south end of the site (photo 5). By examining the photos taken since 2007, it is evident that one half of the thickness of the wall has deteriorated and fallen from the wall since 2007. This has left the wall unstable and in danger of collapse. The wall at the south end of the site is also becoming unstable due to the erosion of soil from behind the wall. RECOMMENDATIONS Due to safety reasons, restoration and stabilization of the tall west wall will require a large amount of deconstruction first. The wall is currently too unstable and unsafe for workers to begin replacing the stone in the collapsed area of the wall. The top portion of the wall, along with the large stones placed at the top, are in danger of falling on the COLLABORATIVE DesignGroup,;,« 5 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4. 2011 workers during restoration. The best method of restoring the wall is disassembly and reconstruction. Re -pointing the entire wall with an appropriate mortar would be required. Reconstruction of the wall will be very expensive, impractical, and ultimately lose the historic character of the wall. Very little of the actual historic construction will remain, and the end result will be a re -constructed duplicate of the original. Our recommendation is to carefully de -construct the tall west wall down to a level approximately four feet above its base. The stones should be removed individually, starting at the top, to avoid collapse of the remainder of the wall and damage to the bottom of the wall. Although this method will result in the loss of a large portion of the historic building, it will result in a safe site for the public to experience this important piece of Minnesota history. Retaining the base of the walls will still show the footprint of the buildings. We have included a drawing of the site (Appendix B) and archival photographs of the wall (Appendix C) as part of this report. The other wall that should be considered for deconstruction is the south wall. Continued erosion of the soil and rock behind the wall are causing instability. This wall should also be deconstructed and stabilized to within approximately four feet of its base. The drainage ditch and culverts should be reconfigured to drain water away from the base of the wall and ruins. Relocating the culverts farther to the north, and filling in the ditch and low areas near the base of the wall will help to stabilize the soils. Slope of the soils should promote drainage away from the ruins site. (COLLABORATIVE DesignGroup,- 6 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4, 2011 APPENDIX A PHOTOGRAPHS COLLABORATIVE DesignGroup,;,,.. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 1 - View of site looking north along trail. Photo 3 - Planing Mill ruins looking north. Photo 2 - View of site looking north along trail. Photo 4 - Planing Mill ruins looking south. February 4, 2011 COLLABORATIVE DesignGroup,.. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 5 — Wall elevation Photo 7 — Wall elevation Photo 6 — Wall elevation Photo 8 — Wall elevation February 4, 2011 COLLABORATIVE Design GTOup,i,��. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 9 — Tall west wall - 7/30/2004 Photo 10 — Tall west wall - 3/26/2007 February 4, 2011 COLLABORATIVE DesignGraup,.,w. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 11 - Tall west wall - 4/30/07 Photo 13 - Tall west wall - 3/24/10 Photo 12 - Tall west wall - 10/5/2009 Photo 14 - Tall west wall - 3/26/2010 February 4, 2011 COLLABORATIVE DesignGroup,. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 15 - Tall west wall - 4/5/2010 Photo 17 - Tall west wall - 4/20/2010 Photo 16 - Tall west wall - 4/8/2010 Photo 18 - Unstable wing wall. February 4, 2011 COLLABORATIVE DesignGroup,. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 19 — Unstable wing wall. Photo 21 — Top portion of wall with large stones. Photo 20 — Unstable wall due to erosion. Photo 22— Collapsed portion of tall west wall. February 4, 2011 COLLABORATIVE DesignGraup,.,w. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 23 — Loss of back-up stone behind face stone. Photo 25 - Stones mortared in place. Photo 24 — Stones mortared in place. Photo 26 — Flooded drainage ditch extending north of site. February 4, 2011 COLLABORATIVE DesignGraup,.,w. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Photo 27 - Drainage ditch flooding base of wall. Photo 29 - Partially clogged steel culvert on river side of trail. February 4, 2011 Photo 28 - View of drainage ditch with steel and PVC culverts. Photo 30 - Outlet of PVC culvert on river side of trail. COLLABORATIVE DesignGroup,;,. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4, 2011 APPENDIX B SITE DRAWING COLLABORATIVE DesignGroup,;,,.. BLUFF LINE NORTH WING WALL DRAINAGE TALL DITCH WEST WALL r SOUTH WALL • - EXISTING LIMESTONE WALLS PVC CULVERT STEEL CULVERT Ce COLLABORATIVE DesignGroup,.. H E RS EY & BEAN PLANING MILL DATE 02-04-2011 SK SCALE 1/16" = 1'-0" SITE PLAN DR. BY MBN CK. BY JOB NO. 10018.00 © COLLABORATIVE DESIGN GROUP, INC. 2009 HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT FEBRUARY 4, 2011 APPENDIX C ARCHIVAL PHOTOGRAPHS COLLABORATIVE DesignGroup,;,,.. HERSEY & BEAN PLANING MILL WALL STABILIZATION REPORT Archive Photo 1 — West wall • Archive Photo 3 — West and North wall Archive Photo 2 — West wall Archive Photo 4 — North wing wall February 4, 2011 COLLABORATIVE DesignGroup,.,i,