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Fort Union Sections of Walls

Analysing in Section
Fort Union’s fragile adobe walls have consistently proven difficult to document given their irregular shapes, complex surface topography, and  layers of protective shelter coats. Understanding the walls’ geometry and massing, including attributes such as wall height, top profile, transverse cross-sections, and planar attitude or plumbness could provide crucial information about the current physical status of individual walls, and help identify  those walls most at risk from collapse. Building on past methodologies, a profilometry system was devised, using a relatively rapid, low tech, approach of recording, to select adobe walls based on cross-sectional profile analysis. This method, in combination with other physical and environmental data, can provide important information in the condition assessment of the ruins, allowing comparative analyses that the NPS can use to develop risk typologies for the standing walls.

Existing Methods of Recording the Site
The documentation methodology presently used to monitor the deterioration of the adobe walls at Fort Union, as outlined by the current NPS maintenance plan, is twofold: digital photographic recording, consisting of ‘before’ and ‘after’ photographs and descriptive written notations to record areas of deterioration, a history of past treatment methods, and procedures for cyclical treatment. In recent years, however, this monitoring practice has proven time consuming, given the number of walls to survey.  Moreover, access to the tops of high walls takes time and can be dangerous if the walls are leaning and unstable. Nonetheless, using photography and notes cannot begin to accurately record the shape of these complex walls. Methods are limited in their ability to show three-dimensional change.

Recording irregular eroded wall shapes accurately is a difficult feat because the partially eroded walls:

1) do not have straight surfaces from which to consistently measure
2) are fragile and friable, so any method of measurement should minimize direct contact to avoid damaging historic fabric
3) are too tall to easily compare the two faces or appreciate the approximate thickness from grade.

Laser Scanning
Team members comparing laser scanner data with the data taken using the profile comb.
Comparing the Profiles
Because Fort Union’s adobe walls were built on top of raised stone foundations of similar width, comparison of the current  adobe wall thickness to the stone foundations ensures a relatively accurate measure of surface loss from weathering (assuming later shelter coats are removed before recording).
By comparing longitudinal wall profiles, rather than transverse cross sections, we are looking at the morphology of discrete wall elevations removed from their context. This visual takes away the context of the wall by only considering one side; however, transverse profiles help create wall types that can assist better in identifying deformations, types and degrees of severity. Longitudinal elevations provide a way of examining the walls that is different from transverse cross section which can be valuable when assessing different sides of a wall and how they are responding to their respective microclimate. For example, we can compare all of the wall faces based on orientation that do not have an adjacent wall to protect them. This comparison would indicate the degree of variability of all of the walls that do not have protection in the form of another wall. While the method does not allow us to measure lean or loss of area, it can help us to examine the micro-morphological differences in the patterns of deterioration that affect the elevation.
Comparing Sections
The transverse cross sections of the walls can illustrate multiple factors that determine overall wall shape. If we consider “plumb” walls to be those that are not experiencing uneven deterioration, deformation, or lean, walls that are not plumb all have factors that are contributing to their lean and/or loss of material. For walls that are middle wasting, something is causing material to be lost at a wall’s approximate midpoint. For bellying, material is lost in certain areas while maintained in others, resulting in a curved line. We can begin to attribute various factors that lead to the shapes seen in the profiles and cross sections such as basal erosion and plastic deformation. Basal erosion from capillary moisture occurs when water or snow sits at the bottom or ledge of a wall. When this water is absorbed by the adobe wall, it travels into the adobe by capillary suction and can cause the clay binder in the adobes to dissociate and the area to lose mass, solubilize and crystallize soluble salts, or freeze and thaw in cold weather, also causing a reduction in basal mass and section. Wall bases that remain damp for long periods of time are also prone to deformation from reduced strength and can contribute to wall lean.  With these illustrations, we can begin to analyze the morphological data while experimenting with new ways to visualize and compare it in a qualitative manner.
A comparison of the measure profile of a wall against its known original shape and height.
Profiling Walls
Team members using a profile comb on a wall.
Advanced Techniques
More advanced methods of recording, such as photogrammetry and laser scanning, can provide a three dimensional digital model of a wall’s surface, its mass, and an infinite number of cross-sections, but have their limitations for small parks with limited budgets. The results of the profilometry method were compared to photogrammetric and laser scanning methods to critically compare the usefulness of each method as well as the relative accuracy of this simple and cost effective approach.
Photogrammetry and laser scanning require relatively high levels of technical expertise, especially for post processing manipulation of data, and have  high initial costs for hardware/software purchase and training unavailable to NPS and other organizations responsible for cultural heritage management. Comparing the profile data with the the highly accurate laser scan data showed that measurements taken with the profile gauge were well within acceptable tolerances for the level of work being accomplished. The ability to record an accurate cross-sectional profile of walls with a profile gauge, developed by the CAC based on profile combs used in carpentry, proved to be a viable low-tech alternative that can accurately record overall geometry and mass shape of a wall as well as plumbness (degree of out-of-plane). The only immediately apparent limiting factor in this method is the extreme locality of the profile for a given length of wall; howver, for the needs of the project, this limitation does not seem to be a significant issue. The rapid assessment form employed in the first step of this assessment process is intended to limit the number of walls which require a more intensive assessment where the profile gauge would be employed.
Comparing profiles to each other by grouping based on potential contributing factors.
This project contributes to the ongoing research by the University of Pennsylvania’s Center for Architectural Conservation (CAC) to develop a risk assessment plan and vulnerability index for ruined structures in Vanishing Treasures parks. Building on work from 2017, which confirmed the accuracy of the profile gauge as a documentation method to capture the morphology of the ruined adobe walls at Fort Union. The profile data recorded during fieldwork was processed using the same methodology, but has several more walls, and wall ‘types.’ In the second part of this project, we critically analyze the usefulness and feasibility of the three methods for documenting and monitoring wall conditions. The results can contribute to the future recording and analysis of risk at FOUN. Although specifically crafted for measuring the adobe walls at Fort Union, the profile gauge method could have applications at other archeological or historic sites where traditional methods of documentation are not suitable or high tech methods unavailable. As conservators, we have a duty to determine the usefulness of such technologies and for what projects they would serve a direct and valuable purpose. This project hopes to provide information that will inform Fort Union’s management and allow an assessment of wall conditions and the vulnerability of the standing adobe ruins now and in the future.
Sections presented below show the extent of variation found in the walls of Fort Union. This variation can be critical for understanding failure in both the immediate and long term future.