Project Agreement Number 2210-13-0001 Between The National Center for Preservation Technology and Training Natchitoches, Louisiana and The Southeastern Archeological Center Tallahassee, Florida
Michael Russo and Chiang Shih
Executive Summary
This report describes the results of the Friction Cone Penetrometer (FCP) project partially funded by the National Park Service’s (NPS) National Center for Preservation Technology and Training (NCPTT) with funds provided in 2013 and the NPS’s Southeastern Archeological Center (SEAC) with funds provided from 2013 to 2016. Using the NCPTT funds, SEAC entered into a Cooperative Ecosystems Study Unit (CESU) agreement with the Department of Mechanical Engineering, Florida State University (FSU) to develop the prototype FCP. In the end, FSU contributed an untold amount of additional funding in support of its students working on the project as they endeavored to fix problems beyond the timeline funded by NCPTT and SEAC.
Ultimately, FSU teams could not manufacture a workable prototype FCP due to mechanical problems whose corrections lay beyond the given time constraints and funding of the project. In December 2016, FSU returned all purchased equipment to SEAC and submitted their final report (Pace 2016; Appendix F) which described the problems with the final prototype, one of three prototypes FSU constructed. In the end, we conclude that the concept of distinguishing archeological soils from non-archeological soils by measuring differences between soil cohesion and soil resistance is theoretically sound. But taking proven large-scale hydraulic technology that measures these differences effectively down to a portable mechanical instrument was too problematic to produce a working prototype with a limited budget.
Background
In 2013, SEAC’s Michael Russo applied for and obtained a grant from NCPTT to develop and test a prototype FCP which would measure soil resistance and cohesion by pushing a small diameter rod (< ½") through the ground. The purpose of the FCP would be to test large tracts of land requiring archeological survey by identifying positive FCP responses for archeological soils, typically called organic midden soils, instead of using more labor intensive shovel tests.
For centuries, the method of pushing simple metal probes through the soil has been used to locate archeological objects and features by registering the operator’s feel of the different resistance and the sound the rod made as when it encountered objects. This simple technique has been used to find pots and skeletons in ancient Native American sites (Moore 1918) and across the world to find archeological objects from small items to large stone pyramids and monuments buried under Egyptian sands. One downside of probes is that they are susceptible to the subjectivity of the prober-some probers may feel an object as the probe grazes it, while others may not. Any positive hit would also require groundtruthing. For the modern archeologist seeking not to find objects, per se, but to define the boundaries of entire sites, hand-pushed probes were of limited utility in that extensive groundtruthing might be required if hundreds of positive hits were encountered. In addition, for archeological sites typically contain mostly soil with only a relatively small number of small artifacts, the chances of a probe hitting a perceivable object are statistically unlikely. As such, surveying land for archeological sites using only a probe that requires skilled and experienced probers, extensive ground truthing, or dense deposits to be successful is problematic. In the absence of skill or dense deposits, entire sites could be overlooked. For these reasons, extensive probing to find or bound sites has never gained favor among most archeologists and simple shovel testing has become the standard archeological survey methodology to find and define site boundaries.
In the 1960s, in addition to the simple metal rod, another type of metal probe, the cone penetrometer (CP) began to be used sparingly by archeologists. Employed in engineering and agriculture, CPs are used to measure soil resistance or compactness to determine the soil’s suitability for road construction or crop growth. Although many CPs are pushed through the ground just as simple metal rods are, others use weights to systematically pound a rod through the soils in question. In either case, CPs overcome the subjectivity of simple hand-pushed metal rods by providing an objective measure of soil resistance through a mechanical cell attached behind the probe tip that can be read by the operator on a mechanical, analog or digital gauge usually attached to the handle. Archeologists have typically to used CPs find unmarked pits at abandoned cemeteries where the disturbed soil of grave backfilled soil is usually less compacted than the surrounding undisturbed soils (e.g., Hailey and Ball 2006; Trinkley 1999, 2007; Trinkley and Southerland 2007; Zeidler 2005).
Adapted from the CP, a much larger, hydraulically driven instrument, the Friction Cone Penetrometer (FCP) has been commercially developed recently to distinguish one type of soil type from another. Mounted on large trucks and used extensively in mining exploration, in building and road construction, and to a lesser degree and more recently in agriculture, the tool measures both the compactness (resistance) of the soil as well as the soil friction and other soil traits to establish whether the behavioral characteristics of the soils are suitable for mining, road construction, or planting crops. Comparing the measures of the FCP to standard soil behavioral types (SBT), traits of soil can distinguish between SBTs such as clay, silts, sands and gravels.
These soils types are by standard definition distinguished by grain sizes. Grain size differences result in differences in resistance and friction as a probe is pushed through the soil. Russo hypothesized that grain size differences and relatively loose compactness are two features that might distinguish archeological middens from their surrounding natural soil matrices. As such, Russo proposed to develop a portable version of the hydraulic FCP to locate archeological midden sites.
National Need
Because current FCPs on the market require enormous trucks to haul the hydraulically driven probe and because the typical probe is too large (>3") to test for an archeological site without destroying large chunks of the site in the process, Russo proposed that a smaller version of the FCP, powered by pushing or pounding the probe through the soil matrix could be developed to test for archeological soils. The probe footprint would be less than ½" (1.3 cm) diameter, thus reducing the amount of soil disturbance associated with the larger hydraulic 3" (8cm) probe and typical 12" (30 cm) shovel tests. The FCP could aid in the discovery and bounding of certain types of archeological sites, i.e., midden sites, without producing a lot of shovel test holes or artifacts, the latter of which are currently overwhelming the limited storage capabilities of curation facilities in the U.S.
This “curation crisis," in part, has arisen over the last half century from the enforcement of the National Historic Preservation ACT (NHPA) Sections 110 and 106 and other government requirements to find and bound the extent of archeological sites. In the recovery of excessive numbers of artifacts and ecofacts resulting from these legally mandated surveys, artifacts languish in museums and other curations facilities awaiting expensive analysis, cataloging, and curation that never seem to come. The proposed FCP would help minimize the number of archeological objects that require expensive processing and storage by producing proxy data for artifacts by identifying the organic midden soils in which they are found at some sites instead of recovering the artifacts themselves. With the use of the FCP in place of shovel testing, the number of artifacts typically associated with large-scale survey recovery could be reduced, while at the same time the extent of a midden site could be demarcated.
The FCP could also be used to mitigate sites in advance of sea level changes. Due to rising sea levels, many coastal and riverine archeological sites are being submerged and lost before archeologists can map and investigate them. Coastal shell middens and mounds are particularly prone to exclusion from intensive survey efforts, in part, because agencies are often not required to excavate in areas of standing or high groundwater where these sites are typically located. Technological tools (e.g., GPR, magnetic resistivity, gradiometery, LiDAR) that could help map site and feature locations in lieu of excavations are also of limited use in these environments due to either the sites’ inaccessibility and/or the remote sensing technologies’ inabilities to operate in fresh- or salt-water-saturated or submerged soils. Russo proposed that the FCP would be a technology that could overcome or reduce the logistic and technological restrictions of near-coast midden sites and could aid in the identification, recordation and even preservation of these marginally recorded sites.
Project Proposal
In 2013 Russo submitted the proposal entitled “Cone and Friction Cone Penetrometer Applications to Archeological Organic Midden Deposits" to NCPTT. He identified the research priorities as adapting an inexpensive and portable technology to measure resistance and other soil characteristics to help archeologists determine the horizontal and vertical extents of midden soils while minimizing excavation. He suggested that use of the minimally invasive tool would reduce the number of artifacts recovered and the concomitant need for their curation when performing Section 110 and 106 level surveys and other tasks requiring the identification and mapping of shell and other organic middens. He noted that if successful, shell and other middens susceptible to coastal erosion could be more quickly found and bounded in mandated surveys using the proposed FCP.
Although through the course of testing prototypes, the partnering Department of Mechanical Engineering at FSU would frequently change the main features of the FCP, initially Russo proposed to adapt an off-the-shelf hand operated CP. The Dynamic Cone Penetrometer Data Acquisition System by Vertex measured only soil resistance. Russo propose to turn it into an FCP by adding a friction sleeve. As Russo envisioned the prototype, the FCP would be equipped with a laser depth gauge, Bluetooth system, and data logger to speed up recording. The speed would make the tool economically efficient for large-scale mapping in logistically difficult terrains.
Project Science
In his own work, Russo had for over 20 years been systematically pushing probes up to 4 meters in length to map the depth and distribution of subsurface archeological shell middens and other mounded deposits (e.g., Russo et al. 2002). When he trained his colleagues in the probing technique, however, he discovered that not all could determine where shell began and ended in the vertical column of the probing rod. Some could not “feel" shell at all if the deposits were not dense. This failure in replicating measures of shell depth among probe practitioners resulted in Russo searching for a more objective and replicative probe. He first looked at off-the-shelf cone penetrometers (CPs) that measured only soil resistance as a possible alternative.
In CPs, Cone Index (CI) is the measure of force required to push a cone point through soil. The amount of force correlates with soil resistance which may be linked to a number of causes including the chemical and granular make-up of the soil or, for the surface soils that archeologists most commonly deal with, the amount of compaction. If a soil is disturbed, dug up and redeposited, the amount of compaction may be less than that of the undisturbed soil surrounding it. For road construction, a CP may be used to test the suitability of soil for supporting the road and the CI is usually compared to a known standard. For archeologists, the amount of compaction/disturbance is typically inferred from the CI when compared to a control, undisturbed sample of the same soil type, usually nearby.
An as yet untested application of the CP in archeology is the identification of differential subsurface resistance due to factors other than soil compaction. Because archeological objects (e.g., pots, bricks, shell) are more resistant than even the most compacted soils, the objects should yield indices of force that differentiate them from the surrounding soil matrices. While using CPs to locate widely dispersed objects such as potsherds or lithic debitage would be like looking for needles in haystacks, identifying the vertical and horizontal extent of dense deposits of objects such as shell or organic midden soils could be quite effective with CPs. CP recordings recovered from systematically placed points across known or unsurveyed areas would allow the location, depth, and thickness of those shell deposits or organic soils to provide a detailed three dimensional map of the middens (e.g., see midden density maps in Russo et al. 2002; Russo et al. 2011).
As mentioned, different soils are classified in part by differences in their grain or particle sizes, with, for example, clays and silts consisting of finer particles while sands and humic layers consist of coarser grains. Because fine-grained sediments have more surface area than coarse- grained sediments, they are more cohesive. That is, they result in a greater amount of friction when a probe is pushed through them because more grain than air rubs against the rod. (Anyone who has worked in soils intuitively knows that clay is harder to dig than sand). This variability in friction among differently-textured soils can be measured with a cohesion sleeve placed above the tip of the cone penetrometer (Kianirad 2011:26-27; Rooney et al. 2001). The addition of the friction sleeve turns the CP into an FCP. The proposed FCP was intended to distinguish organic archeological middens soils (typically composed of coarse sands with coarser-grained organic inclusions consisting in part of decaying plant and animal remains as well as objects of human manufacture) from finer-grained, undisturbed minerals soils such as finer-textured sands, silts, and clays.
While no hand-held portable FCPs existed at the time of the proposal, two types of portable CPs were described in the literature: static and dynamic. Portable static CPs rely on a steady push by its operator into the soil at a specified rate. Static CPs have been criticized due to inter- and intra- operator variability in the required “steady" application of force (Herrick and Jones 2002; Jones and Kunze 2004:3). The claim is that no one, let alone two people can push at the same reliable rate from top to bottom of a probing. However, some claim that with practice, consistent results, assumed to have been derived from consistent application of force can be obtained (Trinkley 1999:8).
In contrast to the static CP where consistency of force may be hard to maintain, the dynamic CP or DCP relies on a given weight being dropped from a known height to obtain a reliable measure of applied force. While the static model is potentially more portable (i.e., fewer parts, less weight to carry around) and faster (Kees 2005:9), Russo proposed to build a dynamic model to assure replicability and quantification of tests. Although somewhat counterintuitive, personal experiences with probes suggested to Russo that due to increased friction, sand required more force than shell to push a probe through. Shell requires quick, momentary impulse force to pierce the shell, but less force to pierce the loosely packed soil and air between shells. That is, to get through shell with a probe, one must lift the probe up and slam it down with a lot of force. Once an obstructive piece of shell is pierced by the probe tip, however, little force may be needed to push it through air pockets or loose soil spaces between shells. Sand, silt and clay-based midden soils, on the other hand, due to less air and more grains would need more impact force overall, meaning more lifts and drops. Part of the proposed laboratory testing goals was to determine the best dynamic weight protocols to use to pound the probe through all types of soil. Russo anticipated that shell deposits would record graphically and numerically as peaks and valleys of greater and smaller resistances as shell and air pockets were encountered alternately. Non-shell bearing soils, he reasoned, would more likely record as an increasing but steady graph line as depth increased. He anticipated that data loggers and strain-gauges to accommodate the wider- ranging force variables would need to be obtained or manufactured.
Developing the Prototypes
One of the initial goals of the project would be to test and determine the limits of stress that the cohesion sleeve and strain gauges could handle. The FSU engineering teams constructing the FCP might need to use stouter sleeves or gauges to facilitate its application to severe archeological conditions that contained dense amounts of hard objects like shell. The overall goal would be to develop an FCP that measures both shell and other organic midden deposits by recording the cone index obtained by the CP, the friction recorded by the FCP, and the ratio of the two in order to differentiate shell middens and other midden deposits lacking shell from background non-archeological soils.
Despite all the inspiration shell middens provided for the initial idea of the FCP, ultimately the idea of testing shell middens would be abandoned. Once into the project, the engineering teams and Russo worried that repeated impacts with shell would break the fragile friction sleeves. In addition, large weights would need to be carried to break shell, thus reducing the idea that the instrument would be lightweight and portable. Difficulties in adjusting weights needed to break through hard shell or other objects had been identified and a research model of an FCP (cf., Kianirad 2011:27). With these caveats in mind, the organic middens that would be tested and to which the FCP would be designed for were limited to organic soils with little or no shell or that contained shell deposits that were not dense.
SCDP Team 16 FCP Prototype
The project began with the award of the NCPTT grant for $25,000 to SEAC in 2013. In June and July, NCPTT and SEAC signed an agreement (Appendix A) outlining the goals of the project, the budget, the tentative schedule, a list of outreach products related to the FCP, and the deliverables, which include this final report. Prior to the award Russo had contacted Dr. Chiang Shih, head of Florida State University’s Mechanical Engineering Department to develop the FCP prototype and testing through his student Senior Design Capstone Program. The program is run through two semesters of the final year of graduating engineering students who have mastered all the skills within the traditional engineering disciplines.
“The purpose of the Senior Design Project is to pull (the engineering disciplines) all together and apply them towards the design and implementation of a ‘product’, and to afford the students an opportunity to experience team-based design under conditions that closely resemble those that will be encountered in industry. Students must develop and sharpen skills in team organization, time management, self-discipline, and technical writing, in order to be successful in this course. An important goal of this course is to expose students to a ‘hands-on’ experience in which they have to specify, design, and produce a full-system beginning from relatively ill-posed needs as stated by a ‘customer’. This objective has to be accomplished while working as a team, and under time pressure."
Russo chose to partner with Shih through Capstone because of Shih’s enthusiasm for the project and the close proximity of his FSU facilities and students (just two buildings down from the SEAC facilities). Alternate professional mechanical engineering firms were approached but were not interested in the project due to low probability of high economic returns. In June of 2013, Shih submitted his proposal and budget for the project (Appendix B), largely modeling it on the NCPTT/SEAC Project Agreement (Appendix A).
In the summer of 2013, Shih and Russo chose the Dynamic Cone Penetrometer Data Acquisition System for the student team to adapt into an FCP (Figure 1). Before the 2013 Capstone project began, Shih hired a student, Richard Carter to work with Russo and get background research completed on off-the-shelf cone penetrometers and other data the Capstone Team would need before they started in the fall. Carter’s report for the students entitled “Dynamic Cone Penetrometer With Friction Sleeve" was included in Russo’s 2014 Progress Report to NCPTT as Appendix 1: “Preliminary Introduction and Guide to the Friction Cone Penetrometer Project" (Appendix C).
Source: U.S. Department of the Interior, National Park Service
