Patent Application
20210123305
The following is a tabulation of some prior art that presently appears relevant:
We, Brian L. Fritz and Allen C. Fritz, have invented an apparatus and method for conducting archaeological surveys and test excavations using a combined bucket drill and soil screen.
An initial step in an archaeological survey is to determine if archaeological deposits are contained within the ground across a given survey area. The long-accepted and established method for finding archaeological deposits and sites is to manually dig or excavate a round or square hole using a spade shovel. These small diameter holes are called shovel test pits (STPs). Hole diameters or widths vary from 30 cm to 57 cm depending upon regulations established by each state or federal agency. STPs are dug at regular intervals across the survey area. An interval of 15 meters or 50 feet is commonly prescribed by regulatory agencies.
Soil is removed from the STP in 5 or 10 cm excavation levels and placed in a portable screen box that is designed to separate and remove cultural artifacts from the soil. A typical hole size for the hardware cloth within the screen box is 4 holes-per-inch, also known as ¼″ hardware cloth. If present, artifacts are collected, bagged, and inventoried from each excavation level within each STP. Cultural artifacts found within a test hole indicates the presence of an archaeological site. The horizontal boundary of an archaeological site can be determined by the presence or absence of cultural artifacts excavated from test holes that are spaced at regular intervals across the survey area. The vertical limits of archaeological deposits can be estimated by documenting the depths of excavation levels from which cultural artifacts are recovered.
Manual excavation of STPs is physically demanding and costly in time and labor. Manually excavated STPs vary in hole diameter or width, causing variations in the volume of soil that is sampled between STPs and reduced accuracy within the test results.
STPs are excavated to the lowest depth at which archaeological deposits can potentially occur. The potential depth of archaeological deposits is dependent upon the geological setting of the survey location. In locations where archaeological deposits are typically found at depths of less than one meter, STPs are manually excavated with spade shovels. As the hole becomes deeper, it is more difficult to maintain the proper hole diameter, resulting in the walls of the test pit sloping inward to a smaller diameter. Undersized STPs result in under sampling of the archaeological deposit at deeper levels, introducing a serious and undesirable bias within the sampling strategy (Fritz 2018). It is important to remember that linear changes in the diameter of a circle result in exponential changes in that circle's area and the volume of any cylinder formed by that circle.
A=πr
2
V=Ah
Whereas, A equals the area of the circle, r equals the radius of the circle or ½ the diameter, h equals the height of a cylinder, and V equals the volume of the cylinder or the volume of the STP excavation level.
In Pennsylvania, guidelines for conducting archaeological surveys established by the Pennsylvania Historical and Museum Commission (PHMC 2017) require excavation of STPs with diameters of 57 cm. In a hypothetical STP, let us assume that the diameter of the STP is 57 cm at the ground surface, but due to the difficulty of excavating with a spade shovel, the walls of the STP slope inward to a diameter of 40 cm at a depth of 80 cm. Soil is removed in 10 cm levels. The volume of soil removed for each 10-cm level can be easily calculated for the two diameters. When comparing the results of these calculations it becomes apparent that the 30% reduction in STP diameter results in a 51% reduction in the volume of soil removed and screened. A 51% reduction in soil volume introduces a serious sampling bias that under samples archaeological deposits at depths of 80 to 100 cm.
The deepest archaeological deposits are buried along streams and rivers where soils have accumulated from multiple episodes of overbank flooding. Due to their small diameter, manually excavated STPs are inefficient for digging to depths of more than one meter. Because of this deficiency many regulatory agencies require the use of larger, manually excavated one-by-one-meter-square (1 m2) test pits to sample archaeological deposits that are more than one meter deep. In this type of excavation pit, workers enter the pit and perform the work from the floor of the pit.
Archaeological deposits that are more than one and one-half meters deep may require even larger test pits or installation of approved wall shoring to meet Office of Safety and Health Administration (OSHA) standards for worker safety due to the increased potential and danger of wall collapse. Therefore, the cost in labor and time for archaeological testing increases as the potential depth for archaeological deposits increases. In addition, excavating test pits deeper than one meter requires workers to enter the test pits, thus increasing the health and safety risks to workers resulting from falls, entrapment from collapsing excavation walls, and breathing air within confined spaces. Costly and sometimes dangerous manual excavation of archaeological test pits represents the predominant prior art in conducting archaeological surveys.
Mechanized soil augers, earth drills, hole diggers, earth boring machines, caisson drills, posthole augers, spiral augers, bucket augers, bucket drills, and similar machines are used in the construction industries to dig STP-sized holes. All employ a prime mover vehicle such as skid-steer loader, excavator, or drill rig from which a mechanism lowers a rotating auger and digging edge into the ground. Once filled with soil, the auger is lifted from the hole, and the soil is emptied from the auger. If the hole needs to be excavated deeper, then the auger is returned to the hole for the next extraction of soil. Earth drills and soil augers are constructed in three basic types, open flights that spiral around a central shaft, enclosed drilling buckets with cylindrical walls and a digging edge with inlet holes in its bottom plate, and a combination of spiral flights and enclosed bucket.
Augers with open spiral flights are unsuitable for archaeological applications because the open flights permit the mixing of soil and artifacts from multiple depths. Drilling buckets with closable inlet ports are better suited for archaeological applications because the enclosure encapsulates the excavated soil from a discrete layer and prevents mixing of soil from multiple depths. Digging edges located along inlet ports in the bottom plate lift soil into the drilling bucket as the bucket is rotated into the ground. Soil is emptied from the drilling bucket through a hinged bottom plate. Examples of drilling buckets are included in U.S. Pat. No. 2,873,950 (Kandle 1959), 6,533,048 (Groce et al. 2003), 8,615,906 (Matthias et al. 2013), and European Union patent 1,640,507 (Reich).
Swivel bottom drilling buckets allow the operator to close the inlet ports prior to lifting the bucket from the hole. When the bucket is rotated in the digging direction the bottom plate partially rotates to a position where the inlet holes are open. Once the bucket is filled, the operator rotates the bucket in the opposite direction and the bottom plate rotates to the closed position. Examples of augers with closable inlet ports include France patent 2,832,438 (Durmeyer et al. 204) and European Union patent 1,640,507 (Reich 2006).
Through my own trials and research, I have determined that these construction machines and methods are unsuitable for archaeological applications. They lack the capacity for precise depth control, and they lack the ability to extract and process discrete volumes of soil without mixing cultural artifacts from multiple excavation depths. None of these construction machines and methods combine the process of excavating soil from STP-sized holes with a process for screening the soil and collecting artifacts from discrete excavation levels. Rotary screens driven by prime movers have been proposed in U.S. patents 928,965 (Hanna 1909), 3,208,593 (Dietert 1965), and 5,301,813 (Schnittier 1994). However, such rotary screens have not been incorporated into a single apparatus for archaeological test pit excavation and soil screening.
One mechanized apparatus and method for excavation of archaeological test pits was proposed by Pasch in Canada patent application 2,946,944 (2016). The proposed apparatus employs an encased spiral soil auger that is rotated by a hydraulic drive motor. The wall of the auger casing contains a multitude of holes or openings of predetermined size. The apparatus is attached to a skid-steer loader which transports the apparatus between test locations and supplies power to the hydraulic motor. To excavate a test hole, the spiral auger is rotated as the skid-steer lowers the apparatus vertically into the ground. Once the desired excavation depth is reached, the apparatus is extracted from the test pit. Soil excavated from the test pit remains trapped in the flights of the auger and surrounding casing. The apparatus is then tilted to a horizontal position above the ground surface and rotated. While in a horizontal position, rotation of the auger allows soil to pass through holes within the auger casing resulting in the separation of artifacts from the smaller soil particles.
Through my own experiments and trials with mechanized soil augers and earth drills, I have identified a number of disadvantages in the apparatus and method proposed by Pasch (2016):
a. The method captures and extracts soil from the entire depth of the test pit resulting in the mixing of the soils and artifacts from all excavation levels. Most established archaeological testing strategies require the separation of soil and artifacts in regularly spaced intervals of depth or excavation levels.
b. Even if soil was captured and extracted from the test pit in excavation levels through multiple insertions and extractions, the lifting and lowering action of the skid-steer loader is not truly vertical but follows an arc. Due to this arc and the free hanging nature of the apparatus from the skid-steer loader, it is difficult to lower and raise the auger within the test pit without disturbing the walls of the test pit and causing soil and artifacts to fall from the walls into the bottom of the test pit. Mixing of soil and artifacts within the test pit is undesirable and causes less accurate test results.
c. With the soil auger directly suspended from the lift arms of a skid-steer loader, it is difficult to control and gage the depth of a soil auger as it enters the ground. Accurate control of excavation depth is necessary for accurate excavation levels.
d. The apparatus does not provide a mechanism to close the bottom of the auger and auger casing to prevent soil from falling out of the bottom of the apparatus when it is extracted from the test pit. Soil falling out of the auger and into the test pits again causes undesirable mixing of soil and artifacts from multiple excavation levels.
One or more aspects of our combined bucket drill and soil screen apparatus and method are superior to the established methods of manually excavating test pits because it:
In addition, one or more aspects are superior to the apparatus and method proposed by Pasch in Canada patent application 2,946,944 (2016) because it:
In accordance with one embodiment, a bucket drill and soil screen apparatus is comprised of a drill mast attached to a prime mover vehicle. From the drill mast a drilling bucket with closable inlet ports is rotated and lowered into the ground for the excavation of an archaeological test pit. The bucket drill extracts soil from the test pit in discrete excavation levels. Soil is emptied from the drilling bucket through a hinged opening and transferred to a rotary screen basket with walls formed by hardware cloth. During rotation, fine soil particles within the screen basket pass through the hardware cloth until the fine soil particles have dissipated from the basket. Cultural artifacts larger than the openings within the hardware cloth are retained within the basket. The contents of the screen basket are emptied by rotating the basket upwardly and around through an arc to a position where the contents fall from the open end of the basket. The contents of the screen basket are transferred to a fixed box screen. Cultural artifacts are sorted and collected from the box screen. The process is repeated until the desired excavation depth is reached within the test pit.
Included are three drawing sheets containing six figures. Component numbers are consistent across all six figures. Table 1 provides a list of components and associated numbers:
A skid steer track loader 7 with an auxiliary hydraulic circuit is used as a prime mover vehicle to move the apparatus between test pit locations and to power the hydraulic motors and actuators (
A hydraulic motor 12 is mounted onto a carriage 10 with two pintles that allow the motor 12 to pivot within the carriage 10. A kickout mechanism consists of a hydraulic actuator 13a that connects to a lever 13b. The upper end of the lever 13b connects to the pintle of the drive motor 12 and the lower end of the lever 13b presses against the drive motor in a manner that permits the hydraulic actuator 13a to push or pivot the lower portion of the drive motor outward away from the drill mast 9. The carriage 10 is designed to slide up and down along the vertical extent of the drill mast 9. The carriage is suspended by a hoist mechanism that consists of roller chains and idler sprockets configured as a bi-directional gun tackle. The roller chains connect to the end of a hydraulic actuator mounted to the backside of the drill mast 9. Extension and contraction of the hydraulic actuator causes the carriage 10 to slide along the drill mast 9 a distance equal to twice the stroke length of the hydraulic actuator.
A square telescoping kelly bar assemblage 14 connects to the shaft of the drive motor 12 (
The lid plate of the drilling bucket 15 connects to cylindrical walls of the drilling bucket through a hinge mechanism and a spring-loaded latch mechanism, each located at opposing positions along the upper rim of the bucket (
A lift arm 17 connects to the drill mast 9 through a spindle 16 that is attached to a fixed arm that extends outward from the drill mast 9. A hydraulic actuator causes the lift arm 17 to rotate on the spindle 16 along an arc of approximately 90-degrees. A screen basket 20 connects to the lift arm 17 through a spindle 18. Two adjustable stops along the radius of the spindle 18 set the rotation limits. A hydraulic motor 19 mounts to the screen basket drive assembly. A roller chain contained within the rectangular drive assembly housing transmits power from the hydraulic motor 19 to the center axle of the screen basket 20. Two fixed handles 21 extend outward from the drive assembly. The handles 21 provide manual control over the drive assembly's rotation around the spindle 18.
The screen basket 20 rotates under hydraulic power along a central axle that is held in place by roller bearings located inside the drive assembly. The screen basket 20 connects to a four-bolt hub at the end of the axle. The screen basket 20 is constructed around a central hub from which radial ribs are welded and extend outward to the bottom ring of the basket. Corresponding vertical ribs are welded to the bottom ring and extend perpendicular to the upper ring of the basket. The rib and ring structure support four-holes-per-inch wire hardware cloth which form the bottom surface and the surface around the circumference of the basket. The upper or outward end of the screen basket 20 is open.
The hydraulic actuator connected to spindle 16 causes the lift arm 17 to rotate in an arc. When rotated to the bottom or low point of the arc, the screen basket 20 is positioned under the drilling bucket 15 when the drilling bucket is placed in its kicked-out position (
The bucket drill and soil screen method and apparatus achieve their result as follows. The track loader 7 is positioned to engage and attach to the drill mast 9 through the quick attachment plate 8 (
To begin excavation, the hydraulic motor 12 is engaged and rotated in a clockwise direction while the carriage 10 is slowly lowered. The rotating drilling bucket 15 cuts into the ground surface as soil is lifted into the drilling bucket by the digging edge. A graduated scale painted onto the front surface of the drill mast 9 serves as a depth gauge as the carriage 10 and drilling bucket are lowered. When the desired depth is reached, the hydraulic motor 12 is stopped and then briefly re-engaged in a counterclockwise direction. The counter rotation closes the bottom plate, thus trapping the excavated soil within the bucket. Carriage 10 is raised to its highest position which lifts the drilling bucket 15 out of the excavated hole.
Transfer of the excavated soil from the drilling bucket 15 to the screen basket 20 begins with engaging the lift arm spindle and actuator 16 so that the lift arm 17 and screen basket 20 move downward in an arc to their lowest position (
The lift arm actuator at spindle 16 is engaged to elevate the lift arm 17 and screen basket 20 to its working position (
Artifacts retained on the sorting screen 22 are collected and placed in a bag with a tag that designates the test hole, excavation level, and depth from which the artifacts were extracted. Any material remaining on the sorting screen 22 is discarded. While the soil and artifacts are being screened and sorted, the drilling bucket 15 is lowered back into the test pit and soil from the next excavation level is captured and lifted out of the hole. This process is repeated until the desired excavation depth is attained within the test pit. The track loader and apparatus are then moved to the next test pit location. Completed test pits are backfilled manually with spade shovels or at the end of the day using the track loader with a standard dirt bucket attachment.
If the archaeological deposits within a test hole extend to a depth below the reach of the collapsed kelly bar assembly 14, then the kelly bar is extended to increase its vertical reach. This requires the additional steps of extending the kelly bar 14, capturing the soil in the next excavation level, and then collapsing the kelly bar 14 so that the drilling bucket 15 can be removed from the hole. The inner kelly bar 14a is extended by removing the linchpin 14c, lifting carriage 10 to the top of the drill mast 9, and re-installing the lynch pin 14c to lock the kelly bar 14 in its extended configuration. This process is reversed to collapse the kelly bar 14. A kelly bar slip clamp 23 is placed around the kelly bar 14 before the linchpin 14c is removed which prevents the outer kelly bar tube 14b and drilling bucket 15 from falling deeper into the test pit. To further increase the excavation depth, additional kelly bar extensions can be inserted between the expanded kelly bar assembly 14 and the hydraulic motor 12 as needed. This first embodiment can extract soil from depths up to 3 meters. Additional kelly bar extensions can be added to increase excavation depth to greater than 3 meters.
At least one embodiment of the combined bucket drill and soil screen provides an alternative method to the manual excavation of archaeological test pits while reducing costs in time and labor and improving worker safety. The above described embodiment reduces the problem of soil mixing between excavation layers, thus improving the separation and recovery of cultural artifacts from discrete excavation levels. My above description of a combined bucket drill and soil screen contains many specificities; however, these specificities should not be construed as limitations, but rather as an example of one embodiment. Many variants are possible.
There are several alternative embodiments in which the combined bucket drill and soil screen method can achieve the same results.
This application claims the benefit of provisional patent application Ser. No. 62/926,662 by the present inventors, which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62926662 | Oct 2019 | US |
