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In 2005, DDS ENGINEERING, PLLC (DDS) was contracted by HDR, Inc., a major international engineering firm, to assist with various surveying and engineering tasks for a five-year Indefinite Delivery/Indefinite Quantity (IDIQ) project at Mammoth Cave National Park.

During that contract, DDS executed numerous tasks including precision cave route surveys, national park boundary retracements, surface mapping operations and detailed inventories and GIS databases for 15 cemeteries located within the Mammoth Cave National Park boundary.

With our vast knowledge of the Park and various underground cave trails, in late 2013, Mammoth Cave Staff recommended that DDS assist Redstone International with the delicate task of accurately sinking two (2) new drilled utility shafts to the Mechanical Room of the Snowball Dining Room area within the cave.

In early December 2013, DDS entered into a contract with Redstone International to provide precise surface locations adjacent to the existing elevator machinery building that provides access to the Snowball Dinning area.

DDS immediately responded by recovering archived files from the previous work for the National Park Service in association with HDR.  These files included the cave trail mapping of the Snowball Dining Room Tours route from the surface to the Dining Area.


With the data in hand, DDS field crews returned to the site and began reconnaissance on the surface at the location of the two (2) proposed drilled shafts.  Shortly thereafter, and in order to assure the most accurate surface locations possible, DDS crews began the process of re-running the exterior-to-interior traverse to the Mechanical Area at the Snowball Dining Room, some 5,500 feet from the entrance.  At this point, it might be interesting to note that we have planned to utilize the Snowball Dining Room for quick access to the cave directly below. But as the ‘plans of mice and men’ sometimes goes, the elevator was out of order and remained so throughout the entire surveying process, thus only adding to the difficulty of completing the task.

As one can imagine, this traverse was run in minimal light conditions but, with the use of Robotic Total Stations and with all angles double turned, the interior traverse results were satisfactory.  However, as any surveyor knows, with an ‘open-ended- traverse’ there is always the possibility of an unconfirmed error.

Upon completion of the interior traverse, both into and out of the cave, the results were compared with the data collected in the original DDS cave survey completed some 6 years earlier.  Luckily, all of the interior cave traverse points were recoverable which assisted in reconciling the current survey.

Being satisfied that the results of the interior survey were accurate, DDS then began work on the exterior portion of the project.  This involved the use of both conventional Robotic Total Stations and GPS survey equipment.

Initially, DDS established GPS control points on the surface near the location of the proposed drilled shafts.  DDS then ran a conventional survey from these GPS points to the surface points near the Snowball Dining Room Tour entrance control points, some 9,000 feet away.  This surface traverse was run with Robotic Total Stations and, even with all angles double turned, another ‘open-ended- traverse’ was created, thus compounding possibility of unconfirmed error.

As luck, nay, probability would have it, the surface survey traverse results, compared to the data collected and results of the interior traverse, were less than satisfactory.  At this point, it was incumbent upon DDS to explore other means and methods to determine which traverse was ‘correct’ and a means to most precisely locate the surface drilled shafts’ location points.

As mentioned earlier, the elevator was out of service, but with the assistance of National Park Service personnel and the elevator repair company, we were able to find a means by which to at least ‘check our work’.

The elevator personnel were able to position and secure the elevator such that the top of the elevator car was at the floor level at the surface.  With the use of a directional visible light laser, we fashioned a devise to accurate position and secure the laser, first at the rear of the elevator car and then at the front of the elevator car.

With one crew member in the cave at the elevator shaft and another at the surface, and with the laser projecting its beam down into the cave via the space between the elevator car and the natural rock shaft, we were able to simultaneously tie to the laser beam positron both on the surface and in the cave with the Robotic Total Stations.  With this data, we were able to theoretically ‘close our traverse’, thereby giving us the ability to accurately analyze both sets of data and accurately determine the precise location at which Redstone International personnel could begin their drilled shaft work.

Since this shaft was going to have to be almost 270 feet straight down into the Snowball Dining Room Mechanical area, we were on ‘pins and needles’ until Redstone first broke through.  Much to our relief, both shafts were drilled into the Mechanical area with a precision of less than two (2) inches!

Project Location

Mammoth Cave, Kentucky


Mammoth Cave National Park


2013 - 2014

Project Type

Surveying (Robotic & GPS)

Departments Involved




Project Management

Redstone International

Project Manager(s)

Dennis D. Smith, PE, PLS


Dennis D. Smith, PE, PLS