Submersible Matting System

TECHNICAL FIELD

The present disclosure relates to a submersible matting system that provides a system to move vehicles from a ship or carrier within a body of water to shore and across land. The submersible matting system provides a stable and rugged pathway or roadway for vehicles, material, and/or supplies to be transported and moved across soft or weak soil, such as beaches and littoral zones.

BACKGROUND

Logistics operations in austere environments are hindered by lack of force mobility across littoral zones, riverine shorelines, and wet/dry gaps. These environments rapidly transition between wet and dry states, present steep slopes, and have weak soils that limit vehicle weight and number of passes.

In-situ soil conditions within littoral zones, bare beaches, and riverbanks do not possess adequate strength to support vehicle operations in much of the world. Soil with sufficient initial undisturbed strength also degrades in strength with repeated vehicle traversals as tires and tracks shift the soil. These regions further challenge mobility as they can rapidly transition from fully submerged to partially saturated and dry conditions with each state having significantly different soil strengths. However, mobility across these regions is a necessary component of force projection for Joint Logistics Over-the-Shore (JLOTS), bridging and gap crossings, emerging robotic convoy concepts, and multi-domain operations. The inability to consistently maneuver along the wet/dry interface at the shore-line due to the soil strength variability is an existing force projection capability gap.

Typically, maneuvering across weak water/shore interfaces in the littoral zone (the portion of a sea, ocean, lake, or river that is closest to the shore) is difficult or sometimes impossible because of the low shear strength of the fully saturated soil. The weakened soil limits operations for delivery of needed equipment and supplies to known ports, expedient piers, or floating causeway systems which require pre-assembly of components and heavy equipment for installation.

Structural mediums are currently utilized to enhance mobility over soft soils at the shoreline. The structural medium typically includes a structural mat, which is a layer of stronger material over the weak layer, or a combination of a soil improvement action and a surfacing mat. Mobility matting utilized by Joint Forces is often deployed in austere dry beach environments where vehicles are transiting and require improved bearing capacity/traction. This type of matting is used in a variety of military, humanitarian, and disaster relief operations where rapid access to otherwise inaccessible areas is essential. The matting is often designed to be self-deploying (for both heavy and light vehicles) to avoid unnecessary personnel exposure to threats of environment or circumstance.

Present JLOTS vehicles of concern include, but are not limited to, those shown in FIG. 1. The Navy and USMC Medium Tactical Vehicle Replacement (MTVR) is a 6×6 truck with a variety of variants supporting supply and logistics missions with a 7-ton capacity. Variants include cargo, dump, gun truck, troop carrier, and fifth wheel. The Logistic Vehicle System Replacement (LVSR) is a U.S. Marine Corps (USMC) variant of the 10×10 Heavy Expanded Mobility Tactical Truck (HEMTT) vehicle. Pay-load is 16.5 tons of supplies and equipment. Variants include troop carrier, fifth wheel, PLS, wrecker, and bridger. The Heavy Expanded Mobility Tactical Truck (Army-HEMTT) is the Army's 8×8 vehicle providing the backbone of off-road logistics and utility support including wrecker, fueler, cargo, bridging, and other variants. The 10×10 variant is known as the Palletized Load System (PLS). Payload is 10 tons of supplies and equipment.

The Logistics Vehicle System (USMC-LVS) is a USMC variant of the 8×8 HEMTT vehicle, outfitted with additional steering capabilities to meet stricter turning radii requirements. Variants include wrecker, flatbed, fifth wheel, bridger, crane, and cargo. Payload is 10 tons of supplies and equipment. The Family of Medium Tactical Vehicles (Army-FMTV) is the Army's family of 4×4 and 6×6 supply and utility trucks. The 8×8 vehicle variant provides the backbone of off-road logistics and utility support including wrecker, fueler, cargo, bridging, etc. variants. Payload is 2.5 or 5 tons of supplies and equipment, varying by type. The Joint Light Tactical Vehicle (JLTV) replaced the High Mobility Multipurpose Wheeled Vehicle (HMMWV) for both the Marines and the Army. Variants include general purpose, utility, and weapons carrier. Any military operation requires engineer support, including the use of heavy equipment and construction vehicles. Excavators include the John Deere 230 LRC, 250G LRC ERDC/GSL TR-22-DRAFT 10 or similar. Dozers include the John Deer 850J and the Caterpillar D9.

Existing matting and site stabilization systems cannot be readily adapted for submerged or partially submerged conditions along the shoreline. Current matting capabilities are not designed to be submersible for any length of time and cannot support traffic while underwater. Most commercially available roll-out aluminum mat systems have not been fully tested for underwater behavior. Traditional single panel mats are heavy and cumbersome, and their assembly is slow above water and nearly impossible underwater. Other heavy plastic mats may float making them difficult to deploy submerged without significant anchorage modifications. Flexible fabric-style mats do not provide adequate strength and interconnected concrete block mats are cumbersome and logistically challenging to employ. Existing systems are thus unsuited to the wet/dry environment present along the shoreline, requiring a new matting system to ensure force projection in a multitude of environments.

SUMMARY

The U.S. Army Engineer Research and Development Center (ERDC) developed a submersible matting (SUBMAT) system for supporting vehicles moving over weak and/or soft soils, such as littoral zones, beaches, riverbanks, and swamps. The SUBMAT system provides an easily deployable pathway or roadway filled with indigenous natural materials that remains stable through sea state 5 and supports multi-wheeled and/or multi-tracked vehicles. The SUBMAT system provides an easily deployable roadway for vehicles to traverse that retains stability with tide changes. The SUBMAT system provides a highly stable and rugged pathway or roadway for vehicles, material, and/or supplies to be transported and moved from a carrier to shore or over ground. The SUBMAT system is easily transported and rapidly deployable from vehicles, from small-craft vessels, or by hand.

The SUBMAT system provides United States Transportation Command (USTRANSCOM) with a capability to negotiate vehicles across the wet/dry interface at shoreline where traction and bearing capacity are limiting for force projection. The small system footprint enables the system to be rapidly transported and deployed in austere locations with limited personnel.

One aspect of the present disclosure is a submersible matting (SUBMAT) for supporting vehicles over soft soils. Various embodiments of the SUBMAT include: a rectangular geotextile mattress having a top and a bottom, and sealed about a perimeter to define an interior mattress filling space; one or more interior baffle in the mattress extending in a longitudinal direction, the one or more interior baffle creating two or more longitudinal tube sections within the mattress; at least two scour tubes positioned longitudinally along a periphery of the mattress, each scour tube being sealed to define an interior scour tube filling space; an outer textile layer covering at least a portion of the top of the mattress; a plurality of fill points spaced at intervals along the mattress, each fill point providing an opening in the mattress and into the mattress filling space; and a plurality of fill points spaced at intervals along each scour tube, each fill point providing an opening in the scour tube and into the scour tube filling space.

Another aspect of the present disclosure relates to a roadway system for supporting vehicles moving over soft soils that includes one or more SUBMAT filled with fill material.

A further aspect of the present disclosure relates to methods of making a roadway to support vehicles moving over soft soils, and include steps of: deploying the SUBMAT at an intended location, wherein the SUBMAT is unfilled; placing a first end of the SUBMAT at a first position of the location, and anchoring the first end; placing a second end of the SUBMAT at a second position, and anchoring the second end; attaching a pumping apparatus to a fill point and pumping indigenous fill material present at the location into the mattress filling space and scour tube filling space; and repeating the attaching and pumping step as needed until the SUBMAT is filled with fill material to an intended capacity.

Various embodiments of the SUBMAT system are designed to meet performance requirements that include, but are not limited to, the following.

Bearing capacity—Embodiments of the SUBMAT system increase the bearing capacity of shoreline soils to support at least Military Load Classification (MLC) 80 tracked/96 wheeled vehicles. This MLC supports most vehicles used during force projection operations and is equivalent to the capacity of the Improved Ribbon Bridge (IRB).

Lateral stability—Embodiments of the SUBMAT system do not shift from the deployed location and eliminate lateral heave of the soil surrounding the SUBMAT units due to insufficient distribution of the vehicle load. This eliminates the operational need to reset or deploy additional SUBMAT units.

Vertical stability—Embodiments of the SUBMAT system do not shift vertically after initial deployment due to either buoyance forces or soft soils.

Transportability—Embodiments of the undeployed SUBMAT system cube are minimized for ease of transport. The undeployed matting collapses to be transported on lighter vessels and vehicle convoys without significant modification to the cargo plans. The undeployed system additionally allows for system stacking within a twenty-foot equivalent unit (TEU).

Deployability—Embodiments of the SUBMAT system are simple and rapid to deploy. Embodiments of the SUBMAT unit are deployable by a single soldier squad. Embodiments of the SUBMAT system also allow multiple SUBMAT units to be joined together for simultaneous vehicle deployment.

Recoverability—While some embodiments of the SUBMAT system stay permanently in a deployed location, the SUBMAT system is designed to be quickly and safely removed.

Affordability—As embodiments of the SUBMAT system are a single use system, minimizing the cost of SUBMAT units is sensible to ensure that the system is widely disseminated and frequently employed.

Various embodiments of the SUBMAT system include a sand, gravel, or sand and gravel-filled mattress-based system. The SUBMAT system includes individual SUBMAT units or sections that are individually deployed either as single SUBMAT units or as a plurality of individual SUBMAT units that coordinate together to form a roadway of the desired length and/or width.

BRIEF DESCRIPTION OF DRAWINGS

Other features and advantages of the present disclosure will be apparent from the following brief description of the drawings, detailed description, and examples, which should not be construed as limiting the disclosure to the embodiments shown and described. The drawings are not necessarily drawn to scale.

FIG. 1 is an illustration of several vehicles that embodiments of the SUBMAT system are designed to accommodate.

FIG. 2 is a plan view of a SUBMAT unit according to an embodiment of the disclosure.

FIG. 3 is a plan view of a SUBMAT unit according to an embodiment of the disclosure.

FIG. 4A is an expanded plan view, and FIG. 4B is a longitudinal view, of a SUBMAT fill point according to an embodiment of the disclosure.

FIG. 5 is a view of cross-section (A-A) of the SUBMAT unit of FIG. 3, according to an embodiment of the disclosure.

FIG. 6A is a plan view of a SUBMAT unit, and FIG. 6B is a view of cross-section (B-B) of the SUBMAT unit of FIG. 6A, according to an embodiment of the disclosure.

FIG. 7 is a plan view of a SUBMAT unit deployed across the swash zone at a beach location, according to an embodiment of the disclosure.

FIG. 8 is a photograph of an embodiment of the SUBMAT system, deployed on the beach.

FIG. 9 is a plan view of a roadway system provided by a plurality of SUBMAT units, deployed across the swash zone at a beach location, according to an embodiment of the disclosure.

FIG. 10 is a diagram illustrating the test site utilized for performance testing and evaluation of various embodiments of the disclosed SUBMAT system.

FIG. 11 is a graph showing the measured average rut depth (in) versus number of traffic passes for MTVR vehicles moving across tested embodiments of the SUBMAT units. Rut depths were measured using LiDAR.

FIG. 12 is a graph showing the normalized average rut depth (in) versus number of traffic passes for HEMTT vehicles moving across tested embodiments of the SUBMAT units. Rut depths were measured using LiDAR. The data set was normalized to show the evolution of the rutting strictly due to the new vehicle traffic, without respect to how deep the rut was prior to trafficking with the new vehicle.

FIG. 13 is a graph showing the normalized average rut depth (in) measured for M1A1 tank vehicles moving across tested embodiments of the SUBMAT units. Rut depths were measured using LiDAR. The data set was normalized to show the evolution of the rutting strictly due to the new vehicle traffic, without respect to how deep the rut was prior to trafficking with the new vehicle.

FIG. 14 is a graph showing the peak pressure (psi), measured by an EPC pressure sensor deployed under a tested embodiment of a SUBMAT unit during traffic intervals for MTVR, HEMTT, and M1A1 vehicles moving across the SUBMAT unit. A peak picking software was implemented to find the peaks in each traffic interval, and the maximum peak of each interval was recorded. The traffic intervals for each vehicle type are shown in the table.

FIG. 15 is a graph showing the peak pressure (psi), measured by an EPC pressure sensor deployed under a tested embodiment of a SUBMAT unit, during traffic intervals for MTVR, HEMTT, and M1A1 vehicles moving across the SUBMAT unit. A peak picking software was implemented to find the peaks in each traffic interval, and the maximum peak of each interval was recorded. The traffic intervals for each vehicle type are shown in the table.

FIG. 16 is a table listing the rut depths (in) measured by LiDAR scans collected through the trafficking tests of MTVR, HEMTT, and M1A1 vehicles after a predetermined number of passes. The collection method allowed rut depth measurements for both wheel paths along the entire length of the SUBMAT unit; only measurements at the quarter point locations along the wheel path (A1, A2, A3 and B1, B2, B3) are presented in the table.

DETAILED DESCRIPTION

While the present disclosure will be described in conjunction with specific embodiments, the disclosure can be applied to a wide variety of applications, and the description herein is intended to cover alternatives, modifications, and equivalents within the spirit and scope of the disclosure and the claims. The description in the present disclosure should not be viewed as limiting or as setting forth the only embodiments of the disclosure, as the disclosure encompasses other embodiments not specifically recited herein. The present disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments.

The present disclosure relates to a submersible matting system that uses individual SUBMAT units or sections filled with indigenous materials to create a stable vehicle roadway system across soft soils. The terms “SUBMAT” and “submersible matting” are equivalent and are used interchangeably throughout. According to various embodiments, the SUBMAT system is a mattress-based system in which individual SUBMAT units or sections are filled with indigenous material (e.g. gravel, sand) to provide adequate bearing capacity, lateral stability, and vertical stability under applied vehicle traffic across the littoral zone and to bridge the gap between low-tide and high-tide at the beach/water interface.

According to various embodiments, the SUBMAT system is easily deployable, remains stable through sea state 5 (rough seas with wave heights of about 8 to 13 ft), and uses indigenous materials while supporting large scale multi-wheeled and/or multi-tracked vehicle maneuvers. The SUBMAT system provides a roadway for vehicles to traverse weak or soft soils, such as the littoral zone, while retaining stability with tide changes. According to various embodiments, the SUBMAT system is filled with granular material such as sand or gravel to create a stable driving surface for offloading vehicles and/or heavy equipment, such as military equipment, from vessels.

According to various embodiments, the SUBMAT system includes one SUBMAT unit or a plurality of SUBMAT units aligned end-to-end and/or side-by-side to form the roadway. In embodiments, a SUBMAT unit is a textile enclosure or mattress having an interior space capable of being filled with indigenous materials. In various embodiments, the textile is a geotextile. Geotextiles are generally made from plastic materials, such as polypropylene and polyester, but also polyethylene, polyamide (nylon), polyvinylidene chloride, and fiberglass. In various embodiments of the SUBMAT system, the geotextile is a woven polypropylene or polyester fabric.

According to various embodiments, the SUBMAT unit is composed of a high strength woven geotextile of polypropylene fibers, stitched or sewn into a rectangular shaped mattress. The mattress is sealed about the periphery and defines an interior mattress filling space. Embodiments of the mattress are sealed by stitching and/or double stitching the geotextile.

In an embodiment, the geotextile is PROPEX® GEOTEX® GT-4×6 polypropylene with heavy woven serrated yarns. GEOTEX® GT-4×6 is a geotextile containing heavy monofilament (warp) and fibrillated (fill) yarns. The individual yarns are woven in a twill pattern to form a strong geotextile having a tensile strength (Grab) of about 600×700 lbs. (ASTM D-4632).

In various embodiments, the SUBMAT unit also includes an outer textile layer covering at least a portion of the top surface of the mattress. In embodiments, the outer textile layer is a UV-stable high performance turf reinforcement matting woven into a three-dimensional lofted pattern. In embodiments, the outer textile layer is composed of polypropylene geotextile matting. In embodiments, the outer textile layer is a netting material. Embodiments of the outer textile layer provide additional reinforcement structure to the mattress and protect the top surface or “wear layer” of the mattress. The outer textile layer provides an additional layer of protection to the mattress and helps to reduce and prevent wear and tear to the mattress caused by vehicles traveling across the SUBMAT unit. In some embodiments, the outer textile layer also provides an extra layer of traction for the vehicles.

In some embodiments, the outer textile layer covers essentially the entirety of the top surface of the mattress. In other embodiments, the outer textile layer covers less than the entirety of the top surface of the mattress. In some embodiments, the outer textile layer is sewn or stitched to the mattress at various locations, such as the interior baffle points and along the periphery of the mattress. In an embodiment, the outer textile layer is PROPEX® PYRAMAT®.

According to various embodiments, the SUBMAT unit includes one or more “scour” tubes, and embodiments include two scour tubes, each positioned along the longitudinal sides of the mattress. The scour tubes are sealed to define an interior scour tube filling space. According to various embodiments, the scour tubes are larger or thicker than the thickness of the mattress. For example, an embodiment of the mattress, when filled, has a thickness (height) of about 9-12 inches, and the scour tubes on either side of mattress, when filled, have a diameter or height of about 18 inches. When the SUBMAT unit is positioned on a beach or littoral zone and filled, the sea and wave action can cause “scouring” or erosion of sand from underneath the SUBMAT unit. The larger scour tubes consequently recede downward or dig into the sand. This protects scouring action from occurring underneath the mattress and the mattress remains stable on the beach surface.

FIG. 2 illustrates a SUBMAT unit according to an embodiment of the SUBMAT system. In this embodiment, the SUBMAT unit 200 includes a rectangular textile mattress 201 having a top 203 and a bottom (not shown in this plan view). The mattress 201 includes six interior tubular or tube sections 202 extending in a longitudinal direction and is about 100 ft long and about 18 ft wide. In various embodiments, interior baffles 206 separate the mattress 201 into the interior tube sections 202 and separate each interior tube section 202 from one another. Each interior tube section 202 is about 3 ft wide, and when “inflated,” i.e. filled with fill material, is about 9-12 inches in height.

In some embodiments of the SUBMAT unit 200, the interior tube 202, when inflated, is in a range of about 2-5 inches, about 3-6 inches, about 5-8 inches, or about 4 inches or about 6 inches in height. Embodiments of the SUBMAT unit include a mattress 201 having two or more interior tube sections 202 such as 2-10, 3-4, or about 6-8 interior tube sections 202. Some embodiments of the SUBMAT unit 200 include a mattress 201 in which the interior tube section 202 is narrower than 3 ft wide, such as about 1-2 ft wide, and other embodiments in which the interior tube section is wider, such as about 4-6 ft wide. In some embodiments, the mattress 201 is shorter in length than 100 ft, such as about 80 ft, 50 ft, 40 ft, or about 20 ft long, and in other embodiments, the mattress 201 is longer, such as about 120 ft, 150 ft, 200 ft, or longer. In some embodiments, the mattress 201 is narrower than 18 ft wide, such as about 16 ft, 12 ft, 10 ft, 9 ft, or 8 ft wide, and in other embodiments, the mattress 201 is wider, such as about 20 ft, 25 ft, 30 ft, or wider.

The SUBMAT unit 200 also includes two outer scour tubular or tube sections 204. Each interior tube section 202 and scour tube section 204 has an interior filling space that is separably fillable with sand, sand and gravel, or other indigenous material. According to various embodiments, the scour tubes 204 are taller (i.e. larger diameter), when filled, than the interior tube sections 202. The scour tubes 204, when filled with sand or gravel, prevent scour under the interior tube sections 202. In the embodiment illustrated in FIG. 2, the scour tubes 204 are about 74 ft long and have a diameter of about 18 inches. In various embodiments, the scour tube 204 is constructed from a geotextile rolled into a cylindrical tube and stitched to form a longitudinal seam 220. Embodiments of the scour tube 204 include additional geotextile overhang material for attaching to the mattress 201.

In embodiments of the SUBMAT unit 200, the scour tubes 204 are correspondingly dimensioned to fit to the dimensions of the mattress 201. Accordingly, if the mattress 201 is shorter in length than the about 100 ft shown in FIG. 2 (e.g., about 80 ft, 50 ft, 40 ft, or 20 ft long) or longer (about 120 ft, 150 ft, 200 ft long), then the scour tube 204 is adjusted in length accordingly. Embodiments include having more than one scour tube 204 on each side of the mattress 201, for example two, three, or four individual scour tubes 204, each being about 18-37 ft long instead of the one scour tube 204 of about 74 ft long shown in FIG. 2.

In various embodiments, the mattress 201 and the scour tubes 204 are composed of a geotextile material that is porous to allow air and water to escape from the mattress and scour tube interior. In various embodiments, the mattress is constructed of a geotextile material that is stitched or sewn to form a sealed rectangular mattress. In some embodiments, the mattress 201 is constructed of two or more subunits that are then joined together. In some embodiments of the mattress 201, each interior tube section 202 is separately constructed and then the individual tube sections 202 are joined together to form the complete mattress 201. In an embodiment of the SUBMAT unit 200 illustrated in FIG. 2, six rectangular interior tube sections 202 are constructed, each being 100 feet long and 3 feet wide. The six tube sections 202 are then stitched or sewn together to form a SUBMAT unit 200 that is 100 feet long and 18 feet wide.

In various embodiments, the interior tube sections 202 are tapered at each end 208. The tapered ends 208 facilitate overlapping of the SUBMAT units 200 to create the roadway system. In the embodiment illustrated in FIG. 2, the tapered ends 208 are about 13 ft long.

According to various embodiments, the SUBMAT unit 200 has a plurality of openings which serve as fill points 210 spaced at intervals along each interior tube 202 and scour tube 204. The fill points 210 enable the addition of sand or gravel at different locations along the length of each of the interior tubes 202 and scour tubes 204. In the embodiment illustrated in FIG. 2, the fill points 210 are spaced at intervals of about 12 ft apart along each interior tube 202 and about 24 ft apart in the scour tube 204. According to various embodiments, the fill point 210 is self-sealing, so when the filling apparatus is removed the fill point 210 closes.

According to various embodiments, the SUBMAT unit 200 includes handles 212, 214 positioned at intervals along the SUBMAT unit 200. In the embodiment illustrated in FIG. 2, handles 212 are included along the periphery on the top 203 of the mattress 201, and handles 214 are included along the edge at either or both ends of the mattress 201. In various embodiments, handles 212 are also included along the periphery on the bottom (not shown in this plan view) of the mattress 201. Embodiments of the handles are made from appropriately strong materials, such as 2.5 inch nylon webbing material, and the like, which are sewn or stitched to the mattress and or scour tube.

According to various embodiments, the SUBMAT unit 200 includes stake rings 216 positioned at intervals of the SUBMAT unit 200. In the embodiment illustrated in FIG. 2, stake rings 216 are spaced along a periphery of the SUBMAT unit 200 at similar intervals along with the handles 214. In various embodiments, stake rings 216 are spaced at similar intervals along with the handles 212 on the top 203 and/or bottom to the mattress 201. Embodiments of the stake rings are made from appropriate materials that can withstand water corrosion, such as stainless steel, and the like.

According to various embodiments, the SUBMAT unit 200 includes straps 218 attached to the mattress 201 and positioned at the fill points 201. The strap 218 provide a leverage point so that the user can grab and pull the strap 218, thereby opening the fill point 210 and facilitating insertion of a filling apparatus. In embodiments, the strap 218 is a highly visible color (e.g. bright yellow) to readily indicate the location of the fill point 210, particularly when the mattress 201 is submerged under water and less visible.

According to various embodiments, the SUBMAT unit 200 includes an outer textile layer covering at least a portion of the top 203 of the mattress 201. In an embodiment illustrated in FIG. 3, the SUBMAT unit 200 includes an outer textile layer 302 on top 203 of mattress 201. In this embodiments, the outer textile layer 302 covers approximately the entirety of the top 203 of mattress 201. In some embodiments, the outer textile layer 302 also covers at least a portion of scour tubes 204.

According to various embodiments, the outer textile layer 302 is a geotextile. According to various embodiments, the outer textile layer 302 is sewn or stitched to the mattress 201 and provides additional reinforcement structure, in particular when the mattress 201 is filled with filling material. The outer textile layer 302 provides an additional layer of protection to the top surface, or the wear layer, of the mattress 201, and helps to prevent wear and tear to the mattress 201 from vehicle traffic. In various embodiments, the outer textile layer 302 is sewn or stitched to the mattress 201 at the periphery of the mattress 201, at the internal baffles 206, or at both locations, and/or at other locations on the mattress 201.

According to various embodiments, the outer textile layer 302 is one or more textile sheets or mattings. In an embodiment corresponding to the dimensions shown in FIG. 2 and FIG. 3, the outer textile layer 302 is a single sheet having a dimension that is approximately the same as that of the mattress 201, i.e., about 100 ft long by about 18 ft wide. The outer textile layer 302 covers approximately the entirety of the mattress 201. In other embodiments, the outer textile layer 302 is more than one sheet. In an embodiment corresponding to the dimensions shown in FIG. 2 and FIG. 3, the outer textile layer 302 is a set of six sheets, each about 100 ft long and about 3 ft wide. Each of the sheets is sewn or stitched at the periphery of the mattress 201 and/or at the internal baffles 206, and/or at other locations on the mattress.

FIG. 4A and FIG. 4B provide more detailed views of a fill point 210 from FIG. 2. The fill point 210 includes opening 402 in the top 203 of the mattress interior tube 202, which is configured to accept a filling apparatus, such as a pump outlet, fill pipe, or hose. In various embodiments, the fill point 210 is a slit 402 that is about nine (9) inches in length and is configured to accept a two to eight (2-8) inch diameter fill pipe 412, such as a three (3) inch or six (6) inch diameter fill pipe 412. The fill point 210 also includes a channel 404 configured to direct the fill material (e.g. sand or gravel) into the mattress interior tube 202. In various embodiments, channel 404 is composed of a fabric or geotextile that covers and closes the slit 402 when the filling apparatus 412 is removed from the fill point 210. Embodiments include a strap 218 that when pulled by the user provides leverage and helps to open the slit 402 of the fill point 210.

In various embodiments, the outer textile layer 302 is sewn or stitched to the mattress interior tube 202 alongside each side of the opening 402, to provide reinforcement to this area. Embodiments of the fill point 210 also include a reinforcement, such as a textile reinforcement patch 414, surrounding the opening 402. Also shown in FIG. 4A are internal baffles 206 that separate the interior mattress tube sections 202 from one another.

In various embodiments, the fill points 210 described above and applied to the internal mattress tubes 202 are likewise applied to the scour tubes 204.

FIG. 5 illustrates a cross-sectional view of an embodiment of the SUBMAT 200 shown in FIG. 3 (Section A-A). In FIG. 5, outer textile layer 302 is shown on top 203 of mattress 201. The mattress 201 is subdivided into six interior tube sections 202 by interior baffles 206. The outer textile layer 302 is sewn or stitched to the mattress 201 at each of the baffle points 502 and along the periphery 504. Also shown in FIG. 5 are a plurality of fill points 210 on each of the interior tube sections 202, and on each of the scour tubes 204. Again, the mattress 201 in the embodiment illustrated in FIG. 5 has a width of about 18 ft, with six interior tube sections 202 of about 3 ft in width. The scour tube 204 has a diameter of about 18 inches, is stitched together with a longitudinal seam 220, and is attached to the mattress 201 by overhang material 506. The scour tube 204 is positioned at about 1 foot from the edge of the mattress 201 to the center point of the scour tube 204.

FIG. 6A illustrates a plan view of a SUBMAT unit 600 according to another embodiment of the disclosure. In this embodiment, the SUBMAT mattress 601 includes seven interior tubes 602, with six interior baffles 606. The locations of the fill points 610 are shown. In this illustrated embodiment, the mattress 601 has a length of about 100 ft and a width of about 21 ft. In the embodiment, the scour tubes 604 extend along the length of the mattress and are about 80 to 90 ft long. FIG. 6B is a view of a cross section (B-B) of the SUBMAT unit of FIG. 6A, showing the tapered ends 608 of the interior tubes 602 and scour tube 604.

According to various embodiments of the SUBMAT system, a SUBMAT unit is a lightweight geotextile enclosure. An embodiment of the unfilled SUBMAT unit that is 100 ft long, by 20 ft wide, by 9 in height, weighs in a range of about 800 to 1000 lb, or about 900 lb. The SUBMAT unit is foldable and when folded it fits on an 8 ft×4 ft storage or transport pallet. According to various embodiments of the SUBMAT system, a group of about 4-8 individuals, for example a squad of 4-8 military personnel, can install a 100-ft long by 20-ft wide SUBMAT unit in about 4-12 hours, or about 8 hours, without requiring material handling equipment (MHE).

According to various embodiments, the SUBMAT system is scalable such that multiple individual SUBMAT units or sections are joined together in series and/or in parallel to create an intended length and width of roadway.

According to various embodiments, the SUBMAT units are scalable in size and dimension. While illustrated embodiments disclosed herein are about 100 feet long and 18-21 feet wide, embodiments of the disclosure include SUBMAT units in a range of about 50-200 feet long and about 10-30 feet wide. Embodiments also include smaller SUBMAT units, such as 10-50 feet long and 4-10 feet wide.

According to various embodiments, during deployment of the SUBMAT system, the unfilled SUBMAT unit or section, prior to filling with material, is held in place utilizing soil anchors. Once filled with granular material, embodiments of the SUBMAT unit weigh about 80 tons or more and are stable in either a ground-mounted or a wave environment. In embodiments where the SUBMAT system is deployed and utilized on a beach, one end of the SUBMAT unit is placed on the beach (i.e., landward end) and anchored on landward corners of the mattress utilizing anchors or anchor stakes, for example, DANFORTH® anchors or steel anchor stakes. In some embodiments, the anchor points are about 15-30 feet further landward beyond the end of the mattress, and the anchors are installed about 35-40 degrees updrift and 20-25 degrees downdrift from parallel to the SUBMAT unit installation alignment. Additional anchors are installed to the seaward corners of the mattress and then positioned seaward several feet beyond, for example about 15-30 feet beyond, the seaward end of the deployed mattress. In some embodiments, the seaward anchors are anchored in water that is less than 4 ft deep, so the anchors are deployed by hand. If the water is deeper than 4 ft, or is otherwise too deep for hand installation of the anchors, then embodiments of the SUBMAT system allow for the landward end of the SUBMAT unit to be adjusted further landward to accommodate installation of the seaward anchors at a shallower depth.

The seaward end of the SUBMAT unit is then pulled seaward to deploy. This takes an appropriate number of personnel depending on sea conditions. As the SUBMAT unit is pulled seaward, slack in the cables attached to the seaward anchors is retrieved landward to keep the SUBMAT unit straight and on alignment. In various embodiments, once the entire length of the SUBMAT unit is deployed and aligned to fit the beach profile, additional anchors, for example arrowhead anchors, are installed along the sides of the length of the mattress. In embodiments, the anchors are installed and attached to the handles on the mattress, using for example carabiners. The unfilled SUBMAT unit is held in place and in alignment prior to beginning the filling operations.

According to various embodiments of the SUBMAT system, the SUBMAT unit is filled with indigenous materials, such as sand, gravel, or sand and gravel, utilizing a dredge pump and pipeline system. In embodiments, a dredge pump intake/suction hose is positioned on the updrift side of the SUBMAT unit in about 2-4 ft of water and at least about 50 ft updrift of the SUBMAT unit installation location. This offset distance prevents the dredge hole from undermining the SUBMAT unit after installation and filling. The pump discharge hose (with rigid wand installed) is positioned at a fill point of the SUBMAT unit, for example at the first or second most seaward updrift fill point. The rigid fill wand is inserted into the fill point and the filling operation is commenced. Filling continues and the fill wand is retreated until that section of the SUBMAT unit is filled with material. The fill wand is then removed and reinserted into the next landward fill point in the same SUBMAT unit chamber, and the filling operation is repeated. This process continues until the updrift chamber of the SUBMAT unit is filled at least to the water's edge.

Next, in embodiments of the SUBMAT system, a second chamber of the SUBMAT unit adjacent to and just downdrift of the filled chamber, is filled by repeating the filling operation. This process continues until the SUBMAT unit is completely filled in the portions deployed in the water. Embodiments of the SUBMAT system then allow position adjustment and alignment of the SUBMAT unit portion deployed on land. Then, the remaining chambers are filled starting updrift and working downdrift until the SUBMAT unit is filled to the desired level. Finally, if desired, additional sand is pumped into any of the SUBMAT unit fill ports to achieve a most uniform section.

FIG. 7 illustrates the deployment of a SUBMAT unit according to various embodiments of the SUBMAT system disclosed herein. The SUBMAT unit 700 is deployed in a littoral zone of a beach, in the “swash zone,” which is the area between the low water mark and high water mark. The SUBMAT unit 700 is deployed across the swash zone with one end positioned on the beach (landward end) and the other end positioned in the sea/water (seaward end). Various embodiments of the SUBMAT unit 700 are anchored in place before the unit is filled.

According to various embodiments, the SUBMAT unit 700 is anchored on the landward end with anchors 702, such as soil anchors, with anchor points extending several feet further landward. The SUBMAT unit 700 is anchored on the seaward end with anchors 703, such as soil anchors, with anchor points extending several feet further seaward. Some embodiments use soil anchors such as DANFORTH® anchors. Various embodiments of the anchors 702 and 703 utilize stake rings 716, handles 712, 714, or a combination thereof to anchor the SUBMAT unit 700 in the intended location on the beach. Various embodiments also utilize anchors 704, such as arrowhead anchors, installed along the sides of the length of the SUBMAT unit 700, again utilizing stake rings 716, handles 712, 714 or a combination thereof to anchor the SUBMAT unit 700.

FIG. 8 demonstrates an embodiment of the SUBMAT system, deployed on a beach and partially submerged. In FIG. 8 the SUBMAT unit 800 includes a rectangular geotextile mattress 801 with the top covered by an outer geotextile layer 802. The scour tubes 804 are partially buried in the sand due to scouring activity from the surf. The scour tubes 804 prevent scouring of the mattress 801 and so the mattress 801 remains on top of the sand.

FIG. 9 illustrates a roadway system provided by a plurality of SUBMAT units, deployed across the swash zone at a beach location, according to an embodiment of the disclosure. According to various embodiments, the disclosed SUBMAT system provides a plurality of SUBMAT units 900 deployed in series and/or in parallel, filled with indigenous filling material, which together provides a roadway having an intended length or width. Various embodiments of the SUBMAT units 900 have tapered ends 908 with dimensions that provide for an overlap junction between adjacent SUBMAT units.

According to various embodiments, the SUBMAT system is applied and used efficiently on the ground as a road surface utilizing sandy/granular material inside the SUBMAT unit. Similar to the submersible environment, such as the littoral zone, multiple SUBMAT units are connected together on the ground in series and/or in parallel to create any size of required roadway or roadbed system.

Various embodiments of the SUBMAT system support weights of at least 70 tons, and successfully supports those vehicles disclosed herein and illustrated in FIG. 1, as well as the M1A1 Abrams main battle tank.

According to various embodiments, the SUBMAT system does not require special storage conditions when not in use. Various embodiments of the SUBMAT system are stored and utilized at any ambient temperature range or water temperature range. No temperature limitations exist for the SUBMAT system either in storage or during deployment or use in the field.

According to various embodiments, the SUBMAT system mattress material is sealed during construction of the SUBMAT unit such that the mattress material is sewn on all seams. The construction allows the mattress or enclosure to capture the solid particles of the fill material and for water and air to escape freely. The filling or fill material is pumped into the mattress as a slurry using a pump system. In various embodiments, the SUBMAT has fill ports that, once the mattress is full, are self-sealing. Embodiments of the fill ports are flap-type ports composed of the same or similar geotextile material as the SUBMAT. The seal is self-equalizing so that no excess pressure will build up inside the mattress. Further, the SUBMAT is porous so that air and/or gas pressure escapes freely.

Various embodiments of the SUBMAT system are essentially a one-use type of system. Filling material can be removed mechanically or manually by hand by cutting the geotextile material and removing the filling material.

According to various embodiments, the SUBMAT is capable of being folded like an accordion and can be unfolded manually by hand by pulling and unfolding as the SUBMAT is deployed. Embodiments of the SUBMAT can be deployed at any water depth, while deployment in water depths greater than about 3.5 feet may require underwater divers to install or to assist in the installation.

According to various embodiments of the SUBMAT system, multiple SUBMAT units can are connected together side-by-side by overlapping the unfilled scour tube and then filling the adjacent SUBMAT unit, or end-to-end by simply overlapping the tapered end of the first SUBMAT unit with the tapered end of a second SUBMAT unit. Various embodiments do not require any special connection.

According to various embodiments, the SUBMAT system is deployed by one or more methods. In one embodiment, the collapsed SUBMAT unit(s) are connected to a vehicle capable of crossing the area of interest (AOI) via chains or cordage. As the vehicle crosses the AOI, it will expand the SUBMAT unit. This type of deployment is used, for example, during riverine, dry beach, and inland use cases.

In another embodiment, for instance in littoral environments, or during JLOTS operations, vehicles are conveyed to the beach via lighter vessels. The lighter provides a platform from which to assemble and deploy the SUBMAT system. The leading edge of the SUBMAT unit is taken onshore to partially deploy the matting as the vehicle leaves the lighter. As the vehicle leaves the lighter, the lighter will debark from the landing, deploying the remainder of the matting under the water surface. In this manner, the wet/dry interface of the shoreline is stabilized. Additionally, if the dry reach of the beach requires stabilization, multiple vehicles can deploy the matting from the lighter in a similar manner.

In another embodiment, the SUBMAT system is deployed by a squad of personnel, allowing it to be rapidly installed to cover larger areas. The collapsed unit is carried to its installation location and extended from its collapsed state. In further embodiments, prior to or during installation, multiple SUBMAT units are joined together.

All parameters presented herein including, but not limited to, sizes, dimensions, times, temperatures, pressures, amounts, quantities, ratios, weights, volumes, and/or percentages, and the like, for example, represent approximate values and can vary with the possible embodiments described and those not necessarily described but encompassed by the invention. For example, an interval spacing of 12 feet apart means about 12 feet apart. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Further, references to the singular forms “a”, “an”, and “the” concerning any particular item, component, material, or product include plural references and are defined as at least one and could be more than one, unless the context clearly dictates otherwise. The terminology employed is for the purpose of describing particular embodiments and is not intended to be limiting in any way.

When a range is given as “(a first number) to (a second number)” or “(a first number)-(a second number)” this means a range whose lower limit is the first number and whose upper limit is the second number. For example, 25 to 100 or 25-100 should be interpreted to mean a range whose lower limit is 25 and whose upper limit is 100. Additionally, it should be noted that where a range is given, every possible subrange or interval within that range is also specifically intended unless the context indicates to the contrary. For example, if the specification indicates a range of 25 to 100 such range is also intended to include subranges such as 26-100, 27-100, etc., 25-99, 25-98, etc., as well as any other possible combination of lower and upper values within the stated range, e.g., 33-47, 60-97, 41-45, 28-96, etc. Note that integer range values have been used in this paragraph for purposes of illustration only and decimal and fractional values (e.g., 46.7-91.3) should also be understood to be intended as possible subrange endpoints unless specifically excluded.

It is to be understood that where reference is made herein to a method or process that includes two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where context excludes that possibility), and the process can also include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all of the defined steps (except where context excludes that possibility). Methods of the disclosure can be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.

For purposes of the disclosure, the term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a range having an upper limit or no upper limit, depending on the variable being defined). For example, “at least 1” means 1 or more than 1. Terms of approximation, such as “about,” should be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise. Absent a specific definition and absent ordinary and customary usage in the associated art, such terms should be interpreted to be ±10% of the base value.

While various embodiments have been described, such embodiments have been presented by way of example and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made without departing from the spirit and scope of the invention. The invention should not be limited by any of the described exemplary embodiments.

The product(s), method(s), and system(s) of the invention are often best practiced by empirically determining appropriate values of the operating parameters or by conducting simulations to arrive at best design for a given application. Accordingly, all suitable modifications, combinations, and equivalents should be considered as falling within the spirit and scope of the invention.

Example Performance Testing

Performance testing of the SUBMAT system was performed under varying soil and environmental conditions to ensure performance requirements were met. Strong and weak soil substrates were evaluated to determine the SUBMAT systems' ability to mitigate their respective failure modes. Strong soils (i.e., sands) fail as repeated passes over the soil cause the soil to shift reducing traction. SUBMAT performance in strong soils was evaluated for its ability to improve lateral confinement thereby preventing soils from shifting under tires and tracks. Weak soils (i.e., silts, clays, and organics) fail as the tires penetrate the soil surface due to a lack of localized bearing capacity. SUBMAT performance in weak soils was evaluated for its ability to distribute vehicle loads across the SUBMAT structure, to improve soil bearing capacity, and prevent tire penetration. Soil heave at the edges of the mat were monitored as an indicator of matting failure.

A report of the results of this study has been published and is publicly available. Rutherford et al., “Full-Scale Trafficability Testing of Prototype Submersible Matting Systems”, US Army Engineer Research and Development Center, Report number: ERDC TR-23-18. The contents of this report are incorporated herein in its entirety.

Deployment Testing

Deployment testing tested the ability of the SUBMAT system to be installed by various means. Tests were conducted to verify deployment times and ensure proper installation. The testing demonstrated the ability of SUBMAT system to expand from its collapsed state, be dragged into position along the soil, and filled with soil. Testing included deployment of single SUBMAT units as well as multiple, connected units.

Vehicle deployment. According to various embodiments, the collapsed SUBMAT unit(s) is connected to a vehicle capable of crossing the area of interest (AOI) via chains or cordage. As the vehicle crosses the AOI, it expands the SUBMAT unit. This type of deployment is an anticipated mechanism during riverine, dry beach, and inland use cases.

Lighter deployment. According to various embodiments, in littoral environments, vehicles are conveyed to the beach via lighter vessels. A lighter is a type of flat-bottomed barge used to transfer goods and passengers to and from moored ships. Under these scenarios, the lighter provides a platform from which to assemble and deploy the SUBMAT system. As in the vehicle deployment case, the leading edge of the SUBMAT unit is taken onshore to partially deploy the matting as the vehicle leaves the lighter. As the vehicle leaves the lighter, the lighter debark from the landing, deploying the remainder of the matting under the water surface. In this manner, the wet/dry interface of the shoreline will be stabilized. Additionally, if the dry reach of the beach requires stabilization, multiple vehicles deploy the matting from the lighter in a similar manner.

Manual deployment. According to various embodiment, the SUBMAT system is deployable by a squad of personnel, allowing it to be rapidly installed and cover large areas. The collapsed unit is carried to its installation location and extended from its collapsed state. In some embodiments, prior to or during installation, multiple units are joined together.

Trafficability Testing

A full-scale test section was constructed and evaluated. All tasks associated with the experimentation, including the construction, testing, and analysis, were accomplished by ERDC personnel. Construction activities were performed using conventional construction equipment and pumping systems.

The field experiment was conducted at an outdoor test site at the ERDC Ground Vehicle Terrain Surfacing Test Facility (GVTSTF) at the Waterways Experiment Station in Vicksburg, Mississippi, USA. The site was located on the northeast end of Brown's Lake in a dredge fill containment area encircled by a gravel-surfaced road (Susquehanna Circle). The soil at the site contained dredged material from Brown's Lake placed in the 1980's. Local soils in the Vicksburg area are loess deposits, and subgrade sediments in the containment area are classified per the Unified Soil Classification System (USCS) as low-plasticity clayey silt (ML-CL).

The subgrade immediately underlying the SUBMAT systems was a locally sourced sand typically used as fine aggregate in concrete. The sand was a pit-run wash sand containing approximately 4% gravel sizes and 2% minus No. 200 U.S. standard sieve size material. It classified per American Society for Testing and Materials (ASTM) D2487 as a poorly graded (SP) sand (ASTM International 2017).

SUBMAT Roadway System

Units of the SUBMAT roadway system were composed of GEOTEX® 4×6 polypropylene geotextile with heavy woven serrated yarns, sewn into a rectangular shaped mattress and protected by an outer layer of PYRAMAT® three-dimensional polypropylene geotextile. The seam strength of the sewing operation was greater than the strength of the geotextile.

SUBMAT unit embodiments were tested at the ERDC to determine performance under military vehicle wheel loading. Testing embodiments were constructed by first sewing a 1 ft high by 7.5 ft wide by 40 ft long rectangular mattress with a longitudinal line of 12 in long internal vertical braces located 3.5 ft from mattress edge. The 12 in long internal vertical braces were located on either a 1.5 ft, 2.5 ft, or 5 ft spacing. In addition, the mattress had three fill sleeves sized to accommodate a 6 in diameter fill pipe. To complete the construction, two of these rectangular mattresses were sewn together to form a 1 ft high by 15 ft wide by 40 ft long SUBMAT unit. Two SUBMAT units were constructed and tested-SUBMAT 1 and SUBMAT 2.

Test Site Construction

The test site is illustrated in FIG. 9. The test site was constructed using an excavator and a skid steer to place sand at the site into a roadway that was about 240 ft long, 30 ft wide, and 6 ft high. Once the sand was roughly leveled, three pits were dug along the length of the sand subgrade. Each pit was 20 ft wide, 40 ft long, and 2 ft deep. The pits were lined with a plastic lining to allow them to retain water. Once lined, the pits were refilled with the original sand, and an earth pressure cell (EPC) was installed in each of the traffic pits approximately 1 in below the surface in the line of the north wheel path of the traffic. The pits were distributed such that each pit was about 30 ft away from the next pit. Transition ramps of AM2 mat were placed over the sand subgrade and between SUBMAT units. The SUBMAT units were deployed within a traffic pit such that the surface of the mattress was roughly flush with the transition ramps between each traffic pit. On the outer edges of the test section SUPRA-TRACT access ramps were placed over the sand subgrade.

Off to the side of the traffic lane, another pit, roughly 30 ft long, 20 ft wide, and 4 ft deep, was excavated. The bottom of this pit was lined with hexagonal plastic mats to protect the plastic liner. This pit was used as a dredging pit to create a sand slurry that could be pumped into the SUBMAT units.

Mat Installation

The SUBMAT units were taken from shipping pallets, unrolled, and carried by the corners of the mats by a team of four. Each SUBMAT unit was placed in its own traffic pit and was ready to be filled by sand pumped from the dredge pit.

The team utilized a Mini Robotic Submersible-Dredge (MRS-D; ERDC) to fill the SUBMAT unit. Although the MRS-D proved capable of filling the SUBMAT unit, the capacity of system was very powerful for the task. To reduce the effect of overfilled sections of the SUBMAT unit, smaller 2 in dredge pumps were implemented to fill in low areas and improve the overall smoothness of the surface of the SUBMAT unit.

Traffic Application

Channelized traffic was applied to the test SUBMAT roadway system using a series of military vehicles according to the traffic path shown in FIG. 10. The vehicles included a 7-ton, 6-wheeled MTVR truck; a 10-ton, 8-wheeled HEMTT truck; and an M1A1 Abrams tank equipped with road pads. The vehicles were driven alternately forward and backward over the test roadway in the same wheel paths at a steady-state condition of approximately 5 to 10 mph. All necessary accelerations and decelerations were performed on the AM2 access ramps beyond the ends of the mat systems being evaluated.

Traffic was paused intermittently to document the condition of the test roadway surface. Prior traffic data from other studies have shown that rut development is exponential in nature, so intervals were selected to have a logarithmic-like distribution. Data were collected at passes 0, 10, 20, 50, 100, 200, 500, and 1000 for the MTVR. The traffic intervals for the HEMTT were 0, 10, 20, 50, 100, 200, and 350 passes, and the traffic intervals for the M1A1 Abrams were 0, 10, 30, 50, 100, and 150 passes.

MTVR (7-ton). In this study, a dump truck variant of the MTVR was utilized to apply traffic. The truck was loaded with 7 tons of uniformly-distributed lead blocks. The tire pressures were set following the recommendations for “cross-country” driving conditions, i.e., 28 psi in the two front tires and 35 psi in the four rear tires. The front axle of the loaded truck carried a load of 15,490 lbf and the combined load on the two rear axles was 29,450 lbf. The contact area of the tire-to-soil was estimated assuming the contact pressure is equal to the air pressure of the tires giving a front and rear contact area of 277 in²and 210 in², respectively. Usually, the actual contact pressure will be higher than the air pressure due to the rigidity of the tire sidewall. In previous studies using the MTVR, the contact pressures have been estimated to be approximately 28 to 32 psi for the front and 35 to 40 psi for the rear tires.

HEMTT A4 Cargo Truck (8-wheel). The HEMTT A4 is a four-axle heavy cargo truck used by the U.S. Army with a nominal capacity of 10 tons. The front axle of the HEMTT was loaded to 13,700 lbf, the second axle to 14,140 lbf, the third axle to 16,240 lbf, and the rear axle to 15,660 lbf. Based on the axle loads and the tire pressure of 70 psi, the contact areas of the tires ranged from about 98 in²to 116 in²with an average of 107 in². This agrees with the nominal tire pressure for a HEMTT of 70 psi with a contact area of 113 in².

M1A1 Abrams Tank. The M1A1 Abrams tank is an armored, tracked vehicle with a 120-mm cannon. The weight of the vehicle is nominally about 127,000 lbs but was not weighed at the time of testing. Its ground pressure is approximately 10 psi. This vehicle was used as a tracked vehicle for testing but was also equipped with road pads to protect paved surfaces.

Data Collection

Rut Depths. Rutting in the SUBMAT units was quantified and recorded via LiDAR. A straight edge and ruler were also implemented at the final pass of each vehicle to supplement and validate the LiDAR data. Because SUBMAT units in this study were filled with sand and not rigid, the rut depth was measured without a weight applied. Typically, the weight is applied to depress the mattress into the rut forming in the subgrade; however, all the SUBMAT units in this study experienced the deformation and rutting within the mattress themselves. A metal straight edge, 6 ft in length, was laid across the north wheel path at the quarter points along the length. A rigid ruler was used to measure the distance from the straight edge to the center of the rut, 1 ft left of center and 1 ft right of center.

EPC measurements. The EPCs were positioned about 1 in below each SUBMAT unit in the center of the north wheel path. They connected to a computer-controlled data acquisition system which manually activated before each traffic interval began. These data provided a means of assessing a given mattress unit's ability to distribute the load of the vehicle.

LiDAR. A Riegl VZ-400 Terrestrial LIDAR Scanner was used to capture the shape of the SUBMAT unit post-filling and prior to being trafficked. Data was collected into point-clouds using RiSCAN PRO collection software. The Riegl VZ-400 is a line-of-sight instrument that is unable to penetrate water, which can cause shadowing behind steep slopes and missing data points in areas of standing water. LiDAR scans were also collected throughout the trafficking tests after a predetermined number of passes to track the progression of rut depths for each test vehicle. Scans were collected after 5, 10, 25, 50, 200, 500, and 1000 passes of the MTVR; 10, 20, 50, 100, 200, 250, 350 passes of the HEMTT; and 10, 30, 50, 100, and 150 passes of the M1A1.

Failure Criteria. A SUBMAT unit was considered failed when it reached one of the following failure criteria: (1) the rut depth in the wheel path reached a critical limit or (2) the mattress unit reached a critical point of physical damage. Note that in many cases, especially in the case of rutting failure, traffic could be sustained beyond the failure point of the mattress unit. Although a SUBMAT unit may have “failed,” traffic in the study continued until the mattress unit could no longer be reasonably repaired, the mattress unit posed a tire hazard, or until rutting became severe enough to cause the differential of the vehicle to come into contact with the mattress unit.

Mat breakage. The critical point for mattress unit breakage has been defined as 20% of the surface area in previous studies (Santoni et al. 2001, Expedient Road Construction Over Soft Soils, ERDC/GSL TR-01-7, U.S. Army Engineer Research and Development Center; Rushing et al. 2007, Evaluation of Expeditionary Mat Surfacings for Beach Roads, ERDC/GSL TR-07-1, U.S. Army Engineer Research and Development Center; Rushing and Rowland 2012, Comparison of Original MO-Mat and Prototype Replicas for Expeditionary Roads, ERDC/GSL TR-12-18, U.S. Army Engineer Research and Development Center; each reference incorporated herein in its entirety), so that criterion was used in this case for direct comparisons. Physical damage for the SUBMAT unit included wearing and tearing holes in the surface of the mattress unit.

Permanent subgrade/mattress deformation. The overall failure of the mattress unit due to permanent subgrade/mattress deformation is vehicle dependent. The failure occurs when the vehicle is physically hindered from traversing the mattress unit. To this end, rutting, which is a measure of subgrade/mattress deformation, was used to quantify failure. In previous studies (Santoni et al. 2001; Rushing et al. 2007; Rushing and Rowland 2012), a critical limit of 3 in deep ruts was used as the failure criterion; however, in this study that criterion is only used as a comparative value, because the vehicles used in this study could still traffic the mattress unit through 3 in deep ruts. Also worth noting, the rut depth in this study was measured in such a way that upheaval from shear flow induced by rutting is included in the rut depth value. In order for the rut depth to cause failure, the rut would need to be at least 8 in deep for the differential of the MTVR or HEMTT to begin dragging on the mattress surface.

Test Results

Mattress performance. The SUBMAT system performed well under the applied traffic. The wearing surface of the SUBMAT unit held up with negligible observable damage throughout the trafficking of the 1,000 passes of the 7-ton MTVR and the 350 passes of the 10-ton HEMTT. Rutting developed in each mattress unit deep enough to reach the 3 in criteria, but the wearing surface held up exceptionally well, and vehicle traffic was not hindered in any significant manner. The wearing surface also held up with some minor observable damage after 50 passes of the M1A1 Abrams tank. The observed damage was tearing along the outside of the track path near the transition ramps. After 150 passes of the M1A1, the tear in the mattress was a little less than 3 ft in length. Continued trafficking with the M1A1 Abrams tank resulted in further tearing in the locations where damage was already observed, but the damage was not significant enough to be considered failure by mattress breakage.

After completion of the MTVR, HEMTT, and M1A1 tank traffic, the SUBMAT system only exhibited minor damage. Therefore, the team decided to traffic the excavator on site on the mattress units. The goal of the additional traffic was to evaluate the effect of tracked vehicle traffic without any protective pads (recall the M1A1 had protective road pads on the tracks). After 26 passes of the excavator, only minor tearing of the wearing surface was observed with no major structural damage to the confining geotextile material underneath the wearing of the surface.

The team then decided to use a nearby D8 bulldozer with more aggressive tracks to gain better traction. Some significant damage was observed after 24 passes in which the tracks gouged slits through the geotextile material and began to tear the wearing surface completely away in other locations. With the slits in the geotextile material, the capability of the SUBMAT system to completely confine the sand material was compromised leading to a degradation in performance. However, the damage was relatively small, so it is possible the matting system would be able to complete the mission with a limited number of passes of vehicles with tracks like the D8 bulldozer.

Rut depth. FIG. 11 is a plot of the average rut depth versus number of traffic passes for the MTVR. Recall that rut depths were measured using LiDAR and verified with a straight edge and ruler. FIG. 12 and FIG. 13 show the normalized average rut depth for the HEMTT and M1A1, respectively. These data sets were normalized to show the evolution of the rutting strictly due to the new vehicle traffic, without respect to how deep the rut was prior to trafficking with the new vehicle.

EPCs. EPCs were deployed underneath each SUBMAT unit at a 1 inch depth to measure each SUBMAT unit's ability to distribute the applied load. EPC data for SUBMAT 1 and SUBMAT 2 are reported in FIG. 14 and FIG. 15, respectively. The raw data were greatly reduced due to their variability. Rather than the imprecision of the instruments, experimental error associated with the speed and steering of the vehicles was thought to be the cause of the inconsistencies in the data. Very slight deviations in the wheel path resulted in large differences in the measured pressures. While a false high pressure is unlikely, a false low pressure would have resulted if the vehicle tire/track did not pass directly over the center of the EPC. Therefore, a peak picking software was implemented to find the peaks in each traffic interval, and the maximum peak of each interval was recorded.

LiDAR. LIDAR scans were collected throughout the trafficking tests after a predetermined number of passes. Scans were collected after: 5, 10, 25, 50, 200, 500, and 1000 passes of the MTVR; 10, 20, 50, 100, 200, 250, 350 of the passes HEMTT; and 10, 30, 50, 100, and 150 passes of the M1A1. These scans produced dense point clouds used to map the overall shape of both SUBMAT unit as well as track the progression of rut depths for each test vehicle. While this collection method allows rut depth measurements for both wheel paths along the entire length of mattress, only measurements at the quarter point locations (A1, A2, A3, B1, B2, B3) along the north wheel path are presented in FIG. 16.

Analysis of Results

Mattress performance. The performance of the SUBMAT system under conditions of this study was excellent in terms of serviceability of the system. While significant rutting was observed well beyond the 3 in criterion, none of the vehicles were hindered by the ruts. The SUBMAT unit wearing surface proved capable of withstanding 1000 passes of the MTVR and an additional 350 passes of the HEMTT without showing any significant damage. Although the M1A1 Abrams caused some minor tearing at the edges of the mattress unit at 150 passes, the damage was not sufficient to cause catastrophic failure in a field deployment.

It should be noted that while trafficking, the M1A1 Abrams tank was equipped with road pads on the track, which are designed to protect paved roadways from being damaged by the tank tracks. These road pads may have also served to reduce the wear and tear on the surface of the mattress unit. After trafficking with the M1A1 Abrams was completed, another 50 passes were made using tracked vehicles that were not equipped with any type of padding. Half of the passes were with an excavator used at the jobsite, and the other half of the passes were done by a bulldozer equipped with bog tracks for greater traction in unstable soil environments. The unprotected tracked vehicles caused significant damage to the matting surface resulting in fraying and tearing across the surface of the mat. Despite the surface damage, the sand remained largely confined and the mat remained trafficable.

Rut depth. The rut profile changed notably when the trafficking vehicle changed; however, this phenomenon was not easily seen in the averaged data. This can be seen in FIG. 12 where the normalized average rut depth at the beginning of HEMTT traffic goes negative. This is likely due to changes in tire shape and pressure. As a result, the initial passes of a new vehicle tended to flatten out the channelized rut formed under the previous vehicle's tires. The same phenomenon was observed when traffic changed from HEMTT to M1A1 Abrams tank (FIG. 13).

It is also worth noting that a difference between SUBMAT 1 and SUBMAT 2 was the amount of sediment filling each mattress unit. However, the SUBMAT 1 unit was filled with more sediment than SUBMAT 2 unit. This resulted in noticeably less rutting in SUBMAT 1, so it is believed that with a better, more evenly distributed filling method, greater resistance to rutting can be achieved. This is attributed to effective confinement of the sand. By filling SUBMAT more completely, the sediment inside the mattress was more confined with less space to move around. As a direct result, the bearing strength of the sediment inside SUBMAT 1 was significantly improved leading to slower rut formation.

After the removal of the SUBMAT units post-trafficking, the team observed that the sand beneath the mattress units showed no signs of rutting. This was expected, because the sand-filled SUBMAT units were capable of accommodating the deformation within the mattress unit itself rather than acting like a rigid unit that disperses pressure across the subgrade. By containing the deformation, the SUBMAT units effectively protected the subgrade soil.

EPC. In general, the peak ground pressure just below the SUBMAT unit increased as the traffic intervals increased. One reason for this is that there were simply more passes in the later traffic intervals increasing the likelihood of the tire passing directly over the EPC. The second reason is that the as the ruts developed, less sand was present to transmit the pressure through the mattress unit. The latter reason is further supported by the logarithmic nature of the increasing pressure. The rutting tends to increase logarithmically with increasing traffic passes, and similarly, the observed peak ground pressure increased logarithmically with traffic intervals as well.

LiDAR. During the filling process, SUBMAT 1 was slightly over filled in some areas, while SUBMAT 2 was slightly under filled in others. Significant rut development occurred rather quickly as vehicle traffic was applied but appeared to reach a steady-state depth over time for each vehicle trafficked as seen in the LiDAR data in FIG. 16. After 25 MTVR passes, significant rutting developed in the under-filled areas of SUBMAT 2. At 50 MTVR passes the rut is almost fully developed, and there is little change in rut shape or depth after 200 MTVR passes.

Conclusions. The SUBMAT system performed above expectations. The SUBMAT units withstood 1000 MTVR passes, an additional 350 HEMTT passes, and 150 more passes with a M1A1 Abrams tank while experiencing only minor damage.

Additional traffic was applied to the SUBMAT units with 26 passes of a tracked excavator and 24 passes of a bulldozer. These tracked vehicles did not have protective padding, and both vehicles caused some minor damage. The tracks on the bulldozer, with protrusions for better traction, caused significant damage including tearing small holes in the geotextile material and completely pulling away the wearing surface in some areas.

The rut formation in the SUBMAT units was significantly deep. However, with a mattress filled more evenly and fully, the SUBMAT unit offers sufficient confinement to protect against rut formation. Once the ruts reached a critical depth, there was enough confinement to prevent any further deterioration of the mattress unit. Furthermore, when heavy vehicles trafficked the same path, the ruts did not get deeper. Rather, the rut profile shifted to match the profile of the new vehicle's tire or tracks.

The LiDAR data was comparable of measuring rut depth potentially allowing faster surveying between traffic intervals in appropriate conditions.

The SUBMAT units proved to be durable and robust in holding up to a wide variety of vehicle traffic in austere conditions.

The ability to fill the SUBMAT units with indigenous native material wherever the system is deployed is a key advantage of the SUBMAT system. This benefit reduces the transportation logistics burden to only the SUBMAT units and the pumping equipment, eliminating the need to transport the filler material.

While inventive concepts have been described and illustrated herein by reference to certain embodiments, various changes and further modifications may be made by those of ordinary skill in the art without departing from the spirit of the inventive concept, the scope of which is to be determined by the following claims.

Submersible Matting System

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