Patent Description:
Modular ground protection flooring is used frequently to provide temporary protection for grass and turfed areas such as sport stadiums as well as to provide temporary access to sites with poor ground conditions including construction, energy and utility installation sites. These modular systems create rigid floor surfaces that provide walkways, roads, parking areas and other types of flooring to support the passage of people and vehicles and allow storage and mounting of equipment. Example modular flooring systems are described in <CIT>; <CIT>; <CIT>; <CIT> and <CIT>.

Some existing plastic ground protection mats are typically hollow honeycomb constructions with examples described in <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>. The honeycomb construction may allow air and light to penetrate to the underlying grass whilst also providing the required rigidity.

Connection and interlocking of the mats to form a unitary structure is important so that they are not displaced during use. Example interlocking mat assemblies are described in <CIT>, <CIT>, <CIT>, and <CIT>. However, existing ground protection apparatus and in particular mat interconnectors typically require relatively precise alignment during coupling and are generally limited for use on flat ground. That is, these existing systems become very difficult to connect when the mats are laid on uneven ground and/or the connector and/or mats change slightly by expansion or contraction due to temperature change. Additionally, existing systems are typically very difficult to interconnect in conditions where the mat interconnectors become heavily coated in mud or other ground debris. In these situations, mating flanges or threads often become blocked. Additionally, when the panels are rigidly connected, undesirably large stress and strain forces are placed on the connectors which are then susceptible to damage or failure.

Furthermore, existing systems are typically associated with large numbers of ground protection mats which typically require large numbers of connectors. In remote locations and particularly in muddy ground conditions and/or where the weather is inclement, it is not always possible to use power tools to install and remove the mats. A larger number of mat connectors presents a significant task for installation staff having to manually rotate conventional connection bolts to provide complete mat coupling. Accordingly, what is required is a fastening arrangement and ground protection apparatus that addresses these problems.

Document <CIT> discloses a panel for a modular floor covering system.

It is an objective of the present concept to provide a fastening device for the releasable interconnection of ground protection mats or panels that is convenient to operate in all manner of environments specifically including muddy, sandy and other ground conditions that may be laden with lose ground material. It is a specific objective to provide connection apparatus and a ground protection system that utilises a fastening device that may be operated conveniently by manual tools via a simple rotational action of the coupler via a minimum number or rotations. It is a specific objective to minimise the time taken for interconnection and dismantling of the ground protection system via a coupler mechanism that is quick and convenient to operate.

It is a further specific objective to provide such a fastening device that provides a reliable and robust connection of adjacent ground protection mats and is resistant to localised movement. It is a further specific objective to provide a fastening device to forcibly draw together misaligned adjacent mats and to provide a fastening device that does not require precise co-locating of mats. It is a yet further specific objective to provide a fastening device having a locking mechanism to retain adjacent mats in interconnected and partially overlapped contact with one another whilst enabling the mats to move so as to accommodate expansion and contraction due to temperature changes or lateral displacement due to other forces. It is a yet further objective to provide a ground protection system providing such features.

The objectives are achieved via a fastening device and connection apparatus and system having a male part and a female part that are mateable together via a rotation of at least the male part, with the connection mechanism being releasably locked together via a biased lock that is resistant to decoupling of the male and female parts. The present fastening device, apparatus and system utilises first and second helical ribs provided at the male and female parts having a minimum axial length. Such a configuration is advantageous to minimise a rotation needed to advance and fully couple the male part within the female part to achieve a fully locked and interconnected coupled joint. This is achieved via cooperating helical ribs at the male and female parts having an axial length that correlates to a pitch of at least the first helical rib on the male part and optionally the second helical rib on the female part. That is, the present coupler comprising the respective helical ribs for interconnection comprises an axial length that is in a range <NUM> to <NUM>% of the pitch of the first and/or second helical ribs.

Reference within this specification to 'pitch' encompasses a distance from a first crest to a second crest of a thread that follows a helical pathway along a shaft of the male part (i.e., a bolt or screw) when viewed from the side and/or at an axial cross section of the shaft that includes the helical thread. The distance between neighbouring or adjacent crests in the axial direction includes the distance between a mid-point of each neighbouring crest (axially closest or adjacent crest) that includes an apex, a mid-plateau region or other mid-point of what may be regarded a crest or peak of the helical thread. Similarly, the term 'pitch' may equally be taken as the distance between the root or trough of the thread with the pitch being the distance from a first root to a next neighbouring or adjacent root when viewed from the side or at the same axial cross section of the shaft upon which the thread extends.

According to the present concept, the axial length of the helical rib on the male part and the female part extends over a range <NUM> to <NUM>° (as defined between the end points of the thread i.e., start and finish points in the axial direction). Optionally, the helical rib extends over a single helical turn of around <NUM>° to start and stop approximately at the same position in a circumferential direction on the shaft (with the start and finish axial ends of the helical rib being aligned or approximately aligned in a circumferential direction).

Within the specification, the reference to the 'axial length' of the helical rib includes a helical rib and optionally none, some, part of or all nodes, projections or flanges that project radially, axially, and/or circumferentially at axial end regions of the helical rib. Accordingly, the axial length of the helical rib may not include any node projections at the rib axial ends. Optionally, the axial ends of the helical rib may be defined as the region immediately starting with an enlarged node projection. Accordingly, the rib is defined as having a generally uniform axial thickness and radial width. However, for the purposes of the calculation of the length of the helical thread, the helical thread may include node projections of enlarged axial thickness and radial width relative to a majority of the length of the helical rib that is enlarged with such node projections positioned at a region along the length of the helical rib i.e., not at the rib axial ends and/or at mid-axial length regions. The present fastening device is suitable for the releasable interconnection of ground protection mats via a face-to-face contact of opposed flanges formed at the mats. Optionally, the flanges extend laterally outward from the mat lengthwise and widthwise sides. Optionally, a separate coupler could be used to couple the mats instead of overlapping flanges provided at each mat. Such a coupler may comprise a generally planar body so as to extend between adjacent neighbouring mats and effectively bridge the neighbouring mats as a bridging unit. The coupler may comprise the same connection mechanism, features and function as described referring to the ground protection mats.

Advantageously, the present fastening device is suitable to couple neighbouring and adjacent mats laid on uneven or lose ground and that may be misaligned due to such ground undulations. The present device is specifically beneficial to draw-together the mats via a simple minimum rotational action of a coupler body. The adjacent mats once drawn-together are then adapted to be releasably locked in their fastened configuration via a releasable lock mechanism. The minimised rotational action of the coupler body is achieved via a minimised axial length of the inter engaging helical ribs provided at the male and female parts. Additionally, the helical ribs are further configured via their respective axial length and radial thickness to provide an interconnection mechanism that is resistant to clogging, blocking and fouling by mud, dirt, dust, sand and other loose ground material. The present connection device and system therefore provides a reliable interconnection mechanism suitable for use in a variety of different ground conditions and being operable using hand/manual tools.

Additionally, the present device via the locking mechanism provides that the mats may not be decoupled without unlocking the lock mechanism whilst allowing the mats some degree of movement or 'play' in both the horizontal/lateral plane and also the vertical plane (perpendicular to the main body of the mats). Such non-rigidly interlocked mats are therefore adapted to provide an interconnected or tessellated ground protection system having a non-rigid interconnected structure capable of following local undulations in the ground and to withstand loading forces and temperature variations that would otherwise impart stress and strain to the fastening devices.

According to one aspect of the present concept there is provided a fastening device to releasably interconnect ground protection mats or panels. According to a first aspect of the present concept there is provided a fastening device to releasably interconnect ground protection mats comprising: a first part of a connection mechanism having a male part; a second part of the connection mechanism having a female part with a bore to receive the male part and configured to connect at least two neighbouring ground protection mats side-by-side by rotation of the male part relative to the female part; the male part comprises a first helical rib projecting radially outward from a shaft and the female part comprises a second helical rib projecting radially inward at the bore configured to receive the shaft, the ribs configured to abut one another, an axial length of the first helical rib being in the range <NUM>% to <NUM>% of a pitch of the first helical rib; an axial and radial lock having a first element at the rib of the male part and a second element at the rib of the female part, the first and second elements configured to engage one another by the rotation of male part relative to the female part; and a bias lock actuator to impose an axial force to the first element to force the first element in engaged contact against the second element and to provide frictional resistance to further rotation of the male part relative to the female part.

Optionally, an axial length of the first helical rib excludes the first element at the rib of the first part if present at an axial end of the rib. Preferably, the first helical rib extends over a range <NUM> to <NUM>°; <NUM> to <NUM>° or <NUM> to <NUM>°. Such an arrangement is advantageous to provide complete interconnection and locking of the ground engaging mats via a fastening device that is time efficient to install by requiring approximately a single <NUM>° rotation to achieve full connection. The single turn helical ribs are also beneficial to provide convenient and reliable coupling of the mats in debris laden environments such as muddy, dusty, stony and sandy ground. The ribs of the present device are robust and suitably enlarged relative to conventional screw threads typically found on conventional bolts that are otherwise difficult if not impossible to operate in muddy, sandy and similar environments.

Preferably, the first and second elements comprise a combination of a node projecting from one of the ribs and a gap in the alternate rib, the gap extending in the circumferential direction of the rib. Optionally, the first element is provided at the rib of the male part and the second element is provided at the rib of the female part. Optionally, the first node is provided at a mid-length region of the rib and the gap is provided at a mid-length region of the alternate rib.

Optionally, the device comprises a second node provided at an axial end of the rib. The axial locking of the fastening device and the engaging mats is accordingly achieved via a simple rotation of the first part relative to the second part. The locking mechanism is provided at the helical rib to provide a reliable and robust cooperative means of both attaching the mats and locking the mats in position.

Preferably, the first and second nodes are separated by a distance in a range <NUM> to <NUM>° or <NUM> to <NUM>° in a circumferential direction. This is beneficial to stabilise the first part within the second part as the axially separated dual locking mechanism is provided at opposite sides of the male part (bolt) being separated by an angular separation of approximately <NUM>°.

Preferably, the second node comprises a length in a circumferential direction being greater than a length of the first node and/or the gap. Preferably, the first node and/or the gap has a length in the circumferential direction being <NUM> to <NUM>% of the length of the second node in a circumferential direction. The first node is accordingly configured to pass the gap in the rib of the second part such that the locking action is engaged only at complete or near complete full engagement of the first part and the second part. This arrangement also provides that the locking action is achieved via a single rotation of the first part relative to the second part and does not require an additional actuation of the locking mechanism relative to the rotation of the first part at the second part. The engagement and coupling of the mats in addition to the locking of the mats is accordingly provided by a single operation i.e. rotation of the male bolt into the barrel that forms the second (female) part.

Preferably, the node is defined in-part relative to the rib by a trailing face that extends axially between a lateral surface of the rib and a crest or plateau of the node, wherein an angle by which the trailing face extends relative to a longitudinal axis of the shaft is in a range <NUM> to <NUM>°, <NUM> to <NUM>° or <NUM> to <NUM>°. The stated angle of the trailing face may also be provided at a leading face of the first node and/or a trailing and/or leading face of a second node at the male rib. This inclined or sloping face at the recited angle represents a balance/compromise between achieving a secure lock (by frictional engagement) and also enabling the male and female parts to be separated via a single rotation in a counter clockwise direction relative to the clockwise direction of rotation for coupling. The inclined faces are accordingly configured to slide past the respective side faces that define the gap within the female rib and/or the end face provided at the terminal end of the female rib.

Optionally, the bias lock actuator comprises an O-ring positioned between a head of the first part that is radially enlarged relative to the shaft and an end face of the second part provided at or towards one axial end of the bore. Optionally, the bias lock actuator may comprise a cone washer, a resiliently deformable flange provided at the male part and/or the female part. Optionally, the bias lock actuator comprises a flexible flange at the first part and projecting radially outward relative to the shaft, the flange capable of flexing axially in contact with a region of the second part. Optionally, the bias lock actuator is provided by a resiliently flexible characteristic of at least one of the ribs at the first and second parts wherein at least one of the ribs is configured to flex axially as the first and second parts are mated. Preferably, the bias lock actuator is provided by a connection by which the node is connected or extends from the rib such that the connection is capable of resiliently flexing axially as the first and second parts are mated. Optionally, the bias lock actuator comprises any one or a combination of: a flexible washer; a spring; a resiliently flexible member; provided and acting between a region of the first part and a region of the second part to provide the axial force to the first part. Preferably, the bias lock actuator is configured to impose an axial force to the first element in an axial direction to separate the first part form the second part.

Preferably, the first part comprises a head provided at and being radially enlarged relative to the shaft, the head comprising a recess and a raised island at a centre of the recess. Preferably, an inner face that in-part defines a sidewall of the recess is sloping relative to a plane of the head that extends perpendicular to a longitudinal axis of the shaft. This prevents or minimises dirt, mud, sand or other debris becoming lodged within the recess at the head of the first part that would otherwise inhibit engagement by a rotational drive tool. Preferably, a perimeter of the head is bevelled or rounded. This avoids the head providing an obstruction that may be susceptible to impact by people, vehicles or objects passing over the mats. Preferably, an end face of the shaft is generally planar or is not pointed or domed. The generally planar end face of the shaft is useful to help expel any dirt or debris present within the bore of the female part.

According to a further aspect of the present concept there is provided ground protection apparatus comprising: a plurality of ground protection mats and a coupler connectable in partial overlapping configuration with the mats, at least some of the mats having a set of holes; and a plurality of fastening devices as described and claimed herein wherein the coupler and/or the fastening devices are at least partially mountable within the holes to releasably interconnect the ground protection mats.

Preferably, the coupler comprises or is formed with a plurality of the second parts and the apparatus comprises a plurality of the first parts engageable with the second parts at the coupler.

According to a further aspect of the present concept there is provided ground protection apparatus comprising: a plurality of ground protection mats provided with respective flanges formed at each of the mats and extending along lengthwise and/or widthwise edges of the mats, the flanges of the mats positionable and connectable in overlapping configuration with neighbouring mats; and a plurality of fastening devices as described and claimed herein at least partially mountable within the mats to releasably interconnect the ground protection mats.

According to a further aspect of the present concept there is provided a fastening device to releasably interconnect ground protection mats comprising: a first part of a connection mechanism having a male part; a second part of the connection mechanism having a female part with a bore to receive the male part and configured to connect at least two neighbouring ground protection mats side-by-side by rotation of the male part relative to the female part; the male part comprises a first helical rib projecting radially outward from a shaft and the female part comprises a second helical rib projecting radially inward at the bore configured to receive the shaft, the ribs configured to abut one another; an axial and radial lock having a first element at the rib of the male part and a second element at the rib of the female part, the first and second elements configured to engage one another by the rotation of male part relative to the female part; and a bias lock actuator to impose an axial force to the first element to force the first element in engaged contact against the second element and to provide frictional resistance to further rotation of the male part relative to the female part.

The second (female) part may be formed integrally with the ground protection mat or may be formed as a separate component. Optionally, the second (female) part is formed non-integrally with and at least partially mountable at each ground protection mat.

Referring to <FIG> and <FIG>, a ground protection system and apparatus comprises a plurality of mats <NUM> capable of being interconnected in partial overlapping configuration so as to provide a tessellated interconnected and unitary base positionable on the ground. The present system and apparatus is suitable for placement on a range of different surfaces but is ideally suited for placement on loose ground material such as ground with dirt, sand, gravel or on surface with organic matter such as vegetation and grass. Each mat <NUM> comprises a generally planar main face <NUM> intended to be upward facing with the mat <NUM> positioned on the ground. According to the preferred embodiment, each lengthwise and widthwise edge of each mat <NUM> comprises a lengthwise and widthwise extending flange <NUM> that projects laterally outward from a main body (that forms the majority of mat <NUM>). Each flange <NUM> comprises a plurality of holes <NUM>, <NUM> to receive a fastening device as described herein to interconnect the mat <NUM>. A first pair of lengthwise and widthwise flanges project laterally outward from a lower region of mat <NUM> and a corresponding pair of widthwise and lengthwise flanges <NUM> project laterally outward from an upper region of mat <NUM>. The separation distance between flanges <NUM> and <NUM> is configured such that the mats <NUM> may be positioned side-by-side with flanges <NUM> of a first mat <NUM> overlapping onto the corresponding flanges <NUM> of a neighbouring mat. In particular and referring to <FIG>, flanges <NUM> comprise upper (upward facing) surface <NUM> configured for positioning in face-to-face contact with corresponding lower (downward facing) face <NUM> of flange <NUM>.

Mat <NUM> comprises a plurality of holes <NUM> formed at each flange <NUM>. Each hole <NUM> comprises an annular surface <NUM> representing a collar surrounding hole <NUM>. Flanges <NUM> similarly comprise a plurality of holes <NUM>. A plurality of satellite bores <NUM> (three bores) are positioned around each hole <NUM> and are configured to receive attachment screws used to attach part of the mat fastening device in position as described herein.

Referring to <FIG>, holes <NUM> and <NUM> are configured to receive a respective fastening device indicated generally by reference <NUM> having a first part <NUM> and a second part <NUM>. First part <NUM> may be regarded a male part and comprises an elongate shaft <NUM> centred on longitudinal axis <NUM> and a radially enlarged head <NUM> projecting radially outward at one end of shaft <NUM>. A helical rib <NUM> projects radially outward from and extends around shaft <NUM> lengthwise in a direction of axis <NUM> from a region immediately in-board of head <NUM> towards a terminal distal end of shaft <NUM>.

Second part <NUM> may be considered a female part and comprises a generally cylindrical barrel <NUM> defining an internal bore <NUM>. Three base lobes (alternatively feet) <NUM> project radially outward from one end of barrel <NUM> representing mounting feet or lugs to mate into corresponding recesses (<NUM> referring to <FIG>) provided at an underside region of flanges <NUM>. As described and illustrated in <FIG>, first (male) part <NUM> may be inserted within hole <NUM> whilst second (female) part <NUM> is inserted within hole <NUM> such that as the male and female parts <NUM>, <NUM> are mated together a corresponding coupling is provided to releasably interconnect neighbouring mats <NUM> in the partial overlapping side-by-side arrangement.

Referring to <FIG>, second part <NUM> also comprises a helical rib illustrated generally by reference <NUM> that projects radially inward from bore <NUM> and in particular a cylindrical bore surface <NUM>. Helical rib <NUM> comprises a first axial end <NUM> and a second opposite axial end <NUM> with ends <NUM>, <NUM> separated axially by a distance approximately equal to an axial length of bore <NUM>. That is, helical rib (alternatively a thread) <NUM> extends over all or a majority of the axial length of bore <NUM>. A gap <NUM> is provided at a mid-axial length position of helical rib <NUM>. Gap <NUM> is positioned at an equal separation distance from rib first end <NUM> and rib second end <NUM>.

Referring to <FIG>, rib <NUM> projecting radially outward at shaft <NUM> of the first part <NUM> comprises a first rib end <NUM> and a second rib end <NUM>. An axial separation distance A of rib first end <NUM> and second end <NUM> is approximately equal to a pitch of the helical rib. In particular, helical rib <NUM> extends over an angular distance of approximately <NUM>° between ends <NUM> and <NUM>. The axial distance A accordingly represents one full helical turn of rib <NUM> extending between ends <NUM> and <NUM>. The axial dimensions and length A of rib <NUM> is also approximately equal to the corresponding axial length of helical rib <NUM> provided at bore <NUM>. Referring to <FIG> and <FIG>, first part <NUM> comprises a first node <NUM> and a second node <NUM> that project axially at regions of rib <NUM>. Each node <NUM>, <NUM> may be considered a projection, hump, nodule or bulge extending both in the axial and circumferential directions. First node <NUM> is provided at a mid-axial length region of rib <NUM> at a corresponding position of gap <NUM> formed within rib <NUM>. Second node <NUM> is positioned at the second terminal end <NUM> of rib <NUM>. Second node <NUM> comprises a greater circumferential length relative to the mid-length first node <NUM>. Referring to <FIG> and <FIG>, first node <NUM> is defined, in part, by an inclined or sloping trailing face <NUM>, a plateau face <NUM> and a corresponding declined or sloping leading face <NUM>. Accordingly, second node <NUM> might be described as tooth shaped or frusto-conical when viewed from the side. The distance in the circumferential direction (relative to axis <NUM>) between faces <NUM> and <NUM> defines a circumferential length of node <NUM> that accordingly comprises a circumferential length that decreases from rib <NUM> towards a plateau face. A length of node <NUM> in the circumferential direction is approximately equal to a corresponding circumferential length of gap <NUM>. Second node <NUM> is similarly defined in part by a trailing or sloping face <NUM> and a plateau face <NUM>. Plateau face <NUM> and <NUM> are angled at a corresponding angle of the helical rib <NUM> such that second node <NUM> comprises a thickness in the axial direction that decreases in its circumferential length. The circumferential length of second node <NUM> is greater than gap <NUM> and greater than the maximum circumferential length between faces <NUM> and <NUM> of the first node <NUM>. The first node <NUM> is positioned at an angular separation distance of around <NUM>° from second node <NUM>.

First part <NUM> comprises an O-ring positioned immediately adjacent head <NUM> and at a position axially between shaft <NUM> and head <NUM>. O-ring <NUM> is seated on an annular concave lip <NUM> that projects axially from an underside surface <NUM> of head <NUM>. O-ring <NUM> is dimensioned so as to project radially beyond lip <NUM> and shaft <NUM>.

Referring to <FIG>, helical rib <NUM> is defined, in part by an upper face <NUM>, a corresponding and opposite lower face <NUM> and a side face <NUM> extending between faces <NUM>, <NUM>. Similarly, helical rib <NUM> at second part <NUM> is defined, in part, by an upper face <NUM>, a corresponding lower face <NUM> and a side face <NUM> extending between faces <NUM> and <NUM>. Each node <NUM>, <NUM> projects axially upward from rib face <NUM> over the respective circumferential distance of each node <NUM>, <NUM>. First part <NUM> and in particular shaft <NUM> is capable of being inserted into bore <NUM> such that rib <NUM> engages rib <NUM>. As first part <NUM> is rotated about axis <NUM> upper face <NUM> of rib <NUM> engages in close touching contact the corresponding lower face <NUM> of rib <NUM> according to a conventional screw thread coupling. The continued rotation of first part <NUM> relative to second part <NUM>, causes second node <NUM> to travel past gap <NUM> due to the larger circumferential length of node <NUM> relative to gap <NUM>. With continued rotation of the first part <NUM>, eventually node <NUM> is rotated to a corresponding position of gap <NUM>. Due to the approximately equal circumferential length of node <NUM> and gap <NUM>, node <NUM> is forced axially upward into gap <NUM>. At the corresponding time, node <NUM> and in particular plateau surface <NUM> clears rib end <NUM> and is similarly displaced axially. In the axially displaced positions, node faces <NUM> and <NUM> abut corresponding side faces 36a, 36b of gap <NUM> so as to frictionally hold and releasably lock first part <NUM> to second part <NUM>. Similarly, face <NUM> of second node <NUM> abuts against an end face of rib end <NUM>. With this face abutment, first part <NUM> is releasably held at second part <NUM>.

The axial biasing of first part <NUM> relative to second part <NUM> is provided by O-ring <NUM>. In particular, and referring to <FIG>, O-ring <NUM> is configured to seat against an annular end face <NUM> of barrel <NUM> with the shaft <NUM> mated fully into bore <NUM>. Full insertion of shaft <NUM> into bore <NUM> requires compression of the O-ring <NUM> with the compression force acting in the axial direction to separate first part <NUM> from second part <NUM>. This axial return force provides the corresponding axial force to drive the axial displacement of node <NUM> into gap <NUM> and also node <NUM> beyond rib end <NUM>.

Referring to <FIG>, head <NUM> comprises a recess <NUM> indented into an upward facing surface. Recess <NUM> is defined, in part, by a sloping sidewall face <NUM>. A central island <NUM> projects axially from a base of recess <NUM> with island <NUM> defined by sidewall faces <NUM> and comprising a generally hexagonal shape profile. A separation distance between faces <NUM> and <NUM> is sufficient to allow insertion of a tool such as a cylindrical socket having an internal cross sectional shape profile corresponding to that of island <NUM>. As such, rotation of the socket and engagement of island <NUM> (via faces <NUM>) provides rotational drive of the first part <NUM> into second part <NUM> via the corresponding mated contacts between ribs <NUM> and <NUM>. Slopping face <NUM> is inclined relative to axis <NUM>. This prevents mud or other ground debris becoming lodged in the recess <NUM> that would otherwise hinder engagement of the first part <NUM> by a rotational drive tool (not shown).

Referring to <FIG>, with the second part <NUM> mounted within hole <NUM> and feet <NUM> fully located within recess <NUM> at a first mat <NUM>, a second mat <NUM> may then be located onto the first mat <NUM> via mating of the flange faces <NUM>, <NUM>. First part <NUM> is then inserted into hole <NUM> such that head underside surface <NUM> abuts against the annular surface <NUM> at the mat upward facing face <NUM>. First part <NUM> may then be rotated via engagement of the tool (not shown) with island <NUM> so as to inter-engage the respective helical ribs <NUM>, <NUM> as described. Complete mating of the first and second parts <NUM>, <NUM> is achieved when node <NUM> is displaced axially to sit into gap <NUM> and second node <NUM> clears rib end <NUM> so as to provide a double lock mechanism being frictionally and mechanically resistant to decoupling of first part <NUM> relative to second part <NUM>. Accordingly, the two mats <NUM> are held in overlapping interconnected position via the frictional contact of the respective ribs <NUM>, <NUM> and the resiliently biased contact of the nodes <NUM>, <NUM> with those respective parts of rib <NUM>.

<FIG> illustrates a further embodiment of the present fastening device in which the first part <NUM> comprises the same features and function as described referring to <FIG> with the exception of the O-ring <NUM> and lip <NUM>. A radially enlarged flange <NUM> extends radially from shaft <NUM> in place of the O-ring <NUM> and comprises a decreasing axial thickness towards an annular perimeter <NUM>. Accordingly, flange <NUM> is configured to deform axially as the first part <NUM> is mated into the barrel <NUM>. In particular, flange <NUM> is configured to abut regions of barrel <NUM> and deform axially so as to provide the corresponding return bias force (as provided by O-ring <NUM> according to the first embodiment).

A further embodiment is described referring to <FIG> in which the first part <NUM> comprises the same features and function as described referring to <FIG> also with the exception of the O-ring <NUM>. According to the further embodiment, the bias force is provided by a conical washer <NUM> housed within bore <NUM> and seated on an annular shelf <NUM> that projects radially inward from cylindrical surface <NUM> of bore <NUM>. Accordingly, as first part <NUM> is advanced into bore <NUM>, conical washer <NUM> abuts the terminal end/tip of first part <NUM> and provides the corresponding axial bias force that drives axial displacement of node <NUM> into gap <NUM>.

Claim 1:
A fastening device to releasably interconnect ground protection mats (<NUM>) comprising:
a first part (<NUM>) of a connection mechanism having a male part;
a second part (<NUM>) of the connection mechanism having a female part with a bore (<NUM>) to receive the male part and configured to connect at least two neighbouring ground protection mats (<NUM>) side-by-side by rotation of the male part relative to the female part;
the male part comprises a first helical rib (<NUM>) projecting radially outward from a shaft (<NUM>) and the female part comprises a second helical rib (<NUM>) projecting radially inward at the bore (<NUM>) configured to receive the shaft (<NUM>), the ribs configured to abut one another, an axial length (<NUM>) of the first helical rib (<NUM>) being in the range <NUM>% to <NUM>% of a pitch of the first helical rib (<NUM>);
an axial and radial lock having a first element at the rib (<NUM>) of the male part and a second element at the rib (<NUM>) of the female part, the first and second elements configured to engage one another by the rotation of male part relative to the female part; and
a bias lock actuator to impose an axial force to the first element to force the first element in engaged contact against the second element and to provide frictional resistance to further rotation of the male part relative to the female part.