Replaceable seat insert for a ground surface access assembly

Abstract

A replaceable seat insert 180 for a manhole cover being arranged to be located between a frame of the manhole assembly and a manhole cover. The insert comprises a cover-engaging base arranged to engage with the cover; the insert further comprising a first interengaging means arranged to be interengageable with a second corresponding interengaging means on the frame to fix the insert to the frame, and wherein the replaceable seat insert comprises a wear indicator arranged to indicate whether the cover-engaging base is worn beyond a threshold amount. The insert may be made from a material that is softer than that of the frame and the wear indicator may be a traffic light wear indicator

Description

Field This invention relates primarily to a replaceable seat insert for a ground surface access assembly (comprising a frame and cover) for mounting on a surface opening, such as (but not limited to) those made to conform to European standard BS EN124. The invention particularly, but not exclusively, relates to an insert arranged to be connected to a frame for mounting on a drainage network component, such as on a gully pot, or on a manhole assembly or inspection chamber assembly or surface box assembly. In this specification, the term "manhole assembly" is not limited solely to arrangements bounding recesses that are sized for human access. The term includes both larger and smaller assemblies. The frame is configured to mount a cover, such as a drainage cover or manhole cover thereon. The invention is particularly useful as part of a drainage or access cover solution in congested, high traffic areas, such as highways. Background Ground surface access assemblies such as manhole covers, gully grates, and surface boxes play an important role in urban infrastructure. Such assemblies are typically installed in roadways, pavements, and other traffic-bearing surfaces to provide access to underground utilities and drainage systems. Constructed predominantly from cast iron (or other suitable materials), these ground surface access assemblies are designed to withstand substantial loads and frequent use. Despite their durability, there are issues associated with their long-term performance, especially under heavy traffic conditions. Technical Features of the Prior Art Ground surface access assemblies (e.g. manhole assemblies, gully grates, and surface boxes) generally comprise a cast iron cover mounted on a cast iron frame. The frame is designed to be securely embedded in the surrounding road surface, usually using a bedding medium such as concrete, mortar, or roadstone. The frame includes multiple seats, often located at the corners or along the sides, upon which the cover rests. These seats ensure that the cover is properly aligned and stable within the frame. The cover typically features friction-enhancing formations on its upper surface to help prevent vehicles from slipping. Challenges with Existing Designs A problem with existing ground surface access assembly designs is the wear and tear that occurs over time, especially due to heavy traffic. The dynamic loads from vehicles passing over the installation can cause both the cover and the frame to deteriorate. This wear can be particularly pronounced at the loadbearing frame seats where the cover contacts the frame. Uneven wear patterns can result at the seat locations. The frame seats can become worn down or the cover can become worn down, or both. The cover and the frame can become misaligned, which compromises the safe functioning of the installed assembly. Additionally, over time, the friction-enhancing formations on the top of the cover also wear away, especially with constant or heavy traffic. As these friction-enhancing formations degrade, the top of the cover becomes smoother, increasing the risk of skidding, which can pose a safety hazard. Ground surface access assemblies usually comprise cast articles (typically cast from iron) that form part of a system that allows access to an underground network via a surface opening, e.g. in a road surface. In this specification, when any type of ground surface access assembly is referred to, it will be apparent that the invention can relate to any other type of ground surface access assembly (e.g. discussion in relation to gully grating assemblies is also applicable to manhole cover assemblies, inspection chamber assemblies etc.). Typically, a ground surface access assembly comprises a peripheral frame (that may define a manhole, or an aperture to gain non-man entry to belowground services including valves and cables, or that may define an aperture through which drainage water flows in the case of a gully grating), the frame having protruding from a lower edge thereof an outwardly extending securing flange. The frame is buried in a bedding medium (e.g. mortar, concrete, roadstone) such that the flange defines the boundary of an aperture formed in a road, highway or other such surface. After installation, movement of the frame is undesirable since it can cause cracking of the set bedding medium and misalignment between the frame aperture and the drainage channel. The ground surface access assembly also comprises a cover, which may be (but is not necessarily) hingedly mounted to the frame within the aperture and rotatable between an open position, in which the cover is upstanding therefrom and so in which access is facilitated, and a closed position, in which the cover lies flush with the frame and access is not facilitated to the underground network. The cover is usually retained captively within the frame. In the open position it is possible to e.g. for manhole assemblies, allow access for a person to enter through the aperture; or e.g. for gully gratings, insert tools such as rods, via the aperture for the purpose of clearing a blocked drain. The ground surface access assembly may include a security mechanism (e.g. a spring bar) arranged to secure the cover in its closed position by default. The cover is typically a cast (e.g. iron) cover. In the case of a gully grating, the cover may be a reticulated cover that permits rainwater to flow through the aperture defined by the frame, while preventing debris, that could otherwise block a drainage system, from falling therethrough. Or, the cover may be a solid cover. In use the cover fits within the frame to substantially fill the aperture, and the cover and the top of the frame are substantially flush with the road surface. The ground surface access assembly is typically installed above an underground network such that access can be facilitated thereto. In high traffic areas (such as on highways), ground surface access assemblies undergo a lot of stress due to the weight, speed and frequency of passing traffic. A typical known highway ground surface access assembly has a substantially rectangular frame, defining a large rectangular aperture, the frame having vertical walls leading to outwardly extending flanges - the footprint of the entire frame is defined by the flanges and is slightly larger than the aperture (due to the width of the flanges). The flanges may extend from only some (e.g. three of the four) lower edges of the rectangular frame. One or more edges may not have a flange, e.g. if they are kerb-side edges arranged to potentially abut against or close to a kerb, or occasionally against a further ground surface access assembly (e.g. against another gully grating assembly). The invention is not limited to rectangular assemblies. The assembly may be square, round or triangular as well as rectangular, and the flange could be all of the aforementioned shapes, regardless of the shape of the surface profile or the opening of the frame. Figures 1 a to 1 g are schematic views of a known ground surface access assembly 2, including its frame 4 and cover 6a, 6b. The assembly 2 is Saint-Gobain’s INTER-AX® access cover assembly, which has a double triangular, non-rock cover design. The frame 4 includes a peripheral, upstanding wall 8 having protruding outwardly from a lower part thereof a flange 10 for anchoring the frame in a bedding medium such as mortar or other materials. The frame is intended to be installed at the top of e.g. a drain, sewer, inspection chamber or similar recess that extends downwardly from a surface such as the ground or a ground-like floor. The frame defines a boundary at the open, upper limit of the recess. The frame comprises multiple frame seats 12 within, and below the upper edge of, the upstanding wall. Each frame seat is arranged to receive one or more parts of the cover such that, in use, the frame seats 12 support the cover 6a, 6b. The cover members are typically heavy, and in the case of manhole covers are substantially imperforate plates that close off the aperture bounded by the frame. In other cases, such as gully grates and drains, the covers are perforated to define a grating - such covers permit the passage of, e.g., rainwater into the recess while simultaneously preventing the passage of leaves, stones and other debris. Regardless of the nature of the cover plates, it is well known to provide sets of three frame seats secured to the upstanding wall in a triangular pattern as shown in Figure 1b. The frame seats typically present essentially upwardly facing surfaces, which may be flat or (in some known arrangements) shaped for co-operation with downwardly facing surfaces of limbs, feet or other features formed in the underside of a cover plate of the kind described hereinabove and as are well known. The use of three frame seats in a triangular pattern renders the cover "non- rocking", since an article supported at three points that are spaced to define a triangle is inherently stable without any need for specific levelling measures. Another advantage of using frame seats defining a triangular pattern is that in the case of a frame that is a parallelogram, and more specifically rectangular when viewed in plan, the triangular pattern of frame seats conveniently lends itself to the use of pairs of triangular cover plates that abut one another along adjacent edges to occupy the aperture bounded by the frame in an efficient manner. Therefore, a square aperture may conveniently be closed by a pair of cover plates that are each right angled triangles supported on frame seats at their apexes and abutting one another along their hypotenuses. A rectangular aperture may similarly be closed by two pairs of such covers each supported in a non-rocking fashion at their apexes by frame seats defining a series of triangular patterns. It is also known to support square and circular covers in similar frames, again through the use of triangular patterns of frame seats in order to define non-rocking supports. Although non-rocking frame and cover combinations as described hereinabove have been widely installed, they nonetheless suffer disadvantages as follows: Non-rocking covers do not remain nonrocking indefinitely. In areas of heavy usage (for example roadways over which many vehicles drive, causing repeated impulses to impinge on the covers), the frame seats for the covers and the covers themselves tend to wear. This can bring further points of the cover into contact with the frame. This potentially produces a rocking arrangement that can be undesirably noisy. This invention addresses a problem of wear of the frame and / or cover leading to misalignment and reduced friction. The invention is particularly useful with non-rocking assemblies, but also useful with other assemblies (i.e. assemblies without non-rocking configuration). For the avoidance of doubt, this invention is not limited to products with three points of contact; the invention works in other applications, such as with mitred seatings. Typically, addressing this problem requires extensive maintenance and assembly replacement, which involves significant labour and disruption, as the road surface must be excavated to replace the worn components (frame and cover). This process is both time-consuming and resource-intensive. This invention aims to provide an improved design for ground surface access assemblies (such as manhole covers, gully grates, and surface boxes). Summary According to an aspect of the invention, there is provided a replaceable seat insert for a ground surface access assembly as claimed in claim 1. According to another aspect of the invention, there is provided a ground surface access frame for a ground surface access assembly as claimed in claim 19. According to another aspect of the invention, there is provided a ground surface access assembly as claimed in claim 24. This invention provides an improved replaceable seat insert and ground surface access assembly as claimed in the independent claims. The inventive replaceable seat inserts protect the frame and cover and facilitate easy replacement when they become worn without the need to remove and replace the frame or entire assembly. In some cases, the cover may not need replacing either. The inventive replaceable inserts provide an easy indication that they have become too worn, i.e. worn beyond a threshold amount (and therefore may need to be replaced immediately or soon). This approach significantly reduces maintenance resource and downtime associated with the repair of ground surface access assemblies. Some key inventive optional or preferable features 1. Material of insert is one or a combination of: • High-Durability Polymer: These materials are chosen for their wear resistance and ability to absorb impact without deforming. (Not cast iron.) • Softer material than the frame and cover: These materials are chosen such that, over time and with use, the replaceable insert becomes worn without the frame and cover becoming significantly worn. The softer material may still be a metallic material, e.g. a softer metallic material than the frame and cover. • Composite Material: Combining the benefits of different materials, such as polymer composites reinforced with steel or ceramic particles, to enhance wear resistance. • A non-metallic material: providing quiet or substantially silent operation. 2. Design of insert: • Modular Components: The inserts are designed to fit precisely within the frame and to co-operate with the cover, ensuring a secure fit with the frame and proper alignment of the cover (relative to the frame and the roadway). • Interchangeable Parts: Standardised sizes and shapes of insert (and corresponding frame) allow for easy replacement without the need for specialised tools or equipment. • Snap-Fit or other Mechanical Anchored (e.g. Bolt-On) Mechanisms: These mechanisms ensure that the inserts remain securely in place under the pressure of traffic loads, and optionally until they are broken out. • Wear indicator: Provided on insert itself, so it can be easily refreshed, replaced and reset when the insert is replaced. The wear indicator can be located to provide easy visibility, in use. 3. Ease of Replacement: • Minimal Disruption: It is easy to tell when an insert is worn out. When an insert wears out, it can be replaced without the need to remove the entire frame from the roadway. This significantly reduces the time and cost associated with repairs. Replacing the inserts typically requires no I minimal excavation or disturbance of the surrounding road surface. • Quick Installation: The replacement process is straightforward and can be completed quickly, often within minutes. Optional features of the invention are as claimed in the dependent claims - various advantages are thereby provided as discussed in the detailed description. Any of these optional features may be combined with any other of the optional features as will be appreciated by those skilled in this art. Brief Description of Drawings Embodiments will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1a schematically shows a prior-art ground surface access assembly comprising a frame and a cover mounted therein; Figures 1 b and 1 c schematically show the frame only of the assembly of Figure 1 a, in a plan view and a perspective view respectively; Figures 1 d and 1 e schematically show the cover only of the assembly of Figure 1 a, in a view from below and a perspective view respectively; Figures 1 f and 1 g schematically show the frame seats of the assembly of Figure 1 a in a first corner and a second corner respectively; Figures 2a and 2b schematically show a replaceable seat insert according to an embodiment of the invention; Figures 2a and 2b schematically show a replaceable seat insert according to an embodiment of the invention in a new and a used, worn condition respectively; Figure 3a schematically shows a replaceable seat insert according a further embodiment of the invention; Figure 3b schematically shows a replaceable seat insert according a further embodiment of the invention; Figure 3a schematically shows a replaceable seat insert according a further embodiment of the invention; Figures 4a and 4b schematically show a ground surface access assembly according to an embodiment of the invention including a frame according to an embodiment of the invention and the replaceable seat insert of Figure 2a in a first exploded view with the insert not installed in the frame and a second exploded view with the insert installed in the frame respectively; Figure 4c schematically shows a cover part and the replaceable seat insert of Figure 2a from below; Figures 5a and 5b schematically show the replaceable seat insert of Figure 2a and the frame of Figure 4a in a first separated configuration and a second interengaged, in-use configuration respectively; Figure 6 schematically shows a replaceable seat insert according to another embodiment of the invention and a frame according to another embodiment of the invention in a separated configuration; Figures 7a and 7b schematically show views of the ground surface access assembly of Figure 4a in its in-use configuration, and a close-up view of a corner region of the same respectively. Figures 8a, 8b and 8c schematically show close-up views of a corner region of the ground surface access assembly of Figure 4a in its in-use configuration when new, after some wear, and after further wear respectively; Figures 9a, 9b and 9c schematically show cross-section views through a corner region of the ground surface access assembly of Figure 4a in its in-use configuration when new, after some wear, and after further wear respectively; Figure 10 schematically shows a replaceable seat insert according a further embodiment of the invention; Figure 11a schematically shows another prior-art ground surface access assembly comprising a frame and part of its corresponding cover mounted therein; and Figures 11b and 11c schematically show close-up views of a corner region of the frame and a central region of the frame (and part of a cover) respectively. Description of Embodiments The exemplary embodiments described in the detailed description and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the scope of the invention. Various embodiments are described. The specific embodiments are not intended as an exhaustive description or as a limitation to the broader discussed and claimed aspects. Features described in conjunction with a particular embodiment are not necessarily limited to that embodiment and can be incorporated into any other embodiment(s). Protection afforded by any applicable doctrine of equivalents is retained to its fullest extent. Terms such as up, down, top, bottom, left, right, vertical, upstanding etc. have been used to simply and clearly describe the invention. These terms are not to be interpreted in a manner that would be limiting. The person skilled in the art will envisage other suitable embodiments within the scope of the invention. Figure 2a shows, according to an embodiment of the invention, a replaceable seat insert 180 for a ground surface access assembly 102 that is arranged to be installed above a ground opening. The assembly comprises a frame 104 and a two-part cover 106a, 106b of the previously-described type. The frame 104 is configured to support the cover 106a, 106b via the insert 180, which is arranged to be located between the frame and a cover in use (as will be described below). The insert 180 is arranged to be fixed to the frame 104. The insert is made from an acoustically damping material that is softer than the material of the frame and the cover (both cast iron in this example), but which is still hard-wearing - in this embodiment, the insert is made from a plastics material having a hardness of about 525 N / mm2. More generally, in some embodiments, the insert is optionally made of a non-metallic material, which has the further benefit of being quiet or silent in operation. The insert 180 comprises a cover-engaging base 182 arranged to engage with a foot 120 of the cover 106a, 106b. The base 182 is in the form of a platform having a substantially flat upper surface 184 in this example, and the foot 120 is arranged to rest on the upper surface of the base 182 in use (described below). The insert also comprises an upstanding wall 188 extending substantially perpendicularly from the base. The shape of the insert is arranged to match the shape of the frame with which it is to be fixed. In this example, the insert has a generally L-shaped profile in cross-section. In some examples, for a frame seat having a complex profile or a cover whose feet have a complex profile, or where multiple feet are to be received on the same replaceable insert, a corresponding complex shaped cover-engaging base may be provided, and / or the insert may comprise more than one cover-engaging base, e.g. at different heights. The inventive insert has a wear indicator 190. The wear indicator is arranged to indicate whether the cover-engaging base is worn beyond a threshold amount. The threshold amount relates to whether the replaceable seat insert should be replaced now or soon or within an indicated amount of time known to the manufacturer (e.g. a few days or a few weeks or a few months assuming a forecasted or reasonable amount of traffic). In this example, the wear indicator is in the form of a visible traffic light system indicator as depicted in figure 2a, located at an upper end 189 of the insert upstanding wall 188. For the avoidance of doubt, the upper end is the distal or free end of the wall that is spaced from the cover-engaging base, and that is uppermost (and so will be flush with the top of the frame) in use. The cover-engaging base 182 has a thickness, t, of about 15mm in this example (this may vary in other embodiments, e.g. between 10mm and 25 mm). Although the base is made from a material that is softer than cast iron, it is still made from a hard-wearing (plastic in this example) material, which will allow for a good amount of wear so that the frame is uncompromised for a reasonable time (before the insert 180 needs to be replaced). Accordingly, the material of the insert has a hardness of between 515 and 539 N / mm2 in most embodiments. The visible wear indicator is between 10mm and 25 mm deep in most embodiments; in this embodiment, it has a depth, d, of about 19mm. This includes an uppermost green strip (about 5mm deep) 192, a lowermost red strip (about 10mm deep) 196 and an intermediate amber strip (about 4mm deep) 194 therebetween. Each strip abuts its adjacent strip without any gap in between in this example (other embodiments may vary). The green strip easily visibly signifies that the insert does not need replacing any time soon, the red strip easily visibly signifies that the insert needs replacing immediately, and the amber strip easily visibly signifies that the insert will need replacing soon (e.g. in a few weeks or months, depending on the amount of traffic). Therefore, in this example, after a threshold amount of wear of about 5mm, the wear indicator provides an indication that the insert should be replaced soon; and after a threshold amount of wear of about 9mm in total (i.e. a further 4mm after the ‘replace soon’ indication), the wear indicator provides an indication that the insert should be replaced immediately. Since the base is 15mm thick, after the ‘replace immediately’ threshold is reached, there is still 6mm thickness of coverengaging portion remaining (this excess portion of cover-engaging portion provides a useful safety net. Different thicknesses of ‘safety net’ may be provided in other examples; in some examples, there is no safety net. In another embodiment, the wear indicator, instead of or additionally to the traffic light system, comprises an alternative type of zone indicator as shown schematically in figure 3a, in which different zones are marked up with text (e.g. ‘GOOD’, ‘WARNIING’, ‘REPLACE’) or letters (e.g. ‘G’, ‘W’, ‘R’ or ‘A’, ‘B’, ‘C’), numbers or any other suitable indicator, instead of colours. The absence of any indicator may also be used as an indication as it may contrast with an adjacent strip or region that does include a visual indicator. Instead of stepped strips, the visual indicator may comprise a gradual indicator, e.g. a colour spectrum moving gradually from green to amber to red. Any text or numbers may be negatively extruded, e.g. with description of each zone. E.g. ‘ZONE’ shown negatively extruded in Figure 3a. In some embodiments only two contrasting wear indicator zones are provided, e.g. a ‘GOOD’ and a ‘REPLACE’ or a green and a red zone I strip etc. In other embodiments, more than three contrasting wear indicator zones may be provided. In any example, one of the zones may have no indicia, but this will still serve to contrast with an adjacent zone that does have a recognisable indicia. In another embodiment, the wear indicator, instead of or additionally to the above-described zone differentiating systems, comprises an alternative type of zone indicator as shown schematically in figure 3b, in which different zones have horizontal width differences of the insert material to differentiate between each zone (and to thereby indicate the amount of wear of the cover-engaging portion in use). The assembly 102 comprises anchoring means arranged to securely fix the replaceable seat insert to the frame in an in-use configuration in which movement between the insert and the frame is prevented. To this end, the insert 180 comprises a first interengaging means 198. The first interengaging means 198 is arranged to securely interengage with second corresponding interengaging means of the frame (described below). The anchoring means may be a click-fit or push-fit or friction-fit arrangement between the insert’s first interengaging means 198 and the frame’s second corresponding interengaging means. The anchoring means keeps the bottom of the cover-engaging base 182 of the replaceable seat insert fixed in position relative to the frame seat upon which it rests, in use. Only the top of the cover-engaging base 182 (that comes into contact with the cover feet through which traffic forces are transferred) gets substantially worn away with use. In this example (not shown), the first interengaging means 198 of the insert comprises a pair of ribs protruding from the back of the insert’s upstanding wall 188. This pair of ribs is arranged to tightly slot through a pair of corresponding apertures 160 in the frame to fix the insert to the frame in a desired aligned, configuration (described further below). In this example, the first interengaging means 198 is provided only on the upstanding wall of the insert (not on the base). In other embodiments, e.g. see Figure 6, the first interengaging means 198’ may be provided additionally on the cover-engaging base (in the form of a wedge-shaped rib) and arranged to tightly slot with a corresponding channel 160’ in the upper surface of the frame seat 112’ to fix the insert to the frame in the desired aligned, configuration. In yet another embodiment (not shown), the first interengaging means may be provided only on the coverengaging base (i.e. not on the upstanding wall) and arranged to slot with a corresponding channel in the upper surface of the frame seat. It will be apparent to the skilled person that any suitable anchoring means may be provided between the insert and the frame, e.g. any click-fit, friction-fit arrangement etc. The anchoring means may comprise a non-reversible interengagement connection arranged to remain in place until broken out. In such cases, the first interengaging means is formed accordingly, e.g. the first interengaging means may be a one-way click or push-fit connector that can be snapped to be broken out when the insert is to be replaced. Figures 4a, 4b, 5a, 7a and 7b schematically show the frame 104 according to an embodiment of the invention. This frame 104 is arranged to be installed above the above-mentioned ground opening in a known manner. Both the frame 104 and the two-part cover 106a, 106b are cast from ductile iron in this example. The frame 104 is generally rectangular, and comprises an open box section 130 defined by upstanding, peripheral front 132, back 134, left 136 and right 138 vertical side walls. The open box section has an upper open box end and a lower open box end, but is otherwise closed around its sides. As a result, the frame 104 is open at its upper and lower ends to provide a closed path therethrough. In other embodiments, the upstanding peripheral wall or walls may not be closed — it / they might be arranged to join with another upstanding peripheral wall or walls to combine to provide such a closed path. In order to facilitate installation, the frame has securing flanges 150 (see Figures 4a, 4b, 7a, 7b). The securing flanges 150 are generally flat, and are located lowermost on the frame such that they are configured to rest on a generally flat installation surface just above the ground surface opening to which access is desired. The securing flanges extend from the lower ends of the side walls that define the frame’s open box section. Typical installation surfaces either extend directly from around the opening, or can be provided on a platform or support above the opening in a known manner. As seen schematically in Figures 4a, 4b, 7a, 7b, extending through the securing flange(s) 150 are through-apertures 152. The through apertures may be suitable for incorporating a levelling system (such as Saint-Gobain PAM’s Install Plus (RTM) system) or providing lifting eyes or providing for bolting the frame to the below ground structure.. A wide range of shapes, sizes, configurations and arrangements of apertures can be provided and therefore may vary widely within the scope of the invention. In other embodiments, there may be no such through-apertures. The frame includes cover mounting means arranged to mount the cover 106a, 106b on the frame and to cover the aperture of the frame. The cover is arranged to be movably mounted within the frame aperture to move between a closed position in which the cover substantially covers the whole area of the aperture such that traffic or pedestrians can safely pass thereover, and an open position in which access to the opening is allowed. In this embodiment, the cover mounting means comprises multiple frame seats 112 (see schematic Figure 5a), similar to those described in relation to the prior art. Each frame seat 112 is a cuboidal block of material that, in the embodiment shown, is cast integrally with the remainder of the frame. In other embodiments, the block constituting the frame seat 112 may be made separately from the frame and subsequently secured thereto e.g. by bolting, pinning, doweling or welding. However, integral casting of the frame seat is the preferred embodiment, e.g. because of the efficiency of manufacturing. In use, when closed, feet of the cover engage the frame seats by resting on them via inserts 180. In this embodiment, the frame seats extend in from corners of the box section - see figures 4a and 4b (and similarly to the seat locations shown in Figure 1b). In other examples, some of the frame seats may be provided near (e.g. just under) pivot pin apertures to provide support at an important location. In other examples, some of the frame seats may be provided to support a free, distal end of the cover to provide support at an important location. In other embodiments, different arrangements of frame seats will be apparent to one skilled in this art. Figure 4c shows schematically, from below, one part 106b of the two-part cover. The other part 106a is conceptually similar. The cover is mountable on the frame of Figure 4a. Together the frame 104, the insert 180 and the cover 106a, 106b form the inventive ground surface access assembly 102. In use, the cover is movable between two positions - open and closed - in a standard manner. In this embodiment, the cover comprises the two cover parts 106a and 106b. When the cover is in its open configuration (i.e. lifted off the frame), access is provided to the opening therebelow. When the cover is in its closed configuration (see Figure 7a), the top surface of the cover is substantially flush with the top surface of the frame - as a result, the top surfaces of the frame and cover can be installed substantially flush with the road surface such that traffic or pedestrians can safely pass thereover. It is noted that the inventive insert 180, when fixed to the frame in use, is also flush with the frame, cover and road surface (see Figures 7a and 7b). The cover may be any type of known access cover, and may take a range of forms as is familiar to a person skilled in the art. The cover is insertable into and removable from a corresponding frame (or frame and fixed insert in the case of this invention). An insert according to this invention can be placed at any mating face or point between the cover and the frame, and is preferably placed at every such mating face or point in use. Therefore, the cover only bears down on the cover-engaging base 182 of the insert. The cover does not bear down on other parts of the insert (e.g. the upstanding wall 188). Therefore, over time only the cover-engaging base 182 (or parts thereof that are most in contact with the foot) gets worn away. Figure 2b schematically shows the insert after part of the cover-engaging base 182 has been worn away forming a hole 185 in the upper surface. The cover comprises multiple feet 120 protruding downwardly from the corners of the cover that are arranged to fit in the corners of the frame in use. The cover’s upper surface has an anti-slip pattern 140 thereon. The anti-slip pattern comprises raised or recessed formations to prevent slipping (e.g. when vehicles turn, brake, accelerate while travelling over the cover) in a known manner. Referring to Figures 8a to 8c and 9a to 9c, which schematically show the assembly wearing over time, the invention will now be described further in relation to an in-use example. Upon installation of the assembly 102 above the ground opening, the frame 104 is first embedded in the surrounding road surface using a bedding medium such as concrete, mortar, or roadstone in a known manner. The inventive frame 104 includes peripheral upstanding frame walls as previously described. The insert 180 is arranged to be pushed into fixed engagement with the frame, e.g. into the previously-described upstanding walls of the frame. When the ribs 198 are pushed into slots 160, the insert is fixed in the frame in a desired alignment. The upstanding walls of the frame include a recessed section 131 (see Figure 5a) arranged to receive the insert 180. The depth of the recessed section is the same as the thickness of the insert’s upstanding wall 188 such that in an in-use configuration, when the insert has been slotted in to the recess of the frame, the insert’s inwardly-facing surface is flush with surrounding regions of the frame upstanding wall’s inwardly-facing surface to provide a smooth, continuous inner frame profile (see Figure 5b). This helps avoid items undesirably snagging at the boundary of the frame and the insert in the in-use configuration. In this example, in the in-use configuration, the insert’s coverengaging base is arranged to bear against the frame seat and the insert’s upstanding wall is arranged to bear against the frame upstanding wall. Therefore, the insert is particularly easy to instal as the installer has two surfaces that are joined at an angle (in this case substantially perpendicular) to push against frame surfaces to achieve correct alignment. After slotting the insert into engagement with the frame, it remains securely fixed to the frame. The cover parts 106a, 106b are next installed by engaging each foot of the cover with the corresponding insert that has been fixed to the corresponding frame seat. In this example, each foot rests on the coverengaging base of the corresponding insert. In some other embodiments, the cover will naturally engage on the wedged vertical frame faces, leaving a gap between the bottom of the cover seat and the top flat surface of the frame seat when first installed. This mechanism stops the cover sinking significantly once trafficked. The present invention is still useful because the cover seat will still eventually come into contact with the frame seat at the seat portion after some trafficked use. In such embodiments, installing the inventive insert between the frame seat and the cover seat provides the advantages described in this document with respect to other embodiments (in which the cover seat and frame seat are in contact (via the insert) when first installed). As seen in Figures 7a and 7b, when the cover is installed and in its closed configuration, the top surface of the cover is substantially flush with the top surface of the frame and also the top surface of the insert -as a result, the entire assembly is installed substantially flush with the road surface such that traffic or pedestrians can safely pass thereover. Further, as previously described, the insert and frame form a smooth inner surface so that a prior art cover can be installed in the inventive insert and inventive frame combination. The fixed anchoring of the insert relative to the frame is such that the insert stays aligned with the frame at its original installed, aligned position. Over time, the cover-engaging base of the insert gets worn away at its upper surface (e.g. see Figure 2b), whilst the bottom of the insert’s cover-engaging base and the insert’s upstanding wall remain fixed relative to the frame due to the nature of the anchoring means interengagement. The cover is in contact with the cover-engaging base that is getting worn away over time. Therefore, the cover sinks relative to the frame over time. Notably in this example, the wear indicator 190 is provided at the upper end of the insert’s upstanding wall 189 and is flush with the top of the frame and cover when first installed. Due to the nature of the anchoring means interengagement, the wear indicator does not sink relative to the frame during use. Note that the cover-engaging base is eroded from its top surface downwards; the upstanding wall is not meaningfully eroded and nor is the bottom of the cover-engaging base. Therefore, during use, the cover sinks relative to the wear indicator. The wear indicator therefore provides a good, easy-to-read indication of the amount of sinkage of the cover relative to the insert (and therefore the frame). Figures 8a to 8c illustrate sinkage of the cover relative to the frame (and insert) over time. Figures 9a to 9c show cross-sectional views through the assembly at the seat regions corresponding to Figures 8a to 8c respectively. Figures 8a and 9a show the assembly after a very small amount of wear - note that the green strip 192 of the wear indicator is visible from above (without having to open or remove the cover). Figures 8b and 9b show the assembly after some wear when the insert should be replaced soon, in this case in a few weeks (due to anticipated traffic in this particular location) - note that the amber 194 and green 192 strips of the wear indicator are visible from above (without having to open or remove the cover). It will be noted that the Figures 8c and 9c show the assembly after significant wear when the insert should be replaced immediately - note that the red 196, amber 194 and green 192 strips of the wear indicator are visible from above (without having to open or remove the cover). As mentioned above, in this example, after a threshold amount of wear of about 5mm, the wear indicator provides an indication (visibility of the amber strip) that the insert should be replaced soon; and after a threshold amount of wear of about 9mm , the wear indicator provides an indication (visibility of the red strip) that the insert should be replaced immediately. Since the base itself is 15mm thick, after the ‘replace immediately’ threshold is reached, there is still 6mm thickness of cover-engaging portion remaining (this ‘extra’ depth of cover-engaging portion after the final ‘replace now’ indication provides a useful safety net to minimise the chance of erosion of the frame seat). Therefore, it can be seen that, once the level of cover sinkage is beyond a threshold level, the wear indicator provides a particularly useful, easy indication that the insert needs replacing. Significantly, the frame seat is not worn away since only the cover-engaging base of the insert becomes worn over time and therefore simple maintenance activity requiring little resource and consuming little time can be made without removing the frame from the ground. Optionally, e.g. if the anti-slip formations are becoming worn, or if there is other damage to the cover, then the cover (or some parts of the cover) can also be replaced at the same time (again, without removing the frame from the ground and thereby saving resource). Compared to the cast iron of the frame and the cover, the insert material can be considered a sacrificial material. In another embodiment (e.g. the insert shown in Figure 6), having anchoring on multiple surfaces of the insert that are not co-planar provides even better anchoring of the insert with the frame. The insert of Figure 6 has first interengaging means on both the cover-engaging base arranged to be interengageable with a second corresponding interengaging means on the frame seat; and on the insert upstanding wall arranged to be interengageable with a second corresponding interengaging means on the frame upstanding wall. Notably the multiple elements of the first interengaging means are arranged to be interengageable with multiple, non-coplanar second corresponding interengaging means on the frame. Another embodiment of the invention will now be described. Most features and concepts in this embodiment are similar to those in the above-described examples; for conciseness, these will not be repeated - the skilled person can use features from the above-described examples in combination with the following disclosure. Referring to Figure 10, the insert 280 of this embodiment has a cover-engaging base 282 arranged to engage with a foot of the cover. The base 282 is in the form of a platform having a substantially flat upper surface 284 in this example, and the foot is arranged to rest on the upper surface of the base 282 in use (described below). The insert also comprises an upstanding wall 288 extending substantially perpendicularly from the base. The base differs from that of the previously-described embodiments in that the base is a multi-region or multi-layer cover-engaging base 282. Different contrasting regions of the multi-region cover-engaging base serve to provide a wear indicator that is neatly built in to the base. The multi-region cover-engaging base 282 comprises a first region 296 having first indicia arranged to indicate that the cover-engaging base is worn beyond a threshold amount and should be replaced immediately, a second, contrasting region 294 arranged to indicate that the coverengaging base is worn beyond another threshold amount and should be replaced soon, and a third contrasting region 292, wherein, in the in-use configuration, the third contrasting region is arranged between the cover and the second region, and the second region is arranged between the cover and the first region such that the third region gets worn away before the second region and the second region gets worn away before the first region. Each region abuts its adjacent region. Each region contrasts visibly with its adjacent region. E.g. the third region 292 is coloured green, the second region 294 is coloured amber and the first region 294 is coloured red. Due to adjacent regions being provided with contrasting visible indicators, upon inspection of the base, if the base has become worn (e.g. in a similar manner to that illustrated in Figure 2b), then there will be an indication as to whether a threshold amount of wear has taken place (e.g. if a ‘lower’ (amber or red) region has become visible). If the amber coloured region 294 is visible, then there is an indication that the third region has been worn away (i.e. a threshold amount of wear of the cover-engaging base has taken place) and that the insert will need replacing soon. If the red coloured region 296 is visible, then there is an indication that the second region has also been worn away (i.e. another threshold amount of wear of the cover-engaging base has taken place) and that the insert needs replacing now. In this example, each region comprises indicia in the form of a distinct colour for the region. In other examples, contrast may be provided by one region having some indicia and its adjacent region having no indicia. In other examples, only two contrasting regions or layers may be provided (e.g. ‘replace now’ and ‘no need to replace yet’). Any of the anchoring means of the previously described examples can be used in combination with the insert of this embodiment. In other embodiments (not shown), it will be apparent to the skilled person that features of this embodiment (wear indicator built in to the insert base, e.g. as seen in Figure 10) can be used together with features of earlier embodiments (wear indicator on the insert upstanding wall (e.g. as see in Figure 2a)) in a further inventive insert. In another embodiment, there may be no upstanding insert wall (the wear indicator is built into the insert base only). In such an embodiment, the frame upstanding wall need not be recessed to accommodate the insert upstanding wall. An easy indication of amount of wear beyond a threshold is still achieved. We have shown one type of assembly and described the invention in relation thereto. Other ground surface access assemblies will have different profiles and shapes. It will be apparent to the skilled person how to provide appropriate inserts within the scope of this invention that work with such other assemblies. For example, Figures 11 a to 11c schematically illustrate an example of another known assembly with a different seat configuration (different seat shapes and locations). This assembly 300 is Saint-Gobain’s OPT-EMAX® access cover assembly, which has a multiple triangular cover design. The cover is provided in four parts (two of which are not shown in Figure 11 a for ease of understanding, i.e. so that frame seats can be seen clearly). Figure 11b shows corner frame seats. Figure 11c shows frame seats located more centrally on a side wall of the frame. The inventive concept is the same as for previously-described examples. These Figures are shown to illustrate that the skilled reader can design an inventive insert, using the teaching in this specification, that is slottable into one or more of: upstanding wall and lateral part of frame seat, and including one or more wear indicators of the types described. The skilled person will understand that the insert profile should match the frame profile to allow for providing a desired final joint profile (combined frame and insert profile). The insert profile should be complimentary to the frame profile and there is provided complimentary interengaging means between them. The insert should also have and an appropriate cover-receiving base. Various modifications may be made to this invention without departing from its scope. For example, the frame may be circular, square, triangular, or any other suitable profile shape -many shapes are known and will be apparent to the person skilled in this field. The invention is not limited to rectangular assemblies. The assembly may be square, round or triangular as well as rectangular, and the flange could be all of the aforementioned shapes, regardless of the shape of the surface profile or the opening of the frame. In most examples, prior art covers are used in the inventive assembly. This allows for efficient manufacturing (only half the amount of existing patterns need be modified). Therefore, in the inventive frame, the frame seat may be thinner than a typical prior art frame seat of a similar frame. The combined depth of the inventive insert’s cover-engaging base plus the inventive frame seat is the same as the depth of a prior art frame seat in such cases. In some examples, instead of a visible wear indicator, the wear indicator may be sensed in another way, e.g. via touch or an electronic sensor arrangement for distinguishing between different regions or strips of the wear indicator. Different parts of the insert may be formed of different materials (keeping in mind the need to form any surfaces that will contact the frame or cover from a material that is softer than the frame or cover). This invention has been described with regard to embodiments in which the frame and cover are cast from iron. In other examples, the frame and cover may be made from any other suitable material, such as (but not limited to) steel or aluminium alloys; steel-reinforced concrete; composite materials; polypropylene (PP), polyethylene (PE), or unplasticized poly (vinyl chloride) (PVC-U); or any other equivalent material; or any other material envisaged by the standard BS EN 124 or other such standards. For the purpose of this specification cast iron includes (but is not limited to) ductile iron and spheroidal cast iron and more generally any cast iron with ductile properties. The insert may be formed of modular parts.

Claims

1. A replaceable seat insert for a ground surface access assembly that is arranged to be installed above a ground opening, the replaceable seat insert being arranged to be located between a frame of the assembly and a cover of the assembly, the insert comprising a cover-engaging base arranged to engage with the cover; the insert further comprising a first interengaging means arranged to be interengageable with a second corresponding interengaging means on the frame to fix the insert to the frame in an in-use configuration in which movement between the insert and the frame is prevented, and wherein the replaceable seat insert comprises a wear indicator arranged to indicate whether the cover-engaging base is worn beyond a threshold amount.

2. The insert of claim 1 wherein the insert is made from a material softer than the material from which the frame is made.

3. The insert of claim 1 or claim 2 wherein the insert is made from a material softer than the material from which the cover is made.

4. The insert of claim 1 wherein the frame and cover are ductile cast iron and the insert is made from a material having a hardness of less than ductile cast iron, e.g. less than about 560 N / mm2.

5. The insert of any preceding claim wherein the wear indicator comprises a visible wear indicator, such as: a traffic light wear indicator; or a zone indicator.

6. The insert of any preceding claim wherein the cover-engaging base has a thickness of about 15mm.

7. The insert of any preceding claim wherein the wear indicator has a height of between 10mm and 20 mm.

8. The insert of any preceding claim wherein the cover-engaging base comprises a cover-engaging platform and an insert upstanding wall extending therefrom.

9. The insert of claim 8 wherein the cover-engaging pad is arranged substantially perpendicularly to the upstanding wall.

10. The insert of claim 8 or claim 9 wherein the wear indicator is located at or near an end of the insert upstanding wall, the end being spaced from the cover-engaging base.

11. The insert of any preceding claim wherein the wear indicator is arranged to indicate that: the insert should be replaced immediately; the insert should be replaced in the near future; or both.

12. The insert of any preceding claim wherein the cover-engaging base is a multi-region cover-engaging base comprising a first region having first indicia arranged to indicate that the cover-engaging base is worn beyond a threshold amount, and a second, contrasting region, wherein, in the in-use configuration, the second region is arranged between the cover and the first region such that the second region gets worn away before the first region.

13. The insert of claim 12 wherein the first indicia comprises a first visible indicia, such as the material of the first region being a first colour, such as red.

14. The insert of claim 12 or claim 13 wherein the second region comprises: no indicia; or a different, second indicia, such as a second visible indicia, such as the material of the second region being a second, contrasting colour, such as green.

15. The insert of any preceding claim wherein the first interengaging means comprises a projection on the insert arranged to fixedly interengage with a corresponding slot in the frame.

16. The insert of any preceding claim wherein the first interengaging means is located on any one or both of:the insert upstanding wall; andthe insert cover-engaging base, such as the bottom surface of said base.

17. The insert of any preceding claim wherein the first interengaging means comprises any one or more of:a click-fit arrangement;a wedge;a fastening clip;one or more push-in ribs; andany other suitable projection-recess or male-female type arrangement.

18. The insert of any preceding claim wherein the first interengaging means is part of a non-reversible interengagement connection arranged to remain in place until broken out.

19. A ground surface access frame for a ground surface access assembly that is arranged to be installed above a ground opening, wherein the frame is open at its upper and lower ends and comprises:an upstanding, peripheral frame wall having protruding outwardly therefrom a flange that is embeddable in a medium so as to retain the frame relative to the ground opening;cover mounting means arranged to mount a cover at or near the upper end, the cover mounting means including a frame seat for supporting the cover, wherein the peripheral wall is arranged to surround at least part of a mounted cover, and the frame seat being arranged to receive the replaceable seat insert of any preceding claim,the frame further comprising the second corresponding interengaging means to fix the replaceable seat insert to the frame in the in-use configuration.

20. The frame of claim 19 when dependent on any of claims 8 onwards, wherein the upstanding, peripheral frame wall has a recessed section arranged to receive the insert upstanding wall.

21. The frame of claim 19 or claim 20 wherein the second corresponding interengaging means is located on any one or both of:the upstanding, peripheral frame wall; andthe frame seat.

22. The frame of claim 20 or claim 21 when dependent on claim 17 or claim 18, wherein the second interengaging means comprises any corresponding interengaging arrangement to the first interengaging means, such as a corresponding frame slot or frame recess.

23. The frame of any of claims 19 to 22 when dependent on claim 18 wherein the second interengaging means is part of the non-reversible interengagement connection arranged to remain in place until broken out.

24. A ground surface access assembly arranged to be installed above a ground opening, the assembly comprising: a frame according to any of claims 19 to 23; a cover that is insertable into the frame; and a replaceable seat insert according to any of claims 1 to 18 and arranged to be located between the frame and the cover, the assembly comprising anchoring means arranged to securely fix the replaceable seat insert to the frame in an in-use configuration in which movement between the insert and the frame is prevented, the anchoring means comprising the first interengaging means of the insert and the second corresponding interengaging means of the frame.

25. The assembly of claim 24 wherein the cover mounting means comprises multiple seats arranged to support the cover at multiple locations, and wherein a replaceable seat insert according to any of claims 1 to 18 is provided between the frame and the cover at each seat location.

26. The assembly of claim 24 or claim 25 wherein, in the in-use configuration, the insert upstanding wall abuts the upstanding, peripheral frame wall and remains fixed thereto.

27. The assembly of any of claims 24 to 26 wherein, in the in-use configuration, the cover-engaging base of the insert rests on the frame seat.

28. The assembly of any of claims 24 to 27 wherein, in the in-use configuration, the top of the insert upstanding wall is flush with the top of the upstanding, peripheral frame wall.

29. The assembly of any of claims 24 to 28 wherein, in the in-use configuration, the wear indicator is arranged to be visible while the cover is inserted in the frame.

30. The assembly of any of claims 24 to 29 wherein the cover comprises an upper surface having an antislip pattern thereon.

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