Patent Publication Number: US-8118517-B2

Title: Manhole cover device

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to manhole covers. More particularly, the present invention relates to a resilient pad that is attachable to a manhole cover. 
     2. Related Art 
     Manholes are common structures in streets and roadways for allowing access to underground utilities such as water and sewer lines or stored materials or equipment. Manholes provide an opening to allow workmen to descend beneath the surface to obtain access to these underground items. Manholes and manhole covers are typically subject to significant loads, such as the weight of roadway vehicles and impact loads from them, and thus must be made of strong and durable materials. The top of a manhole typically includes a strong metal (e.g. cast iron) frame having a projecting ledge around the circumference of the opening, with a heavy cast iron cover that rests on the ledge and closes the manhole. The cover is designed to support surface loads, and the frame transmits those loads to the underground supporting structure. Manhole covers are generally made heavy to resist unintentional opening or vandalism, and in many cases are bolted down in order to make the installation water tight and tamper-proof. 
     One challenge associated with manhole installations is maintaining the manhole cover flush with a surrounding roadway elevation. When a street is repaved, the pavement elevation increases by a few inches. Manholes can also settle over time, producing an elevation difference with surrounding pavement. If these conditions are not corrected, the manhole location can present a road hazard, the manhole cover and supporting structure will be subjected to increased impact loads from passing vehicles, and the surrounding pavement is likely to degrade more quickly. To avoid these problems, road paving crews sometimes simply pave over an existing manhole. Unfortunately, this defeats the whole purpose of the manhole, and hides its location from view. 
     More commonly, when a street is repaved or a manhole has settled, existing manholes in the street are typically raised to match the elevation of the pavement. This process typically involves the installation of new grade rings or other structures atop the manhole frame to raise its elevation, and may also involve the installation of a new concrete collar surrounding the manhole to reinforce the transition from asphalt pavement to the rigid cast iron manhole top. Unfortunately, raising manholes in a street can be an expensive and time-consuming process, thus adding to the financial burden that highway maintenance agencies face in building and maintaining roadways. 
     SUMMARY 
     It has been recognized that it would be advantageous to develop a system for raising manhole elevations that is simple and inexpensive. 
     It has also been recognized that it would be advantageous to have a manhole grade adjustment system that makes manhole covers more useful. 
     In accordance with one embodiment thereof, the present invention provides a manhole cover device that includes a bottom layer of rubber material, suitable for attaching to a top of a metal manhole lid, having a top surface, and a first top layer of vulcanized rubber material, having different material properties than the bottom layer. The top layer is affixed to the top surface of the bottom layer, the top and bottom layers functioning as a single unit. 
     In accordance with another embodiment thereof, the invention provides a manhole cover device for attachment to a metal manhole lid, including a manhole lid of metal, disposed below an elevation of surrounding pavement, and a cover, attached atop the manhole lid. The cover includes at least two bonded layers of rubber material of differing properties, and has an overall thickness sufficient to substantially match the elevation of the surrounding pavement. 
     In accordance with yet another embodiment thereof, the invention provides a rubber manhole cover, suitable for attaching to a top of a metal manhole lid. The rubber manhole cover includes at least two bonded layers of rubber material of differing properties, including a bottom layer of a first rubber material, and a top layer of vulcanized rubber material, the top and bottom layers functioning as a single unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention, and wherein: 
         FIG. 1  is an exploded perspective view of a manhole cover assembly and an embodiment of a manhole cover device in accordance with the present disclosure; 
         FIG. 2  is a side, cross-sectional view of a manhole cover assembly and an embodiment of a manhole cover device in accordance with the present disclosure; 
         FIG. 3  is a side, cross-sectional view of a manhole cover assembly and another embodiment of a manhole cover device in accordance with the present disclosure; 
         FIG. 4  is a perspective view of an embodiment of a manhole cover device in accordance with the present disclosure, having indicia disposed upon the top layer; and 
         FIGS. 5-7  are top views of three embodiments of manhole cover devices in accordance with the present disclosure, having different types of indicia associated with the top surface; 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention. 
     As noted above, the relative elevation between a manhole cover and surrounding pavement can change due to settlement of a manhole or repaving of a street. In some cases manhole covers are simply paved over when a road is resurfaced. This is not only annoying for drivers and damaging to pavement, but it also hinders access to the manhole. Workers must chip away the pavement before opening the manhole cover, leaving a pothole in the surface. For these and other reasons there is often a need to raise existing manholes to match the elevation of the surrounding pavement. This ordinarily involves some digging in the road to install new manhole rings or other relatively expensive devices to bring the manhole cover up to the new grade level. 
     Advantageously, the inventors have developed a simple and relatively inexpensive system for adjusting the grade of existing manholes. Shown in  FIG. 1  is an exploded view of one embodiment of a manhole cover system  10  in accordance with the present invention. As is well known, conventional manholes typically include a manhole lid  12  that is configured to be supported in the rim  14  of a manhole ring or frame  16 . The frame and manhole lid are typically of strong and durable metal, such as grey cast iron. The frame  16  is configured to rest atop a manhole substructure (not shown in  FIG. 1 ), which can be of pre-cast concrete, and typically includes a cone section at its top. The frame sits atop the cone section, or on one or more ring sections that are atop the cone section. The manhole frame also frequently includes a horizontal flange  18 , which extends outward, allowing compacted road base, pavement, concrete, or other material placed around the manhole rim to hold the rim in place. The frame can also include gussets  20  which extend between the vertical wall of the frame and the flange, for added strength, and to further help anchor the frame in surrounding material. 
     Typical manhole lids, like the manhole lid  12  shown in  FIG. 1 , often include ridges or lugs  22  or other protrusions cast into their top surface to increase the physical roughness of the surface and thereby provide additional traction for vehicles that ride over the cover. Manhole lids also frequently include words or other indicia  24  cast into their top surface. The manhole lid can also include openings that pass through its top surface, such as an opening  26  at the edge of the lid, and holes  28  or other openings in any area of the lid. The edge opening  26  or holes  28  can be used to allow a lifting tool to be inserted for opening the manhole. The holes  28  can also be used for bolts to secure the lid in place. The manhole lid can also include a recessed lifting bar  30  that is cast into its top surface, for insertion of a lifting tool for opening the manhole. It is to be understood that the openings and features of the manhole lid  12  shown in  FIG. 1  are exemplary only. The number and types of openings and features in the manhole lid can vary widely. 
     In order to allow the manhole cover to be adjusted to grade easily, the present invention provides a manhole cover device  32 . The manhole cover device is a durable cover or pad, indicated generally at  34 , that attaches to the top of the cast iron manhole lid to approximately match the level of the surrounding pavement. Cross-sectional views of various manhole structures having manhole lids provided with various embodiments of a manhole pad or cover in accordance with the present disclosure are provided in  FIGS. 2-3 . In these figures the manhole frame  16  and its parts are shown, as is the top of an underlying manhole structure  17 . 
     As shown in  FIGS. 1 and 2 , the pad  34  can include apertures or openings that allow access to the manhole lid below. For example, the pad can have an elongate aperture  36  at an edge to allow access to the edge opening  26  of the manhole lid. It can also have holes  38  in its body to allow access to corresponding holes  28  in the metal manhole lid  12 . It can also have a rectangular opening  40  that allows access to the recessed lifting bar  30  of the manhole lid. 
     The manhole pad or cover  34  includes at least two layers of resilient material, such as rubber, or rubber-like material. The pad has a bottom layer  42  of one type of material, and at least one top layer  44  of a different type of material. The top and bottom layers can be affixed together with chemical adhesive, such as industrial strength sag resistant adhesive, rubber-to-rubber adhesive, fasteners, such as large staples, or cement type adhesives. The bottom layer can be of a relatively soft rubber material, and the top layer can be of a harder and/or more durable material. This multi-ply configuration provides several advantageous features. The bottom layer can be of recycled rubber, which is relatively inexpensive. Other materials, such as neoprene, can also be used. The bottom layer can be soft enough to deform around the lugs  22 , protrusions, indicia  24 , and other irregularities in the manhole lid  12 . The bottom layer can be made out of recycled rubber. The bottom layer can have a durometer of about 60+/−5 Shore A, hardness of 60 lb/ft, compression recovery of about 98%, and tensile strength of about 300 psi. Other materials that can be used include various rubber combinations, such as butyl rubber, chlorobutyl, epichlorhydrin, ethylene propylene rubber, hydrogenated nitrile rubber, natural rubber, nitrile rubber, polychloroprene, polyurethane rubber, and styrene butadiene rubber. 
     The top layer  44 , on the other hand, can be of a vulcanized rubber material that is more durable under the wear and tear of roadway traffic. In one embodiment, the top layer is neoprene (polychloroprene) rubber. In another embodiment, the top layer can be a blend of SBR (styrene butadiene rubber), CR (neoprene) and NBR (nitrile) rubbers, which gives it a 55-65 durometer, minimum tensile strength of 725 psi, temperature range of −40° to 200° F. Resistance to UV radiation is also desirable for the top layer. Accordingly, materials can be selected that have a high EPDM, making the top layer UV resistant. Other rubbers which can be used include butyl rubber, chlorobutyl, epichlorhydrin, ethylene propylene rubber, hydrogenated nitrile rubber, natural rubber, nitrile rubber, polychloroprene, polyurethane rubber, and styrene butadiene rubber. More durable vulcanized rubber materials tend to resist deformation around deformities beneath them, but are durable against wear and the elements, and provide a non-skid surface. Recycled rubber materials, on the other hand, more readily conform to, even grind into irregularities, but are less durable and resistant to the elements. Using these two types of layers together allows the bottom layer to smooth out the irregularities, and provide a smooth durable top surface. 
     Having two layers also helps resist curling or warping of the pad  34 . Single ply vulcanized rubber pieces have a tendency to curl at the edges, due to internal stresses created during the vulcanization process. A manhole cover that curls at the edges is not only unsightly, but can present a road hazard, and can wear out faster than one that is flat. Additionally, pads that are curled up at the edges can be pulled up or torn up by a snowplow or the like, and can be prone to vandalism. The multi-ply configuration disclosed herein reduces curling and warping by adhering the curl-prone vulcanized top layer  44  to a bottom layer  42  of material that is not as prone to warping. The bottom layer thus helps resist the tendencies of the top layer, and keeps the whole assembly more flat. 
     The relative thicknesses of the top and bottom layers  44 ,  42 , can vary. As shown on the left side in  FIG. 2 , the bottom layer  42   a  can be significantly thicker than the top layer  44   a . This can reduce the overall weight of the pad  34  (since the bottom layer can be less dense than the top layer) and also provide more dimensional stabilization (e.g. warp resistance) to the top layer. Different thickness ratios can also be used. For example, as shown on the left side of  FIG. 3 , the bottom layer  42   a  can be of a similar thickness to the top layer  44   a . In general, the inventors have found that a bottom layer of from about ¼ to 2.5 inches thick and a top layer that is about ¼ to ½ inch thick is useful. More generally, the bottom layer can be from ¼ to 7 inches thick, and the top layer can be from ¼ to 5 inches thick. 
     More than two layers can also be provided, and these can be in various configurations and thickness combinations. For example, shown on the right side of  FIG. 3 , a pad  34   d  comprises a bottom layer  42  and three top layers  44   d, e, f . The top layers can be of the same or similar thickness, or can be different thicknesses. It should be understood, that multiple layers of differing thicknesses can be affixed together to produce a desired overall thickness of the top layer  44  and of the pad  34  as a whole. 
     The manhole pad or cover  34  can be attached to the manhole lid  12  using mechanical fasteners or chemical adhesive. For example, shown on the left side of  FIG. 2 , the manhole cover pad  34   a  is attached using a chemical adhesive, without mechanical fasteners. Suitable adhesives for attaching a rubber manhole cover to a metal manhole lid include chemical adhesive, such as industrial strength sag resistant adhesive, any rubber-to-metal adhesive, or cement adhesives of various types. However, on the right side of  FIG. 2 , a part of an embodiment of a manhole cover  34   b  is shown having a bolt  46  extending through an aperture  28  in the lid and a corresponding aperture  38  in the pad  34 . This bolt is representative of any type of mechanical fastener. Bolts, staples, or other mechanical fasteners can be used. The aperture in the pad can include a recessed top portion  48 , so that the head  50  of the bolt will lie below the top surface of the top pad  44   b . Fasteners that hold down the pad  34  can also be used to fasten the lid  12  in place, as shown on the right side of  FIG. 2 , where the bolt attaches to a lid latch device  52  that holds the lid to the manhole frame  16 . 
     The manhole cover  34  can be of different shapes and sizes, and can be used in a variety of installation conditions. The manhole pad shown in  FIG. 1  is circular, and this may be the most common shape for most manhole installations. However, the pad is not limited to a circular shape. Manhole covers of various shapes can be used for different applications, whether circular, square, rectangular, or any other desired shape. 
     The size of the manhole cover can also vary. For example, shown on the left side of  FIG. 2 , the manhole cover  34   a  substantially completely covers the manhole lid  12 , but does not extend over the rim edge  54   a  of the manhole frame  16 . This view depicts a situation where a manhole frame is surrounded by a first layer of pavement  56 , and the rim of the frame is flush with this pavement. However, a subsequent layer of pavement  58  has been placed on top of the first layer, raising the elevation of the pavement. In this situation a manhole cover pad  34   a  of a similar overall thickness as the new layer of pavement is attached to the top of the manhole lid  12 , thus substantially matching the elevation of the new pavement. In this embodiment there is a small gap between the pad  34  and the new pavement, directly above over the rim edge  54   a  of the manhole frame. 
     In another embodiment, shown on the right side of  FIG. 2 , the manhole pad  34   b  extends out to the edge of a concrete collar  60  that surrounds the manhole frame  16  and extends to the edge of a first layer  62  of pavement. Such collars are a common feature and are typically cast in place around manhole frames after a paving operation. These collars provide a transition between the metal manhole frame and the edge of asphalt pavement, providing a more durable installation. In the embodiment shown on the right side of  FIG. 2 , a new layer of pavement  64  has been placed atop the first layer  62 . This new layer is placed up to the beginning of the concrete collar. Rather than removing and replacing the concrete collar  60 , which is relatively expensive and time-consuming, the resilient pad  34  extends over the collar to meet the new pavement edge, matching the elevation of the new pavement. 
     The configuration shown on the left side of  FIG. 3  represents a settled manhole situation. Here the manhole frame  16  has settled or dropped some amount relative to the adjacent pavement  66 . In this situation, a manhole cover or pad  34   c  is placed atop the manhole lid  12  to bring the level up to match the existing pavement. In this case, unlike that on the left side of  FIG. 2 , the pad extends over the rim edge  54   c  of the manhole frame, leaving substantially no gap between the pad and the pavement. 
     Shown on the right side of  FIG. 3  is another situation where a roadway surface has been repaved multiple times. In this configuration, the first layer of pavement  70  substantially matched the elevation of the rim edge  54   d  of the manhole frame. When a second layer of pavement  72  was placed, a first pad  34   d  having a bottom layer  42   d  and a top layer  44   d  was attached to the manhole lid  12  to match the elevation of the new pavement. Then, when a subsequent new layer of pavement  74  was placed, two additional top layers  44   e  and  44   f  were added to the top of the first pad  34   d . This embodiment demonstrates how new layers can be added to an existing manhole cover when a pavement elevation changes. Alternatively, when a pavement elevation changes around an existing pad  34 , the existing pad can be removed and a new pad having a desired total thickness can be placed back on the manhole lid. 
     The manhole pad or cover  34  can be provided in a number of other variations, too. For example, rather than being intended to deform around irregularities in the top surface of a manhole lid (e.g. lugs  22  in  FIGS. 1 &amp; 2 ), the bottom layer can be made with indentations preformed in its bottom surface, so as to conform to the shape of the manhole lid. One possible way to do this is to press the bottom layer  42  against the respective manhole lid or a mold having a comparable shape, so that the bottom layer becomes molded to conform to the lid. 
     Another feature that is provided by the manhole cover disclosed herein is that the pads  34  provide a location for useful or desirable indicia. The manhole covers or pads disclosed herein can have alphanumeric characters, linguistic characters, ornamental designs, marks, logos, visual targets, or any other type of indicia provide on their top surface. For example, shown in  FIG. 4  is a perspective view of a manhole cover pad  34  having a decorative logo  80 , comprising words and design elements. As in this figure, the indicia can identify a location, a city, an owner of infrastructure facilities, maker of products, or it can serve as advertising or any other type of indicia. Shown in  FIG. 5  is another embodiment of a pad  34   f  in which the indicia  82  comprise words that identify the function or type of the installation. This sort of indicia can be helpful for public utility identification and maintenance. For example, a city public works department or public utility can use specially-designed manhole cover pads that identify and distinguish the manhole covers that are of interest to the particular company or department. These could include words, as shown in  FIG. 5 , or they could use more abstract identification numbers, letters, etc. 
     Other examples of indicia are shown in  FIGS. 6-7 . These indicia provide targets or geometric shapes, such as a cross  84  in the cover  34   g  in  FIG. 7 , and a square  84  in the cover  34   h , shown in  FIG. 8 . These sorts of large shapes or targets can be used to help make the location of the manhole easily visible from far away, such as for aerial photography and aerial surveying. These targets can use highly contrasting colors and different target shapes corresponding to different types of manholes (e.g. storm drain vs. sanitary sewer, etc.). Such high visibility indicia can be useful for creating and maintaining global information systems (GIS) by municipalities and other entities. 
     The method for applying indicia to the manhole cover pad can vary. It will be apparent that paints or pigments can be used. Advantageously, the configuration of the manhole cover pad  34  disclosed herein lends itself to a more durable method for providing desired indicia by providing rubber inlays of contrasting color to produce words, letters, logos, etc. The top layer  44  of rubber material can be cut and material removed to create cutouts of any desired shape inside the boundary of the manhole cover. Corresponding pieces of the exact size and shape of the cutouts can be cut from other pieces of rubber having the same thickness and a contrasting color. Highly accurate cutting of the cutouts and the inlay pieces can be done using water jet cutters and other cutting devices that are well known and widely available. The inlay pieces can then be inlaid into the cutouts in the manhole cover pad, and the cover with the contrasting color inlay pieces can then be vulcanized as a unit, fusing the inlays and surrounding material into an integral unit. This method provides the desired indicia as integrally vulcanized color inlays in a single manhole cover pad. The indicia will be highly durable because they are integral with the material of the top layer of the cover, and will provide the desired shape and color over the life of the manhole cover, even as the top surface wears. 
     Cross-sectional views of top layers  44  having inlaid pieces are shown in  FIG. 3 . On the right side of  FIG. 3 , it can be seen that the top layer  44   d  includes several inlaid pieces  90 , which can be part of a desired indicia. The inlaid pieces comprise integral parts of the top layer, but are of a contrasting color. Then, when new top layers were placed to match a new pavement elevation, the same (or a different) indicia is provided in the new topmost layer  44   f  using inlaid pieces  92  in the same manner. In this way, a top surface of the manhole cover can always be provided with the desired indicia in a durable, highly visible format. Multiple inlay pieces can be used in any desired color or combination of colors to provide a durable, aesthetically pleasing manner. 
     This manhole cover disclosed herein thus provides a durable, non-skid surface, and eliminates the need for more expensive grade rings or other devices to bring a manhole lid up to grade. The manhole cover can be attached to a manhole lid using mechanical fasteners or adhesive, and comprises multiple layers, thus helping it remain geometrically stable while also being economical and easily conformable to the shape of the top of the underlying manhole lid. Decorative and/or functional indicia can be provided on the top surface of the manhole cover, such as with rubber inlays, thus giving the pad an additional function in a durable configuration. 
     It is to be understood that the above-referenced arrangements are illustrative of the application of the principles of the present invention. It will be apparent to those of ordinary skill in the art that numerous modifications can be made without departing from the principles and concepts of the invention as set forth in the claims.