CA1085889A - Gasket seal between sewer pipe and manhole opening - Google Patents

Abstract

ABSTRACT
An improved seal for closing the space between a pipe and the wall of an opening through which it passes, using a linear extrusion of elastomeric material, of predetermined length to form a gasket. The extru-sion has a pear-shaped head formed integrally with a T-shaped anchoring flange. It is curled into the form of a right cylinder, and its mating ends are vulcanized together. The pear-shaped portion is deflected radially inwardly and the T-shaped anchoring flange outwardly, the latter being then embedded in concrete used to wall the opening for the pipe. The pear-shaped portion is free in space and is preferably hollow. The hollow head provides a pneumatic cushion for the pipe.

Description

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This invention deals with the installation o~ sanitary sewers and is particularly concerned with a gasket for sealing the space between a sewer pipe and an opening in the wall of a manhole through which that pipe passes.
This application is a division of Canadian application No. 292,374 filed December 5, 1977.
The new form of gasket represents an improvement in the structure shown in my Canadian Patent No. 996,150, issued August 31, 19760 That patent shows a gasket made from an extruded rubber strip, having a cross section in the shape of a capital Ao ~hen properly positioned in the man-hole opening, the apex of the A is exposed, and extends radially inwardlyto make firm contact with the surface of the pipe 0 The legs of the A extend outwardly, and are embedded in cementitious material which lines the open-ing in the manhole wall, as is shown in my Canadian Patent No. 971,997, issued July 29, 1975. The method of constructing such a seal is described in my United States Patent no. 3,832,438, dated August 27,1974.
In these earlier patents, in which the elastomeric gasket was made from an extrusion in the cross-sectional fo~m of a capital A, it required some distortion of the gasket~ as explained at page 6, lines 16 et seq., of Canadian Patent No. 996,150, to fit this gasket onto the mold rings, but the webs or skirts (corresponding to the lower legs of the A) were fairly flexible, so the difficulty of installation proved to be slight.
In spite of the provision of concentric serrations in the web or skirt portions of the gasket, however, there seemed to be a possibility that, under severe conditions, the pipe might impose so great a stress on the gasket as to cause the rubber in the skirt portion under tension to thin out and pull away from the surface of the concrete in which it was embeddedO
In order to reduce this potential area of vulnerability, experimentation with other shapes of extrusions was carried outO

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The basic problem was to provide an improved technique for positi-ve-ly and permanently anchoring the gasket in the cementitious material which defines the inner surface of the opening. Preferably the gasket has a double-walled head portion, which has a continuous circular cavity therein.
This cavity is walled with rubber or similar elastomer, and its walls are air-tight, so that it affords a pneumatic cushion.
The problem did not appear to be solvable by the use of individual ly molded unitary gasket washers~ since they lacked sufficient resistance to ; compression in their lower~ inner portion, which carries the major load, and were too subject to peripheral separation from the pipe in their upper portions. Furthermore, such washers would have to be stocked in many sizesO
Nor did it appear to be feasible or practical to mold a unitary gasket ring in the form of a washer with a continuous circular cavity, such as could be made by using the A-shaped extrusionO
The endless cavity of the A-section gasket provided an answer to the compressibility problem in the pipe-contacting part, but the difficulty of installation, because the diameter of the inner opening is so much less than the diameter at the extreme ends of the webs or "legs" of the A, dis-couraged any attempt to use cross-sectional forms which have to accommodate an even greater difference between the inner and the outer diameter of the washer-like gasket, in order to complete installation~
The cross-sectional pattern of the anchoring member of the molded washer shown in the Netherlands patent to Raatjes, NoO 290,612 of 1963, seemed to be likely to remain embedded in its surrounding concrete, no matter how severe the stress upon it might become. But there seemed to be no way to convert a lineal extrusion having this cross-sectional shape into a disk-like washer, and no practical way to provide the endless cavity unless it could be formed by extrusion.
~"washers" as used herein, refers to centrally-apertured articles of disk-like shapeO
_ 2 -Combining an extruded triangular head with a T-shaped anchoring part seemed to be quite out of the question, for this would greatly increase the overall height of the extrusion, and thus create an even greater difference between inner and outer diameter of the finished washer than the A-shaped gasket entailed.
It would apparently be practically impossible to roll the gasket into place in the molding rings.
It has now been discovered that a seal or gasket having all of the desired properties can be made by utilizing an extru-sion having a pipe-contacting part which, instead of being A-shaped, is pear-shaped in section and is unitarily provided with a T-shaped anchoring part, the stem of the T being united with the bottom of the pear-shaped part and affording, when longitudinally considered, a web of substantial height and thickness. Such an extrusion can be used effectively if handled in the manner hereinafter set forth.
ccording to one aspect of the invention there is provided a washer-like gasket of elastomeric material in the form of a surface of revolution generated by rotating a generatrix about an axis of revolution, the outline of said generatrix including a generally pear-shaped head portion integrally joined to the foo~ of ?~-L~e-~e~-T-shaped flange member in the mid-region of the bottom of the pear-shaped portion, the axis of revolution being parallel to the arms of the T member, the pear-shaped head portion projecting inwardly toward the axis of revolution and wherein the inner peripheral portion of the washer-like gasket is in compression and the outer peripheral portion is in tension.
According to another aspect of the invention there is ,,, ; . , .: ; . ;. . ,. ~

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IIQ~S~ 3 .~ provided Eor use in forming a fluid-tight seal between a pipe and , a wall opening through which said pipe passes, a washer-like gasket having inner circumferential portions which are in compression and outer circumferential portions which are in tension, said gasket comprising a section of a linear extrusion of elastomeric material, a cross-section of said extrusion in a plane normal to the axis of extrusion including a T-shaped flange and a generally pear-shaped head portion said head portion having a broad base and tapering along a central axis thereof, said T-shaped flange having a stem and two arms, said stem bein inte-at~g~ce~ ;s grally attached to said broad base of said head portion~, said D section of extrusion having ends thereof bonded together to form a ring having an axis offset from and normal to said axis of extrusion, wherein said central axis of said head portion and said stem of said T-shaped flange are initially parallel to said ring axis and said ring is subsequently deflected so that said central axis of said head portion and said stem of said T-shaped flange are perpendicular to said ring axis with said head portion projecting toward said ring axis.
When installing the cut and spliced extrusion in a manhole opening, the right cylinder is preferably positioned on the inner portion of a mold, and is rolled inwardly, so that the pear-shaped pipe-contacting portion is deflected radially inwardly and the outer flange (corresponding to the cross-bar of the T in section) and is pulled outwardly, in a manner analogous to that employed in fitting the bead of a tire to the metal rim of an automobile wheel. When the inward deflection of the pipe-contacting part has progressed sufficiently to ~ - 4 - ,. : .
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allow it, the complementary part of the mold is slid into place, and its clamp is drawn up, applying pressure as needed, to force the tubular part of the ring into the groove which extends peripherally of the mold.

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~ suitable mold ring for utilizing the novel gasket of this inven-tion most effectively is the two-part mold which is described and claimed in Canadian Patent No. 971,9970 ~s there isseen~ mold consists of inner and outer shells of frustoconical shape which are so configured that when assem-bled they define between them a peripheral groove which encloses the apex of the A, leaving the legs of the A free. In the method herein described, the pear-shaped head of the extrusion is received by the peripheral groove formed by the mold rings, and the T-shaped flange projects radially out-wardly therefrom. ~oncrete or other cementitious material is then applied to enclose the flange and define the peripheral wall of the opening in the manhole wall. Upon separation and removal of the mold parts, the cementit-ious material lining the opening covers the peripheral flange and embeds it, but the tubular pear-shaped portion is exposed, and yields to receive the pipe inserted therein.
One of the advantages of the present invention is the unexpected discovery that extrusions having the cross-sectional form described can ; often be used with pipes of different sizes~ without altering their cross-sectional dimensions. All that is necessary is to change the length of the extrusion and the diameter of the mold ringsO This capacity to coact with pipe of many different sizes is believed to be due, in part at least, to the fact that the manner of use places considerable compression on the inner portion of the gasket, and causes t~nsion on its periphery~ As a consequence the gasket described herein hugs the pipe more tightly than would be the case if the gasket were initially molded as an apertured disk or washer.
It must be realized that the part of the gasket which lies at the bottom of the opening when in use will have to sustain mostof the load of the pipe and its contents, and in addition will have to resist environmental stresses, which may be împosed upon the pipe outside of the manhole by the weight of the fill, or by impacts due to traffic shock, or by the dead weight of passing vehiclesO If an ordinary washer is used, it may yield too much under these stresses, and become overly compressed at the bottom of the opening. The pipe may then pull away from the gasket ~t the upper part of the opening, thereby allowing fluid to pass the sealO Since the stresses imposed may sometimes be measured in thousands of poundS,particularly where the pipe is large - say 24" or 30" in diameter, it is difficult to employ a molded gasket ring which will manifest both sufficient resistance to compression at the bottom of the opening and sufficient capacity for expan-sion at the top.
me pear-shaped head of the gasket described herein is remarkably adapted to meet this problem. Its walls are of substantial thickness, which means that a sufficient mass of elastomeric material will be present to carry the weight imposedO The volume of the preferred circular cavity is sufficient to afford increased flexibility while the pipe is being installed.
~t the same time, elin~nation of the legs (or webs) of the A of the prior device avoids formation of a thin edge at the interface with the concrete, and the rounded edges of the pear-shaped bottom permit a self-accommoda-ting rolling movement under axial stress.
The other major need is to ensure that the gasket ring is so firmly anchored in the concrete as to resist any stress which might tend to dislodge it. This is ensured by the deep embedding of the T-section flange in the surrounding concrete.
The entire gasket is subjected to substantial distortion as it is deflected from the cylindrical form which is first produced into an aper-tured disk or washerO Because the inner diameter of the opening formed by deflecting the cylinder walls is substantially less than the cut length ofthe : . : :, .:: :. ~, ': , . ~;. ' '. ' " '' .~ :
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extrusion, the inner edge of the gasket will be under compression, and con-versely, because the outer diameter of the washer-shaped finished gasket is substantially greater than the length of the cut extrusion, it will be under considerable tension. These twin forces cause the gasket to hug very tightly the pipe which it surrounds.
Other features and advantages will be apparent from a consideration of the detailed description which follows, and from reference to the accom~
panying drawings, which illustrate the preferred embodiment of the invention, and in which:
Figure 1 is an elevation, partly in section, of a manhole structure, with the gasket seal in position;
Figure 2 is a perspective view of an extrusion used in the method of the invention, Figure 3 is a transverse section on the line 3-3 of Figure 2;
Figure 4 is a perspective view, showing the extrusion being pre-pared for use as a gasket;
Figure 5 is a perspective view of the completed gasket;
Figure 6 is a perspective view showing upper and lower mold forms~
with the gasket ring of Figure 5 in process of installation between them;
Figure 7 is an elevational view , partly in section, showing the gaslcet of Figure 5 in place in its mold; and Figure 8 is a vertical sectional view of the completcd installation, with the sewer pipe in placeO
Turning llOW to Figure 1: The manhole structure 10 is shown with the sewer pipe 11 passing through it by way of the openings 12,12~ A gasket 13 is shown in the distorted position which it assumes upon insertion of the pipe 11.
The gasket 13 is formed from a continuous extrusion 14 of rubber _ ~ _ : : . . . :. , . ~ .

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or the like, illustrated in Figure 2. Preferably, it conforms to ~STM
Specification C 4~3-63T. As seen in the cross-section of Figure 3, the general configuration of the extrusion is one in which there is a head portion 15 which is pear-shaped and preferably encloses a symmetrical hollow or cavity 160 Extending from a mid-part of the outer surface of the pear-shaped head is a web 17 which interconnects the head 15 with a ~ Y C~t~l a~s base flange 18 which is normal to the vertical center line~CL of the extru-D sionO As seen in Figure 2, the form of the extrusion in lengthwise eleva-tion is that of a tubular head 15 connected by a verticalweb 17 t~ the longitudinal flange 18 9 The vertical center line CL defines a plane containing the long axis of the head portion 15 and extending lengthwise with respect to the extrusion 14~ The base flange or flange structure 18 extends laterally of the plane and is symmetrical with respect thereto The web means 17 lies generally in the plane D
It is the apex of the head 15 which makes first contact with a pipe 11 being inserted in the manhole opening 12. To facili.tate insertion of the pipe, the apex 20 is rounded, as at 21. Lhlring installation, the base or anchoring portion~ which consists of the web 17 and the flange 18~ are .~ 20 embedded in concrete or other cementitious material. The finish line of the .;~ concrete which will ultimately be present has been suggested by the dashed .
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line 19-19, added to Figure 30 This illustrates the fact that the outer angles of the pea.r-shaped part are rounded and the concrete is emplaced in such a way as to avoid a sharp edge of contact with the lower portions of the pear-shaped tubeO Thus a possibility of accomm~dating some rolling move ment of the tubular portion of the gasket is provided, to reduce stress on insertion of the pipe. The cavity 1~ within the tube is preferably sym-metrical with its outer contour, and is so dimensioned as to provide a fairly S~

substantial wall thicknessO The web 17 spaces the base of the head from the top of the flange sufficiently to afford a substantial channel to be filled with concrete.
The proportions of the various parts of the extrusion are, in the preferred embodiment of this invention, substantially as follows. if the wall thickness be taken as 2x, then 3x is the thickness of the flange 18 and also the thickness of the web 17; furthermore, the radius of the rounded corners of the pear shape is also 3x, 4x is the height of the web, and 6x is the widest dimension of the cavity 16. The total height of the base (web plus flange thickness) is 7x, which is also the height of the cavity 16. The width of the base flange is 8x, and the widest part of the pear-shaped head is llxo The height of the pear-shaped portion is 14x. The exterior surfaces of the pear-shaped portion diverge at an angle of about 40 (20 on each side of the vertical) and the base angles are 70 each. The area of the rubber in the walls of the pear-shaped head is preferably about two and a half times the area of the cavity.
It is, of course, possible to vary these proportions within limits, but they have yielded excellent results for most installations. Abnormal conditions~ such as severe traffic load~ may justify some changes, such as in-creasing wall thickness without altering other dimensionsO
In order to convert the rectilinear extrusion into a ring gasket, it is first necessary to cut a piece of it to the desired lengthO Experience has shown that handling of the completed ring is easier if the length of the extrusion is 3.26 times the diameter of the pipe to be fitted.
The cut section of the extrusion is then curled into the form of a right cylinder, and its ends are brought together and vulcanized, as seen in Figure 4a In order to avoid distortion of the tubular portion of the extru-sion during vulcanization, it is desirable to insert a dowel pin 23, shaped to fit the cavity, into the adjacent ends of the tubeO ~he vulcaniz-_ g _ ing clamps are applied when the tube ends have been browght firmly together~
The dowel pin is made of some readily-frangible material, such as plaster of Paris, and after vulcanization has been completed, it is reduced by hammering to a fine powder, which does not block the continuous cavity in the head portion of the gasket.
Figure 5 shows the completed ring, after vulcanization and be~ore installation in the mold ring to be next described. It will be noted that the vertical axis of the extrusion is parallel to the cylinder axis, whereas its intended use requires that the extrusion assume the character of a disk, extending at right angles to the cylinder axis. In order to effect the indicated change in form, it is necessary to deflect the walls of the cylin-; drical gasket into a plane which extends transversely of the axis of the ring, and then to secure the distorted and deflected base flange by embed-ding it in concrete or similar cementitious material, with the tubular pear-shaped portion extending radially inwardly to engage the pipe which is to be mounted therein.
To accomplish these procedures, it is best to use a mold of the type described and claimed in Canadian Patent No. 971,997, to which reference may be had for full detailsO A brief description will suffice for present purposes~
Figure 6 illustrates the general form of the mold referred to.
It consists of two frustoconical rings 24,25 adapted to be clamped together and configured to embrace, between them, the tubular, pear-shaped portion 15 of the gasket. Figure 7 is a sectional view of the assembled mold, but with the parts in inverted position as compared to Figure 60 This clearly shows how the mold rings provide space between them to receive the tubular, pear-shaped part of the gasket.
Returning to Figure 6, it will be seen that the gasket ring .,: , .
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shown in Figure 5 has been stretched to fit the mold ring 25, and is being deflected radially inwardly, with the tubular pear-shaped part about to be forced still further down into contact with the mold flange 26 in the mold ring 25. A truss 27 spans the ring 25 diametrally being welded to a lug 28 which is long enough to slip through and beyond the aperture 29 in the corresponding truss 30 which spans the mold ring 24. A quoin key 31 is used to urge the mold rings together, being inserted into the keyway 32 in the lug 28 after the rings have been brought togetherO
Figure 7, in addition to showing the gasket ring in its final position in the assembled mold, also shows the base flange 18 and the web 17 fully embedded in the concrete. The tubular portion of the gasket, being within the mold, will be free in space after the mold is removed. This figure illustrates the relationship of the concrete to the pear-shaped tube, indicated by the dashed lines 19-19 in Figure 30 The concrete should reach fairly well up on the lower rounded corners of the tube, but not so far as to permit the formation of a "feather-edge"O Indeed, it is believed to be desirable to so form the mold as to limit the concrete to a level approximately the same as the upper surface 16a of the base of the cavity, so that the gasket may roll a little under the stress imposed by insertion of the pipe 11.
In Figure 8, the mold rings have been separated and removed and ;; the pipe 11 has been inserted. This causes a fairly extensive distortion of the tubular part of the gasket, more or less schematically indicated at 13a. The dot-and-dash outline 13 in Figure 8 indicates the position of the gasket before the pipe 11 is inserted.
The sloping conical faces 33,3~ are provided for the purpose of accommodating misalignment of the pipe 11, The curvature of the dash lines 35,36 indicates the projected circumference of the manhole wall which lies ;
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above and below the locus of the opening 120 For convenience it may be desirable to conduct much of the work involved in the shop rather than in the field. If this is desired, the mold may be assembled within an outer form, so that the concrete in which the flange is embedded is in the shape of a tubular concrete plug, preferably cylindrical, of a size to fit the opening in the manhole wall. It is then carried to the site, and cemented into place within the opening.
In any event, after the gasket is in place and the concrete is sufficiently cured, the pipe 11 is inserted through the gasket 13, causing substantial distortion of the tubular portion, as suggested at 13a. This greatly extends the contact area, so that there is very little chance that minor pits or defects in the pipe will escape the sealing action.
The wall thickness of the head and the si~e of the ca~ity within ; it are so related as to ensure the presence of enough rubber or rubber-like material to sustain the weight imposed and yet cushion the load to protect against shocks and momentary stressesO At the same time, the tension imposed on the circumference of the gasket ensures that tight contact will be main-tained at the upper surface of the pipe, no matter how extensi~ely the tub-ular head may be compressed at its lower portion.
This combination of factors, including the expanded area of contact and the cushioning action, protect against minor defects in the pipe surfaceO
Should there be a situation in which the pipe at the locus of the gasket is seriously out of round, or locally flattened, it may be desirable to increase the tightness of the seal by injecting a non-hardening, self-sealing material into the circular cavity, using a syringe with a fine point for this pur-pose. The material injected is placed under sufficient pressure to expand the tubular head into close contact with the pipeO The pressure needed may be supplied mechanically by the syringe, or chemically, as by - 12 _ . ~ . : , , ~t using urethane and a foaming agent, in controlled proportions, When the syringe is withdrawn, the self-sealing material inserted closes the opening made by the point of the syringeO Needless to say, this expansion-producing material is not employed until the pipe is in place.
It is noted that the contours of the A-shaped gasket previously used are significantly less well adapted to the need than is the new con-tour. The inverted "T" which forms the base element of the extrusion is so firmly embedded in concrete as to be practically incapable of removal , since the thrust imposed by insertion of the pipe is substantially normal to the web 17, and is transmitted through a very substantial body of rubber-like material, whereas the thrust, when using the A-shaped washer, is almost parallel to the leg of the A which is first contacted by the entering pipe, thus incurring the likelihood that the leg (or skirt portion) will be stretched and thinned out, and possibly torn out by the roots, so to speak.
The rounding of the lower corners of the pear-shaped contour, in contrast, permits the gasket to roll a little to accommodate stress, while the embedding of the T-shaped anchoring part of the gasket positively prevents dislodgement. The avoidance of any feather-edge at the interface between gasket and concrete eliminates any tendency o~ the concrete to break away or chip out in that location.

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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A washer-like gasket of elastomeric material in the form of a surface of revolution generated by rotating a genera-trix about an axis of revolution, the outline of said generatrix including a generally pear-shaped head portion integrally joined to the foot of a T-shaped flange member in the mid-region of the bottom of the pear-shaped portion, the axis of revolution being parallel to the arms of the T member, the pear-shaped head portion projecting inwardly toward the axis of revolution and wherein the inner peripheral portion of the washer-like gasket is in compres-sion and the outer peripheral portion is in tension.

2. A ring or gasket according to Claim 1 wherein the pear-shaped head is hollow.

3. A ring or gasket according to Claim 2 where the hollow is symmetrical with the external contour of the head portion.

4. A ring or gasket according to Claim 2 wherein the cross-sectional area of the pear-shaped head is about two and one half times the cross-sectional area of the hollow.

5. For use in forming a fluid-tight seal between a pipe and a wall opening through which said pipe passes, a washer-like gasket having inner circumferential portions which are in compression and outer circumferential portions which are in tension, said gasket comprising a section of a linear extrusion of elastomeric material, a cross-section of said extrusion in a plane normal to the axis of extrusion including a T-shaped flange and a generally pear-shaped head portion said head portion having a broad base and tapering along a central axis thereof, said T-shaped flange having a stem and two arms, said stem being in-tegrally attached to said broad base of said head portion at said central axis, said section of extrusion having ends thereof bonded together to form a ring having an axis offset from and normal to said axis of extrusion, wherein said central axis of said head portion and said stem of said T-shaped flange are initially parallel to said ring axis and said ring is subsequently deflected so that said central axis of said head portion and said stem of said T-shaped flange are perpendicular to said ring axis with said head portion projecting toward said ring axis.

6. A ring or gasket according to Claim 5 wherein the pear-shaped head is hollow.

7. The gasket of Claim 6 in which the hollow is symmetri-cal with the external contour of the head portion.

8. The gasket of Claim 6 or 7 in which the cross-sectional area of the head portion is about two and a half times the cross-sectional area of the hollow.

9. For use in forming a fluid-tight seal between a pipe and a wall opening through which said pipe passes, the combin-ation of a plug of settable material externally configured to generally conform in size and shape to the wall opening and having an opening therethrough and a gasket according to Claim 1 or 2 extending circumferentially about the plug opening with the entire flange member being embedded in the material forming the plug and with the head portion of the gasket protruding into the plug opening.

10. For use in forming a fluid-tight seal between a pipe and a wall opening through which said pipe passes, the combination of a plug of settable material externally configured to generally conform in size and shape to the wall opening and having an open-ing therethrough and a gasket according to Claim 5 or 6 extend-ing circumferentially about the interior of said plug opening with the entire flange member being embedded in the material form-ing the plug and with the head portion of the gasket protruding into the plug opening.

11. In combination a concrete manhole structure having a wall opening through which a sewer pipe can pass and a gasket accord-ing to Claim 1 or 2 positioned between the inner and outer walls of the manhole and extending circumferentially about the wall opening with the entire flange member being embedded in the con-crete surrounding the manhole opening and with the head portion of the gasket protruding into the manhole opening on the peri-phery thereof.

12. In combination a concrete manhole structure having a wall opening through which a sewer pipe can pass and a gasket accord-ing to Claim 5 or 6 positioned between the inner and outer walls of the manhole and extending circumferentially about the wall opening with the entire flange member being embedded in the concrete surrounding the manhole opening and with the head portion of the gasket protruding into the manhole opening on the periphery thereof.