AU635849B2 - Precast manhole base - Google Patents

Description

S F Ref: 185681 AUSTRALIA 3 PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT 0

ORIGINAL

S

Name and Address of Applicant: r Frank Edward Brown 92 Bringelly Road Leppington New South Wales 2171

AUSTRALIA

Frank Ec'ward Brown Actual Inventor(s): Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Precast Manhole Base 41 Invention Title: ASSOCIATED PROVISIONAL APPLICATION DETAILS [311 Application No(s) [331 Country [32) Application Date PK1426 AU 27 July 1990 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815/3 -2- The present invention relates to sewerage manholes such as are formed at the intersection of two or more sewerage lines and, in particular, to a pre-cast concrete manhole base and a method of constructing manholes using such a base.

Large numbers of manholes are constructed each year for the various sewerage authorities at different locations and the typical time for construction of a manhole is approximately 4 days in order to allow sufficient time for poured concrete to set and harden. Even allowing for this curing period, a minimum of two days is required because of the construction techniques used.

The object of the present invention is to reduce the construction time for manholes and it is envisaged that a construction time of the 'order of two hours per manhole can be achieved in accordance with the preferred embodiments of the present invention.

15 According to one aspect of the preselt invention there is disclosed S"a m6thod of forming a sewerage manhole at the intersection of two or more sewerage lines of a sewerage system, said method comprising the steps of: excavating a hole at the intended location of said sewerage manhole, (ii) excavating at least two trenches each corresponding to said sewerage lines, each of said trenches leading up to said hole, (lii) locating a pre-cast concrete manhole base in said hole, said S"base comprising a substantially cylindrical side wall and a substantially -flat bottom, a pipe outlet and at least one pipe inlet formed In said 25 side wall adjacent said bottom with said inlet(s) each being connected to said outlet by a corresponding channel formed in benches cast with said bottom, (iv) locating a pipe in each of said trenches and sealingly connecting each said pipe to the corresponding one of said inlet(s) or outlet, creating a tube above said base until ground height is reached, and (vi) backfilling around said base and tube.

In accordance with another aspect of the present invention there is disclosed a pre-cast concrete sewerage manhole base when used to carry out the above described method, said base comprising a substantially cylindrical side wall and a substantially flat bottom, a pipe outlet and 1/17620 2A at least one pipe inlet formed in said side wall adjacent said bottom with said inlet(s) each being connected to said outlet by a corresponding channel formed in benches cast with said bottom.

A preferred embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a series of 8 drawings illustrating the prior art construction, method, the drawings labelled A to D respectively representing first to fourth sequential steps in the prior art method, whilst the drawings labelled 1 being a vertical cross section through the manhole and the drawings labelled 2 being a plan view, Fig. 2 is a perspective view of the pre-cast concrete manhole base of the preferred embodiment, s *se*: o• o *o LMM/1762o Fig. 3 is an exploded perspective view of a manhole utilising the pre-cast concrete manhole base of Fig. 2, and Fig. 4 is a vertical cross sectional view of the completed manhole schematically illustrated in Fig. 3.

Manholes are generally constructed at the Intersection of two sewerage lines, one of which Is the "straight through" line and the other of which Is the branch or joining line. In addition, manholes can be constructed at intermediate points on extremely long runs of straight lines, or at dog legs or other such turning points on a single line.

Clearly, an intersection can include two or more joining lines as well as a single through line, so there are a large number of possible configurations. However, for the present purposes of description the intersection between a single through line and a single joining line will be described.

Fig. 1 illustrates the prior art method of forming such a manhole.

In the first step illustrated in the drawings labelled Al and A2, a generally cylindrical hole 1 is excavated at the intersection of three trenches 2-4. Within each of the trenches 2-4 is placed a sewerage pipe Each of the trenches 2-4 has a slight fall to enable liquid to flow along the pipes 5. Although not illustrated in Fig. 1, each of the trenches 2-4 can enter the hole 1 at a slightly different depth below the ground level 6.

After the hole 1 has been excavated and the pipes 5 placed in position, the ends of the pipes are temporarily blocked by means of rags 7, for example and then approximately 0.6 cubic metres of concrete 8 is poured into the hole 1. The depth of the concrete is sufficient to cover the pipes Within approximately 2 hours it is essential that the concrete 8 be manually cut away by means of a shovel, for example, to rough out the locations of the channels 9 which interconnect the pipes 5. This step Is illustrated In the drawings labelled C In Fig. 1. The concrete removed must be discarded and it is essential that this step be carried out before the concrete 8 has hardened beyond a certain stage less the channels 9 not be able to be created (except by some extraordinarily expensive means such as a jackhammer).

The next step is that the first of a series of concrete sleeve shaped components 10 must be placed in position. The lower edge of the HRF/0480o -4components 10 is preferrably provided with three inverted U-shaped semi-circular cut-outs of appropriate diameter and radial spacing to enable the pipes 5 to mate with the sleeve 10. In practice, such cut-outs are rarely so desirably shaped since they are often quickly formed by knocking out the lower edge of the component 10 with a hammer or similar implement.

After these cut-outs (not illustrated) have been formed, the component is lowered into position.

Ideally, this step should be carried out before the concrete 8 has taken its initial set in order to enable the component 10 to sink partially into the concrete 8. In practice, this is rarely achieved since if the component 10 is lowered too soon the concrete cannot support it and the weight of the component 10 displaces the pipes 5. Alternatively, if the 00" component 10 is lowered too late, then it does not sink into the concrete 8 to any appreciable extent at all. Under these circumstances it is then *'15 necessary to form a sparge joint with cement around the inner and outer surfaces of the lower edge of the component Once this step has been completed, the remaining components (illustrated as item 11 in Fig. 3) can be placed in the manhole and earth then backfilled between the components and the hole 1.

In order to complete the manhole a manhole plasterer is required to descend into the crampotd work space of the manhole with cement of the desired consistency and trowel smooth the channels 9 and form the benches 12 as schematically illustrated in Fig. l(D2) but better illustrated in Fig. 2 (the benches 12 of Fig. 2 being of substantially conventional configuration).

It will be apparent that the above described procedure includes a number of very substantial disadvantages. For example, the amount of concrete 8 to be placed in each of the holes 1 is only 0.6 cubic metres and thus approximately six manholes are needed for a single full load of concrete delivered by a concrete mixer truck. As a consequence of this requirement, many manholes are dug and then within the next few days concrete is delivered to the various holes. This leaves the excavated holes in a dangerous open state representing a hazard to passersby. In addition, the holes may be damaged by vandals rolling rocks into them, for example. Rain can also fall and partially fill the holes with water.

The requirement that the channels 9 be roughed out within about 2 hours of pouring the concrete 8 provides a severe time constraint on the HRF/04800 pouring of concrete. This means that no concrete should be poured, within say, the last three hours of each working day. Again this substantially lowers productivity. In addition, the U-shaped cut-outs on the lower edge of the lower most component 10 are sometimes poorly formed and thus the component 10 does not form a good seal with the pipes 5. Finally, plastering of the channels 9 and benches 12 is a difficult task performed "underfoot" under extremely cramped conditions and such plasterers are tradesmen in short supply.

In accordance with the preferred embodiment of the present invention most of the above mentioned difficulties are overcome by the provision of a pre-cast concrete manhole base 20 as illustrated in Fig. 2. It will be m seen that the base is cast as a single piece of concrete with an in line inlet 21, an in line outlet 22 and a branch line inlet 23.

The base 20 is also provided with a flat bottom 24 and an upstanding ,15 cylindrical side wall 25 through which the inlets and outlets 21-23 pass.

The upper edge of the side wall 25 is stepped so P; to co-operate with conventional step sealing arrangements on the components 10, 11 (Fig. 3) which generally utilise an annular rubber ring or mastic sealing compound in known fashion.

Integrally formed with the base 20 and its bottom 24 are the channels b 9 which interconnect the inlets 21, 23 and outlet 22 which are cast smooth to the desired configuration and extend between'the benches 12. As indicated in Fig. 2 a sealing join can be effected between the inlets/outlets 21-23 and the pipes 5 by means of a conventional rubber ring 26. Any type of pipe 5 such as earthenware, concrete, plastic, fibro,steel or cast iron can thereby be accommodated.

Fig. 3 illustrates in exploded perspective fashion the various components which go to make up the tube, shaft or barrel of the manhole, the components 10 and 11 being essentially conventional. In Fig. 3 the pipes 5 are shown in their final Installed position.

Fig. 4 illustrates the completed manhole with the base 20 positioned at the bottom of the hole 1, the lower most component 10 positioned above the base 20, and the remaining components 11 positioned up to ground level 6. When all these concrete components are in position, the hole 1 is backfilled at 28 to complete the procedure.

Because there are plans produced to describe the sewerage line to be constructed, and from which tenders are called, it Is known in advance the HRF/0480o geometrical relationship of the various pipes 5 leading into the manhole.

Accordingly, it is possible to derive from such plans the information necessary to accurately and individually cast each of the bases required for all the different manholes. It is then a relatively simple matter to supply the necessary pre-cast components for each manhole site.

As a consequence of the application of this organisational method before the hole Itself is dug, the entire operation can be completed in a matter of a few hours, no concrete pour needs to be organised, and the hole is excavated and completed before vandals or rain have a chance to disrupt the work.

an o It was previously known to provide a pre-cast manhole base which consisted essentially of a flat bottom and a cylindrical side wall. Only an outlet was cast In the side wall. No inlets were cast in the side wall Snor were any channels or benches cast. The intention of such an arrangement was that openings for the Inlets should be cut by means of a cylindrical diamond saw in the required locations. However, this often proved impractical since the information coming to the precast concrete supplier from workmen at the site was often inaccurate and therefore such holes were often cut in the wrong locations. This created substantial O additional expense and delay. It was also intended that the channels and benches be entirely created by the manhole plasterer. For these reasons the above described prior art arrangement has not been commercially successful.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, the height of the side wall 25 is increased for pipes 5 of increased diameter and/or steel reinforcement added for larger openings.

In addition, the adaption of the base 20 of Fig. 2 to a manhole requiring the intersection of two branch lines with a through line will be obvious to those skilled in the art. Similarly, it is not necessary that the base 20 be used with prefabricated components 10, 11 as illustrated in Figs. 3 and 4. Alternatively, these components can effectively be cast in-situ by using a collapsable formwork onto which concrete is poured.

After the concrete has set the formwork Is removed from the interior of the manhole.

Furthermore, it is possible to build the manhole with only one trench HRF/0480o leading up to it, connect the manhole base to the pipe in that trench, and then form the remainder of the manhole. At a later time the remaining trenches can be excavated and a pipe placed in each new trench and then connected to the manhole base.

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a 3 HRF/0480o

Claims (9)

1. A method of forming a sewerage manhole at the Intersection of two or more sewerage lines of a sewerage system, said method comprising the steps of: excavating a hole at the intended location of said sewerage manhole, excavating at least two tronches each corresponding to said sewerage lines, each of said trenches leading up to said hole, (Iii) locating a pre-cast concrete manhole base Ii said hole, said base comprising a substantially cylindrical side wall and a substantially flat bottom, a pipe outlet and at least one pipe inlet formed in said side wall adjacent said bottom with said inlet(s) each being connected to 'said outlet by a corresponding channel formed in benche cast with said bottom, (iv) locating a pipe in each of said trenches and sealingly connecting each said pipe to the corresponding one of said inlet(s) or e.0* outlet, creating a tube above said base until ground height is S reached, and (vi) backfilling around said base and tube.

2. A method as claimed in claim 1 wherein a plurality of pre-cast concrete sleeves are located one above the other above said base S* up to ground level to form said tube.

3. A method as claimed in claim 1 wherein said tube is formed from concrete poured in-situ on a collapsible formwork, known per se, and supported on said base.

4. A method as claimed in any one of claims 1 to 3 wherein the position of each said' inlet of said base relative to said outlet is determined from a plan of said sewerage system.

A method of forming a sewerage manhole at the intersection of two or more sewerage lines of a sewerage system, said method being substantially as described with reference to Figs 2 to 4 of the drawings.

6. A pre-cast concrete sewerage manhole base when used to carry out the method of any one of claims 1 to 5, said base comprising a substantially cylindrical side wall and a substantially flat bottom, a pipe outlet and at least one pipe inlet formed in said side wall adjacent said bottom with said inlet(s) each being connected to said outlet by a s corresponding channel formed in benches cast with said bottom. <-'LMM/17620 -9-

7. A base as claimed in claim 6 wherein said side wall has an upper edge having a profile shaped to sealingly engage the lower edge of a pre-cast concrete sleeve known per se.

8. A base as claimed in claim 6 or 7 having at least two said inlets, a through channel interconnecting one of said inlets and said outlet and a corresponding branch channel interconnecting each said remaining inlet with said through channel.

9. A base as claimed in claim 8 wherein the angle of each said remaining inlet and corresponding branch channel relative to said through channel is determined from a plan of the sewerage system into which said base is to be installed. 7 sewerage manhole substantially as described with reference to Figs 2 to 4 of the drawings. DATED FIRST day of JANUARY 1993 Frank Edward Brown Patent Attorneys for the Applicant SPRUSON FERGUSON S I MMl' 7 I n Precast Manhole Base Abstract of the Disclosure The present invention discloses a base (20) for a manhole. The base (20) is pre-cast from concrete from the plans of the sewerage system of which the manhole forms a part. The base (20) includes an inlet (21) and outlet (22) for a through sewerage line as well as inlets (23) for branch lines which can be located at any angle relative to, or on either one or both sides of the through sewerage channel. Integrally formed with the base (20) are channels which interconnect the inlets and outlet and benches (12) through which the channels pass. A method of forming a manhole utilising the pre-cast base (20) is also disclosed which substantially reduces the construction time for such manholes. 4 S. S S S S (Figure 2) JED/6728D