GB2465644A

GB2465644A - Flexible plastic shuttering for manhole construction

Info

Publication number: GB2465644A
Application number: GB0909430A
Authority: GB
Inventors: David Shaw
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-11-29
Filing date: 2009-06-02
Publication date: 2010-06-02
Anticipated expiration: 2029-06-02
Also published as: GB2465644B; GB0909430D0; GB0821895D0; GB2465804A

Abstract

A manhole chamber is formed from a liner 3 comprising a plurality of rigid concrete sections which are placed in an excavation to define the walls of the manhole chamber, and the sections are held together by an outer layer of concrete 4 which is cast around the liner in situ to hold the sections together. The Concrete 4 is cast in an annular gap between the liner 3 and shuttering 21 which is assembled from a plurality of substantially flat shuttering sections of resiliently flexible plastics which are joined together at opposite edges so that the inherent resilience of the sections causes them to conform to a cylindrical shape. The shutter sections may be formed from a fluted or sandwich type sheet and have slots and lugs for joining their edges.

Description

MANHOLE CHAMBERS

TECHNICAL FIELD OF THE INVENTION

This invention relates to manhole chambers formed from a liner comprising a plurality of rigid sections which are assembled to define the walls of the manhole chamber, and the sections are held together by an outer layer of concrete which is cast around the liner in situ to hold the sections together. For brevity, such a manhole chamber will be referred to herein as "a manhole chamber of the kind set forth".

BACKGROUND

Inspection chambers for storm water or foul sewers are often constructed using a cylindrical pre-cast concrete liner formed from a number of ring sections which are held together by an outer layer of concrete which is cast around the liner in situ to hold the sections together.

Normally the outer concrete layer is poured into the gap between the liner and re-usable steel shuttering, which is subsequently removed after the concrete has achieved its initial set. The outer layer of concrete protects the liner against external forces which might otherwise disturb the alignment of the pre-cast concrete sections, the result being a strong water tight chamber. Despite its widespread use, steel shuttering has a number of disadvantages. Firstly, the shuttering is expensive, and although it is designed to be reusable it has a limited life. Secondly steel shuttering is difficult to place and accurately position, requiring the use of heavy lifting machinery. Thirdly, the shuttering is bulky and heavy to transport and handle. Fourthly, the shuttering must remain in situ until the poured concrete has set, the shuttering can be removed and the hole backfilled, which may hold up other on-site operations or present a safety hazard. Fifthly, removing the steel sections can be difficult, and it takes time to strike and remove the shuttering.

For speed and general convenience the steel shuttering is sometimes omitted, the pre-cast liner being simply surrounded with concrete and the excavated hole filled with rubble or earth. However, this produces a sub-standard product which is prone to admit ground water, and also wastes expensive concrete.

One solution to this problem has already been proposed in GB 2 258 872 A, in which a manhole is constructed by securing a series of vertical elongate cage-like spacers in spaced circumferential positions around the pre-cast liner by means of circumferential bands. Shuttering formed of flexible plastics mesh is then placed around the spacers and the resulting gap between the liner and the mesh is filled with concrete while air is expelled through the mesh. Although this system is economical in the use of concrete and overcomes many of the disadvantages of steel shuttering it still requires time and skill to be used effectively. This specification also states that the use of plastics mesh without the spacers has not been successful since the mesh has a tendency to move as the concrete is poured.

Most plastics do not adhere to concrete, and it is generally known that plastic elements can be used to form voids in poured concrete. For example, CH 679 792 A discloses a shuttering.element which comprises an outer shell made from a curved plastic panel and equipped with two reinforcing discs at its ends. Two edges of the panel can be joined together to make a cylinder by a system of tongues and slots, while other slots are provided to engage with tabs on the reinforcing discs.

The present invention seeks to provide a new and inventive form of shuttering for use in constructing a manhole chamber of the kind set forth, which overcomes the disadvantages of steel shuttering whilst being economical in terms of concrete usage, time, and the amount of skill required.

SUMMARY OF THE INVENTION

The present invention proposes shuttering for use in constructing a manhole chamber of the kind set forth, which is constructed from a plural number of substantially flat shuttering sections of resiliently flexible plastics material which are joined together at opposite edges in such a way that the inherent resilience of the sections causes them to conform to a substantially cylindrical shape.

Since the shuttering sections are substantially flat they are easy to store and transport. However, the inherent resilience of the sheets allows semi-rigid cylindrical shuttering to be constructed and used without requiring spacers in the gap between the shuttering and the liner. Such inexpensive sacrificial shuttering can be left in place and the excavation backfilled immediately.

For strength and flexibility the shuttering sections are preferably formed of fluted sheet, with the flutes running circumferentially. A preferred form of sheet material comprises spaced inner and outer skins joined by substantially parallel bridging walls forming the flutes.

Each shuttering section preferably has opposite ends provided with co-operating tabs and slots for joining the sections together. The tabs preferably shaped to be self-locking when inserted into the slots.

Preferably the shuttering comprises at least five sections.

The invention further provides a method of constructing a manhole chamber of the kind set forth which includes: -placing the rigid liner sections in an excavation to form the liner; -assembling shuttering from a plurality of substantially flat shuttering sections of resiliently flexible plastics material which are joined together at opposite edges in such a way that the inherent resilience of the sections causes them to conform to a substantially cylindrical shape; -positioning the shuttering around the liner leaving an annular gap; and -substantially filling the gap with concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a side view of a shuttering section for use in constructing shuttering in accordance with the invention; Figure 2 is a general view of a number of shuttering sections joined together to form a cylindrical shuttering; and Figure 3 is a general view of the shuttering in place around a pre-cast concrete liner during the construction of a manhole chamber of the kind set forth.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Fig. 1, the shuttering section 8 is stamped or otherwise formed from a single sheet of resiliently flexible plastics material such as polycarbonate. The section 8 includes a body portion 10 of substantially rectangular shape having substantially parallel top and bottom edges 11 and 12 and opposite ends 13 and 14. One of the ends 13 is provided with a plural number of mutually spaced lugs 1 (in this case four) which are integrally formed to project substantially coplanar with the body portion 10. Each lug comprises an arrowhead 15 which is connected to the body portion by a neck 16. The opposite edge 14 is provided with a row of slots 2 which are inset from the respective edge 14 and arranged to correspond with the lugs I both in number and in position relative to the top and bottom edges 11 and 12. Furthermore, the length of each slot is substantially equal to the corresponding dimension (width) of the neck portions 16. The inset detail shows a cross-section through part of the sheet taken between the top and bottom edges 11 and 12. This shows that the shuttering section is formed of twin-walled plastics having inner and outer skins 17 and 18 joined by a series of integral equally-spaced parallel bridging walls 19. The sheet thus contains parallel flutes which extend between the ends 13 and 14 parallel to the top and bottom edges 11 and 12. This is important because although the sheet is relatively lightweight it allows the sheet to be flexed between the ends 13 and 14 without creasing. Attempting to flex the sheet in the perpendicular direction between the edges 11 and 12 simply causes angular creases to form.

The Jugs 1 and slots 2 allow several sheet sections 10 (preferably five or more) to be joined together to form cylindrical shuttering 21, as shown in Fig. 2. This is achieved by inserting the lugs 1 of one section through the slots 2 of the next section and so on until all of the sheets are joined in a continuous ring. It is important to note that the lugs must be inserted from the outside towards the inside of the cylinder so that as the section is curved the Jugs bear against the inside face of the adjacent sheet. It will also be noted that the arrowhead shape of the lugs locks them into the slots so that they cannot be pulled out again. Since the sheets are substantially identical, stressing the sheets in this way causes them all to adopt a similar smooth radius of curvature and form a pre-stressed semi-rigid cylinder.

Referring to Fig. 3, a liner 3 formed of pre-cast concrete rings stacked one upon another is first positioned in an excavation (not shown). The diameter of the cylindrical shuttering 21 is larger than that of the liner 3, so that the shuttering can be lowered over the liner. A concrete mix 4 is then placed into the annular gap formed between shuttering and the liner, and the excavated void around the external perimeter of the shuttering can immediately be backfilled. A vibrating poker is used to remove voids in the wet concrete, so that in practice the absence of any apertures in the shuttering does not result in entrapment of air. Since the shuttering is relatively inexpensive it can be left in place.

The diameter of the shuttering can be varied by changing the number of shuttering sections which are connected together, and in practice one size shuttering section can be used to produce suitable shuttering for all the standard liner diameters. The shuttering thus allows faster construction times and provides significant cost savings on site.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.

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Claims

CLAIMS1. Shuttering for use in constructing a manhole chamber of the kind set forth, which shuttering is constructed from a plural number of substantially flat shuttering sections of resiliently flexible plastics material which are joined together at opposite edges in such a way that the inherent resilience of the sections causes them to conform to a substantially cylindrical shape.
2. Shuttering according to Claim 1 in which the shuttering sections are formed of fluted sheet, with the flutes running circumferentially around the shuttering.
3. Shuttering according to Claim 2 in which the fluted sheet material comprises spaced inner and outer skins joined by substantially parallel bridging walls,
4. Shuttering according to any preceding claim in which the shuttering sections are formed of polycarbonate.
5. Shuttering according to any preceding claim in which each shuttering section has opposite ends provided with co-operating lugs and slots for joining the sections together.
6. Shuttering according to Claim 6 in which the lugs are shaped to be self-locking when inserted into the slots.
7. Shuttering according to any preceding claim in which each lug comprises an arrowhead which is connected to the remainder of the shuttering section by a neck.
8. Shuttering according to Claim 7 in which the length of each slot is substantially equal to the width of the neck of the corresponding lug.
9. Shuttering according to any preceding claim which comprises at least five shuttering sections.
10. A method of constructing a manhole chamber of the kind set forth which includes: -placing the rigid liner sections in an excavation to form the liner; -assembling shuttering from a plurality of substantially flat shuttering sections of resiliently flexible plastics material which are joined together at opposite edges in such a way that the inherent resilience of the sections causes them to conform to a substantially cylindrical shape; -positioning the shuttering around the liner leaving an annular gap; and substantially filling the gap with concrete.
11. Shuttering substantially as described with reference to the drawings.
12. A method of constructing a manhole chamber of the kind set forth which is substantially as described with reference to the drawings.* * * * * * * *