Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)

Height Levelling of the Manhole tops Without Removal

In this rehabilitation measure, neither the manhole tops, nor the surrounding covering and carrier layers, are removed. There follows only the lifting or lowering of the frame that has previously been loosened with the aid of special mechanical or hydraulic machines (Image 5.2.2.2.2-1) (Image 5.2.2.2.2-2) (Image 5.2.2.2.2-3) (Image 5.2.2.2.2-4) [WPCFFD6] [NASSCO85a] [WPCF85].

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Image 5.2.2.2.2-1: 

Height regulation of a manhole top - Lifting the manhole frame to road surface

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Image 5.2.2.2.2-2: 

Height regulation of a manhole top - Lifted manhole frame

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Image 5.2.2.2.2-3: 

Height regulation of a manhole top - Filling the joint with free-flowing grout (hose shell)

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Image 5.2.2.2.2-4: 

Height regulation of a manhole top - Manhole frame after completion of work

The raising of the level is carried out by means of bedding the raised frame with reduced-shrinkage, quick-hardening, special cement grouts based on cement or reaction resins or with the aid of support wedges of polymer concrete. In both cases, the combined height between manhole throat and frame may not exceed 240 mm according to ATV-A 241E [ATVA241d].

When bedding with free-flowing grouts [FI-ERGEL] [FI-Müche] [FI-Siriu], then after lifting the manhole frame to the required level (Image 5.2.2.2.2-1) (Image 5.2.2.2.2-2) (Image 5.2.2.2.2-3) (Image 5.2.2.2.2-4) and cleaning the joint thus formed, a former (hose former) (Image 5.2.2.2.2-1) (Image 5.2.2.2.2-2) (Image 5.2.2.2.2-3) (Image 5.2.2.2.2-4) or metal former (Image 5.2.2.2.2-5) (Image 5.2.2.2.2-6) (Image 5.2.2.2.2-7) (Image 5.2.2.2.2-8) (Image 5.2.2.2.2-9) (Image 5.2.2.2.2-10) (Image 5.2.2.2.2-11) (Image 5.2.2.2.2-12) is inserted for complete sealing between the lower part of the manhole frame and the upper surface of the support.

After lightly inflating the hose former to approx. 0.3 bar, pouring and venting pipes are installed between the former and the frame and the previously site-prepared dry grout is poured in.

The short hardening time of the grout permits the removal of the former after 10 - 15 minutes and loading after approx. a further 20 - 25 minutes, i.e. after reaching a compressive strength of > 9 N/mm2. This information assumes an ambient temperature of 20° C [FI-Glomb].

As the application of sealing grouts, especially for masonry manholes, requires an expensive sealing of the hose former, the bedding is here generally carried out by means of manual filling of the joint with the use of a folding manhole grout sheet (Image 5.2.2.2.2-8). The manhole grout sheet is removed immediately after the completion of the pointing work.

In the patented bedding with wedges of polymer concrete, joints between 2.5 and 5.5 cm can be pointed up.

The exact and stepless height regulation is achieved by means of mutual movement together of two different types of wedges with different heights (Image 5.2.2.2.2-13) (Image 5.2.2.2.2-14) (Image 5.2.2.2.2-15) (Image 5.2.2.2.2-16) (Image 5.2.2.2.2-17), whose radii are adapted to that of the manhole top.

After fixing the wedges, the intermediate spaces are filled with cement, plastics- modified cement or pure reaction resin grout [FI-AcoSe].

For lowering the level, a gap is created below the frame of the manhole top by means of milling (Image 5.2.2.2.2-18).

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Image 5.2.2.2.2-18:  Lowering a manhole frame by means of joint cuts with the aid of a milling cutter with reference to [FI-Loos] [Image: S&P GmbH]

Milling out is possible in grout, sewer bricks as well as concrete and reinforced concrete with little reinforcement [FI-Loos].

The intermediate space remaining after lowering the frame is then filled, as mentioned above, with special grout or a bedding with wedges of polymer concrete is undertaken.

Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)