|
1. High pressure cleaning of manhole shafts
Automated shaft cleaning with the Turbo Special Shaft Cleaning-jet (TSSR)
|
1.2 Introduction
High pressure water and related technology have long been used in automated sewer renovation, both for cleaning operations and for substrate preparation. For sewer cleaning there is a wide range of different cleaning jets available to cover all possible requirements.
Automation has not been the norm in shaft cleaning up till now. Shaft cleaning has usually been carried out using a hand-held lance. This places a heavy burden on the health and safety of the operatives. When it came to thorough substrate preparation, the quality of the results left a great deal to be desired because it depended so much on the staff. Results were frequently unsatisfactory. Automated cleaning by TSSR is to be recommended for cleaning shafts where the climbing rungs have disappeared or are broken, making it impossible to climb down into the shaft; in shafts at disposal sites; or where there is the danger of toxic gases.
It is particularly appropriate where men and plant need to be considered, or where a top quality result is required.
|
The TSSR Turbo shaft special cleaning jet (Pic.1)
is used for cleaning manhole shafts.
|
Used for DN50 to DN1200 diameter shafts. A 12 volt electric motor rotates the cleaning jets at a steady low speed, giving the water jet time to clean the walls. The jets can be set to turn at two different speeds. An electric drill is used to separate the nozzles or to bring them together, from 500mm to 1100mm distance apart. This is directed from street level. As long as no climbing rungs prevent it, the distance between the cleaning jet nozzle and the side-wall should be < 20cm. The smaller the distance that can be chosen, the more effective the outcome. The optimal distance is about 5cm. The rotating nozzles at the end of each arm can be chosen to suit the pressure supplied by the pump. The standard practice is to work with 290 bar and 24 litres/min. It is better to increase the volume of water rather than the water pressure. The TSSR is controlled by a winch in the shaft in ‘stop & go’ mod. The operation covers about 20cm per minute. ird an einer Winde im Schacht langsam im "stop and go" Betrieb gefahren. Die Leistung beträgt ca. 20 cm/min. |
| 2. Substrate preparation |
2.1 Basics
Substrate preparation in shafts needing renovation includes all necessary steps to ensure the concrete substrate is sound and any reinforcement is in a suitable condition. Substrate preparation also includes:
- the removal of concrete as per the repair plan as well as any that is revealed to be necessary when the section is inspected
- dexposing reinforcement
Unless otherwise instructed, the contractor must choose the appropriate procedures and equipment to ensure that the characteristics and the quality of the concrete substrate, as well as of the reinforcement and its efficiency, are not impaired..
2.2 Concrete substrate
General
The concrete substrate must be prepared in such a way that a solid and durable bond can be created between the new concrete or protective coating and the concrete substrate. Once the preparation has been completed, the concrete substrate must
- be free of loose and friable material and flaking layers of the same material
- not threaten to lift away either in sheets or in individual patches
- be free of sharp edges and ridges
- be free of foreign material such as old coating, release agents, ***, efflorescence, oil or vegetation
- be free from synthetic coatings or other organic and inorganic deposits which prevent adhesion
- be free of running or standing water
- have a surface which is sufficiently rough for the new concrete or surface protection which is to be
applied; and
- be uniformly sound
Faulty and hollow patches in the concrete must be properly cut back and opened up. At the start and finish of the substrate preparation, the contractor must make a visual inspection of the cracks, gaps, corroded reinforcement and other defects, in the presence of the client. If the condition of the site is different from the underlying assumptions on which the renovation plan is based, the client, perhaps working in conjunction with the contractor, will decide how to proceed.
2.3 Concrete substrate for repairing with fresh concrete
Unless otherwise agreed, where there is aggregate of > 4mm diameter near the surface, firmly embedded, at least the top of each stone must be exposed once the substrate preparation is completed.
2.4 Reinforcement
At the end of substrate preparation, all loose corroded material must be removed from the exposed reinforcement or fittings. Rust removal must meet cleanliness standard St2 or Sa2 (or where RL SIB DafStb renovation code C is applied, then cleanliness standard Sa2 1/2) across the whole area being exposed. If ERGELIT dry mortar is applied to a depth of 10mm, then cleanliness standard Sa2 is sufficient.
|
| 3. Substrate preparation procedures |
3.1 General
The advisability of the chosen preparation procedure should be demonstrated in the client’s presence at the start of operations by treating test areas in appropriate points within the area to be renovated. In any substrate preparation procedures which might lead to structural disturbance in the surface area of the original concrete – e.g. chiselling, hammering, or milling– the areas must receive an appropriate follow-up treatment ( high pressure jetting etc). If compressed air is used as the substrate preparation procedure, or as part of such a procedure, the residual oil content of the air must be <0.01 ppm. Oxy-acetylene may only be used for substrate preparation with the express agreement of the client and is generally not appropriate in a sewer. Chemical treatment of the concrete substrate also requires the client’s express agreement. Chemical treatments would include cold solvents for removing oil.
3.2 High pressure water jetting
Jetting with high pressure water is the most usual procedure in sewers. The following parameters are important:
1) Water pressure (bar)
2) Volume of water (litres per min)
3) Distance between nozzle and substrate
4) Nozzle type - spot nozzle
- flat nozzle
- rotating nozzle (rotating spot nozzle)
5) Spray angle
6) Duration of spray
If a good result is to be obtained both from a technical and and economic point of view, all parameters must be taken into account. In sewer renovation, a high volume of water is always preferable to high pressure. In this way, salts which have built up in the top layer of the concrete are washed out.
Table 1 (see appendix) gives the different pressure/ water volume ratios which produce similar jet pressure.
Field 1 < 150N thrust
Field 2 150 – 250N thrust
Field 3 > 250N thrust
The following figures consider high pressure jet in relation to the TSSR system
HIGH PRESSURE HOSE
In all high pressure procedures, including the TSSR, care must be taken over loss of pressure in connection with hose length. Pressure loss arising with a sewer-cleaning hose made of rubber, is set out in the table below.
|
|
L/min
|
DN 10 = 3/8"
|
DN 13 = 1/2" |
DN 20 = 3/4" |
DN 25 =
1" |
DN 32 = 1 1/4" |
DN 38 = 1 1/4" |
| 15 |
0,82 |
0,17 |
0,01 |
|
|
|
| 20 |
1,46 |
0,33 |
0,04 |
0,01 |
|
|
| 25 |
2,29 |
0,54 |
0,06 |
0,02 |
|
|
| 30 |
3,29 |
0,81 |
0,08 |
0,02 |
|
|
| 40 |
5,86 |
1,48 |
0,18 |
0,05 |
|
|
| 50 |
9,16 |
2,36 |
0,26 |
0,09 |
|
|
| 60 |
13,20 |
3,45 |
0,41 |
0,11 |
0,02 |
|
| 75 |
20,62 |
5,45 |
0,59 |
0,21 |
0,05 |
0,02 |
| 100 |
|
9,80 |
1,14 |
0,37 |
0,09 |
0,04 |
| 125 |
|
15,02 |
1,76 |
0,58 |
0,16 |
0,07 |
| 150 |
|
21,83 |
2,50 |
0,84 |
0,22 |
0,10 |
| 175 |
|
|
3,38 |
1,14 |
0,33 |
0,12 |
| 200 |
|
|
4,58 |
1,49 |
0,41 |
0,14 |
| 225 |
|
|
5,74 |
1,89 |
0,50 |
0,17 |
| 250 |
|
|
7,04 |
2,34 |
0,65 |
0,20 |
| 275 |
|
|
8,47 |
2,83 |
0,77 |
0,29 |
| 300 |
|
|
10,31 |
3,37 |
0,96 |
0,36 |
| 325 |
|
|
12,02 |
3,96 |
1,09 |
0,45 |
| 350 |
|
|
13,87 |
4,59 |
1,32 |
0,52 |
| 375 |
|
|
15,84 |
5,28 |
1,48 |
0,62 |
| 400 |
|
|
20,67 |
6,52 |
1,81 |
0,69 |
| 450 |
|
|
|
8,21 |
2,29 |
0,79 |
| 500 |
|
|
|
10,09 |
2,76 |
0,98 |
| 550 |
|
|
|
12,08 |
3,48 |
1,20 |
| 600 |
|
|
|
14,00 |
4,00 |
1,40 |
| 750 |
|
|
|
21,50 |
6,30 |
2,10 |
| 900 |
|
|
|
|
9,05 |
2,90 |
| 1050 |
|
|
|
|
12,00 |
3,90 |
| 1200 |
|
|
|
|
16,00 |
5,00 |
Pressure loss diagram for rubber sewer cleaning hose
Pressure loss given in bar per 10 metres of hose
|
3.3 Dependency of spray power on distance
The relationship between the TSSR’s spray power and its distance from the shaft wall has been investigated under laboratory conditions using a percussion plate. The following diagram plots the values of spray power N in relation to the distance between jet-nozzle and percussion plate in cm. It is clear that increasing distance means diminishing cleaning power.
Diagram 1: Spray power in relation to distance |
Distance jet-nozzle to percussion plate (cm) |
3.4 Result of physical evaluation
Effective cleaning depends not only on spray power, but also on the energy input into the layer to be removed. This in turn depends on the volume of water used, the water pressure and the velocity of ther water column (nozzle cross-section). The ratios set out in simplified form above can be expressed as efficiency ratings – given as [h] in the following table:
Table 4: performance measurement and efficiency rating h |
| Nozzle |
Distance |
Flow |
Pressure at
the nozzle |
Spray
power |
Spray
pressure |
P
up to
|
P
from |
h |
| Nr. |
[cm] |
[l/min] |
[bar] |
[N] |
[bar] |
[W] |
[W] |
[1] |
| 1 |
10 |
11,9 |
228,1 |
31,4 |
127,4 |
4526 |
2528 |
0,56 |
| 20 |
227,6 |
23,2 |
69,9 |
4518 |
1338 |
0,31 |
| 30 |
226,3 |
14,7 |
27,8 |
4491 |
552 |
0,12 |
| 35 |
224,1 |
11,6 |
17,5 |
4448 |
346 |
0,08 |
| 2 |
10 |
11,9 |
204,0 |
27,7 |
179,1 |
4048 |
3554 |
0,88 |
| 20 |
202,6 |
28,2 |
103,1 |
4021 |
2046 |
0,51 |
| 30 |
202,1 |
19,3 |
48,0 |
4010 |
953 |
0,24 |
| 35 |
185,7 |
12,8 |
21,3 |
3685 |
423 |
0,11 |
| 3 |
10 |
11,9 |
201,9 |
35,5 |
163,3 |
4007 |
3240 |
0,81 |
|
As with spray power, efficiency ratings also drop off with increasing distance between the nozzle used and the shaft wall. The following diagram shows that this connection is not linear but curved. Laboratory figures for 3 types of nozzle are shown.
Table 5: Diagram showing mean scouring levels obtained at 15 second bursts, ignoring rotational speed. |
 |
3.5 Effect of TSSR on removal of material
In order to assess the operation of the TSSR, it is important to look at the rate of material removal in respect of different levels of hardness, distance and time. The following table gives the results of trial series for material removal. According to the hardness of the samples, different lengths of time (s) were used in order to achieve measurable effects. |
|
Series
|
Nozzle |
Distance |
Material |
Hardness |
Duration |
ts |
tm |
mean
amount removed (t) |
comment |
| |
No. |
[cm] |
|
[N/mm2] |
[s] |
[mm] |
[mm] |
[mm] |
|
| 1 |
1 |
5 |
PB |
2 |
15 |
18,8 |
14,8 |
16,1 |
|
| 4 |
./. |
./. |
./. |
could not
be evaluated |
| KS |
12 |
120 |
5,5 |
4,8 |
5,0 |
|
| 2 |
1 |
5
|
PB |
2 |
15 |
25,0 |
25,0 |
25,0 |
|
| 4 |
16,0 |
13,8 |
14,5 |
|
| KS |
12 |
120 |
5,0 |
4,2 |
4,4 |
|
| 3 |
1 |
10 |
PB |
2 |
15 |
16,6 |
11,9 |
13,4 |
|
| 4 |
11,4 |
7,2 |
8,6 |
|
| KS |
12 |
120 |
3,1 |
2,5 |
2,7 |
|
| 3,9 |
2,3 |
2,8 |
|
| 4 |
1 |
20 |
PB |
2 |
15 |
8,3 |
4,7 |
5,9 |
|
| 4 |
5,5 |
3,1 |
3,9 |
|
| KS |
12 |
120 |
2,4 |
1,5 |
1,8 |
|
| 5 |
1 |
20 |
KS |
12 |
300 |
5,4 |
2,9 |
3,7 |
|
| 6 |
1 |
20 |
PB |
2 |
15 |
7,9 |
3,8 |
5,1 |
|
| 4 |
5,6 |
3,0 |
3,9 |
|
| 7 |
1 |
20 |
KS |
12 |
600 |
10,2 |
6,0 |
7,4 |
|
| 8 |
3 |
20 |
PB |
2 |
15 |
0,0 |
0,0 |
0,0 |
no effect
apparent |
| 4 |
0,0 |
0,0 |
0,0 |
| 2 |
120 |
0,0 |
0,0 |
0,0 |
| 4 |
0,0 |
0,0 |
0,0 |
|
| In the graph below, removal ratings are given in relation to the speed of the nozzle-arm in revs per min, and time taken. |
Lines join points of equal strength per 15 secs of duration of test
|
| Table 3: Adhesive strength spec of the concrete substrate after completion of preparatory treatment |
| |
1 |
2 |
3 |
4 |
| |
System |
median value |
smallest
value |
| N/mm2 |
N/mm2 |
| 1 |
concrete |
not reinforced |
> 1,5 |
> 1,0 |
| 2 |
with anchors & reinforcement |
no spec |
no spec |
| 3 |
sprayed mortar /
sprayed concrete |
not reinforced |
> 1,5 |
> 1,0 |
| 4 |
with anchors & reinforcement |
> 1,5 |
> 1,0 |
| 5 |
SPCC |
> 1,5 |
> 1,0 |
| 6 |
PCC |
> 1,5 |
> 1,0 |
| 7 |
OS |
OS-A |
no spec |
no spec |
| 8 |
OS-C |
> 1,5 |
> 1,0 |
| 9 |
OS-D |
ohne Freispachtel |
> 1,0 |
> 0,6 |
| 10 |
mit Freispachtel |
> 1,5 |
> 1,0 |
| 11 |
OS-F |
> 1,5 |
> 1,0 |
|
| 4. Substrate testing |
Adhesive strength of the concrete substrate after completion of preparatory work should be assessed every 250 m2 of the structure, or at least once per site, taking a set of 5 separate samples spread equally over the area to be evaluated. The adhesive test must take place within a test area delimited by an annular groove. The groove must penetrate approx 10 cm into the concrete substrate. The test should be supervised by the client, who should be apprised promptly of the results.
It is advisable, if the client agrees, to avoid drilling. That may give somewhat higher test result figures, but we may ignore that. Drilling cannot be carried out in a narrow pipe without physically affecting the test sample
If an individual value is found below the smallest permissible value given in Table 3, at least 2 separate tests must be made nearby (within about 1 metre) to establish if this is just a stray result. If the extra readings obtained are satisfactory, the first reading is discarded. If the original reading is confirmed, the area should be divided up on the basis of a grid. Hollow spots should be examined by tapping and dragging a hammer across the surface. If thin layers (1-2 mm) have come loose, that can be heard as a papery noise. In the case of thicker layers (> 5mm), hollow patches give lighter sounds which are clearly audible. In most sewer renovation sites it is difficult to carry out a substrate tensile strength test. A useful alternative is to test compressive strength with a percussion hammer, also known as a Schmidt hammer.
4.1 Substrate for M-Coating
The following details apply to shaft coating circular shafts up to 1.20m in diameter.
Surface testing
- compressive strength by Schmidt hammer
- where coating is < 15mm
- concrete tensile strength > 1.0N/ mm2
- concrete compressive strength > 20N / mm2
- where coating is > 15mm
- concrete tensile strength > 0.5N / mm2
- concrete compressive strength > 15N/ mm2
- where coating is > 40mm
- no specifications for compressive or tensile strength
Where masonry grouting has been damaged, this only needs to be raked out to a depth of 20-30mm. The blocks must be sound and clean. Where there is water penetration, this must be sealed off with for example ERGELIT injection mortar.
- Surfaces must be damp to wet as per DafStb. RiLi SiB
- No sand must crumble off the surface if one rubs it with the hand.
As described above, not only are water volume and pressure important, but so too is the distance between the nozzle and the surface being treated.
|
| 5. Inspection, hand-over, guarantee |
|
The planned new concrete or surface protection system can only be started once the client has given the go-ahead.
5.1 The substrate before and after coating
Before ERGELIT is applied, the areas for treatment must be sufficiently wetted, at least 24 hours in advance, if they are not normally in direct contact with water. Inj closed situations, shafts and pipes, such preliminary wetting is only necessary in exceptional cases; whereas in open situations it is normally unavoidable. The surface areas should be matt-damp to wet, according to the RiLi SIB standards. ‘Wet’ means that there is water in the pores of the concrete.
Appropriate steps must be taken to ensure that surfaces that have been prepared in readiness for SPCC treatment do not get dirty again. That applies in particular to spray drifting across from neighbouring sections of the worksite.
|
|
|