Chapter Four - Pg 2
3. Sliplining

 

The sliplining technique was demonstrated in lalan University, Petaling laya. The existing main to be rehabilitated comprised of 1500 meters of 24 inch AC main which was about 30 years old and exhibited leakage at joints. The new liner used was a 500mm dia MDPE PNIO pipe. The original AC main had one scour and one air valve but no ferrule connections or branch connections.

Sliplining involves the installation of a new MDPE pipeline within the existing main. The method used is illustrated in Fig. 3. The new MDPE pipe is not a close fit on the existing pipeline and is installed by winching the new pipeline directly into the existing pre-cleaned main.

 

 

Using this technique, several hundreds of meters of pipeline can be rehabilitated at one time. Large radius bends in the existing pipeline can be accommodated.

Advanced butt fusion equipment was not available to weld MDPE pipes of this size. Therefore great care was taken to ensure that the available butt fusion techniques would produce reliable joints. This involved a substantial amount of site and factory testing of the joints.

Electrofusion couplers are normally used for insitu jointing of MDPE pipes. However, due to the size of pipe used for this technique no electrofusion couplers were available and therefore insitu joints were effected using site designed and locally manufactured couplings. Similar joints were devised to connect the new MDPE pipe to the existing AC main because 500mm dia Maxifit couplings are not yet available in Malaysia.

The use of the sliplining technique has proven its' technical applicability under the conditions of the trial which could be characterised as follows:

• Very heavily trafficked dual carriageway and

• Very little space in which to weld together substantial pipe strings.

However, modern butt fusion and electrofusion techniques and compatible couplings are only available for pipes up to 400mm in diameter. It is suggested therefore that until jointing technology has advanced to cater for bigger diameter pipes, the use of MDPE pipes in Malaysia should be limited to those of diameters not exceeding 400mm.

4. Cement Mortar Lining

The application of this technique was demonstrated in a particularly heavily trafficked section of Jalan Tun Razak, Kuala Lumpur. 150m of the existing 6 inch cast iron main which was heavily encrusted internally was rehabilitated using this technique.

Cement mortar lining involves the rehabilitation of cast iron mains by the application of a cement mortar lining on the inside of the previously cleaned main. The method used is shown in Fig. 4.

 

 

Access holes are dug at 100m to 150m intervals along the main to be rehabilitated. The main is cleaned by power boring or drag scaping. It is then plunged and proved to ensure that not only all debris are removed but also there will be no other obstruction inside the main.

Lining is carried out by pumping a mixture of 1:1 graded sand and cement mortar from a purpose-built mixing unit. A spray head is inserted into the main and cement mortar is pumped through hoses to the spray head. As the spray head is slowly withdrawn through the main, cement mortar is centrifugally sprayed onto the wall of the pipe. To achieve a smooth surface finish, a trowelling tool is attached to the spray head. The lining is then left to be cured for 16 to 24 hours and then is chlorinated and flushed before returning the main to service.

Cleaning of the trial main was carried out by drag scraping. The main was found to be heavily encrusted, with an average of 20mm of nodular growth of iron products. Because of the thick encrustation the amount scraped off built up in front of and eventually blocked the progress of the scraper. It was judged that a rack feed boring technique should be adopted in future.

The use of the cement mortar lining technique has proven its technical applicability under the conditions of the trial which could be characterised as follows:

• Very heavily trafficked road and
• Restriction imposed by City Hall on access and the method of working.

This method allows aged cast iron mains to be put back into service in an as-new condition, without substantial excavation along the line of the existing main.


C. Project Costs

This pilot pipeline rehabilitation project had two objectives, (i) to assess the technical applicability, and (ii) the cost effectiveness of modern NO-DIG techniques under Malaysian conditions. The technical applicability of the four techniques has been dealt with in the earlier part of this Paper. This part examines the costs of the work carried out for each of the techniques and the financial applicability in the Malaysian context.

The considerable cost data generated has been analysed to produce costs for each of the four separate techniques. The results of this analysis are shown in Table 1.

The principal cost elements for each of the four techniques are:

• Specialist plant hire (foreign)

• Specialist labour (foreign)

• Foreign materials (electrofusion couplings etc)

• Local plant (JCB, lorries, compressors etc)

• Local labour (engineer, technicians and labourers)

• Local materials (all pipes and fittings)

Table 1 – Unit costs of implantation by techniques

            Techniques

Pipe Diameter (mm)
Unit Cost (RM/m)
Pipebursting
225
356
Swagelining
250
362
Sliplining
500
737
Cement Mortar Lining
150
213

The percentages of these cost elements apportioned to each of the techniques are shown in Table 2.


Table 2 – Cost breakdown (in percentage) by techniques & principal cost elements

 

Cost Element

 

Techniques

Pipebursting

Swage lining

Sliplining

Cement Mortar lining

Specialist plant

11%

11%

8%

14%

Specialist labour

44%

43%

34%

59%

Foreign materials

3%

4%

0%

2%

Local plant

6%

8%

6%

10%

Local labour

6%

6%

5%

8%

Local materials

   30%

28%

47%

7%

It can be seen from Table 2 that specialist labour constitutes a very significant portion of the total cost (average 45%). This is because NO-DIG techniques are new to Malaysia and experienced local personnel are not yet available. The foreign specialists are initially required to train local engineers and operatives and to ensure proper transfer of technology. It is expected that this transfer of technology will be achieved fairly rapidly and as a result the requirement for expensive foreign specialists will be reduced.

In the long term, when local engineers and operatives are able to apply these techniques, the apportionment of specialist labour will be reduced from an average of 45% to, say, 15%. Using the latter figure, costs for future projects would then be as shown in Table 3.

Table 3 - Estimated unit costs of implementation by techniques assuming there is a significant reduction in expatriate specialist input

Technique

 

Pipe Diameter (mm)
Unit Cost (RM/m)
Pipebursting
225
252
Swagelining
250
260
Sliplining
500
597
Cement Mortar Lining
150
119

                                                                                                                                   1USD = 2.5 RM


D. Finacial Applicability

NO-DIG technology was developed to rehabilitate and upgrade public utility services in the least disruptive manner to society. Therefore in order to assess the cost effectiveness of NO-DIG techniques, realistic costs of traditional open cut pipe laying including the social disturbance element have to be determined.

Costs of Pipelaying by Open Cut Method

In order that a fair comparison can be made between NO-DIG and open cut, the same MDPE pipe material has been assumed for each method. Plant, materials and labour for open-cut activities have all been assumed to be available locally.

The unit costs of pipelaying by open-cut method are summarized in Table 4 below.

Diameter (mm) Unit Cost (RM/m)
Unit cost (RM/m)
150
134
225
182
250
213
500
593


(1) An allowance for nightime working, which is required in urban areas like Kuala Lumpur and Petaling Jaya,
(2) An allowance for temporary steel plating over trench excavatios,
(3) An allowance to accommodate compliance with local authorities and
(4) Social disturbance costs.

Social Disturbance Costs

The principal reason for using NO-DIG techniques in rehabilitating pipelines is to minimise the disruption caused to traffic, businesses and the public in general.

The simplified approach adopted in deriving social disturbance costs has been to:

1. Measure traffic flows at affected locations and
2. Evaluate the reduction in traffic flows which would be caused by open-cut methods.

From (1) and (2) above an estimate of the delay has been made using traffic model simulation techniques and having estimated the extent of the delay, the 'standing costs' of vehicles and the 'time costs' of travellers can be determined.

Of the four locations where pilot NO-DIG techniques have been carried out, only Jalan Banting in Pandamaran is considered not to have caused traffic delays. Using the approach outlined above the social disturbance costs for the other three locations have been estimated and are summarised in Table 5.

Table 5 - Estimated social disturbance costs at locations where NO-DIG techniques were used

Location

Technique

Estimated Social Disturbance Cost (MR/m)

Jalan Tun Razak

 

Jalan University

 

Jalan Tandang

 

Jalan Banting

Cement mortar lining

 

Sliplining

 

Swagelining

 

Pipe bursting

240

 

1570

 

300

 

-

Cost Comparison Open-Cut vs No-Dig

Having established all costs applicable to each location, a realistic cost comparison can be made and this is shown in Table 6.

Table 6 - Cost comparison between Open Cut and NO-DIG methods of pipelaying showing impact of social disturbance and expatriate specialist costs


 

Location
(technique used)

 

 

Open-Cut

No -Dig

Basic cost

(RM/m)

Disturbance cost

(RM/m)

Total

 

(Rm/m)

Short Term Cost (Foreign Labour)

Long Term Cost (RM/m)

(Local Labour)

Jalan Tandang

(Swageling)

213

300

   513

 362

 

260

Jalan University

(Slip lining)

593

   1570

2163

    737

 

597

Jalan Tun Razak

(Cement Mortar lining)

134

240

 374

 213

 

119

Jalan Banting

(Pipe Bursting)

182

       ---

182

    356

 

252

From Table 6, the following conclusion can be drawn:

(1) Generally, open cut method of pipe replacement is more economical in areas which are not heavily trafficked e.g. rural areas. However, in the long term, cement mortar lining is still an attractive option even in the rural environment.

(2) In heavily trafficked urban areas, where if social disturbance costs are taken into consideration, the adoption of NO- DIG pipelaying techniques provides very significant overall cost savings.

(3) In the long term, when local staff have been trained and are able to apply the NO-DIG techniques, the cost savings of using NO-DIG pipelaying techniques will be more significant compared to the traditional open cut method.

E. Conclusion

Trenchless technology has been developed for urban centres overseas to provide a quick and efficient means of rehabilitating old pipelines. In those countries, the public no longer tolerates the delays and disruption associated with open excavations in footpaths and road pavements. The public in Malaysia is becoming less tolerant and so the Selangor Government took the initiative to try out four 'No-dig' techniques with a view to:

(a) Resolving any technical problems with the introduction of this new technology into Malaysia, and

(b) Establishing the cost effectiveness of such techniques when compared to traditional open cut methods

A total length of 5200m of leaking water main has been successfully rehabilitated in conditions where hold-ups to traffic were unacceptable and where the City Authorities imposed severe limitations on the excavation of open trenches.

Virtually all the 'technical' problems encountered were associated with the non-availability of items of plant or materials that would have been readily avaialble overseas. This highlighted the fundamental need for:

(a) A comprehensive investigation of all the features of the main to be rehabilitated (variations in diameter, location of all valves and fittings etc.), and

(b) A programme of work that is complete and includes specific contingencies for action should unforeseen difficulties arise.

With respect to cost effectiveness a simple analysis has been conducted to establish the cost of delays to traffic as a result of hold-ups caused by open trench excavations. This has demonstrated that 'No-dig' techniques are a cost efficient alternative to traditional methods, offering savings up to 65% in the short term, when foreign specialists are required, and 72% in the long term when the experience has been successfully transferred to local staff.

This latter point is crucial to the general acceptance of 'No-dig' technology in Malaysia. The technical aspects of each method are relatively straightforward and can be easily learned. The more difficult aspect is to know what to do in the event of an unexpected problem on site, for example if a pipe string becomes jammed in the host main. This knowledge can only be acquired by experiencing and dealing with such problems. Initially in Malaysia that experience will come from foreign specialists. What is needed, therefore, is an ongoing programme of pipeline rehabilitation work so that local staff can be properly equipped and trained to deal with any problem that occurs. In this way the Malaysian public will benefit from a technology designed to overcome the frustrations of open trench excavation in heavily trafficked streets.

Notes:

1. The major part of the above write-up was published in the Journal Of Water Supply Research And Technology – AQUA under “Pilot pipeline renovation in Malaysia using “no-dig techniques” in June 1994.

2. After the successfully completion of the above demonstration project, none of the water supply authorities  and contractors in Malaysia had initiated any pipe rehabilition project using any one of the No-Dig techniques. The training of our staff and the purchase of all the equipments were all came to nought!

Pg 2

End of Chapter Four                                                                                        Go to Chapter Five       

 

 

 
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