Trenchless through the Badrina biotope – enthusiastic visitors follow the pipe pulling-in process at the site open day

1 Introduction

The Delitzsch-Rackwitzer water supply association (DERAWA) was faced with one of its largest investment projects in Badrina: in order to stabilize the raw water supply for Delitzsch and its surrounding communities in Saxony it was necessary to replace an old pipeline which in part runs through the Badrina biotope (Figure 1). The outstanding feature in Badrina is the oligotrophic (low in nutrients and humus) to mesotrophic (medium level of nutrients), calcareous standing water.

Bodies of water of this habitat type are very rare in the natural environment. The ponds, left in their natural state, consist of bodies of clear water relatively low in nutrients which have populations of stonewort spread over large areas. They are in a good state of preservation. Although there is direct access from the road, anthropogenic interference is low. However use as fishing or angling waters or driving over the land with heavy machines would massively endanger the present favourable state of preservation [1].

The biotope in Badrina is part of the “Natura 2000” network [2], the official name of a coherent network of protected areas which has been established within the European Union in accordance with EEC Directive 92/43 (fauna/ flora habitat directive, or FFH directive). Its aim is to protect endangered native plants and animal species and their natural habitats in the countries of Europe. The network of protected areas also includes those areas designated in EEC Directive 79/409, known as the wild birds directive [3].

2 The initial situation

The Delitzsch water supply association draws its raw water from the Prellheide North and South well catchment areas and from the Spröda district. A 16 km long DN 500 steel transport pipeline was laid specifically for this purpose in the 1970’s. The pipeline stretches from Badrina, a district of Delitzsch, to Scholitz through sensitive biotopes such as wetland meadows and reed beds. Unfortunately over recent years it has often been necessary to carry out repair work because the steel pipeline has been afflicted by corrosion damage. The susceptibility of the 40-plus year old pipeline to faults and failures had been steadily increasing. Therefore the replacement of the section of pipeline in the Badrina biotope was looming for DERAWA.

It was the largest and most expensive investment for many years. It cost around half a million euros to put the new pipeline in the ground in place of the old one [4]. The local supply company depends on this pipeline for the supply of drinking water to the 48,000 inhabitants in its service area as well as the industrial, business, commercial and agricultural concerns and public institutions established there.

3 Planning

The planning of this measure took DERAWA more than a year. Four nature reserves appear on the construction plans for the 480 m long pipeline, so the planners decided on trenchless installation using the HDD technique with DN 500 ductile iron pipes with BLS^® restrained push-in joints and cement mortar coating to EN 15542 [5]. Because of the local circumstances described, the only method to use was the environmentally friendly horizontal directional drilling process according to DVGW worksheet GW 321 [6], in this case with gyrocompass control. This uses navigation software and a ring laser gyroscope to direct and control the drill so that it stays on the reference line with centimetre precision between the starting pit and the target pit.

This special version was used because of the ban on entering the biotope; the directional drilling technique normally used involves controlling the laying process with magnetic tracking systems along the route. In this case the path between starting and target pit was controlled on the computer monitor only. The Badrina soil was pushed out metre by metre by a bentonite suspension – a mixture of natural clay and water – discharged under high pressure from the tip of the drill head. The suspension supports the drill hole and is later recycled. Because of the restricted space available, the pipeline was assembled using the single pipe technique on an angled assembly ramp; an advantage when there is a lack of space around the starting pit.

Contrary to some initial concerns regarding the time that assembly would take using cement mortar coated shrink-on sleeves, after a short familiarisation period some very short assembly times were achieved. So, despite the single-pipe assembly, the pipeline was able to be pulled in within a few hours. A robust and resistant joint protection with shrink-on sleeves keeps both the directional drilling suspension and the groundwater of the biotope away from the joint gap. A time window of around 48 hours reserve supply was available at the waterworks until the reconnection of the new pipeline.

4 Construction work

For the directional drilling, the Beermann Bohrtechnik GmbH company from Zeitz used drilling equipment with a traction force of 1,000 kN. The first 200 mm drilling was completed within a day and the six workers from the drilling company did not come up against any obstacles. In the second run, the diameter was increased to 750 mm and finally widened to 920 mm. Using heavy-duty equipment, the string of new, 6 m long DN 500 pipes were pulled through this borehole. The single-pipe assembly of the DN 500 BLS^® pipes was carried out by the construction company Josef Pfaffinger Leipzig Baugesellschaft mbH. An assembly ramp was used to introduce the pipes into the borehole at a target entry angle of 11° (Figure 2). The excavation pit was approximately 15 m long. Before pulling in, the joint of the ductile iron pipe was protected with a shrink-on sleeve and a sheet steel cone.

The pipes were assembled quickly and without complication with the help of an excavator standing ready on site. The BLS^® push-in joints were “locked” using the traction of the drilling equipment. The operation of pulling in the pipes was commenced on 16.09.2015 at about 2.30 pm and it was finished at 3.00 am the next morning without any particular incidents. After a brief orientation phase, assembly times of around 9 minutes were able to be achieved. The pipe pulling was monitored with a tensile force gauge (Figure 3).

Once the pipes had been successfully pulled in the new pipeline was connected up to the existing system with PN 10 ductile cast iron fittings. The starting and target pits were dismantled and the whole job was finished by the end of October.

5 Site open day in Badrina

Together with the water supply company, the pipe manufacturer used this particular project as an opportunity to invite interested parties, planners and clients from the surrounding communities to a site open day on 16.09.2015. After a tour of the waterworks in Delitzsch the visitors could see for themselves just how uncomplicated, fast and perfect the trenchless installation of ductile iron pipes can be.

The guests followed the assembly of the BLS^® push-in joints and the subsequent pulling-in process with great interest. There was a high degree of enthusiasm, especially since most of the visitors were aware of how much depends on the successful installation of the main Delitzsch-Rackwitzer water supply pipeline.

6 Project data

• HDD single pipe assembly, DN 500, BLS^®
• External pipe protection: cement mortar coating to EN 15542 [5]
• Joint protection: shrink-on sleeve and sheet steel cone
• Length of pipeline: 432 m
• Maximum tensile force of the drilling machine: 1,000 kN
• Permissible tensile force for DN 500 ductile iron pipes: 860 kN
• Maximum tensile force measured: 60 kN
• Average assembly time for the completion of a DN 500 BLS^® push-in joint using a shrink-on sleeve and sheet steel cone: 12 min

7 Conclusion

It is precisely in complicated situations with obstacles and particular requirements that the trenchless HDD technique in combination with ductile iron pipes has proved its worth time and again. The robustness of the pipes, maximum security against the internal pressures occurring and the high external load capacity are guarantees of high operational reliability and a long working life. The new pipeline of ductile iron pipes should now last for at least the next 50 years.

Thanks to the flexible BLS^® push-in joints the pipeline could be installed through the Badrina biotope safely and rapidly using the trenchless laying technique. And nobody went in to disturb the sensitive ecosystem.

Bibliography

[1] Managementplan für das Gebiet Nr. 210, Vegetationskunde und Landschaftsökologie (IVL) [Management plan for area no. 210, Vegetation and landscape ecology], Leipzig 2010
[2] Tables of European protection areas (Natura 2000) and protected landscapes, Source: Wikipedia 2011-07-10
[3] EUR-Lex l28076 – EU: 1992-05-21
[4] Jacob, C. Badrinaer Biotop entscheidet über Wasserversorgung der Region, Article in the Leipziger Volkszeitung 2015-09-10
[5] EN 15542: 2008
[6] DVGW worksheet GW 321: 2003-10

(Primary Publication: GUSS-ROHRSYSTEME - Information of the European Association for Ductile Iron Pipe Systems • EADIPS^®)

More News and Articles