WET News

Project sPecs • Construct a new pipeline to replace an existing trunk main that crosses a flood plain • Construct a single, larger diameter tunnel to contain the pipes techKnow • Uploading the pipe's 3D model to the excavator increased operator accuracy • Aquadams were used to help the project cross a main river and two ordinary watercourses • About 7,800 tonnes of rock were crushed, processed and reused as backfill for the shafts • A steel cutting shoe was installed at the base of the caisson the VerDIct The scheme is considered a success, having been delivered within acceptable time, cost and performance standards in the face of significant challenges. SEPTEMBER 2017 wet news 11 The 1,600mm diameter tunnel sections neeD to Know 1 During construction, one of the project's key land stakeholders entered administration 2 The scheme's eastern section – from Burham WTW to the River Medway crossing – was subject to an archaeological investigation 3 Access for repair is difficult due to the marshland conditions 4 carbon saving of more than 450 tonnes CO2e was achieved the shas could be sunk under- water or in the dry, allowing the team to quickly adapt to the changed conditions. The high ground water volume and asso- ciated pressure meant it was no longer safe, or practical, to seal the tunnel and sha following the TBM's breakthrough. Instead the shas were inten- tionally flooded to balance the pressures, and the sha sealed using a team of divers aer the TBM was removed. Once the shas and tunnels were complete, twin 600mm ID ductile iron pipes were jacked into the tunnel using the same jacking frame used for the tun- nelling process, thus eliminat- ing the hazard of stored energy involved with the typical use of Tirfor hoists and winches. An important efficiency was realised by reuse of rock exca- vated during the construction of the tunnels and shas. About 7,800 tonnes of rock were crushed, processed and reused as backfill for the shas, avoid- ing the need to import fill. Gran- ular fill was specified so the shas could be easily excavated in the future by suction or other methods. This efficiency not only pro- vided a financial saving but also represented a carbon saving of more than 450 tonnes CO2e. During construction, Ayles- ford Newsprint (ANP), one of the project's key land stakehold- ers, entered administration. The former operational land where the pipes and shas were to be located was re-allocated for commercial and residential development. The original route through the site had been designed to minimise construc- tion-impact on the newsprint's operations. Following ANP's closure, the project team worked closely with its administrators, KPMG, to rapidly find alterna- tive pipeline routes that would maximise the development potential of the site. This change of emphasis resulted in a more technically challenging route involving crossing Environment Agency and Southern Water culverts but the collaborative approach between SEW, Farrans and ANP helped minimise delays to the programme and control costs. This scheme faced a wide range of environmental con- straints and challenges, includ- ing sites designated for ecologi- cal and archaeological interest, dealing with flagship and pro- tected species such as nightingales and great crested newts, and open cutting through designated watercourses. Progress through the Ley- bourne Lakes Local Wildlife Site and Country Park was achieved with minimal environmental disruption by using appropriate timing and construction meth- ods. The main works were undertaken during the winter months, before the nightingales returned to breed, and reducing the risk of reptiles entering the works area. A main river and two ordi- nary watercourses were crossed using 'Aquadams' and fluming. This removed the need for large amounts of soil or other mate- rial being placed in the water- course and removed again aer- wards, reducing the risk of silt pollution. This method was also very quick, allowing each water- course to be crossed within a single day. Other protected spe- cies along the route included reptiles, great crested newts and water voles and mitigation was implemented to prevent any impacts to these. The eastern section of the scheme from the Burham WTW to the River Medway crossing was subject to an archaeologi- cal investigation because of the proximity of a Scheduled Monu- ment – the Eccles Roman Villa complex. A series of trial pits were excavated along the alignment to determine the depth of cover to the archaeological horizon. Where there was at least 300mm depth of soil (following topsoil strip), it was agreed that any archaeological remains would be protected from the construc- tion vehicles running above. As a result, only a single short length required full-scale exca- vation and data recovery. The scheme was delivered within acceptable time, cost and performance standards in the face of significant challenges. • 24/7 Emergency Breakdown | Flood Dewatering Planned Maintenance • Bespoke and tailored Rental Solutions • We offer ATEX submersible pumps • We hire only our own Flygt and Godwin pumps • Full range of pipework and accessories available PLUS telemetry and monitoring equipment • Free site survey and system design • Same day installation available* Xylem Rental at Birkenburn Reservoir, Scotland SUBMERSIBLE AND DIESEL PUMP HIRE 24/7 RAPID RESPONSE NATIONWIDE AVAILABILITY DIRECT FROM THE MANUFACTURER FOR ULTIMATE PEACE OF MIND *subject to availability 0845 707 8012 fgb.rental@xyleminc.com | www.xylem.com/uk flygt_godwin rental advert rev aug 2017_Layout 1 04/08/2017 15:16 Page 1

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