Elan Aqueduct, Frydd Wood

The BNM Alliance (a joint venture between Barhale and North
Midland Construction) awarded Aarsleff Ground Engineering
the contract to design, supply and install a soil nailed slope to
allow, with associated works, the launching of a TBM (Tunnel
Boring Machine) for the Severn Trent Elan Valley Aqueduct
Rehabilitation project in Wales.

The original aqueduct was built between 1893 and 1904. Fast
forward over 100 years and the aqueduct still provides drinking
water from the Elan Valley to Severn Trent’s customers in
Birmingham. The aqueduct transports high quality water
entirely by gravity. Having supplied water for over 100 years, the
aqueduct is beginning to tire in three key locations and offline
replacements are necessary.

8No test nails were installed on the 17th July. These were tested
to destruction to confirm the design prior to production works
starting. With its Klemm 806 rig, Aarsleff will then installed 670no
100mm diameter fully galvanised R32 -280 self-drilling soil nails of
6-16m in length.

In addition to the soil nails, approximately 670no head plate
and nut were supplied and fixed. The soil nailed wall has an
estimated 1250m2 area to which Aarsleff has supplied and fixed a
steel mesh and geotextile facing. Aarsleff were on site from 24th
July with completion 15th September 2017. Aarsleff showcased
its previous work in soil nail projects of similar size to the
main contractor before winning the contract to demonstrate
its technical capabilities and expertise whilst simultaneously,
assuring the client of cost, time and quality. Aarsleff Ground
Engineering has sought value engineering primarily through
optimisation of the soil nail layout and facing mesh.

The self-drilling soil nails were procured from Barnsley-based
Minova and possess a hollow bar, which is used for drilling
ether with water flush, air flush or cement grout flush and are
extended by using couplers. The standard couplers have a
design which ensures end-to-end bearing of the hollow bars to
transfer percussive energy from the top hammer to the drill bit
whilst a sealing ring in the centre stop, minimised flush spillage
during drilling. The soil nails also possesses a sacrificial drill bit.

The rig we employed is designed for the use of powerful
double head drilling units, hydrualic drifters or rotary heads.
It can also be equipped with drill masts either with feed gear
or cylinder feed systems, with the option of fitting lattice mast
extensions, the modularity of which, allows the adaption of a
variety of options, which makes the drill rig ideal for anchoring,
micro piling, jet grouting and even geothermal drilling. After
completion, two percent of all working nails will be ‘Acceptance’
tested to validate the design and provide confidence as to the
quality of the installation.

Speaking about the work for the Elan Aqueduct, Aarsleff’s
Assistant Department Manager for Ground Engineering Jonathan
Greener said: “I am pleased to secure yet another soil nail job for
such a prestigious scheme. It enables us to directly transfer all
our skills from one project to the next, allowing us to continually
improve and achieve the best results in ground engineering.”