| As
part of the permanent and temporary works, Single Bore Multiple
Ground Anchors (S.B.M.A.) were used to support one of the largest
circular sheet pile cofferdams constructed in Europe. |
|
Project
As part of the construction of Welmore Lake Sluice, the scheme required
permanent propping of the two wing walls together with the temporary
propping of half of a circular cofferdam wall. Both the permanent
and temporary props required high loads, which were initially believed
to be unsuitable for conventional ground anchors. The original scheme
was therefore based on the use of tie rods and internal propping.
Soil
Conditions
The ground conditions consisted of soft alluvium overlying firm
becoming very stiff sandy clay with chalk gravel (glacial till).
Solution
After a detailed study of the conforming propping scheme, Keller
proposed an alternative ground anchor scheme comprising temporary
SBMA anchors with working loads up to 925kN for the cofferdam and
permanent SBMA anchors to the wing walls. To prove the ground anchor
design proposed, 2 trial anchors were installed within the cofferdam,
and were tested up to 2000kN without failure (over twice the working
load)
Construction
All ground anchors within the cofferdam were constructed using a
Keller SM400 machine, with anchors on the wing wall constructed
using a Keller long reach machine specially converted to allow under-slung
drilling from an off-shore platform. The boreholes were formed using
rotary duplex drilling systems wiht anchor lengths from 30 to 40
metres. All ground anchors were successfully tested to 1.5 x working
load specified by BS8081.
| Client |
Environment
Agency |
| Engineer |
Lewin
Fryer Partners |
| Main
Contractor |
Jackson
Civil Engineering Ltd. |
| Specialist
Sub-contractor |
Keller
Ground Engineering |
|
