case study - Hynds Pipe Systems

CASE STUDY
SH20 Manukau Extension
Stormwater Ponds
Lusit Angle Support Retaining System
Infrastructure Retaining System
0800 WE PIPE (93 7473)
•
www.hynds.co.nz
As a result of Lusit’s success in solving a stormwater pond retaining issue at the Highbrook
Industrial Park, Leighton Works approached Lusit to determine whether they could provide
a cost effective solution to retain the Plunket Avenue Stormwater ponds. These ponds were
part of the stormwater management plan for the $260 million SH20 Manukau Extension
project in Auckland.
The Plunket Ave stormwater ponds had to be located in a
relatively narrow section of the SH20 extension, with
occupied industrial land on one side, and the SH20 motorway
on the other side. Site constraints meant It was not possible to
construct the ponds in the conventional manner using
battered earth and contoured slopes.
The design engineers had originally planned to use a system
of sheet-piles to form retaining to the long sides of the ponds,
with a 500mm clay base liner and earth sloped ends.
However the client, surrounding land owners and Leighton
Works were after a more cost effective and aesthetically
pleasing solution.
Leighton Works were initially interested in using the Lusit
Angle Support System because of the attractive design and
vertical retaining solution that the system offers. LAS Elements
can also be designed to handle specific load surcharges.
In addition, the LAS Elements would enable the stormwater
ponds to be located directly on the boundary between the
SH20 corridor and the surrounding industrial land.
The Lusit Angle Support system normally works with
approximately 75% of the typical soil types encountered
within New Zealand. However the geotechnical soil analysis
in the proposed stormwater ponds location indicated some of
the “weakest” soils Lusit had yet encountered, with modulus of
elasticity as low as 2 MPa.
In conjunction with Leighton Works, and the geotecnical
engineers (Tonkin & Taylor), an initial re-design was
proposed, involving a series of 8m deep colmix columns. This
would provide enhanced bearing capacity and improve the
global stability along with installing 3m+ high Reverse LAS
Elements along both sides of the stormwater ponds.
HIGHBROOK POND DURING CONSTRUCTION: LAS Elements sitting at
top awaiting installation.
Following further design iterations and input from the German
knowledge base behind the 32 year old Lusit Angle Support
System, the retaining solution eventually evolved into a
“concrete beam and bath” methodology. This involved using
2.9m tall 20er Reverse LAS Elements (i.e. LAS Elements with
the foot towards the airside) together with a series of
HIGHBROOK POND COMPLETED
LAS INSTALLATION: Made easy with the special Lusit Quick Hitch.
0800 WE PIPE (93 7473)
•
www.hynds.co.nz
600 x 200mm reinforced concrete beams linking these LAS
Elements across the pond. Lastly a 100mm thick concrete
topping was poured to provide the pond base. This did away
with the need to enhance the weak soils and removed the
need for the clay base liner.
To further reduce installation time and costs, Lusit
manufatured the Reverse LAS Elements in 1.5m widths,
together with a shortened 1000mm long precast foot, with
rebar extenders (to enable an insitu stitch beam to be poured).
During the installation, it became apparent that any water in
the area behind the retaining wall could not be drained by
normal means. Lusit and its consultants then devised an
alternative solution of pressure relief holes allowing
hydrostatic pressure to equalise between the pond and the
surrounding areas.
Installation of LAS Elements was done by Waiau Earthmovers
who simply used a 20 tonne digger. To speed up the
installation, Lusit developed a special lifting Quick Hitch which
attached onto the digger’s tilt hitch and then onto each of the
LAS Elements. This provided safe, quick and full installation
movement (in, out, side to side with 360 degree rotation).
REVERSE LAS ELEMENTS AFTER GROUTING
PREPARING TO INSTALL THE CONCRETE “BEAMS AND BATH”
The Reverse LAS Elements were lifted onto the foundation pad
and installed on precast shims. They were then aligned and
levelled with the use of panel bars and grouted into place
once sufficient runs of 30m or more had been placed. All
installation work was undertaken by a small team comprising
of a digger operator and 3 dogmen.
EASTERN STORMWATER POND COMPLETED
Project Summary:
LAS Elements:
164no. 1.5metre wide, 20er Reverse LAS
Design Loads:
12kN/m2
LAS heights:
2.9m
LAS weights:
2780kg
Wall foundation:
50mm Cemix non-shrink grout, on 100mm thick 17.5MPa lean concrete pad, on 200mm compacted
hardcore
Main Contractor:
Leighton Works (JV between Leighton Contractors PTY Ltd and Works Infrastructure Ltd)
Installation Contractor: Waiau Earthmovers
0800 WE PIPE (93 7473)
•
www.hynds.co.nz
0800 WE PIPE (93 7473)
•
www.hynds.co.nz