Project Overview
The total length of the line required 870 lineal metres of 450mm diameter GRP pipe encased with a Ø660 steel casing. The maximum length of a single drive was 180m. The grade was designed at the very flat value of 0.240%. Lend Lease awarded the works which included open cut sections to Trazlbat. Trazlbat subcontracted the microtunnelling to Pezzimenti Tunnelbore.
Self-Supporting Ground Conditions
The ground was a weathered shale to clay. The first 4 microtunnels were created using the freebore method, then the steel casing was inserted, followed by the pipes and the annular void grouted. The last bore in clay was pipejacked to maintain stability of the bore during microtunnelling.
Site Set-up: The top section of the ground was cut down to allow excavation of the lower 6 metres of the shaft.
Freeboring in shale
Piepejacking the steel casing in ground which was not self-supporting.
Sliplining a SN20,000 GRP collared Pipe
MICROTUNNEL 1.
Pipe in a Pipe by Freebore Method
Length. 175m
Diameter. 690
Ground. Sandstone / Shale
Casing Pipe. 660 Steel
Carrier Pipe. 450 GRP SN20K
Grade 0.26%
MICROTUNNEL 2.
Pipe in a Pipe by Freebore Method
Length. 145m
Diameter. 690
Ground. Sandstone / Shale
Casing Pipe. 660 Steel
Carrier Pipe. 450 GRP SN20K
Grade. 0.26%
MICROTUNNEL 3.
Pipe in a Pipe by Freebore Method
Length. 175m
Diameter. 690
Ground. Sandstone / Shale
Casing Pipe. 660 Steel
Carrier Pipe. 450 GRP SN20K
Grade. 0.26%%
MICROTUNNEL 4.
Pipe in a Pipe by Freebore Method
Length. 174m
Diameter. 690
Ground. Sandstone / Shale
Casing Pipe. 660 Steel
Carrier Pipe. 450 GRP SN20K
Grade 0.24%
MICROTUNNEL 5.
Pipe in a Pipe by Pipejack Method
Length. 176m
Diameter. 690
Ground. Clay / Shale
Casing Pipe. 660 Steel
Carrier Pipe. 450 GRP SN20K
Grade. 0.24%
