This is a rehabilitation project where sections of a 100 year old structure, Elan Valley Aqueduct (EVA) needed to be replaced. The EVA is an extremely crucial resource as it supplies water to Birmingham and its adjacent areas. The aqueduct is approximately 120 km long, discharges 300 million liters of water every day into the reservoir at Frankley Water Treatment Works (WTW) in Birmingham, and currently supplies water to about 1.2 million people. There was a need to refurbish and modernize the aqueduct so that it can be preserved for the future. For this, a new conduit with a tunnel of 1.8 km long and 3.0 m diameter was proposed to be constructed. For the construction of the bypass conduit, a horizontal working platform of 160m long and maximum 14.0 m high was required to support the construction traffic, the 1000 ton crane used to assemble the Tunnel Boring Machine (TBM) and the 150 ton TBM.
The solution consisted of a Reinforced Soil Wall using StrataGrid™ of 120 and 60 kN/m and “site-won” cohesive material as part of the cut-and-fill balance of the project.
To complicate the challenge the entire reinforced soil was required to be made with the site-won material which has a very high content of fine soils, and was very susceptible to weather conditions.
The Innovative Solution
This project was launched by Severn Trent Water as an alternative source of portable water to Birmingham city (population 1.2 million) in future cases of emergency.
To have smooth construction traffic and support the 1000 ton crane, which would be used to assemble the Tunnel Boring Machine (TBM) for the construction of the tunnel, it was necessary to construct a levelled and horizontal working area at one end of the new bypass tunnel, downstream of the project.
For this it was proposed to construct a Reinforced Soil Wall with StrataGrid™and on-site won material to surround the location of the cofferdam for the TBM launch shaft. The length of the RSW was 160m, with a maximum height of 14 m, a slope angle of 85 degrees. A reinforced working platform was constructed, on top of the Reinforced Soil Wall, with selected granular material of 970mm thickness and biaxial geogrid to distribute the load. For the face a steel mesh B1131 was used to achieve the slope angle of 85deg and each layer was protected with Landlok erosion control mat.
The total height of the Reinforced Soil Wall comprised 43 layers of primary reinforcement with uniaxial StrataGrid™ 120kN/m and 60 kN/m allowingthe use of on-site won material as part of the cut-and-fill balance exercise, a key aspect of the project.
Value Addition to Customers
- Saved considerable amountof cost as compared to the conventional method of constructing a concrete wall
- Environment friendly solution, low carbon emission
- Technically sound and robust system
- Rapid construction