Humes segmental shafts have been used on many high-profile projects throughout Australia. These include: the Sydney Desalination Pipeline, where Humes was commissioned to design and supply segmental shafts for the construction of two temporary shafts to be used as jacking pipe launch and retrieval pits, with 7.5 m internal diameters and depths of approximately 12 - 15 m; the NPI - Stage 2 where Humes constructed two 6 m segmental shafts with depth of 7 m and 14 m for receiving DN1500 jacking pipe; and the Brisbane City Works, where the company constructed an 8 m deep launch shaft for DN1650 butt joint jacking pipe at a site located in the heart of a residential and commercial area.
Shaft solutions (applications)
Humes’ precast concrete shafts are proving to be an economical and safe solution for permanent and temporary underground structures.
They are ideal for a variety of applications including: ventilation shafts, escape shafts, launch and retrieval shafts for pipe jacking applications, storage overflow and pump stations, water harvesting and reuse.Article continues below…
Features and benefits
Precast shafts provide installation contractors with a number of significant benefits over traditional shaft construction methods including greater installation efficiencies, cost benefits, and a safer work environment. Humes’ precast shafts also help to reduce the environmental impact of construction.
- Installation time is significantly reduced as excavation and ring placement can be on a continuous cycle.
- The precast concrete segments provide a one-pass finished shaft, so no further concrete work is required to finish the structure.
- There is no requirement for specialist labour and a small team should be capable of managing the entire installation process.
Safer work environment
- The majority of work can be carried out above ground.
- Overhead services hazards are eliminated as no large cranes are required.
- The system has a built-in safety barrier created by the installation of the top ring.
Minimal environmental impact
- Noise and ground vibration are virtually eliminated because no hammering is required.
- The excavation and site storage areas are minimal, as the precast units are relatively compact at less than 2.5 m wide.
- Shaft installation does not require the use of water or wet concrete (except for the base).
- The shaft can be installed accurately due to the high degree of control over the rate and direction of installation.
- No bracing is required due to its structurally-efficient circular shape. The shaft gains structural stability from the surrounding soil so tie-backs or ring-beams are not required to support the segments.
- Installation methods used mean the shaft is suited to a variety of soil conditions.
- The extensive diameter range from 3 to 25 m diameter makes the shafts suited to virtually any project.
- A unique external fixing is used to join the segments, eliminating the need for specialist trades, like welders, on site.
Construction in any soil condition
There are three techniques available to install a precast concrete segmental shaft. These are the caisson method, which is generally used in softer soils with or without the presence of ground water. Caissons are either installed as a ‘wet caisson’ where the water level inside the caisson is slightly higher than the external ground water level, or as a ‘dry caisson’ where the inside of the caisson is open to the atmosphere. In the caisson method, the precast concrete elements are erected at the surface and are then lowered into the ground whilst excavation progresses. Secondly, the underpin method can be used in competent ground that is suitable for the required depth to install the shaft lining. In this method, the precast concrete elements are progressively installed at the base of the excavation. The last method is a combination of the previous two, ideal for use if the soil condition varies. Installation commences with the caisson method (using a special choker ring) and then shifts to the underpin method when the hard soil ground is reached. With some ground conditions it may be necessary or cost effective to stop the caisson at a certain depth.
To view a Humes video on the installation methods, click here.
Humes, Australia’s largest civil precast concrete manufacturer, provides a large range of solutions for bridges and platforms, road and rail infrastructure, tunnels and shafts, retaining walls pipeline systems, water treatment, detention and reuse, drainage and traffic management.