Jacked Arch Method
A patented method for the installation of large underground structures is the Jacked Arch Method.
The process consists of the following stages :
Stage 1. The installation of man-entry foundation boxes or tubes designed for foundation loads and the soil conditions. These are jacked in to position.
Stage 2. After driving the boxes or foundation tunnel a guide path for the arch is set manually inside the boxes
Stage 3. The main structure is formed from pre-cast arch sections (2 or 3 pin) which are jacked in behind a shield to form the canopy structure. The base of the arch sections, as they are driven forward, are located and slide in the guide path (installed at Stage 2). The foundation boxes have lids which can be removed progressively from inside the arch shield to expose the track.
Stage 4. Internal finishes and a floor are installed appropriate to use.
This method is ideal for many types of underpass and cost effective in creating deep underground metro stations and caverns.
This approach has a number of advantages.
- It can be undertaken from a smaller working area.
- It utilizes precast concrete sections that can be produced to a higher quality than in-situ work
- It allows a large number of permutations to deal with most soil conditions and shapes of structures.
- Full scale roadways to international standards can be provided.
- The individual unit weight of precast sections is such that it does not require high capacity cranes.
- The depth of cover can be as little as 1 meter.
- Depending on spans the arch units can be either 2 pin or 3 pin. Up to 30metre spans can be achieved with a 3 pin arch
- Compared to box jacking the frictional loads and thus the jacking capacity required is much less
- We are able to incorporate a guaranteed water proofing system between elements.
A number of variations are possible including using elements of the modular system to create vertical walls combined with flat arches. It is also possible to use circular foundation tubes rather than boxes. Such a configuration could allow the use of pressure balance tbms where ground conditions and water tables are a concern.
Some possible variations are set out in more detail below.
Jacked Arch Options
The jacked arch is a highly adaptable approach which can be used to create underpasses and some alternative approaches are set out below
The range of spans that can be installed is illustrated by reference to two pin precast arch units. Alternative precast arch designs including three pin can be used.
The following set out some possible applications but the combinations and variations are limitless
Standard Single Span Jacked Arch
Where the requirement is to install an underground structure without disruption to the surface and traffic or where the overburden is considerable.
This could be to create a suitable arch structure for a road , rail track or water course below any existing facility which could be an existing highway, rail track or building. A particularly common situation is where the road or rail is on a raised embankment. Another possibility is where a short road tunnel is required and it is not economic to open cut. Other possibilities are to create a metro station with minimum disruption.
Multi Span Jacked Arches
Where the requirement is to install more than a single arch for aesthetic or technical reasons such as span limitations it is possible to install multi arches.
This could be to create a suitable arch structure for a road, rail track or water course below any existing facility which could be an existing highway, rail track or building. A particularly common situation is where the road or rail is on a raised embankment. Another possibility is where a short road tunnel is required and it is not economic to open cut.
Semi-circular or Flat Arch on Wall and Foundation Boxes
There may be situations which require a relatively short span but a greater rise.
By creating jacked foundation and then walls to create abutments it is possible to provide this greater internal height.
There are many variations that can be made to suit the site conditions. The foundation boxes are designed to carry the design loads and can be varied to suit. Normally rectangular boxes are used. Wall boxes are rectangular and can be varied in number and height.
The only excavation that needs to be undertaken at the time of arch installation is over the depth of the arch down to the top of the wall box. The excavation below can be carried out once the structure is in place using traditional excavating equipment
Where a flat arch is used it is envisaged that at least two wall boxes on top of each other may be required to provide the internal structure height
The only excavation that needs to be undertaken at the time of arch installation is the depth of the arch down to the top of the wall box. The excavation of the main soil mass can be carried out once the structure is in place using traditional excavating equipment