The box will be 130 metres long and 24 metres deep, with 1.5-metre thick walls constructed by diaphragm piling, with top and intermediate levels of reinforced concrete props.
The base slab of the crossover box will be supported by 77 piles, installed 20 metres into the ground below the slab level.
The sheet piling work has been carried out by Dawson Wam for main contractor Skanska Costain Strabag Railways Joint Venture (SCS Railways).
The Victoria Road crossover box site is to the west of where the HS2 Old Oak Common station is being constructed. The underground box structure being built will house a crossover track mechanism that will allow trains to switch between tracks, up to a design speed of 62 mph, on the approach and descent from Old Oak Common station.
The installation of 200 metres of sheet piling was the final piece of enabling work before permanent works can begin.
The site at Victoria Road is also being prepared to launch the Northolt tunnel boring machines which will drive 3.4 miles northwest, as part of the construction of the 8.4-mile Northolt tunnel.
The site will also be home to the Victoria Road ancillary shaft, which will provide ventilation and emergency access to the rail line during operation. The shaft will have an internal diameter of 25 metres and be constructed using precast rings at the top and sprayed concrete at the bottom.
SCS managing director James Richardson said: "Our team are making great progress on constructing the crossover box at Victoria Road and are working collaboratively with other construction partners to deliver this exceptional programme of work."
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