In its basic form, a tunnel is a tube hollowed through soil or stone. Constructing a tunnel, however, is one of the most complex challenges in the field of civil engineering. Tunnels are typically horizontal passageways that are located underground usually constructed through excavation. There are many ways to excavate a tunnel, including manual labour, explosives, rapid heating and cooling, tunnelling machinery or a combination of these methods. There are various categories of tunnels: residential, mining, public works, transportation and so on. Mine tunnels are used during ore extraction, enabling laborers or equipment to access mineral and metal deposits deep inside the earth. Public works tunnels carry water, sewage, or gas lines across great distances. Before there were trains and cars, there were transportation tunnels such as canals – artificial waterways used for travel, shipping or irrigation. The purpose behind building residential tunnels may vary but often, it is to gain better access especially for residences located near the harbour or the ocean. A tunnel can significantly increase the value of the property.
The Perfect Contracting team is especially skilled in residential tunnelling and provides tunnelling services all around Sydney. Since Sydney is surrounded by waterbodies especially the Eastern and Northern suburbs like Bondi, Coogee, Mosman, Maroubra, Vaucluse, Clovelly etc., tunnels make a great solution to issues regarding access and passage. There are two basic techniques to advance a tunnel. In the full-face method, the entire diameter of the tunnel is excavated at the same time. This is most suited for tunnels passing through strong ground or for building smaller tunnels. The second technique is the top-heading-and-bench method. In this technique, workers dig a smaller tunnel known as a heading. Once the top heading has advanced some distance into the rock, workers begin excavating immediately below the floor of the top heading; this is a bench. One advantage of the top-heading-and-bench method is that engineers can use the heading tunnel to gauge the stability of the rock before moving forward with the project.
One of Perfect Contracting’s tunnelling jobs involved excavating a pair of tunnels under a residential property at Sydney’s north shore. The Perfect crew tunnelled through 65 meters of sandstone and bored down 25 meters for the lift shaft. Using modern demolition robots and small excavators and all spoil was extracted by barge as it was the only access available. Utilising one of our Brokk 200’s, a Perfect Kubota 2.5t excavator and scores of bulker bags, excavation began in May 2021. Initially, the scope of work was focused on concrete cutting and demolition in the existing house to accommodate drilling the vertical shaft. Then the crew began moved on to work on the horizontal shaft.
The first tunnel was built to create easy access to the waterline. The 51m long passage links to an 18 metre deep vertical shaft that houses a lift. That makes the passage over six storeys from street to sea. Due to the proximity of the tunnel to the harbour and the need for constant mist for dust suppression, a false floor was built at the tunnel entrance consisting of multiple layers of geofab. The floor was also ringed with a watertight lip to catch any runoff. Using the speed and efficiency of the Brokk excavator, the Perfect crew began tunnelling toward the vertical shaft. Due to the limited property access, anything of bulk had to be moved by barge including any machinery and all waste. Spoil was loaded into bulker bags with the excavator and stored until the weekly load out onto the barge. The owner had specified retrofitting a 19m tall internal lift complete with panic room. This second tunnel connects to an equally fictional, more horizontal shaft that led out to the picturesque Cobbler’s Bay. It was several months of work until the teams broke through, linking the shafts, followed by detailed excavation and project completion soon after.
Several additional factors have to be considered for residential tunnelling services. Residential locations mean a low tolerance for vibration and noise. The tunnel design is often considered a confined space and thus can be quite restrictive in terms of machinery. Even excavators like the Brokk and Kubota cannot be usually turned around inside, so they have to be tracked to the entrance and re-entered. Dust and waste need to be extracted through exhaust fans and air-monitored constantly. It was several months of work until both teams broke through, linking the shafts. Detailed excavation was then completed, with handover occurring soon after.
Tunnelling not only increases the value of the property but increase access to the amazing Sydney harbour. Perfect Contracting has the expertise and experience to excavate tunnels or lift shafts even in the difficult terrains of the eastern and northern suburbs like Mosman, Neutral Bay, Coogee, Vaucluse, Rose Bay, Dover Heights and so on.
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