Lining and support systems
The microtunnels, can be performed by different technologies, all of them included within the so-called Trenchless technologies or No-Dig.These technologies, according to the ISTT, are the following: here
What is a lining?
Material employed to cover the inside of a pipe, channel or tunnel surface with the aim of waterproofing, wear and erosion decreasing or friction reducing
Royal Engineering Academy (Spain)
Layer placed upon a constructive basis element or support. Batter of walls in vertical constructive elements; floor layers, carpets and suspended ceilings in horizontal constructive elements are considered as linings.
Technical Building Code (Spain)
What is a support?
In underground works it is mandatory that the excavated space remains stable and with the expected section, so for this purpose acting on the ground, increasing its support capacity, is necessary by means of injections and draining. If the previous is not feasible, it is necessary to install elements with enough strength to bear with the ground loads against the excavation edges, during the construction as well as after the initial starting of the operation, those elements form the support. Among the possible solutions we can find grouting and bolting, and in special situations metallic truss, forepoling, Bernold plates and others.
FLC Construction Dictionary
In general, lining and support of microtunnels built by the explained methods and technologies, can be divided into:
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Jacking Pipes: Which can be made of different materials such as reinforced concrete, steel, ceramic or plastic-based materials.
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Segments: These are precast elements, usually made of reinforced concrete, which are fastened with each other making part of a tapered ring which constitutes the final lining of the tunnel.
Even it is possible to differentiate between lining and support, most of the elements included in microtunneling works can perform both functions at the same time. Is only in few scenarios like, oil&gas pipelines, sewer systems, amongst others, where it is possible to separate the elements which carry out these functions within the tunnel structure.