A tunnel boring machine (TBM), also known as a “mole”, is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can bore through anything from hard rock to sand. Tunnel diameters can range from a metre (done with micro-TBMs) to 19.25 metres to date. Tunnels of less than a metre or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs. Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional “hand mining” in soil.
FSI or floor space index is the upper limit to the built space you may construct on a given plot. It is the ratio of allowed built-up area to the plot area. For example, on a 10,000 ft2 plot which has an FSI of 2, you may construct a maximum of 20,000 ft2 of area, and no more. FSI can also be called FAR or floor area ratio. Certain types of spaces, such as basements, parking areas, and utility rooms, are exempt from FSI, which means that they do not need to be counted in the FSI calculations.