MADRID TRADITIONAL METHOD | BTSYM


As will be discussed later, the exact origins of the


nomenclature of the Belgian Method may be lost in history. However, the technique was further developed over more than 100 years in Madrid’s soils and is currently known as the Madrid Traditional Method (MTM). From its humble beginning with Line 1, the Madrid


metro rapidly expanded to become a network of almost 300 km (186 miles) of tunnels, covering 12 districts of the capital. The expansion of the network was particularly busy between 1995 and 2017, when several Tunnel Boring Machines (TBMs) were used for the longer tunnels (several miles), and the MTM was reserved for shorter tunnels and galleries (hundreds of yards). Gran Vía station is another of the original stations


of Line 1. This station was upgraded in 2021, while maintaining the operation of Lines 1 and 5. The upgrade works included step-free access and several technological updates: LED lighting; information screens; larger and modern gates; and the latest generation ticket machines. This is the first 4.0 (4th Industrial Revolution) station in Spain, offering advanced design and features, with large display screens, contactless payment, and improved user interface. The upgraded station also pays tribute to the


original 1919 entrance pavilion by building a granite replica of the original structure, conceived by Antonio Palacios (the architect mastermind of Madrid’s first metro lines).


MADRID TRADITIONAL METHOD (MTM) According to the literature (‘La construcción del Metro de Madrid y la M-30’, Manuel Melis Maynar, 2012), the first reference to the Belgian Method comes from the construction of the Godarville Tunnel between 1827 and 1841 for the Charleroi Canal, in Belgium. However, some recent references claim that there


is not enough evidence that the method was brought from Belgium, and that it might have been used by Belgian engineers working on Line 1, back in 1919, and subsequently referenced them, and so was named after them. Nevertheless, after more than 100 years of


development of this method in the ground conditions of Madrid, this ‘Belgian Method’ is now well-established as a tunneling technique and as such its name has become known as the Madrid Traditional Method (MTM). The MTM consists of a sequential excavation with the


following main steps (see Figure 3): 1. Miners excavate a small pilot gallery and support it with timber planks, waler steel beams and timber struts. The short gallery is 2.5m (8.2ft) long and is used to identify ground conditions ahead of the main excavation


2. Lateral widening and shoring of the top heading are then undertaken, with five pocket excavations at each side with typical round lengths of 2.5m


3. Formwork installation and casting of the unreinforced concrete crown is performed (typically 3 sets of 2.5m long formworks are used)


4. Repetition of steps 1 to 3, up to 7 round lengths of the top heading


5. Excavation of the walls with excavators and casting of the unreinforced concrete side walls are then undertaken (in a staggered way and maintaining a maximum of 7 round lengths to the top heading face)


6. Construction of the unreinforced concrete invert slab is the final step to close the tunnel section


There are many examples of the application of this method in Spain, and also in some tunneling projects abroad that were designed and built by Spanish companies, such as in Quito metro, in Ecuador. The experience of constructing tunnels with this


method in the soils of Madrid has demonstrated the safety of the technique. The sequence of works follows a series of steps perfected and improved over the years by the experience of Madrid’s miners and engineers, and by studying the lessons learned from previous projects. Although this construction process requires specialized labor, it is a very versatile method that allows for a high degree of adaptation to the constraints of an urban environment. This methodology is based on the principle of carrying out small excavations (less than 5m2 ”


(54ft2 )),


which greatly limit the open excavation face, to guarantee its stability during construction. As previously mentioned, the excavation begins with a small pilot gallery that is gradually shored and widened to form the top heading of the tunnel, always with a temporary support for each widening stage. In this way, the open face for each excavation plane is reduced and, therefore, the stability conditions are more favorable. This advance gallery also acts as a pilot tunnel


to identify any contingency or uncertainty about the state of the soil, thus allowing the adaptation of the construction procedure to respond to these singularities. The contingencies can include ‘toolbox’ items, such as reducing the round length or installing timber planks at the open face. In more challenging ground conditions, the face is also supported with timber planks, but these are not normally necessary. Advance lengths of 1.25m or 2.5m are normally used,


depending on the ground conditions, with shoring installed systematically. There are exceptions, linked to singular sections, either due to geotechnical conditions or to the need to adapt the construction methodology in sections with special needs, such as at junctions. After the construction of the invert slab, the back of


the concrete liner in contact with ground is filled with grout. The purpose of this process is to fill any gaps that may remain at the top heading extrados between the concrete, the timber shoring, and the excavation profile, and to reduce water ingress through the joints between the pours. The injection pressure must be limited to avoid excessive loads on the lining. The grouting pressure is usually limited to 1 bar.


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