The most frequently searched terms online include: “trench formwork”, “trench shoring”, “trench shoring for sale”, “trench formwork for sale”, “trench shoring rental” or “trench formwork rental”, ll referring to the same product under different names. It may be worth knowing the correct terminology and using it consistently in both engineering and commercial communication. Why, even decades after the introduction of modular shoring systems for temporary excavations, do we still use so many different names?
In this brief article, I will attempt to answer these questions and establish the correct terminology. These systems were not invented in Poland. They were pioneered by Mr. Josef Krings in Germany in 1949. Much like the early days of the bicycle, box-type shoring systems were initially referred to colloquially as “krings” by the people who used them. This name, however, did not take hold, and other terms were sought. One contributing factor was that the company Kopras began manufacturing such equipment in Poland shortly after 1990, and at some point clients even began asking for “kopras” by name. As for where the term “trench formwork” originated, I honestly do not know. Let us turn to Wikipedia.
“Formwork (recommended term: shuttering; colloquial: boarding, sheeting), a type of mould used to give shape to a concrete mix.” Long ago, when excavations were dug by hand, workers would shore up the trench walls manually using timber planks and beams, a process then described as “formworking” (szalowanie). Nowadays, you would be hard-pressed to find workers who can do this correctly and in accordance with applicable standards.
With the development of excavators, specifically the transition from cable-operated to hydraulic excavators, the use of prefabricated components in trenches became technologically feasible. It is no longer appropriate to say that someone is “formworking” a trench in the same sense as forming concrete. In my view, “shuttering” (deskowanie) is not merely the recommended term, it is the only accurate and correct one.
Wikipedia then took an even broader, and arguably misguided, stance on “trench formwork”: “One type of formwork is trench formwork. As the name suggests, these are used to stabilise excavations in all types of soil, preventing the surrounding ground from collapsing into the open trench. Light aluminium formwork is also available for small excavations (e.g. small sewers), and despite the name, these are not truly lightweight, they can weigh up to 1,400 kg. Medium-duty formwork is used, for example, in residential construction excavations. Heavy-duty formwork, made from very thick steel plate, is used primarily in industrial construction. Trench formwork is classified as: light, medium, and heavy.” I will refrain from commenting on this. I invite each reader to compare this with their own professional knowledge. If most of Wikipedia’s information is of similar quality, that speaks for itself.
Now we know the origin of the term “trench formwork”. People continue to confuse concrete shuttering with excavation shoring systems, largely because of this misleading word: “szalunek” (formwork).
I propose that we now set aside the search for the origins of this incorrect term and instead, drawing on applicable standards, legislation, and regulations, make the case for the correct terminology, so that everyone, from the operative on site through to the engineer and the investor, knows precisely what we are talking about.
Standard PN-EN 13331-1:2004 Trench Lining Systems, Parts 1 and 2, is entirely dedicated to the equipment described in this article. I quote the definition: “Trench lining system, an assembly of prefabricated components intended to support the vertical walls of excavations.” Consulting this standard, it becomes clear that it specifically covers modular shoring systems for temporary excavations. It is well worth reading, and owning, as it serves as a definitive reference document on retaining structures of this type, or shoring systems as some prefer to call them. Can we use the terms “shoring” or “protection”? In my view, either of these is preferable to the word “formwork”.
In the Regulation of the Minister of Infrastructure of 6 February 2003 on health and safety during construction works, for example, Article 162 states: “The installation of shoring or pipes in a pre-excavated trench with vertical walls at a depth exceeding one metre requires the temporary protection of personnel by means of protective cages or prefabricated shoring.” The text refers to “shoring” and “excavation support”, there is no mention whatsoever of “formwork”. This pattern is consistent throughout the other articles of the Regulation. I strongly encourage reading this document, it may clarify what we are doing correctly and what could be improved in earthworks practice.
Eurocode 7 does not address temporary braced shoring systems that do not extend below excavation formation level, for understandable reasons, a dedicated European standard exists for these, as cited above. Eurocode 7, in Chapter 9 (Retaining Structures), lists: massive/gravity retaining walls, embedded retaining walls, and composite retaining structures. It can therefore be stated that an excavation shoring
system is, in effect, a braced retaining wall, using various types of struts as specified in PN-EN 13331, but it is most certainly not formwork.
To conclude this section of the article, it must be stated that terms such as “trench formwork”, “formwork cages”, and “formwork boxes” are incorrect and should not be used even in informal speech. I address this point particularly to young engineers, do not adopt the terminology used by so-called “old hands” simply because it has been in common use for years.
I conclude this article with a reflection on the correct term for a retaining wall consisting of H-section steel profiles driven by vibratory hammers, with lagging made from the same prefabricated plates used in slide-rail shoring systems. The simplest designation for such a wall is a “Berlin wall”, and this is accurate, since lagging is indeed one of the elements of a traditional Berlin wall. Lagging is most commonly made of timber planks, sometimes of precast concrete slabs or steel stampings. However, given that the primary element here is the prefabricated plate, installed using the “cut and lower” method employed in modular shoring systems, the term “post-and-plate wall” is, in my view, more appropriate. In a Berlin wall, the lagging is installed from below by hand; in a post-and-plate wall, it is installed from above by mechanical means. We speak of a “Paris wall” even though it is structurally similar and differs only in the type of lagging. English and American engineers use the term “soldier pile and lagging wall”, which translates precisely as: post-and-plate wall. I have also encountered the term “segmental wall”, though for me a segmental wall is one composed of narrow or wide vertical segments that allow obstruction crossings of various kinds.
Dr. Eng. Marek Kopras