Contracting civil engineers, on the whole, do much fewer design and calculations than consulting civil engineers. A broad stereotype would say that consultants stay in an office and design a project, and contractors go out on site and build it, but all engineers must have a technical and practical understanding of engineering. Contracting and consulting may seem like two completely different careers, but the common theme is that civil engineers must have a knowledge of engineering principles whether on site or in the office. This includes understanding forces, load paths and failure modes. The Institution of Civil Engineers requires all professional engineers to be able to undertake design and development of engineering solutions and be able to evaluate their effectiveness.
Design work that contractors are more frequently involved with is temporary works design. Temporary works are anything which is required to be built in order to construct the permanent works and includes items such as scaffolding, formwork and ground retention. I undertook a placement in the Temporary Works department as part of my training towards professional membership of the Institution of Civil Engineers. I gained experience in the production and checking of temporary work schemes requested by all sectors of Vinci Construction UK and Taylor Woodrow International, including geotechnical solutions, concrete, timber, formwork, propping, earth retaining structures and scaffolds. I am familiar with the use of British Standards and Eurocodes as well as many industry guides and technical documents.
Tottenham Court Road station redevelopment
Aerial view of Tottenham Court Road underground station redevelopment during phase one construction works
During my placement I designed a major ground retention scheme, for use during the demolition of the existing Tottenham Court Road underground station redevelopment. During Phase two of the project, the existing ticket hall was demolished to allow for construction of a new ticket hall. This involved excavating a 7m deep excavation adjacent to Oxford Street, one of London busiest shopping streets.
I designed a ground retention scheme which would withstand lateral earth pressures from Oxford Street, whilst also providing adequate space on the construction side to carry out demolition and new construction works. There were numerous constraints involved with this task such as the presence of many services and a critical public interface at Oxford Street.
The solution was a king post design anchored at the base 7m below ground level, and continuing 9.7m vertically to also support the site hoarding. Over the length of the structure the imposed loads were wind loading, lateral earth pressure, increased surcharge from the highway and crowd loading. As the king post was anchored at the base producing a long lever arm, the imposed forces were too great thus leading to failure and deflection, even when using expensive and excessively large steel columns.
My final design involved two schemes. The first solution was a kingpost solution where the line of columns ran along an existing passenger tunnel beneath the street level. The tunnel would be filled with structural concrete and the kingposts columns tied into the concrete block using walings and tie rods. This reduced the lever arm leading to reduced forces and provided additional support at the base of the structure. As half of the site did not have a passenger tunnel which could be filled with concrete, my second design involved a different approach. Instead, a section of Oxford Street, 1.5m wide, would be excavated and replaced with concrete tied into the existing roof of the underground station. This would remove the lateral earth pressure completely and eliminate the requirement for a king post wall.
I completed these designs myself using British Standards and design software. I also completed all steelwork detailing, contributed to the CAD drawings and wrote 'approved in principle' (AIP) documentation and a design risk assessment to support the design.