1 Victoria Street, London

Wentworth's engagement began with a comprehensive pre-demolition structural investigation, scanning over 100 structural elements using Ground Penetrating Radar (GPR) to map reinforcement and concrete cover. We designed and implemented hydraulic load tests on floor slabs to verify capacity for heavy demolition plant. During demolition, we provided agile temporary works designs, including basement retention analysis and early piling solutions. Our work combined archive drawing studies, 3D geotechnical ground modelling, and utility damage assessments and structural finite element analysis to optimise the demolition sequence and enable early foundation works for the new structure.

We are now designing the temporary works during the construction phase of the new building by undertaking extensive structural modelling to assess the stability of the 2No cores in the temporary condition, and design the steel grillages for the tower cranes that will be installed on top.

Before Keltbray could bring heavyweight 13te excavators and bobcats onto the existing floors to start the demolition works, we had to verify that the 1965-era concrete floor slabs could safely support the heavy loads. The building's age and limited original documentation meant that the slab capacities were uncertain, adding significant risk for both the demolition programme and overall site safety.

Wentworth’s in-house site and investigations team designed and implemented hydraulic load test systems, applying controlled loads to selected slabs while recording deflection and monitoring slab condition throughout testing.

Our GPR scanning of over 100 structural elements provided reinforcement geometry and concrete cover data, which we correlated with breakout surveys and core samples to build a complete structural picture. This combination of non-destructive testing and targeted intrusive investigation confirmed realistic load capacities without extensive breakouts.

The verified slab capacities gave Keltbray certainty to mobilise its demolition plant, enabling an efficient top-down demolition sequence across the nine-storey structure.

The 7,400m² footprint included two basement levels that would eventually accommodate new foundations, but temporary propping of the retaining walls during demolition would impede access. Traditional temporary works approaches would have filled the basement with propping, limiting plant movement until the upper levels are removed and creating congestion.

We conducted detailed studies of archive drawings, developed 3D geotechnical ground models, and carried out utility damage assessments to understand the existing retaining wall construction and surrounding ground conditions. Through finite element analysis of the walls and soil-structure interaction plus movement analysis for utility damage assessments, we demonstrated that the existing retaining walls could safely cantilever without temporary support throughout the demolition phase.

This unrestricted basement access increased both safety and efficiency of the construction works, enabling Keltbray to complete demolition down to B2 level across the full footprint without the constraints of internal propping.

To protect the programme, Keltbray wanted to start the piling works for the new 10-storey post-tensioned concrete frame before the full demolition was complete. However, the existing concrete cores were still in place and providing lateral stability to the building, making early pile installation around them highly complex and a risk.

To mitigate this risk, Wentworth developed a streamlined, minimally invasive engineering solution involving partial slab removal and notch openings in the core walls. This approach was carefully coordinated with the demolition programme to manage evolving load conditions as the structure came down. Rather than extensive propping, our final design relied on minimal proprietary propping, selected specifically to accommodate pile rig access and movements.

Due to this solution, Keltbray was able to work simultaneously on both demolition and piling operations optimising the programme speed.

We selected various concrete elements for a trial application of an MCI product. When applied in a liquid form, the MCI penetrates cementitious materials, forming a protective layer on embedded reinforcing. Wentworth applied the product and monitored corrosion rates over a six-month period. This type of system can potentially extend the lifespan of structural elements by 15+ years.