Tate St Ives

Project achievements and benefits

This project has added 600 square metres of galleries, and created spectacular new studios for learning activities giving enough space to accommodate 1/4 million visitors each year –three times the original number. Tate St Ives has initiated a new £5 a year Locals’ Pass to the gallery, encouraging local tourism, with over 5,000 being sold since opening.

Due to an increase in visitors to the gallery there will be economic benefits for St Ives and Cornwall, leading to an increase of an additional £11 million into the local economy. In terms of long term impact, Tate St Ives will attract an additional 77,000 visitors each year, generating an additional £87million for the local economy in the ten years post project delivery. This income will create and sustain 198 indirect tourism jobs and safeguard 68 jobs.

The project also created 54 direct jobs at Tate St Ives and 236 construction jobs during delivery, as well as four salaried year-long internships. The visitor experience team has also grown, with 20 casual visitor experience roles and an additional 35 volunteers engaged.

Project elements

The initial site investigation revealed the ground conditions consisted of varying depths of made ground overlying Mudstone of the Mylor Slate formations, with intrusions of a hard igneous rock, known locally as Blue Elvan.

The Mudstone had a good allowable bearing pressure of 500kN/m², and was relatively straightforward to excavate using conventional breakers and excavators. However, the bedding planes in the Mudstone twist and dip in different directions. Where they dip towards the back of the site the rock is stable but where they dip towards the beach the rock becomes potentially unstable. A geologist was on site throughout the excavation to assess the stability of the face at each stage and to specify the number of rock anchors required to maintain stability. A combination of rock anchors, netting and sprayed concrete maintained the stability of the face and kept workers safe.

Along the eastern boundary the proximity of adjacent buildings meant that a series of Odex Piles were installed before excavation started, to ensure that there was no risk of ground movement. Additional rock anchors and walings were installed as excavation proceeded.

The Blue Elvan was much harder rock, unaffected by weathering, and very stable with an allowable bearing capacity of 5000kN/m². The Blue Elvan was extremely difficult to excavate by conventional methods, so difficult that the team considered using a variety of methods including dynamite, although the risks involved quickly ruled this out.

After trialling several different approaches, the most successful and productive proved to be the largest breaker machine the team could get into the excavation. Occasionally, the end of the pecker would become so hot it would catch on fire, and so whenever progress became impossible the team would pre-drill the Blue Elvan and fracture it using expanding grout. This approach was slow and time-consuming.

Reinforced concrete was the chosen material for the structure of the gallery due to its durability in the harsh maritime environment and its suitability for below ground structures. The concrete within the gallery has been left exposed for two reasons: to give the space a rugged feel reminiscent of the Cornish landscape; and to provide thermal mass which could help moderate fluctuations in ambient conditions within the gallery.

For the superstructure, a number of options were investigated for the structural form of the gallery roof. The flexibility offered by having a single column free space out-weighed any savings that came from having internal columns and the preferred solution was a simple ribbed concrete slab spanning the full width of the gallery.

The infill and extension were all in reinforced concrete and the new RC frame has columns which go down through the existing building to the existing footings. These columns support a new RC beam at 4th floor level and a large RC ring beam at eaves level which cantilevers out to support the roof above. The columns supporting the ring beam are set back to maximise the views meaning that the eaves level ring beam is working in torsion.