Cut & cover retainer walls in quick clay using drilled, tubular piles
For the Strindheim highway tunnel in Trondheim city, Norway, a novel solution was developed for the retainer walls. The 4-lane tunnel entrance in the densely built-up city had to cross through soft and partly quick clay by a 300 m long cut & cover section. The challenge was to provide safe, 20 m deep open pit without draining nor disturbing the extremely “brittle” quick clay and save as much as possible of the neighbor buildings under heritage protection from having to be removed. The paper describes the challenges and the joint effort to develop the novel concept of interlocking, tubular sheet piles which were driven through soil and drilled further into the bedrock. This solution gave considerable advantages such as unusually stiff walls and transition into rock which is favorable for high pressure grouting. The properties of the surrounding quick clay as well as partly irregular rock surface and tricky leakage patterns gave particular challenges, for which solutions and risk limiting measures had to be decided during construction phase.