Interaction between a large-scale triangular excavation and adjacent structures in Shanghai soft clay. (August 2015)

• Record Type: Journal Article
• Authors: Shi, Jiangwei; Liu, Guobin; Huang, Pei; Ng, C.W.W.
• Is Part Of: Tunnelling and underground space technology. Volume 50(2015)
• Page Start: 282
• Page End: 295
• Publication Date: 2015-08
• Subjects: Large-scale triangular basement excavation -- Column movement -- Wall movement -- Tunnel movement Pipeline settlement; Tunneling -- Periodicals; Underground construction -- Periodicals; Tunnels -- Periodicals; Underground areas -- Periodicals; 624.193
• DOI: 10.1016/j.tust.2015.07.013
• Languages: English
• ISSNs: 0886-7798

Abstract

Highlights: Deformation characteristics of a large-scale triangular basement are studied. Triangular excavation causes substantial lateral movement at the top of wall. Heave is induced in cut-and-cover tunnel located within excavation zone. Shield tunnel located outside basement experiences settlement during excavation. Long-term pipeline settlement increases by 120%. Abstract: Despite much attention being paid to the performance of rectangular basement excavation, the deformation characteristics of triangular excavations and their effects on nearby structures are not fully studied. A large-scale triangular basement with a final excavation depth of 22.8 m excavated at two sides of a cut-and-cover tunnel was extensively instrumented in Shanghai soft clay. Differing from the wall deflection in rectangular excavations, the lateral movements at the top of retaining walls in a triangular excavation was up to 70% of the maximum wall defection even though the first concrete props were cast before commencement of the main excavation. Upon completion of the base slabs, the maximum lateral wall deflection ( δ hm ) ranged from 0.05% H to 0.35% H (excavation depth). During subsequent construction of remaining concrete slabs, δ hm increased by up to 50%. Prior to completion of the base slabs, heaves were induced in interior column and diaphragm wall resulting from excavation-induced stress relief. Measured maximum heaves in the interior column and diaphragm wall were 0.08% H and 0.06% H, respectively. Different deformation mechanisms were observed in the cut-and-cover tunnel and shield tunnel. Heave was induced in the cut-and-cover tunnel located within excavation zone with a maximum value of 7.9 mm. On the contrary, settlement was observed in the shield tunnel located outside of excavation zone with a maximum value of 8.0 mm. Because of corner effects in basement excavation, three-dimensional deformation mechanisms were observed in the existing pipelines running parallel and behind the retaining walls. Due to post-excavation wall deflection induced ground settlement, the incremental maximum pipeline settlement was up to 120% of that upon completion of the base slabs.