A tunnel boring machine (TBM) retrieval shaft was constructed in porous limestone using deep soil mixing (DSM) in Miami, Florida. The retrieval shaft had an inner diameter of 28 ft (8.5 m) and extended to a depth of 87 ft (26.4 m). A 15 ft (4.6 m) thick base plug was constructed to resist the uplift forces at the bottom of the shaft. The design of the shaft was carried out using a three dimensional finite element model. The expected stresses in the soil cement mix shaft walls were initially estimated using analytical closed form solutions. The design was later refined by simulating the construction sequence in a finite element model including staged excavation, back-fill, and tunnel break-in. Quality control tests for unconfined compressive strength and tensile strength were obtained during installation of production DSM columns. The retrieval shaft was instrumented using inclinometers and settlements points during construction to monitor the deformations.
展开▼
