Measured characteristics of a deep soft soil excavation in complex environment

The monitoring data of a 17.4 m~19.8 m-deep multi-strutted soft clay excavation built on hard shell layer soft soil foundation in Hangzhou is analyzed. The deep excavation is supported by a concrete diaphragm wall and multi-storey reinforced concrete brace. The monitoring includes soil and wall deflections, surface and subsurface ground settlements, axial forces of concrete struts. This study shows that the maximum horizontal displacements are 0.24%H_m~0.75%H_m, in which H_m is the total excavation depth. The maximum horizontal displacement is larger than 100 mm, in which the proportions of creep deformation reach up to 44%~56%. The horizontal creep rates are in 0.15~0.76 mm/d and closely related with the excavation depth and the properties of the soils near the base. The technology of T-diaphragm wall and partition wall can reduce the horizontal displacement of the excavation to some extent. The distribution of the lateral settlement is in a parabolic shape and the longitudinal settlement is in a saddle shape. The maximum settlements are 0.26%H_m ~0.7%H_m and the settlement rates are 0.1~0.6 mm/d. The relationship between the maximum settlements is between and 2.57, in which is the maximum horizontal displacement. The axial forces of the struts change dynamically during the excavation and construction or removal of the adjacent braces.