Stability of long trench in soft soils by bentonite-water slurry

A series of centrifuge model tests exploring the effects of different types of slurry on long-trench stability in soft clay were conducted. The influence of groundwater conditions relative to trench stability was examined by constructing long trenches using different slurries. The soil deformation and surface settlement induced by the excavation of the trench are found to be closely related to slurry type and excavation depth of the long trench. Increasing the bentonite concentration of the slurry has beneficial effects on stability: 1) larger particles can improve local and global stability in cases where filter cakes do not form, and 2) larger viscosity can promote filter cake formation on the walls of long trenches excavated in soft clay and enhance their stability.

2D and 3D stability analysis of slurry trench in frictional/cohesive soil

A 2D and 3D kinematically admissible rotational failure mechanism is presented for homogeneous slurry trenches in frictional/cohesive soils.Analytical approaches are derived to obtain the upper bounds on slurry trench stability in the strict framework of limit analysis.It is shown that the factor of safety from a 3D analysis will be greater than that from a 2D analysis.Compared with the limit equilibrium method,the limit analysis method yields an unconservative estimate on the safety factors.A set of examples are presented in a wide range of parameters for 2D and 3D homogeneous slurry trenches.The factor of safety increases with increasing slurry and soil bulk density ratio,cohesion,friction angle,and with decreasing slurry level depth and trench depth ratio,trench width and depth ratio.It is convenient to assess the safety for the homogeneous slurry trenches in practical applications.

Numerical Modeling of Ground Response during Diaphragm Wall Construction

Construction of diaphragm wall panels may cause considerable stress changes in heavily overconsol- idated soil deposits and can induce substantial ground movement. The 3D Lagrangian method was adopted to model the mechanical response of ground, including horizontal normal stress and shear stress, lateral ground displacement and vertical ground surface settlement, during the slurry trenching and concreting of diaphragm wall panels. Numerical results show that slurry trenching leads to horizontal stress relief of ground, reducing the horizontal stress of the ground from initial K0 pressure to hydrostatic betonite pressure. Wet concrete pressure lies between the hydrostatic bentonite pressure and the initial K0 pressure, so it can compensate partially the horizontal stress loss of the ground adjacent to the trench and thus reduce the lateral movement of the trench face as well as the vertical settlement of the ground surface.