Abstract:  In practice, dewatering for pressure relief is commonly undertaken during ongoing excavation to secure
bottom stability against basal upheaval. Simultaneously, through unloading, wall deflection is obviously observed.
Noticing that both cause soil deformations, this research is to study the effect of wall deformation on dewateringinduced
settlement. A coupled numerical analysis of finite-difference software is employed to model Shanghai
soft soils under multi-aquifer-aquitard systems (MAASs) by analyzing the results in association with an empirical
approach. Consequently, through gradual force reduction, shear strength at soil-wall interface is significantly
diminished. As wall deformation increases instantaneously upon lower loading, wall surface becomes deformedly
bending; this condition causes the challenge to workability of shear strength. Moreover, wall deformation caused
by unloading affects dewatering-induced settlement substantially. Under smaller loading, large wall deflection
is observed; soil plane of failure caused by both sliding and compression occurs along slip curve, with weaker
shear-strength soils at r_D = 0.4 and stronger shear-strength soils between r_D = 0.4 and r_D = 0.65, where r_D is the
distance from the wall that is normalized by the depth measured from ground surface. During dewatering, stronger
soils tend to drag weaker soils upward to reduce large differential settlements caused by additional compression.
Consequently, settlement becomes larger at r_D = 0.4 and smaller at r_D = 0.65. Remarkably, at r_D > 2.3,
both settlement curves that result from numerical analysis and empirical method show overlapping; this indicates
that the unloading effect on dewatering-induced settlement at r_D > 2.3 is insignificant. Furthermore, as wall
reaches maximum allowable wall deflection by 67% applied force, additional compression caused by dewatering
after loading remains smaller than that under 70% applied force, contributing to smaller dewatering-induced
settlement.

Key words: dewatering| wall deformation| confined aquifer| groundwater| ground surface settlement

摘要：   In practice, dewatering for pressure relief is commonly undertaken during ongoing excavation to secure
bottom stability against basal upheaval. Simultaneously, through unloading, wall deflection is obviously observed.
Noticing that both cause soil deformations, this research is to study the effect of wall deformation on dewateringinduced
settlement. A coupled numerical analysis of finite-difference software is employed to model Shanghai
soft soils under multi-aquifer-aquitard systems (MAASs) by analyzing the results in association with an empirical
approach. Consequently, through gradual force reduction, shear strength at soil-wall interface is significantly
diminished. As wall deformation increases instantaneously upon lower loading, wall surface becomes deformedly
bending; this condition causes the challenge to workability of shear strength. Moreover, wall deformation caused
by unloading affects dewatering-induced settlement substantially. Under smaller loading, large wall deflection
is observed; soil plane of failure caused by both sliding and compression occurs along slip curve, with weaker
shear-strength soils at r_D = 0.4 and stronger shear-strength soils between r_D = 0.4 and r_D = 0.65, where r_D is the
distance from the wall that is normalized by the depth measured from ground surface. During dewatering, stronger
soils tend to drag weaker soils upward to reduce large differential settlements caused by additional compression.
Consequently, settlement becomes larger at r_D = 0.4 and smaller at r_D = 0.65. Remarkably, at r_D > 2.3,
both settlement curves that result from numerical analysis and empirical method show overlapping; this indicates
that the unloading effect on dewatering-induced settlement at r_D > 2.3 is insignificant. Furthermore, as wall
reaches maximum allowable wall deflection by 67% applied force, additional compression caused by dewatering
after loading remains smaller than that under 70% applied force, contributing to smaller dewatering-induced
settlement.

关键词: dewatering| wall deformation| confined aquifer| groundwater| ground surface settlement