Abstract
Excavation beneath existing buildings may cause the superstructure to tilt and crack, which seriously affects the normal use of the superstructure. Due to the new working conditions of excavation beneath existing buildings, related case reports are rare and limited. In the case of No. 3 section basement construction project of Ganshuixiang, we monitored the excavation construction by burying test instruments at the designated location. Afterwards, Plaxis 3D finite element software was used to establish an underpinning pile‐cap‐excavation model, which can analyze the influence of different pile cutting sequences on the bearing behavior of new basement structural pillars. By comparing the in situ measurement data with the finite element model, it can be concluded that when the excavation depth rises, the axial force of the underpinning pile gradually increases, and the pile skin friction is slowly exerted from top to bottom. Different cutting sequences will influence the bearing behavior of the structural pillar. Moreover, the pile cutting process also significantly impacts its bearing behavior and the settlement behavior of the superstructure. Compared with the clockwise pile cutting sequence, the symmetrical pile cutting is more advantageous. In the whole process of the storey adding and reconstruction, the superstructure settlement is related to the working condition of digging and adding layers. In the stage from soil excavation to the concrete curing period of the structural pillar, it increases slowly with time and tends to be stable in the concrete curing period. However, in the pile cutting stage, the superstructure settlement increases sharply, and after pile cutting, it becomes stable.
Highlights
With the booming economy and urbanization, the size of cities continues to expand
Afterwards, a 3D solid model of 7C cap-underpinning pileexcavation was established through Plaxis 3D finite element software, which can simulate the influence of different pile cutting sequences on the structural pillar’s bearing properties
Due to the rare cases of similar excavation, the influences of soil excavation on the bearing behaviors of the underpinning pile and superstructure, and the influence of the pile cutting process on the bearing capacity of the structural pillar, have not been clarified. erefore, in No 3 section basement construction project of Ganshuixiang, the vibrating wire rebar strain gauge was welded beside the steel pipe underpinning pile at 7C, 7D, and 13D caps and the middle position of the new basement structural pillar, respectively
Summary
With the booming economy and urbanization, the size of cities continues to expand. In this process, some “urban diseases” begin to emerge, such as traffic jams and parking issues. e development of cities is limited by land resources, but high-rise development will only increase the density of buildings and reduce their ability to resist catastrophes. Shan et al [10] considered the complex pile-pile and pile-soil interactions between group foundation piles and used this method to study its effect on the pile top settlement performance of group foundation piles In those projects based on soft soil areas in Hangzhou, a softening phenomenon might be triggered by the skin friction of the pile with the rise of excavation depth [11]. In projects of excavation beneath existing buildings, the soil excavation will increase the free length of the foundation pile It may cause buckling instability there and lead to catastrophic consequences. Afterwards, a 3D solid model of 7C cap-underpinning pileexcavation was established through Plaxis 3D finite element software, which can simulate the influence of different pile cutting sequences on the structural pillar’s bearing properties
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