Deformation Behavior of Deep Foundation Pit under Both Overloading and Unloading Conditions

Abstract

A deep foundation pit in a station of the Hangzhou subway is adjacent to new high-rise residential buildings on the north side and to the Evergrande foundation pit being excavated on the south side. This work considers the excavation of the foundation pit in the subway station as the research subject, focuses on the difference of the deformation and Earth pressure between the north side and the south side of the foundation pit under these special working conditions through the analysis of the measured data, and compares it with an ordinary foundation pit. Analyzing the measured data reveals that the horizontal displacement of the retaining wall and the ground settlement are far larger on the north side than on the south side, and both often exceed the deformation alarm value; the deformation of the ordinary foundation pit is between the deformation of the overloaded (north) side and that of the unloaded (south) side of the foundation pit. Moreover, the maximum rate of the horizontal creep of the soil and the maximum rate of the creep caused by the ground settlement on the north side of the foundation pit are larger than those on the south side of the foundation pit; the maximum rate of the horizontal creep of the ordinary foundation pit is between the two. The active Earth pressure on the pit wall on the north side is higher than that on the south side of the foundation pit, and because of the surrounding unloading, passive Earth pressure is generated at the bottom of the pit wall on the south side of the foundation pit, which causes it to shift to the outside of the foundation pit. The settlement of the surrounding high-rise buildings and the settlement of the columns are all within the range of the alarm values; also, the buildings settle evenly. Due to the excavation and unloading on the south side of the foundation pit, the uplift of the columns is not considerable.

Deformation Characteristics of the Foundation Pit of the Underpass Viaduct and Grey Relational Analysis of the Maximum Horizontal Deflection of the Retaining Wall

“…e surface settlement had a typical concave profile, which corresponded to the type shown in Figure 1(b); and δ vm mainly occurred between 0.25 H e and 0.87 H e behind the wall. e measured δ vm values ranged between δ vm � 0.02% H e and δ vm � 0.13% H e , which were smaller than that those reported in the literature [6,7,10,36]. When x/H e � 0.48, δ vm increased and reached the maximum value in the region where 0 ≤ x/H e ≤ 0.48 and gradually decreased in the region where 0.48 ≤ x/H e ≤ 1.9.…”

“…(4) In stage 4, the second support was activated at −6.66 m. (5) In stage 5, excavation to the base −12.5 m was conducted; each layer did not exceed 3 m; and the excavation was completed in two layers. (6) In stage 6, the concrete floor was activated, and the excavation was completed.…”

“…To explore the deformation characteristics of excavations and adjacent facilities, previous researchers used theoretical analysis to analyze the deformation characteristics of supporting structures during foundation pit excavation [2,3]. As data measured in the eld can re ect actual deformation during projects, researchers used large amounts of data to analyze the deformation characteristics of supporting structures and environments caused by excavation and dewatering processes [4][5][6][7][8]. ese eld data are extremely valuable and can be used to calibrate numerical simulations of similar projects in the future.…”

Deformation and Strength Characteristics of Structured Clay under Different Stress Paths

“…Ng et al [2] described the stress paths in the soil units around the pit walls in deep foundation-pit excavation, compared and examined the eld stress paths with the laboratory stress path tests, and proposed that the mechanical behavior of many soils such as sti clay depends on their e ective-stress and stress history. Much research [3][4][5][6][7][8][9][10][11][12][13][14][15] has shown that the mechanical properties of the rocksoil body are very complex, with characteristics of nonlinearity, elastoplasticity, shear dilation, and anisotropy; the mechanical properties and failure modes not only depend on the current and nal stress state of the rock-soil body, but also are closely related to the stress history, subsequent loading direction, and the rock-soil body types; the rock-soil body may show di erent mechanical properties under different stress paths.…”