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This study investigates the effect of dewatering on wall deformations of deep excavations through numerical analyses. A hydro-mechanical coupled method is proposed for deep excavations with dewatering activity. The groundwater flow and soil consolidation are described by Darcy’s law and Biot consolidation theory, respectively. The coupled method is...
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Citations
... Additionally, the coupling of the seepage field and stress field during dewatering is rather complicated. Thus far, its mechanism and effect on the stability and deformation behavior of the deep excavation have not been well understood [26][27][28]. Thus, the safety risk of deep excavations in water-rich areas is extremely severe compared to that in arid areas. ...
Deep excavations play an important role in the construction of urban infrastructures such as metro stations and high-rise buildings [...]
... The geology is significantly affected by groundwater seepage and subsequent soil consolidation. Dewatering behaviors are applied to ensure the stability of deep excavations conducted above confined aquifers (Bevan et al., 2010;Lyu et al., 2021;Peng et al., 2022). Although deep-buried sealing curtains have been widely used to reduce the impact of dewatering and unloading (Pujades et al., 2014;Shen et al., 2017;Li et al., 2020;Zeng et al., 2022;Chen et al., 2022), groundwater seepage is unavoidable due to a series of reasons, such as leakage in aquitards and thick aquifers (Puller, 1994;Pujades et al., 2016;Wu et al., 2020;Zeng et al., 2022;Zheng et al., 2022). ...
... Therefore, the parameters of the HS-Small Wang et al., 2013). Notably, the availability of the set of input parameters has been verified by Peng et al. (2022), which illustrates the detailed selection method. Moreover, the following three case studies further confirmed the availability of the set of input parameters and the numerical model. ...
... Other mechanical and hydraulic boundary conditions were identical to the representative model. More detailed information with respect to the construction processes can be found in Zhu et al. (2015) and Peng et al. (2022). ...
... Excavation usually adopts the dewatering scheme which pumps groundwater inside the foundation pit to work in dry conditions [17][18][19][20]. This process can improve the safety of the foundation pit and increase stability of the soil around it, preventing flowing stand, piping effect and other related accident from happening. ...
The dewatering of foundation pits with a suspended waterproof curtain causes different groundwater drawdowns inside and outside the pit, resulting in the drawdown difference between the inside and outside the pit. Maintaining a groundwater drawdown difference between the inside and outside of a foundation pit can eliminate the adverse effects of dewatering on the surrounding environment. According to previous studies on unsteady flow, an analytical solution of the groundwater drawdown with a suspended waterproof curtain under unsteady flow has been proposed. The analytical solution of unsteady flow and the formula of groundwater drawdown difference with a suspended waterproof curtain were validated by comparing pumping tests and finite-element method (FEM), in which a good agreement was observed. The magnitude of the drawdown difference generally represents the extent of surrounding groundwater affected by groundwater drawdown inside the pit. This paper also investigated the effects of sensitivity parameters on the drawdown difference for minimizing the effect of surrounding environment. During the process of dewatering with a suspended waterproof curtain, the groundwater drawdown (Sh) should not exceed the length of the waterproof curtain (L), and the optimal radius of foundation pit (Rw) and length of waterproof curtain (L) were found, i.e., Rw/H0 = 0.781 and L/H0 = 0.813 (H0 is 32 m). Beyond these values, the drawdown difference tends to be stable. The drawdown difference is also significantly affected by the dewatering time. When t < 48 h, the groundwater drawdown difference decreases rapidly; when t > 48 h, the groundwater drawdown difference stabilizes.
... Therefore, the composite retaining wall using the ground-freezing method could significantly reduce the lateral wall deflection and ensure the safety of construction. In general, the composite retaining wall played an important role in controlling the lateral deflection and the deformation characteristic was greatly different from the behaviors of the conventional diaphragm wall (Ou et al., 1998;Peng et al., 2022;Poh and Wong, 2001;Sizkow and El Shamy, 2021). ...
A novel composite retaining system that combines artificial ground freezing (AGF) and diaphragm walls for a real construction project is presented in this work. In this project, a deep excavation was conducted above a tunnel with a minimum clearance of 0.8 m between the final excavation surface and the tunnel crown. The diaphragm walls were constructed as retaining walls. However, the existence of the underlying tunnel impedes the integrality of the diaphragm walls around the tunnel and causes the problems of poor reinforcement and unblocked seepage paths. To address this conflict, several freezing pipes were drilled and installed outside the diaphragm wall to form a large-scale frozen curtain. Through the composite retaining wall, the generation of the dual effect of ground reinforcement and waterproof sealing was also accomplished. Field measurements were conducted to investigate the performance of the excavation including temperature distributions, deformation variations, and pore-water pressure developments. From the acquired field data, it was revealed that a 7 m-width × 3 m-thickness frozen wall was formed for the subsequent excavation and the vertical displacement of the underlying tunnel was controlled at a distance of 9.3 mm to guarantee the safe operation. On top of that, during the AGF construction, the composite retaining wall met the requirements of high strength and stiffness, as well as practically zero permeability. From this case study, it is demonstrated that the proposed construction technology possesses comparative advantages in resolving the conflict between the adjacent excavation and the existing tunnels for controlling the excavation-induced deformation and decreasing the construction risk.
... The model parameters of soil layers involved are summarized in Table 2. Additionally, a set of specific parameters (i.e., normal stiffness of EA = 2.40 Â 10 7 kN/m, the bending stiffness of EI = 1.28 Â 10 6 kNÁm 2 /m, and the thickness of 0.8 m) were defined for the diaphragm walls (Peng et al., 2022). Seven horizontal struts with compression stiffness of EA = 1.68 Â 10 7 kN and horizontal spacing distance of 5 m were installed in the PIP excavation . ...
... Soil parameters used in FELA(Peng et al., 2022). Poisson's ratio in unloading/reloading at reference pressure d Secant Young's modulus in triaxial compression under confining pressure E ref Young's modulus in unloading/reloading at reference pressure E ref ...
Pit-in-pit (PIP) excavations in an aquifer-aquitard system may be subjected to
catastrophic failures under hydraulic uplift, whilst the associated undrained stability
problem was not well analyzed in the past. To this end, a hypothetical model
of PIP braced excavation in typical soil layers of Shanghai, China is developed using
finite element limit analysis (FELA). The FELA solutions of safety factors (FS) against
hydraulic uplift are verified with the results from the finite element analysis with strength
reduction technique (SRFEA) and existing design approaches. Subsequently, FELA is
employed to identify the triggering and failure mechanisms of PIP braced excavations
subjected to hydraulic uplift. A series of parametric studies considering the various
geometric configurations of the PIP system, undrained shear strengths of aquitard, and
artesian pressures are carried out. The sensitivities of relevant design parameters are
further assessed using a multivariate adaptive regression splines (MARS) model that is
capable of accurately capturing the nonlinear relationships between a set of input
variables and output variables in multi-dimensions. A MARS-based design equation
used for predicting FS is finally presented using the artificial dataset from FELA for
practical design uses.
... Fourth, methods for determining and calibrating parameters of soil creep models need to be further studied and extended considering the accuracy of results and the convenience of application. Finally, the coupling between soil creep and soil consolidation in a deep braced excavation requires further exploration through field observations, experiments, and hydro-mechanical coupled numerical simulations recently reported by Peng et al. [52]. ...
This paper describes recent advances in the effect of soil creep on the time-dependent deformation of deep braced excavation. The effect of soil creep is generally investigated using the observational method and the plain-strain numerical simulation method. The observational method is more applicable for deep braced excavations in soft clays constructed using the top-down method. The plain-strain numerical simulation method can be conveniently used for parametric analysis, but it is unable to capture the spatial characteristics of soil creep effect on lateral wall deflections and ground movements. The additional lateral wall deflections and ground movements that are generated due to the soil creep effect can account for as large as 30% of the total displacements, which highlights the importance of considering the effect of soil creep in deep braced excavations through soft clays. The magnitude of the displacements due to soil creep depends on various factors, such as excavation depth, elapsed period, unsupported length, and strut stiffness. Parametric analyses have indicated several effective measures that can be taken in practice to mitigate the detrimental effect of soil creep on the deformation of deep braced excavation. Based on the literature review, potential directions of the related future research work are discussed. This paper should be beneficial for both researchers and engineers focusing on mitigating the adverse effect of soil creep on the stability of deep braced excavations.
