Soil Creep Effect on Time-Dependent Deformation of Deep Braced Excavation

Panpan Guo,Xunjian Hu,Lina Luo,Gang Lei,Xiaonan Gong,Haibo Hu,Yixian Wang,Baojian Li,Yonghong Wang

doi:10.1155/2022/5655592

Abstract

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.

Highlights

Deep braced excavations are ubiquitous in construction engineering such as subway stations [1,2,3], building basements [4,5,6], and launch shafts for shield tunneling machines [7, 8]
As the soil creep effect tends to be coupled with consolidation and/or relaxation, the existing analytical solutions for excavation-induced ground and wall responses have hardly taken account of the soil creep effect. erefore, the methods used for investigating the effects of soil creep on the timedependent performance of deep braced excavation mainly include the observational method and numerical simulation method. e numerical simulation method can be classified into finite element analysis and finite difference analysis, according to the numerical analysis software adopted such as PLAXIS, ABAQUS, and FLAC
By using FLAC with the build-in rate-dependent soil creep model, a parametric analysis was performed by Kung [32] to investigate the difference of the soil creep effect on the wall deflection between the top-down and bottom-up construction methods through four hypothetical deep excavation cases as illustrated in Figure 2. e four cases include one deep braced excavation constructed using the top-down method (TDM) and three deep braced excavations constructed using the bottom-up method (BUM). e final excavation depths for the four cases are identical with a magnitude of 19 m. e BUM cases consist of three types which are different in the cover depths of steel struts and excavated surfaces

Summary

Introduction

Deep braced excavations are ubiquitous in construction engineering such as subway stations [1,2,3], building basements [4,5,6], and launch shafts for shield tunneling machines [7, 8]. Based on the results of field observations in Shanghai soft clays, Liu et al [25] found that the time-dependent ground surface settlements occurring during a 60 days concrete curing period were attributed to the primary consolidation rather than creep effects. For a 13m-deep excavation in Chicago soft clay reported by Finno et al [26], 13 mm of the 38 mm of maximum lateral soil movement and 12 mm of the 40 mm of maximum ground surface settlement occurred as a result of soil creep and reduction of wall stiffness. From the studies mentioned above, it can be indicated that the opinions about the effect of soil creep on the time-dependent performance of deep braced excavation are divided. A review of this topic is necessary for deepening our understanding of the soil creep effect

Methods

Results

Discussion

Conclusion