Deterministic and probabilistic analysis of great-depth braced excavations:A 32 m excavation case study in Paris

The Fort d’Issy-Vanves-Clamart(FIVC)braced excavation in France is analyzed to provide insights into the geotechnical serviceability assessment of excavations at great depth within deterministic and probabilistic frameworks.The FIVC excavation is excavated at 32 m below the ground surface in Parisian sedimentary basin and a plane-strain finite element analysis is implemented to examine the wall deflections and ground surface settlements.A stochastic finite element method based on the polynomial chaos Kriging metamodel(MSFEM)is then proposed for the probabilistic analyses.Comparisons with field measurements and former studies are carried out.Several academic cases are then conducted to investigate the great-depth excavation stability regarding the maximum horizontal wall deflection and maximum ground surface settlement.The results indicate that the proposed MSFEM is effective for probabilistic analyses and can provide useful insights for the excavation design and construction.A sensitivity analysis for seven considered random parameters is then implemented.The soil friction angle at the excavation bottom layer is the most significant one for design.The soil-wall interaction effects on the excavation stability are also given.

主动学习型克里金模型在掌子面可靠度分析中的应用——以双层土隧道为例（英文）

本文旨在研究双层土壤中隧道开挖时掌子面的稳定性问题。首先,假设双层土壤的分界面位于隧道拱顶上方,以极限分析方法为依据,采用旋转破坏机制构建掌子面失稳模型,同时,考虑了开挖介质的剪切强度参数随机性对掌子面稳定性的影响。采用克里金模型代替其原始的功能函数,进而采用蒙特卡洛法计算掌子面的破坏概率,从而大大提高了计算效率和节约了计算成本。本文采用主动学习函数对克里金模型进行训练,因此,可以确保其对掌子面破坏概率的预测高效而不失准确性。本文首先建立了隧道掌子面破坏模型,通过计算分析,验证了所提出模型的正确性,随后讨论了随机变量的初始采样点数、相关系数、分布类型和变异系数等对隧道掌子面稳定性的影响。研究结果表明该方法是一种高效精确的可靠度分析方法,可以为隧道设计提供一定的理论指导和依据。

Effect of surcharge loading on horseshoe-shaped tunnels excavated in saturated soft rocks

Underground facilities are usually constructed under existing buildings,or buildings are constructed over existing underground structures.It is then imperative to account for the current overburden loads and future surface loadings in the design of tunnels.In addition,tunnels are often constructed beneath the groundwater level,such as cross-river tunnels.Therefore,it is also important to consider the water pressure impact on the tunnel lining behaviour.Tunnels excavated by a conventional tunnelling method are considered in this paper.The hyperstatic reaction method(HRM)is adopted in this study to investigate the effect of surcharge loading on a horseshoe-shaped tunnel behaviour excavated in saturated soft rocks.The results obtained from the HRM and numerical modelling are in good agreement.Parametric studies were then performed to show the effects of the water pressure,surcharge loading value and its width,and groundwater level on the behaviour of the horseshoe-shaped tunnel lining,in terms of internal forces and displacements.It displays that the bending moment,normal forces and radial displacements are more sensitive to the water pressure,surcharge loading and groundwater level.

Soil spatial variability impact on the behavior of a reinforced earth wall

This article presents the soil spatial variability effect on the performance of a reinforced earth wall.The serviceability limit state is considered in the analysis.Both cases of isotropic and anisotropic non-normal random fields are implemented for the soil properties.The K arhunen-Loeve expansion method is used for the discretization of the random field.Numerical finite difference models are considered as deterministic models.The Monte Carlo simulation technique is used to obtain the deformation response variability of the reinforced soil retaining wall.The influences of the spatial variability response of the geotechnical system in terms of horizontal facing displacement is presented and discussed.The results obtained show that the spatial variability has an important influence on the facing horizontal displacement as well as on the failure probability.

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing(TDM)pile-supported embankments over soft soils.The uncertainties of the mechanical properties of the in-situ soil,pile,and embankment,and the effect of the pile shape are considered simultaneously.The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging(using adaptive sampling algorithm).Individual and system failure probabilities,in terms of the differential and maximum settlements(serviceability limit state(SLS)requirements),are considered.The reliability results for the embankments supported by TDM piles,with various shapes,are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes.The influences of the inherent variabilities in the material properties(mean and coefficient of variation values)on the reliability of the piled embankments,are also investigated.This study shows that large TDM piles,particularly those with a shape factor of greater than 3,can enhance the reliability of the embankment in terms of SLS requirements,and even avoid unacceptable reliability levels caused by variability in the material properties.