Reliability assessment for serviceability limit states of stiffened deep cement mixing column-supported embankments

The reliability and deterministic analyses of wood-cored stiffened deep cement mixing and deep cement mixing column-supported embankments(referred to as WSCSE and DCSE,respectively)considering serviceability limit state requirements are presented in this paper.Random field theory was used to simulate the spatial variability of soil
cement mixing(SCM)material in which the adaptive Kriging Monte Carlo simulation was adopted to estimate the failure probability of a column
supported embankment(CSE)system.A new method for stochastically generating random values of unconfined compressive strength(qu)and the ratio(Ru)between the undrained elastic modulus and qu of SCM material based on statistical correlation data is proposed.Reliability performance of CSEs concerning changes in the mean(μ),coefficient of variation(CoV),and vertical spatial correlation length(θv)of qu and Ru are presented and discussed.The obtained results indicate that WSCSE can provide a significantly higher reliability level and can tolerate more SCM material spatial variability than DCSE.Some performance of DCSE and WSCSE,which can be considered satisfactory in a deterministic framework,cannot guarantee an acceptable reliability level from a probabilistic viewpoint.This highlights the importance and necessity of employing reliability analyses for the design of CSEs.Moreover,consideration of only μ and CoV of qu seems to be sufficient for reliability analysis of WSCSE while for DCSE,uncertainties regarding the Ru(i.e.both μ and CoV)and θv of qu cannot be ignored.

Improved prediction of pile bending moment and deflection due to adjacent braced excavation

Deep excavations in dense urban areas have caused damage to nearby existing structures in numerous past construction cases.Proper assessment is crucial in the initial design stages.This study develops equations to predict the existing pile bending moment and deflection produced by adjacent braced excavations.Influential parameters(i.e.,the excavation geometry,diaphragm wall thickness,pile geometry,strength and small-strain stiffness of the soil,and soft clay thickness)were considered and employed in the developed equations.It is practically unfeasible to obtain measurement data;hence,artificial data for the bending moment and deflection of existing piles were produced from well-calibrated numerical analyses of hypothetical cases,using the three-dimensional finite element method.The developed equations were established through a multiple linear regression analysis of the artificial data,using the transformation technique.In addition,the three-dimensional nature of the excavation work was characterized by considering the excavation corner effect,using the plane strain ratio parameter.The estimation results of the developed equations can provide satisfactory pile bending moment and deflection data and are more accurate than those found in previous studies.

Numerical investigation on the responses of existing single piles due to adjacent twin tunneling considering the lagging distance

This paper presents an assessment of the influence of the lagging distance between two horizontal tunnel faces of the side-by-side twin tunnels on the responses of the adjacent existing single pile by a series of three-dimensional numerical analyses.Two different relative positions between the pile tip and the tunnel are considered to cover the short and long pile behaviors.The responses of the existing pile in terms of pile head settlement,axial force,lateral movement and bending moment are considered and discussed.The numerical results indicate that the lagging distance between twin tunnel faces significantly affects not only the soil movements but also the responses of the existing single pile.The critical case that produces unsatisfactory pile responses due to twin tunneling is when the lagging distance between the second tunnel and the preceding tunnel equals to the shield length.It is recommended that the lagging distance be not less than three times of shield length when the two tunnels need to be concurrently excavated.

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.