Design and Performance of Excavations and Tunnels in Soft Clay

This paper presents the results of analyses on the behavior of in situ walls, using the measured data collected from various deep excavation sites with multilayered ground conditions of soils overlying rock in Korea. A variety of in situ wall systems from >60 excavation sites were considered, covering a wide range of wall types, including H-pile, soil cement, cast-in-place pile, and diaphragm. The measured data were thoroughly analyzed to investigate the effects of wall and support types on lateral wall movements as well as apparent earth pressures. A series of 2D finite-element analyses were also performed to provide insights regarding the in situ wall behavior. Based on the results, lateral wall movements and apparent earth pressures are related to primary influencing factors affecting the wall behavior and information is presented in forms to provide tools that can be used for design and analysis.

Behavior of Braced and Anchored Walls in Soils Overlying Rock

This paper reports the limitation of the conventional Bishop's simplified method to calculate the safety factor of slopes stabilized with anchors, and proposes a new approach to considering the reinforcing effect of anchors on the safety factor. The reinforcing effect of anchors can be explained using an additional shearing resistance on the slip surface. A three-dimensional shear strength reduction finite element method (SSRFEM), where soil–anchor interactions were simulated by three-dimensional zero-thickness elasto-plastic interface elements, was used to calculate the safety factor of slopes stabilized with anchors to verify the reinforcing mechanism of anchors. The results of SSRFEM were compared with those of the conventional and proposed approaches for Bishop's simplified method for various orientations, positions, and spacings of anchors, and shear strengths of soil–grouted body interfaces. For the safety factor, the proposed approach compared better with SSRFEM than the conventional approach. The additional shearing resistance can explain the influence of the orientation, position, and spacing of anchors, and the shear strength of soil–grouted body interfaces on the safety factor of slopes stabilized with anchors. Copyright © 2003 John Wiley & Sons, Ltd.

Reinforcing mechanism of anchors in slopes: a numerical comparison of results of LEM and FEM

Numerical models are commonly used to estimate excavation-induced ground movements. Two-dimensional (2D) plain strain assumption is typically used for the simulation of deep excavations which might not be suitable for excavations where three-dimensional (3D) effects dominate the ground response. This paper adapts an inverse analysis algorithm to learn soil behavior from field measurements using a 3D model representation of an excavation. The paper describes numerical issues related to this development including the generation of the 3D model mesh from laser scan images of the excavation. The inverse analysis to extract the soil behavior in 3D is presented. The model captures the measured wall deflections. Although settlements were not sufficiently measured, the predicted settlements around the excavation site reflected strong 3D effects and were consistent with empirical correlations. Copyright © 2010 John Wiley & Sons, Ltd.

Three-dimensional inverse analyses of a deep excavation in Chicago clays

Ground anchor and soil nail retaining systems are designed to stabilize and support natural and engineered structures and to restrain their movement using tension-resisting elements. The basic design concept consists of transferring the resisting tensile forces generated in the inclusions into the ground through the friction (or adhesion) mobilized at the interfaces. These systems allow the engineer to efficiently use the in-situ ground in providing vertical or lateral structural support. They present significant technical advantages over conventional rigid gravity retaining walls or external bracing systems that result in substantial cost savings and reduced construction period. Therefore, during the past few decades, ground anchors, and more recently soil nails, have been increasingly used in civil engineering projects.

Ground anchors and soil nails in retaining structures

Parametric finite element studies are described that illustrate the relative performances of braced and tied-back wall systems. Key factors in the different performances of the two systems are isolated and the degree of their influence demonstrated. Circumstances are shown where tied-back wall systems perform better than braced wall systems and vice versa. Additionally, the influence of prestress load, wall stiffness, tie-back stiffness, excavation depth, and tie-back spacing on tied-back wall performance are investigated. By judicious choice of these parameters it is shown that the designer can significantly reduce wall movements and soil settlements.

Yuet Tsui

Papers

Performance of Tied-Back Walls in Clay

Plane Strain Approximations in Finite Element Analyses of Temporary Walls

Closure to “Performance of Tied-Back Walls in Clay”