FLAC3D

This paper examines the impact of different pile configurations and geometric parameters on the bearing capacity and the settlement response of a combined pile–raft foundation system utilizing FLAC3D software. The configurations considered were: (1) uniform piles (denoted as CONF1), (2) shorter and longer piles uniformly distributed on the plan view of the raft (CONF2), (3) shorter piles at the center and longer piles at the edge of the raft (CONF3), and (4) longer piles at the center and shorter piles at the edge of the raft (CONF4). In the same framework, different pile diameters and raft stiffnesses were examined. The piles are considered to float in a cohesive–frictional soil mass, simulating the thick cohesive soil deposit found in Addis Abeba (Ethiopia). During simulation, a zero-thickness interface element was employed to incorporate the complex interaction between the soil elements and the structural elements. The analyses indicate that the configuration of piles has a considerable effect on both the bearing capacity and the settlement response of the foundation system. CONF1 and CONF3 improve the bearing capacity and exhibits a smaller average settlement than other configurations. However, CONF3 registers the highest differential settlement. On the other hand, the lowest differential settlement was achieved by the CONF4 configuration; the same configuration also gives ultimate load resistance comparable to those provided by either CONF1 or CONF3. The study also showed that applying zero-thickness interface elements to simulate the interaction between components of the foundation system is suitable for examining piled raft foundations problem.

Este tutorial explica las acciones necesarias para obtener rápidamente un primer modelo FLAC3D. Se dedica muy poco tiempo a explicar los distintos elementos de la interfaz de usuario que se utilizan. Más bien, la atención se centra en conseguir algo y proporcionar una familiaridad básica con la interfaz de usuario.

Underground excavations usually consist of different shapes, varying from circular shapes in tunnels to complex shapes in hydroelectric projects. The stress distribution around an underground opening and resulting deformations are important to analyze in order to assess the stability of the excavation and design a suitable support system. While circular shapes can be well analyzed through analytical solutions, complex shapes may need a three-dimensional numerical analysis. As the arrangement of different components of excavation becomes complex, the analysis of excavation becomes more demanding. For the design of shotcrete lining for tunnels and cavern arches, development of shotcrete strength and stiffness with time is a very crucial aspect which is seldom paid enough attention to. This paper presents an approach to address the age-dependent shotcrete behavior in convergence confinement method for circular tunnels and discusses its impact in the design of shotcrete lining. Further, this behavior is incorporated in a FLAC3D analysis carried out to assess the stability of the excavations for a hydroelectric project that includes two caverns, eight tunnels and four shafts with different sizes and arrangement. The geology in the area was classified in two groups with different behavioral types. Two different material models namely the classical Mohr-Coulomb model and strain softening ubiquitous model were used to simulate isotropic behavior of a relatively weak rock mass and anisotropic behavior of a schistose rock mass characterized by strongly pronounced discontinuities. 1. Introduction Shotcrete is an important support element for tunnels excavated in accordance with the New Austrian Tunneling Method (NATM). The design of primary shotcrete lining can be done using various approaches including analytical and numerical solutions. The state of stresses and strains prevailing in the shotcrete lining is a major factor in all approaches for assessing its stability and eventually the stability of the tunnel or other underground openings. While design of shotcrete lining is also based on structural mechanics, it differs from the design of structural members of a building. For example, unlike building foundations, the loads that the tunnel support should carry are not easy to determine and furthermore the ground-support interaction plays a critical role in determining the stress state in the support as well as in the ground. The interaction near the tunnel face is governed by the non-linear time-dependent material behavior of shotcrete and the time-dependent excavation process. Modeling the excavation advance and support installation near the face is essentially a 3D problem which can be analyzed through complex numerical models which may not always be economic in terms of computational time. In such cases, simple analytical methods can be used to understand how a rock mass surrounding a tunnel deforms and how the support systems act to control this deformation. This paper is an attempt to analyze the influence of age-dependent behavior of shotcrete on the rock-shotcrete interaction. This is done by introducing a pseudo-dynamic approach to the commonly used " Convergence confinement method ". Finally, this behavior is also incorporated in a three-dimensional numerical analysis for a complex underground excavation involving two caverns and many intersecting tunnels.

The use of slurry impoundments has traditionally been the primary method of disposal of fine waste slurry resulting from the recovery of fine coal from coal preparation plants. However, disposal of coal waste has become challenging with stringent regulations for surface disposal facilities. The process of backfilling of mine void space is called slurry backfilling. This method would eliminate environmental, health, and safety risks associated with the surface disposal facilities such as impoundment failure due to ground motion, subsidence, etc. Although slurry backfilling has significant advantages, it may raise some mine stability concerns. As the floor or pillars of the mine are exposed to moisture, they may soften and lose strength. In this study, the slurry backfilling effect on stability of two Illinois underground coal mines is investigated. The mine floor consists of non-durable claystone material with various thicknesses. The geotechnical and geological information of the mine will be analyzed. The stability of these mines will be evaluated using empirical and numerical methods considering the softening of floor beds and pillars with slurry.