Displaying Items By Tag: Stability

The paper describes five different dike failures that occurred in recent decades. The case histories were located on different rivers and involved different loading conditions. The observed failure mechanisms involved erosion and stability problems. The types of erosion observed were both internal erosion due to extreme groundwater flow and external erosion caused by the river flow and wave action. The case involving instability was caused by uplift, i.e., increased hydraulic head led to a sharp reduction in maximum shear strength between subsoil layers. Two cases demonstrate the importance of dike management and maintenance. Despite the variations in the loading conditions and failure mechanisms, all the cases show that the strength of a dike depends not only on the material used to build the dike but also on the strength of the subsoil.

A 30-m long railroad embankment failure that occurred on May 25 2011 in the city of Ann Arbor, Michigan, is presented. Emphasis is given on the field observations of the failure, the characterization of the site conditions and the seepage and slope stability analyses, all of which represent important components of the training and practice of a geotechnical engineer. The failure occurred following a record wet season that resulted in ponding water against the embankment and high enough water pressures and exit gradients that resulted in instability of the railroad embankment. Detailed background material and the methodology for using the case history in geotechnical engineering education are presented.

This work, carried out by members of the University of Parma’s Department of Civil and Environmental Engineering and Architecture, analyzes the stability of the ancient underground quarries at Viggiù (Varese,Italy). The objective of the study was to verify the actual structural predisposition to instability phenomena in the ancient ornamental stone quarries for a historical and cultural valorization as well as the recovery of the Danzi and Beltrami quarries. Although completely abandoned, these sites could be used as a tourist attraction and/or as a teaching environment. They are a wonderful example of industrial architecture, presenting audacious compositions of filled-in trenches and room and pillar techniques (Hedley and Grant, 1972). With such objectives in mind, a monitoring system that aims to control the most significant joints and discontinuities of the site has been realized. A numerical model of the entire rock mass has been developed in order to analyze the stability of the underground openings. A route for visitors has also been identified.

Pillar stability is one of important aspects for underground mines. Generally, the stability of the pillars is evaluated empirically based on case studies and site-specific rock mass conditions in mines. Nevertheless the empirical approach applicability can sometimes be constrained. The numerical-based approaches are potentially more useful as parametric studies can be undertaken and, if calibrated, can be more representative. Both empirical and numerical approaches are dependent on the strength evaluation of the pillars while the strain developing in the pillars is seldom taken into consideration. In this paper, gypsum and sandstone samples were tested in laboratory with different width-to-height ratios (W/H) to adapt the strain evaluation method to the laboratory-based pillars. A correlation was then developed between the strain and the width-to-height ratio for pillar monitoring purposes. Based on the results, a flowchart was created to conduct back analysis for the existing pillars to evaluate their stability and design new pillars, considering the strain analysis of the existing pillars with the W/H ratios modelled.

Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels Himachal Pradesh, India) are taken for in-depth analysis of the stability of to asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and in-equidimensional noncircular tunnel.