Blog

Fragility Analysis Presentation

Nov 29,20

We are pleased to announce that Dr. Zamiran will present a lecture in fragility and earthquake analysis of retaining walls at the 5th Annual Live Streaming Web Conference of Geo-Institute. In this investigation, the seismic response of retaining walls constructed with cohesive and cohesionless backfill materials was studied. Fully dynamic analysis based on the finite difference method was used to
evaluate the performance of retaining walls during different earthquake events. The analysis response was verified by the experimental study conducted on a retaining wall system with cohesive backfill material in the
literature. The effects of cohesion and free-field peak ground acceleration (PGA) on seismic earth thrust, the point of action of earth thrust, and maximum wall moment during the earthquake were compared with analytical and experimental solutions. The motion characteristics of the retaining wall during the earthquake were also considered. The relative displacement of the walls with various backfill cohesion, under different ground motions, and free-field PGAs were investigated. Current analytical and empirical correlations developed based on Newmark sliding block method for estimating retaining wall movement during earthquakes were compared with the numerical approach. Based on the developed model, fragility analyses were conducted to determine the probability of damage to the retaining walls during an earthquake event. Multiple earthquake ground motions were used to investigate the fragility response of the retaining walls. To evaluate the fragility of the studied model, a specific failure criterion was chosen for retaining walls. The failure criterion was selected based on different case histories of retaining wall failures and damages. It is demonstrated to what extent a small amount of cohesion in backfill material can influence the displacement of a retaining wall and the probability of damage in seismic conditions. According to the findings, practical correlations were presented for conducting the seismic design of retaining walls.

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Geomechanical Considerations of Anisotropic Behavior of Shale Layers

Jul 16,20

One of the major reserves of hydrocarbon explorations is shale reservoirs with unconventional geomechanical characteristics. The vast energy capacity of the mentioned reservoirs has led them to become one of the major targets of investment by the oil industry. However, due to the unconventional behavior of these reservoirs including anisotropic elastoplastic characteristics of shale layers and low permeability of the medium, traditional drilling methods do not lead to an appropriate strategy of oil extraction. On the other hand, a rigorous drilling method for operation of an oil field requires a precise comprehension of the geomechanical behavior of shale layers. The substantial aspects of geomechanical characteristics of shale layers include elastoplastic properties of the layers and stress and pore pressure distribution along the wellbore...

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An Overview of Deformation-Based Design Approaches of Retaining Walls

Mar 15,20

Several retaining wall deformations and failures have been reported during historical earthquakes. The most well-known method for predicting the seismic deformation of retaining wall is known as Newmark sliding block method. The Newmark sliding block method requires the acceleration time history of an earthquake in the free-field. However, as the acceleration time history might not be available for a practical design, some investigators including Richards and Elms (1979) developed empirical correlations to evaluate maximum retaining wall displacement in seismic conditions. The Richards and Elms empirical correlation (R&E) has been suggested in different design guidelines including Army Corps (Whitman and Liao 1985) and AASHTO LRFD Bridge Design Specifications (AASHTO 2007). In a more recent study conducted by Anderson et al. (2008) and as part of The National Cooperative Highway Research Program (NCHRP) study, an updated correlation was provided based on various Newmark analyses. The updated NCHRP equation has been embedded in the recent guidelines including Caltrans. More advanced Newmark based pseudo-static methods have also been developed to evaluate the sliding deformation of the retaining walls. Examples include works performed by Biondi et al. in 2014 and Conti et al. in 2013...

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Coal Mine Stability Concerns Due to Slurry Backfilling

Nov 16,19

Surface disposal is used for fine coal refuse by many mining industries as a traditional method. However, the surface disposing causes many environmental issues including contamination of groundwater and fields. One of the effective alternatives for surface disposal would be slurry backfilling which allows injection of fine coal refuse into void area of abandoned room-and-pillar coal mines. Due to the vast mined area in the US, slurry backfilling method has become more common approach for coal waste disposal than surface disposal. Decreasing environmental and health issues and increasing sustainability is one of the most important advantages of slurry backfilling. On the other hand, due to the existence of underground coal in the levels deeper than groundwater aquifers, the disposal material would not jeopardize environmental aspects of water resources. Furthermore, as coal seams in most of the underground mines are nearly flat strata, slurry backfilling would not cause leakage problem for mining industries in most cases. One of the typical lithologies of coal seams consists of weak underclay stratum beneath the coal seam. The ‎immediate weak underclay causes frequent floor instability problems in many underground mines specifically in Illinois underground coal mine regions... ‎

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