All posts by Mohr Academy

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...

Read More

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... ‎

Read More