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Reliable rock mass characterization is needed to design safer and more economical roof support systems of coal mines. Coal Mine Roof Rating (CMRR) index is a commonly used method by roof control engineers to characterize immediate rock units above the underground coal mines. This index ranges from 0 to 100 and was developed by studying the performance of the roofs in the Appalachian coal fields, which have typically strong roof units. Application of CMRR for weak and moisture sensitive rocks such as shale roof units in the Illinois Basin may misrepresent the rock mass. In this study, the rock laboratory test results are conducted to characterize the moisture sensitivity, axial and diametral strengths of roof units. The CMRR indexes and designed roof systems in a coal mine located in Illinois Basin will be presented. A sensitivity analysis is also performed to identify the most influential CMRR rock mass characterization parameters in weak rocks. This study shows while CMRR rock mass characterization has many advantages, it should be cautiously used for roof support design in weak and moisture sensitive roof conditions.

One of the major reasons of levee failure is erosion due to overtopping. The overtopping of levees is occasionally the consequence of a flood or Hurricane. In these events, the surface layers of levees become saturated in advance of any overtopping due to rain and storm events. In this investigation, the effect of the saturation ratio and almost vertical impingement of overtopped water from floodwall on scour development are studied. For this purpose, laboratory physical models of a typical levee on the banks of Mississippi river with a scale of 1:20 were constructed. A 2.4 mm thick wooden plate, which was embedded in the crest of the levee represented the floodwall. Silty soil materials with various saturation ratios were used to observe scour potential of the soil. In all the tests, the scour development and the stability of the wall were monitored and analyzed for each test during overtopping. Hydraulic and geometric parameters including Densimetric Froude number, compaction level, water content and levee dimensions were recorded to have a representative comparison between the laboratory models and constructed levees in practice. In addition, the erodibility of the levee materials was determined using Erosion Function Apparatus (EFA). The results of EFA tests were compared to physical model test results to explore and discuss the vulnerability of levee systems to erosion when the surface soils are saturated and floodwall overtopping is experienced.

Geomechanical properties of rocks are important parameters in the design procedure and construction of various geotechnical projects such as underground excavation, rock slope stabilities and blasting in rock medium. These parameters have also wide applications in the mining industry since they are employed in the rock mass classification of coal mine roofs and roof control design. The strength indexes of the rocks are affected by changes in their moisture contents. Understanding of this correlation for rock medium is critical for mining companies during mine development. In this paper, an extensive database containing geomechanial properties of three different rock units including shale, limestone and claystone is developed by collecting and performing tests on roof core samples of a coal mine in the Illinois Basin. These properties include moisture content, unit weight, unconfined compressive strength, indirect tensile strength index, axial point load index, diametral point load index and slake durability index. In this study, a correlation between moisture content and strength of examined rock samples is investigated. It is also discussed how the results could affect the timing for the development of mine panels, keeping the main entries open and dealing with moisture sensitive rocks during the mining activity.

Current engineering design methods for evaluating the seismic lateral earth pressures of retaining walls are based on limit equilibrium Mononobe-Okabe method. In limit equilibrium method, the effect of dynamic loading is introduced to the soil wedge behind the retaining wall as lateral and vertical inertia forces. The two most important simplifications of these methods are application of pseudo-static solution procedure for a fully dynamic problem and assumption of cohesionless backfill material. In this investigation, a full dynamic numerical modeling on a retaining wall with low frictional angle backfill material is conducted to evaluate the seismic performance of retaining wall and lateral earth pressure variation during the earthquake. A 6-meter high cantilever wall with a base width of 4 m and thickness of 0.5 m is represented by structural element. The concrete wall was assumed to perform elastically and the Mohr-Coulomb constitutive model was selected for soil material. The interaction between concrete wall and soil was modeled by using elasto-plastic bilinear model to account for shear sliding and normal separation of wall and soil. The performance of the retaining wall was analyzed under three distinct earthquakes. The lateral earth pressure distribution along the wall height was evaluated during the earthquakes and was compared to static earth pressure. Furthermore, a set of dynamic analysis were conducted with normalized peak ground acceleration, PGA, of the earthquakes. The dynamic lateral earth pressure coefficients along the stem, middle and heel of the wall during the earthquake were analyzed for various horizontal PGAs induced by earthquakes. Consequently, the lateral earth pressure coefficients along the wall were compared to those concluded by Mononobe-Okabe method. According to the results, in low frictional angle soil backfills that have some cohesion, the lateral earth pressures are overestimated by Mononobe-Okabe method.