Resilient Deformation Characteristics of Unsaturated Subgrade Materials of Rail Tracks under Cyclic Moving Wheel Loads

Water content of rail track subgrade materials fluctuates throughout the year due to the number of wetting and drying cycles, introducing unsaturated properties into the subgrade. Conservative rail track design guidelines are, however, mainly based on two extreme saturation conditions: fully dried or fully saturated. Current knowledge on the effects of subgrade water content on residual and resilient behaviour of the track foundation under the effects of Principal Stress Axis Rotation (PSAR) is limited and the potential of expansibility of foundation materials further upsurge the complexities towards the designing of the rail tracks. This study demonstrates the contributions of the PSAR on the resilient behaviour of foundation materials. Three different materials, including an expansive soil type have been subjected to drained cyclic vertical and torsional shear tests in a Modified Multi-Ring Shear (MMRS) apparatus and it is concluded that the resilient behaviour of the foundation materials is functions of the PSAR, material type, water content, and potential of expansibility.</p

Strength properties of composite clay balls containing additives from industry wastes as new filter media in water treatment

Pebble matrix filtration (PMF) is a water treatment technology that can remove suspended solids in highly turbid surface water during heavy storms. PMF typically uses sand and natural pebbles as filter media. Hand-made clay pebbles (balls) can be used as alternatives to natural pebbles in PMF treatment plants, where natural pebbles are not readily available. Since the high turbidity is a seasonal problem that occurs during heavy rains, the use of newly developed composite clay balls instead of pure clay balls have the advantage of removing other pollutants such as natural organic matter (NOM) during other times. Only the strength properties of composite clay balls are described here as the pollutant removal is beyond the scope of this paper. These new composite clay balls must be able to withstand dead and live loads under dry and saturated conditions in a filter assembly. Absence of a standard ball preparation process and expected strength properties of composite clay balls were the main reasons behind the present study. Five different raw materials from industry wastes: Red Mud (RM), Water Treatment Alum Sludge (S), Shredded Paper (SP), Saw Dust (SD), and Sugar Mulch (SM) were added to common clay brick mix (BM) in different proportions. A comprehensive experimental program was performed to evaluate influence burning temperature on crushing strength of composite hand-made clay balls, using uniaxial compression test to establish the best material combination on the basis of strength properties for designing sustainable filter media for water treatment plants. Performance at both construction and operating stages were considered by analyzing both strength properties under fully dry conditions and strength degradation after saturation in a water bath. Approximately 50 mm diameter composite clay balls fired at 800 0C provided sufficient strength for water treatment applications at both construction and operational stages due to their higher strength at dry conditions, and no strength degradation at soaked conditions. The use of water treatment sludge as an additive produced the lowest strength of composite clay balls, with a failure load of 1.4 kN. However, this value is much higher than the effective load on each clay ball of 0.04 kN in a typical filter assembly (safety factor of 35), therefore, can still be used as a suitable filter material for enhanced pollutant removal.Authors wish to thank Queensland Alumina Limited (QAL) and Seqwater for supplying Red Mud and water treatment sludge for the experiments. The support of PGH Bricks and Pavers for firing composite clay balls in their factory is greatly acknowledged. Also, the support of technical and professional staff of the geotechnical laboratory at Queensland University of Technology during testing is highly appreciated.This is a metadata record relating to an article that cannot be shared due to publisher copyright

Strength properties of composite clay balls containing additives from industry wastes as new filter media in water treatment

Pebble matrix filtration (PMF) is a water treatment technology that can remove suspended solids in highly turbid surface water during heavy storms. PMF typically uses sand and natural pebbles as filter media. Hand-made clay pebbles (balls) can be used as alternatives to natural pebbles in PMF treatment plants, where natural pebbles are not readily available. Since the high turbidity is a seasonal problem that occurs during heavy rains, the use of newly developed composite clay balls instead of pure clay balls have the advantage of removing other pollutants such as natural organic matter (NOM) during other times. Only the strength properties of composite clay balls are described here as the pollutant removal is beyond the scope of this paper. These new composite clay balls must be able to withstand dead and live loads under dry and saturated conditions in a filter assembly. Absence of a standard ball preparation process and expected strength properties of composite clay balls were the main reasons behind the present study. Five different raw materials from industry wastes: Red Mud (RM), Water Treatment Alum Sludge (S), Shredded Paper (SP), Saw Dust (SD), and Sugar Mulch (SM) were added to common clay brick mix (BM) in different proportions. In an effort to minimize costs, in this study clay balls were fired to 1100°C at a local brick factory together with their bricks. A comprehensive experimental program was performed to evaluate crushing strength of composite hand-made clay balls, using uniaxial compression test to establish the best material combination on the basis of strength properties for designing sustainable filter media for water treatment plants. Performance at both construction and operating stages were considered by analyzing both strength properties under fully dry conditions and strength degradation after saturation in a water bath. The BM-75% as the main component produced optimum combination in terms of workability and strength. With the material combination of BM-75% and additives-25%, the use of Red Mud and water treatment sludge as additives produced the highest and lowest strength of composite clay balls, with a failure load of 5.4 kN and 1.4 kN respectively. However, this lower value of 1.4 kN is much higher than the effective load on each clay ball of 0.04 kN in a typical filter assembly (safety factor of 35), therefore, can still be used as a suitable filter material for enhanced pollutant removal