Influences of nonassociated flow rules on seismic bearing capacity factors of strip footing on soil slope by energy dissipation method

Seismic bearing capacity factors of a strip footing placed on soil slope were determined with both associated and nonassociated flow rules. Quasi-static representation of earthquake effects using a seismic coefficient concept was adopted for seismic bearing capacity calculations. A multi-wedge translational failure mechanism was used to obtain the seismic bearing capacity factors for different seismic coefficients and various inclined angles. Employing the associated flow rule, numerical results were compared with the published solutions. For bearing capacity factors related to cohesion and equivalent surcharge load, the maximum difference approximates 0.1%. However, the difference of bearing capacity factor related to unit weight is larger. With the two flow rules, the seismic bearing capacity factors were presented in the form of design charts for practical use. The results show that seismic bearing capacity factors related to the cohesion, the equivalent surcharge load and the unit weight increase greatly as the dilatancy angle increases, and that the nonassociated flow rule has important influences on the seismic bearing capacity.

Influence of varying bedding thickness of underclay on floor stability

The variation in bedding thickness of the weak immediate floor has long been a challenge in the lllinois basin coal mines when it comes to floor stability. The vertical thickness of the immediate floor is not constant throughout the mines and can vary over short horizontal distances. The biggest misconception from a design standpoint is to use the maximum or average thickness found from core logs taken from various locations on the mine property. The result of this practice is oversized pillars in the areas where the weak immediate floor has thinned vertically. This over-design leaves coal in situ which could have otherwise been extracted. This paper presents a plane strain numerical model to illustrate the effect of a change in bedding thickness of a weak immediate floor across one or two coal pillars. The floor bearing capacity of the variable floor below each pillar where then compared to the consistent floor. The results show that the varying bedding thickness of weak underclay has an impact on the bearing capacity of the floor. Geometrically with the decrease in bedding thickness for constant pillar width, the B/H ratio increases exponentially. The influence of varying bedding thickness on the floor bearing capacity is apparent at higher B/H ratios. The floor bearing capacity under a single pillar is in variable floor model if the average thickness remains constant. For single pillar, the average of the bedding thickness can be considered and for pillars in a panel, and a safety factor has been proposed to take into account this change in bedding thickness.

Load Settlement Characteristics of Model Footings Resting on Surface Treated Coir Fiber Reinforced BC Soil Overlying Loose Stratum

In nature there are situations where in foundation had to be placed over loose soil deposits. In such cases, deep foundations are recommended which increases cost of the structure. Black cotton soils, because of its high swelling and shrinkage characteristics, have been a challenge to geotechnical engineers, increasing the strength of Clayey soil which is formed introducing randomly distributed fibers results in comparatively more homogeneous soil mixture and is one of the popular methods of soil stabilization. In the present study, model footing resting on BC soil reinforced with optimum percentage of treated and untreated coir fiber underlain by loose soil deposit was conducted to study its influence on bearing capacity and settlement. Loose soil deposit has been simulated by compacting sawdust in prefabricated steel tank. BC soil reinforced with optimum percentage of treated and untreated coir fibers has been compacted over loose sawdust and load settlement characteristics were determined at various D/B ratio of 1,2, 3 and for different sized model footings. The results indicated that settlement of model footings is significantly small at lower D/B = 1 and 2 ratios. Bearing capacity of BC soil is also found to be significantly affected by fiber reinforcement.