Abstract: Workers are often required to enter unsupported trenches during the construction process, which may present serious risks. Trench failures can result in death or damage to adjacent properties, therefore trenches should be excavated with extreme precaution. Excavation work is often done in unsaturated soils, where the critical height (i.e. maximum depth that can be excavated without failure) of unsupported trenches can be more reliably estimated by considering the influence of matric suction. In this study, coupled stress/pore-water pressure analyses are conducted to investigate the critical height of sloped unsupported trenches considering the influence of pore-water pressure redistribution caused by excavating. Four different wall slopes (1.5V:1H, 2V:1H, 3V:1H, and 90°) and a vertical trench with the top 0.3 m sloped 1:1 were considered in the analyses with multiple depths of the ground water table in a sand. For comparison, the critical heights were also estimated using the limit equilibrium method for the same excavation scenarios used in the coupled analyses.
Abstract: Double heterogeneity of randomly located pebbles in
the core and Coated Fuel Particles (CFPs) in the pebbles are specific
features in pebble bed reactors and usually, because of difficulty to
model with MCNP code capabilities, are neglected. In this study,
characteristics of HTR-10, Tsinghua University research reactor, are
used and not only double heterogeneous but also truncated CFPs and
Pebbles are considered.Firstly, 8335 CFPs are distributed randomly
in a pebble and then the core of reactor is filled with those pebbles
and graphite pebbles as moderator such that 57:43 ratio of fuel and
moderator pebbles is established.Finally, four different core
configurations are modeled. They are Simple Cubic (SC) structure
with truncated pebbles,SC structure without truncated pebble, and
Simple Hexagonal(SH) structure without truncated pebbles and SH
structure with truncated pebbles. Results like effective multiplication
factor (Keff), critical height,etc. are compared with available data.