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When roadways are constructed above or adjacent to heavily mined regions, the ground subsidence caused by pillar collapse inflicts severe damage on these roadways. In this study, some surface subsidence events were first reviewed to present roof caving characteristics caused by pillar failure. The bearing characteristic and failure pattern of a single pillar with or without effect of discontinuity were further numerically simulated using distinct element code (3DEC). It was found that the spalling of pillar or slippage of discontinuity would damage the bearing capacity of pillar during the failure process. The stress at the pillar core could be greater than uniaxial compressive strength of the pillar. However, when a discontinuity runs through a pillar, the slippage of discontinuity would significantly degrade the bearing capacity of the pillar. In pillar support system, if any pillar unexpectedly degrades or loses its bearing capacity, the load transferred from the degraded pillar acts on neighboring pillars, and the shear force also increases at relevant positions. However, the roof cutting and surface subsidence characteristics would perform in different patterns. In some cases, surface subsides slowly; in the worst scenario, shock bump may be induced by pillar and roof collapse.

Pseudostellaria wuyishanensis, a new species from the Wuyishan National Park, Fujian, China, is described and illustrated. Morphologically, Pseudostellaria wuyishanensis resembles P. heterantha. However, the new species can be distinguished by presence of stolons, 1 line of hairs on the stem, smaller leaf blades, shorter pedicels, and ovary with 2 styles.