Grassland Evolution Under Soil Degradation: Numerical Simulation and Test

Both theoretical and field observations were examined to study the close relationship between soil degeneration and the evolution of grassland vegetation. A general n-species model of equal competition under different degrees of soil degradation was applied to field data in order to probe the dynamic processes and mechanisms of vegetation evolution due to the effects of the soil's ecological deterioration on grassland vegetation. Comparisons were made between the theoretical results and the practical surveys with satisfactory results.

堆载作用下土岩复合地层隧道坍塌特征及演变规律研究

受地面堆载作用影响,城市地铁隧道易发生坍塌事故。结合特定的土岩复合地层,明确隧道坍塌演变及其特征规律是隧道坍塌防控的前提和基础。通过模型试验及数值模拟,研究了堆载作用下不同土岩比的复合地层隧道坍塌演变及特征规律,并得出以下结论:1)模型试验过程表明,隧道坍塌呈现为连续破坏、渐进破坏,其动态演绎为岩层拱腰及拱顶松动塌落—岩层顶板剪切断裂—土层连续拱形坍塌—土层塌穿至地表;2)土岩复合地层坍塌最终形态呈“漏斗”形,岩层破裂区域狭窄且近似与水平面垂直贯通,土层破坏区域开口扩大;3)结合模型试验过程,统计分析了隧道坍塌特征并得出规律——土层、岩层破裂角均随岩跨比增大而减小,土层、岩层破裂口径均随岩跨比增大而增大;4)借助离散元模拟PFC,验证了模型试验破坏过程的合理性。通过对土岩复合地层坍塌演变规律的探索与讨论,以期为隧道的坍塌防控提供参考。