顶板-支护系统准共振诱发冲击地压机制研究

冲击地压的发生机制与防治是煤矿动力灾害研究的重要问题。巷道顶板-支护系统在围岩扰动作用下存在接近共振状态的准共振现象将诱发顶板支护系统的冲击灾害,表现为顶板的位移、速度、加速度3种准共振强响应。依据支护失稳及支护塑性屈曲判别条件,给出支护动载破坏的3个安全系数及相应的危险扰动频率比区间,同时针对顶板支护系统准共振诱发的冲击灾害给出支护阻尼防冲控制分析。结果表明：在外界扰动力幅值低于静载下的支护临界破坏载荷时,顶板-支护系统的准共振现象是导致支护冲击破坏的主要原因;支护破坏的准共振危险扰动频率比区间与顶板支护系统的阻尼比及力幅比有关,随着阻尼比的增加,顶板准共振时的位移、速度及加速度响应幅值均减小,支护阻尼是对3种准共振响应均敏感的控制量;随着顶板支护系统阻尼比的增大或力幅比（外界扰动力幅值与支护静载破坏临界载荷之比）的下降,支护的危险扰动频率比区间范围将缩小甚至消失,同时阻尼比和力幅比取值均较小时,顶板支护系统在3种准共振下的危险扰动频率比取值区间较为接近。该研究将丰富对冲击地压发生机制的认识,同时对支护防冲控制设计具有参考价值。     

Very high-rate GPS for measuring dynamic seismic displacements without aliasing: performance evaluation of the variometric approach

Very high-rate global positioning system (GPS) data has the capacity to quickly resolve seismically related ground displacements, thereby providing great potential for rapidly determining the magnitude and the nature of an earthquake’s rupture process and for providing timely warnings for earthquakes and tsunamis. The GPS variometric approach can measure ground displacements with comparable precision to relative positioning and precise point positioning (PPP) within a short period of time. The variometric approach is based on single-differencing over time of carrier phase observations using only the broadcast ephemeris and a single receiver to estimate velocities, which are then integrated to derive displacements. We evaluate the performance of the variometric approach to measure displacements using 50 Hz GPS data, which were recorded during the 2013 M_W 6.6 Lushan earthquake and the 2011 M_W 9.0 Tohoku-Oki earthquake. The comparison between 50 and 1 Hz seismic displacements demonstrates that 1 Hz solutions often fail to faithfully manifest the seismic waves containing high-frequency seismic signals due to aliasing, which is common for near-field stations of a moderate-magnitude earthquake. Results indicate that 10–50 Hz sampling GPS sites deployed close to the source or the ruptured fault are needed for measuring dynamic seismic displacements of moderate-magnitude events. Comparisons with post-processed PPP results reveal that the variometric approach can determine seismic displacements with accuracies of 0.3–4.1, 0.5–2.3 and 0.8–6.8 cm in the east, north and up components, respectively. Moreover, the power spectral density analysis demonstrates that high-frequency noises of seismic displacements, derived using the variometric approach, are smaller than those of PPP-derived displacements in these three components.     

城市气象研究国际前沿动态综述

通过梳理2018年8月在美国纽约举行的第十届城市气候国际会议主要研究成果,分类汇总了城市气象研究的最新国际进展与发展趋势,包括城市气候过程、城市环境下气候变化适应与应对、气候条件下城市规划和管理、最新城市气象探测技术、城市环境数值模拟、大城市气候、城市遥感、城市地区极端天气等方面。在此基础上,根据我国城市化发展特性,探讨了我国城市气象研究的未来发展方向。     

Comparative study of flash flood in ungauged watershed with special emphasizing on rough set theory for handling the missing hydrological values

Natural Hazards - Prediction of the flash floods in ungauged or poorly gauging watershed is one of the challenging tasks in the field of hydrology and needs implication of advanced techniques to...     

Thermo-hydro-mechanical process and damage mechanism of a cold-region canal under coupled wetting–drying and freezing–thawing cycles

Acta Geotechnica - In cold regions, periodic wetting–drying and freezing–thawing (WDFT) actions lead to frequent and heavy canal damage, weakening the water-conveyance capacities of...     

波致海底缓倾角无限坡滑动稳定性计算分析探讨

波浪作用下海底无限坡滑动稳定性计算的极限平衡法中,忽略了坡体水平向应力状态的影响,为此,针对波浪作用下海底缓倾角无限边坡的特点,提出直接基于滑动面处土体应力状态的滑动稳定性计算方法(简称应力状态法),并分析了其适用范围。对具体算例的分析表明,应力状态法计算得出的安全系数大于极限平衡法的安全系数,且随着滑动面深度的增加、土体泊松比以及边坡坡角的增大,两种计算方法得出的安全系数的差异会逐渐增大;对于波浪作用下的海底缓倾角无限边坡,在失稳时极可能沿具有一定厚度的滑动带而不是单一的滑动面而滑动,且波致最大剪应力所在的深度,常常不是斜坡体最易失稳滑移的深度。     

大气负荷效应对浙江地区的影响分析

利用全球大气模型及浙江地区气象站数据，依据大气负荷理论，采用移去-恢复法计算大气压引起的区域负荷形变场及重力场变化。结果表明，在浙江地区大气负荷引起的垂直形变达12.1 mm，产生的地面重力变化超过12 μGal，对水平形变及垂线偏差影响较小，且大气负荷具有明显的年周期及季节性变化规律。     

The Study of Paleoearthquakes on the Weihe Fault Zone

It is indicated by historical records and the exploratory trench on the Weihe fault that the Yaodian-Zhangjiawan segment of the Weihe fault zone has experienced a historical earthquake and 3 paleoearthquake events in the past 9110a. The historical earthquake, namely, event Ⅳ, occurred between 1487 and 1568 AD. The date of paleoseismic event Ⅰ is （9110 ＋ 90） a, and the ages of events Ⅱ and Ⅲ are unknown. The coseismic vertical displacement of events Ⅰ, Ⅱ and Ⅲ is 0.5m, 0.5m and 0.2m, respectively. The exploratory trench also indicates that the Yaodian-Zhangjiawan segment of the Weihe fault was active in the Holocene.