裂隙各向异性介质横波双折射特性研究

借助于有限元方法,对裂隙各向异性介质一雏四分量弹性波场中横波双折射的有关问题进行了研究。它们是裂隙方位与相速度,双折射与震源主频,双折射与裂隙丰度,双折射与能量分配,双折射与延迟时,双折射及其振幅谱等。这些问题对深入认识横波双折射特性,对理论和实际工作都有一定帮助。     

粘土干湿循环中裂缝演变过程的数值模拟

在非饱和土简化固结理论基础上,对粘土在干湿过程中,表面裂缝从形成、发展到闭合的发展过程进行了数值模拟,模拟结果说明,本文采用的基于非饱和简化固结理论的计算方法是可行、实用的.     

Temporal change in scattering and attenuation associated with the earthquake occurrence—A review of recent studies on coda waves

The study of coda waves has recently attracted increasing attention from seismologists. This is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured, since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations, compared with the direct ray paths. To date, we have had many reports on the temporal variation of the relation between coda duration and amplitude magnitude, and that of the coda attenuationQ _c ^–1 which is estimated from coda amplitude decay. Some of these have shown a precursor-like behavior; however, others seem to have shown a coseismic change. We have critically reviewed these reports, and discussed what these observational facts tell us about the change in the heterogeneous crust. We found significant temporal variations, not only in the mean but also in the scatter ofQ _c ^–1 , associated with the mainshock occurrence. The formation of new cracks, the reopening and growing of existing cracks, the interaction of these cracks, and the pore water movement through these cracks might correspond to such variations. In addition, we may expect an inhomogeneous distribution of crack clusters in a fairly large region, compared with the aftershock region. The gradual appearance of such crack clusters seems to be the most plausible mechanism by which coda decay gradients are caused to largely scatter in the stress accumulation stage.     

Origin and post-glacial evolution of surface cracks: A case study from the area of the Last Glaciation,north-eastern Poland

The analysis of LiDAR-based digital elevation models revealed the existence of groups of longitudinal fractures in the ground in northern Poland at the limit of the ice sheet's extent during its last maximum. Our research on the closed elongated depressions (CEDs) of the Jedwabno test field (Szuć site, north-east Poland) focuses on explaining their origins and their post-glacial history. This region was covered by an ice sheet and glacitectonically active during the Vistulian, and at least some surface fractures are possible witnesses to this activity. Using geomorphological mapping, sedimentological and geophysical research, we assumed it was related that the origin of these features here is associated with groundwater migration at the end of the Vistulian glaciation or later when groundwater flow intensified due to a rapid climate warming that caused permafrost to melt. The thawing of permafrost caused to transition from continuous permafrost to discontinuous, which in turn created groundwater flow that was probably responsible for the development of the surface cracks (fractures). Radiocarbon, palaeobiological (pollen, Cladocera) and geochemical studies allowed for an estimation of the formation time of these unique surface cracks in the Older Dryas. Prevailing conditions were also reconstructed for the later dynamic changes of the end of the Late Vistulian glaciation and in the Late Holocene until the Subatlantic Period (Megalayan stage). The surface cracks with steep slopes, despite their small area, are extraordinary sedimentation traps that have, in a special way, retained an almost complete record of the environmental and climate changes of the Late Glacial. There are sedimentological gaps in the Holocene, especially after the Preboreal (old part of the Greenlandian Stage), caused by changes in water levels, aeolian processes and human activity.     

关于恐龙化石在发掘过程中因应力释放造成风化破坏的研究

在恐龙化石发掘过程中不仅机械扰动会直接导致化石或围岩的破碎,应力释放也会导致化石及围岩表面裂隙的产生及扩张,这些节理裂隙又为水和空气的活动提供了通道,使风化破坏作用更加迅速。作者以分层开挖理论为基础,建立了模拟化石开挖过程的数值模型。通过计算机模拟开挖过程中0m、11m、14m、19m四个深度的等效应力变化过程和XZ方向应力的变化过程发现:开挖前后化石表面的最大等效应力差达到0.34MPa,围岩表面的最大等效应力差达0.3MPa;埋深越大的化石,在开挖露出地面后等效应力的回弹现象越明显,即应力释放越严重;虽然化石表面所受剪应力不大,但其对化石风化的影响比在压应力条件下要大的多,这是导致卸载裂隙产生的主要原因。因此,恐龙化石发掘要逐层缓慢开挖,使化石逐渐达到新的应力平衡,以便减少应力快速释放对化石造成的风化破坏,特别是要做好护坡,最大限度地防止剪应力的产生。     

岩层阻水性能与其结构成分、组合形式的关系

根据室内水力压裂试验的结果,通过分析裂痕端部应力强度因子的变化情况,研究了不同结构成分岩层的各自阻抗水压致裂的能力,分析了岩性变化、交界面性质对水压致裂裂隙扩展的影响,提出了阻抗水压致裂裂隙扩展和防止承压水导升的较优岩层组合形式。      

夏季新建码头混凝土面层裂缝的原因分析

针对夏季施工的码头混凝土面层产生的连续裂缝,分析了裂缝产生的原因,并提出以后的施工作业中应注意的问题,以防止类似现象再次发生。