利用声发射和波速变化判定岩石损伤状态

对岩石受单轴压缩损伤过程中的声发射和超声波波速进行了同步测量,对比分析了声发射和波速随损伤过程的变化规律。研究表明,岩石损伤过程可分成几个阶段,不同阶段声发射和声波波速变化呈现不同特征;利用超声波波速的相对变化能够稳定可靠地鉴别岩石的"加载强化"与"加载弱化";声发射b值对裂隙的非稳定扩展更加敏感,可以作为岩石失稳预警参数;岩石声发射和波速都对损伤具有记忆性,重复加载下的声发射和超声波波速变化可提供更丰富的岩石损伤状态信息。     

Occurrence of soil erosion after repeated experimental fires in a Mediterranean environment

In the Mediterranean area, forest fires have become a first-order environmental problem. Increased fire frequency progressively reduces ecosystem recovery periods. The fire season, usually followed by torrential rains in autumn, intensifies erosion processes and increases desertification risk. In this work, the effect of repeated experimental fires on soil response to water erosion is studied in the Permanent Field Station of La Concordia, Valencia, Spain. In nine 80 m² plots (20 m long × 4 m wide), all runoff and sediment produced were measured after each rainfall event. In 1995, two fire treatments with the addition of different biomass amounts were applied. Three plots were burned with high fire intensity, three with moderate intensity, and three were unburned to be used as control. In 2003, the plots with the fire treatments were burned again with low fire intensities. During the 8-year interval between fires, plots remained undisturbed, allowing regeneration of the vegetation–soil system. Results obtained during the first 5 months after both fire experiments show the high vulnerability of the soil to erosion after a repeated fire. For the burned plots, runoff rates increased three times more than those of 1995, and soil losses increased almost twice. The highest sediment yield (514 g m^− 2) was measured in 2003, in the plots of the moderate fire intensity treatment, which yielded only 231 g m^− 2 of sediment during the corresponding period in 1995. Runoff yield from the control plots did not show significant temporal changes, while soil losses decreased from 5 g m^− 2 in the first post-fire period to 0.7 g m^− 2 in the second one.     

Recent crustal deformation of İzmir, Western Anatolia and surrounding regions as deduced from repeated GPS measurements and strain field

To investigate contemporary neotectonic deformation in İzmir, Western Anatolia and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2001. Combination of three spatially dense GPS campaigns in 2001, 2003 and 2004 with temporally dense campaigns between 1992 and 2004 resulted in a combined velocity field representing active deformation rate in the region. We computed horizontal and vertical velocity fields with respect to Earth-centered, Earth-fixed ITRF2000, to Eurasia and to Anatolia as well.The rates of principal and shear strains along with rigid-body rotation rates were derived from velocity field. Results show east–west shortening between Karaburun Peninsula and northern part of İzmir Bay together with the extension of İzmir Bay in accordance with general extension regime of Western Anatolia and Eastern Agea. East–west shortening and north–south extension of Karaburun Peninsula are closely related to right-lateral faulting and a clockwise rotation. There exists a block in the middle of the peninsula with a differential motion at a rate of 3–5 ± 1 mm/year and 5–6 ± 1 mm/year to the east and south, respectively.As is in Western Anatolia, north–south extension is dominant in almost all parts of the region despite the fact that they exhibit significantly higher rates in the middle of the peninsula. Extensional rates along Tuzla Fault lying nearly perpendicular to İzmir Bay and in its west are maximum in the region with an extension rate of 300–500 ± 80–100 nanostrain/year and confirm its active state. Extensional rates in other parts of the region are at level of 50–150 nanostrain/year as expected in the other parts of Western Anatolia.     

Centrifuge modelling of SCR vertical motion at touchdown zone

Steel catenary risers (SCR) connect seabed pipelines and flow lines to floating structures used for oil and gas production in deep waters. Waves and currents induce motions of the structure and the risers. The repeated motions of the risers at the touchdown zone in turn induce loads on the seabed soil and might eventually cause fatigue damage to the risers. The analysis of riser fatigue damage is heavily dependent on the soil model. Soil behaviour at touchdown zone such as soil remoulding, stiffness degradation and deformation of the seabed at the touchdown zone further complicate the accurate assessment of riser fatigue damage, which is currently not appropriately quantified in existing design methods. This paper presents centrifuge model tests simulating the repeated vertical movement of a length of riser on clay seabed with increasing undrained shear strength with depth. During the tests, the pipe was subject to cyclic motion over fixed vertical displacement amplitude from an invert embedment of 0.5-3.5 pipe diameters into the soil. The test results show a significant progressive degradation of soil strength and diminution of excess pore water pressure with increasing number of riser penetration/uplift cycle. In view of the different types of environment loadings experienced by floating platforms and various soil conditions, tests were also conducted to investigate the effect of soil strength, riser displacement rate and loading mode on riser-soil interaction during repetitive penetration/uplift motion of the riser.     

赫尔默特方差分量估计在混合水准网平差中的应用

测量中有些时候会碰到定权不统一的问题,导致了平差后的结果不理想.本文主要讨论的是通过赫尔默特方差估计的方法消除由于定权的不合理而产生的精度超限问题.通过实例进行分析表明,利用赫尔默特方差分量估计在进行迭代定权非常实用,大大提高了其精度.     

鲜水河断裂带的现今水平形变及构造动态

据鲜水河断裂带水平测距的新成果,讨论该带现今构造运动的动态特征。在分析水平形变的基础上,联系表层构造形变和区域背景,探讨地块沿断裂带运动的模式。认为该带的现今运动主要表现为断裂带两侧地块往东南的同向不等速滑动,其地表形变效应则与左旋走滑相一     

断陷盆地层滑带的发育特征及矿山开发条件下的再变形分析

层滑带在华北断陷盆地中具有普遍性,是影响地下矿山工程围岩稳定的重要因素之一。本文以鲁西矿区为例,阐述了断陷盆地层滑带的发育特征及其形成机制,进行了开挖、运营条件下层滑带再变形分析,并指出了层滑带发育区巷道设计及维护中应注意的某些问题。     

甘肃祁连山主动源重复探测项目建设及震源重复性分析

甘肃祁连山主动源重复探测激发源位于甘肃省张掖市祁连山西流水水库,2015年7月9日各系统开始正式运行,11月10日完成了为期40天的连续激发实验。观测资料处理结果表明,气枪震源具有良好的一致性和可重复性,整个观测系统能比较清晰地记录到震源激发的信号。祁连山主动源项目建设取得的结果可为主动源探测工作提供宝贵经验和科学借鉴,不断取得的观测数据为跟踪了解祁连山地区的深部结构时空变化提供了可能。     

Unsaturated resilient behavior of a natural compacted sand

Granular materials are generally used in unbound layers of road pavement structures. The mechanical behavior of these materials is widely studied with repeated load triaxial tests (RLTT) in which the elastic response is defined as the resilient behavior. Usually observed under total stress conditions, the effect of pore pressure changes during loading are not usually included in design. Further, the unbound layers frequently exist under partially saturated conditions. The influence of the unsaturated state, i.e., the suction, on the mechanical behavior, of unbound granular materials for roads has not been sufficiently studied and is generally not taken into account in models used for these materials.     

Detection of small hydrological variations in gravity by repeated observations with relative gravimeters

Recently, a new application of time-dependent gravity observations is emerging: the study of natural hydrological mass changes and their underlying processes. Complementary to GRACE data and continuous recordings with superconducting gravimeters, repeated observations with relative instruments on a local network may contribute to gain additional information on spatial changes in hydrology. The questions that need to be addressed are whether the results of these repeated measurements will be of sufficiently high resolution and accuracy, as well as how unique the information obtained will be. To examine this, a local gravity network with maximum point distances of 65 m was established in a hilly area around the Geodynamic Observatory Moxa, Germany. Using three to five LaCoste & Romberg relative gravimeters repeated measurements were carried out in a seasonal rhythm as well as at particular events like snowmelt or dryness in 17 campaigns between November 2004 and April 2007. The standard deviations obtained by least squares adjustment range from ±9 to ±14 nm/s² for a gravity difference of one campaign, thus for gravity changes between two campaigns from ±13 to ±20 nm/s². Between the points of the network, spatial gravity changes of up to 171 nm/s² (139 nm/s² between two successive campaigns) could be proven significantly. They correlate with changes in the local hydrological situation. Particularly, a steep slope next to the observatory is identified as a gravimetrically significant hydrological compartment. The results obtained contribute to an improved reduction of the local hydrological signal in continuous gravity recordings and provide constraints to hydrological models.