Reprint of “Multi-step and two-step experiments in heterogeneous porous media to evaluate the relevance of dynamic effects”

The determination of hydraulic properties in non-stationary experiments is suspected to be affected by dynamic effects. This is based on thermodynamic considerations on the pore scale displacement of wetting and non-wetting phase. But also macroscopic heterogeneities at the continuum scale may influence the dynamics of water during drainage and wetting. In this paper we investigate both aspects. Firstly, we present the results of typical multi-step outflow experiments in heterogeneous sand columns which are compared with two-step outflow experiments covering the same pressure range. The discrepancies caused by pressure steps of different size reveal the impact of dynamic effects due to the non-stationarity of the experiments.     

Experimental solidification of anhydrous latitic and trachytic melts at different cooling rates: The role of nucleation kinetics

Two sets of cooling experiments were run at atmospheric conditions for two anhydrous starting latitic and trachytic melts: 1) five cooling rates (25, 12.5, 3, 0.5, and 0.125 °C/min) between 1300° and 800 °C, and 2) a 0.5 °C/min cooling rate from 1300 °C with quench temperatures at 1200°, 1100°, 1000° and 900 °C. Trachytic run-products are invariably glassy. Nucleation is also suppressed in the latitic run-products at the three highest cooling rates. Conversely, in the 0.5 and 0.125 °C/min runs, latites have a crystal content of  90 vol.%. The phases are: plagioclase, clinopyroxene, glass and iron-bearing oxide (in order of abundance). The variable quench temperatures, investigated by coupling experiments with Pt wire and Pt capsule sample containers in set 2, again did not produce crystallization of trachyte, whereas latitic samples are characterized by  10 vol.% of oxides, pyroxenes and plagioclase (in order of appearance), at temperature < 1000 °C. Effects of (preferential) heterogeneous nucleation on sample holders, of superheating degree, and chemical species loss during cooling are absent for both melt compositions. The difference of solidification paths between these two silicate melts can be ascribed only to their small chemical differences. In comparison with calculated equilibrium conditions all the experimental latitic and trachytic run-products revealed strong kinetic effects, interpretable in the light of the nucleation theory. The glass-forming ability (GFA) of trachyte is higher, whereas their critical cooling rate (Rc) is lower (< 0.125 °C/min), in comparison to latitic melts (Rc > 0.5 °C/min). The experimental results carried out in this study can be applied to lava flows and domes; trachytic lavas are able to flow for longer period with respect to latitic ones in a metastable condition. Glass-rich terrestrial lavas, i.e. obsidians, can be the result of sluggish nucleation kinetics due to the relative high polymerisation of evolved silicate melts.     

旧路改建高速公路中地基强夯效应测试与工艺参数分析

旧路改建高速公路遇到的最主要的问题是地基的不均匀沉降。数值分析表明,对新的天然地基进行处理是解决这一问题的关键。强夯是加固地基的一种有效措施,为了对强夯工艺参数进行优化研究,对夯锤冲击地面过程中产生的动孔隙水压力、动土应力以及夯后超静孔隙水压力的消散过程进行了跟踪测试与分析。结果表明,对以风化料为主的地基,最大夯击数不宜超过4击,而且铺底夯完成2d后就可进行满夯。     

压实过程对红黏土的孔隙分布影响研究

为研究压实作用对红黏土孔隙分布的影响,采用液氮冻干法对经过压力板仪脱至残余含水率后的压实试样进行干燥,继而利用孔隙仪测试其孔隙分布特征。结果表明,不同干密度试样的孔隙分布特征在孔径d >10 μm范围内差异性比较明显,干密度越大分布在该范围内的孔隙越少,但所有试样的大部分孔隙主要分布在孔径d <0.1 μm的范围内,并且分布密度十分相似。换言之,常规压实作用只能改变土体某一较大孔径范围内的孔隙,而对小孔径的孔隙改变不大,这也对于说明红黏土路基填料的压实,常规的压实作用对提高土体的压实度幅度有一定范围。     

Using micro-catchment experiments for multi-local scale modelling of nature-based solutions

The Q-natural flood management project has co-developed with the Environment Agency 18 monitored micro-catchments (~1 km²) in Cumbria, UK installing calibrated flumes aimed at quantifying the potential shift in observed flows resulting from a range of nature-based-solutions installed by local organizations. The small-scale reduces the influence of variability characterizing larger catchments that would otherwise mask any such shifts, which we attempt to relate to a shift in model parameters. This paper demonstrates an approach to applying donor-parameter-shifts obtained from modelling two of the paired micro-catchments to a much larger scale, in order to understand the potential for improved distributed modelling of nature-based solutions in the form of additional tree-planting. The models include a rainfall-runoff model, Dynamic Topmodel, and a 2D hydrodynamic model, JFlow, permitting analysis of changes in hillslope processes and channel hydrodynamics resulting from a range of distributed measures designed to emulate natural hydrological processes that evaporate, store or infiltrate flows. We report on attempts to detect shift in hydrological response using one of the paired-micro-catchment moorland versus forestry sites in Lorton using Dynamic Topmodel. A donor-parameter-shift approach is used in a hypothetical experiment to represent new woodland in a much larger catchment, although testing all combinations of spatial planting strategies, responses to multiple-extremes, failure-modes and changes to synchronization becomes intractable to support good decision making. We argue that the problem can be re-framed to use donor-parameter-shifts at multi-local-scale catchments above communities known to be at risk, commensurate with most of the evidence of NbS impacts being effective at the small scale (ca. 10 km²). This might lead to more effective modelling to help catchment managers prioritize those communities-at-risk where there is more evidence that NbS might be effective.     

Differences Between Mode I and Mode II Crack Propagation

Although mode I and mode II crack propagation show many similarities, in particular when analysed by linear elastic fracture mechanics, they differ significantly in the micro-structural behaviour. These differences, which are clearly noticeable in the fracture surface morphology, lead to fundamental differences in the macroscopic behaviour. Thus, mode II crack expansion under remote loading, appears to obey micro-structural scaling laws, implying that the dimensions of the process region stay essentially constant during crack expansion, rather than increasing with crack length. Therefore, expanding mode II cracks can almost reach the Rayleigh velocity, and actually also intersonic velocities. An expanding mode I crack, on the other hand, seems to obey continuum scaling laws, implying that the dimensions of the process region increase in proportion to crack length, leading to self-similar crack expansion at a velocity significantly below the Rayleigh speed and dependent on the remote load.     

2004年印尼8.7级强震前昌黎台的远场电性异常特征探讨

分析了在2004年12月26日印尼8.7级地震前河北昌黎台记录到的自然电位及电场异常, 结果显示昌黎台自电位、 电场正常时段观测到的半日、 半月潮汐波周期变化在震前1个多月发生畸变, 周期消失, 变化幅度相应减小, 震后快速恢复, 且潮汐波记录比震前正常时段更加清晰。 该台地电阻率的观测结果显示起始下降变化比较平缓, 震前一周左右, 变化加剧, 出现多次阶变。 究其原因, 在强震发生前断层的蠕滑作用导致孔隙压力变化, 产生一种可以在岩石中传播的应变波, 由于台站下方岩土层对小应变信号具有很好的放大作用, 所以记录到了这种小幅度的应变波, 也就是远场的静态应变效应。 随着地震临近, 应力作用加强, 远程应变波引起台站下方水位、 水化学性质以及岩石孔隙度、 渗透率等的改变, 导致电阻率、 电场大幅度的阶变, 这反映了远场应变波的动态效应。 当然就异常幅度而言, 应变波的效应还嫌弱一些, 因此昌黎台异常变化可能还叠加了震源区激发的电磁波。     

Results from a new model of river basin evolution

This paper briefly describes a model of the erosional development of catchments and their channel networks. The model differentiates between the dominant transport processes in hillslope and channels. The development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms. The growth of a river basin is qualitatively described. The model concepts are used to study the basin during periods of growth (transient periods), as well as during dynamic equilibrium. This leads to hypotheses about the relationship between slopes, relief, tectonic uplift, erodability, runoff, and catchment area. It is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation.     

动三轴试验机轴向摩擦解决的研究

介绍了20 kN动三轴试验机机械工作原理,分析了该仪器轴向摩擦力的产生原因,提出了解决办法并加以具体实施.     

直记式强震加速度仪的动态特性与高频误差分析

本文在时域、频域范围内，对直记式ＱＺＹ型（中国）、ＳＭＡ—１型（美国）、ＳＭＡＣ—Ｂ２型（日本）强震加速度仪的动态特性进行了分析，给出了评价系统跟踪和复现地震加速度信号的快速性、平稳性和准确性的动态性能指标．在此基础上，分析和讨论了直记式加速度仪的高频误差，给出了系统幅频，相频相对畸变误差公式和系统参数设置的误差估计方法，计算了加速度仪系统的高频误差分布．最后，讨论了高频误差的校正方法．