Surface conductivity in rocks: a review

Electrical properties of rocks depend on composition (i.e. bulk properties of the constituents), micro structure (i.e. geometrical arrangement of the constituents) and interfacial effects. We consider here a rock as a three component system — grains, pores, and interfaces — in order to account for the observed behaviour. We review first the main results relative to DC. conductivity. Surface conductivity effects show up clearly in the case of shaly formations or at low salinities. Although Archies' law (1942) and Waxman and Smits model (1968) are widely used, a more physically based model is that of Johnson and Sen (1988). We review also the variable frequency conductivity (complex conductivity) data and models. The important effect in that case is the enhancement of the dielectric constant at low frequencies (Knight and Nur, 1987) which can be interpreted as a geometrical effect although electrochemical interactions may also play an important role at low frequencies, depending on the rock type.     

咸淡水驱替过程中含水介质渗透性变化的试验研究

在野外水文地质调查的基础上,采集青岛市大沽河下游咸水入侵区砂样,首先对含水介质的粒度和矿物组成进行了分析,然后通过室内砂槽模拟试验,对咸淡水驱替过程中含水介质的渗透性变化规律进行了研究。结果表明,当咸淡水相互驱替时,含水介质的渗透性会发生显著变化,这种变化主要是由于驱替液盐浓度的变化,使得伊利石、高岭石和绿泥石等非膨胀性粘土矿物经释放、迁移、絮凝和沉积,从而重新分布所引起的。含水介质渗透性的变化具有明显的非均质性,即位于距入水处不同水平距离以及不同高度处的含水介质,其渗透性变化规律有所不同。     

Analysis on variation characteristics of geothermal response in Liaoning Province

Due to energy shortage and increasing environmental awareness, resources in shallow underground space have been rapidly exploited and utilized. So that studying variation characteristics of geothermal response in gneiss is necessary for effective and rational use of underground heat. Based on field test of thermal response in gneiss under hydrogeological survey project carried out in shallow geothermal energy development zone in Liaoning Province, this thesis analyzes mathematical statistics of geothermal response characteristics in main gneiss of Laoning Province. The initial formation temperature ranges from 10.80℃ to 15.80℃ according to field test. The statistical results show that in the condition of natural water content, the average thermal conductivity of Quaternary loose rocks comes as clay silty silty fine sand medium sand coarse sand gravelly sand. This order is consistent with thermal conductivity characteristics of gneiss obtained in the laboratory. Formation temperature recovery in different strata follows as granite medium sand clay. This order is opposite to the absolute value of temperature recovery curve slope of corresponding lithology, which shows that the stratum with higher temperature recovery rate has lower temperature recovery curve slope.     

土热传导系数及模型的研究现状和展望

近年来,随着全球能源消耗的增加,对新能源的开发和利用日益重要。地热资源作为一种清洁环保的新能源已经开始引起广泛的关注,对岩土材料的热性质研究也逐渐受到国内外学者的重视。土的热性质包括热传导系数、热扩散系数和比热容。其中,热传导系数作为其中最重要的性质,它不仅决定了热量在土体中的传播速度和土体温度场的分布,同时也是各种地热泵、能量桩等建筑热工结构设计中需要考虑的主要参数之一。首先介绍了土热传导系数的工程背景和研究意义,描述了土中的热量传播方式和类型,阐述了热传导系数的概念,并分析了土热传导系数的各种影响因素（含水率、密度、矿物成分、温度等）。在此基础上,总结了目前国内外土热传导系数模型的研究现状,并对各个模型的优缺点进行了简要的分析和评价。最后,提出了对土传导系数及模型研究的建议和展望。     

唐山M 4.8地震地磁谐波振幅比变化

针对2012年5月28日河北唐山M 4.8地震,采用地磁谐波振幅比方法,分析昌黎、静海、红山及承德地磁台2007年1月至2015年12月地磁观测数据,结果显示：各台站10 min周期的计算结果波动性明显,其他周期形态较为一致;距震中最近的昌黎地磁台Y_ZHx（NS）测向的10-40 min周期地磁谐波在下降至极低值后,开始转折时发生地震,而Y_ZHy（EW）测向未出现明显转折现象;位于河北平原地震带中部的静海地磁台对此次地震反应显著,2个测向在震前均出现下降-转折-上升的变化特征。通过对比位于不同地区的4个地磁台站地磁谐波振幅比变化,发现受大范围整体构造应力场作用的影响,计算结果具有相似的趋势性变化特征,具体到局部地区或断裂带内部,各台站之间显示出一定差异。     

Fluid permeability of sedimentary rocks in a complete stress–strain process

The permeability of sedimentary rocks during triaxial compression tests was investigated to relate it to the complete strain–stress process. It was found that the permeability was not constant, but varied with the stress and strain states in the rocks. Prior to the peak strength, the permeability decreases with increasing load. A dramatic increase in permeability occurs during the strain softening period. In the present study, in situ measurements of fluid flow and pressure in floor strata was carried out in a double longwall mining face in the Yangzhuang colliery. These measurements show that both the strata pressure and the position with respect to the mining face influence the hydrogeologic properties. The permeability increased in the floor strata behind the mining face because those mining induced fractures opened as the strata pressure decreased. To better understand this change in hydraulic behavior around the mining faces, 3-D numerical modeling was carried out. The model provides the general picture of the stress distribution and failure zone both in the floor and roof strata. The field and model results demonstrate the importance of changes in the stress and strain states on the hydrogeology of a site.     

Improving groundwater-flow modeling using optimal zoning methods

Hydraulic conductivity sometimes exhibits complicated spatial variation over a site. A thorough understanding of the spatial distributions of hydraulic conductivity helps to make deterministic models of groundwater more accurate. This study presents a novel procedure that combines simulated annealing algorithms (SA) and the shortest distance method (SD) with the modular three-dimensional groundwater flow model (MODFLOW). The procedure is applied to a hypothetical site with groundwater-monitoring wells to minimize the difference between simulated and observed hydraulic head for optimal zoning of the spatial distribution of hydraulic conductivity. The results of this optimal zoning method indicate that this new procedure not only improves the efficiency of optimization, but also increases the probability of finding the global optimum, minimizing the errors of the hydraulic head simulated by MODFLOW in two scenarios, one with known and the other with unknown hydraulic conductivity. The results also illustrated that the procedure can effectively determine and delineate hydrogeological zones.     

Microstructure and hydraulic conductivity of a compacted lime-treated soil

Under a given compaction energy and procedure, it is known that maximum dry density of a soil is lowered due to lime addition. This modification of maximum dry density could alter the hydraulic conductivity of the soil. The main object of this study was to assess the impact of lime-stabilization on a silt soil microstructure and then on saturated hydraulic conductivity. An investigation at the microscopic level with mercury intrusion porosimetry showed that lime treatment induced the formation of a new small class, with a diameter lower than 3 × 10³ Å in the compacted soil. This class is responsible for the difference in dry density between the treated and the untreated sample after compaction. It is shown that this small pores class was not altered by the compaction water content, the compaction procedure or the dry density. As in untreated soils, only the larger pores were modified by the compaction water content and the compaction procedure in the lime treated samples. The hydraulic conductivity appeared to be only related to the largest pores volume of the tested silt, regardless of lime treatment. Therefore, this study demonstrated that even if addition of lime resulted in a dramatic change of the maximum dry density of the tested silty soil, its effect on hydraulic conductivity is limited.