The numerical study of wave-induced pore water pressure response in highly permeable seabed

The coupling numerical model of wave interaction with porous medium is used to study waveinduced pore water pressure in high permeability seabed.In the model,the wave field solver is based on the two dimensional Reynolds-averaged Navier-Stokes(RANS) equations with a k-ε closure,and Forchheimer equations are adopted for flow within the porous media.By introducing a Velocity-Pressure Correction equation for the wave flow and porous flow,a highly efficient coupling between the two flows is implemented.The numerical tests are conducted to study the effects of seabed thickness,porosity,particle size and intrinsic permeability coefficient on regular wave and solitary wave-induced pore water pressure response.The results indicate that,as compared with regular wave-induced,solitary wave-induced pore water pressure has larger values and stronger action on seabed with different parameters.The results also clearly show the flow characteristics of pore water flow within seabed and water wave flow on seabed.The maximum pore water flow velocities within seabed under solitary wave action are higher than those under regular wave action.     

透水管桩加速超静孔压消散的单桩模型试验研究

基于室内模型试验,研究透水管桩促进桩周土超静孔压消散的效果和规律。通过透水管桩和普通管桩单桩沉桩模型试验对比,发现使用透水管桩更有利于桩周土超静孔压消散,其促进作用沿深度方向递增,沿水平方向递减。在桩周土超静孔压消散前期,透水管桩的促进作用最明显,有利于加快施工进度。改变透水管桩初始排水时刻,观察桩周土超静孔压消散情况,发现初始排水时刻设在沉桩完成时的情况下,桩周土超静孔压峰值明显减小。试验结果表明,沉桩施工中,透水管桩提高了施工进度,降低了对周围环境的影响。     

Enzyme activities in the water column and in shallow permeable sediments from the northeastern Gulf of Mexico

The activities of extracellular enzymes that initiate the microbial remineralization of high molecular weight organic matter were investigated in the water column and sandy surface sediments at two sites in the northeastern Gulf of Mexico. Six fluorescently labeled polysaccharides were hydrolyzed rapidly in the water column as well as in permeable sediments. This result contrasts with previous studies carried out in environments dominated by fine-grained muds, in which the spectrum of enzymes active in the water column is quite limited compared to that of the underlying sediments. Extracts of Spirulina, Isochrysis, and Thalassiosira were also used to measure hydrolysis rates in water from one of the sites. Rates of hydrolysis of the three plankton extracts were comparable to those of the purified polysaccharides. The broad spectrum and rapid rates of hydrolysis observed in the water column at both sites in the northeastern Gulf of Mexico may be due to the permeable nature of the sediments. Fluid flux through the sediments is sufficiently high that the entire 1.5 m deep water column could filter though the sediments on timescales of a few days to two weeks. Movement of water through sediments may also transport dissolved enzymes from the sediment into the water column, enhancing the spectrum as well as the rate of water column enzymatic activities. Such interaction between the sediments and water column would permit water column microbial communities to access high molecular weight substrates that might otherwise remain unavailable as substrates.     

盆地内渗透性地层超压形成机制及钻前压力预测

在世界范围内,沉积盆地高超压区的压力预测和安全钻井是长久未能解决的难题。在钻井过程中可能引起各种钻井工程事故的主要原因是渗透砂支内的高压,而现在通用压力预测和监测方法却建立在低渗透的泥质岩内超压产生及对其岩性、物性变化影响的基础上。本文讨论了沉积盆地内异常高压分布的特征,着重探讨了在渗透砂岩层中异常流体压力产生的机制,划分出自源、邻源和他源３种成因类型,并讨论了各类超压对钻井工程的危害性和可预测性     

苯、甲苯对粒状铁去除四氯乙烯影响的柱实验研究

挥发性氯代烃和石油烃类污染是地下水中最常见的混合污染类型,而且这两类污染物毒性极强,对人类危害非常严重。文中选取具有代表性的四氯乙烯、苯和甲苯为研究对象,采用柱实验的方法研究苯和甲苯在粒状铁反应系统中吸附平衡后,对粒状铁去除四氯乙烯的机理及反应动力学的影响。在实验装置运行的过程中,苯、甲苯和四氯乙烯的浓度始终控制在2mg/L左右的水平。实验结果表明:苯或甲苯的存在对被还原的产物组成没有影响,主要氯代中间产物均为TCE、1,1-DCE、cis-1,2-DCE和VC,但组成比例略有不同。苯和甲苯的存在对去除速率有影响,即苯对四氯乙烯的去除有促进作用,去除速率平均提高13.5%;而甲苯则抑制四氯乙烯的去除,去除速率平均降低13.8%。对比控制柱,苯和甲苯存在时对出水水化学变化的影响没有明显差异。     

Seismic isolation effect of lined circular tunnels with damping treatments

The Havriliak-Negami model for dynamic viscoelastic material behavior and Biot＇s theory of poroelasticity are employed to develop an exact solution for three-dimensional scattering effect of harmonic plane P-SV waves from a circular cavity lined with a multilayered fluid-filled shell of infinite length containing viscoelastic damping materials and embedded within a fluid-saturated permeable surrounding soil medium. The analytical results are illustrated with numerical examples where the effects of liner/coating structural arrangement, viscoelastic material properties, liner-soil interface bonding condition, seismic excitation frequency, and angle of incidence on the induced dynamic stress concentrations are evaluated and discussed to obtain representative values of the parameters that characterize the system. It is demonstrated that incorporating viscoelastic damping materials with a low shear modulus in the constrained layer configuration is an efficient means of enhancing the overall seismic isolation performance, especially for near-normally incident seismic shear waves where the amplitudes of induced dynamic stresses may be reduced by up to one-third of those without isolation in a relatively wide frequency range. Some additional cases are considered and good agreements with solutions available in the literature are obtained.     

Impacts of permeable interlocking concrete pavement on the runoff hydrograph: Volume reduction,peak flow mitigation,and extension of lag times

Permeable pavements are implemented to provide at-source treatment of urban stormwater runoff while supporting vehicular and pedestrian use. Studies on these systems have mainly focused on those treating only direct rainfall and installed atop well-drained soils which typically provide substantial hydrologic mitigation through exfiltration that may not be representative of more hydrologically taxing conditions. A single lane parking area retrofitted with permeable interlocking concrete pavement in Vermilion, OH, USA was monitored over a 15-month period to quantify its hydrologic performance under such conditions. The 470 m² permeable pavement was underlain by silt loam soils and a shallow bedrock layer and treated run-on from the adjacent 324 m² asphalt drive lane. Observed data were compared to a calibrated SWMM model developed to simulate the pre-retrofit conditions of the site (i.e., a completely impervious parking lot). Cumulative runoff volumes were reduced by 43% across all events in the monitoring period compared to a fully impervious parking lot. While median peak flows were reduced by 75%, substantial mitigation was limited to smaller, lower intensity events with longer antecedent dry periods (i.e., non-flood producing events). The permeable pavement significantly delayed the occurrence of peak flows from the site following peak rainfall intensity by a median 29 min. Results from this study demonstrate that permeable pavements which receive run-on from adjacent imperious cover and are installed atop poorly drained soils can significantly reduce runoff volumes and peak flow rates and delay the occurrence of peak discharge. The modelling approach implemented can provide a better estimation of diffuse inflows to green infrastructure stormwater controls and aid in refining design features which enhance the hydrologic performance in systems underlain by poorly drained soils.     

岩体渗透性空间对河谷地下水形态的控制作用 以洮河九甸峡水利枢纽坝区为例

河谷区的地下水水位线形态表征着河谷区地下水的流场特征,其成因关系到水库渗漏和工程的可行性。岩土的渗透性对河谷地下水形态具控制性作用,在同一工程区内岩土体渗透性在空间上的分布也常常是不均一的,在我国西南部的高山峡谷地区,岩体的渗透性空间具明显的各向异性和分区分带特征,这使得地下水水位线形态在横剖面上呈现缓U型、斜W型和W型,在河流两岸产生地下水低凹带。通过对甘肃洮河九甸峡坝区地质条件的研究表明,河谷两岸地下水低凹带并非一定是存在强渗流通道所致,河谷区岩体渗透空间具有的分层分带和强各向异性特性足以使得河谷两岸出现地下水低凹带。这有效地解决了因坝区存在地下水低凹带而带来的疑虑和担忧,有力地推动了工程的进展,同时对于其他地区工程的开展具重要的借鉴意义。     

Numerical study for waves propagating over a porous seabed around a submerged permeable breakwater: PORO-WSSI II model

The phenomenon of the wave, seabed and structure interactions has attracted great attentions from coastal geotechnical engineers in recent years. Most previous investigations have based on individual approaches, which focused on either flow region or seabed domain. In this study, an integrated model (PORO-WSSI II), based on the Volume-Averaged/Reynolds-Averaged Navier-Stokes (VARANS) equations and Biot's poro-elastic theory, is developed to investigate the mechanism of the wave-permeable structure-porous seabed interactions. The new model is verified with the previous experimental data. Based on the present model, parametric studies have been carried out to investigate the influences of wave, soil and structure parameters on the wave-induced pore pressure. Numerical results indicated: (i) longer wave period and larger wave height will obviously induce a higher magnitude of pore pressure at the leading edge of a breakwater; (ii) after a full wave-structure interaction, the magnitude of pore pressure below the lee side of a breakwater decreases with an increasing structure porosity while it varies dramatically with a change of structure height; and (iii) the seabed thickness, soil permeability and the degree of saturation can also significantly affect the dynamic soil behaviour.     

〖HT2H〗低渗透砂岩油层相对渗透率曲线特征、影响因素及其对开发的影响

低渗透储层油、水两相渗透率特征及其影响因素的研究,是认识、分析低渗透储层油、水两相渗流机理的重要途径,是合理开发油田的基础。本文在总结低渗透油藏油水相对渗透率曲线特征的基础上,对以火山岩、凝灰岩岩屑为主的岩屑砂岩相对渗透率曲线特征进行研究,并分析了其影响因素,研究表明低渗透储层的岩石学特征,碎屑颗粒的成份、结构,其表面的粗糙程度,及其粘土矿物的产状对相对渗透率曲线有明显的影响。这一研究成果对合理开发此类低渗透油田有着十分重要的意义。