透壁通风管增强开放碎石路堤降温效果试验

通过4种不同实验条件下透壁通风管开放碎石路堤试样室内试验研究了通风情况对透壁通风管增强开放碎石路堤降温效应的影响。比较4种实验结果发现,透壁通风管开放碎石路堤存在碎石表面单纯热传导传热、外界空气通过碎石路堤开放表面与碎石层内孔隙空气直接循环产生的强迫对流传热、通风管管壁与管内空气的对流换热以及管内空气通过管壁透气小孔与附近碎石层内孔隙空气直接循环产生的强迫对流传热4种传热过程。对于仅负温通风的透壁通风管开放碎石路堤,通过开放表面及管壁透气小孔使外界冷空气与碎石层内孔隙空气形成循环,从而显著增强了路堤冬季冷空气引起的降温效应。     

Subsurface Airflow Induced by Natural Forcings

Subsurface airflow can be induced by natural processes,such as atmospheric or barometric pressure changes, water table fluctuations,topographic effects,and rainfall infiltration．Barometric pressure fluctuations are the most common cause of subsurface airflow,which can be significant under favourable geological conditions．This process has been studied most extensively because of its application to passive soil vapor extraction．Soil airflow induced by water table fluctuations can be significant,particularly where the fluctuations are of high frequency,for example,in tidal-influenced coastal areas．Top-ographic effects can lead to strong subsoil airflow in areas with great elevation differences．Rainfall infiltration usually produces only weak airflow.Air flow induced by these natural processes has important environmental and engineering implications．Among the different processes,airflow induced by tidal fluctuations has been studied the least,although it has exciting applications to coastal engineering projects and environmental remediation．     

利用斯通利波衰减反演渗透率的方法改进

利用严格的Biot介质模型,针对阵列声波测井情况,建立了基于物理统计方法的利用斯通利波幅度衰减反演储层渗透率之线性化最小二乘反演模型。作为对方法可行性的检验,运用该方法对理论合成数据进行了处理,结果表明运用统计方法后反演渗透率的偏差变小,证明了方法的可行性。     

边界条件对碎石层降温效果及机理的影响

对平均粒径为22.1 cm, 厚度1.3 m, 边界为开放和封闭的碎石层进行了一系列的实验. 从环境温度为最高和最低时刻封闭碎石层内的温度和速度分布可知: 当碎石层上表面温度低于下表面时,碎石层自下向上的散热由空气对流和碎石间的热传导来完成; 当上表面温度高于下表面时, 自上向下传递的热量由碎石接触面间的热传导完成, 此时, 由于其内部的空气几乎静止, 能阻隔热量的传入, 因此封闭边界的碎石层具有热半导体特性. 而开放边界的碎石层, 当平均温度为 0.5℃的空气从上表面吹过时, 碎石体内的热量传递主要是靠强迫对流来完成, 热半导体效果不明显, 不利于使其下面的冻土降温.     

海潮引起的滨海地区包气带气压周期性变化的数值模拟

滨海地区的地下水位由于海潮而上下波动, 这早已是为人熟知的事实.但是, 滨海地区包气带中气压也会随海潮的起伏而作周期性变化, 这一点却很少为人注意.如果地表由渗透性差的材料如水泥或沥青路面覆盖(这种情况在香港高度城市化的近海地区很常见), 海潮的起伏会产生幅度异常高的气压波动.在某些情形下, 足够高的气压会引起如路面拱起等工程问题.因此, 研究海潮引起的包气带气流, 不仅具有理论意义, 还对滨海地区土木工程有实际指导作用.以香港某滨海地区为例, 建立了该地区一剖面上水气两相流的二维数学模型, 并用TOUGH2程序进行了数值模拟.通过数值敏感度分析, 探讨了影响沥青路面下气压的主要水文地质因素.在根据该地区实际水文地质情况选取了适当的模型边界条件和模型参数后, 沥青路面下气压的数值模拟结果和观测数据吻合程度良好.      

Groundwater Behaviour in Layered Slope Rock Mass And Finite Element Simulation

The paper deals with the relatively weak permeable layer in a layered structure of a slope rock mass and itseffect on groundwater behaviour in the rock mass. When the whole groundwater table is declined in such typeof slope rock mass, the permeability of the relatively weak permeable layer in the middle will be several timeslower than that of the upper and lower permeable layers and consequently the water level in layers of differentpermeability will fall in different rates which will lead to a discontinuous phenomenon of the water body. Amethod of finite element simulation on a vertical two-dimensional profile is suggested for the study of the phe-nomenon and its application to practical situation is described. The calculation result shows that the existingweak permeable layer in a layered slope rock mass exerts unnegligible influence on the variation of water levelin the rock mass of a slope. The result also proves the applicability of the finite element simulation method.     

碎石集料变形机理的块体元数值试验分析

块碎石作为道砟材料能够分散列车动荷载, 加之其内部含有大量空隙, 具有良好的对流换热特性, 作为冷却冻土路基的材料在青藏铁路建设中被广泛使用。但在列车荷载的作用下, 碎石集料会发生压密、 变形乃至破碎从而影响冷却效果。因此, 研究碎石层的变形过程及机理具有十分重要的现实意义。基于块体离散元法, 对块碎石集料的三轴剪切试验进行了数值分析, 将所得应力-应变曲线与室内试验结果进行了对比, 发现两者能较好地吻合, 说明块体离散元法能够较好地模拟块碎石集料的受力变形过程。结果表明： 增大围压或块体粒径, 块体单元受到的作用力加强, 集料的偏应力强度和抗剪强度值也随之增大。碎石块体在剪切作用下沿其接触面滑动分离, 形成X形剪切带是集料变形的主要形式, 此外在径向方向出现不同程度的扩张。基于试验和块体元研究路基碎石层的思路和方法可为今后评估青藏铁路碎石路基的热力稳定性提供理论依据和参数储备。     

岩石变形破坏过程中渗透率演化规律的试验研究

利用伺服试验机对灰岩和砂岩进行了应力应变全过程渗透性试验,研究了岩样变形和破坏过程中的轴向应变与渗透率之间的关系,分析了岩样环向应变对渗透率的影响规律,探讨了岩样变形破坏前后渗透压差随时间的变化关系。结果表明,岩样渗透率与应力状态密切相关,渗透率的峰值滞后或超前于应力应变峰值,这与岩石介质本身的特性有关;渗透率-环向应变曲线与渗透率-轴向应变曲线有相同的变化趋势,但岩石环向变形比轴向变形更能灵敏地反映渗透率的演化规律;岩样变形破坏峰值前后的渗透压差与时间均遵循负指数关系。最后对岩石变形破坏过程中的渗透机理作了讨论。     

〖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。     

平朔露天煤矿复垦区不同地质层组岩土质量综合评价

露天煤矿生态地质环境系统恢复过程中,排于地表的不同年代地质层组的岩土剥离物都有可能成为复垦土壤母质。为科学合理利用矿区岩土剥离物,重构高质量复垦土壤,并指导后期分类排放,以平朔露天矿区黄土母质作为对照,评价不同类型岩土理化性状差异,从复垦土壤母质来源进行造地的源头控制,为露天煤矿土地复垦与生态修复提供依据。结合单项养分含量及有益微量元素含量分析结果,借助修正的内梅罗综合指数法,评价各岩土层肥力质量;借助单因子质量指数法,评价各岩土层环境质量。结果表明:各岩土层综合肥力系数位于0.40～1.26范围内,属贫瘠或一般水平;安家岭矿中2个煤矸石层的有机质或全氮含量、上部页岩层的全钾含量,以及东露天矿中炭质泥岩层的全磷含量丰富,显著高于黄土母质层;东露天矿底部细砂岩层及安家岭矿中泥灰岩层硫含量过高;东露天矿镉元素环境质量指数为1.05,属轻微污染等级;安家岭矿底部细砂岩层pH值低至4.25,酸度过大。平朔露天矿大多岩土层环境质量较好,但综合肥力质量较差,其中单项养分含量丰富,环境质量安全且易于风化的岩土层,适宜作为重构复垦土壤的备选材料。     

Site response studies in Mumbai using (H/V) Nakamura technique

The importance of characterizing the site effects in urban areas, especially Mumbai, the commercial capital of India, with a quarter of land below sea level, is well realized. Mumbai is built on a cluster of seven basaltic islands that were merged together through reclamation of land from the Arabian Sea. Due to rapid urbanization, the demarcation between reclaimed areas and original islands is blurred. A pilot study is undertaken to investigate and characterize the local site effects at 27 locations in Mumbai. The Nakamura technique is used to estimate the fundamental frequency of soft soils at each site, characterized by the ratio (H/V) of the Fourier spectra of the horizontal and vertical components of ambient noise measurements made with a 3-component short period (1 Hz) seismograph. Validation of peak frequency was done using both pre-event and event data. The peak amplification was also validated through measurements at a 10-m exposed soil section and over a soil dump. Overall, the site responses correlate well with the local geology and the lithologs obtained at 40 boreholes at 8 locations The reclaimed areas are characterized by resonance frequencies ranging from 3.3 to 4.6 Hz with significant peak amplification (>4) in contrast to hard rock sites that do not exhibit peak amplification. The hard rock sites with soil cover exhibit peak amplification in the frequency range 3.3–10.5 Hz indicating large variations in soil thickness. The H/V curves at most sites exhibit clear single peaks with large amplitude, which could be associated with sharp discontinuities corresponding to a uni-model of a single layer with large velocity contrast overlying the basement. The low resonance frequencies together with large amplification of site responses enable identifying and demarcating reclaimed areas that form important inputs in the seismic microzonation of Mumbai.     

海底泉对在海底有限延伸的越流含水层系统中地下水潮汐效应的增强作用

海底泉在滨海地下水排泄过程中起着重要的作用。本文给出了含有一个海底泉的在海底延伸的越流承压含水层系统中地下水水头在海潮作用下波动的近似解析解。该含水层顶底板隔水且向海底延伸有限距离。假设含水层的海底露头被一层隔水层覆盖,海底泉由一个渗透性很好的完全穿透海底含水层硕板的圆柱体渗漏天窗（海底泉孔）来表示。近似解析解中包含了6个参数：承压含水层的海潮传播参数,海底泉孔中心到海岸线的距离,表示泉的圆柱体的等效半径,海底泉孔中心到含水层海底露头处的距离,承压含水层的海潮载荷效率和弱透水层的越流。分析表明,如果海底泉孔中心到海岸线的距离远大于泉孔的等效半径,且海底泉孔中心到含水层海底露头处的距离远大于泉孔的等效半径时,解析解的近似误差可以忽略。然后本文讨论了解析解的两个基本性质,分析了海底泉对海底地下水水头波动的影响。     

表面条件对透壁通风管碎石路堤降温效果的影响

针对青藏高原冻土区高速公路拟采用的透壁通风管碎石路堤,进行了表面开放和封闭透壁通风管碎石试样降温效果的室内试验,分析比较了表面开放和封闭边界条件对透壁通风管负温通风增强碎石路堤降温效果的影响差异。分析表明,表面开放和封闭透壁通风管碎石路堤都以外界空气通过管壁透气小孔与通风管附近碎石区域孔隙空气循环产生的强迫对流传热增强降温作用,另外,表面封闭透壁通风管碎石路堤能够在上部碎石区域产生孔隙空气循环的自然对流降温效应。因此,表面封闭透壁通风管碎石路堤的降温效果更为显著。     

Analytical solution for two-dimensional dynamic consolidation in frequency domain

An analytical solution to the two-dimensional wave propagation in fluid-saturated half-space subjected to a strip load with vertical harmonic oscillation at the surface is presented. The basic equations have been derived on the basis of Biot's linear theory of poro-elasticity and then solved using Fourier complex transform for the horizontal direction. The importance of a number of soil characteristics including compressibility, degree of saturation and soil permeability has been examined. It is shown that the effect of pore fluid is dominant only for fully saturated soils with incompressible solid grains and low permeability. For partially saturated, compressible or very permeable soils, the stresses would be mainly transferred to solid part and there will be considerable reduction in pore pressure amplitude.     

青藏铁路块石气冷结构路堤下冻土温度场变化分析

基于青藏铁路沿线多年冻土区温度监测断面,选取了不同冻土分区中的8个块石路堤结构(块石路基、块石护坡、块石路基加块石护坡)断面,对其下温度场的变化分析研究.结果表明:经过2~3个冻融循环后,块石结构路堤下冻土上限已抬升了1.4~5.3 m,说明块石路堤结构已起到了积极调节下伏冻土温度的作用.结果也显示,在上限抬升的同时,其下部的冻土地温也在升高,但是这种过程已逐渐被块石路堤结构的降温所抑制,而这种抑制程度受控于不同的冻土区域.在不同的冻土分区中,无论是何种形式的块石路堤结构,其降温趋势是不同的.Ⅳ和Ⅲ冻土区块石路堤基底的负温积累比较明显,而I和Ⅱ区的较弱.     

碎(块)石路堤孔隙空气对流运动的Darcy定律适用性

针对青藏高原多年冻土区路基工程中采用的碎石路堤地温调控技术,分析了碎石层孔隙空气对流运动符合Darcy定律的适用范围及其可能偏离Darcy定律的非线性效应,并给出了考虑非线性效应的Darcy定律修正方程.同时,讨论了适合于路堤碎石层的空气渗透系数及其表征空气流动非线性效应的Ergun常数的估算公式.     

无砟轨道聚氨酯碎石防水联结层单元模型试验研究

基于无砟轨道基床表层水力损伤病害产生机制,提出一种在基床表层上设置聚氨酯碎石防水联结层的水力损伤控制措施。通过建立级配碎石组(J-0)、透水型聚氨酯碎石组(J-5)及致密型聚氨酯碎石组(J-10)3组试验模型,研究聚氨酯碎石防水联结层的静动力特性、疲劳特性与防水特性。结果表明：静力加卸载作用下,J-10残余应变为2.6×10–6,最大位移约为1.0 mm,与下部基床表层级配碎石层变形适应性良好,耗能效果明显,在列车动力荷载水平作用下,可减小基床表层动变形与动应力幅值,增大动应力扩散范围;在长期动力循环荷载作用下,J-0与J-5在注水后结构层动力响应显著增大,而J-10动力响应在加载次数1～2万次后基本保持稳定;试验过程中J-10能够有效防止水分进入基床表层级配碎石层,而J-0与J-5水分不断下渗,引起级配碎石细颗粒损失。研究成果对整治多雨地区无砟轨道基床表层水力损伤病害具有重要的应用价值。     

青藏铁路多年冻土地区碎石护坡路基非线性分析

为了研究碎石护坡对冻土区路基温度场的影响,以青藏铁路试验段现场观测的气候和地质资料为上边界条件,运用带相变瞬态温度场有限元数值解法,对不同厚度的碎石护坡路基进行了分析。结果表明:粒径为10 cm的碎石护坡对多年冻土区路基的稳定性有保护作用;碎石护坡对路基坡脚附近地温影响较大,采用碎石护坡对防止路基纵向裂缝的产生有一定的作用;实际应用中碎石层厚度不能太厚。     

裂隙岩体渗透结构类型分析

岩体的渗透结构控制着裂隙岩体的宏观渗透特征,而控制着岩体渗透结构类型的地质因素却是复杂多样。在实际工程岩体中,裂隙岩体的渗透结构通常是由基本渗透结构经过组合叠加而形成的复合渗透结构类型。本文通过野外调研和室内统计分析,总结了裂隙岩体中广泛存在的5种基本渗透结构类型及其4种组合形式的复合渗透结构类型及其渗流特征,分别归为Ⅰ-Ⅱ型、Ⅲ-Ⅳ型、Ⅰ-Ⅱ-Ⅲ型和Ⅰ-Ⅲ-Ⅳ型。并选择一工程实例,运用裂隙岩体复合渗透结构类型的分析方法,分析了西南某水电站主厂房和开关站边坡岩体的复合渗透结构类型以Ⅲ-Ⅳ型和Ⅰ-Ⅲ-Ⅳ型为主,更符合实际情况。     

Microcrack-based coupled damage and flow modeling of fracturing evolution in permeable brittle rocks

Microcracks in brittle rocks affect not only the local mechanical properties, but also the poroelastic behavior and permeability. A continuum coupled hydro-mechanical modeling approach is presented using a two-scale conceptual model representing realistic rock material containing micro-fractures. This approach combines a microcrack-based continuous damage model within generalized Biot poroelasticity, in which the tensors of macroscopic elastic stiffness, Biot effective stress coefficient and of overall permeability are directly related to microcrack growth. Heterogeneity in both mechanical and hydraulic properties evolves from an initially random distribution of damage to produce localized failure and fluid transmission. A significant advantage of the approach is the ability to accurately predict the evolution of realistic fracturing and associated fluid flow in permeable rocks where pre-existing fractures exert significant control. The model is validated for biaxial failure of rock in compression and replicates typical pre- and post-peak strength metrics of stress drop, AE event counts, permeability evolution and failure modes. The model is applied to the simulation of hydraulic fracturing in permeable rocks to examine the effects of heterogeneities, permeability and borehole pressurization rate on the initiation of fracturing. The results indicate that more homogenous rocks require higher hydraulic pressure to initiate fracturing and breakdown. Moreover, both the fracturing initiation pressure and breakdown pressure decrease with permeability but increase with borehole pressurization rate, and the upper and lower limit of the initiation pressure are seen to be given by the impermeable (Hubbert–Willis) and permeable (Haimson–Fairhurst) borehole wall solutions, respectively. The numerical results are shown to be in good agreement with the experimental observations and theoretical results. This coupled damage and flow modeling approach provides an alternative way to solve a variety of complicated hydro-mechanical problems in practical rock engineering with the process coupling strictly enforced.