共查询到18条相似文献，搜索用时 109 毫秒
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在MTS伺服压机上对不同饱和状态的砂岩、大理岩标本进行了垂直层理和平行层理两个方向的正弦波加载试验,研究了饱和岩石的各向异性及非线性黏弹性行为. 在最大载荷低于岩石的屈服点时,获得的衰减、杨氏模量、泊松比、波速都表现出显著的各向异性,同时它们还具有较明显的应变振幅效应和频率效应. 随着应变振幅的增大,衰减近似呈线性增长,杨氏模量和泊松比近似呈线性下降. 在0.005-4Hz频段内除衰减不明显依赖频率以外,杨氏模量、泊松比、波速对频率的依赖性都较强; 当频段扩大到15Hz时,这4个参数都表现出较强的频率效应. 饱和岩石的衰减、杨氏模量、泊松比、波速均随饱和液体的黏滞系数增大而增大. 相似文献
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结晶岩的水化膨胀研究 总被引：3，自引：0，他引：3
室温下的应变实验表明 ,低孔隙度的结晶岩如花岗岩、片麻岩、闪长岩和变基性岩 ,水饱和时膨胀 ,干燥时收缩 ,这种效应是可重复的 .用水的吸附和解吸 （在相对湿度下 ） ,也可以观察到膨胀和收缩 .膨胀效应是由于表面力 （VanderWaals吸引、双电层排斥及溶剂化排斥 ）引起的 .水饱和体应变约为其孔隙度的 1 /1 0 .用庚烷饱和的体应变比用水饱和的小 .用CaCl2 溶液饱和的应变随着盐克分子浓度的增加而减小 .杨氏模量E、切变模量G、品质因数Q的准静态测量表明 ,随着相对湿度的增加 ,E、G、Q减少 ,吸附水的增加改变了孔隙内表面分子的相互作用力 .大约在岩石孔隙表面吸附达到 3个水分子层时 ,可观察到最强烈的膨胀效应 . 相似文献
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《世界地震工程》2017,(1)
通过室内动三轴试验,分析了饱和细砂的动剪切模量演变特性和孔压效应,同时分析了循环荷载作用下相对密度、初始围压等因素的影响,提出了考虑孔压效应条件下饱和细砂动剪切模量的衰减特性,建立了动剪切模量比随孔压比增大而衰减的经验公式。结果表明:不同相对密度饱和细砂的应力-应变滞回圈的变化趋势显著不同;动孔压波动频繁并随时间逐步增长,并且不同的围压和相对密度对孔压比的增长有一定的影响;饱和细砂的动剪切模量随着孔压比的增大而逐渐减小,但不同相对密度饱和细砂的衰减趋势有所不同。通过拟合的曲线可以描述并预测不同相对密度饱和细砂的动剪切模量比随孔压比的衰减特性,具有较好的效果。 相似文献
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地球介质的非线性弹性造成了岩石动态和静态弹性模量在数值上的差异。本文用超声波速度测量得到岩石的动模量，用含有小循环的加卸载实验得到小循环模量，用大循环的应力、应变曲线斜率得到静模量，用测点的应力、应变之比得到杨氏模量。通过改变小循环的应变振幅来研究模量与应变振幅的关系，进而比较用不同测量方法得到的模量值的差异。结果表明，动模量值最大，小循环模量值次之，大循环静模量值再次之，而杨氏模量最小。岩石非线性模量既是所受应变水平的函数，也是应变振幅的函数，模量随应变振幅的增加以指数形式下降，随应变水平增加以指数形式上升。最后简要介绍了P-M模型的基本概念，用岩石中微裂缝具有不同的分布密度，不同的打开和关闭压力来解释模量与应变振幅的关系。 相似文献
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孔隙介质对波的衰减极为显著,因此,它能有效降低介质中冲击波的能量。普遍来说,地球浅层介质均可视为孔隙介质,即可作为应对冲击波的天然防护材料,这对大型地下结构的安全防护有着重要的意义。本文通过对大振幅应力脉冲通过水或冰充填的人工节理孔隙介质的测量结果分析,讨论了节理中固相/液相水对爆炸效果的作用。基于双孔隙模型和部分饱和模型计算预测的P波速度以及岩石衰减和频散规律,与实测数据相一致。实验与模型预测均表明,节理中的水和冰对冲击波有较大的衰减,但是充水节理更为明显,且由于填充材料的不同会导致不同的介质性质。因此,在地球介质孔隙节理中充填不同衰减特性材料,可以满足不同情况下的冲击波防护需要。 相似文献
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通过大型动三轴试验研究堆积体在不同应力水平、不同循环荷载幅值下残余应变与振次的关系,同时进行不同初始条件下残余应变的对比。试验发现堆积体在循环荷载下的残余应变与lg(1+N)有较好的线性关系(N≤30),沈珠江经验公式适用于堆积体在循环荷载下累积残余应变的计算。初始条件对堆积体的残余应变有重要影响,饱和不排水条件下残余剪应变最大,饱和排水条件次之,风干排气条件最小。应用沈珠江残余应变公式进行堆积体循环荷载下残余变形计算时应选取与工程实际条件相匹配的参数。 相似文献
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地震波传播激发的不同尺度的流固相对运动(宏观、中观和微观)是许多沉积岩地层中地震波频散和衰减的主要原因,然而野外观测和试验测量都难以对非均匀多孔介质孔隙压力弛豫物理过程进行精细刻画.通过数字岩石物理技术,本文建立了三个典型的数字岩心分别用于表征孔隙结构、岩石骨架和斑状饱和流体引起的非均质性,利用动态应力应变模拟技术计算数字岩心的位移和孔隙流体增量图像.通过分析和比较三个数字岩心的位移和孔隙压力增量图像,细致刻画了发生于非均匀含流体多孔介质内的宏观、中观和微观尺度的流固相对运动:1)宏观尺度的波致孔隙流体流动导致波长尺度上数字岩心不同区域的孔隙压力和位移差异;2)中观尺度的流体流动发生在软层与硬层之间、气层与液层之间;3)微观尺度的流体流动发生在孔隙内部或相邻孔隙之间.数值模拟试验也证明基于数字岩心的动态应力应变模拟技术可以从微观尺度上更好的理解波致孔隙流体流动发生的物理机理,从而为建立岩石骨架、孔隙流体、孔隙结构非均质性和弹性波频散-衰减特征的映射关系奠定基础. 相似文献
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The effect of surface phenomena occurring at the interfaces between immiscible fluids and a solid on the seismic attributes of partially saturated rocks has not yet been fully studied. Meanwhile, over the past two decades considerable progress has been made in the physics of wetting to understand effects such as contact line friction, contact line pinning, contact angle hysteresis, and equilibrium contact angle. In this paper, we developed a new rock physics model considering the aforementioned effects on seismic properties of the rock with a partially saturated plane-strain crack. We demonstrated that for small wave-induced stress perturbations, the contact line of the interface meniscus will remain pinned, while the meniscus will bulge and change its shape through the change of the contact angles. When the stress perturbation is larger than a critical value, the contact line will move with advancing or receding contact angle depending on the direction of contact line motion. A critical stress perturbation predicted by our model can be in the range of ∼102−104 Pa, that is typical for linear seismic waves. Our model predicts strong seismic attenuation in the case when the contact line is moving. When the contact line is pinned, the attenuation is negligibly small. Seismic attenuation is associated with the hysteresis of loading and unloading bulk moduli, predicted by our model. The hysteresis is large when the contact line is moving and negligibly small when the contact line is pinned. Furthermore, we demonstrate that the bulk modulus of the rock with a partially saturated crack depends also on the surface tension and on the contact angle hysteresis. These parameters are typically neglected during calculation of the effecting fluid moduli by applying different averaging techniques. We demonstrate that contact line friction may be a dominant seismic attenuation mechanism in the low frequency limit (<∼10 Hz) when capillary forces dominate over viscous forces during wave-induced two-phase fluid flow. 相似文献
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Cyclic shearing and liquefaction of soil under irregular loading: an incremental model for the dynamic earthquake-induced deformation 总被引：1，自引：0，他引：1
V. A. Osinov 《Soil Dynamics and Earthquake Engineering》2003,23(7):535-548
The paper presents a mathematical model for the deformation of soil under irregular cyclic loading in the simple-shear conditions. The model includes the possible change in the effective pressure in saturated soil due to the cyclic shearing, the reciprocal influence of the effective pressure on the response of the soil to the shear loading, and the pore pressure dissipation due to the seepage of the pore fluid. The hysteresis curves for the strain–stress relationship are constructed in such a way that they produce both the required backbone curve and the required damping ratio as functions of the strain amplitude. At the same time, the approach enables the constitutive functions involved in the model to be specified in various ways depending on the soil under study. The constitutive functions can be calibrated independently of each other from the conventional cyclic shear tests. The constitutive model is incorporated in the boundary value problem for the dynamic site response analysis of level ground. A numerical solution is presented for the dynamic deformation and liquefaction of soil at the Port Island site during the 1995 Hyogoken-Nambu earthquake. 相似文献
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A constitutive model of rocks subjected to cyclic stress–temperature was proposed. Based on statistical damage theory, the damage constitutive model with Weibull distribution was extended. Influence of model parameters on the stress–strain curve for rock reloading after stress–temperature cycling was then discussed. The proposed model was initially validated by rock tests for cyclic stress–temperature and only cyclic stress. Finally, the total damage evolution induced by stress–temperature cycling and reloading after cycling was explored and discussed. The proposed constitutive model is reasonable and applicable, describing well the stress–strain relationship during stress–temperature cycles and providing a good fit to the test results. Elastic modulus in the reference state and the damage induced by cycling affect the shape of reloading stress–strain curve. Total damage induced by cycling and reloading after cycling exhibits three stages: initial slow increase, mid-term accelerated increase, and final slow increase. 相似文献
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Laboratory data on dry and saturated rocks show that pore fluid has the most important effect on rock attenuation. It is known
that viscous and inertial coupling between the frame of a porous rock and its pore fluid dissipates seismic energy by conversion
to heat and hence cause attenuation. We show that attenuation peaks, in saturated rock have the same property as that of typical
thermally activated relaxations. In the frequency domain, a plot of attenuation versus frequency shows an obvious systematic
shift to higher frequencies with increasing temperatures. Similarly, the attenuation versus temperature curve moves to higher
temperature with increasing frequencies. The attenuation peaks are somewhat broader than that for a Zener relaxation. A Cole-Cole
distribution of relaxation times closely matches the attenuations. This behavior can be explained theoretically by local flow
mechanisms. 相似文献
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地震波在地下含流体孔隙介质中传播时,会引起中观尺度的"局域流",进而产生地震波震电效应.基于Biot(1941)固结理论的准静态方程,在频率域中采用空间有限差分方法,正演模拟虚岩石物理岩样的地震波衰减和震电效应.与时间域虚岩石物理方法相比,该方法既可以直接求取任一频率下的地震波衰减和电势,便于应用于实际岩样的预测分析,也避免了讨论岩样外表面施加的力源函数表达式及时间剖分稳定性条件等问题.首先利用周期性层状介质模型验证了本文所描述方法的有效性,并进一步求取分析了周期性层状介质两种不同特征单元的渗流电流密度及电势,数值模拟结果表明由中观尺度"局域流"引起的震电效应电势振幅数量级在实验室测量范围之内,随后,分析研究了四种不同高渗介质占比值的地震衰减及震电效应特征.最后,将本文提出的震电效应数值计算方法推广至二维,并求取了二维斑块饱和模型的地震波衰减、速度频散、电势的振幅和相位角数值结果. 相似文献
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Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus defect and velocity dispersion in real seismic data. The main attenuation and dispersion phenomenon is wave induced fluid flow due to the heterogeneity in pore fluids or porous rock. The identification of pore fluid type, saturation and distribution pattern within the pore space is of great significance as several seismic and petrophysical properties of porous rocks are largely affected by fluid type, saturation and fluid distribution pattern. Based on Gassmann-Wood and Gassmann- Hill rock physics models modulus defect, velocity dispersion and attenuation in Jurassic siliclastic partially-saturated rocks are studied. For this purpose two saturation patterns - uniform and patchy - are considered within the pore spaces in two frequency regimes i.e., lower frequency and higher frequency. The results reveal that at low enough frequency where saturation of liquid and gas is uniform, the seismic velocity and bulk modulus are lower than at higher frequency where saturation of fluid mixture is in the form of patches. The velocity dispersion and attenuation is also modeled at different levels of gas saturation. It is found that the maximum attenuation and velocity dispersion is at low gas saturation. Therefore, the dispersion and attenuation can provide a potential way to predict gas saturation and can be used as a property to differentiate low from high gas saturation. 相似文献
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Alexander Y. Rozhko 《Geophysical Prospecting》2020,68(2):631-656
It is evident from the laboratory experiments that shear moduli of different porous isotropic rocks may show softening behaviour upon saturation. The shear softening means that the shear modulus of dry samples is higher than of saturated samples. Shear softening was observed both at low (seismic) frequencies and high (ultrasonic) frequencies. Shear softening is stronger at seismic frequencies than at ultrasonic frequencies, where the softening is compensated by hardening due to unrelaxed squirt flow. It contradicts to Gassmann's theory suggesting that the relaxed shear modulus of isotropic rock should not depend upon fluid saturation, provided that no chemical reaction between the solid frame and the pore fluid. Several researchers demonstrated that the shear softening effect is reversible during re-saturation of rock samples, suggesting no permanent chemical reaction between the solid frame and the pore fluid. Therefore, it is extremely difficult to explain this fluid–rock interaction mechanism theoretically, because it does not contradict to the assumptions of Gassmann's theory, but contradicts to its conclusions. We argue that the observed shear softening of partially saturated rocks by different pore fluids is related to pore-scale interfacial phenomena effects, typically neglected by the rock physics models. These interface phenomena effects are dependent on surface tension between immiscible fluids, rock wettability, aperture distribution of microcracks, compressibility of microcracks, porosity of microcracks, elastic properties of rock mineral, fluid saturation, effective stress and wave amplitude. Derived equations allow to estimate effects of pore fluids and saturation on the shear modulus and mechanical strength of rocks. 相似文献