Determination of the elastic modulus set of foliated rocks from ultrasonic velocity measurements

Ultrasonic measurements of compressional and shear wave velocities under hydrostatic pressure up to 70 MPa were carried out on cylindrical specimens cored across and along the foliation planes. Our measurements revealed that the foliation of the metamorphic rocks induces a clear velocity anisotropy between two orthogonal directions; faster along the foliation plane and slower across the plane in most rock types. All velocity components monotonically increase with the confining pressure, probably due to the closure of microcracks distributed in rock specimens. We determined the complete set of dynamic moduli of foliated metamorphic rocks with two assumptions; transverse isotropy due to the foliation and ellipsoidal seismic energy propagation from a point source. The calculated elastic moduli referring to different directions could be valuable for the design of various engineering structures in planar textured rock mass.     

岩体波速与坝基岩体变形模量关系

岩体变形模量是岩体工程设计最重要的参数之一,尽管其可以通过各种现场试验来获得,但因其耗时、费力、投资大,使得许多中小型工程及大型工程的初步设计阶段无法通过试验来得到这一参数。因此,许多研究者建立了诸多岩体变形模量与岩体物理力学参数或岩体质量分级之间的相关关系,如岩体变形模量与RQD、RMR分级、Q分级、岩体纵波速度等之间的关系,从而利用这些关系估算岩体变形模量。总结了已有估算岩体变形模量的各种方法,讨论了其应用条件及预测结果,重点分析了利用岩体纵波速度估算岩体变形模量的方法及存在的问题,并以玛尔挡坝址为实例,建立了相关预测公式。通过与已有估算方法的对比研究,阐明了各种方法预测结果的异同,表明其建立的估算公式与Barton等公式具有较好的一致性,可以用来估算岩体的变形模量     

卸荷过程岩体中弹性波波速变化分析

伴随岩体卸荷过程,岩体内部应力状态要进行调整,同时岩体内部几何结构也要发生变化。由于卸荷过程应力状态变化很复杂,文中利用卸载过程中岩体内部几何结构的变化来反映卸载过程,通过岩体几何结构对弹性波传播的影响来分析卸载过程的波速。为考虑弹性波作用下局部裂纹的相互作用,采用双裂纹模型近似分析。在双裂纹体系内部采用“相互作用”分析法,以部分考虑波在岩体内的多次散射;在双裂纹体系之间采用线性叠加分析法,以考虑岩体中缺陷影响的局部化。通过节理裂隙的张开程度和节理裂隙的张开率描述卸载过程对双裂纹体系的影响,由此,对比分析了开挖卸载过程中四种不同的玄武岩与主频25 kHz和主频1 kHz对应的弹性波波速的变化。结果表明,随着卸载过程的推移,主频25 kHz声波和主频1 kHz地震波对应的相对波速逐渐减小,但声波波速的减小幅度要比地震波减小的幅度小,声波波速可以降低到原来的80%,而地震波波速可以降低到原来的50%。结论对于水利工程、隧道工程等建基面的验收和评价有很好的指导意义     

致密岩石纵横波波速各向异性的比较研究

通过对板岩、千枚岩、糜棱岩和变质砂岩等4种岩石在平行和垂直层理、板理的3个正交方向上的纵、横波波速试验,提出了致密岩石纵波波速的各向异性与横波波速的各向异性普遍存在着一致性和差异性两种特征。一致性特征主要表现为致密岩石的横波各向异性随纵波各向异性的增强而增强;差异性特征主要表现为在平行和垂直层理、板理的两个方向上,纵波波速的各向异性指数大于横波,亦即纵波波速的各向异性比横波更为显著。从横观各向同性弹性介质的波速方程出发,通过具体的算例对这两种特征进行了较好的理论分析。     

Decompaction mechanism of deep crystalline rocks under stress relief

Within a geological massif in a stable geodynamical situation contacts on the grain boundaries in polycrystalline rocks at great depths are continuous and firm. The stress release of those rocks during drilling and excavation to the surface is accompanied by their disintegration (decompaction). The reason for the decompaction is generation of microcracks during stress release due to the difference between the elastic moduli of crystalline grains at their contacts. The mechanism of decompaction may occur not only in polymineral but in polycrystalline rocks as well. The method of decompaction evaluation of deep crystalline rocks under stress relief is presented. According to the calculations the initial manifestation of the decompaction effect in biotite gneisses will occur when they are extracted from the deep range of 0.8–1 km. The first microcracks arise on the grain borders between quartz–biotite and oligoclase–biotite. It is shown that the uplift of gneiss–granite varities of the rocks cut by the Kola superdeep borehole from depths exceeding 13–15 km will be possible in a form of separate mineral grains. Practical importance of the presented method is in an opportunity to evaluate the level of excavated decompaction. The method allow estimating the depth, from which the rock will be extracted only in a sludge form.     

Delamination and ultra‐deep subduction of continental crust: constraints from elastic wave velocity and density measurement in ultrahigh‐pressure metamorphic rocks

Thirty‐three samples, including 22 eclogites, collected from the Dabie ultrahigh‐pressure (UHP) metamorphic belt in eastern China, have been studied for seismic properties. Compressional (V_p) and shear wave (V_s) velocities in three mutually perpendicular directions under hydrostatic pressures up to 1.0 GPa were measured for each sample. At 1.0 GPa, V_p (7.5–8.4 km s^?1), V_s (4.2–4.8 km s^?1), and densities (3.2–3.6 g cm^?3) in the UHP eclogites are higher than those of UHP orthopyroxenite (7.3–7.5 km s^?1, 4.1–4.3 km s^?1, 3.2–3.3 g cm^?3, respectively) and HP eclogites (7.1–7.9 km s^?1, 4.0–4.5 km s^?1, 3.1–3.5 g cm^?3, respectively). Kyanitites (with 99.5% kyanite) show extremely high velocities and density (9.37 km s^?1, 5.437 km s^?1, 3.581 g cm^?3, respectively). The eclogites show variation of V_p‐ and V_s‐anisotropy up to 9.70% and 9.17%, respectively. Poisson’s ratio (σ) ranges from 0.218 to 0.278 (with a mean of 0.255) for eclogites, 0.281–0.298 for granulites and 0.248 to 0.255 for amphibolites. The σ values for serpentinite (0.341) and marble (0.321) are higher than for other lithologies. The elastic moduli K, G, E of kyanitite were obtained as 163, 102 and 253 GPa, respectively. The V_p and density of representative UHP metamorphic rocks (eclogite & kyanitite) were extrapolated to mantle depth (15 GPa) following a reasonable geotherm, and compared to the one dimension mantle velocity and density model. The comparison shows that V_p and density in eclogite and kyanitite are greater than those of the ambient mantle, with differences of up to ΔV_p > 0.3 km s^?1 and Δρ > 0.3–0.4 g cm^?3, respectively. This result favours the density‐induced delamination model and also provides evidence in support of distinguishing subducted high velocity materials in the upper mantle by means of seismic tomography. Such ultra‐deep subduction and delamination processes have been recognized by seismic tomography and geochemical tracing in the postcollisional magmatism in the Dabie region.     

基于地基现场横波波速测试评判建筑场地类别的研究

工程场地纵、横波波速测试是近年来在工程勘察中取得一定效果的原位测试方法之一。以工程实例为依据,结合新型XG-1型悬挂式单孔波速测井仪测试结果,说明了横波波速可以确定场地土类型、判定建筑场地类别、估算场地卓越周期、评价岩(土)体质量,为场地工程地质评价和工程设计提供科学依据。     

基于弹性波波速的降雨型滑坡预警系统

降雨是诱发滑坡最主要的因素。为减少滑坡灾害造成的人员伤亡和经济损失,滑坡早期预警系统成为了最佳选择之一。根据弹性波传播的基本原理和基于降雨型滑坡变形破坏的特点,提出利用弹性波波速来反映边坡表面土体含水率和位移的变化。开发研制了一套三轴渗流-弹性波测试三轴仪和相关系统。该装置能让水从底部渗入土体,模拟降雨入渗土体的过程,同时能测试弹性波波速。试验过程中同步测试含水率、变形和弹性波波速的变化。还进行了降雨滑坡模型试验。利用三轴弯曲元注水试验和降雨滑坡模型试验,深入分析和研究降雨引起的土体滑坡过程与弹性波波速演化规律,揭示波速与含水率和变形的耦合关系。研究结果表明,弹性波波速随着含水率的增大而缓慢减小,随着变形的增大而急剧减小,临近失稳时,波速骤然减小。根据试验结果对含水率和变形导致弹性波波速减小可能的机制进行了解释,提出弹性波在波速骤然减小时发出滑坡预警。研究结果为滑坡防灾减灾和预测预报提供新的方法和可靠的依据。     

Stress‐dependent hardening and failure surfaces of dry sand

During several triaxial compression experiments on plastic hardening, softening, and failure properties of dense sand specimens, it was found on various stress paths that the size of the failure surface was not constant. Instead, it changed depending on the current state of hydrostatic pressure. This finding is in contrast to the standard opinion consisting of the fact that the failure surface remains constant, once it has been reached during an experiment or in situ. In general, the behaviour of cohesionless granular‐material‐like sand is somehow characterised in between fluid and solid, where the solid behaviour results from the angle of internal friction and the confining pressure. Although the friction angle is an intrinsic material property, the confining pressure varies with the boundary conditions, thus defining different solid properties like plastic hardening, softening, and also failure. Based on our findings, it was the goal of the present contribution to introduce an improved setting for the plastic strain hardening and softening behaviour including the newly found yield properties at the limit state. For the identification of the material parameters, a complete triaxial experimental analysis of the tested sand is given. The overall elasto‐plasticity concept is validated by numerical computations of several laboratory foundation‐ and slope‐failure experiments. The performance of the proposed approach is compared with the standard concept of a constant failure surface, where the corresponding yield surfaces are understood as contours of equivalent plastic work or plastic strain. Copyright © 2012 John Wiley & Sons, Ltd.     

Continuum large cracking in a rate‐dependent plastic–damage model for cyclic‐loaded concrete structures

Formulation and algorithmic treatment of a rate‐dependent plastic–damage model modified to capture large tensile cracking in cyclic‐loaded concrete structures are presented in detail for a three‐dimensional implementation. The plastic–damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi‐hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic–damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single‐element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate. Copyright © 2012 John Wiley & Sons, Ltd.     

基于波速测试的裂隙岩体固结灌浆效果分析

以福建某坝基固结灌浆工程实例为研究对象,采用单孔、跨孔声波测试及地震波测试技术对灌浆前、后岩体纵波波速进行检测。采用弹性理论计算动弹性模量,研究灌浆前、后变形参数的变化;对Hoek-Brown准则进行修正,用波速计算Hoek-Brown准则的强度参数,研究灌浆前、后强度参数的变化。研究结果表明,固结灌浆效果受岩体本身的可灌性控制,并受岩体结构影响。不同方向的固结灌浆效果是不同的,对于强风化岩体,垂直向固结效果优于水平向;对于具有缓倾结构面的中风化岩体,水平向固结效果优于垂直向。动弹性模量提高率与波速提高率呈二次函数关系。强风化岩的m（为Hoek-Brown常数）和s（为与岩体质量有关的常数）值提高率与波速提高率均呈一次函数关系,中风化岩则均呈三次函数关系。研究成果对灌浆设计和施工有重要的指导意义。     

基于弹性波速比的岩体强度参数估算方法

针对传统的岩体强度参数估算方法考虑风化程度的研究成果较少的不足,引入弹性波速比λ,提出了岩体强度参数的估算方法。以贵州省二叠系两种典型岩体(灰岩和泥岩)为例,讨论了参数λ和正应力σ_n对岩体强度参数的影响。主要研究成果为：基于弹性波速比与Hoek-Brown强度准则,探讨了不同风化程度岩体抗剪强度参数折减系数的确定方法;研究了正应力与弹性波速比对不同风化程度灰岩与泥岩岩体瞬时抗剪强度参数的影响,结果表明,岩体所处的环境与风化程度是影响岩体剪切强度参数的主要因素;通过多项式拟合,建立了灰岩与泥岩扰动与未扰动情况下不同风化程度强度折减系数的计算公式,从理论上探讨了两种主要岩体不同风化程度对强度参数的影响。     

岩体工程特性研究中弹性波速参数取值方法探讨

工程岩体的各向异性特征导致了弹性波速的各向异性。因此，在岩体工程特性研究、岩体质量评价等方面，应注意合理地应用岩体弹性波速资料。笔者分析了岩体波速的各向异性特征，并指出：由于波速各向异性的存在，在岩体完整性系数计算中，岩体波速应取不同方向波速的几何平均值。当利用文中所给公式进行岩体孔隙率计算时，建议波速取最小值；在进行节理、裂隙发育的优势方向判断时，则取不同方向的波速值分别进行计算；当计算弹性模量时，必须取与岩体受力方向相一致的波速值。并给出了利用波速进行有关参数计算的实例。     

Response of shear wave from a corrugated interface between elastic solid/viscoelastic half‐spaces

The propagation of plane shear wave at a corrugation interface between elastic solid and viscoelastic liquid half‐spaces has been investigated. Adopting Rayleigh's method of approximation, the reflection and refraction coefficients corresponding to reflected and refracted SH‐waves have been derived for the first order of approximation of the corrugated interface. These coefficients are derived in the closed form for a periodic interface. Numerical computation has been performed for a particular model and the results are depicted graphically. The results of Asano (Bull. Earthquake Res. Inst. 1960; 38 (2):177–197) and Kielczynski and Pajewski (J. Acoust. Soc. Am. 1987; 81 (3):599–605) are recovered from this study. Copyright © 2010 John Wiley & Sons, Ltd.     

中国大陆科学钻探主孔100～2000m岩石弹性波速度：对地震深反射的约束

在常温常压条件对中国大陆科学钻CCSD主孔岩心的700样品进行了弹性波速度测量,并建立了主孔2000m的波速(Vp和Vs)连续剖面,为检验地球物理模型的合理解释提供了岩石物理学方面的宝贵资料。主孔中新鲜榴辉岩纵波速度(Vp)最大(7.86km／s),正副片麻岩波速最小,又分别为5.53km／s和5．71km／s,榴辉岩的波速随着退变质作用的增强而明显减小。主孔2000m总平均Vp速度为6．2km／s,它与地球物理探测方法获得的大别-苏鲁造山带上地壳具有6.2-6．3km／s高速层结论是一致的。大部分岩石具有明显地震波各向异性。水饱和度使岩石纵波(Vp)速度和剪切波速度(Vs)分别增加19％和6％,而使Vp的各向异性降低3％～4％。不同岩性界面的反射系数(Rc)是产生地震反射的主要原因。金红石榴辉岩与片麻岩之间具有很高的反射系数(0.24-0．31)。韧性剪切带中糜棱岩化片麻岩和面理化榴辉岩使岩石各向异性和反射强度明显增加。岩石微裂隙与主孔原位波速变化有密切关系。饱水岩石速度(Vp和Vs)可以代表CCSD主孔原位状态的地震波速度。上述成果为本区地震反射体成因提供了重要的岩石物理性质约束。     

弹性模量、波速与应力的关系及其应用

为充分了解不同尺度地质系统的岩石动力学特征,更好利用不同规模勘探资料有效解释地质系统的特征,在岩石物理实验对岩石弹性模量、波速与应力的关系进行研究总结的基础上,探讨野外实际地震勘探中地震波速与地应力的关系。研究表明,岩石、岩体或地质系统是多相(固液气)、多种矿物、各种构造的综合体,不论尺度如何均可以用多重介质孔隙裂隙地质模型描述,而波速是一定尺度不均匀地质体的等效波速,在一定地质条件下,各种尺度介质波速、岩石弹性模量与有效应力存在依存关系。坚硬的岩石通常很脆,如果岩石处于很大的应力之下,应力的释放将在岩石中产生微裂隙,微裂隙会降低地震速度。只要把岩石恢复到原来的应力状态就可能消除所引发的微裂隙。在岩体未达到破坏时,应力越大,波速愈高。压力释放引发的微裂隙有助于现场确定最大/最小水平应力方向,波速的椭圆长轴即为主应力方向。而上覆地层压力不变(或变化很小),净储层压力的影响正好与储层压力对地震特性的影响相反。随着净储层压力的增加,所有岩石的地震特性都增高。这种增高的量级取决于若干其它的因素(孔隙形状、孔隙度、孔隙流体、岩性等等)。不论野外地震勘探还是实验研究,地震波速与地应力的一致性为地质系统的正反演解释提供了宏观控制依据:通过测量弄清     

遇水冷却的高温大理岩力学与波动特性分析

岩石经历高温作用冷却后工程特性的变化情况,直接影响着地下深部空间及资源的开发与利用、核废料的存储以及突发性高温灾害后地下工程的稳定性评价。以大理岩为研究对象,对遇水冷却和自然冷却后的高温岩样进行单轴压缩试验和声波测试,分析和比较岩样在不同状态下峰值强度、弹性模量、衰减系数、纵波波速和主频的变化情况。结果表明：随着温度的不断升高,遇水冷却高温大理岩的峰值强度、弹性模量和纵波波速总体上均呈现减小趋势;低于400 ℃时,随着温度的升高,衰减系数逐渐增大,主频逐渐减小;但高于400 ℃时,随着温度的升高,衰减系数和主频并未完全呈现单调递增或递减趋势,出现了高温拐点;在经历相同高温作用后,遇水冷却大理岩的峰值强度、弹性模量和主频均低于自然冷却,而纵波波速、衰减系数均高于自然冷却。研究结果可以为遇水冷却的高温岩石工程性状的检测和稳定性的评价提供参考,对经历高温作用的岩石冷却方式的选择具有指导意义。     

Elasto‐plastic modelling of stress‐path‐dependent behaviour of interfaces

A single‐surface elasto‐plastic model developed by Desai and his coworkers is used to predict the behaviour of an interface between sand and a steel plate. The loading in the experiments and in their predictions followed various stress and displacement paths. The results of predictions of the two‐ and three‐dimensional behaviour of the interface under both constant normal stress and constant normal stiffness conditions are presented. The predictions are compared with their corresponding experimental results. The model parameters were determined on the basis of 2‐D conventional experiments under the condition of constant normal stress and they were used in the prediction of the interface behaviour in various stress paths. There is, in general, a good agreement between the predicted and experimental results. Copyright © 2000 John Wiley & Sons, Ltd.     

Effective elastic properties of the double‐periodically cracked plates

In this paper, the interaction of double‐periodical cracks is accurately solved based on the isolating analysis procedure, superposition principle, pseudo‐traction method, Chebyshev polynomial expansion and crack‐surface collocation technique. The jump displacement crossing crack faces, the average additional strain and therefore the effective compliance of the double‐periodically cracked plate are directly determined. The numerical results for axial‐symmetrically distributed double‐periodical cracks, general double‐periodical cracks with one collinear direction as well as two sets of double‐periodical cracks with same size and square distribution are given in this paper. And the partial typical numerical results are compared with the previous works. The analysis shows that the anisotropy induced by the general double‐periodical cracks is generally not orthogonal anisotropy. Only when the double‐periodical cracks are axial‐symmetrically distributed, is the anisotropy orthogonal. In this special cases, the effective engineering constants (consist of effective elastic modulus, the effective Poisson's ratio, the effective shear modulus) of cracked plate versus crack spacing, in the plane stress and plane strain conditions, respectively, are analysed. Copyright © 2005 John Wiley & Sons, Ltd.