软岩三轴加-卸载试验的破坏特征及抗压强度取值方法研究

软岩三轴加、卸载试验中的抗压强度参数取值是一个非常关键的问题,目前还没有比较确定的方法,通常根据经验或工程要求确定。基于此,结合一组砂质泥岩的三轴加、卸载试验进行了详细研究,试验结果表明:(1)当围压大于10 MPa时,不论是三轴加载试验还是卸载试验,砂质泥岩均表现出明显的应变硬化特性;(2)砂质泥岩在三轴压缩和三轴卸荷两种应力路径的力学响应差别明显,在卸荷条件下通常只存在一条完整的剪切破坏面,而压缩条件下岩样没有明显的控制破裂面,并且剪胀效应明显;(3)将半对数法引入到软岩三轴加、卸载试验数据分析中,可以比较方便地确定软岩三轴加、卸载试验的抗压强度;(4)基于三轴加、卸载试验过程中的应力、应变增量分析,将软岩变形破坏过程分为3个阶段:平滑阶段、规则跳跃阶段和急剧跳跃阶段,各阶段划分的意义明确,可以作为抗压强度确定时的重要参考,因此,在软岩三轴试验数据分析时,可以综合采用这两种方法。研究提出的抗压强度确定方法可操作性强,在其他软岩三轴试验数据分析中值得参考借鉴。     

岩石声波综合数据处理系统的试验研究

本文是在岩石声波测试综合数据处理系统研究总结的基础上写成的。该系统以SYC岩石声波仪为前端设备,配接微型计算机和单板机,构成既可在室内也可在野外使用,又能综合分析的积木式测试系统。为用声波法测定岩石和其它固体介质的力学特性的测试技术和理论研究,提供了自动化的设备。本文介绍了系统的主要功能,基本结构和接口方法选取分析,软件设计分析,测试结果对比等方面。并对应用计算机控制测试设备、实现测试实验自动数据采集和处理提出我们的看法。     

Experimental Study of Synthesis Processing System for Rock Acoustical Measurement

The system consists of SYC rock acoustical measurement instrument, microcomputer and single board computer. It is a building block system used in both laboratory and field testing to measure rock acoustical data. In this paper the main performances, the fundamental configuration, the interface technique and software design methods are presented, and measurement result analysis is made. An idea was proposed of the automatic acquisition and processing of test data by means of micro-computer control over the test device.     

A semi‐empirical method for the liquefaction analysis of offshore foundations

This paper presents a relatively simple method for three‐dimensional liquefaction analysis of granular soil under offshore foundations. In this method, the Mohr–Coulomb model, which defines the elasto–plastic stress–strain relationship under monotonic loading, is modified to accommodate the plastic strains generated by cyclic loading. The effects of cyclic loading, evaluated from the results of laboratory tests on saturated samples of soil, are incorporated into the model. The method is implemented in an efficient finite element program for analyses of three‐dimensional consolidating soil. The practicability of the model is demonstrated by analysis of a typical offshore foundation, and the predictions of the numerical analysis are compared with the observed behaviour of the foundation. Copyright © 2000 John Wiley & Sons, Ltd.     

Micromechanics of vortices in granular media: connection to shear bands and implications for continuum modelling of failure in geomaterials

Recent analysis of data from triaxial tests on sand and discrete element simulations indicate the final pattern of failure is encoded in grain motions during the nascent stages of loading. We study vortices that are evident from grain displacements at the start of loading and bear a direct mathematical connection to boundary conditions, uniform continuum strain and shear bands. Motions of three grains in mutual contact, that is, 3‐cycles, manifest vortices. In the initial stages of loading, 3‐cycles initiate a rotation around a region Ω^* where the shear band ultimately develops. This bias sets a course in 3‐cycle evolution, determining where they will more likely collapse. A multiscale spatial analysis of 3‐cycle temporal evolution provides quantitative evidence that the most stable, persistent 3‐cycles degrade preferentially in Ω^*, until essentially depleted when the shear band is fully formed. The transition towards a clustered distribution of persistent 3‐cycles occurs early in the loading history—and coincides with the persistent localisation of vortices in Ω^*. In 3D samples, no evidence of spatial clustering in persistent 3‐cycle deaths is found in samples undergoing diffuse failure, while early clustering manifests in a sample that ultimately failed by strain localisation. This study not only delivered insights into the possible structural origins of vortices in dense granular systems but also a tool for the early detection of the mode of failure—localised versus diffuse—a sample will ultimately undergo. Copyright © 2014 John Wiley & Sons, Ltd.     

Controls of phosphorus loading and transport in the Cuyahoga River of northeastern Ohio,USA

An urban stream differs from a natural stream in that it commonly contains anthropogenic nutrients from a variety of diffuse and point sources (e.g., urban runoff, industrial and municipal effluents). The Cuyahoga River as one of such stream systems receives on average 30% of water from over a dozen wastewater treatment plants (WWTPs) and exports over 300 Mg/yr of total phosphorus (TP) into Lake Erie. Municipal effluents account for at least two thirds of the TP loading and 90% of the effluent TP is in the form of soluble reactive phosphorus (SRP), i.e., the highly bioavailable form in aquatic ecosystems. Owing to its dominance of the effluent P, the Cuyahoga River may pose a disproportionately greater ecological risk to Lake Erie. Here we report results of TP and SRP as measured on water samples collected from 12 locations along the Cuyahoga River and its major tributary – Tinkers Creek under three different flow conditions in July 2007 through May 2008. Our results show that the loadings of SRP and TP increased progressively with the effluent inputs increasing from the upper basin downstream. We found the loadings of SRP and TP are not only affected by the amount of effluent P input but also regulated by stream flow regimes. Effluent P is more likely to be transformed during storm runoff events, whereas TP is more likely to be retained under low flow conditions. As a result, most of the TP loading was exported during the storm and intermediate flow conditions, whereas most of the SRP loading was delivered during the low and intermediate flow conditions. These results suggest that stream hydrology has played an important role in the loading and transport of P across the Cuyahoga River as it dictated the amount, form, and timing of P exported to Lake Erie.     

Effect of cyclic loading on the residual strength of over-consolidated silty clay in a ring shear test

In this paper, the effect of cyclic loading on drained residual strength of over-consolidated silty clay is examined based on the results from ring shear tests which were conducted with a sophisticated ring shear apparatus. Initially sheared to form shear zones under different pre-consolidation pressures and at different shear rates (SRs), soil samples were then tested under cyclic loading. After the cyclic loading application, the samples were re-sheared while the corresponding shear strengths were measured. The results show that the effect of cyclic loading on residual strength is noticeable. The effect is related to pre-consolidation history and SR of the soil samples. Under conditions of relatively low over-consolidation ratio (OCR), the soil samples show an increase in residual strength with decreasing SR after cyclic loading. Most of the peak strength values after cyclic loading are higher than the residual strength values obtained before cyclic loading. Two effects of cyclic loading on the residual strength are identified: (a) If OCR is less than or equal to 3.0, the residual strengths measured after cyclic loading are larger than those before cyclic loading; (b) If OCR is greater than or equal to 3.5, the residual strengths after cyclic loading tend to become lower than those in the shear tests before cyclic loading.     

The Use of Acoustical Log for Exploration of the Rock Foundation

This paper describes how the acoustical log technique is applied to the exploration work on rock foundation . In order to analyze the results obtained from the acoustical measurement by single hole and cross-hole transmission techniques, two modelling tests were carried out. By the use of acoustical refraction and transmission technique, the authors have been conducted a lot of field tests since 1973 in several engineering works to determine the size of underground cavities.     

声波测井在岩石地基探测中的应用

本文介绍我所声波测井技术在岩质地基勘测中的应用情况.作者自1973年以来在这方面进行了大量的野外工作,为了进一步阐明单孔测井及孔间透射波测井中所遇到的岩体声学问题,先后进行了两次室内模型模拟试验研究.在此基础上,用声学的原理和方法阐述了折射波测井及采用孔间透射波法测量溶洞大小的方法.并介绍这些方法在工程实践中的应用.     

Multiscale modeling of a sensitive marine clay

This paper examines the mechanical behavior of a sensitive marine clay. Various laboratory tests on intact and reconstituted samples of Guinea Gulf marine clay were performed under isotropic compression and drained triaxial compression at constant confining stresses. Microstructure analysis on intact and reconstituted samples was also carried out under different loading conditions. The effect of inter‐aggregates bonding on mechanical properties is discussed. Based on experimental analysis, a new modeling method is proposed. In this approach, the clay is regarded as an assembly of aggregates of clay particles. An inter‐aggregate contact law is introduced relating contact forces to aggregates relative displacements. The deformation of the assembly can be obtained by integrating the movement of the inter‐aggregate contacts in all orientations. Thus, the effect of inter‐aggregates bonds and debonding is considered in a direct way. The model is evaluated through comparisons between the predicted and measured results on Guinea Gulf marine clay. The evolutions of local stresses, strains, and bonds in inter‐aggregates planes are discussed to explain the anisotropy induced by the applied loading. Copyright © 2010 John Wiley & Sons, Ltd.     

循环加载时围压对岩石动力特性的影响

针对砂岩岩样,探讨了在不同围压作用下和轴向循环加载时岩样的动力力学性质,研究围压对砂岩岩样的动力力学性质的影响。采用的试验设备是MTS－815岩石和混凝土试验系统,5组围压分别为10、20、30、40、50 MPa。岩样为汶川地区的干砂岩,轴向荷载施加的频率为1 Hz。结果表明,（1）随着围压的逐渐增加,试样的残余轴向应变和体变逐渐增加,且剪胀发生时的残余体变也逐渐增加;（2）动力荷载作用时岩样在高围压比低围压下的初始刚度和强度高;（3）不同围压作用下,当应力比Rs较大时,岩样在较小的循环次数下发生破坏;（4）试样的破坏模式为剪切破坏,动力荷载作用下试样形成的局部化破坏带更宽。     

Effects of Frequency on the Dynamic Properties of Intact Rock Samples Subjected to Cyclic Loading under Confining Pressure Conditions

A series of laboratory tests was performed to assess the effects of frequency on the dynamic properties of sandstone samples subjected to cyclic loading in the confining stress state. Three levels of confining pressure (2.0, 10.0, and 40.0 MPa) and three sets of frequencies (0.1, 1.0, and 3.0 Hz) were applied for the axial cyclic loading tests by the MTS-815 Rock and Concrete Test System. The results from the cyclic loading tests indicate that frequency has a strong influence on the dynamic deformation, the dynamic stiffness, and the failure mode at the same confining pressure. With an increase in the frequency, the axial strain and the number of cycles at failure increased at the same confining pressure, the residual volumetric strain increased when dilatancy occurred at the same confining pressure, and the number of cycles at failure increased. A new damage variable D was defined that describes the degradation process of sandstone samples upon dynamic cyclic loading. The larger the frequency, the wider the localized band. Sandstone samples subjected to dynamic cyclic loading responded with a significantly higher initial stiffness. The higher the initial stiffness, the greater the frequency.     

单轴压缩下多裂隙类岩石材料强度试验与数值分析

采用伺服控制单轴加载系统对预制多裂隙水泥砂浆试件进行加载试验,探索裂隙角度和分布密度对多裂隙类岩石材料断裂破坏强度的影响规律。对试验数据整理分析,应用FLAC3D建立应变软化模型,进行数值模拟。试验数据和数值分析结果表明,裂隙分布密度相同时,裂隙倾角对试件断裂破坏强度的影响比较显著,25°附近取得最小值;裂隙角度相同时,裂隙分布密度对试件断裂破坏强度的影响与裂隙倾角有关,角度较小时,影响比较显著,随着角度的增大,影响越来越弱。试验所得结论,对于预测地下工程中多裂隙情况下围岩强度变化规律提供了依据。     

Palynofacies and organic geochemistry studies of organic matter from a wetland system of southern Brazil influenced by different hydrological regimes in the Quaternary

The main goal of this study was to quantitatively and qualitatively characterize the sedimentary organic matter (OM) and demonstrate the usefulness of geochemistry and palynofacies analysis for obtaining paleoenvironmental data for the Holocene in southernmost Brazil. The results indicate that during the time interval from 10,586 cal yr BP to the present, the study area housed a wetland characterized by different hydrologic regimes. The basal peaty deposits correspond to a phase influenced mainly by the groundwater table, whereas the upper deposits composed of silty organic mud indicate fluvial influence related to river overflow events. In a similar manner, the TOC (total organic carbon) and TS (total sulfur) contents are higher in the basal portion of the profile, decreasing toward the top. These findings could be related to granulometry alterations that are linked to hydrologic regimes or anthropogenic interference in the landscape dynamics. Anomalous TS content observed in one of the samples might be due to an external source and perhaps related to the presence of thermal springs in the region. These types of areas have potential as a modern reference that can be applied in the reconstruction of past analogous environments such as coal deposits associated with fluvial paleoenvironments.     

动载作用频率对海相沉积软土动态流变特性影响试验研究

动态载荷作用下软弱岩土加速流变,引发更多的岩土工程事故和地质灾害。采集厦门海相沉积软土,采用人工重塑试样,在动态三轴仪上测试正弦荷载作用及不同频率条件下试样流变过程的动应力-应变、流变过程动应变-时间、流变应变等动态流变力学特性,对比分析了动载作用频率对海相沉积软土动态流变特性影响。试验测试分析表明：软土的动态流变特性对低频动载作用更敏感,流变效应更明显,而在高频动载作用下流变敏感性差,流变变形缓慢。研究结论为探索动载作用频率对软弱岩土动态流变力学特性影响,揭示动载作用诱发重大岩土地质灾害的流变动力学机制等具有一定的理论和现实意义。     

X射线衍射旋转撒样法分析氟金云母多型组成与含量

合成氟金云母多型种类与含量对云母的物理化学性质具有重要的影响.然而在X射线粉晶衍射(XRD)制样过程中云母00l基面极易产生择优取向,严重制约了云母多型组成和含量的分析.传统撒样法可促使晶体取向随机分布,但制备的试样表面不够平坦.本文对传统撒样法进行改进,在撒样过程中使样品架均匀旋转,从而获得表面平坦的试样.XRD测试...     

陕西延安Q_2原状黄土抗拉强度试验研究

对陕西延安新宝塔山隧道Q2原状黄土进行了不同加载速率的无侧限抗压与贯入抗拉试验,研究了Q2原状黄土抗压与抗拉强度的影响因素。结果表明:加载速率对宝塔山Q2原状黄土抗压和抗拉强度影响较大,抗压强度与抗拉强度随加载速率增大而增大;高径比对抗拉强度也有较大影响,试验时当高径比控制在1.0左右时,高径比对宝塔山Q2原状黄土的抗拉强度影响相对较小,因此采用轴向压裂法测量黄土的抗拉强度时,高径比宜控制在1.0;在试验加载速率范围内,加载速率对宝塔山Q2原状黄土的压拉比影响不大,其压拉比在9.88~13.68范围内变化。     

Mg and Ca isotopic study of individual microscopic crystals from the Allende meteorite by the direct loading technique

We have developed a direct loading technique for determining the isotopic composition of Mg in chemically unseparated samples. This technique has a sensitivity and precision comparable with those of the conventional technique of analyzing pure Mg salt and eliminates contamination introduced during the chemical separation of Mg. This results in a significant reduction in sample size required for an analysis. This technique was combined with other characterization techniques of microscopic samples (e.g. optical microscopy, SEM, EPMA), and was applied to four single crystals of pure phases from an Allende inclusion ranging in size from 25 to 150 μm. Using a total sample of 4 μ, we found an anorthite crystal showing an enrichment in ²⁶Mg of 10% and were able to construct an ²⁶Al-²⁶Mg isochron which confirms our previous results obtained on macroscopic samples of the same inclusion. The isotopic composition of Ca was also measured along with Mg, on a directly loaded anorthite crystal from this inclusion, during the same mass spectrometer run and was shown to be essentially normal. Thus, the direct loading technique is applicable to Ca and will be useful in a correlative study of isotopic effects of different elements on individual microscopic samples. The extension of this technique to other elements appears feasible but will require extensive testing to control possible interferences.     

Hydrogeochemical evolution and potability evaluation of saline contaminated coastal aquifer system of Rajnagar,Odisha, India: A geospatial perspective

The present article reports the results of a comprehensive hydrogeochemical study carried out across the coastal aquifer system of Rajnagar block, Kendrapara district, Odisha, India. The research involved collection of representative groundwater samples during the pre- and post-monsoon seasons with in situ as well as laboratory measurement of various hydrogeochemical variables. Analysis of the subsurface water samples portrays an alkali dominated water type during the pre-monsoon season whereas alkaline earth has a significantly increased influence during the post-monsoon period. However, the aquifer system displays an even distribution of strong and weak acids for both the monsoonal regimes. The hydrogeochemistry is controlled by aquifer lithology with a general occurrence of ion exchange and acid–base reaction processes across the study area. Spatial disposition of major cations indicates freshening of this coastal aquifer system in S–N and SW–NE directions. Potability analysis of the samples is suggestive of widespread unsuitability for domestic, agriculture and industrial uses. The extensive occurrence of salinity hazards, sodium hazards and magnesium hazards across the terrain makes the groundwater unsafe for domestic and agricultural utilization while industrial potability analysis suggests the aquifer system is moderately corrosive but non-incrusting. Post-monsoon however, the subsurface waters display a general decrease in hazardous nature with increased suitability for various uses.     

Inversion of calcite twin data,paleostress reconstruction and multiphase weak deformation in cratonic interior – Evidence from the Proterozoic Cuddapah basin,India

Paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the Proterozoic Cuddapah basin, India. Application of Turner's P–B–T method and Spang's Numerical dynamic analysis on Cuddapah samples provided paleostress orientations comparable to those derived from fault-slip inversion. Results from the neighborhood of E–W faults cutting through the Paleoproterozoic Papaghni and Chitravati groups and the Neoproterozoic Kurnool Group in the western Cuddapah basin, reveal existence of multiple deformation events − (1) NE–SW σ₃ in strike-slip to extensional regime along with an additional event having NW–SE σ_3, for lower Cuddapah samples; (2) compressional/transpressional event with ESE–WNW or NNE–SSW σ₁ mainly from younger Kurnool samples.Integrating results from calcite twin data inversion, fault-slip analysis and regional geology we propose that late Mesoproterozoic crustal extension led to initial opening of the Kurnool sub-basin, subsequently influenced by weak compressional deformation. The dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern Indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the Proterozoic.