An experimental study on creep of welded tuff

This paper presents results of five creep tests conducted in uniaxial compression at room temperature. The test specimens were from the welded Topopah Spring tuff formation at Yucca Mountain, Nevada. The specimens exhibited brittle failure. Multiple stress levels were applied in steps to each specimen. Each stress level was maintained for 3 days or longer. The transient creep for all the stress levels can be well described by power functions. The transient creep is caused by an elastic aftereffect. The tuff does not show real steady-state creep. The so-called steady-state creep rate decreases with time. In general it is very low, typically in the range of 10⁻⁷ h⁻¹. For the first 50 h, the so-called steady-state creep rate may be described as a power function of stress. The specimen failed shortly after it entered into the accelerating creep phase.     

Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities

The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 × 10² pfu l⁻¹ of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 × 10⁵ and 5.0 × 10⁵ pfu l⁻¹ of coliphages, depending upon the E. coli host strain used for assay, and 2.0 × 10⁹ colonies l⁻¹ of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 × 10⁻¹ and 3.0 × 10⁻¹ MPN m⁻³, coliforms from aerosol emissions were 2.1 × 10² colonies m⁻³. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.     

Heavy metals in animals of Lake Balaton

Hg, Cd, Cu, Pb, Zn, Fe and Mn concentrations were measured in Chironomidae larvae, Crustacea plankton, as well as in various organs of mussels and fishes collected from the open water area of Lake Balaton. The values were comparatively low. However, there were significant differences in the metal concentrations of species and tissue.Most Cd was found in the gill of Unio pictorum L., most Pb, Zn and Mn in the gill of Anodonta cygnea L., most Cu in Crustacea plankton and in the liver of Abramis brama L., and most Hg and Fe in Chironomidae larvae. Low concentrations occurred in fishes, the lowest in the flesh of Stizostedion lucioperca L.Accumulation of metals in organs as compared with their concentration in the lake water was in the range of 3.4 × 10²−2.6 × 10³ for Hg; 7.0 × 10²−6.8 × 10³ for Cd; 3.3 × 10²−9.7 × 10³ for Cu; 6.9 × 10²−8.1 × 10³ for Zn; 1.5 × 10³−2.4 × 10⁴ for Pb; 3.5 × 10²−3.1 × 10⁴ for Fe; and 5.0 × 10¹−3.5 × 10⁵ for Mn.     

2种岩石直接拉压作用下的力学性能试验研究

 利用Instron1342液压伺服机对2种典型硬岩和软岩试样进行单轴试验,包括单轴压缩试验和直接拉伸试验,研究这两种岩石在直接拉压作用下的力学性能,对比2种岩石的单轴抗压强度和单轴拉伸强度。试验过程中监测岩石试样的轴向应变和水平应变,并记录岩石试样的声发射特征,得到2种岩石在单轴拉压下的应力–应变曲线和声发射计数率曲线,对比2种岩石在单轴拉压下的声发射变化规律。试验发现,直接拉伸下2种岩石在加载初期较大范围内基本无声发射事件发生,直到破坏前声发射事件数才突然增大。讨论2种岩石在不同加载模式下的弹性模量和泊松比变化关系,发现单轴压缩下,硬岩的弹性模量随载荷变化先增大而后趋于稳定,当载荷超过单轴抗压强度的80%时又变小;而单轴拉伸下,硬岩的弹性模量初始较大,随后随着载荷增大而逐渐减小。单轴压缩下2种岩石的泊松比为0.2～0.3,而单轴拉伸下岩石的泊松比很小,几乎可以忽略。比较2种岩石的破坏角、内摩擦角以及黏聚力,讨论2种岩石在直接拉压作用下的不同破坏模式。利用三维表面形貌扫描仪对直接拉伸试样的破坏断面进行三维扫描,得到破坏面细观结构图和裂纹面表面粗糙度曲线。     

Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.     

Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.     

Micromechanical modelling of the mechanical properties of a granite under dynamic uniaxial compressive loads

A micromechanics-based model is used to study the mechanical properties of a granite under dynamic uniaxial compressive loads. The model is based on interacting sliding cracks uniformly distributed in the rock material. A dynamic crack growth criterion, which is related to crack growth velocity and dynamic fracture toughness of the rock material, is employed in the analysis. Under dynamic loads at strain rates from 10⁻⁴ to 10⁰ s⁻¹, the crack growth velocity is small compared to the critical crack growth velocity and the effect can be ignored. The strengths of the granite obtained by micromechanical modelling agree with the experimental results. A constitutive relation of the granite is derived from the energy equilibrium equation and correlated with the experimental results.     

盐岩应力松弛效应的研究

系统介绍了单轴及三轴应力松弛试验研究装置及试验结果。研究结果表明：盐岩在整个应力松弛试验过程中,其横向应变近乎是常数,也即体应变保持不变。盐岩预蠕变对应力松弛具有较大的影响;盐岩的最低蠕变极限是存在的。     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

Numerical studies of the influence of microstructure on rock failure in uniaxial compression — Part II: constraint, slenderness and size effect

Numerical simulations of uniaxial compression have been conducted to evaluate the effects of the loading system and specimen geometry on the deformation and failure behavior of brittle and heterogeneous rock. This was done using the Rock Failure Process Analysis program (RFPA^2D). Numerical model specimens with different Young’s modulus ratios of platen to specimen (Ep/Es=0, 0.1, 1, 2, and 10), different slenderness in terms of height to width ratios (H/W=0.5, 0.67, 1, 1.5, and 3), and different sizes (H×W=30×20, 100×67, 120×80, 150×100, and 190×127 mm) have been numerically analyzed. The numerical simulations not only qualitatively reproduce the experimentally observed pre- and post-peak failure phenomena of the loaded specimens, but also provide a quantitative evaluation of the influence of the parameters studied on the complete stress–strain curves and the strength characteristics. The results presented here indicate that a more ductile response is simulated and the peak strength increases when the end constraint increases. The crack patterns show that almost-vertical splitting cracks develop in specimens loaded with softer loading platens, and the well-known hour-glass failure mode develops in specimens loaded with stiffer loading platens. The peak stress sustained by a specimen decreases with increasing slenderness of the specimen. The pre-peak portion of the stress–strain curves shows no significant dependence on slenderness; however, the post-peak curves are highly dependent on the ratio of specimen height to width. As far as the effect of size is concerned, numerical results reveal a strength reduction with an increase in specimen size, whereas the change of the specimen size does not obviously change the failure patterns.     

Bromide concentration in Swedish precipitation, surface and ground waters

The occurrence of bromide in precipitation, surface and ground waters in Sweden has been investigated (300 samples). The concentration of bromide in precipitation is 0.05–0.15 μM in the south and <0.05 μM in the north of Sweden. The concentrations of bromide and chloride are well correlated. For river water the same areal distribution pattern as for precipitation is found, but the concentrations are 2–4 times higher. The molar ratio Br/Cl is 1 × 10⁻³ which is lower than that for sea water (1.54 × 10⁻³) and, most likely, also lower than for precipitation. A detailed study of Lake Mälaren has been made. The north-eastern feeder streams, passing an area of post-glacial clay, showed unusually high bromide concentrations (0.3–3 μM) and Br/Cl quotients (2 × 10⁻³-8 × 10⁻³). No correlation between the concentrations of bromide and chloride was found. Rough calculations indicate that fertilizers and chemicals added to the fields could only contribute a minor fraction of the bromide found. Analysis of 18 ground water samples indicated increased bromide levels as compared to surface waters.     

The removal of colour from effluent using various adsorbents—IV. Silica: Equilibria and column studies

The rate of adsorption of Astrazone Blue, a basic dye, on Sorbsil Silica has been studied. The parameters studied include particle size, initial dye concentration, agitation and dye solution temperature. The rate controlling step is mainly intraparticle diffusion, although a small boundary layer resistance is experienced. The activation energy for the adsorption of Astrazone Blue on silica is 13.2 ± 0.6 kJ kg⁻¹. The diffusion coefficients vary from 9 × 10⁻⁹ cm² s⁻¹ at 20°C to 10 × 10⁻⁸ cm² s⁻¹ at 82°C.     

A study of the copper-complexing compounds released by some species of cyanobacteria

The production of copper-complexing extracellular material by cyanobacteria was studied by using ion specific electrodes. The species studied were Plectonema boryanum and Anabaena cylindrica. The values of the conditional stability constants for the copper complexes (K′), for the two species at pH 6.60 (±0.05) were, respectively 2.8 (±0.8) × 10⁶ and 5.9 (±2.0) × 10⁷. A strain of P. boryanum that was made tolerant to a concentration of 1 × 10⁻⁶M copper produced greater amounts of copper-complexing products than the normal strain although the K′ value for the copper complexes was the same. When stressed with copper, P. boryanum and A. cylindrica produced more complexing material than under the usual growth conditions.     

The dynamics of suspended algal populations in the lower Wye catchment

The algae of the R. Wye and its tributary the R. Lugg were described principally from samples collected from 7 sites in the lower Wye catchment during 1980 and 1981. The density of algae in the Wye was found to be correlated with river flow and solar radiation, highest numbers (12.5 × 10⁵ cells ml⁻¹), principally of Scenedesmus and Cyclotella, occurring at low stable flows and relatively high solar radiation. Algal populations in the Lugg were much smaller ( 1.3 × 10³cells ml⁻¹) than those of the Wye and were principally composed of species derived from the periphyton. Downstream increases in load (cell density × flow) of both Scenedesmus and Cyclotella in the Wye were generally equivalent to about 0.3 division d⁻¹; these rates were lower than those obtained in laboratory culture and this was probably largely related to underestimates arising from algal removal by filter feeders (principally simuliid larvae). Potential problems arising from the treatment of Wye water supporting substantial algal growths are considered: these include haloform production, deoxygenation in a transfer pipeline, algal penetration into potable supply and taste and odour.     

Variation in strength and creep life of six Japanese rocks

In this paper, variations in strength and creep life are investigated for rocks under various conditions: dry and wet, uniaxial and triaxial, and compressional and tensile. A number of parameters are introduced for this purpose; to assess the time-dependent failure under constant and monotonic loading the following parameters are used: the parameter of time dependency δ, coefficient of creep life α and coefficient of strength β. δ explains the rate dependency of strength or stress level dependency of creep life. α and β are related to each other. Variations in β have been evaluated using data from previous experiments. It is confirmed here that δ, β and variations in β determined by creep tests are in most cases identical to those determined using strength tests. Variation in β in the wet condition is almost the same as that in the dry condition; however, variation in tension increases more than in compression. Under confining pressure, variation in β is reduced for Neogene sedimentary rocks, and does not appear to change for igneous rock and welded tuff.     

论文的评审与写作

<正>0引言随着中国岩土工程学术队伍的成长和扩大,学术水平的不断提高,投向《岩土工程学报》的论文数量也在逐年增多。现在攻读博士硕士学位、晋升职称、评奖、完成重要科研项目等,都要看学报发表论文的情况,因此广大学者和研究生十分踊跃地向学报投稿。面对这些来稿,如何科学和公正地评审、取舍,就成了审稿人的重要任务。这不仅要对论文作者负责,同时也关系到学报的质量和水平。     

Stress–strain–electrical resistance effects and associated state equations for uniaxial rock compression

This paper reports stress–strain–electric resistance experiments for diabase, limestone and marble containing NaCl solution during the whole process of uniaxial compression. We obtained the complete testing data for the stress–strain curve and the associated electrical resistance–strain curve. The change caused by internal cracking of the rock causes the corresponding variation of rock electrical resistance. There is a minimum value for all the electric resistance–strain curves, corresponding to the cracking stress σ_c or the initial cohesion c_i. Based on the experimental results and stochastic property analyses of the rock fracture variation, we put forward a group of state equations for rock in sections to express the characteristics of rock during the whole process of uniaxial compression. The three variables, stress, strain and electrical resistance, together with data-fitted parameters, α₁,α₂ and β, are contained in the equations. The equations are used to express the inelastic response which intensifies with the propagation of cracking.     

On computing normal reliabilities

No expression currently used for computing reliabilities given by the normal distribution is adequate over the entire range of interest in structural design. Although the expressions may involve small absolute errors, they introduce excessively large relative errors in the failure probabilities over some ranges. It is impractical to have two expressions depending on the reliability index β. Two equations are proposed here. The simpler one involves relative errors smaller than 1.7% when β 1. The other introduces relative errors smaller than 2 × 10⁻⁴ when B 0 and smaller than 4.5 × 10⁻⁵ when β 1.     

Septage disposal in waste recycling ponds

Experiments were carried out to investigate the feasibility of septic tank sludge (septage) disposal into pilot-scale waste recycling ponds for the production of algae and fish. A septage loading of 100 kg COD ha⁻¹ day⁻¹ to four 4-m² single-stage ponds resulted in the production of algal biomass and dissolved oxygen in the pond water, suitable for Tilapia growth. Some microbiological investigations of this waste recycling scheme were undertaken using ten earth ponds (each with the dimensions of 20 × 10 × 1.3 m: length × width × depth). It was found that the densities of coliform bacteria and bacteriophages in the pond water and sediment tended to increase with increased septage loadings and loading periods. The ponds fed with septage at the loading of 100 kg COD ha⁻¹ day⁻¹ were found to contain higher densities of these microorganisms than those of the control pond without septage feeding. The possible public health impact resulting from this practice was assessed.     

A viscoplastic degradation model for rocks

In this paper a viscoplastic constitutive model for rocks is proposed in which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension to a general stress state has been also presented. Our model is capable to sufficiently well predict both the pre-peak hardening and post-peak softening response of rock material in compression providing good simulation of material response in both stable and post-critical stages of deformation. Such behaviour can be obtained for both low and high strain rates. In our examples, model parameters are determined from uniaxial compression tests performed on sandstone at different strain rates.