Direct shear tests on Mexico City clay with reference to friction pile behaviour     

E. Ovando-Shelley 《Geotechnical and Geological Engineering》1995,13(1):1-16

Summary This paper presents results of static and cyclic direct shear tests performed on undisturbed and remoulded samples of Mexico City clays, including results of soil-on-interface tests. Experiments show that the static adhesion coefficient depends on the soils' liquidity index and that it diminishes due to the effect of repeated dynamic loads. Dynamic overstrength effects were not apparent, as has been observed when testing this clay in other apparatus. Interface strength in remoulded clays is initially less than half the strength of interfaces with undisturbed materials but it increases with time. At least in the materials tested in this research, it did not equal the strength of interfaces with undisturbed materials. Correction factors derived from experimental data can be used to modify the adhesion coefficient to account for dynamic and remoulding effects.  相似文献   

哀牢山-红河剪切带的热年代学研究——多重扩散域模式的应用实例   总被引：22，自引：3，他引：19       下载免费PDF全文

陈文寄 Harr.  M 《地震地质》1992,14(2):121-128

洛弗拉等人(1989)把Dodson(1973)建立的单一扩散域模式扩展成矿物扩散域不连续分布的模式,即多重扩散域模式,与之对应具有某一封闭温度范围,因此利用单个K-长石矿物样品可以揭示更长时间段上的冷却过程。对云南哀牢山-红河剪切带的K-长石样品(FA-2-1)进行40Ar/39Ar同位素分析,利用多重扩散域模式,揭示在距今约20～19Ma问该带存在一快速冷却过程,这与西藏南部曲水地区快速抬升的时间是一致的  相似文献   

饱和软土压缩曲线的“反常”现象     

冯铭璋  王兴涛 《上海国土资源》1990,(3):30-37

饱和软土压缩试验时,经常出现压缩曲线“反常”、压缩系数“倒大”的现象。它是土的原始结构发生破坏前后的不同压缩性的客观反映。饱和软土的结构力很微弱,唯质量好的原状土才能见到这种“反常”。应从成孔、取样、测试及资料整理等多个环节保证其工程意义。  相似文献   

Low temperature volatile production at the Lost City Hydrothermal Field, evidence from a hydrogen stable isotope geothermometer   总被引：1，自引：0，他引：1  

Giora Proskurowski  Marvin D. Lilley  Deborah S. Kelley  Eric J. Olson 《Chemical Geology》2006,229(4):331-343

Although commonly utilized in continental geothermal work, the water-hydrogen and methane-hydrogen isotope geothermometers have been neglected in hydrothermal studies. Here we report δD-CH₄ and δD-H₂ values from high-temperature, black smoker-type hydrothermal vents and low-temperature carbonate-hosted samples from the recently discovered Lost City Hydrothermal Field. Methane deuterium content is uniform across the dataset at − 120 ± 12‰. Hydrogen δD values vary from − 420‰ to − 330‰ at high-temperature vents to − 700‰ to − 600‰ at Lost City. The application of several geothermometer equations to a suite of hydrothermal vent volatile samples reveals that predicted temperatures are similar to measured vent temperatures at high-temperature vents, and 20-60 °C higher than those measured at the Lost City vents. We conclude that the overestimation of temperature at Lost City reflects 1) that methane and hydrogen are produced by serpentinization at > 110 °C, and 2) that isotopic equilibrium at temperatures < 70 °C is mediated by microbial sulfate reduction. The successful application of hydrogen isotope geothermometers to low-temperature Lost City hydrothermal samples encourages its employment with low-temperature diffuse hydrothermal fluids.  相似文献   

Strength and stability of frictional sliding of gabbro gouge at elevated temperatures   总被引：7，自引：1，他引：7  

Changrong He  Wenming Yao  Zeli Wang  Yongsheng Zhou   《Tectonophysics》2006,427(1-4):217

To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10^− 3 mm/s and 1.22 × 10^− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes.  相似文献   

Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength   总被引：2，自引：0，他引：2  

S. Okubo  K. Fukui  Qi Qingxin 《International Journal of Coal Geology》2006,68(3-4):196-204

The mechanical characteristics of coal under uniaxial compressive stress and uniaxial tensile stress are key factors in investigations of the stability of galleries and coal faces, and are vital considerations for the efficient design of coalmines, disaster prevention, and environmental preservation. These mechanical characteristics have long been a topic of research, but remain insufficiently understood. In this study we performed uniaxial compression tests and uniaxial tension tests on coal, with particular attention to two concerns. The first was to measure the loading rate dependence of the peak strength of coal. Coal shows high sample-to-sample scatter in strength; test methods that are successful in comparatively homogeneous rock types cannot be used for coal. We therefore used an alternative test method that was recently developed by the authors. Anthracite samples were subjected to alternating slow and fast strain rates. Measured variations in stress during this process were used to estimate the loading rate dependence of peak strength. The second objective was to obtain complete stress–strain curves for coal under uniaxial tensile stress. It is difficult to hold samples secure during a tensile test; consequently, such curves have yet to be obtained. This study presents a successful application of the authors' method to the analysis of coal samples, yielding a complete stress–strain curve under tensile stress. The two methods presented here hold promise for application not only to anthracite but also to a wide variety of coals. It is possible to derive the values of the constants used in constitutive equations from the obtained experimental results. Once these equations are determined, they can be incorporated into finite-element software to investigate various time-dependent behaviors of coal and aid in the efficient design of coalmines and the prevention of subsidence and mine disasters.  相似文献   

Effects of dynamic shear strength and time-histories stress analysis on newmark sliding block analyses     

LI Hong-jun  CHI Shi-chun  LIN Gao 《岩土力学》2006,27(Z1):1063-1068

A simplified procedure for evaluating aseismic stability of slope subjected to earthquake shaking, in which the effect of dynamic shear strength and time-history stress on the yielding angular acceleration of sliding block is taken into account, is presented. The fundamental feature of this procedure is the dynamic shear strength. The numerical computations are performed by using the proposed method. It is shown that the computed sliding displacement for a given core dam, with either method of dynamic shear strength properly considered, is more rational compared with the conventional computational results based on static shear strength.  相似文献   

Three-dimensional model and late stage warping of the Plattengneis Shear Zone in the Eastern Alps     

Martin Putz  Kurt Stüwe  Mark Jessell  Philippe Calcagno   《Tectonophysics》2006,412(1-2):87-103

The Plattengneis shear zone is a 250–600 m thick, flat lying, Cretaceous, eclogite facies, mylonitic shear zone, with north-over-south transport direction, that is exposed over almost 1000 km² in the Koralpe region along the eastern margin of the Alps. Although the shear zone is one of the largest in the Alps, its role in the Eoalpine metamorphic evolution and the subsequent exhumation of the region, remain enigmatic and its large-scale geometry is not well understood. The outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn- and antiforms with wavelengths of about 10 km. Eclogite bodies occur above, within and below the shear zone and there is no metamorphic grade change across the shear zone. In the south, the fold axes strike east–west and plunge shallowly to the east. In the north, the fold axes are oriented in north–south direction and form a dome shaped structure of the shear zone. Total shortening during this late stage warping event was of the order of 5%. Indirect evidence constrains this folding event to have occurred between 80 and 50 Ma and the fold geometry implies that the final exhumation in the Koralpe occurred somewhat later than further north. Interestingly, the shear zone appears to strike out of the topography in the south and dip into the topography in the north, so that north of the shear zone only hanging-wall rocks are exposed and south of it only foot-wall rocks. Possibilities for the geometric relationship of the Plattengneis shear zone with the surrounding south dipping detachments are discussed.  相似文献   

Up-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocks   总被引：1，自引：0，他引：1  

C. CLARK  M.  HAND  K.  FAURE  A. SCHMIDT MUMM 《Journal of Metamorphic Geology》2006,24(5):367-387

The Walter‐Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid‐crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610–1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower δ¹⁸O values (as low as 1‰) than their unsheared counterparts (7–9‰), and calculated fluid δ¹⁸O values (5–8‰) consistent with a surface‐derived fluid source. Hydrous minerals show a decrease in δD_(H2O) from ?14 to ?22‰, for minerals outside the shear zones, to ?28 to ?40‰, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near‐surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low δ¹⁸O fluid that is channelled through shear zones related to Delamerian Orogenic activity.  相似文献   

Impact of Changes in Redox Conditions on Leaching of Some Elements from MSW Fly Ash     

Lallan Prasad Gupta    Hodaka Kawahata    Mio Ltakeuchi  Hidekazu Ohta  Yoshiro Ono 《Resource Geology》2006,56(2):191-196

Abstract. Oxidation and reduction processes can influence extent of leaching of elements from solid waste. Three samples of municipal solid waste combustion fly ash were subjected to oxidizing and reducing conditions in order to evaluate leaching of elements in the Milli-Q water and fly ash (liquid to solid ratio, 100) mixtures. Although the oxidizing and reducing conditions were applied for 6 hours only, elements like Cs, Li, Mg, Sb, Tl and V leached more under oxidizing condition than under reducing condition in the case of all three ash samples. Cadmium, Pb and Zn leached more from all samples under reducing condition than under oxidizing condition. Leaching of other elements like Al, Ba, Cr, Cu, Ni and Rb was inconsistent with oxidizing or reducing conditions and varied from sample to sample, suggesting that factors other than redox may be more important in controlling leaching of these elements. Strong acid neutralization capacity of the fly ash samples let the pH vary within a narrow range, and thus severely limited the extent of leaching during the course of the experiment. Lead and Zn were the most sensitive while K and Na were the least sensitive to changes in redox conditions.  相似文献