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The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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在河南周口市淮阳县地热井施工中,发生了粘性土粘附卡钻、砂桥卡钻等事故,首先采用提拔、碱泡、爆破等措施进行处理,仍有较长钻具遗留在孔内,然后采用套铣方法进行处理,成功将遗留钻具从孔内提出,完成了孔内事故的处理。总结了该孔处理经验,可供类似工程参考借鉴。 相似文献
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Approximations of the Scattering Phase Functions of Particles 总被引：1，自引：0，他引：1
Based on anomalous diffraction theory and the modified Rayleigh-Debye approximation, a physically realistic model in bridging form is described to approximate the scattering phase function of particles. When compared with the exact method, the bridging technique reported here provides a reasonable approximation to the Mie results over a broader range of angles and size parameters, and it demonstrates the advantage of being computationally economic. In addition, the new phase function model can be essentially extended to other shapes and conveniently used in more complicated scattering and emission problems related to the solutions of the radiative transfer equations. 相似文献
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塔河油田SX2井3709～4025 m为二叠系火成岩地层,该地层裂缝发育,在该井段及下部井段钻井过程中多次发生漏失。通过多次桥接堵漏和水泥堵漏,效果不好,仍然存在漏失,钻穿二叠系至5340 m发生失返性漏失。利用化学固结堵漏技术对SX2井二叠系火成岩漏失层进行了封堵。化学固结堵漏浆承压能力达到17 MPa,抗温达到180 ℃,地面条件下流变性较好,便于泵送。将SX2井二叠系漏失层分成2段,利用化学固结堵漏技术分别进行封堵,堵漏施工后试压,漏失层承压能力由1.20 g/cm3提高至1.56 g/cm3,满足了后续钻井施工的要求。化学固结堵漏技术对于破碎性、裂缝性漏失层有较好的封堵效果。 相似文献
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The concurrent multiscale method, which couples the discrete element method (DEM) for predicting the local micro‐scale evolution of the soil particle skeleton with the finite element method (FEM) for estimating the remaining macro‐scale continuum deformation, is a versatile tool for modeling the failure process of soil masses. This paper presents the separate edge coupling method, which is degenerated from the generalized bridging domain method and is good at eliminating spurious reflections that are induced by coupling models of different scales, to capture the granular behavior in the domain of interest and to coarsen the mesh to save computational cost in the remaining domain. Cundall non‐viscous damping was used as numerical damping to dissipate the kinetic energy for simulating static failure problems. The proposed coupled DEM–FEM scheme was adopted to model the wave propagation in a 1D steel bar, a soil slope because of the effect of a shallow foundation and a plane‐strain cone penetration test (CPT). The numerical results show that the separate edge coupling method is effective when it is adopted for a problem with Cundall non‐viscous damping; it qualitatively reproduces the failure process of the soil masses and is consistent with the full micro‐scale discrete element model. Stress discontinuity is found in the coupling domain. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献