黑龙江东部盆地群早白垩世早期海侵作用续探——以鸡西盆地鸡D7井为例

黑龙江东部盆地群是我国东部重要的中生代陆相含油气区,属东北含油气亚区的一部分。早白垩世以陆相湖泊沉积为主,但有多次规模不等的海侵事件发生,本次研究进一步对鸡西盆地鸡D7井下白垩统城子河组和穆棱组砂岩的结构构造、矿物排列、碎屑岩组分、胶结物、综合结构系数、重矿物等特征进行了综合分析研究:在早白垩世地层发现了具典型滨海潮下带特征的双粘土层构造;该层位砂岩多为少石英或者石英含量在25%左右的长石岩屑砂岩和岩屑长石砂岩;胶结物以碳酸盐为主;受海侵作用影响,城子河组砂岩综合结构系数平均值为20.16,穆棱组平均值为46.65,表明穆棱期比城子河期受海侵影响更为明显;并且在砂岩中发现重矿物20余种,呈条带状富集,尤其是特征矿物海绿石、自生独居石、莓状黄铁矿及自然金等具明显海侵相特征。本次研究为黑龙江东部盆地群海侵的存在提供了一系列沉积学证据。     

疏浚淤泥流动固化土的压汞试验研究

采用压汞法对疏浚淤泥流动固化土进行了微观孔隙结构的研究,分析了固化土的孔隙体积及入口孔径分布特征与固化材料掺量及固化土龄期的关系,并将微观试验结果与固化土的物理指标和强度特性进行了比较。结果表明,采用压汞法研究疏浚淤泥流动固化土的微观孔隙空间分布是成功的,压汞试验得到的微观孔隙特征与众多学者通过宏观力学试验得出的强度规律是一致的,微观结构试验能够很好地解释宏观物理力学性状。随着固化材料掺量的增加和龄期的增长,淤泥固化土的孔隙体积和D50孔径明显减小,入口孔径分布特征亦发生了相应变化。所得流动固化土的入口孔径主要分布在0.01～10 ?m之间,最大分布孔径在0.5～2 ?m之间。     

Ionizing radiation-induced defects in smectite clays

 The interaction of γ-rays with smectites induces paramagnetic defects in the structure of these clay minerals. The EPR spectra of three different smectites detect the creation of structural defects and trapping of organic free radicals in the clay structure upon irradiation. The defects are assigned to positive holes or trapped electrons stabilised by existing local charge imbalances in the mineral lattice. The organic radicals are derived from organic compounds present as impurities in the crystal lattice of the clay minerals. In addition, γ-rays cause migration of small interlayer cations (such as Li⁺) into the layers, as clearly evidenced by EPR and FT-IR reflectance spectroscopies. Received: 20 April 2000 / Accepted: 2 December 2000     

The shear strength of clay-filled bedding planes in limestones - back-analysis of a slope failure in a phosphate mine, Israel

The failure of a slope in a phosphate mine by shear-sliding along a clay-filled bedding plane in limestone, and by separation across a tension crack at the back, is back-analysed. The failure cannot be explained using laboratory measured values of the shear strength parameters. In order to simulate field conditions better two physical models of the bedding plane were prepared for testing under triaxial compression. Cylindrical cores with an inclined saw-cut discontinuity were filled with remoulded montmorillonite. It is shown that failure in the models initiates along the contacts between the clay infilling and the limestone boundaries, and not through the clay itself, as would be intuitively expected. Furthermore, it is argued that in the analysis of rock slope stability in general, and particularly in the case of clay-filled discontinuities, the influence of paleo-overburden stress on frictional resistance must be resolved before the appropriate constitutive law can be established for analysis.     

Numerical analysis of suction embedded plate anchors in structured clay

As offshore energy developments move towards deeper water, moored floating production facilities are increasingly preferred to fixed structures. Anchoring systems are therefore of great interest to engineers working on deep water developments. Suction embedded plate anchors (SEPLAs) are rapidly becoming a popular solution, possessing a more accurate and predictable installation process compared to traditional alternatives. In this paper, finite element analysis has been conducted to evaluate the ultimate pullout capacity of SEPLAs in a range of post-keying configurations. Previous numerical studies of anchor pullout capacity have generally treated the soil as an elastic-perfectly plastic medium. However, the mechanical behaviour of natural clays is affected by inter-particle bonding, or structure, which cannot be accounted for using simple elasto-plastic models. Here, an advanced constitutive model formulated within the kinematic hardening framework is used to accurately predict the degradation of structure as an anchor embedded in a natural soft clay deposit is loaded to its pullout capacity. In comparison with an idealised, non-softening clay, the degradation of clay structure due to plastic strains in the soil mass results in a lower pullout capacity factor, a quantity commonly used in design, and a more complex load–displacement relationship. It can be concluded that clay structure has an important effect on the pullout behaviour of plate anchors.     

Gravitational Sedimentation Behavior of Sensitive Marine Ariake Clays

It has been well documented that natural marine Ariake clays are sensitive clays. In this study, extensive data of marine Ariake clays are obtained to investigate the gravitational compression behavior for sensitive clays. Analysis results indicate that the compression behavior of remolded Ariake clays is not different from that of other remolded/reconstituted soils. But natural Ariake clays do not follow the gravitational compression pattern reported by Skempton (1970) for natural sedimentary soils. At a given value of effective overburden pressure, the void ratios of natural Ariake clays are almost independent of liquid limits. Most natural Ariake clays lie above the sedimentation compression line proposed by Burland (1990). When the liquid limit is larger than 90% and the ratio of natural water content over liquid limit ranges 0.8-1.1, the natural Ariake clays lie around the sedimentation compression line. In addition, the natural Ariake clay with higher value of the ratio of natural water content over liquid limit lies above the natural Ariake clay with lower value of the ratio of natural water content over liquid limit. Salt removal is the most probable cause for such a phenomenon.     

Strength Sensitivity of Marine Ariake Clays

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.     

Modelling chemo‐hydro‐mechanical behaviour of unsaturated clays: a feasibility study

Effective capabilities of combined chemo‐elasto‐plastic and unsaturated soil models to simulate chemo‐hydro‐mechanical (CHM) behaviour of clays are examined in numerical simulations through selected boundary value problems. The objective is to investigate the feasibility of approaching such complex material behaviour numerically by combining two existing models. The chemo‐mechanical effects are described using the concept of chemical softening consisting of reduction of the pre‐consolidation pressure proposed originally by Hueckel (Can. Geotech. J. 1992; 29 :1071–1086; Int. J. Numer. Anal. Methods Geomech. 1997; 21 :43–72). An additional chemical softening mechanism is considered, consisting in a decrease of cohesion with an increase in contaminant concentration. The influence of partial saturation on the constitutive behaviour is modelled following Barcelona basic model (BBM) formulation (Géotech. 1990; 40 (3):405–430; Can. Geotech. J. 1992; 29 :1013–1032). The equilibrium equations combined with the CHM constitutive relations, and the governing equations for flow of fluids and contaminant transport, are solved numerically using finite element. The emphasis is laid on understanding the role that the individual chemical effects such as chemo‐elastic swelling, or chemo‐plastic consolidation, or finally, chemical loss of cohesion have in the overall response of the soil mass. The numerical problems analysed concern the chemical effects in response to wetting of a clay specimen with an organic liquid in rigid wall consolidometer, during biaxial loading up to failure, and in response to fresh water influx during tunnel excavation in swelling clay. Copyright © 2005 John Wiley & Sons, Ltd.     

Simulation of cyclic strength degradation of natural clays via bounding surface model with hybrid flow rule

Strength loss of natural clays subjected to seismic loading is a critical factor contributing to earthquake‐induced ground failure and associated hazards. This work proposes a bounding surface constitutive law to simulate cyclic strength degradation of natural clays resulting from the loss of structure and attendant accumulation of excess pore pressures. The proposed model employs an enhanced plastic flow rule that can simulate accurately the development of pore pressure and explicitly incorporates soil structure effects. The validation of the model with reference to the experimental evidence available for 3 structured clays shows that with a single set of parameters the proposed model can reasonably represent the mechanical behavior of natural clays under various loading conditions (1D compression, monotonic shearing in compression and extension, cyclic loading, and postcyclic shearing). Particularly, its satisfactory performance in terms of quantification of cyclic strength degradation encourages the use of the model in simulating boundary value problems related to the stability of geotechnical facilities under earthquakes.     

A multisurface kinematic hardening model for the behavior of clays under combined static and undrained cyclic loading

In dynamic geotechnical problems, soils are often subjected to a combination of sustained static and fast cyclic loading. Under such loading conditions, saturated and normally consolidated clays generally experience a build-up of excess pore water pressure along with a degradation of stiffness and strength. If the strength of the soil falls below the static stress demand, a self-driven failure is triggered. In this paper, a constitutive model is presented for the analysis of such problems, based on a general multisurface plasticity framework. The hardening behavior, the initial arrangement of the surfaces, and the nonassociated volumetric flow rule are defined to capture important aspects of cyclic clay behavior. This includes nonlinear hysteretic stress-strain behavior, the effect of anisotropic consolidation, and the generation of excess pore water pressure during undrained cyclic loading along with a degradation of stiffness and strength. The model requires nine independent parameters, which can be derived from standard laboratory tests. A customized experimental program has been performed to validate the model performance. The model predictions show a good agreement with test results from monotonic and cyclic undrained triaxial tests, in particular with respect to the strain-softening response and the number of loading cycles to failure. A procedure for a general stress-space implicit numerical implementation for undrained, total stress-based finite element analyses is presented, including the derivation of the consistent tangent operator. Finally, a simulation of the seismic response of a submarine slope is shown to illustrate a possible application of the presented model.