Size and shape evolution of pores in a viscoplastic matrix under compression

The frequent use of soils and earth materials for hydraulic capping and for geo‐environmental waste containment motivated our interest in detailed modelling of changes in size and shape of macro‐pores to establish links between soil mechanical behaviour and concurrent changes in hydraulic and transport properties. The objective of this study was to use finite element analysis (FEA) to test and extend previous analytical solutions proposed by the authors describing deformation of a single macro‐pore embedded in linear viscoplastic soil material subjected to anisotropic remote stress. The FEA enables to consider more complex pore geometries and provides a detailed picture of matrix yield behaviour to explain shortcomings of approximate analytical solutions. Finite element and analytical calculations agreed very well for linear viscous as well as for viscoplastic materials, only limited for the case of isotropic remote stress due to the simplifications of the analytical model related to patterns and onset of matrix‐yielding behaviour. FEA calculations were compared with experimental data obtained from a compaction experiment in which pore deformation within a uniform modelling clay sample was monitored using CAT scanning. FEA predictions based on independently measured material properties and initial pore geometry provided an excellent match with experimentally determined evolution of pore size and shape hence lending credence to the potential use of FEA for more complex pore geometries and eventually connect macro‐pore deformation with hydraulic properties. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of large-diameter pipe pile driving on surrounding marine soils and adjacent submarine pipelines

Abstract

With the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing.     

Role of dykes in induced seismicity at Bhatsa reservoir,Maharashtra, India

The geological and hydrological conditions near the reservoir site play an important role in the generation or absence of seismic activity. Near Bhatsa reservoir, along the west coast of India intense seismic activity occurred during August–September 1983, after a lag of six years of initial impounding. From July 1983 to September 1990, 15,388 earthquakes (mostlyM ₁<3.0) were recorded, the largest being of magnitude 4.9. The spatial distribution of well located 172 earthquakes suggest a strong correlation between the epicenters and the disposition of dykes and faults around the Bhatsa region. It is inferred that these dykes have acted as barriers for the diffusion of water from the reservoir, thereby becoming zones of instability due to increased pore pressure not only along them but also over the volume they bound.     

Coal-generated oil in Tuha Basin

The Turpan-Harmi (abbreviated to Tuha below) Basin is a typical basin of coal-generated oil accumulation in China. The Middle-Lower Jurassic coal measures are considered the main source beds. Hence, both desmocollinite and suberinite are considered the contributors for coal-generated oil. Principal geochemical features of the crude oil in the Tuha Basin are rich in alkanes (70%—80%), high pristane/phytane ratio (6—8), abundant heavy carbon isotope (δ¹³C PDB= -26%–-23%) and absolute GP sterane predominance. The hydrocarbon generation process from the coal series is characterized by multistages, early generation and early expulsion.     

Monitoring and modelling of pore water pressure changes and riverbank stability during flow events

Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer‐piezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective of investigating pore pressure changes in response to ?ow events and their effects on bank stability. The saturated/unsaturated ?ow was modelled using a ?nite element seepage analysis, for the main ?ow events occurring during the four‐year monitoring period. Modelling results were validated by comparing measured with computed pore water pressure values for a series of representative events. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern‐Price), using pore water pressure distributions obtained by the seepage analysis. The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of ?ow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the con?ning pressure of the river during the initial drawdown were responsible for triggering the mass failure. Results deriving from the seepage and stability analysis of nine selected ?ow events were then used to investigate the role of the ?ow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd.     

Experimental study on pore water pressure dissipation of mucky soil

Pore water pressure has an important influence on mechanical properties of soil. The authors studied the characteristics of pore water pressure dissipating of mucky soil under consolidated-drained condition by using refitted triaxial instrument and analyzed the variation of pore pressure coefficient with consolidation pressure. The results show that the dissipating of pore water pressure behaves in different ways depends on different styles of loading. What is more, the pore water pressure coefficient of mucky soil is less than 1. As the compactness of soil increases and moisture content reduces, the value of B reduces. There is a staggered dissipating in the process of consolidation, in which it is a mutate point when U/P is 80%. It is helpful to establish the pore water pressure model and study the strength-deformation of soil in process of consolidation.     

鄂尔多斯盆地吴旗地区长6储层孔隙结构特征

孔隙结构研究是油藏精细描述、储层综合评价的重要内容,采用铸体薄片、扫描电镜、铸体图像分析、高压压汞和恒速压汞等多种技术手段,对鄂尔多斯盆地吴旗地区长6储层的孔隙结构进行了深入分析和研究.鄂尔多斯盆地吴旗地区长6储层具有高孔低渗的特征,储层以原生剩余粒间孔为主,长石、岩屑及早期碳酸盐胶结物的溶解是形成次生孔隙的主要原因.中孔和小孔是油气的主要储集空间,细喉和中喉则是长6的基本渗流通道.铸体薄片、孔喉图像分析表明,吴旗长6储层具有复杂的孔喉分布特征,不同微相孔喉分布及孔隙结构特征是造成油井产能差异的重要因素.     

利用扫描电镜、压汞法、氮气吸附法评价近海黏土孔隙特征

近海地区黏土的微观结构单元--黏土畴中含有大量的粒内孔隙,其孔径小至纳米级,这部分孔隙对黏土的物理指标、水稳性、膨胀性、收缩性等具有重要影响,一般方法很难准确地描述其孔隙特征。试验利用扫描电镜、压汞法、氮气吸附法对湛江黏土的微观孔隙特征及其孔隙发育的控制因素分析,建立微观结构与物理指标、力学行为的相互关系与灵敏性分析。结果表明,湛江黏土具有不良物理性质和良好力学特性指标的异常组合,是一种高灵敏性的强胶结结构性黏性土,其机制主要是：湛江黏土的微观结构为带有胶质联结特性的、定向性无序的开放式絮凝结构,孔隙结构为具有较高的强度和空间稳定性的边－面－角联结的空间网架系统。由于特殊的孔隙网架结构以及“墨水瓶”型孔隙的存在,导致退汞过程出现滞留现象及产生吸附回线。研究表明,联合扫描电镜、压汞法、氮气吸附法能够准确、完整地对近海地区黏土孔隙体系特征进行定性与定量的评价。