【作者】 虞海珍；

【导师】 赵文光； 汪稔；

【作者基本信息】 华中科技大学 ， 结构工程， 2006， 博士

【摘要】 钙质砂是海洋生物成因富含碳酸钙或其它难溶碳酸盐类物质的特殊岩土介质,具有与普通陆源砂迥异的工程力学性质,在我国南海海域有着广泛的分布。处于海洋环境并作为海工建筑物地基的钙质砂不仅处于复杂的初始固结应力状态,而且承受着风、浪、流、地震等复杂动应力作用,其动力稳定性直接影响着上部结构物的安全。但目前国内外对复杂应力条件下饱和钙质砂动力特性的研究相对较少,因此进行复杂应力条件下钙质砂动力特性的研究,对于进一步发展与完善钙质土力学性质的研究、指导海洋荷载作用下钙质砂海域海床稳定性分析以及实际工程的设计和施工,对于南海诸岛丰富石油资源及岛礁旅游业的开发和保卫,都具有重要的理论价值和实际工程意义。本文采用先进的土工静力-动力液压三轴-扭剪多功能剪切仪较好地模拟了海洋环境复杂的初始固结应力状态和复杂的动应力条件,对我国南沙群岛的钙质砂进行了大量的大应变幅值和微幅应变条件下的竖向-扭向循环耦合剪切试验、扭剪试验,竖向拉-压剪切试验、动三轴试验等系列试验,对复杂应力条件下饱和钙质砂动力特性做了较为系统地研究,主要研究内容和研究成果如下:1、进行大应变幅值条件下的动强度试验,研究复杂应力条件下钙质砂的动应变特性,分析初始偏应力比、初始平均有效固结压力、初始主应力方向角、中主应力系数等因素和循环荷载的施加方式对钙质砂的动应变发展的影响,提出饱和钙质砂动应变的发展模式:Boltzmann曲线或双曲线。2、分析孔隙水压力发展的时程曲线,研究钙质砂的动孔隙水压力增长特性,分析各种因素对动孔隙水压力增长特性的影响,建立了复杂应力条件下钙质砂峰值孔隙水压力的发展模式;探讨复杂应力状态下钙质砂峰值孔隙水压力与累积广义剪应变之间的联系,建立峰值孔隙水压力随累积广义剪应变的发展模式。3、分析钙质砂的液化特性,获得复杂应力条件下饱和钙质砂的液化机理。均压固结与非均压固结条件下的液化机理不同:均压固结条件下,液化机理为流滑或循环活动性;偏压固结时各种试验条件下均不液化。4、在动应变和动孔隙水压力增长特性及液化特性分析基础上,研究饱和钙质砂的动强度特性,建立动强度方程,并对各种循环荷载条件下的动强度进行了比较。5、开展微幅应变条件下的动力试验,研究钙质砂的动应力～动应变特性以及动模量和动阻尼比特性,获得动应力～动应变关系的骨干曲线模式,并分析各种因素对骨干曲线的影响;研究复杂应力条件下钙质砂动弹性模量和动剪切模量特性,并建立了动弹性模量和动剪切模量的计算模式;探讨复杂应力条件下钙质砂轴向阻尼比和扭向阻尼比特性,并比较各种因素对轴向阻尼比和扭向阻尼比的影响。更多还原

【Abstract】 Calcareous sand is a special geotechnical medium which composes much carbonate and has obvious different mechanical properties from the general sand. It is generated in marine environment and widely distributed in South China Sea. In the ocean conditions and as the foundation of marine structures, calcareous sand is not only under complex initial consolidated stress state, but also subjects complicated dynamic load induced by wind, ocean wave and earthquake shaking, so its dynamic stability directly influenced the safety of the above building. Since the dynamic behavior of calcareous sand under complex stress condition is seldom researched, so it has very significant academic meanings and engineering value to study the calcareous sand’s dynamic behavior under complex stress condition, which can develop and perfect the mechanical behavior investigation of calcareous soils, guide design, construction and assessing the stability of practical projects in marine condition, it can also exploit and defend the rich petroleum resource and reef island tourism in our South Sea.The dynamic behavior of calcareous sand under complex stress condition is studied systematically by performing a large number of tests such as vertical-and-torsional coupling cyclic shear test, simple trosional shear test, simple cyclic vertical shear test and simple triaxial shear test, using an advanced universal triaxial and torsional shear apparatus which can perfectly simulate the complex initial consolidated stress state and complicated dynamic stress. The main work and research findings are listed below.1、The dynamic strength experiment under high strain conditions is carried out to study the dynamic strain character of calcareous sand in complex stress state. Some factors influenced the development of dynamic strain are analysed such as initial deviator stress ratio, initial mean effective consolidated stress, initial direction angle of principal stress, parameter of intermediate principal stress and application way of cyclic load. The development model of dynamic strain has been put forward, that is Boltzmann curve or hyperbola.2、The development character of dynamic pore water pressure is investigated by analyzing the pore water pressure test curves and various effected factors. Then the development model of dynamic peak pore water pressure has been suggested. The determination method of peak pore water pressure with the accumulative generalized strain is proposed based on the relationship of peak pore water pressure and the accumulative generalized strain.3、The liquefaction nature of calcareous sand is studied and the liquefaction mechanics in complex stress condition is obtained. Mechanics of liquefaction under isotropic consolidation is different from under anisotropic. The liquefaction mechanics under isotropic consolidation is cyclic mobility or flow slide, while under anisotropic it isn’t liquefyied in all test condition.4、Based on the analysis of dynamic strain, pore water pressure and liquefaction nature, the dynamic strength character is researched and the strength equation is suggested. Then the dynamic strength under various cyclic load is compared.5、The character of dynamic stress-dynamic strain combat combined with dynamic modulus and damping ratio are studied by dynamic tests of low strain. The skeletal curves model of dynamic stress-dynamic strain is achieved and all the factors affected it are analysed. Then features of dynamic elastic modulus and dynamic shear modulus are researched and the calculational methods of then are proposed. At last, the axial damping ratio and torsional damping ratio are studied.更多还原