【作者】 涂国祥；

【导师】 黄润秋；

【作者基本信息】 成都理工大学 ， 地质工程， 2010， 博士

【摘要】 在我国西南一些大江大河的河谷地带广泛分布一套形成于第四纪更新世冰水堆积体,这些冰水堆积体大多规模巨大,体积动辄数百万m3,甚至数千万m3。在漫长的形成演化历史过程中,受沉积环境变化影响,这些冰水堆积体大多具有复杂的沉积和结构特征。本世纪以来,随着上述地区各类大型基础建设的陆续上马,上述大型冰水堆积常常构成了人类工程建设的地质背景条件,成为制约人类工程建设活动一个重要因素,因此针对该类古冰水堆积体的工程特性以及工程中面临的突出问题展开专门深入研究显得尤为迫切。本文通过对西南河谷地区数个冰水堆积体的沉积特征、颗粒组成、结构特征的详细调查和分析,在大量试验及相关工程资料收集的基础上对西南河谷典型古冰水堆积体的渗流特性、强度特性以及变形特性等进行了较为深入的分析和研究,最后结合三个古冰水堆积体,对其主要工程问题及其处理措施进行了深入分析和探索,取得了以下主要成果:(1)揭示了在冰水堆积体漫长形成演化历史工程中,受气候环境条件变化的影响,古冰水堆积体大多具有复杂的沉积特征和结构特征。具体表现为:沉积特征的宏观分层性和单层沉积特点差异性,古冰水堆积体主要以巨颗粒、粗颗粒为主局部富集细颗粒物质,不同沉积层水动力沉积环境存在较大差别,以粗颗粒为主的沉积层大多具有一定分选、磨圆和沉积韵律性,而以巨颗粒为主的沉积层大多分选磨圆差;结构上古冰水堆积体表现明显的二元性、粗颗粒巨颗粒之间嵌合紧密、普遍具有泥质胶结局部具钙质胶结的结构特征,即以粗颗粒、巨颗粒为骨架,细颗粒物质填充其间,构成骨架的粗颗粒、巨颗粒嵌合紧密,往往具有一定程度的泥质胶结,当含钙质成分较多时往往还具有较好的钙质胶结特点。(2)初步建立了从物质来源、沉积特点、结构特征等几个方面入手的古冰水堆积体野外辨别方法。即首先从物质来源、运移通道上判断是否存在冰水堆积的可能,然后根据其是否存在宏观成层性、水流作用形成的沉积韵律特点,构成堆积体主体的粗颗粒、巨颗粒物质结构上是否表现出二元性、嵌合性以及胶结特点等综合判断是否属冰水成因堆积体。(3)根据大量测年结果以及冰水堆积体与河流相覆盖层、古风化残积粘土层的接触关系,探讨了其沉积特点与古气候特点、冰川融水动力条件、古地形地貌之间的关系,认为在晚更新世末次间冰期和中更新世倒数第二次冰期间冰阶期间至少出现两次较大规模气温升高、冰川消融地质事件,并且揭示了形成于晚更新世的冰水堆积体多存在侵占河道,掩埋河流相覆盖层的现象;同时在间冰期期间古气候曾出现多次反复,导致冰川消融多次间断,堆积体接受风化剥蚀,从而在堆积体内形成古风化残积粘土层。(4)根据大量试验成果,得出了西南河谷地带古冰水堆积体大多具有渗透能力弱、抗渗能力强的渗流特点,揭示了在水力梯度较小时,冰水堆积体渗流规律基本满足达西定律,当水力梯度较大时,渗流速度与水力梯度表现出较为明显的非线性关系,此时渗流本构关系可描述为v = KJ0.7,并初步建立了古冰水堆积体渗透系数估算方法和公式ucK = 0.5e2CC。(5)在大量物理力学试验基础上揭示了冰水堆积体大多具有结构密实、高密度、孔隙体积小的特点,属典型的高承载力、低压缩性土。冰水堆积体大多具有较好的抗剪强度,天然状态下,内聚力可达150～400KPa,摩擦角约35°～39°;饱水条件下内聚力也保持在60～100Kpa,内摩擦角约30°～37°;且C值对水的敏感要比φ强烈的多,一般饱水条件下会导致内聚力降低一半左右,而φ值的变化几乎不超过1～3°。揭示了不同的应力条件对冰水堆积体的强度特性存在明显的影响,具体表现为在低应力环境下强度包络线满足莫尔-库仑定律,而在较高应力条件下,冰水堆积体的强度包络线表现出明显非线性特点。(6)通过对三个典型古冰水堆积体的稳定性研究,认为古冰水堆积体与一般松散堆积体的最主要区别之一在于其具有复杂的沉积和结构特征,构成冰水堆积体的物质不仅有高强度的碎块石土,还有强度较低的各种软弱层带,若上述软弱层带与堆积体临空条件下没有构成有利组合,堆积体大多具有较好的稳定性,一旦受某些因素影响,改变了堆积体的临空条件,且与软弱层带构成有利组合,就可能诱发堆积体沿软弱层带失稳破坏。因此工程上面临这类古冰水堆积体时应准确把握其沉积和结构特征,切不可草率地将其当作均质介质。更多还原

【Abstract】 In southwest China, a set of outwash congeries forming at the the Pleistocene Epoch of Quaternary widely spread in the valley terrace with large rivers. Many of them are huge, often with the volume of millions m3, or even tens of millions m3. Influenced by the changes of sediment environment, the outwash congeries have formed into complicated sediment properties and structures during the long history of evolution. In this century, with the successive commencement of infrastructure projects in the valley areas, the outwash congeries, as a geological background of engineering construction, become an important condition for engineering construction. Therefore, it is rather necessary to make an intensive study of the engineering properties of the ancient outwash congeries and the prospective problems which might be encountered in the engineering practice.This paper, after intensive investigation and analysis on sediment properties, particle assocaiation,and structure properties of several outwash congeries in the southwestern valley, conducts an intensive analysis and study on seepage properties, strength properties, and deformation properties of the typical outwash congeries, on the basis of a large number of experiments and the collection of the relevant data. Besides, illustrated with three examples of the ancient outwash congeries, three main types of problems in the engineering geology and the treatment measures are deeply analyzed and discussed. The main results are as follows: (1) During the long history of evolution and as a result of climate changes, the sediment properties and structure properties of ancient outwash congeries are usually complicated, featuring with the macroscopic stratification of the sediment properties and the diversity of the sediment properties in single-layer structures, to be specific. The ancient outwash congeries mainly consist of giant particles, coarse particles, and partially concentrating fine-grained materials. As the difference existing in hydrodynamically sedimentary environments among sedimentary stratums, those who mainly consist of coarse particles are often featured with the rhythmicity of separation, roundness, and deposition; while those mainly consisting of giant particles are relatively inferior in separation and roundness. Structurally, the ancient outwash congeries are distinctly binary, with closely interlocking of giant particles and coarse particles. It is usually characterized with the structure properties of mainly argillaceous binding and partially calcareous binding. That is, the solid matrix is made by giant particles and coarse particles, congested by fine-grained materials. Thus, the giant particles and coarse particles are closely interlocked, often featured with argillaceous binding to some extent; when calcium is high, they usually show some superior calcareous binding characteristics.(2)The way of determining ancient outwash congeries has been established in terms of sediment sources, sediment properties, and structure properties. Firstly, we should estimate the feasibility that the congeries forming with outwash deposits by Material source and movement pathway, then, we can Confirm wethere it is an outwash congeries or not, by wethere it with the macroscopic stratification of the sediment properties, wethere it having the rhythmic sedimentation characters, and wethere it having binary and Cementation characters in structure.(3)According to a large amount of dating data and the contact relation of the outwash congeries with the fluvial cover and the palaeo-weathered residual clay, the relationship between the sediment properties and palaeoclimate features, glacier melt hydrodynamics and palaeotopography are discussed. It is deemed that in the last interglacial of Late Pleistocene and in the Interstadial of last second glacial stage of Middle Pleistocene there were at least two times of large-scaled geological events with temperature elevation and glaciers ablation. It is also revealed that the channel is often occupied and the fluvial cover is often buried by the outwash congeries forming at Late Pleistocene. Meanwhile, during the interglacial period, paleoclimate repeated many times, resulting in several times interruptions of glaciers ablation, weathering and degradation of congeries, and the formation of palaeo-weathered residual clay inside the congeries.(4)According to a large amount of experiments, it finds that the ancient outwash congeries in the southwestern valley are featured with inferior seepage abilities and strong anti-seepage abilities. Also, when hydraulic gradient is small, the seepage of outwash congeries basically meet Darcy criterion; and when hydraulic gradient is large, it shows a nonlinear relationship between permeability velocity and hydraulic gradient is indicated, thus the seepage constitutive can be described as v = KJ0.7, and the estimation methods and formulas of the leakage factor of ancient outwash congeries can be established asucK = 0.5e2CC.(5)It is shown from large physic experiments that the outwash congeries, characterized with compactness, high-density, and small gap, is a typical kind of soil with high capacity and low compression. Outwash congeries are often with preferable shearing strength. Naturally, the cohesion can reach to 150～400KPa, and friction angle can be about 35°～39°; when under the saturated condition, the cohesion can keep at 60～100Kpa, and internal friction angle can be about 30°～37°. Moreover, the value of C is much more sensitive to water than that ofφ. Generally, under the saturated condition, the cohesion may be reduced by half or so, but the change of the value ofφis almost within 1～3°. It is also shown that different stress conditions have distinct influence on the strength properties of outwash congeries. That means the strength envelope meets Mohr– Coulomb criterion under low stress; while the strength envelope is nonlinear under high stress.(6) The study on the three typical ancient outwash congeries’stability finds that one of the major distinctions between the ancient outwash congeries and the general loose deposits is that the ancient outwash congeries are featured with complicated sediment properties and structure properties. The materials forming outwash congeries are not only gravelly soils with high strength, but also weak zones with low strength. In most time, the stability of the congeries are good if the weak zones and the free faces of congeries are not combines favorably, but if the free face is changed by someway and combined favorably with weak zones, the congeries will slide along the weak zones possibly. Therefore, it is suggested that the sedimentary and structural features of the outwash congeries be studied carefully, and mistaken treatment of them as isotropic medium be avoided when it comes to the ancient outwash congeries in engineering.更多还原