心墙掺砾土料的动强度特性研究

发布时间：2018-04-13 01:03

本文选题：土石坝 + 心墙　；参考：《大连理工大学》2014年硕士论文

【摘要】：土石坝具有投资省、施工快以及对地质条件的适应范围广等优点,是国内外重点发展的坝型之一。近年来,土石坝的高度有了很大发展,正在实现150m级向300m级高坝的跨越。如双江口(312m)、两河口(293m)、糯扎渡(261.5m)等等。高土石坝多采用掺砾黏土料作防渗心墙。这种人工掺砾土料的级配宽,有相当的黏粒含量,小颗粒充分填充大颗粒孔隙,可获得很高的干密度,因而具有良好的防渗性,同时粗颗粒能够形成骨架,抗剪强度和弹性模量均较高,应用于高土石坝作心墙料,既起防渗作用,又与两侧坝壳料的强度变形特性相差不大,较好地承担荷载,改善心墙的应力状态,减少发生水力劈裂的可能性。高土石坝的坝壳料一般有向外变形的趋势,这会引起心墙应力减小,一旦发生地震心墙顶部容易出现动强度不足的问题,甚至产生裂缝,若继续加震将导致大坝顶部坝坡失稳等。心墙土料掺砾可以提高其地震动强度,但掺砾后心墙与坝壳刚度差别变小,在地震引起剪应力的分担上,掺砾土料心墙分担的比例比黏土心墙大。因此掺砾心墙的动强度能否满足要求需要进一步研究。本文采用GDS三轴仪进行了一系列饱和掺砾土料的静力和动力试验,研究了心墙顶部的掺砾土料在低围压下的动强度特性。本文的主要工作如下： (1)进行了静力三轴固结不排水试验,得到了掺砾料的应力—应变、孔压、有效应力路径曲线,求得其静强度指标。 (2)进行了动力三轴试验,研究了掺砾土料的动力特性,得到了掺砾土料的动模量和阻尼比曲线及参数。 (3)进行了动强度试验,得到如下规律：①相同围压作用下试样的动强度一般随固结应力比先增大后减小。②试样的掺砾比例增大可以提高其动强度,且随着围压的增大动强度提高愈显著。动摩擦角φd随掺砾比例提高而变大,但动粘聚力cd随掺砾比例提高而变小。掺砾比例变化引起其动力指标的变化与静力情况下的变化相似。③试样的动应变随振次N的变化与rc的大小有关,rc为动应力和土样的固结不排水强度之比。动应变随振次的变化曲线存在一个转折点,在转折点出现以前,应变随振次变化缓慢；转折点出现以后应变急剧增长。④通过3组不同固结比动强度试验,绘制出地震总应力抗剪强度线并求得地震总应力强度参数。
[Abstract]:Earth-rock dam is one of the most important dam types at home and abroad because of its advantages of low investment, fast construction and wide adaptability to geological conditions.In recent years, the height of earth-rock dam has been greatly developed, and the span from 150m to 300m is being realized.Such as Shuangjiang Estuary (312m), Liangkou (293m), Nuozhadu (261.5m) and so on.High earth-rockfill dams often use gravel clay as anti-seepage core wall.The gradation of the artificial gravel soil is wide, and the content of clay is considerable. The small particles can fill the pores of large particles to obtain a very high dry density, so it has good impermeability, and the coarse particles can form a skeleton.The shear strength and elastic modulus are both high. When used as core wall material of high earth-rock dam, it not only acts as an anti-seepage effect, but also has little difference with the strength and deformation characteristics of both sides of dam shell, so it can bear the load better and improve the stress state of the core wall.Reduce the possibility of hydraulic fracturing.Generally speaking, the shell material of high earth rockfill dam tends to deform outward, which will cause the stress of the core wall to decrease, and once the earthquake occurs, the problem of insufficient dynamic strength on the top of the core wall is likely to occur, and even cracks will occur.If the earthquake continues, it will lead to the instability of the dam slope at the top of the dam.The strength of ground motion can be increased by adding gravel to core wall, but the difference between the stiffness of core wall and dam shell becomes smaller after adding gravel, and the proportion of core wall with gravel is larger than that of clay core wall in shear stress sharing caused by earthquake.Therefore, whether the dynamic strength of gravel core wall can meet the requirements needs further study.In this paper, a series of static and dynamic tests of saturated gravel admixture are carried out with GDS triaxial instrument. The dynamic strength of gravel admixture at the top of core wall under low confining pressure is studied.The main work of this paper is as follows:1) the static triaxial consolidation undrained test was carried out, and the stress-strain, pore pressure and effective stress path curves of gravel admixture were obtained, and the static strength index was obtained.(2) dynamic triaxial test was carried out, and the dynamic characteristics of gravel soil were studied, and the dynamic modulus and damping ratio curves and parameters were obtained.(3) the dynamic strength tests have been carried out. The results show that the dynamic strength of the specimen under the same confining pressure is generally increased with the increase of the consolidation stress ratio first and then decreased by the increase of the proportion of gravel admixture of the sample. The dynamic strength of the specimen can be increased by increasing the ratio of gravel to gravel.With the increase of confining pressure, the dynamic strength increases more significantly.The dynamic friction angle 蠁 d increases with the increase of boulder ratio, but the dynamic cohesive force CD decreases with the increase of gravel ratio.The change of dynamic index caused by the ratio of mixed gravel is similar to that under static condition. The dynamic strain of specimen changes with the vibration degree N and the magnitude of RC is related to the ratio of dynamic stress to consolidation undrained strength of soil sample.There is a turning point in the curve of dynamic strain with vibration times. Before the turning point appears, the strain changes slowly with vibration times, and the strain increases sharply after turning point.The shear strength line of seismic total stress is drawn and the parameters of seismic total stress intensity are obtained.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV641;TV41

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