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Unified principle for determining the safety factor of structures against sliding


Optimal anchoring force against sliding of a body on two planes


Two failure patterns against sliding are analyzed.


The stability of shallow foundation must be checked against sliding failure and bearing capacity failure.


The results of these tests are used in an analysis of stability against sliding along the given interface.

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 In this paper a discussion on the adoption of the seismic coefficients and on safety evaluation in aseismatic design of gravity dams on rock foundations is presented.The discussion is based on further investigations the seismic response of the Xinfengjiang Dam, the Koyna Dam and some other gravity dams selected.In aseismatic design of gravity dams, usually based on static method or socalled pseudostatic method using conventional seismic coefficients and static parameters for calculating the shearing strength,... In this paper a discussion on the adoption of the seismic coefficients and on safety evaluation in aseismatic design of gravity dams on rock foundations is presented.The discussion is based on further investigations the seismic response of the Xinfengjiang Dam, the Koyna Dam and some other gravity dams selected.In aseismatic design of gravity dams, usually based on static method or socalled pseudostatic method using conventional seismic coefficients and static parameters for calculating the shearing strength, a basic evaluation of the overall stability against sliding of the dam subjected to earthquake, though far from being satisfactory, can usually be obtained. Stress calculation based on such methods, however, is often misleading. Therefore, it is advisable to take a different approach.Applicating the method of dynamic analysis and adopting a design seismic coefficient for the expected ground motion of the dam foundation to estimate the earthquake loadings and stresses, combining them with those produced by normal loads and comparing them with the paremeters for static strength, one may then arrive at a reasonable safety evaluation of a dam.This paper deals mainly with the problem of stability against sliding.The authors present the concept of relative seismic stability, which shall be helpful to indicate the rule of stability against sliding of dams subjected to earthquake and, consequently, to make sure the safety of the dam.In the investigation the dynamic coupling action between the dam and the reservoir water was taken into consideration,the dam and the reservoir water being treated as an assemble of finite elements.The analysis was carried by both the methods of response spectrum and timehistory. And the combined effects of dynamic and static loadings were introduced.  本文在通过对新丰江和柯依那(Koyna)大坝的震害情况进一步分析,和选择了其它一些重力坝进行研究后,提出了岩基上重力坝抗震设计地震系数的采用及安全性估算的意见. 在重力坝的抗震设计中,按照静力法或拟静力法和经验的地震系数、抗剪强度的静力指标检验大坝的抗滑稳定性,是可以得到基本估计的,但还存在某些问题;尤其是,在进行坝体强度校核时,往往会使人产生误解.因此,作者认为有必要采用动力分析法和预计的设计坝基地震系数,以估算地震荷载和应力,并与正常荷载的情况组合,取强度的静力指标作出比较,才能得到近乎合理的安全估算. 文中着重研究了大坝滑动稳定性问题,提出了抗震的稳定相对安全率的概念,它有助于揭示地震时大坝抗滑稳定的变化规律,并作出安全的估算. 在分析时,将坝体和库水作为有限单元的集合体,考虑了坝体与库水在振动时耦合作用,按反应谱法和时程法进行动力分析,得出了动力和静力的综合成果.  The Gezhouba Project on the Yangtze River is situated at 2.3 km downstream of Nanjingquanthe lower mouth of the Three Gorge. The second channelsluice is the main spillway of the project. It has 27 bays, each bay is 65×18.5and 40m high. The sluices lie on clay sandstone with characters of low strengthand mudded intercalations in it. Owing to the lower shear strength of themudded intercalations,the factor of safety against sliding of the structure without any special treatment cann't reach 1.3 as required... The Gezhouba Project on the Yangtze River is situated at 2.3 km downstream of Nanjingquanthe lower mouth of the Three Gorge. The second channelsluice is the main spillway of the project. It has 27 bays, each bay is 65×18.5and 40m high. The sluices lie on clay sandstone with characters of low strengthand mudded intercalations in it. Owing to the lower shear strength of themudded intercalations,the factor of safety against sliding of the structure without any special treatment cann't reach 1.3 as required by the specification.How can prevent the structure from sliding along a plane at a certain depth under the sluice foundation was to be a major problem in the design work. As asolution for the problem, an antisliding slab accompanying with a concretecutoff were adopted after a thorough study and gave a good result. The resisting force offered by the bed rock just behind the sluice toe playsan important roll in considering stability of the structure where a weak planeexisted in the foundation rock. The results obtained from a large scale modeltest and computations have demonstrated that to take account of a certainamount of the resisting force can ensure the structure safe and make designeconomical. The deformation of the foundation rock and the stress distribution underthe sluice foundation were analysed by twodimensional nonliner finit elementmethod. The mechanism of fracture of the sliding along a weak plane infoundation rock and the factor of safety against sliding were also studied. Themagnitude of the foundation rock deformation depends mainly upon its deformation modulus. By computating, the horizontal deformation of the sluicefoundation is about 10mm during normal pool level, and the factor of safetyagainst sliding is larger than 2. According to the prototype observation for about one year since the reservoir has been impounded, the deformation is very close to the design and thenthe structure works safely.  长江葛洲坝水利枢纽位于三峡出口,距南津关下游2.3公里处。二江泄水闸是本枢纽工程主要的泄水建筑物,共27孔,闸室长65米,宽18.5米,高40米,闸底板高程37米。基岩为粘土质粉砂岩,岩层内含有泥化夹层,层面抗剪强度很低,若不采取阻滑措施不能满足规定的抗滑安全系数1.30的要求。因此沿泥化夹层的深层滑动乃是设计中研究的主要问题之一。经反复比较,最后采用了防渗板与混凝土齿墙的综合阻滑措施,收到了较好的效果。文中论述了岩体抗力在深层抗滑稳定中,有着重要的作用。通过现场大型岩体的抗力试验和计算证明,恰当地利用岩体的抗力是合理的,有助于提高工程的安全性和经济性;对于较软弱和存在地质缺陷的岩体,可采用基桩等措施进行加固以提高安全度。本文还应用平面非线性有限单元法,计算了闸室部分基岩的位移及其应力分布;探讨了深层滑动的破坏机制和安全度。闸室的位移量主要取决于基岩的变形模量,在设计水位下,闸室的水平位移量在10毫米左右,抗滑安全度在2.0以上。根据二江泄水闸建成蓄水一年来的原型观测资料证明,实测数据与设计计算基本相符,均在允许范围以内。  The stability of giavity dams on rock foundations are generally ex pressed in terms of its factor of safety against sliding, the ratio of the frictional force along the foundation to the force tending to cause slid ing, but the cohesive force is neglected.It has merely been expressed as K_s=f·∑V/∑H ·Where f is the coefficient of friction between the dam and its foundation,∑H the summation of horizontal forces acting on the gravity dam and ∑V the summation of vertical forces acting on it. It is... The stability of giavity dams on rock foundations are generally ex pressed in terms of its factor of safety against sliding, the ratio of the frictional force along the foundation to the force tending to cause slid ing, but the cohesive force is neglected.It has merely been expressed as K_s=f·∑V/∑H ·Where f is the coefficient of friction between the dam and its foundation,∑H the summation of horizontal forces acting on the gravity dam and ∑V the summation of vertical forces acting on it. It is obvious that the value of friction coefficent greatly affects safety and economy of a dam. In this article the author pointed out that the values of friction coefficient of gravity dams adopted in China were rather too small, and proposed some experimental data in designing for various types of dams of small and mediumsized reservoirs so as to reduce the construction cost.  在我国,岩基上重力坝的抗滑稳定往,以往普遍采用不计及凝聚力的摩擦公式计算。抗剪摩擦系数(简称摩擦系数)值的大小,对重力坝工程的安全性与经济性的影响颇大。本文目地在于:1、论证我国重力坝的抗剪摩擦系数取值一般偏低,2、提出抗剪摩擦系数的推荐值供中小型重力坝工程设计中使用,以求降低工程造价。   << 更多相关文摘 
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