Settling of large buildings and structures erected on clay loess grounds

Conclusions 1. Some 60% of foundation settling in clay grounds of the type considerered here takes place during the construction period. The settling continues for 10 years, and then for an additional 20–25 yr at a very low rate.2. The II-B.5–67 scheme of pile foundation, proposed by the SNiP from the analysis of deformations, is substantiated by the actual settlings.3. Settlings calculated by different methods differ but little among themselves and are in fair agreement with the actual settlings. The single instance of great discrepancy between the theoretical and actual data evidently is due to changes in ground facies and the rate of compactions.4. The published data [1, 2] on a marked discrepancy between the theoretical and actual data on settleling for the large structures should be regarded as anomalies associated with foundations in sandy grounds and acted upon either only by the static loads (minor settlings) or by the combined static and dynamic ones (large subsidences).5. Observations of settling should start with the construction, at loads not exceeding the operational, with accurate records kept on loads transmitted to the foundation.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 29–31, September–October, 1971.     

静动力作用下高拱坝坝肩稳定性三维分析

 按照静载设计、动载复核的设计原则,基于地质勘测资料,针对坝肩抗滑稳定问题的三维特性,采用关键块体理论来识别和描述被结构面切割的岩体,确定相应的控制性滑块,进而运用程序实现三维刚体极限平衡法,选取不同高程的试算面对某水电站300 m级高拱坝左、右岸坝肩的静动力抗滑稳定性进行计算分析。在动力分析中,将坝体、库水及其地基作为整个体系,充分考虑坝体、地基和库水三者的动力相互作用。静动综合计算分析的结果表明,拱坝左、右岸坝肩在静力作用下是安全的,且安全富裕较大;在地震作用下也是安全的,但安全裕度不大。这为该拱坝的设计和论证提供了重要的科学依据。     

Vibration-rotational pushing of tubular elements into the ground

The writers discuss a method of sinking a pile element by vibration-rotational pushing under the action of a static force and an alternating torsional moment about the axis of sinking. This combination of actions makes it possible to reduce by a factor of 3–5 the static force required for pushing and to eliminate for all practical purposes the dynamic forces on adjacent structures.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 13–17, January–February, 1992.     

饱和尾矿砂动强度特性试验研究

通过对饱和尾矿料的动三轴液化试验，研究了尾矿料在往返加荷条件下的动强度特性，针对影响尾矿砂动强度的几种因素进行了分析和讨论，所得结论可为尾矿坝设计提供理论依据。     

Effect of pore water pressure on tunnel support during static and seismic loading

The support of underground structures must be designed to withstand static overburden loads as well as seismic loads. New analytical solutions for a deep tunnel in a saturated poroelastic ground have been obtained for static and seismic loading. The static solution accounts for drainage and no-drainage conditions at the ground–liner interface. Linear elasticity of the liner and ground, and plane strain conditions at any cross-section of the tunnel are assumed. For tunnels in which ground stresses and pore pressures are applied far from the tunnel center, the drainage conditions at the ground–liner interface do not affect the stresses in the liner. The analytical solution shows that the stresses in the liner are exactly the same whether there is drainage or not at the ground–liner interface. Hence, if the drainage conditions in the tunnel are changed from full drainage to no-drainage or vice versa the stresses in the liner are not affected. However, the stresses and displacements in the ground change significantly from drainage to no-drainage conditions. For seismic loading a new analytical formulation is presented which provides the complete solution for the ground and the liner system for both dry and saturated ground conditions. The formulation is based on quasi-static seismic loading and elastic ground response; for a saturated ground, undrained conditions are assumed which indicate that the excess pore pressures generated during the seismic event do not dissipate. The results show that the racking deformations of a liner in dry or saturated ground are highly dependent on the flexibility of the liner.     

变形场和渗流场耦合作用下的尾矿坝静力稳定性分析

对尾矿坝稳定性分析中的几种方法进行了对比，建立了能考虑塑性变形、温度、饱和度和孔隙比等对材料特性影响、土一水特性曲线并采用扩展的Mohr—Coulomb屈服准则、以屈服接近度为安全指标的尾矿坝流固耦合有限元分析模型，对龙都尾矿坝干滩面为100m和初期坝堵塞两种工况下的饱和一非饱和渗透场和变形场的耦合响应特性进行了模拟，获得坝体变形、浸润线等重要指标，以及考虑各种影响因素的屈服接近度分布，据此可直观全面地了解不同工况下坝体安全的全场信息，对尾矿坝的稳定性分析评价以及加固与维护决策具有一定的参考价值。     

Experimental investigations of the reactive strength of soil in the bed of a circular footing subjected to short-term dynamic loads

Conclusions 1. The distribution of contact stresses along the foundation slab of a rigid circular footing in a sandy soil subjected to dynamic loads in a steady-motion regime is saddle-shaped in nature and agrees with corresponding literature data derived from static tests. In this case, an increase in contact stresses from 0.2–0.5 to 1.0–1.5 MPa at the center of the plate will effect a reduction of from 1.60–1.80 to 1.30–1.50 in the concentration factor; this is associated with the enhancement of the role played by plastic deformations in the bed.2. The reactive strength of the soil in the bed of a circular rigid footing subjected to short-term dynamic load can be represented in the form of Eq. (1). In this case, the computed velocity a₁ should be determined with allowance for the actual ₁() curve, which corresponds to the work of the soil beneath the plate under conditions of a certain deformation regime.3. Use of the hypothesis that we have cited will make it possible to predict with an accuracy sufficient for practical calculations the maximum loads on foundation slabs placed on the surface of the ground for structures, and the parameters of their motion under blast-induced loads of rather high intensity.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 10–12, May–June, 1990.     

Some aspects of dynamic interactive buckling of composite columns

The static and dynamic problem of interaction of global buckling modes in compressed columns with complex open cross-sections was considered in this paper. Columns made of laminate composites were assumed to be simply supported at both loaded ends. A plate model was adopted in the analysis. Within the frame of the first order nonlinear approximation, the dynamic problem of modal interactive buckling was solved by the transition matrix using a perturbation method. Distortions of cross-sections and a shear-lag phenomenon were taken into consideration. A modification of the Kleiber–Kotula–Saran quasi-bifurcation dynamic criterion [Kleiber M, Kotula W, Saran M. Numerical analysis of dynamic quasi-bifurcation. Eng Comput 1987;4:48–52.] was proposed. A comparison of the proposed modification to the Budiansky–Hutchinson criterion [Budiansky B, Hutchinson JW. Dynamic buckling of imperfection-sensitive structures. In: Goetler H, editor. Proceedings of the eleventh international congress of applied mechanics, Munich, 1966. p. 636–51.] was presented for rectangular pulse loading.     

Static and dynamic stability assessment of slopes or dam foundations using a rigid body–spring element method

A rigid body–spring element method is used to evaluate the static and dynamic stability of slopes or dam foundations. The versatility of the method applies well to both static and dynamic problems for blocks of arbitrary polyhedral shape with various re-entrant surface features. Examples show that the safety factor obtained in this way agrees well with theoretical solutions. The dynamic safety factor determined with this method varies with time, which differentiate it from the results of the limit equilibrium method or the finite element method. The method also makes it possible to search for the most probable sliding mass.     

Influence of end constraints on the collapse of axially impacted frusta

The energy absorption performance of right circular frusta subjected to dynamic axial load is studied and compared with the results of quasi-static tests. Frusta of different geometric ratios and end constraints were axially crushed using a drop hammer at initial velocities in the range of 2–5 m s. The effect of heat treatment on the collapse behaviour and energy absorption is also investigated. The experimental observations indicate that the effects of end constraints and heat treatment on energy absorption were qualitatively similar to those observed under quasi-static testing. Due to inertia effects, the absolute values of the energy absorbed by similar frusta were higher under dynamic loads than under quasi-static loads. It has been established that constraining the frusta enhances their energy absorption capacity under static and dynamic loading particularly at the top (smaller diameter). The optimum geometric parameters for maximum energy absorption performance are identified when residual stresses and strain hardening characteristics, arising from spinning the frusta, were removed.     

Evaluation of pile bearing capacity by dynamic tests

Conclusions 1. In determining the bearing capacity of piles, dynamic resistance should be understood to mean that maximum value of soil reaction which is generated during the hammer blow. However, this concept should not be confused with the resistance obtained from the results of dynamic pile tests.2. Upon the delivery of a dynamic blow, as pile penetration proceeds, an increase in soil reaction occurs which reaches the limiting and then the critical load values as obtained from static tests. Therefore, the results of dynamic tests if the latter are correctly performed should coincide with the critical load obtained from static tests. Experience has shown that for this condition to be fulfilled, the total refusal of piles due to a single blow should be not less than 10–15 mm and the residual part of the refusal should be not less than 2 mm.3. The results of the dynamic tests enable the static pile resistance to be determined for the soil condition at the given instant. As is shown by graphs of the dynamic and static tests, the limiting pile resistance depends not on the type of test but on the condition of the soil and the degree of its thixotropic recovery.4. The determination of pile bearing capacity by the dynamic method, taking their "resting" into account, should be based on the results of the initial blows.Scientific-Research Institute of Foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 11–13, March–April, 1975.     

地震荷载作用下饱和砂层孔隙水压力的增长与消散

本文用有限元法对地震荷载和不同排水条件下陡河水库土坝砂基中孔隙水压力的增长与扩散过程,以及振动结束后孔隙水压力的重分布与消散过程进行了计算分析。通过动力三轴试验,给出了饱和砂的残余孔隙水压力的全量表达式和不同液化破坏阶段的临界孔隙水压力比的表达式。本文定义了液化势评价准则,并对该坝在1976年唐山大地震时的稳定性进行了分析。得到的结果能较好地说明宏观破坏现象,同时也表明砂砾井和砂砾层有明显的排渗作用。     

长期往复荷载作用下近海饱和软黏土强度和刚度的弱化特性

长期往复荷载作用下,饱和软黏土强度和刚度的衰减是近海桩基础设计必须考虑的,利用带弯曲元的循环三轴仪对原状饱和软黏土进行了一系列等向固结和非等向固结条件下不排水单调和循环加载三轴试验,并在循环加载过程中通过弯曲元测试土体剪切波速。试验结果表明,在相同的固结条件下,随循环次数的增加和动应力比的提高土体的强度和刚度衰减显著;在相同动应力比作用下较小的有效固结应力和偏压固结减缓了土体刚度的弱化。已有的相对偏应力水平参数不能反映不同固结条件下近海饱和软黏土强度和刚度循环弱化特性,为此引入了动偏应力水平参数,考虑了有效固结应力、固结静偏应力、动偏应力的相互影响,利用动偏应力水平对饱和软黏土的强度和刚度循环弱化特性进行描述。     

循环荷载下冻结裂隙砂岩动疲劳特性研究(英文)

通过在砂岩样中预制裂隙的方法来模拟实际裂隙岩体 ,借助于中低频率 (2 0 .0Hz和 2 .0Hz)动循环加载和常规加载试验 ,对烘干、饱水和饱水冻结砂岩样在循环作用下引起的低周疲劳特性和不同加载频率下的速率效应进行了研究 ,试验结果表明 :①疲劳效应 ,冻结状态下 ,裂隙砂岩样比无裂隙砂岩样疲劳效应明显 ;②冻结效应 ,冻结作用减弱了试样的疲劳效应 ,尤其是对无裂砂岩隙样 ;③加载 (频率 )率效应 ,冻结作用降低了裂隙砂岩样加载率效应 ,意味着饱水岩样强度随加载 (频率 )率增加而增加的幅度较冻结样明显。     

孔隙水运移特性及对尾矿细观结构作用机制试验研究

 利用自行研制的尾矿细微观力学与形变观测试验装置,研究尾矿充水过程、荷载作用和排水过程中孔隙水的运移特征及其对尾矿细观结构作用机制。结果显示：尾矿水位线实际达到高度大于计算获得的水位线高度;受荷载作用,充水条件下各层尾矿颗粒沉降位移显著大于未充水条件下相同位置颗粒的沉降位移;充水条件下尾矿颗粒沉降位移随荷载的增加可分为线性增长阶段、显著增长阶段和稳定阶段,显著增长阶段出现在200～400 kPa荷载下;受荷载与孔隙水的作用,尾矿细观结构会形成曲折复杂供水运移的通道,该通道的形成过程发生在尾矿颗粒沉降位移的显著增长阶段;孔隙水夹带尾矿小颗粒运移,对尾矿颗粒分布有一定的影响;尾矿颗粒沉降位移与细观结构受排水影响较小,其变化主要在排水初期。最后,提出水的毛细管作用下尾矿坝实际浸润线的概念与计算方法,研究孔隙水与荷载综合作用下尾矿细观结构变形破坏机制,为深入探索水引起的尾矿坝灾变机制及稳定性评价等具有重要的实际意义。     

Engineering Evaluation of the Consolidation of a Saturated Loess Stratum with a Blast-Disturbed Structure

The compression of a saturated structurally disturbed loess stratum during its compaction by the hydraulic-blasting method is discussed. Results of prediction of the development of post-blast deformation are compared with actual data on soil densification from a specific project.__________Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 26–29, May–June, 2005.     

Control negative effects of blasting waves on concrete of the structures by analyzing of parameters of ground vibration

In the most of civil projects, many activities are done in the vicinity of each other. Synchronic of concreting and blasting causes cracks and reduction of final resistance of concrete because of dynamic waves induced by blasting. This qualification is more negative for long term using structures and those which is relevant with under pressure water. This paper introduces dynamic waves and their influence on the underground structures; controlling methods of dynamic waves induced by blasting in the base of peak particle velocity and finally design of surge tank storage shafts excavation in Gotvand dam neighbor of concrete structures in these storages. The dynamic site factors that are calculated from seismographic tests in Bakhtiary conglomerate shows that constant dynamic factors K & β are 40.859 and 1.8717, respectively. Furthermore with combination of Nonel and electric detonator we achieved the reduction of negative effects caused by blasting of each construction as well as a significant reduction in excavation costs in each stage.     

基于改进CM模型的土石坝三维弹塑性地震反应分析

基于交变移动性（CM）模型,引入饱和度作为状态变量,给出了改进的土体塑性势面方程、屈服方程和协调方程,推导了新的硬化参量计算公式,发展了可连续描述非饱和与饱和土体静动力学特性的弹塑性本构模型。通过转换应力法,将模型从试验应力状态拓展到一般应力状态,使得本构模型可用于复杂三维河谷场地上修建的土石坝的弹塑性地震反应分析。数值模拟了汶川地震中典型震损土石坝的震害过程,模拟结果与实际震害吻合较好。对比研究了输入地震动强度对土石坝弹塑性地震反应分析结果的影响,结果表明土体的弹塑性特性对坝-基动力相互作用有着较大影响。     

深厚覆盖层上高土石坝的动力稳定分析

在高地震烈度区修建深厚覆盖层上的高土石坝面临许多新问题,如大坝的动力稳定、坝基液化问题等。以直粘土心墙及坝基截渗墙土石坝为例,采用三维动力固结有限元方法,研究强震区深厚覆盖层上的高土石坝的动力稳定问题。三维动力固结有限元程序以动力固结方程为基础,采用能够反应土体非线性、滞后性以及不可恢复性动变形特性的拟等效弹塑性本构模型,放弃了动孔压上升模式,在震动全过程中跟踪孔隙水压力产生、扩散和消散的发展变化,实现了动力渗流与动力反应分析的真正耦合,可较好地反映土体在地震过程中的实际性态,避免了动本构模型与动孔压模型有时难以合理搭配的问题。计算结果表明,深厚覆盖层上修筑的直心墙土石坝的静应力和静位移均较大,但它的动应力、动位移及加速度的反应值却均较小,且坝底的孔压比也较小,可满足稳定性要求。     

Hazard potential of zones of weakness in gravity dams under impact loading conditions

Dam constructions worldwide are designed and constructed in view of the strictest safety aspects for all static and dynamic load cases. As experience shows, however, formation of cracks in the “homogeneos concrete” as well as unsatisfactory compound behavior of lift joints are not to be excluded. These zones of weakness especially on the upstream side of the dam—exposed to high water pressure (static and dynamic)—represent an increased risk of safety. The main investigation, apart from the computation of the dynamic effects on the dam as a global structure, focuses on the stability analysis of a pressure-water filled crack configuration subjected to “dynamic loading” in the form of seismic action on the dam-reservoir-system and alternatively by “impact spot-loading” within sectors of the reservoir. A fracture mechanics based analysis shows an excessive potential of damage for the afflicted structure.