胶南晚中生代大珠花岗岩岩体的脆性变形机制

在长期变化的构造应力作用下,胶南大珠山花岗岩岩体自早白垩世冷凝冷却以来发生强烈的脆性破裂变形,形成了多样的破裂类型如岩脉、节理和断层。在该岩体冷凝冷却早期侵入的细晶花岗岩脉和稍后形成的N-S向节理组反映出与同期区域构造应力场协调的N-S向挤压作用,而后伴随着揭顶剥蚀,出现了交替变化的构造应力场形成了岩体内主导的NW-NNW向和NE向节理组。整体上,恢复出的岩体内构造应力场发生顺时针方向旋转,最大水平挤压由早期的N-S向偏转为晚期的近E-W向。构造应力场的长期变化、平行节理作用和节理断层化作用造成了研究区复杂的破裂型式和破裂序列。     

Development of grabens and associated fault-drags: An experimental study

Experiments on extensional faulting were performed with semi-brittle talc-sand beds resting on a ductile clay base. The experiments show that the development of graben in the talc-sand beds is controlled by the deformation in the ductile basement. Graben-like structures form only when there is a non-uniform stretching in the basement. Uniform extension at the basement level fails to produce any such structures. Grabens initiate as large synclinal structures (sag). The sag is generated either by a downward flexing of the talc-sand bed on a ductile basement or by non ****-uniform thinning of beds. Listric master faults bounding the grabens intersect the basement at high angles. The master faults that initiate as curved shear planes rotate further with continued extension. At the initial stage, the graben structures are associated with normal drags, and with progressive deformation, drag patterns change from normal to a reverse one.     

An improved SPH method for saturated soils and its application to investigate the mechanisms of embankment failure: Case of hydrostatic pore‐water pressure

The method of smoothed particle hydrodynamics (SPH) has recently been applied to computational geomechanics and has been shown to be a powerful alternative to the standard numerical method, that is, the finite element method, for handling large deformation and post‐failure of geomaterials. However, very few studies apply the SPH method to model saturated or submerged soil problems. Our recent studies of this matter revealed that significant errors may be made if the gradient of the pore‐water pressure is handled using the standard SPH formulation. To overcome this problem and to enhance the SPH applications to computational geomechanics, this article proposes a general SPH formulation, which can be applied straightforwardly to dry and saturated soils. For simplicity, the current work assumes hydrostatic pore‐water pressure. It is shown that the proposed formulation can remove the numerical error mentioned earlier. Moreover, this formulation automatically satisfies the dynamic boundary conditions at a submerged ground surface, thereby saving computational cost. Discussions on the applications of the standard and new SPH formulations are also given through some numerical tests. Furthermore, techniques to obtain the correct SPH solution are also proposed and discussed throughout. As an application of the proposed method, the effect of the dilatancy angle on the failure mechanism of a two‐sided embankment subjected to a high groundwater table is presented and compared with that of other solutions. Finally, the proposed formulation can be considered a basic formulation for further developments of SPH for saturated soils. Copyright © 2011 John Wiley & Sons, Ltd.     

岩土工程加固分析的弹塑性力学基础

研究了弹塑性计算中不平衡力的性质,揭示了它和加固力、结构稳定性的密切关系。弹塑性有限元分析迭代过程实质上就是一个逐步消除不平衡力的过程。可以采用弹塑性分析中的不平衡力来指导加固设计：只要施加和不平衡力大小相 等、方向相反的加固力,结构就是平衡、稳定的。在所有加固方案里,弹塑性分析确定的加固力是最小的,并归结为应力转移的最小余能原理和加固力上限定理,弹塑性计算确定的加固力和真解相比偏于安全。拱坝计算实例表明,不平衡力分析对分析结构稳定性、指导加固设计是有助益的。     

平行F42-9发育的结构面对锦屏水电站高边坡稳定性的影响

锦屏一级水电站左岸高边坡F42-9断层及煌斑岩脉组合的滑块对左岸缆机平台及拱肩槽边坡的稳定性起到控制性的作用。针对F42-9断层两侧平行结构面的发育程度,进行了锚固边坡开挖过程中的弹塑性力学行为分析。结果表明：平行于F42-9断层发育的结构面使锚固边坡岩体的性状急剧下降,现有的加固方案无法满足边坡稳定性的要求。建议根据边坡及抗剪洞开挖过程中揭露的地质信息,及时制定合理的边坡加强、加固措施。     

古构造应力场反演的理论与实践——基于断层滑动矢量分析

古构造应力场恢复是重建区域地质演化历史的重要手段之一。断层作为地壳浅表发育的脆性变形构造,为恢复古构造应力场提供了重要地质条件。关于利用断层滑动矢量反演古构造应力场,前人进行了长期探索。目前其相关理论基础、研究方法与实际应用均取得重要进展。在断层滑动矢量反演古构造应力场的理论方面,改进的安德森模式描述了在发育先存薄弱带的情况下断层形成与演化的规律,克服了安德森模式只适用于均匀变形域的理论局限性;在研究方法方面,突破了在沉积盆地内部变形相对单一的限制,在造山带前陆或者叠加褶皱区等复杂变形区有效地开展了相关研究,并通过断层相关褶皱与同褶皱变形的滑动矢量分析,厘定出同造山作用的古构造应力场。这一方法在大巴山造山带强变形区得到了有效应用,为探讨其构造演化提供了基础。     

Transient creep and semibrittle behavior of crystalline rocks

We review transient creep and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing deformation in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient creep data for crystalline rocks at elevated temperatures are analyzed but are poorly understood because of lack of information on the deformation processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient creep at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the creep rate. Empirical transient creep equations are extrapolated at 200° to 600°C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17×10² to 3.17×10⁸ years. At the higher temperatures, appreciable transient creep strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic.     

向家坝水电站地下厂房围岩稳定的黏弹塑性有限元分析

考虑流变作用,建立三维有限元模型进行数值计算,以洞室变形和点抗滑安全系数为指标,针对向家坝水电站地下厂房围岩的特殊性进行稳定性研究,结果表明,随着围压的增高,流变速率逐渐减小,初始应变逐渐减小;软弱夹层处流变速率较其他岩体减小缓慢,且开挖后流变达到稳态状态时软弱夹层最终流变位移较大;黏弹塑性下围岩位移分布及变化规律与弹塑性一致,但黏弹塑性下计算位移明显要比弹塑性大;流变效应对岩体变形和稳定性,以及对支护结构有重要影响;黏弹塑性情况下,洞室围岩特征点抗滑安全系数比弹塑性条件下小,软弱夹层出露处和拱顶点抗滑安全系数较低,点抗滑安全系数分析还表明,软弱夹层对其稳定性影响明显,验证了位移分析结果。     

大型整体式贮煤筒仓基础有限元分析

采用有限元分析了不同土体的弹性本构关系和不同堆煤荷载施加方式对筒仓基础的影响;在此基础上分析了煤压力、桩土之间的接触压力、桩的内力与变形、土体沉降等变化规律。从计算结果可知,考虑土体的弹性模量随土层的压实而提高,并考虑煤与筒仓、基础土体之间的相互作用,使得筒仓基础的受力状态与实际情况更接近,从而得到优化的筒仓基础设计。     

非饱和土三轴压缩应力路径试验的数值模拟研究

应力路径对土的强度和变形性质具有重要影响。相对于饱和土而言,控制吸力条件下的非饱和土三轴压缩状态的应力路径研究更加复杂。随着非饱和土本构理论的不断发展,理论和试验研究结果表明,非饱和土弹塑性本构模型可以用来近似地描述非饱和土的强度和变形性质。因而,运用非饱和土弹塑性本构模型对控制吸力条件下的3种非饱和土三轴压缩应力路径试验进行数值模拟是一种有效的理论研究手段。采用Barcelona模型能够对此类试验进行较好的数值模拟,其研究结果表明,在控制吸力条件的三轴压缩状态下应力路径对非饱和土的强度和变形性质具有重要影响。