黏度时变性宾汉体浆液的柱-半球形渗透注浆机制研究

浆液黏度时变性对注浆扩散范围计算值影响很大。基于宾汉体浆液的流变方程与流体黏度时变性方程,建立了黏度时变性宾汉体浆液的流变方程与渗流运动方程,并依据某些假设,推导了时变性宾汉体浆液柱-半球形渗透注浆机制及探讨了半球体部分扩散半径l1与柱体部分扩散长度m的关系：m=(2l1 /3)(2n+1)。通过设计室内注浆试验对其进行了验证,结果表明：由黏度时变性宾汉体浆液的柱-半球形渗透机制计算的半球体部分扩散半径、圆柱体部分扩散长度及注浆扩散体体积的理论值与试验测量值虽分别有15%、10%及40%左右的差异,但都处于可接受误差范围内,因而,在总体上能较好地反映黏度时变性宾汉体浆液的柱-半球形注浆渗透规律,对注浆设计、施工和理论研究等方面具有一定的参考价值与指导作用     

岩土类材料率相关性及硬化-软化特性模型研究

岩土类材料具有显著的率相关性,其应力-应变关系全过程一般表现为硬化-软化特征,研究如何描述这两类特征具有重要的意义。基于岩土类材料的物理变形机制分析,考虑到其结构性特征,采用弹黏塑性本构模型,引入反映材料结构变化的可变结构黏滞系数及其演化方程,并将其嵌入到弹黏塑性本构模型中去,建立能够反映材料结构变化的弹黏塑性本构模型。利用玄武岩常规三轴常应变率试验结果对所建立的模型进行试验验证,结果表明：所建立的弹黏塑本构模型能够完整、合理地描述岩土类材料应力-应变关系全过程以及材料本构关系的率相关性,同时还能够反映材料的峰值强度、残余强度特征。     

结构性软土的黏滞系数

黏滞系数是表征土的蠕变和流动特性的重要指标。对黄石、漳州、青岛地区结构性软土进行电子显微镜扫描、颗粒分析、X衍射试验和化学分析试验,测试结果表明,软土的粒度成分、矿物成分、物理化学性质、结构类型对黏滞系数影响较大。软土蠕变过程中,结构单元体发生定向排列或产生滑动,其相对运动使结合水的黏滞性反映出来,进而引起黏滞系数的变化。进行直接剪切蠕变试验,并通过陈氏法处理蠕变试验数据。试验结果表明,黏滞系数随剪应力的增加达到峰值,固结压力越大,峰值体现越明显,峰值对应的剪应力也越大,这主要是微观结构随剪应力增大逐渐破损所引起的。固结压力增大,结合水膜厚度变薄,土颗粒间连接力增强,黏滞系数也随之增大。用不同固结压力下黏滞系数峰值对应的剪应力代替临界抗剪强度,提出了一个新的求取长期强度的方法,并通过试验数据验证了方法的正确性。该研究有助于进一步认清蠕变机制,对修正或建立较为符合实际的本构模型有一定意义。     

介质黏滞性质对余震活动影响的数值模拟

假定主震破裂面上残余凹凸体的破裂导致余震,残余凹凸体尺度符合分形分布,在破裂面上随机分布,残余凹凸体破裂/失稳强度符合对数正态分布;以岩石圈下部粘弹介质震后应力松弛作为导致残余凹凸体破裂的动力输入,加载应力按负指数形式衰减;以库仑破裂准则作为失稳判据,考虑残余凹凸体破裂对附近区域的应力加载,在不同条件下模拟生成包含时、空、强三要素的人工"余震"序列。通过G-R关系及修改的大森公式,检测模拟输出与实际余震活动统计特征的吻合程度,以此作为进一步调整模型参数的依据。在此基础上重点讨论介质黏滞性质对余震活动的影响。结果显示:表征岩石物理特性的黏滞系数对余震活动持续时间、衰减快慢起重要的控制作用,黏滞系数与衰减系数之间显示负指数的相关关系。余震序列G-R关系与黏滞系数关系不大,主要受控于残余凹凸体的尺度分布,即与构造不均匀性关系更为密切。     

考虑时变性影响的盾构壁后注浆浆液固结及消散机制研究

在盾构管片壁后注浆时,由于浆液渗透压的存在,浆液会向外渗透,浆体本身逐渐固结,作用在管片上的注浆压力逐渐消散。考虑到浆液往周边地层渗透过程中由于黏度的变化会引起地层渗透系数的变化,推导了基于浆液黏度时变性的浆体固结变形方程和浆液压力消散方程,分析了浆液固结、消散及浆液压力沿管片外壁分布规律,为精细化分析施工阶段管片受力提供了计算依据。计算结果表明：浆液从注浆口喷出后,浆液黏性的增大使浆液流动性减小,注浆压力消散幅度减小,浆液消散持续时间变短。浆液配比与围岩渗透系数变化对注浆压力消散幅度及消散持续时间存在一定影响。现场实测结果与理论计算结果较为一致。在进行壁后注浆时,应充分考虑时变作用下浆液消散作用的影响。     

复杂应力路径下堆石料本构关系研究

已有研究表明,土石坝内堆石料在坝体填筑过程的应力路径可近似为等应力比的路径（q/p=常数）,水库蓄水时应力路径将发生转折,呈复杂的应力路径形态（dq/dp=常数）。在大型三轴仪上进行了两种应力路径的排水试验,即等应力比路径下的偏压试验和复杂应力路径下的剪切试验。根据试验结果提出了一个堆石料应力路径增量非线性弹性模型,模型采用三模量形式除可以描述堆石料等应力比路径的应力-应变特征外,通过转折后的路径特征构造合适的柔度矩阵,能够表达转折应力路径下的本构关系。对试验曲线进行拟合表明,应力路径模型能够较好地反映堆石料在复杂应力路径下的应力与变形特性。     

水汽对大气重力负荷效应的影响

通过构建水汽影响模型,并以武汉超导重力观测台站为例,根据1998年武汉地区每日两次的无线电探空数据,精确计算水汽对重力观测的影响数值。解算结果表明,水汽对武汉重力观测站的影响可达1.6×10 ^-8 ms ^-2,由此可见,精密重力观测中不能忽视水汽的作用。     

Calculating Skempton constant of aquifer from volume strain and water level response to seismic waves at Changping seismic station

Based on linear poroelastic theory of ideal poroelastic media, we apply the mathematic expression between pore pressure and volume strain for well-aquifer system to analyzing the observed data of water level and volume strain changes aroused by Sumatra MS8.7 (determined by China Seismic Networks Center) seismic waves at Changping, Beijing, station on December 26, 2004 from both time and frequency domain. The response coefficients of water level fluctuation to volume strain are also calculated when seismic waves were passing through confined aquifer. A method for estimating Skempton constant B is put forward, which provide an approach for understanding of the characteristics of aquifer.     

Viscosity-excluded formulations of 2-D river flow with a new wetting and drying algorithm

An efficient method for simulating 2-D river flow is developed in which horizontal turbulent shears are omitted from the 2-D depth-averaged momentum equations. It is shown that a pseudo-viscosity can be reproduced to take into account the lost shear action, by incorporating the vertically integrated continuity equation to the momentum equations and transforming the latter into a discrete integral form. To simulate river flows with wet and dry areas, negative water depths are allowed when solving the continuity equation. The concept of negative water depth enables us to track flow boundaries with about the same accuracy but much less effort as compared with traditional numerical methods. An optimal threshold value defining dry areas is first obtained by one-dimensional theoretical analysis and then sought by trial-and-error for two-dimensional flow simulation with tolerable node-to-node spurious oscillations, while mass is best conserved. Numerical solutions using the new procedure are compared with the one-dimensional benchmark solution of the Saint Venant equations and the experimental data from a two-stage channel. Robustness of the present approach is also tested through the study of water flow in a natural river and a hypothetical channel with several bumps.     

Effects of plate and slab viscosities on the geoid

The effects of plate rheology (strong plate interiors and weak plate margins) and stiff subducted lithosphere (slabs) on the geoid and plate motions, considered jointly, are examined with three-dimensional spherical models of mantle flow. Buoyancy forces are based on the internal distribution of subducted lithosphere estimated from the last 160 Ma of subduction history. While the ratio of the lower mantle/upper mantle viscosity has a strong effect on the long-wavelength geoid, as has been shown before, we find that plate rheology is also significant and that its inclusion yields a better geoid model while simultaneously reproducing basic features of observed plate motion. Slab viscosity can strongly affect the geoid, depending on whether a slab is coupled to the surface. In particular, deep, high-viscosity slabs beneath the northern Pacific that are disconnected from the surface as a result of subduction history produce significant long-wavelength geoid highs that differ from the observation. This suggests that slabs in the lower mantle may be not as stiff as predicted from a simple thermally activated rheology, if the slab model is accurate.