基坑开挖孔隙水压力变化规律试验研究

讨论了基坑开挖及降水过程中,基坑周围土体孔隙水压力的变化过程,根据现场量测数据进行了分段线性拟合,得到了土体中孔隙水压力的变化规律。并对基坑周围土体孔隙水压力的变化机理及过程进行了分析。     

盾构隧道施工引起的土体初始超孔隙水压力分布研究

盾构施工会对周围土体产生扰动,形成超孔隙水压力,引起工后固结沉降。运用应力释放理论推导与衬砌相邻的土体初始超孔隙水压力计算公式。假定扰动范围边界呈圆弧状,确定初始超孔隙水压力的分布范围;同时运用应力传递理论,推导分布范围内任一点土体的初始超孔隙水压力计算公式。通过对实测资料的分析可知,计算值与实测值吻合较好。算例分析表明,与衬砌相邻的土体初始超孔隙水压力呈近似圆形（顶部小、底部大）;随着到衬砌的径向距离增加,土体初始超孔隙水压力呈凹曲线形状;隧道底部的等值线最密,即变化最快;隧道顶部上方土体、不同深度处土体初始超孔隙水压力,以隧道轴线处为最大,呈现类似Peck曲线形状。     

水中填筑围堰边坡稳定的流-固耦合分析

详细地介绍了在流-固耦合分析过程中,特征时间和渗透边界条件的给定方法。并将其应用到泰安抽水蓄能电站围堰的流-固耦合分析中,同时,分析了基础开挖过程对围堰和基础边坡稳定性的影响。在开挖过程中,由于给定了透水边界和较合理的特征时间,最终结果表明,围堰和基础内的孔隙水压力明显下降,是由于开挖后透水边界增长,以及计算流体的特征时间增长的缘故。说明了用FLAC进行流-固耦合分析时,考虑特征时间和渗透边界条件是很重要的。     

基于MIDAS的尾矿边坡三维流固耦合稳定性分析

针对尾矿坝边坡稳定性问题,使用三维有限元软件计算,对吉林省集安石墨尾矿坝进行渗流-应力-边坡耦合分析。渗流分析基于三维介质达西定律,通过不断改进工况条件来降低浸润线溢出部位,保证坝体不会发生渗透破坏。同时,尽量降低溢出部位的应力坡降,保证坝体不会发生流砂、管涌等形式渗透破坏。在渗流计算的基础上,进行渗流-应力-边坡耦合,不断改进尾矿边坡的坡角和高度等要素,得到强度折减法下的尾矿边坡稳定性系数。通过理论计算和验证,提出了一种便于施工的排渗体布置方式,并验证了排渗体的可靠性,为尾矿坝具体施工提供了技术支持。     

基于流固耦合的围岩后注浆对大型水封石油洞库水封性影响分析

基于多孔弹性连续介质流固耦合理论,通过合理选取围岩主要物理力学参数,建立了大型石油储备地下水封洞库全断面开挖后洞室涌水量计算模型,利用大型商业软件Comsol对黄岛国家石油储备地下水封洞库地下水渗流场和位移场进行数值模拟分析。通过不同注浆方案及不同注浆厚度情况下地下水渗流量的比较分析发现,并不是注浆圈的厚度越大对洞室渗水量的控制效果越好,而是存在相对经济合理的阈值。研究表明,最佳的注浆方式是形成全断面闭合注浆圈,最佳注浆厚度为5 m。     

Cone penetration-induced pore pressure distribution and dissipation

The excess pore water pressure distribution (u) induced by the penetration of a piezocone into clay and its dissipation behaviour have been investigated by laboratory model tests, theoretical analysis and numerical simulation. Based on the results of the tests and the analysis, a semi-theoretical method has been proposed to predict the piezocone penetration-induced pore pressure distribution in the radial direction from the shoulder of the cone. The method can consider the effect of the undrained shear strength (s_u), over-consolidation ratio (OCR) and rigidity index (I_r) of the soil. With a reliably predicted initial distribution of u and the measured curve of dissipation of pore water pressure at the shoulder of the cone (u₂), the coefficient of consolidation of the soil in the horizontal direction (c_h) can be back-fitted by analysis of the pore pressure dissipation. Comparing the back-fitted values of c_h with the values directly estimated by a previously proposed method indicates that the previously proposed method can be used reliably to estimate c_h values from non-standard dissipation curves (where u₂ increases initially and then dissipates with time).     

基于加载动力效应对孔压滞后现象的一个解释

在底部可测孔压的固结仪内进行单面排水固结试验时,观测到试样底部的孔压可出现滞后现象。为分析其原因,考虑加载引起的动力效应,建立以竖向应变为求解对象的一维动力固结方程,并用有限差分法进行求解。引入新指标CD来综合考虑试样压缩模量、渗透系数、密度以及土样厚度等4个参数对动力效应的影响,探讨了该指标对固结过程中孔隙水压力的影响。计算结果表明,瞬时加载引起的动力效应是引起试样内孔压滞后的一个原因,并且对于压缩模量或渗透系数较大的试样,更易出现孔压滞后现象,同时动力效应对固结度的影响则主要体现在固结的前期。最后讨论了固结分析时可以忽略动力效应的范围。     

基于流固耦合理论水下隧道冻结壁厚度优化研究

水下隧道对冻结壁厚度设计有特殊要求,针对珠机城际轨道交通项目下穿马骝洲水道段联络通道冻结壁设计改进问题,基于流固耦合分析理论,利用有限差分数值计算方法对水下隧道冻结壁稳定性进行研究,通过对不同厚度冻结壁响应情况的对比研究,实现对于冻结壁厚度的优化设计。研究表明:相较无渗流模型,流固耦合模型冻结壁应力分布规律相同,但整体量值增大明显,水的作用不可忽略;水的存在使冻结壁受力趋于"均匀",应力集中现象缓解,但高剪应力区范围扩大,使其剪切破坏风险加大,且冻结壁受力形式有从受压向受拉改变的趋势,对结构稳定不利;冻结壁在流固耦合作用下变形加剧,且随厚度减小而愈发显著,模型厚度达到2.0m以上时变形基本稳定;流固耦合模型塑性区多集中于两侧拱脚区域,3.0 m和2.5 m模型整体完好,2.0 m模型两侧拱脚出现相向发展塑性区,1.5 m模型塑性区厚度接近贯穿,1.0 m冻结壁拱脚已形成明显贯穿破坏;综合选定2.5 m为冻结壁改进厚度,成果直接应用于4#联络通道冻结法施工,经现场监测表明该优化方案有效、可行,对类似工程冻结壁厚度设计具有重要的推广应用价值。     

Effects of anisotropic permeability on stabilization and pore water pressure distribution of poorly cemented stratified rock slopes

Slopes composed of stratified and poorly cemented rocks that fail during heavy rainfalls are typical in the outer zone of Taiwan's Western Foothills. This study investigates how hydraulic conductivity anisotropy influences pore water pressure (PWP) distributed in stratified, poorly cemented rock slopes and related slope stability through numerical simulation. The notion of representing thin alternating beds of stratified, poorly cemented rocks as an equivalent anisotropic medium for ground‐water flow analysis in finite slopes was validated. PWP was then derived in a modelled slope comprising an anisotropic medium with suitable boundary conditions. Simulation results indicate the significance of the principal directions of hydraulic conductivity tensor and the anisotropic ratio on PWP estimation for anisotropic finite slopes. For a stratified, poorly cemented rock slope, estimating PWP utilizing a phreatic surface with isotropic and hydrostatic assumptions will yield incorrect results. Stability analysis results demonstrate that hydraulic conductivity anisotropy affects the slope safety factor and slip surface pattern. Consequently, steady‐state groundwater flow analysis is essential for stratified, poorly cemented rock slopes when evaluating PWP distribution and slope stability. This study highlights the importance of hydraulic conductivity anisotropy on the stability of a stratified, poorly cemented rock slope. Copyright © 2006 John Wiley & Sons, Ltd.     

基于流固耦合理论某尾矿坝失稳特性及稳定性分析

选用典型的尾矿库工程实例,采用流固耦合和强度折减法相结合对其尾矿坝进行稳定性分析,确定尾矿库渗流场分布及浸润线的位置,该浸润线位置与实测浸润线位置吻合较好。建议强度折减过程中尾矿坝的失稳准则,计算安全系数,确定潜在滑裂面的位置,并与极限平衡法计算出的安全系数及临界滑裂面位置进行比较,表明强度折减法得出的结果与Bishop法结果接近,流固耦合-强度折减法在尾矿库稳定性分析的可行性。在该基础上研究尾矿坝潜在的失稳模式,将尾矿坝潜在的失稳模式分为局部失稳和整体性失稳两种,局部失稳为尾矿坝的部分坝面发生滑移,整体失稳为整个尾矿坝坝体发生失稳,并分析导致该尾矿坝两种失稳模式的主要因素,认为浸润线埋深过浅是导致局部失稳的主要原因。     

基于超静孔压消散的静压桩极限承载力研究

预制桩承载力的时间效应是岩土工程中一个重要的课题。基于饱和软土中静压桩单桩引起的三维超静孔隙水压力的消散和桩周土的固结,考虑桩土接触面的破坏形式,获得了估算考虑时间效应的单桩极限承载力的解析解。分析表明,在饱和软土中静压预制桩单桩在50 d时的极限承载力可达到最终极限承载力的70 %左右。最后,通过2个工程实例验证了该方法的可行性。     

饱和粉土孔隙水压力性状试验研究

采用多功能静动液压剪切仪进行了室内动力循环试验,研究了饱和重塑粉质土孔压变化规律。其特殊之处在于试验是在达到液化标准后继续施加动荷载直至孔压平稳为止。这个过程模拟了液化后严重破坏情况以及孔压发展的完整过程。研究发现,粉质土孔压可以用一个改进的指数形式来描述。该表达式能拟合较多的前人研究孔压成果,而且弥补了前人研究成果中可能出现的极限孔压比围压大的缺陷。理论分析和数据验证都表明该表达式具有较好的适用性。     

The effect of pore water pressure on tunnel face stability

The kinematic approach in combination with numerical simulation is used to examine the effect of pore water pressure on tunnel face stability. Pore water pressure distribution obtained by numerical calculations using FLAC^3D is used to interpolate the pore water pressure on a 3D rotational collapse mechanism. Comparisons are made to check the present approach against other solutions, showing that the present approach improves the existing upper bound solutions. Results obtained indicate that critical effective face pressure increases with water table elevation. Several normalized charts are also presented for quick evaluation of tunnel face stability. At the end of the paper, the influence of anisotropic permeability on tunnel face stability is also discussed, showing that the isotropic model leads to an overestimation of the necessary tunnel face pressure for anisotropic soils. Copyright © 2016 John Wiley & Sons, Ltd.     

初始剪应力与加荷速率共同作用下饱和软黏土孔压模型试验研究

通过GDS循环三轴试验系统,对循环荷载作用下饱和软黏土的孔压变化规律进行了研究,分析了循环应力比,初始剪应力与振动频率对孔隙水压力的影响。研究结果表明：随着循环应力比的增加,孔压发展速度增快。循环荷载作用下饱和软黏土存在临界循环应力比,通过孔压也可以确定其值大小。在循环初期,孔压率较大,随着循环时间的增加,孔压率逐渐减小。随着循环应力比的增加,孔压率增加。振动频率对孔压比-循环次数关系影响明显,随着频率的增加,孔压比减小;然而,当振动频率大于1 Hz时,振动频率对孔压比-时间与孔压率-时间关系影响不明显。随着初始剪应力的增大,孔压增加。初始剪应力对应变率具有显著影响;随着初始剪应力的增加,应变率增加。在对数坐标下,孔压率与时间呈线性关系。在上述试验基础上建立了孔压率与时间关系表达式,通过积分得到了循环荷载作用下饱和软黏土的动孔压模型     

Effect of coupling excess pore pressure and deformation on nonlinear seismic soil response

The excess pore pressure (\(\Delta p_w\)) generation and consequent reduction in effective stress lead to the softening of a liquefiable soil deposit that can alter ground motions in terms of amplitude, frequency content and duration. However, total stress models, which are the most currently used, do not take into account coupling of excess pore pressures and soil deformations. To assess this effect, two analyses were made: (1) a Biot hydraulic and mechanical computation of a saturated soil deposit with coupling pore pressures and soil deformations and (2) a mechanical computation of a decoupled model with same initial behaviour. Both analyses were performed with a fully nonlinear elastoplastic multi-mechanism model. As \(\Delta p_w\) depends on the soil properties, two soils were analysed: loose-to-medium and medium-to-dense sand. The results regarding the profile of maximum accelerations and shear strains, the surface accelerations and their corresponding response spectra are analysed. The mean values of the normalized response spectra ratio of surface accelerations between the coupled and decoupled model show a deamplification of low and high frequencies (i.e. at frequencies lower than 1.0 Hz and higher than 10 Hz) that tend to increase with the liquefaction zone size. Coupling of \(\Delta p_w\) and soil deformation is therefore of great importance to accurately model the ground motion response. On the contrary, while peak acceleration predictions could be conservative, the amplification on the low frequencies could be largely underestimated which could be highly prejudicial for flexible buildings.     

Quantitative identification of cutoff wall construction defects using Bayesian approach based on excess pore water pressure

Acta Geotechnica - Cutoff wall has been widely used as a barrier to prevent the migration of contaminants in aquifers. Hydraulic impermeability and homogeneity should be ensured before operation....     

吹填土自重沉淤阶段孔隙水压力消散的试验研究

利用真空预压法处理吹填土时,细颗粒常堵塞排水管,导致土体排水不畅。为提高吹填土固结效率,采用自重沉淤排水与加负压排水固结相结合的方式在室内进行吹填土固结试验。试验第一阶段用排水管作为吹填土自重沉淤的竖向排水通道;第二阶段以装入中粗砂的排水管作吹填土排水通道,同时也是压力传递通道。试验监测到吹填土固结过程中不同位置孔隙水压力的变化,通过监测数据着重研究自重沉淤排水阶段吹填土的固结规律。借助渗流平衡方程确定吹填土在自重沉淤阶段孔隙水压力变化主要由排水管中水位、单位土面积控制,解释自重沉淤阶段孔隙水压力变化机理。同时,为了减小由于排水距离远近造成的固结不均,利用自重沉淤与加压固结结合的方法使吹填土达到较为理想的固结效果,将砂井设计理论与孔隙水压力变化曲线相结合确定排水管有效排水范围等效直径,为实际工程提供排水管间距的设计参数。     

黏土不透水层确定及水压力分布规律试验研究

工程上将满足一定条件下的黏土层介质视为隔水层。通过模型试验的方法,对黏土层为不透水层的确定方法以及黏土层内部的水压力分布规律进行了研究。通过试验分析得出了某给定黏土层为隔水层的特定条件：即找出了黏土层的厚度、渗透系数及层上水头高度三者的关系和给定黏土层的起始水力坡降,得到了黏土层内已渗透水部分的水压力分布规律。试验结果对工程实际具有一定的指导作用。     

考虑孔压积累-消散耦合的等效有限元方法

交通荷载往复作用下饱和软土路基会发生显著的工后沉降,并引起不均匀沉降。采用基于室内循环三轴或空心圆柱扭转试验建立的经验显式模型与等效有限元相结合方式,在预测路基长期沉降方面取得了较好的效果。然而,其采用的瞬时积累、逐步消散的孔压模型与实际工程中孔压积累与消散同时进行有着明显的差异。忽略这种差异将会使得计算结果低于实际值。采用能反映自然排水条件下震动孔压长消规律的解析公式,对以上的不足作出改进,并用改进的孔压模型计算了上海浦东国际机场第一跑道的长期运营沉降。分析表明,与瞬时积累、逐步消散的孔压模型相比,考虑孔压积累与消散耦合效应的孔压模型,计算结果更接近实测资料。     

Determination of consolidation parameters based on the excess pore water pressure measurement using a newly developed U-oedometer

In this study, the U-oedometer, a novel modified oedometer cell equipped with tailor-made needle probes, is developed to easily and accurately measure the excess pore water pressure (\(\Delta u\)) during 1D consolidation tests and to determine the coefficient of consolidation (\(c_{\text{v}}\)). The 3D printing technique is applied to make simple yet robust modifications to the conventional oedometer cell for facilitating the installation of the needle probes. The tailor-made needle probes are designed in such a way that the volumetric compliance is lowered to avoid measurement bias. Subsequently, the \(\Delta u\)-based method is proposed to determine \(c_{\text{v}}\), with the target of avoiding the intervention of human judgement and therefore minimizing the degree of subjectivity. The experimental results demonstrate that the measured \(\Delta u\) matches the theoretical values of the Terzaghi 1D consolidation theory, showing that the estimated \(c_{\text{v}}\) is sufficiently reliable. In addition to the determination of \(c_{\text{v}}\), the U-oedometer allows additional measurements of other soil properties during consolidation, including the coefficient of permeability (\(k\)) and the coefficient of earth pressure at rest (\(K_{0}\)). It is observed that k decreases with the reduction in void volume, due to the increase in the effective vertical stress (\(\sigma_{\text{v}}^{'}\)). Further, the secondary compression seems to be a continuation of the primary consolidation, where the soil sample continues to deform at a relatively slower rate, associated with the slight decrease in \(k\). A constant value of \(K_{0}\) is observed at any value of \(\sigma_{\text{v}}^{'}\) in the loading path, while during secondary compression, \(K_{0}\) slightly increases with time.