粘土固结不排水三轴连续剪与分级剪试验的对比

对15组粘土分别进行分级剪与连续剪试验,分析、对比、统计检验试验数据得出,两种方法所得的抗剪强度参数C、及C′、′无显著差异,而连续剪所得的C值与分级剪所得的C′值有一定的差别。只有通过对连续剪所得的C值进行适当修正,粘土的固结不排水连续剪切试验结果才更加接近分级剪切试验结果。     

GCTS空心圆柱扭剪仪反压饱和试验探究

GCTS空心圆柱扭剪仪是研究土体在循环荷载下的主应力轴旋转的理想仪器。如何使用GCTS空心圆柱扭剪仪对软土空心试样进行反压饱和才能使后续试验结果更精确,探究了以GCTS空心圆柱扭剪仪为试验平台,对空心试样进行了反压饱和的试验方法。总结了空心扭剪仪反压饱和的3种加压方式：手动加压、自动加压和连续加压方式。通过一些试验探究了每种加压方式所对应的合理性参数。确定了适合吹填土的压差为15kPa。确定了孔压稳定的标准为：如果孔压在1min内的变化值小于围压和反压之间压力差的5％,则认为孔压稳定。     

不同围压下饱和砂土不排水循环扭剪试验研究

利用河海大学与日本圆井株式会社共同研制的一种新型的多功能静动三轴仪进行了不排水循环扭剪试验。通过对空心圆柱体试样的动力扭剪不排水试验研究了相同相对密度在不同固结围压下的动力不排水响应。试验初步研究了通过用初始有效平均正应力归一化的有效应力路径,归一化有效应力路径有很好的一致性。如果保持相同的剪应力比,由初始有效平均正应力归一化的有效应力路径不受初始有效平均正应力的影响。     

饱和软黏土动力学特性循环扭剪试验研究

以饱和软黏土的循环扭剪试验研究为基础,阐明不固结不排水条件下饱和软黏土的动力学特性。在循环扭剪和循环三轴两种不同试验应力状态下,通过研究不同围压和不同静、动应力组合下饱和软黏土的应力等效破坏关系和应变等效破坏关系,提出在循环荷载作用下饱和软黏土的循环破坏同样遵循Mises屈服准则,且在Mises屈服准则下,饱和软黏土的循环强度趋于不变量。循环破坏的过程可以等效为一种拟静力弹塑性循环蠕变,建立了饱和软黏土循环累积变形随静荷载、循环荷载以及循环破坏振次之间的关系式。上述结论分别从应力和变形两个方面阐述饱和软黏土的动力学特性,与试验应力状态和围压无关,可以推广到一般应力状态下。     

粗粒土剪胀性大型三轴试验研究

剪胀性是土体显著区别于一般弹性材料的基本特性,与土体的强度和变形特性密切相关。通过4组不同初始密度的塔城砂砾石常规大型三轴试验,研究剪胀性对粗粒土强度和变形特性的影响。试验结果表明,（1）若体变速率（体变和轴向应变均以压缩为正）先从正值减小到负值并达到最小值,随后又有所增大但仍小于0,则应力-应变曲线为软化型,在比值为最小值时土体剪胀性最大,对应于峰值强度,若体变速率从某一正值单调减小并一直大于0,则应力-应变曲线为硬化型;（2）体变变化趋势取决于剪胀性和压缩性的大小,剪切后期若剪胀速率大于压缩速率,则体变先压缩后膨胀,应力-应变曲线呈软化型,反之若剪胀速率小于压缩速率,则体变一直是压缩的,应力-应变曲线呈硬化型。研究结果对于加深认识粗粒土的强度和变形特性具有重要意义。     

主应力轴旋转下K0固结饱和粉质黏土孔压及变形特性试验研究

主应力旋转将加速孔压和塑性应变的累积,影响土体的力学特性。为研究主应力轴循环旋转对 固结饱和粉质黏土孔压和变形的影响,利用GDS-HCA试验系统开展了不同应力路径的 固结饱和粉质黏土不排水循环三轴试验和循环扭剪试验,研究了主应力轴循环旋转对 固结饱和粉质黏土累积塑性应变、孔压等动力特性的影响。结果表明：动剪应力幅值、心形应力路径所包围的面积、循环偏应力幅值等均随循环剪应力比和循环动应力比的增大而增大。试样未发生破坏时, 固结饱和粉质黏土的孔压比随着振动荷载作用次数的增加而增大;当试样发生破坏时,孔隙压力迅速消散,孔压比急剧下降。循环扭剪试验时试件产生的轴向累积塑性应变始终大于循环三轴试验产生的累积塑性应变,说明主应力轴循环旋转会加速试件轴向应变的累积。试件的累积塑性应变随循环剪应力比和循环动应力比的增大而增大。循环动应力比越大时,主应力轴旋转造成的轴向累积塑性应变差异越显著。在Monismith幂次函数模型的基础上,建立了主应力轴循环旋转条件时K0固结饱和粉质黏土累积塑性应变方程,并对模型的可靠性进行了分析和验证。     

土工静动力液压三轴扭转剪切仪控制软件系统研究

根据土工试验使用要求,应用计算机自动化控制技术,将大连理工大学与日本诚研社合作研制的新型土工静力-动力液压三轴-扭转多功能剪切仪,配备了完善的控制软件系统。采用VC++6.0语言作为编程平台,利用现代计算机技术中的多线程技术、精确定时技术、绘图技术,结合现代的单神经元自适应PID控制理论,实现了三轴-扭转试验机的自动控制及数据采集处理功能,能够完成静态、动态等各种组合试验,并可实时监测试验全过程的应力、应变和位移等12种数据,绘制实时动态曲线,更加方便试验者操作,进一步提高了系统的控制精度。     

钱塘江冲海积粉土剪胀性三轴试验研究

钱塘江两岸广泛分布着冲海积粉土.通过大量的三轴固结不排水CU和固结排水CD试验,探讨饱和粉土的应力应变性状和剪胀特性。试验表明,钱塘江冲海积粉土显著的特性之一是在剪切中膨胀,剪胀主要与粉土的密度和围压有关。CU试验中密(e=0.739～0.866)的原状样在围压600kPa范围内剪切膨胀,稍密(e=0.890～0.906)的击实样在围压低于400kPa剪切膨胀。由于粉土膨胀的本质不排水强度在剪切中保持增加,对于这种情况就没有惟一的"不排水强度";CD试验稍密(e=0.889～0.945)的击实样在围压低于400kPa时剪切膨胀。钱塘江冲海积粉土的剪切破坏要经历一个大的变形过程,固结排水剪切过程的应力应变性状可分为4个阶段。取应变继续而没有进一步体积变化的临界状态做破坏标准,确定粉土排水剪切强度指标较合理。     

冻土扭剪强度与其它试验结果的比较

本在试验研究的基础上，将由冻结黄土扭转试验得出的扭剪强度与其它试验结果进行对比分析，结果表明，冻土的剪切强度不仅与土的物理性质有关外，而且还与其试验条件和方法有关。     

三轴试验抗剪强度指标线性回归方法的讨论

利用线性回归统计抗剪强度指标是岩土工程中的常用手段。对于常规三轴试验,可以通过线性拟合p-q曲线或者拟合大小主应力的方法来求解抗剪强度参数,并给出了这两种方法的完整计算公式,同时应用矩法和线性回归方法统计了小浪底64组320个固结排水三轴试验和多个水利工程大坝填筑料的试验资料,发现对于常规三轴试验,拟合p-q曲线求解抗剪强度参数存在高估摩擦系数、低估粘聚力的问题;利用概率理论对两种方法进行了对比分析也发现了同样的趋势。因此,根据常规三轴试验统计抗剪强度参数时采用直接拟合大小主应力更为合理。     

Validation of Hyperbolic Model by the Results of Triaxial and Direct Shear Tests of Municipal Solid Waste

The increasing demand of engineering landfills requires that designers propose a framework for landfill design, construction, repair and maintenance. As municipal solid waste (MSW) is a major part of a landfill, the analysis should consider MSW mechanical behavior using a constitutive model. To investigate this, 18 direct shear (DS) and triaxial (TX) tests were conducted on MSW samples with different fiber contents. Different shearing mechanisms lead to understand effects of fibers on stress–strain response. Based on obtained results the hyperbolic model Duncan and Chang (J Soil Mech Found Div 96(5):1629–1653, 1970) has been employed to simulate the TX results indicating the ability of the model to predict stress–strain behavior of MSW. This model could also be employed to the DS test results with some assumptions. The model can capture DS stress–strain response well whereas for TX tests the predictions were just enough. The experimental results and two sets of proposed MSW parameters of hyperbolic model have been compared and discussed.     

A Fully Coupled Chemo-Poroelastic Analysis of Pore Pressure and Stress Distribution around a Wellbore in Water Active Rocks

Water active rocks consist of minerals that hold water in their crystalline structure and in pore spaces. Free water from drilling fluid can be attracted by the formation depending on the potential differences between pore space and drilling fluid. The fluid movement into the formation or out of the formation can lead to a change in effective stress, thus causing wellbore failures. In all previous studies it is found that the solute transport from or to the formation is primarily controlled by diffusion process and the effect of advection on solute transfer is negligible for a range of very low permeable shale formations (>10⁻⁵ mD). In this study a range of permeable shale formations (10⁻⁵ to 10⁻³ mD) commonly encountered in drilling oil and gas wells are considered to investigate the solute transfer between drilling fluid and formation due to advection. For this purpose a finite element model of fully coupled chemo-hydro-mechanical processes was developed. Results of this study revealed that the solute transfer between the drilling fluid and the shale formation is controlled primarily by permeability of the shale formations. For the range of shale formations studied here, there exists a threshold permeability below which the solute transfer is dominated by diffusion process and above which by fluid in motion (fluid flow). Results from the numerical experiments have shown that when the permeability of shales is greater than this threshold permeability, the chemical potential gradient between the pore fluid and drilling fluid reaches equilibrium faster than that when the permeability of shales is below this threshold value. Also it has been found that when advection is taken into account, effective radial and tangential stresses decrease around the wellbore, particularly near the wellbore wall where the solute concentration has reached near equilibrium.     

孔隙水压力量测的延迟效应分析

从理论上考虑，用压力传感器量测土中变化的孔隙水压力会存在延迟效应，本文阐明了延迟效应的机理，并以饱和土孔压消散试验为例进行了深入的分析，研究表明，延迟效应的主要影响因素是体积压缩系数和传感器敏感元件的刚度因数，从计算结果看出，除硬粘性土外，延迟效应对孔压量测结果影响甚小。     

典型浅层孔隙水和岩溶水中多环芳烃分布特征

近几年多环芳烃(PAHs)在地下水中的检出报道逐渐增多,但关于我国主要水文地质单元地下水中PAHs的研究匮乏。为研究不同水文地质条件地下水中PAHs分布特征,本文在华北平原、珠江三角洲平原及西南岩溶区采集浅层孔隙地下水和岩溶地下水样品共82组,使用气相色谱-质谱仪进行测试,采取统计学方法对比分析各区PAHs的检出率、浓度和组成。结果表明:检测的16种PAHs,每种PAH至少在一个样品中被检出,检出率最高的是(6.10%),检出浓度最大的是萘(5.41μg/L),仅苯并(a)芘超过《地下水水质标准》Ⅲ类水限值,超标率为2.44%。地下水中PAHs以2～4环为主,但三个研究区存在差异,北方孔隙水4环PAHs的相对比例(52.48%)较高;南方孔隙水与西南岩溶水分别是3环(56.60%)、2环(95.66%)PAHs占优。北方孔隙水PAHs主要是燃烧源,南方孔隙水PAHs来源与珠江三角洲产业布局相关,西南岩溶水PAHs则主要受大气降水影响。PAHs在各区检出差异与其理化性质、区域水文地质条件、污染源和气象水文等因素有关。研究结果可为我国地下水PAHs污染监测和地下水相关标准制定提供基础支撑。"     

孔隙水压力对岩石力学参数的影响

多孔多相的岩石介质中,孔隙水压力的变化会引起岩石的变形,其力学参数随之改变,而岩石的力学参数变化反过来会引起渗流场发生改变.本文利用岩石力学参数在其中的作用,推导出孔隙水压力变化时,岩石变形与孔隙度、压缩系数和体积弹性模量间的关系式.通过理论计算与分析表明,在渗流场和变形场的非线性程度不很高,参数关系不足很复杂的情况下,利用岩石力学参数的更新来进行耦合分析的方法,对于近期丁程应用行之有效.     

Estimation of Pore Water Pressure of Soil Using Genetic Programming

Soil–water characteristic curve (SWCC) is one of the input components required for conducting the transient seepage analysis in unsaturated soil for estimating pore water pressure (PWP). SWCC is usually defined by saturated volumetric water content (θ_s), residual water content (RWC) and air entry value (AEV). Mathematical model of PWP could be useful to unearth the important SWCC components and the physics behind it. Based on authors’ knowledge, rarely any mathematical models describing the relationship between PWP and SWCC components are found. In the present work, an evolutionary approach, namely, multi-gene genetic programming (MGGP) has been applied to formulate the relationship between the PWP profile along soil depth and input variables for SWCC (θ_s, RWC and AEV) for a given duration of ponding. The PWP predicted using the MGGP model has been compared with those generated using finite element simulations. The results indicate that the MGGP model is able to extrapolate the PWP satisfactory along the soil depth for a given set of boundary conditions. Based on the given AEV and saturated water content, the PWP along the depth can be determined from the newly developed MGGP model, which will be useful for design and analysis of slopes and landfill covers.     

扭转三轴试验综述

阐述了扭转三轴仪的特点，优点和局限性以及它的设计原则。讨论了试验时如何控制不同的应力状态和应力路径。提出了各类参数的计算公式     

高压喷射注浆法产生的超孔隙水压分析

介绍了高载射注浆法的作用机理,探讨了在施工过程中高压喷射注浆法引起的超孔隙压。根据半无限土体中小孔扩张问题的解,分析了在超孔隙水压作用的瞬时,土体中的应力、变形等,并提出了经验公式。结合一具体工程事故的成功处理,验证了所建议超孔隙水压公式的可行性,同时提出了减少超孔隙水压的对策和方法。