粉质粘土结构性参数试验研究

为合理描述外部环境改变引起土体结构性的变化规律,基于综合结构势理论,通过三轴剪切试验,研究了应力比结构性参数(mη)随试验条件的变化规律。试验结果表明:粉质粘土应力-应变曲线包括应变软化型曲线、理想弹塑性曲线、应变硬化型曲线3种形式;粉质粘土强度随着含水量的增大而减小,随着围压的增大而增大。粉质粘土应力比结构性参数随着含水率和围压的增大而减小。采用初始应力比结构性参数和结构性损伤量参数两个参数,建立了粉质粘土结构性应力-应变数学模型。将试验结果与模型计算结果进行了对比分析,结果表明二者强度误差小于3%,说明了所建立模型的合理性。     

考虑围压效应的冻结砂土动态本构模型研究

为描述主动围压作用下冻结砂土的动态力学特性，通过在朱-王-唐模型的非线性体上串联塑性体，建立了能够考虑围压效应的冻结砂土动态损伤本构模型；分析了损伤参数对应力-应变曲线特征、屈服点、峰值应力和峰值应变的影响规律，基于冻结砂土动力学试验数据确定了模型参数；通过将模型和试验数据进行对比，并对不同试验条件下模型的预测误差进行分析，验证了模型的适用性和准确性。结果表明，损伤参数对应力-应变曲线弹性阶段和屈服点无明显影响，而对塑性阶段和破坏阶段的影响较为显著，本构模型预测的应力-应变曲线与试验结果具有较好的一致性。模型能够预测围压引起冻结砂土塑性阶段占比大和屈服点明显的特征，且能够描述围压对冻结砂土动态强度的增强效应；不同负温和主动围压条件下，模型对峰值应力和屈服强度的预测效果优于峰值应变和屈服应变。     

压实粉土非线性应力-应变关系的试验研究

对京九线路基粉土用GDS三轴仪进行固结不排水剪试验,研究不同围压、含水量、压实度下压实粉土样的应力-应变关系。结果表明:压实粉土在低围压下为应变软化,高围压下为应变硬化,存在一个屈服应力;含水量和压实度对粉土强度和应力-应变关系影响显著,随着含水量的减小、压实度的增大,压实粉土样强度增大,应力-应变曲线上升。对围压小于屈服应力的应变软化曲线,用常规的土的软化关系式进行拟和;对围压大于屈服应力的应变硬化曲线,用邓肯-张模型进行拟和;这二者的结合能描述压实粉土的应力-应变关系曲线,效果良好。     

ANALYSIS OF MECHANICAL CHARACTERISTICS OF FROZEN CLAY AND MODIFIED S-M CREEP MODEL1)

为合理描述人工冻结法施工的矿井土层力学特性,对某矿井土样的重塑土进行单轴抗压强度实验和单轴压缩蠕变实验,得到重塑冻结黏土在不同温度及载荷加载等级下的应力-应变曲线和蠕变曲线。实验结果表明：冻结温度越低,土样的单轴强度越大;相同冻结温度下,土样的蠕变变形随着应力水平的升高而增大。单轴压缩蠕变的等时应力-应变曲线随时间发展向应变轴靠拢;土样经历初始蠕变和等速蠕变两个阶段,在较高应力水平下有进入加速蠕变的趋势;对S-M模型中各参数的意义进行修正并考虑温度的影响,得到人工冻结黏土改进S-M蠕变显式模型,然后采用粒子群算法对人工冻结黏土S-M蠕变模型参数进行优化。改进S-M蠕变显式模型理论计算值与实验值吻合良好,表明改进S-M蠕变显式模型能较好模拟人工冻结黏土的蠕变特性。改进S-M蠕变显式模型为人工冻土蠕变计算提供一种新方法。     

冻结黏土力学特性分析及改进S-M蠕变模型

为合理描述人工冻结法施工的矿井土层力学特性,对某矿井土样的重塑土进行单轴抗压强度实验和单轴压缩蠕变实验,得到重塑冻结黏土在不同温度及载荷加载等级下的应力-应变曲线和蠕变曲线。实验结果表明:冻结温度越低,土样的单轴强度越大;相同冻结温度下,土样的蠕变变形随着应力水平的升高而增大。单轴压缩蠕变的等时应力-应变曲线随时间发展向应变轴靠拢;土样经历初始蠕变和等速蠕变两个阶段,在较高应力水平下有进入加速蠕变的趋势;对S--M模型中各参数的意义进行修正并考虑温度的影响,得到人工冻结黏土改进S--M蠕变显式模型,然后采用粒子群算法对人工冻结黏土S--M蠕变模型参数进行优化。改进S--M蠕变显式模型理论计算值与实验值吻合良好,表明改进S--M蠕变显式模型能较好模拟人工冻结黏土的蠕变特性。改进S--M蠕变显式模型为人工冻土蠕变计算提供一种新方法。     

软化Mohr-Coulomb材料强度参数的测定方法

为了得到试件的粘聚力和内摩擦角随轴向塑性压应变变化的曲线提出本方法。试件的弹塑性本构关系遵循相关联的Mohr-Coulomb强度准则;对常规三轴试验,试件受力进入塑性状态后,处在棱椎状屈服面的棱上,加载过程遵循Koiter流动法则。按经典塑性力学理论,推导得到轴向塑性压应变与轴向应力与轴向应变的关系;在常规三轴试验机上获得不同围压下试件的全程应力-应变曲线,进而可得到各自围压下轴向塑性压应变随加载过程的变化曲线;把来自不同围压下对应同一轴向塑性压应变的应力分别代入屈服面方程,即可求得对应的粘聚力和内摩擦角。结果表明,Mohr-Coulomb材料的两个强度参数的变化由轴向塑性压应变确定。轴向塑性压应变可以作为塑性变形的状态参数,它和试件的受力过程可以唯一确定试件的变形过程。     

冻结黏土侧限压缩变形的S-M模型

为合理设计冻结壁及确保施工安全,掌握人工冻土侧限条件下压缩变形特性非常必要。对山西省某煤矿深部黏土在不同冻结温度、含水率下,采用分级加载的方式进行侧限一维压缩试验,得到一维压缩应力-时间-轴向压缩变形之间的关系,并根据曲线变化分析可知:同一含水率及加载应力下,温度越低,轴向压缩变形量越小;相同温度下,随着含水率和加载应力的增加,压缩变形量也逐渐增大。引入Singh-Mitchell(S-M)模型,同时考虑温度、含水率和加载应力为模型自变量,建立改进S-M模型,通过对轴向压缩变形取对数的方式计算改进S-M模型参数。将改进S-M模型计算结果与侧限一维压缩变形试验结果进行比较,研究发现:模型计算曲线与试验曲线吻合度较高,模型计算曲线能够反映冻土从初始变形状态到稳定变形状态的变形特性,能准确预测压缩变形曲线的变化趋势,且改进S-M模型涉及参数较少,实际应用价值高。     

三种红层岩石常规三轴压缩下的强度与变形特性研究

利用MTS815Teststar程控伺服岩石力学试验系统研究了川东地区一红层边坡中的砂岩、粉砂岩和泥岩围压为0³MPa的应力-应变全过程曲线,建立了峰值强度、峰值强度前弹性模量以及峰值强度后的弹性模量和围压的关系。将低围压下红层的全应力-应变曲线概化成5个阶段,分别为压密段、弹性段、屈服段、应变软化段和塑性流动阶段。试验结果得出,红层弹性模量随围压的增加而提高且变化明显,砂岩和粉砂岩在此围压内为脆性破坏,泥岩为塑性破坏的规律。     

散粒体卸载特性的三轴伸长试验研究

根据岩土体的加卸载变形过程和应力状态,卸载曲线分为弹性卸载段和卸载伸长段.采用三种不同粒径的玻璃珠和标准丰浦砂散粒材料进行了三轴伸长卸载试验,对比分析了不同材料、初始偏应力和不同围压下散粒体的卸载特性.研究表明散粒体的单向伸长卸载强度主要取决于与卸载方向垂直的围压和颗粒的内摩擦,且与围压成线性关系,初始偏应力状态及各向异性对于散粒体的伸长强度无影响,但影响其破坏发展形态.此外,材料特性包括表面粗糙度和级配、孔隙率等对内摩擦及伸长卸载特性均有影响.     

正常固结饱和黏性土三剪有限变形弹塑性本构模型研究

基于三剪统一强度准则,利用等量代换法和坐标平移法分别推导出正常固结饱和黏性土的三剪破坏应力比,并将其与修正剑桥模型相结合,得到三剪统一屈服面方程。为反映饱和黏性土的变形非线性及大变形特性,基于有限变形理论,建立了正常固结饱和黏性土的三剪统一有限变形等量代换法和坐标平移法2种弹塑性本构模型。为验证模型的适用性,取江西红黏土制备三种不同压实度的试样,在不同围压下进行常规三轴固结不排水和固结排水压缩试验。将试验数据与本文所提2种有限变形模型及相应的2种小变形模型计算结果进行了对比分析,结果表明,随着变形的发展,有限变形模型相对于小变形模型更接近试验结果,能较好地反映黏性土因高孔隙率（低初始压实度、小围压及压缩变形前期）而产生的大变形特性,虽然小变形模型的计算偏差会随着土样初始压实度和所施加围压的增大而减小,但有限变形模型对不同压实度和围压的计算偏差均相对较小,其中,等量代换法有限变形模型在初始压实度较大或者围压较高时所得计算偏差相对最小。对所提本构模型所做真三轴分析表明,中间主应力影响系数b和初始压实度对土体的强度和变形特性具有一定的影响。主应力差、孔隙水压力和体应变与b值呈正相关性,主应力差与初始压实度呈正相关性,孔隙水压力和体应变与初始压实度呈负相关性。     

三向受力条件下淡水冰破坏准则研究

为了更清楚地认识含冰冻结壁力学特性、解决复杂冰岩耦合问题以及给冰工程设计和数值仿真分析提供参数,有必要对冰在三向受力条件下的力学特性进行深入研究.以内蒙古自治区东胜煤田石拉乌素矿立井井筒建设为背景,参考现场水文地质资料在室内制作相似冰样,利用TDW-200低温冻土试验机,进行了4组温度和7组围压的人工淡水柱状冰三轴压缩强度试验,加载速率为0.5 mm/min,加载方向垂直于冰的晶轴方向.结果表明:在恒定温度条件下,柱状冰随围压增大塑性增强,而恒定围压条件下,柱状冰随温度降低脆性增强;在试验温度范围内,淡水柱状冰和多晶冰强度均随围压、温度升高而增大,但同条件下柱状冰强度高于多晶冰;采用D-A模型、Teardrop模型解释了高压下偏应力与围压之间的非线性关系,从不同角度对拟合得到的破坏准则综合考虑,认为D-A准则更适合用于描述淡水冰的破坏特征.研究结果可为后期同条件冰-岩耦合、数值模拟研究提供参考.     

Experimental Investigation on Mechanical Behavior of Coarse Marble Under Six Different Loading Paths

A series of triaxial compression experiments were preformed for the coarse marble samples under different loading paths by the rock mechanics servo-controlled testing system. Based on the experimental results of complete stress-strain curves, the influence of loading path on the strength and deformation failure behavior of coarse marble is made a detailed analysis. Three loading paths (Paths I–III) are put forward to confirm the strength parameters (cohesion and internal friction angle) of coarse marble in accordance with linear Mohr-Coulomb criterion. Compared among the strength parameters, two loading paths (i.e. Path II by stepping up the confining pressure and Path III by reducing the confining pressure after peak strength) are suggested to confirm the triaxial strengths of rock under different confining pressures by only one sample, which is very applicable for a kind of rock that has obvious plastic and ductile deformation behavior (e.g. marble, chalk, mudstone, etc.). In order to investigate re-fracture mechanical behavior of rock material, three loading paths (Paths IV–VI) are also put forward for flawed coarse marble. The peak strength and deformation failure mode of flawed coarse marble are found depending on the loading paths (Paths IV–VI). Under lower confining pressures, the peak strength and Young’s modulus of damage sample (compressed until post-peak stress under higher confining pressure) are all lower compared with that of flawed sample; moreover mechanical parameter of damage sample is lower for the larger compressed post-peak plastic deformation of coarse marble. However under higher confining pressures (e.g. σ ₃?=?30 MPa), the axial supporting capacity and elastic modulus of damage coarse marble (compressed until post-peak stress under lower confining pressure) is not related to the loading path, while the deformation modulus and peak strain of damage sample depend on the difference of initial confining pressure and post-peak plastic deformation. The friction among crystal grains determines the strength behavior of flawed coarse marble under various loading paths. In the end, the effect of loading path on failure mode of intact and flawed coarse marble is also investigated. The present research provides increased understanding of the fundamental nature of rock failure under different loading paths.     

黄河三角洲粉质土的动模量和阻尼比试验研究

结合室内共振柱和动三轴实验,对黄河三角洲饱和原状粉质土体(粉土、粉砂、粉质粘土)动模量和阻尼比的影响因素和发展规律进行了详细的研究。研究表明,在粉粒和粘粒含量对动模量的共同影响中,粉粒含量起着举足起重的作用;侧限压力对归一化剪模比和阻尼比的影响均较显著,相比粘粒含量的影响不大。通过与Seed建议的砂土及饱和粘土的G/Gmax~γ曲线和λ~γ曲线进行对比,结果显示研究区的粉质土相比一般的砂土和饱和粘土而言,其动力变形特性更接近于砂土,但是与砂土也存在着非常明显的差异;其发展规律与其他地区沉积粉质土也较为不同,具有明显的区域性。采用修正了的Hard in-D rnevich模型和对数模型分别对G/Gmax~γ曲线和λ~γ曲线进行拟合,给出了三类粉质土的归一化动力变形G/Gmax~γ/γr关系曲线,对模型中有关参数的影响因素做了初步的探讨。     

Yield criterion and elasto-plastic damage constitutive model for frozen sandy soil

A series of triaxial compression tests was carried out on a frozen sandy soil under confining pressures of 0–18 MPa at −6 °C. The experimental results indicate that, the strength of frozen sandy soil increases versus the increase in the confining pressures when σ₃ ? 3 MPa, but decreases when σ₃ > 3 MPa. This phenomenon is called the strengthening and weakening effects of confining pressures. A yield function, considering both effects, is proposed using the experimental method according to Drucker’s postulate, and the mathematical expression of the hardening parameter, which can describe the softening and hardening phenomenon, is provided. An elasto-plastic constitutive model for frozen sandy soil is developed. Based on the continuum damage theory, the cross anisotropic damage variables are deduced and their change regularities are investigated. Then the elasto-plastic damage constitutive model is proposed by introducing damage variables into elasto-plastic constitutive model. The validity of the model is verified by comparing its modeling results with experimental results obtained from triaxial tests. It is found that, this model can predict the deformation regularity of frozen soil exactly. It can simulate the stress–strain process under high confining pressures when pressure melting phenomena appear especially well.     

含水率和围压对安家岭泥岩峰后力学特性影响的试验研究

为分析含水率和围压对泥岩峰后力学特性的影响,从山西安家岭矿取泥岩,制成不同含水率的5组试样,在YAW2000电液伺服试验机上开展了三轴试验,获得了不同含水率泥岩试样三轴全程应力应变曲线,使用激光共聚焦显微镜观测了泥岩增水过程中微观结构变化。利用试验结果,分析了围压和含水率对泥岩峰值强度、残余强度、弹性模量、破坏应变和脆性模量的影响规律和泥岩增水过程中微观结构的变化规律。引入脆性模量系数和强度退化指数来描述围压对泥岩峰后强度退化过程和残余强度的影响,与FLAC中的SS模型结合,建立了考虑围压影响的泥岩应变软化力学模型,模拟了围压对泥岩应变软化行为的影响。研究结果表明:(1)随着围压增加,泥岩的峰值强度、偏应力峰值、破坏应变和残余强度都增长,峰后强度降低速率趋缓,强度退化指数和脆性模量系数可以较好地描述围压对泥岩残余强度和峰后强度退化过程的影响。(2)泥岩增水过程中,岩样内微裂隙及尺寸增长,泥岩的力学性质劣化。随着含水率增加,泥岩的弹性模量、峰值强度和残余强度降低,破坏应变增长。含水率与泥岩的弹性模量、峰值强度和破坏应变之间近似服从线性关系。(3)本文基于脆性模量系数的岩石应变软化模型能较好地描述三轴压缩泥岩的全程变形行为。     

浙东大运河非饱和粉质黏土抗剪强度特性的试验研究

浙东大运河绍兴段的土体整体上受河流相和海相沉积的影响,地质条件非常复杂．其中粉质黏土作为浅表层土体,受雨水影响较大,其状态经常处于饱和状态与非饱和状态之间．为了进一步探究绍兴段典型非饱和粉质黏土的稳定性差异,以及本构关系和强度指标的变化规律,通过全自动非饱和土应力路径三轴仪,对试验土样进行了三轴剪切试验．试验结果表明,初始干密度从1.4 g/cm3增加到1.6 g/cm3时,土体的抗剪强度、总黏聚力、有效内摩擦角和吸附内摩擦角均增大,应力-应变关系曲线由应变硬化型向应变软化型转变,并且基质吸力和净围压越大,区别越明显;基质吸力从0增加到300 kPa时,土体的抵抗变形能力提高,抗剪强度和总黏聚力增大,有效内摩擦角基本无明显变化,吸附内摩擦角逐渐减小．研究结果揭示了浙东大运河绍兴段非饱和粉质黏土的抗剪强度特性的变化规律,为该地域土质边坡、基坑等工程提供理论依据．     

Experimental investigation on strength and failure behavior of pre-cracked marble under conventional triaxial compression

Fractures in natural rocks have an important effect on the strength and failure behavior of rock mass, which are often evaluated in rock engineering practice. The theoretical evaluation of mechanical behavior of fractured rock mass has no satisfactory answer due to the role of confining pressure and crack geometry. Therefore, in this paper, conventional triaxial compression experiments were carried out to study the strength and failure behavior of marble samples with two pre-existing closed cracks in non-overlapping geometry. Based on the experimental results of a number of triaxial compression tests, the effect of crack coalescence on the axial supporting capacity and deformation property were investigated with different confining pressures. The results show that intact samples and flawed samples (marble with pre-existing cracks) have different deformation properties after peak stress, which change from brittleness to plasticity and ductility with the increase of confining pressure. The peak strength and failure mode are found depending not only on the geometry of flaw, but also on the confining pressure. The strength of flawed samples shows distinct non-linear behavior, which is in a better agreement with non-linear Hoek–Brown criterion than linear Mohr–Coulomb criterion. For a kind of rock that has been evaluated as a Hoek–Brown material, a new evaluation criterion is put forward by adopting optimal approximation polynomial theory, which can be used to confirm more precisely the strength parameters (cohesion and internal friction angle) of flawed samples. For intact samples, the marble leads to typical shear failure mode with a single fracture surface under different confining pressures, while for flawed samples, under uniaxial compression and a lower confining pressure (σ₃ = 10 MPa), tests for coarse and medium marble (the coarse and medium refer to the grain size) exhibit three basic failure modes, i.e., tensile mode, shear mode, and mixed mode (tensile and shear). Shear mode is associated with lower strength behavior. However, under higher confining pressures (σ₃ = 30 MPa), for coarse marble, the axial supporting capacity is not related to the geometry of flaw. The friction among crystal grains determines the strength behavior of coarse marble. For medium marble, the failure mode and deformation behavior are dependent on the crack coalescence in the sample. The present research provides increased understanding of the fundamental nature of rock failure under conventional triaxial compression.     

沉积方向和粒径组成对砂土力学特性的影响

运用砂土毛细效应所形成的假凝聚力制备具有不同沉积方向的试样,开展三轴固结排水剪切试验,研究粒径组成对初始各向异性砂土力学特性的影响,分析了粒径组成、沉积方向、强度特性和体积变化之间的相互关系。研究结论表明,试样剪切带的形成受到颗粒级配的影响,它是应力应变关系中陡降阶段的产生原因。沉积方向对粗砂和细砂的偏应力峰值强度均有影响,对残余强度的影响受制于颗粒级配。沉积方向与试样破坏面接近时,试样强度低、剪胀变形小且更容易破坏,粒径组成对砂土三轴剪切力学特性的影响更显著。