关于岩石K_(IC)和J_(IC)的测定及其与岩石地质特点关系的研究

本文介绍了测定岩石K_(1C)和J_(1C)的方法及设备。提供了混合斑状花岗岩、斜长混合花岗岩等测试结果。并对试验中的疑难问题做了初步论述。另外,关于岩石结构和构造以及微裂隙对岩石断裂韧度K_(IC)和J_(1C)的影响,也作了初步的探讨。     

我国老粘土地基承载力问题

一、概述 工业民用建筑地基基础设计规范(TJ7—74)(以下简称规范)和工程地质勘察规范(TJ21—77)[1][2][3]对粘性土按时代、成因和土的工程地质特征分为老粘性土(指第四纪晚更新世(Q_3)及以前沉积的粘性土),一般粘性土(第四纪全新世(Q_4)沉积的粘性土),新近沉积的粘性土(文化期以来新近沉积的粘性土),和几种特殊土(软土、红粘土、人工填土等)。     

半圆盘三点弯曲法测定页岩断裂韧度(K_(IC))的实验研究

为了准确测试页岩的I型断裂韧度K_(IC),分别采用直切槽半圆盘试样(NSCB)和人字形切槽半圆盘试样(CCNSCB),在3种预制切槽布置模式(splitter、arrester、divider)下,开展三点弯曲加载实验。通过标准差和变异系数分析两类方法 K_(IC)测算值的离散性,并评价各自适用性。使用光学显微镜观察试件破裂后的裂纹扩展路径和破裂面断口形态。基于断裂力学理论,给出页岩试件粗糙起伏断口表面能计算公式,分析页岩试件实测值K_(IC)离散的原因,并用最小耗能原理解释裂缝在页岩试件扩展过程中形成粗糙断裂面的机理。对比分析两种试样类型测试的K_(IC)值,认为两种方法在切槽平行层理布置的情况下测算值离散程度一致,二者都适用;对于切槽垂直层理两种布置方式下NSCB试件更容易发生裂缝偏转,导致产生Ⅰ-Ⅱ复合型断裂,使试验失效;CCNSCB试件的韧带具有良好的裂缝扩展导向作用,某种程度上抵消了加载配置非对称性带来的不利影响,CCNSCB比NSCB测得的K_(IC)值离散性更小,更适用于各向异性页岩的K_(IC)测试。     

不同预制裂缝方法及长度对岩石三点弯曲试验的影响

为选择岩石三点弯曲试验合适的预制裂缝方法和裂缝长度以获得相对准确可靠的岩石I型断裂韧度K_(IC),并了解岩石三点弯曲宏观断裂过程和细观断裂特征,采用线切割、锯片切割和水刀切割3种方法预制花岗岩和大理岩三点弯曲梁试样直切槽裂缝,以研究不同预制裂缝方法对岩石K_(IC)的影响,结合场发射扫描电镜比较了不同切割方法岩样的细观断裂特征,试验结果表明线切割方法对岩石K_(IC)测试结果的影响最小。另对含无量纲裂缝长度0.1、0.2、0.3、0.4和0.5的花岗岩及大理岩试样进行试验测得岩石K_(IC)随裂缝长度增加呈先增大后减小的趋势,建议使用a=0.3的裂缝长度进行试验以得到有代表性的岩石K_(IC)值。岩样破坏宏观上经历变形局部化带萌生、局部化带发展、裂纹起裂、最终扩展断裂的过程,声发射过程显示岩样破坏的脆性特征明显,裂缝开口位移与声发射累计曲线趋势一致,可视为试样内部破坏发展过程的宏观表征。     

测定原状粘性土渗透系数的渗透固结仪已投入使用

渗透系数(K)是一个重要的水文地质参数。近年来,随着科学的发展,对地面沉降、越流补给等问题的研究逐步深入,人们越来越感到了解原状粘性土渗透系数的重要性。以往求解越流系数(B=K/M),一般采用抽水试验方法,但误差往往较大。近两年来,我系“渗透固结实验室”采用了张人权、曹文炳等讨论设计的渗透固结仪,通过试验,能够较好地测定原状粘性土的渗透系数。我们利用这种仪器已为河北地质九队、山西水文一队等测试了一些原状粘性土的渗透系数,一般亚矿土、亚粘土渗透系数在10~(-6)~10~(-7)(cm/sec)之间,粘土可达10~(-9)(cm/sec)。     

往返荷载下粘性土的强度及取值标准试验研究

通过对粘性土进行一系列动三轴试验，测定并分析了动荷载作用下为粘性土的动剪应力，轴向应变及超孔隙水压力随时间的变化规律，分析了破坏时不同固结比的粘性土对静，动剪强度和孔隙水压力影响规律，得出了粘性土的动剪强度随固结比变化的关系式，并对粘性土的动剪强度判别方法的标准进行探讨，得出了有益的结果。     

对“新近沉积粘性土”的一些看法

土的工程性质与其生成年代、形成方式和后期的演变条件有关,一般说来,同一成因类型的土具有某些相近的工程特性.根据土的特性,在总结了大量实际资料的基础上,《工业与民用建筑工程地质勘察规范》(TJ21-77规范)[1]将粘性土按其堆积年代划分为三大类.第四纪晚更新世(Q_3)及其以前沉积的粘性土定为老粘性土,全新世(Q_4)沉积的粘性土     

筑坝土料不饱和(三轴UU)非线性弹性参数与反复荷载模量K_(ur)的测定

本文根据小浪底项目组中美联合设计组提出的要求,选用小浪底筑坝土料中具有代表性的重粉质壤土和中粉质壤土,进行非饱和土三轴UU非线性弹性参数和反复荷载模量K_(ur)测定,为小浪底大坝稳定分析提供了所需的计算参数。还进一步探讨了湿度对反复模量K_(ur)的影响,在周压力σ_3=29.4MPa下,试样中含水量增加3—4％的中粉质壤土、重粉质壤土模最E_(ur)分别降低20—51％。     

无定形态游离氧化铁脱水老化对粘性土物理性质的影响

无定形态游离氧化铁以其自身的特性及其脱水老化作用,对粘性土的物理性质、水理性质乃至工程性质产生了一定程度的影响。本文就粘性土的物理性质、水理性质及力学性质在无定形态游离氧化铁脱水过程中的变化进行了初步研究,期望对粘性土的土工测试方法及参数的合理测定有所裨益。     

徐州市市区岩土体工程地质特征研究

徐州市区岩体可分碎屑岩(碎屑硬质岩、碎屑软质岩)及碳酸盐岩(碳酸盐岩碎屑岩硬质与软质岩互层、碳酸盐岩硬质岩)。土体可分为砂土类、粉土类和粘性土(新粘性土、老粘性土)。根据各类土体物理力学性质的分析可知,基岩和老粘土一般可作为高层建筑持力层。一般砂土、粉粘土、粉土等可作一般建筑物地基。对易液化的砂性土、淤泥质软土则需做一定的地基处理。     

冻土断裂韧度KIC的测试研究

应用断裂力学理论，参照有关的测试方法，制作三点弯曲试样，对冻土的断裂韧度ＫＩＣ进行了实验测试，结果表明，含水量、温度及加载速度等是影响ＫＩＣ值的主要因素，通过对试验数据的分析处理，获得ＫＩＣ与主要因素之间的定量表达式。     

Linear Elastic and Cohesive Fracture Analysis to Model Hydraulic Fracture in Brittle and Ductile Rocks

Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern–Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone effect on the ductile rock fracture.     

压实黏土的脆性断裂模型及有限元算法

利用弥散裂缝理论,提出了压实黏土拉伸状态下的脆性断裂模型.当压实黏土达到其极限抗拉强度后,通过建立单元的各向异性刚度矩阵,将土体裂缝弥散于实体单元,构造了平面应变条件下考虑压实黏土脆性开裂的有限元计算模式.通过对某压实黏土单轴拉伸试验成果的模拟计算,验证了构建的脆性断裂模型和有限元算法对土体拉伸破坏特性和裂缝发展过程的适用性.本文还进行了模拟软弱面水压“楔劈效应”的简单数值试验,表明压实黏土脆性开裂模型和算法可较好地模拟裂缝扩展行为.     

冰煤断裂韧度的测试研究

通过对冰煤在-30℃低温状态下的断裂韧度K_IC的测试试验, 得出了在不同预制裂纹长度条件下冻结煤体的断裂韧度变化情况. 试验中制备了三点弯曲试样并制作了低温环境下的三点弯曲实验装置, 对冰煤的试样制备、试验装置、 K_IC计算公式以及裂纹尖端塑性区的大小等断裂力学问题进行探讨, 并且对试样尺寸的有效性进行了验证. 结果表明, 断裂韧度K_IC与裂纹深度a/W的变化方向相反, a/W越大, K_IC越小, 此时裂纹越易开裂.     

层理面特性对砂岩断裂力学行为的影响研究

层理弱面对层状岩石的力学特性影响较显著，为了研究层理面特性对岩石断裂力学特性的影响，开展了具有不同层理方向的砂岩试样三点弯试验，探讨了砂岩断裂韧度及断裂模式的各向异性。之后基于有限元中的黏聚单元建立了数值模型，采用数值模拟方法研究了层理面强度对各层理角度试样断裂力学行为的影响规律。结果表明：层理方向影响下砂岩的断裂韧度及模式存在各向异性；同一层理方向试样的断裂韧度随层理面强度的增大而增大，且试样的层理面与加载方向夹角越小，断裂韧度受层理面强度变化影响越明显；试样的断裂模式不仅与层理面强度有关，还受层理倾角的控制，层理面与加载方向夹角θ = 0o试样断裂模式基本不受层理面强度影响，θ = 30o试样主要沿层理面张拉或剪切破坏，且沿层理面的破裂长度随层理面强度的降低逐渐增大；层理面强度较大时，θ = 45o试样主要沿层理面张拉破坏，θ = 60o～90o试样主要以贯穿层理的张拉破坏为主；层理面强度较小时，θ = 45o～90o试样均以沿层理面的剪切破坏为主，其中θ = 45o试样沿层理剪切长度最大。另外，通过数值模拟结果分析了层理面强度及方向对试样的起裂角及裂纹扩展路径产生的影响。该研究成果可作为层状岩石断裂力学理论的有益补充。     

有机组分土-水分配系数的确定(英文)

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi     

Numerical modelling of a field soil desiccation test using a cohesive fracture model with Voronoi tessellations

Numerical modelling of a field soil desiccation test is performed using a hybrid continuum-discrete element method with a mix-mode cohesive fracture model and Voronoi tessellation grain assemblages. The fracture model considers material strength and contact stiffness degradation in both normal and tangential directions of an interface. It is found that the model can reasonably reproduce the special features of the field soil desiccation, such as curling and sub-horizontal crack. In addition, three significant factors controlling field desiccation cracking, fracture energy, grain heterogeneity and grain size are identified.     

Lagrangian meshfree particles method (SPH) for large deformation and failure flows of geomaterial using elastic–plastic soil constitutive model

Simulation of large deformation and post‐failure of geomaterial in the framework of smoothed particle hydrodynamics (SPH) are presented in this study. The Drucker–Prager model with associated and non‐associated plastic flow rules is implemented into the SPH code to describe elastic–plastic soil behavior. In contrast to previous work on SPH for solids, where the hydrostatic pressure is often estimated from density by an equation of state, this study proposes to calculate the hydrostatic pressure of soil directly from constitutive models. Results obtained in this paper show that the original SPH method, which has been successfully applied to a vast range of problems, is unable to directly solve elastic–plastic flows of soil because of the so‐called SPH tensile instability. This numerical instability may result in unrealistic fracture and particles clustering in SPH simulation. For non‐cohesive soil, the instability is not serious and can be completely removed by using a tension cracking treatment from soil constitutive model and thereby give realistic soil behavior. However, the serious tensile instability that is found in SPH application for cohesive soil requires a special treatment to overcome this problem. In this paper, an artificial stress method is applied to remove the SPH numerical instability in cohesive soil. A number of numerical tests are carried out to check the capability of SPH in the current application. Numerical results are then compared with experimental and finite element method solutions. The good agreement obtained from these comparisons suggests that SPH can be extended to general geotechnical problems. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of pumping parameters in fluid‐driven fractures in weak porous formations

In this work, we investigate the main pumping parameters that influence a fluid‐driven fracture in cohesive poroelastic and poroelastoplastic weak formations. These parameters include the fluid viscosity and the injection rate. The first parameter dominates in the mapping of the propagation regimes from toughness to viscosity, whereas the second parameter controls the storage to leak‐off dominated regime through diffusion. The fracture is driven in weak permeable porous formation by injecting an incompressible viscous fluid at the fracture inlet assuming that the fracture propagates under plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory. Pore fluid movement in the porous formation is based on the Darcy law. The coupling follows the Biot theory, whereas the irreversible rock deformation is modeled with the Mohr–Coulomb yield criterion with associative flow rule. Fracture propagation criterion is based on the cohesive zone approach. Leak‐off is also considered. The investigation is performed numerically with the FEM to obtain the fracture opening, length, and propagation pressure versus time. We demonstrate that pumping parameters influence the fracture geometry and fluid pressures in weak formations through the viscous fluid flow and the diffusion process that create back stresses and large plastic zones as the fracture propagates. It is also shown that the product of the propagation velocity and fluid viscosity, µv that appears in the scaling controls the magnitude of the plastic zones and influences the net pressure and fracture geometry. These findings may explain partially the discrepancies in net pressures between field measurements and conventional model predictions for the case of weak porous formation. Copyright © 2014 John Wiley & Sons, Ltd.