爆炸作用下岩石破裂块度分布特点及其物理机理

就岩石在爆炸载作用下破坏块度分布的物理机理进行了分析。从分析可以看出,岩石破坏块度的对数正态分布与材料的多重破坏有关。在封闭爆炸情况下这种分布描述爆心附近岩石破坏块度的分布,此处材料处于静水压力状态,应变率很高,材料的破坏为多重破坏。而Rosin-Rammler分布主要描述离爆心较远处岩石破坏的块度分布,此处岩石的破坏主要是由环向拉力引起的径向裂纹所致,以单重破坏为主。     

初始地应力对隧洞开挖爆生裂隙区的影响研究

隧洞开挖过程中控制爆炸对岩体的损伤,减小爆破裂隙范围,对保证工程安全具有重要意义。基于爆炸应力波作用下爆生裂隙形成机制的研究,采用摩尔-库仑准则及最大拉应力准则,研究了初始地应力对爆炸应力波作用下爆生裂隙区比例半径的影响。研究结果表明,初始地应力对爆生裂隙范围有显著影响。在压剪破坏模式下,爆生裂隙区比例半径随地应力的增大而减小,地应力侧压系数影响爆生裂隙区比例半径在洞壁圆周的分布。考虑围岩应力卸荷影响后,沿隧洞径向的爆生裂隙区比例半径比不考虑卸荷的小。拉伸破坏导致的岩体爆生裂隙区比例半径一般比压剪破坏模式下爆生裂隙比例小,爆炸应力波作用下隧洞围岩更容易沿结构弱面发生压剪破坏。     

新型锚固类结构抗爆性能数值分析

采用LS-DYNA有限元软件,对分别使用单一锚固结构和新型复合锚固类结构加固的洞室在抗爆炸荷载作用下的性能进行了数值模拟。分析了在爆炸条件下应力波传播及爆坑形成过程、爆炸近区围岩中的压力波和复合锚固结构构造措施断裂缝形成过程,与试验结果的可靠性相互验证,并对其作用机理得出一些初步认识。结果表明：两个模型的计算爆坑大小与试验结果基本吻合;复合锚固构造措施段使得锚固区外的介质内出现了局部自由面,当爆炸应力波经过自由面时产生反射拉伸波在此处产生了裂缝;复合锚固结构洞室拱顶垂直向振动加速度峰值比单一锚固结构洞室的约小23.7 %;单一锚固结构洞室比复合锚固结构洞室更容易出现结构性的冲切破坏和拉伸剥落破坏。     

土-结爆炸冲击相互作用模爆试验相似设计方法

模爆试验是研究爆炸冲击荷载作用下地基动力性能、土-结爆炸冲击相互作用及埋地防护结构抗爆能力与破坏机理等的重要手段之一。模型相似设计是确保模爆试验能够尽可能真实地反映原型爆炸冲击动力性状的关键之一。以上覆饱和砂土层对浅埋地下圆拱直墙式防护隧道免遭炸弹触地爆炸触发地冲击波破坏的保护效应为研究目的,基于目前广泛应用的Bockinghamπ定理,采用量纲分析方法,并且结合考虑土-结体系非线性爆炸冲击动力响应、土-结接触面爆炸冲击动力响应以及爆炸地冲击波-结构动力相互作用等的相似性,求解土-结爆炸冲击相互作用模爆试验的模型设计相似关系。     

深隧道围岩稳定性的数值模拟与模型试验研究

在大型真三轴模型试验机上进行隧道的超载试验,试验过程中采用内窥摄影实时监测试件的破坏演化全过程,确定了高应力条件下隧道的变形特征和裂纹演化特征;采用应变测量技术对隧道关键部位的应变值进行了测量,据此分析了围岩体的应力变化规律。针对相似材料的力学特性,建立了应变软化模型,采用与模型试验相同的边界条件进行了数值模拟分析,对围岩体的塑性应变变化过程和应力场进行了研究。结果表明,两种手段反映的破坏演化过程是基本吻合的,所反映的围岩体应力变化规律也是一致的。     

岩土材料不同应力路径下脆性变化的二元介质模拟

试验研究表明,岩土材料在加卸荷时表现出不同的变形破坏特性,卸荷时脆性增加。建议了一个可以描述材料脆性变化的脆性指数 ,并验证了B指标能较好地描述岩土材料在加卸荷时的脆性变化。应用二元介质模型,对岩样在卸载周围应力过程中的应力-应变关系进行了模拟,表明这一模型不但可以模拟岩样在低围压下的应变软化到高围压下的应变硬化现象,而且可以模拟岩样在卸载周围应力过程中的变形破坏过程,特别是对于表现为应变软化的岩样,可以反映出应力峰值前后卸围压时的变形破坏过程的差别。     

泡沫混凝土隧道减震层减震机制

基于泡沫混凝土隧道减震材料,通过室内试验研究了不同密度、围压、应变率条件下泡沫混凝土材料的力学特性。试验结果表明：随着密度的增加,试样的单轴破坏形态由骨架坍塌破坏逐渐转化为劈裂剪切破坏,峰后应变软化与材料脆性增强;随着围压的增加,材料强度增加且延性增强,峰后由应变软化逐渐转换为应变硬化。在中等应变率范围内（10?5/s ～10?3/s）,随着应变率的增加,泡沫混凝土材料的强度近似呈指数增长,同时峰后残余应力增长明显,且塑性应变越大,应变率对峰后应力的影响越大。基于上述试验结果初步建立了泡沫混凝土材料的本构模型。依托嘎隆拉隧道,采用数值方法研究了减震层剪切模量、厚度及减震层-衬砌界面特性3个因素对减震效果的影响规律,相关研究成果可为高烈度区隧道工程减震层的设计提供参考。     

动载作用下岩石类材料破坏模式及能量特性

对岩石类材料的破坏模式和能量特性进行分析研究,利用ANSYS/LS_DYNA数值模拟软件模拟SHPB冲击的整个过程。通过对试验和数值模拟所得测试曲线进行对比确定模型的有效性,进而分析试件中有效应力的传播过程,提出试件张应变破坏、轴向劈裂拉伸破坏、压碎破坏的3种破坏模式;通过对数值模拟所得试件的内能-时间历程分析表明,试件的内能具有显著的应变率效应,在应变率较低时,可以划分为2个阶段,而在应变率较高时,可以划分为4个阶段。     

基于SPH-FEM耦合法的土体爆炸效应数值研究

岩土体爆炸破坏问题是岩土工程领域的研究热点,为开展小当量集团装药在不同埋置深度时的土中爆炸效应分析研究,在LS-DYNA框架内建立基于光滑粒子流体动力学-有限元耦合方法（SPH-FEM）的砂土地基爆炸效应分析模型。计算结果表明：浅埋装药时最大爆坑深度到达时刻远在最大爆坑直径之前,地基表层砂土体剪切流场对爆坑直径的发展具有决定性作用;随着药包埋置深度的增加存在一个临界爆坑直径,爆坑直径近似认为只与药包当量和埋置深度相关,经简化与经验假定之后得到的爆坑直径与埋药深度之比与比例距离近似呈直线关系;砂土中爆炸波在近区表现为强间断的冲击波形式,压缩作用是造成近区砂土大变形流动的主要因素,而在爆炸远区则转变为连续的应力波形式;土中爆炸波峰值压力随比例爆距的衰减规律与经验曲线基本一致。研究结果可以为地基工程的抗爆设计及加固提供参考。     

模型相似材料内部应变光纤量测应变传递

应用光纤传感技术测量模型相似材料内部应变,必须解决光纤与相似材料耦合的问题。传统的研究中普遍存在应变传递理论分析结果无法通过试验检验的问题。设计实现了一种基于光纤-胶体-相似材料3层应变传递结构的光纤Bragg光栅（FBG）相似材料一维传感器。通过对该传感器应变传递特性和标定方法的研究探索解决光纤与相似材料耦合性的问题。该传感器采用无涂覆层的光纤Bragg光栅作为传感元件,将光纤埋入相似材料应变试件内部直接测量轴向中心应变。通过应变传递理论分析、数值模拟以及全新设计的标定试验研究3种方法研究了该相似材料光栅传感器的应变传递特性。平均应变传递率结果显示3种方法所得到的数值非常接近,表明该传感器的光纤、胶体、相似材料具有良好的耦合性以及应变测量的准确性。该方法为解决模型相似材料内部三维应变测量提供了可行方案。     

Fuzzy-random probabilistic analysis of rock mass responses to explosive loads

This paper addresses the effects of randomness of initial damage in a rock mass and the critical tensile strain of the rock material on its dynamic responses and damage under explosive loads. A fuzzy definition is proposed to describe the fuzzy nature of failure phenomenon in a rock mass. The initial damage of the rock mass is estimated using the longitudinal and transverse elastic wave velocities. By using statistical analysis, the initial damage of the rock mass is found having the Beta distribution. The statistical estimation of a damage state and properties of randomly damaged rock mass are evaluated by the Rosenbluth's point estimate method. In numerical calculation, an isotropic continuum damage model with the initial damage and the cumulative damage dependent on an equivalent tensile strain is suggested to model the rock mass behavior under blast loads. A Beta distribution is proposed to represent the probabilistic distribution of the damage variable of the rock mass under explosive loads. Several types of membership functions are suggested to represent the fuzziness of material failure. Based on the fuzzy–random probabilistic theory, a model including both the effects of randomness and fuzziness is proposed for the failure analysis of rock mass under explosive loads. The suggested models are coded and linked with an available computer program AUTODYN2D through its user's subroutine capacity. The fuzzy failure probability and dynamic responses of the rock mass are calculated. Numerical results are compared with those obtained from independent field tests.     

爆炸应力波对新浇混凝土衬砌的影响研究

爆炸应力波作用下新浇混凝土衬砌的破坏模式及安全振动速度是水电、铁道工程隧洞建设中需要解决的重要问题。根据弹性P波及SV波在介质中的传播规律,讨论了P波及SV波在薄层混凝土衬砌中的传播及近似处理方法,依照莫尔-库仑准则、极限拉应力准则、极限拉应变准则,研究了爆炸应力波作用下新混凝土衬砌的破坏模式及安全振动速度。结果表明,入射应力波及衬砌中的折射波对衬砌的破坏作用最主要,折射波在衬砌内产生的反、折射波将降低衬砌中的应力,具有卸载效果;混凝土衬砌的安全振动速度随着龄期的增大而增大,P波入射时,安全振动速度随着入射角的增大而增大,入射角较大时,胶结面容易发生剪切破坏,较小时,容易发生拉伸破坏,SV波入射时,较小角度下容易发生剪切破坏,较大角度时容易发生拉伸破坏;围岩弹性模量越高,衬砌的安全振动速度越小。     

Two-dimensional dynamic finite element simulation of rock blasting

In the present study, the two-dimensional blast model has been simulated using finite element software Abaqus/CAE. The John–Wilkins–Lee equation of state has been used to calculate the pressure caused by the release of the chemical energy of the explosive. Detonation point from center of hole has been defined for the traveling path of explosive energy. Elastoplastic dynamic failure constitutive with kinematic hardening model was adopted for rock mass responses under high explosive pressure to understand the mechanism of blast phenomena. In this model, it is assumed that failure of rock occurs under tensile failure when yield plastic stress exceeded to its static tensile strength. The hydrostatic pressure was used as a failure measure to model dynamic spall or a pressure cut off. Variation of detonation velocity has been measured in terms of simulation blast output energies index results.     

Analysis of the vane test considering size and time effects

An analysis of the vane test using an Arbitrary Lagrangian–Eulerian formulation within a finite element framework is presented. This is suitable for soft clays for which the test is commonly used to measure in situ undrained shear strength. Constitutive laws are expressed in terms of shear stress–shear strain rates, and that permits the study of time effects in a natural manner. An analysis of the shear stress distributions on the failure surface according to the material model is presented. The effect of the constitutive law on the shear band amplitude and on the position of the failure surface is shown. In general, the failure surface is found at 1–1·01 times the vane radius, which is consistent with some experimental results. The problem depends on two dimensionless parameters that represent inertial and viscous forces. For usual vane tests, viscous forces are predominant, and the measured shear strength depends mainly on the angular velocity applied. That can explain some of the comparisons reported when using different vane sizes. Finally, the range of the shear strain rate applied to the soil is shown to be fundamental when comparing experimental results from vane, triaxial and viscosimeter tests. Appart from that, an experimental relation between undrained shear strength and vane angular velocity has been reproduced by this simulation. Copyright © 1999 John Wiley & Sons, Ltd.     

Simulation of debris flow on an instrumented test slope using an updated Lagrangian continuum particle method

We present an updated Lagrangian continuum particle method based on smoothed particle hydrodynamics (SPH) for simulating debris flow on an instrumented test slope. The site is a deforested area near the village of Ruedlingen, a community in the canton of Schaffhausen in Switzerland. Artificial rainfall experiments were conducted on the slope that led to failure of the sediment in the form of a debris flow. We develop a 3D mechanistic model for this test slope and conduct numerical simulations of the flow kinematics using an SPH formulation that captures large deformation, material nonlinearity, and the complex post-failure movement of the sediment. Two main simulations explore the impact of changes in the mechanical properties of the sediment on the ensuing kinematics of the flow. The first simulation models the sediment as a granular homogeneous material, while the second simulation models the sediment as a heterogeneous material with spatially varying cohesion. The variable cohesion is meant to represent the effects of root reinforcement from vegetation. By comparing the numerical solutions with the observed failure surfaces and final free-surface geometries of the debris deposit, as well as with the observed flow velocity, flow duration, and hot spots of strain concentration, we provide insights into the accuracy and robustness of the SPH framework for modeling debris flows.

     

Modeling Strain Rate Effect of Heterogeneous Materials Using SPH Method

The strain rate effect on the dynamic compressive failure of heterogeneous material based on the smoothed particle hydrodynamics (SPH) method is studied. The SPH method employs a rate-insensitive elasto-plastic damage model incorporated with a Weibull distribution law to reflect the mechanical behavior of heterogeneous rock-like materials. A series of simulations are performed for heterogeneous specimens by applying axial velocity conditions, which induce different strain-rate loadings to the specimen. A detailed failure process of the specimens in terms of microscopic crack-activities and the macro-mechanical response are discussed. Failure mechanisms between the low and high strain rate cases are compared. The result shows that the strain-rate effects on the rock strength are mainly caused by the changing internal pressure due to the inertial effects as well as the material heterogeneity. It also demonstrates that the inertial effect becomes significant only when the induced strain rate exceeds a threshold, below which, the dynamic strength enhancement can be explained due to the heterogeneities in the material. It also shows that the dynamic strength is affected more significantly for a relatively more heterogeneous specimen, which coincides with the experimental results showing that the poor quality specimen had a relatively larger increase in the dynamic strength.     

Effects of open gaps on particle velocity measurements

Summary Joints and bedding planes are present in nearly all geologic media. These discontinuities vary in the extent to which they are open and the material with which they are filled. The presence of such discontinuities affect the ground motions that result from the detonation of an explosive source. The effects of these discontinuities are especially important if it is desired to predict the size of the explosive source from measurements of ground motion — such as particle velocity or stress. In this paper we present results from a series of model tests conducted to investigate the effect of open gaps on the particle velocity that can be transmitted across them. Electromagnetic velocity gages were used to record particle velocities at several locations on either side of an open gap of known width. The study was restricted to the transmission of particle velocities normal to the gap and to the case where the gap was located in a region for which the stress was high but not greatly above the elastic limit of the material. The experimental results were compared qualitatively to results obtained from WONDY — a one dimensional Lagrangian finite difference code. Although the tests were conducted in laboratory models, the results can be scaled to compare to the full scale situation.     

Numerical Analysis of Blast-Induced Stress Waves in a Rock Mass with Anisotropic Continuum Damage Models Part 1: Equivalent Material Property Approach

Summary This paper uses the concept of anisotropic damage mechanics to analyze dynamic responses of a granite site under blasting loads. An anisotropic continuum damage model is suggested to model rock mass behavior under blasting loads. The effects of existing cracks and joints in the rock mass are considered by using equivalent rock material properties obtained from both field and laboratory test data. The anisotropic damage accumulations are simulated by continuous degradation of equivalent material stiffness and strength during loading process and are calculated using the exponential function with respect to the principal tensile strain in three directions. The suggested models are programmed and linked to an available computer program Autodyn3D through its user's subroutine capability. Stress wave propagation and damage zone in the rock mass induced by underground explosions are simulated. Numerical results of damaged area, peak particle velocity and acceleration attenuation as well as acceleration time histories and Fourier spectra are compared with those from independent field tests.     

缓倾角层理各向异性岩体隧道稳定性的物理模型试验研究

层状岩体的广泛分布是地下工程无法回避的现实。以渝湘高速公路共和隧道为工程背景,采用自行研制的弹脆性模型相似材料,制作出层状岩体隧道模型。采用大型真三轴岩土工程模型试验机进行加载试验,采用围岩应变监测、洞室内窥摄影、试件破坏形态的研究与分析,从而对缓倾角层理岩体中隧道的二次应力分布特征及破坏机制进行研究。试验中还通过超载系数,提供了一个安全储备的定量评估指标。试验的破坏特征与隧道实际破坏一致,说明了模型试验的正确性,同时也为顺层偏压隧道的加固机制研究及加固设计提供了试验基础。