Modelling of blast-induced damage in tunnels using a hybridfinite-discrete numerical approach

This paper presents the application of a hybrid finite-discrete element method to study blast-induceddamage in circular tunnels. An extensive database of field tests of underground explosions above tunnelsis used for calibrating and validating the proposed numerical method; the numerical results areshown to be in good agreement with published data for large-scale physical experiments. The method isthen used to investigate the influence of rock strength properties on tunnel durability to withstand blastloads. The presented analysis considers blast damage in tunnels excavated through relatively weak（sandstone） and strong （granite） rock materials. It was found that higher rock strength will increase thetunnel resistance to the load on one hand, but decrease attenuation on the other hand. Thus, undercertain conditions, results for weak and strong rock masses are similar.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

加锚固体的三维复合单元模型研究

首先提出了复合单元的概念，然后将其应用于建立砂浆固结锚杆的分析模型。该模型考虑了岩体、砂浆、锚杆、岩体/砂浆接触面，砂浆/锚杆接触面等多重介绍，借助阶谱的概念，复合单元可以纳入常规有限单元法分析中去，当某单元不含锚杆时，即退化为常规有限单元。应用该模型进行加固布设优化分析，当单元内锚杆的数量与方向改变时，计算网格无需变化，从而为大规模三维复杂结构计算分析的前处理提供较大便利，模型在有限单元软件CORE3中实现，并提供了计算实例。     

裂隙岩体稳定/非稳定渗流数值模拟

 发展裂隙岩体稳定/非稳定的渗流数值模型,一方面,依照裂隙面的密度、产状、位置、大小和开度的统计分布规律,使用蒙特卡罗模拟技术将完整岩石切割为三维不规则块体集合。根据相邻块体单元间产生的裂隙单元,构建三维裂隙网络系统,并附加各裂隙单元的水力特性;另一方面,对裂隙单元进行三角形单元的有限元网格划分,运用变分原理导出裂隙单元的渗流有限元求解方程。采用离散元方法中的动态松驰技术,在无须组装整体渗透矩阵的情况下求解裂隙网格各结点的水头值。最后,通过典型算例验证程序的可靠性及适用性。     

Preliminary analysis of the dynamic interaction between Norra Länken and a subway tunnel for Stockholm, Sweden

A large infrastructure project called “Ring road Around Stockholm” is presently being planned. A large proportion of the roads will be constructed underground. All kinds of hazardous materials; even explosive gases and liquids, will be allowed to be transported. At Roslagstull, which is located at the northern boundary of the city, five underground road tunnels will cross over an existing subway tunnel, with only about 3 m of rock between them. A scenario in which a truck loaded with explosive gas or liquid starts to leak and then explodes has been proposed by Stockholm's Street and Traffic Administration. Consequently, the effect on rock and the reinforcement surrounding the subway tunnel must be evaluated. This paper presents the results of a study based on two-dimensional distinct element modelling of the rock mass and reinforcement response to a load caused by an exploding truck as described above. Two different assumptions regarding the explosion load have been simulated—namely, static load and fully dynamic load. The study (i) provides general information about the rock mass and reinforcement response for a specific assumption regarding the rock mass conditions, and (ii) compares the results from the two different assumptions regarding the representation of the explosion load. Both unreinforced and reinforced conditions have been modelled for each loading condition (i.e., a total of four models). The results indicate that for the unreinforced models, the differences in the model response are not dramatic when compared to the models with static and dynamic representation of the explosion load. On the other hand, the reinforced models indicate major differences, particularly in the reinforcement response. All numerical analyses presented in this paper were performed using the two-dimensional distinct element code UDEC (Itasca 1992).     

2D and 3D finite element analysis of underground openings in an inhomogeneous rock mass

The finite element analysis of the underground openings excavated for Koyna hydroelectric project, Maharashtra, India, has been conducted. 2D and 3D models have been developed assuming that the rock mass obeys Drucker–Prager failure criterion. The computed deformations and the stress distribution, around these openings, have been compared with the in situ measurements. The study reveals that the 2D elasto-plastic analysis underestimates the deformations. On the other hand, the 3D elasto-plastic analysis yields results, which compare reasonably well with the in situ measurements. The effect of weak zones in the rock mass and creation of multiple cavities in the nonhomogeneous rock mass has also been considered in the analyses. Such a study is found to be very helpful for evaluating the stability of underground openings when extensive realistic input data is available for nonhomogeneous rock mass.     

岩体尺寸效应及其特征参数计算

 岩体的尺寸效应包括完整岩块的尺寸效应与节理岩体的尺寸效应,但两者之间还缺乏有机联系。基于物理力学试验与细观参数统计分布理论,建立试样尺度的随机概率模型。通过统计宏观节理分布,建立包含随机分布节理的岩体尺度模型。将实验室获得的岩块强度应用于岩体的计算中,提出一种从细观层次、宏观层次的多尺度岩体工程计算方法,建立2种尺度效应的联系。最后,就非均匀性、围压与节理密度对岩石尺寸效应的影响问题展开探讨。随着均值度的增加,试样的特征尺度逐渐减小。随着围压的增大,岩体特征强度逐渐增大,而岩体力学参数的特征尺寸增大不明显。随着节理密度的增大,特征尺寸和相应的特征强度都是减小的。本方法试图建立细观与宏观力学参数之间的桥梁,获得岩体计算的力学参数,为解决工程岩体参数取值与计算提供一条思路。     

裂隙岩体渗流应力耦合机制研究

隧洞开挖前,岩体中的地下水与围岩应力处于一种相对平衡状态,由于隧洞的开挖,一方面使地下水排泄有了新的通道,加速了水循环,破坏了原有的补给一运移一排泄系统的平衡;另一方面,造成围岩应力重分布,部分结构面由于增压而闭合,部分岩体卸荷松弛或产生剪切滑移,人为破坏了原有的地下水渗流条件,使得隧洞自身成为地下水向外排泄的地下廊道...     

含复杂裂隙网络岩体渗流特性研究的复合单元法

研究含复杂裂隙网络岩体渗流特性的复合单元法，该方法首先利用蒙特卡罗方法随机生成符合给定概率分布特征的复杂裂隙网络；然后通过叟切和拓扑运算将各裂隙段置于常舰有限单元内部，形成内含由多个裂隙段分划而成的子单元的复合单元，根据推导的公式计算渗流场进而分析岩体的渗透特性。该方法具有以下几个主要特点：（1）可与传统的有限冗法融合;（2）可考虑每条裂隙的具体位置、产状、开度、长度和渗透性质；（3）可考虑岩石的渗透性及其与裂隙间的流量交换；（4）可计入不连通裂隙对渗流场的影响；（5）复合单元的拓扑信息由裂隙网络与常规有限单元边界的交切及其单元内部裂隙段的相互交切面生成，由于先没有考虑裂隙，故复合单元前处理简单。用复合单元法分析含复杂裂隙嘲络岩体的渗流行为及其渗流特性是一种新的数值模拟手段。算例分析表明该方法的可行性和有效性。     

不连续岩体温度场的复合单元模型初步研究

 基于复合单元法原理和不稳定温度场的隐式解法,提出针对不连续岩体温度场的复合单元法。该算法的特点是每个复合单元可以含有任意的不连续面,如断层或节理,且当结构中含有需在计算中离散处理的不连续面时,网格的生成不受不连续面的数量、位置和方向的影响。初步研究针对含1条节理的复合单元模型展开,假定岩块中无对流和辐射影响,推导岩块子单元和不连续面的热传导计算式,得到不连续岩体温度场的复合单元算法基本方程组,然后将该算法整合到传统有限元分析程序中。分别采用传统有限单元和复合单元法模拟热水流过单条裂隙时岩体温度场的变化过程,二者的计算结果非常接近,表明不连续岩体温度场的复合单元算法是合理和有效的,但其配套的温度场等值线后处理程序有待进一步完善。该算法的提出为深部岩体的多场耦合研究提供又一思路。     

Three-dimensional nonlinear analysis for the coupled problem of the heat transfer of the surrounding rock and the heat convection between the air and the surrounding rock in cold-region tunnel

According to the basic theories of heat transfer, geocryology and fluid mechanics, taking the coupled problem of the heat transfer of the rock surrounding the tunnel and the heat convective between the air in the tunnel and the rock surrounding the tunnel into account, three-dimensional calculating model of the coupled problem are presented. The finite element formulae of this problem are obtained by Galerkin’s method, and the computer program of the finite element is compiled. Using the program, three-dimensional nonlinear analyses for the coupled problem of the heat transfer of the rock surrounding the tunnel and the heat convective between the air in the tunnel and the rock surrounding Fenghuo mountain tunnel on the Qinghai–Tibet Railway are made. The agreement between the calculated results and the in-situ observed data is seen to be very good. The calculated results illustrate that the freezing–thawing situation of the rock surrounding the tunnel can correctly be predicted even if the air temperature distribution along the tunnel is unknown. In thus way, the large cost of in-situ observation for the air temperature in the tunnel can be saved.     

Composite element method for the bolted discontinuous rock masses and its application

This paper presents a composite element method (CEM) for discontinuous rock masses reinforced by fully grouted bolts. This element allows one to generate mesh without considering exactly the existence of bolts and joints, which further allows for an important simplification in the pre-process work. The sub-elements of rock, grout, bolt, joint, rock/grout interface and bolt/grout interface are defined using corresponding mapped nodal displacements at the composite element. The mapped nodal displacements can be determined using the governing equations established by means of the virtual work principle. Based on the mapped nodal displacements deformation and stress in each sub-element can be further obtained. The comparative study of the CEM and the conventional finite element method (FEM) has been carried out for the preliminary verification example. The numerical study for the rock bolt crane girder of an underground powerhouse by FEM and CEM is presented as the engineering application example, in which the attention has been paid to the portion of the contact face between the girder and surrounding rock masses, the contact faces between the bolts and surrounding rock masses, as well as to the portion where the rock bolt penetrates the contact face. The comparative and application studies show the validation and advantages of the CEM.     

岩体工程有限元分析中弱面的力学模型——弱面单元分析

本文较系统地讨论了模拟岩体弱面的等厚度四节点弱面单元,着重分析了岩体转动对弱面单元的影响。并指出:即使弱面厚度很小,但只要弱面产状处在不太有利位置,或绕弱面单元端点转动,都会给单元剪应力从正或负的方面带来很大影响,甚至改变单元由滑动所产生的剪应力的符号。文中详细的推导了考虑转动影响的弱面单元的几何矩阵[B]~e、单元应力矩阵[S]~e、单元刚矩度阵[K]~e以及单元初始应力所引起的等效结点荷载等计算公式。文中还证明了古德曼节理单元是等厚度弱面单元的一种特殊情况--即δ/l趋于零的情况.     

含锚杆钻孔线单元的3D-FSM·DDM 边界元数值系统开发

 为了将已开发的3D-FSM·DDM边界元数值系统应用于新奥法施工中锚杆支护之类的实际问题,在原数值系统的基础上,尝试开发了含锚杆线单元的三维边界元数值系统。其基本思路是,首先使锚杆单元和与之重合的锚杆钻孔单元始终点的位移差相等;其次,将全长黏结式锚杆钻孔单元简化成线单元,并且根据Kelvin基本解求其锚杆线单元的影响系数;最后与自由单元一并考虑并进行耦合,形成求解同一个模型边值问题的三维边界元数值系统。     

基于离散元方法的PDC钻头破岩仿真研究

针对前人对PDC(聚晶金刚石复合片)钻头破岩仿真研究多采用有限元法,忽略了岩体的各向异性、不均匀性以及不连续性等问题。提出了采用离散元法来研究PDC钻头的破岩仿真过程,利用离散元软件PFC3D建立了虚拟单轴压缩实验和虚拟巴西劈裂法实验,推导出了岩石的三维离散元模型的细观参数,确定了岩石的本构模型。在此基础上建立了PDC单齿切削岩石的离散元模型,讨论了侧倾角对切削力的影响关系,并与单齿切削岩石的有限元模型进行了对比。结果表明:离散元模型与有限元模型结果比较接近,离散元数值模拟的求解时间为有限元数值模拟的1/3,离散元方法具有潜在的高效率。在单齿切削岩石的离散元模型的基础上建立了全钻头破岩离散元模型,研究了PDC钻头动态破岩过程中各切削齿所受扭矩和钻压的分布规律。并通过全钻头破岩室内台架实验对模型的准确性进行了验证。     

刚体离散元动力方法在基于位移的岩坡地震响应分析中的应用

当前岩坡地震动力响应分析中,多采用极限平衡方法分析拟静力安全系数,采用Newmark滑块分析动力永久位移,假设较多,工程实用性受限。将刚体离散元方法引入岩坡地震动力稳定性评价工作中。通过与强度折减法、Newmark法中的永久位移评价相结合,提出一种复杂岩坡静动力稳定性分析方法。初步认识表明:(1)采用极大节理刚度可以减少节理刚度带来的弹性接触位移,使得刚体离散元用于求解岩坡楔形块体的静/动力稳定性问题。(2)刚体离散元强度折减法可以无需假设块体运动方向或假定滑动形式,直接求解获取安全系数、下滑力等结果,可以考虑复杂形状块体,相比传统方法更具优势和实用性。(3)与4个经典静力算例与3个动力算例的对比验证,表明提出的刚体离散元方法及程序实现的正确性。(4)采用提出的方法,研究幅值、节理面交线倾角等参数对岩坡地震响应永久位移的影响规律研究,表明刚体离散元方法可以根据参数变化得到正确的得到相应的结果变化规律。且对比发现在某些特定条件下拟静力安全系数不能正确反映岩坡地震响应的陡增程度。(5)在工程实例中,采用刚体离散元方法进行K1块体基于位移的地震稳定性评价,给出基于超越概率的支护设计方案。相比拟静力安全系数设计方案,在满足使用条件的前提下优化程度更高。研究可为岩坡静动力稳定性分析提供一种新的思路。     

A 3D FEM methodology for simulating the impact in rock-drilling hammers

A three-dimensional (3D) finite element approach for modeling impact as it occurs in impact tools used in rock drilling is presented. The model permits one to simulate the energy transmission to the rock, the bit–rock interaction, and the process of rock fragmentation, all of which are important in the study and evaluation of such tools. The finite elements method (FEM) analysis allows one to simulate the impact in 3D stress–strain problems, to consider linear material properties, and to include post failure fracture propagation. Anisotropic elements have been used to model the rock post failure behavior. Infinite domain elements have been used to characterize boundary conditions far away from bit–rock interaction. The accuracy of the model has been evaluated both theoretically by comparing the result to those obtained with a model based on impulse–momentum principle as well as experimentally.     

Modification of thermo-elasto-viscoplastic model for soft rock and its application to THM analysis of heating tests

In deep geological disposal for high level radioactive waste, one of the most important factors is to study the thermo-hydraulic-mechanical (THM) behavior of the natural barrier, usually a host rock, during the heat process and hydraulic environment change. In this paper, a thermo-elasto-viscoplastic model proposed by Zhang and Zhang (2009) is firstly modified by adopting the t_ij concept (Nakai and Mihara, 1984) so that the influence of intermediate stress can be properly considered. The performance of the modified model is confirmed with drained triaxial compression tests and creep tests on soft sedimentary rock and manmade soft rock under different temperatures. Based on the modified model, a program called ‘SOFT’, using the finite element method (FEM) and the finite difference method (FDM) in the soil–water–heat coupling problem, has been developed to simulate the aforementioned THM behavior of geological materials. In order to verify the applicability of the program, an isotropic element heating test for soft rock under drained condition with different initial overconsolidation ratio (OCR), is firstly simulated by the proposed THM FE-FD program. In the test, the thermal volumetric change was found to be dependent on OCR. The simulated results show that the THM phenomenon observed in the laboratory test can be explained by the proposed numerical method. Meanwhile, a real-scale field heating test reported by Gens et al. (2007) is also simulated by the same THM FE-FD program. The material parameters of the rock involved in the constitutive model are determined based on the element tests for the rock in the laboratory. It is shown that the simulated results agreed well with the test results such as the time change of the temperature, the excess pore water pressure (EPWP) and the heat-induced strain.     

Engineering geological evaluation and preliminary support design for the metro extension tunnel,Ankara, Turkey

The paper reports an assessment of the engineering geological characteristics of the rock mass to be encountered between Mecidiye and Gazino stations on the new extension of the Ankara metro and the determination of appropriate support and excavation methods. The rock mass quality was estimated using the rock mass rating (RMR), geological strength index (GSI) and rock mass quality (Q) systems and the tunnel divided into sections. The RMR, Q and NATM systems were used to determine the support and excavation methods in these areas. The deformations and stress concentrations around each tunnel section were investigated and the interaction of the support systems with the rock mass was analyzed using finite element software. It is concluded that rock mass classification systems should be used in tandem with numerical tools, although it is emphasized that the estimation of rock mass properties is not an exact science and both rock properties and numerical models should be refined based on observations and the results of instrumentation installed during the construction of a tunnel.      

Effect of interface adhesion factor on the bearing capacity of strip footing placed on cohesive soil overlying rock mass

The problem related to bearing capacity of footing either on pure soil or on pure rock mass has been investigated over the years. Currently, no study deals with the bearing capacity of strip footing on a cohesive soil layer overlying rock mass. Therefore, by implementing the lower bound finite element limit analysis in conjunction with the second-order cone programming and the power cone programming, the ultimate bearing capacity of a strip footing located on a cohesive soil overlying rock mass is determined in this study. By considering the different values of interface adhesion factor (α_cr) between the cohesive soil and rock mass, the ultimate bearing capacity of strip footing is expressed in terms of influence factor (I_f) for different values of cohesive soil layer cover ratio (T_cs/B). The failure of cohesive soil is modeled by using Mohr−Coulomb yield criterion, whereas Generalized Hoek−Brown yield criterion is utilized to model the rock mass at failure. The variations ofI_f with different magnitudes of α_cr are studied by considering the influence of the rock mass strength parameters of beneath rock mass layer. To examine stress distribution at different depths, failure patterns are also plotted.     

基于微观矿物含量的灰岩细观参数标定研究

随着对岩体力学研究的深入,宏微观岩体力学的研究方法发展迅速。但岩体微观性质改变对引起岩体宏观力学各向异性行为的影响研究却较为缺乏,而在离散元分析方法中,岩体宏观力学行为的准确表征不仅需要合理的细观强度参数,也需要考虑岩体中微观矿物的成分和含量。以灰岩为研究对象,制作灰岩薄片标本,用偏光显微镜观察灰岩样本以确定矿物成分及含量,并以此为依据生成基于矿物含量的离散元模型,以接触软化接触模型模拟矿物间的细观力学行为。分别建立与室内试验对应的单轴压缩模型和巴西劈裂模型,使用试错法不断调整细观强度参数,最终使细观模型表现出的宏观力学性质与实际情况一致。研究结果表明,数值模拟得到的宏观参数与室内试验结果相吻合,说明基于微观矿物含量的岩体离散元模型参数标定方法能够很好地标定出颗粒的细观强度参数,同时细观强度参数又能够很好地表征岩体宏观力学强度,以该参数作为岩体力学响应分析的输入参数,能够更准确认识岩体的力学行为。