Numerical method to determine mechanical parameters of engineering design in rock masses

This paper proposes a new continuity model for engineering in rock masses and a new schematic method for reporting the engineering of rock continuity. This method can be used to evaluate the mechanics of every kind of medium;and is a new way to determine the mechanical parameters used in engineering design in rock masses. In the numerical simulation, the experimental parameters of intact rock were combined with the structural properties of field rock. Theexperimental results for orthogonally-jointed rock are given. The results included the curves of the stress-strain relationship of some rock masses, the curve of the relationship between the dimension Δ and the uniaxial pressure-resistant strength σc of these rock masses, and pictures of the destructive procedure of some rock masses in uniaxial or triaxial tests, etc. Application of the method to engineering design in rock masses showed the potential of its application to engineering practice.

Mechanical response of roof rock mass unloading during continuous mining process in underground mine

Taking the test stopes during continuous mining induced roof caving of Tongkeng ore-body No.92 as example, the calculation flow of unloading analysis was established. According to the unloading region division method of the affected zone theory, and the deterioration laws of mechanics parameters of unloading rock mass, the continuous mining process in underground mine was analyzed by the software MIDAS/GTS, the mechanical response of roof rock mass unloading was studied, and the differences were analyzed with the conventional simulation. The result shows that the maximum tensile stress, subsidence displacement and equivalent plastic strain of roof rock mass are 1.5 MPa, 20 cm and 1.5% in the unloading analysis, while 1.0 MPa, 13 cm and 0.9% in the conventional analysis. The values of unloading analysis, which are also closer to the actual situation, are greater than those of conventional analysis; the maximum step in continuous mining is 48 m, which shows that the induced treatment of the roof should be carried out after 2 mining steps

Determination of rock mass integrity coefficient using a non-invasive geophysical approach

Determination of rock mechanical parameters is the most important step in rock mass quality evaluation and has significant impacts on geotechnical engineering practice.Rock mass integrity coefficient(KV)is one of the most efficient parameters,which is conventionally determined from boreholes.Such approaches,however,are time-consuming and expensive,offer low data coverage of point measurements,require heavy equipment,and are hardly conducted in steep topographic sites.Hence,borehole approaches cannot assess the subsurface thoroughly for rock mass quality evaluation.Alternatively,use of geophysical methods is non-invasive,rapid and economical.The proposed geophysical approach makes useful empirical correlation between geophysical and geotechnical parameters.We evaluated the rock mass quality via integration between KV measured from the limited boreholes and inverted resistivity obtained from electrical resistivity tomography(ERT).The borehole-ERT correlation provided KV along various geophysical profiles for more detailed 2D/3D(two-/three-dimensional)mapping of rock mass quality.The subsurface was thoroughly evaluated for rock masses with different engineering qualities,including highly weathered rock,semi-weathered rock,and fresh rock.Furthermore,ERT was integrated with induced polarization(IP)to resolve the uncertainty caused by water/clay content.Our results show that the proposed method,compared with the conventional approaches,can reduce the ambiguities caused by inadequate data,and give more accurate insights into the subsurface for rock mass quality evaluation.

Advances in statistical mechanics of rock masses and its engineering applications

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.

An Anisotropic Geomechanical Model for Jointed Rock Masses at Taishan Nuclear Power Station, Southern China

An anisotropic geomechanical model for jointed rock mass is presented. Simultaneously with deriving the orthotropic anisotropy elastic parameters along the positive axis, the equivalent compliance matrix for the deflection axis orthotropic anisotropy was derived through a three- dimensional coordinate transformation. In addition, Singh＇s analysis of the stress concentration effects of intermittent joints was adopted, based on two groups of intermittent joints and a set of cross- cutting joints in the jointed rock mass. The stress concentration effects caused by intermittent joints and the coupling effect of cross-cutting joints along the deflection-axis are also considered. The proposed anisotropic mechanics parameters method is applied to determine the deformation parameters of jointed granite at the Taishan Nuclear Power Station. Combined with the deterministic mechanical parameters of rock blocks and joints, the deformation parameters and their variability in jointed rock masses are estimated quantitatively. The computed results show that jointed granite at the Taishan Nuclear Power Station exhibits typical anisotropic mechanical characteristics; the elastic moduli in the two horizontal directions were similar, but the elastic modulus in the vertical direction was much greater. Jointed rock elastic moduli in the two horizontal and vertical directions were respectively about 24% and 37% of the core of rock, showing weakly orthotropic anisotropy; the ratio of elastic moduli in the vertical and horizontal directions was 1.53, clearly indicating the transversely isotropic rock mass mechanical characteristics. The method can be popularized to solve other rock mechanics problems in nuclear power engineering.

The improved neutral network and its application for valuing rock mass mechanical parameter

The artificial neutral network(ANN) has the ability that self-study and self-remember, its 3 layers BP network has been applied extensively, but sometimes because of serious multi-correlation between the variables, and a few observations while many variables, there usually will result into paralyzing in study, and the neutral network further development is restricted in the system to some extent. The partial least square regression(PLS) has its advantage of building the calculation model between the variables with strong multi-correlation, especially much effective on a few data and many variables. So a new and effective method-improved neutral network has been introduced-the neutral network based on the PLS. The results of example show the improved method has a few calculations and high accuracy, and provide a new way for valuing the rock mass mechanical parameters.

Study on mechanical parameters of fractured rock masses

The equivalent strength parameters of fractured rock masses are prerequisite for stability analysis of geotechnical engineering projects constructed in fractured rock masses which are encountered frequently in western china.Based on generated mesh of fractured rock masses,combined with statistic damage constitutive model of intact rock and damage model of structural plane,progressive failure of fractured rock masses is studied using finite element method(FEM) .Furthermore,Scale effect and anisotropy of compressive strength of fractured rock masses are studied.Study results show that the strength decreases and tend towards stability rapidly from intact rock to fractured rock masses,and the anisotropy of strength of fractured rock masses is not significant.At last,based on numerical simulation conducted on 10 m scale rock masses under different confining pressures,the equivalent strength parameters of fractured rock masses are gained and the results are compared with Hoek-Brown criteria.The method developed is helpful for determination of strength parameters of fractured rock masses.

Study on Estimation Method of Rock Mass Discontinuity Shear Strength Based on Three-Dimensional Laser Scanning and Image Technique

The estimation of shear strength of rock mass discontinuity is always a focal, but difficult, problem in the field of geotechnical engineering. Considering the disadvantages and limitation of exist- ing estimation methods, a new approach based on the shadow area percentage （SAP） that can be used to quantify surface roughness is proposed in this article. Firstly, by the help of laser scanning technique, the three-dimensional model of the surface of rock discontinuity was established. Secondly, a light source was simulated, and there would be some shadows produced on the model surface. Thirdly, to obtain the value of SAP of each specimen, the shadow detection technique was introduced for use. Fourthly, compared with the result from direct shear testing and based on statistics, an empirical for- mula was found among SAP, normal stress, and shear strength. Data of Yujian （~ River were used as an example, and the following conclusions have been made. （1） In the case of equal normal stress, the peak shear stress is positively proportional to the SAP. （2） The formula for estimating was derived, and the predictions of peak-shear strength made with this equation well agreed with the experimental re- suits obtained in laboratory tests.

寒区露天矿板岩冻融力学特性及边坡稳定性研究

为了探究寒区板岩边坡在冻融条件下的力学参数劣化规律及其失稳机理,通过室内冻融循环力学试验,并基于广义Hoek-Brown强度准则计算岩体内聚力和内摩擦角随冻融循环次数的衰减规律,以此修正未考虑冻融损伤的白云鄂博南帮内聚力和内摩擦角块体模型,实现南帮岩体力学参数的时空演化表征,最后通过数值模拟分析白云鄂博铁矿主矿区南帮边坡在冻融效应下的循序破坏机理。结果表明:经20次冻融循环后,矽质板岩、云母化板岩、碳化板岩、断层岩内聚力降低率分别为21.64%、22.66%、28.09%、28.53%,内摩擦角降低率分别为12.76%、14.72%、19.37%、21.35%;在冻融效应下,南帮边坡稳定系数由1.19逐渐降至0.92,1650~1570 m区域剪应变逐渐增大,最终滑体于1570 m平台滑移剪出。

岩体基本质量指标BQ与岩石坚固性系数f之间的关系研究

为了建立岩石坚固性系数f与岩体基本质量指标BQ、岩体各力学参数指标之间的关系,采用下列方法进行研究:(1)已知岩石单轴抗压强度R_C和BQ、f都存在相关关系,以R_C作为中间量,建立BQ与f的关系式;(2)已知岩体体积节理数J_V和岩石质量指标D_(RQD)、完整性指数K_V都存在相关关系,以J_V作为中间量,建立D_(RQD)与K_V的关系式,再经推导可得出BQ、f、D_(RQD)之间的关系式;(3)根据BQ、f、D_(RQD)之间的关系式,建立岩体各力学参数与f之间的关系方程;(4)将得到的研究结果用于吉尔吉斯斯坦南北路隧道工程的岩体分级及岩体各力学参数估计,据此确定施工方案,沉降变形监测结果表明,该工程施工效果良好。

岩体工程力学参数取值方法研究Ⅰ:原位试验与定量类比

针对合理确定岩体工程力学参数的难题,在原位试验技术、定量类比方法和数值仿真试验等方面开展了系统研究,形成了包含“一设备、一库、一平台”综合确定岩体工程力学参数的方法体系。本文研发了适用于常规地质钻探的岩体质量随钻测试和岩体力学参数原位试验设备,建立了依据随钻实测参数评价岩体质量的方法以及岩体强度、耐磨性指标与随钻参数的定量关系,提出了通过孔内弹模剪切试验快速获取不同岩层岩体抗剪强度和弹性模量的技术和方法;同时,构建了包含81个工程681组不同类型岩体抗剪强度试验资料数据库,深入研究了不同类型岩体抗剪强度参数的统计特性,提出了基于Bayes方法和可靠度理论,利用大样本数据库资料和少量具体工程试验成果来确定岩体参数的定量类比方法。

岩体工程力学参数取值方法研究Ⅱ:数值仿真试验

针对复杂节理岩体力学参数确定的瓶颈难题,对复杂节理岩体数值仿真试验开展了深入系统的研究,提出了基于岩体结构面网络计算机模拟的岩体结构定量化表征方法,以及基于拓扑矩阵表达和虚拟节理处理的数值试样快速生成技术,通过在数值流形法中引入断裂力学理论建立了复杂节理岩体受力、变形、破坏、扩展直至贯通的全过程模拟方法,在此基础上构建了节理岩体数值仿真试验平台,为通过仿真试验确定节理岩体的工程力学参数提供了一条新的途径。

基于Hoek-Brown准则的岩体力学参数确定

国内外岩体力学参数测定的方法多不胜数,其中室内岩石力学参数试验法能较准确地确定岩体各类参数。以昆阳某磷矿为工程背景,进行现场采样并制备标准试件,分别对顶板、磷矿层以及底板岩样进行室内岩石物理力学参数试验。为提高参数结果的准确性,以及使数据更接近工程实际情况,将采用Hoek-Brown准则对参数计算结果进行折减,并进一步对经验准则中引入的扰动系数D、地质强度指标GSI以及完整岩石材料常数mi的取值进行分析。经过折减后,其结果表明,经折减后的力学参数综合考虑了更多的现场因素,使试验结果更准确,提高了后续现场相关工作的准确性。

基于Hoke-Brown准则的某矿山岩体力学参数确定

岩体力学参数的确定对实际工程问题的稳定性分析以及相关设计参数的确定有着非常重要的作用。本文在具体矿山进行了现场工程地质调查、确定工程岩体的RMR分级、现场取样、室内岩石力学实验获取岩石力学参数,结合霍克布朗准则对矿山工程岩体的岩体力学参数进行确定,为矿山今后的工作奠定基础。

基于GSI的深部节理化岩体工作面稳定性分析

针对节理岩体力学参数选取困难问题,基于地质强度指标GSI,结合损伤力学原理和广义Hoek-Brown准则构建考虑节理强度的节理岩体力学模型,对深部节理化岩体工作面进行了稳定性分析。结果表明:所给出的节理等效系数能较好地描述节理间距与GSI之间的关系,节理岩体的破碎程度对工作面的稳定性产生了影响,随着岩体破碎程度的提高,工作面易发生顶板冒落、煤壁片帮等现象;当岩体较为破碎时,顶板失稳主要由节理的发育、贯通引起;岩体的完整性较好时,顶板的稳定性受采空区悬臂段顶板的影响较大。

表层喀斯特带溶蚀岩体单轴压缩力学特性模拟研究

研究表层喀斯特带溶蚀岩体的力学特性,有助于岩溶区边坡稳定性分析。本文以表层岩溶带溶蚀特征为依据,设定溶蚀率和溶蚀均匀系数作为溶蚀特征参数。基于元胞自动机算法思路,在颗粒离散元软件中构建不同溶蚀特征的岩体模型。对溶蚀岩体进行单轴压缩数值试验,检测岩体加载过程中声发射事件。试验结果表明:溶蚀岩体加载过程可分为:(1)压密阶段;(2)弹性变形阶段;(3)稳定破裂发展阶段;(4)不稳定破裂发展阶段;(5)峰后缓慢软化阶段;(6)峰后快速软化阶段。随溶蚀率增加,岩体弹性变形阶段曲线缩短,岩体抗压强度降低;岩体由脆性破坏逐渐转为延性破坏;同时,溶蚀率增加,岩体抗压强度下降速率由最初快速降低转为缓慢降低,最终收敛。溶蚀均匀系数增加,不稳定破裂阶段曲线增长,岩体由局部破坏转为整体性破坏。研究发现溶蚀岩体单轴抗压强度与溶蚀特征参数呈负指数关系,该关系式可用作溶蚀岩体强度取值,实际工程中应增加溶蚀均匀系数对岩体质量的影响。溶蚀岩体裂纹扩展机理有助于边坡失稳机理研究。

国际水电工程地质勘察实践探讨

作为国际水电工程勘测设计的主要基础性资料,地质勘察成果的国际工程咨询审批进度往往对工程进度甚至成本有较大影响。在总结对标研究工作成果、中国水电技术标准“走出去”之工程测量与地质勘察篇研究成果的基础上,结合国际水电工程地质勘察实践,对地震参数确定、坝基岩体力学参数确定、边坡稳定分析、洞室围岩分类及支护建议等关键技术问题进行了初步分析,总结了中外技术标准的主要差异,初步提出了探讨性的对策及建议,可供业内人士参考。

透明岩石相似材料配比试验研究

针对传统岩石相似材料不透明而导致内部变形破裂过程无法直接观测的难题,使用透明材料制作相似模型是有效的解决方法。采用E-44型环氧树脂作为骨料,三乙醇胺作为固化剂,外加酒精松香饱和溶液(RSS)调节脆性,应用全面试验方法,研究了环氧树脂与三乙醇胺质量比和RSS含量对透明岩石相似材料密度、单轴抗压强度、峰值应变、弹性模量、抗拉强度、黏聚力和内摩擦角的影响规律。研究结果表明:环氧树脂与三乙醇胺质量比对材料抗压强度、弹性模量、抗拉强度、黏聚力和内摩擦角起主导作用,而RSS含量对相似材料的密度和峰值应变起主导作用。密度和峰值应变与环氧树脂与三乙醇胺质量比呈正相关,与RSS含量呈负相关。在环氧树脂与三乙醇胺质量比为3∶1时,试件的抗压强度与RSS含量呈负相关,而在其他比例时,抗压强度变化不显著。试件的弹性模量和内摩擦角与环氧树脂与三乙醇胺质量比呈正相关,在环氧树脂与三乙醇胺的质量比为3∶1时,试件的弹性模量和内摩擦角与RSS含量呈负相关,在其他比例时,则与RSS含量呈正相关。抗拉强度和黏聚力随着RSS含量的增加而降低,随着环氧树脂与三乙醇胺质量比的增加而先增加后减少。在同一环氧树脂与三乙醇胺质量比中,抗拉强度和黏聚力与RSS含量呈负相关。基于多元线性回归分析建立了透明岩石力学性能与环氧树脂与三乙醇胺质量比和RSS含量间的经验公式,为透明岩石相似材料配比提供借鉴参考。

裂隙岩体力学性质的颗粒流模拟研究

工程岩体中含有大量内部裂隙,对岩体力学性质具有控制作用,但由于试验制备困难等问题对含内部裂隙的岩体的研究较少。为了研究内裂隙对岩体力学性质的影响,采用PFC3D建立贯穿单裂隙岩体数值模型,利用单轴与三轴压缩模拟结果与理论以及试验结果的对比验证了模拟的准确性。随裂隙倾角的增加,岩体力学参数的变化呈现出“U”型趋势,反映了岩体力学特征的各向异性。围压的增大弱化了岩体的各向异性,裂隙面积比的增大强化了岩体的各向异性。采用等效岩体方法分析了裂隙尺寸、倾角以及密度对含内部多裂隙岩体力学参数的影响。同一裂隙密度下,裂隙尺寸的增大对含有倾角在45°附近的裂隙岩体力学参数的影响较大,而对含有倾角为0°和90°的裂隙岩体力学参数的影响较小,即对岩体力学特征的各向异性影响较大;同一裂隙尺寸下,裂隙密度的增加对于含有不同倾角裂隙的岩体力学参数的影响基本一致,即对岩体力学特征的各向异性影响较小。

岩溶砂化白云岩岩质边坡力学参数取值探讨与思考

白云岩砂化是玉溪、昆明、保山等云南地区高速公路项目、大型工业项目施工中遇到的典型工程地质问题之一,剧烈砂化、强烈砂化的白云岩岩体极为破碎,因难以采集到满足室内试验条件的原状岩块试样,准确获取砂化白云岩岩质边坡稳定性计算的力学参数具有非常重要的意义。基于此,文中采用现场调查、现场钻探、大单容试验、岩体现场直剪试验等手段,对剧烈砂化、强烈砂化的白云岩进行地层分层和原位试验,为边坡工程项目的勘察、设计、施工等提供重要的技术支撑,对类似砂化白云岩岩质边坡项目提供借鉴。