Application and prospects of 3D printing in physical experiments of rock mass mechanics and engineering:materials,methodologies and models

The existence of joints or other kinds of discontinuities has a dramatic efect on the stability of rock excavations and engineering.As a result,a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects.In recent years,3D printing technology has become a promising tool in the feld of rock mass mechanics and engineering.This study frst reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects.Then,based on the comprehensive analysis of previous research,the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects.The frst is the printing material.Although there are many materials for 3D printing,it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited.After research,we summarize and evaluate printing material that can be used for rock mass mechanics studies.The second is the printing methodology,which mainly introduces the current application forms of 3D printing technology in rock mass mechanics.This includes printed precise casting molds and one-time printed samples.The last one is the printing model,which includes small-scale samples for mechanical tests and large-scale physical models.Then,the benefts and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed.Compared with traditional rock samples collected in nature or synthetic rock-like samples,the samples made by 3D printing technology have unique advantages,such as higher test repeatability,visualization of rock internal structure and stress distribution.There is thus great potential for the use of 3D printing in the feld of rock mass mechanics.However,3D printing materials also have shortcomings,such as insufcient material strength and accuracy at this stage.Finally,the application prospect of 3D printing technology in rock mass mechanics research is proposed.

Anisotropic creep behavior of soft-hard interbedded rock masses based on 3D printing and digital imaging correlation technology

Three-dimensional(3D)printing technology is increasingly used in experimental research of geotechnical engineering.Compared to other materials,3D layer-by-layer printing specimens are extremely similar to the inherent properties of natural layered rock masses.In this paper,soft-hard interbedded rock masses with different dip angles were prepared based on 3D printing(3DP)sand core technology.Uniaxial compression creep tests were conducted to investigate its anisotropic creep behavior based on digital imaging correlation(DIC)technology.The results show that the anisotropic creep behavior of the 3DP soft-hard interbedded rock mass is mainly affected by the dip angles of the weak interlayer when the stress is at low levels.As the stress level increases,the effect of creep stress on its creep anisotropy increases significantly,and the dip angle is no longer the main factor.The minimum value of the long-term strength and creep failure strength always appears in the weak interlayer within 30°–60°,which explains why the failure of the layered rock mass is controlled by the weak interlayer and generally emerges at 45°.The tests results are verified by comparing with theoretical and other published studies.The feasibility of the 3DP soft-hard interbedded rock mass provides broad prospects and application values for 3DP technology in future experimental research.

3-D fracture network dynamic simulation based on error analysis in rock mass of dam foundation

Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network model and measured data,a 3-D fracture network dynamic modeling method based on error analysis was proposed.Firstly,errors of four fracture volume density estimation methods(proposed by ODA,KULATILAKE,MAULDON,and SONG)and that of four fracture size estimation methods(proposed by EINSTEIN,SONG and TONON)were respectively compared,and the optimal methods were determined.Additionally,error index representing the deviation between fracture network model and measured data was established with integrated use of fractal dimension and relative absolute error(RAE).On this basis,the downhill simplex method was used to build the dynamic modeling method,which takes the minimum of error index as objective function and dynamically adjusts the fracture density and size parameters to correct the error index.Finally,the 3-D fracture network model could be obtained which meets the requirements.The proposed method was applied for 3-D fractures simulation in Miao Wei hydropower project in China for feasibility verification and the error index reduced from 2.618 to 0.337.

Modeling wave propagation across rock masses using an enriched 3D numerical manifold method

The three-dimensional numerical manifold method(3DNMM) method is further enriched to simulate wave propagation across homogeneous/jointed rock masses. For the purpose of minimizing negative effects from artificial boundaries, a viscous nonreflecting boundary, which can effectively absorb the energy of a wave, is firstly adopted to enrich 3DNMM. Then, to simulate the elastic recovery property of an infinite problem domain, a viscoelastic boundary, which is developed from the viscous nonreflecting boundary, is further adopted to enrich 3DNMM. Finally, to eliminate the noise caused by scattered waves, a force input method which can input the incident wave correctly is incorporated into 3DNMM. Five typical numerical tests on P/S-wave propagation across jointed/homogeneous rock masses are conducted to validate the enriched 3DNMM. Numerical results indicate that wave propagation problems within homogeneous and jointed rock masses can be correctly and reliably modeled with the enriched 3DNMM.

A state-of-the-art review of automated extraction of rock mass discontinuity characteristics using three-dimensional surface models

In the last two decades,significant research has been conducted in the field of automated extraction of rock mass discontinuity characteristics from three-dimensional(3D)models.This provides several methodologies for acquiring discontinuity measurements from 3D models,such as point clouds generated using laser scanning or photogrammetry.However,even with numerous automated and semiautomated methods presented in the literature,there is not one single method that can automatically characterize discontinuities accurately in a minimum of time.In this paper,we critically review all the existing methods proposed in the literature for the extraction of discontinuity characteristics such as joint sets and orientations,persistence,joint spacing,roughness and block size using point clouds,digital elevation maps,or meshes.As a result of this review,we identify the strengths and drawbacks of each method used for extracting those characteristics.We found that the approaches based on voxels and region growing are superior in extracting joint planes from 3D point clouds.Normal tensor voting with trace growth algorithm is a robust method for measuring joint trace length from 3D meshes.Spacing is estimated by calculating the perpendicular distance between joint planes.Several independent roughness indices are presented to quantify roughness from 3D surface models,but there is a need to incorporate these indices into automated methodologies.There is a lack of efficient algorithms for direct computation of block size from 3D rock mass surface models.

Numerical simulations of failure behavior around a circular opening in a non-persistently jointed rock mass under biaxial compression

Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations.First,the micro parameters of the PFC^(3D) model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models.Then,a parametrical study was undertaken of the effect of stress condition,joint dip angle and joint persistency.Under low initial stress,the confining stress improves the mechanical behavior of the surrounding rock masses;while under high initial stress,the surrounding rock mass failed immediately following excavation.At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern;whereas,at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern.Moreover,the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

裂隙岩体内3维裂隙体的分形描述

针对裂隙岩体研究过程中的裂隙定量化描述及其与强度参数间的对应关系等问题,通过对完整煤岩进行预加载而获取含裂隙的裂隙岩体试件。基于此,对其试件进行CT扫描探测并重构裂隙岩体模型,以获取表征其分布特征的点云数据,然后利用分形理论,采用立方体覆盖法对岩体内3维裂隙体进行定量化描述,并对CT扫描后的裂隙岩体试件进行单轴抗压试验,进而分析其定量描述指标与强度参数间的关系。结果表明:通过CT扫描获取的3维裂隙体点云数据能够很好地表征其空间分布特征;岩体内3维裂隙体具有自相似性,是一种自然分形,其分形维数能够作为其定量描述指标;在统计意义上,裂隙岩体定量评价指标的分形维数与其单轴抗压强度呈对数关系,且随着裂隙复杂程度的提高,其强度参数呈降低趋势。

瞬变电磁法在红旗岭铜镍矿3号岩体勘查中的应用与研究

作为一个拥有五十余年历史的老矿山,红旗岭铜镍矿,保持矿产资源开采的持续性可谓当务之急。瞬变电磁法(TEM)因其探测深度大、对低阻体敏感等特点在红旗岭矿区的危机矿山接替资源找矿续作项目中发挥了重要的作用。

吉林省红旗岭矿区3号含矿岩体同位素年龄研究

通过对红旗岭矿区3号含矿岩体同位素年龄研究，该岩体锆石U-Pb年龄为（207±3）Ma，黑云母Ar-Ar年龄为（212.5±2.5）Ma，矿石Re-Os等时线年龄为（234±28）Ma，表明该含矿岩体形成于三叠纪晚期。该年龄和近年来对含矿基性-超基性岩体同位素年龄测定结果基本一致（205-230 Ma），说明它们均为三叠纪晚期岩浆作用的产物。根据岩体围岩年龄（Rb-Sr全岩等时线年龄（524±16）Ma和（357±23）Ma），认为该岩体成岩成矿主要形成于印支中晚期，是同一期构造岩浆活动的产物，岩浆及成矿物质来源具有同源性，从而形成了具有相同成因的矿床类型。

Application of Three-Dimensional Laser Scanning and Surveying in Geological Investigation of High Rock Slope

The appearance of 3D laser scanning technology is one of the most important technology revolutions in surveying and mapping field. It can be widely used in many interrelated fields, such as engineering constructions and 3D measurements, owing to its prominent characteristics of the high efficiency and high precision. At present its application is still in the initial state, and it is quite rarely used in China, especially in geotechnical engineering and geological engineering fields. Starting with a general introduction of 3D laser scanning technology, this article studies how to apply the technology to high rock slope investigations. By way of a case study, principles and methods of quick slope documentation and occurrence measurement of discontinuities are discussed and analyzed. Analysis results show that the application of 3D laser scanning technology to geotechnical and geological engineering has a great prospect and value.

Development of an improved three-dimensional rough discrete fracture network model:Method and application

Structure plane is one of the important factors affecting the stability and failure mode of rock mass engineering.Rock mass structure characterization is the basic work of rock mechanics research and the important content of numerical simulation.A new 3-dimensional rough discrete fracture network(RDFN3D)model and its modeling method based on the Weierstrass-Mandelbrot(W-M)function were presented in this paper.The RDFN3D model,which improves and unifies the modelling methods for the complex structural planes,has been realized.The influence of fractal dimension,amplitude,and surface precision on the modeling parameters of RDFN3D was discussed.The reasonable W-M parameters suitable for the roughness coefficient of JRC were proposed,and the relationship between the mathematical model and the joint characterization was established.The RDFN3D together with the smooth 3-dimensional discrete fracture network(DFN3D)models were successfully exported to the drawing exchange format,which will provide a wide application in numerous numerical simulation codes including both the continuous and discontinuous methods.The numerical models were discussed using the COMSOL Multiphysics code and the 3-dimensional particle flow code,respectively.The reliability of the RDFN3D model was preliminarily discussed and analyzed.The roughness and spatial connectivity of the fracture networks have a dominant effect on the fluid flow patterns.The research results can provide a new geological model and analysis model for numerical simulation and engineering analysis of jointed rock mass.

Strength test of 3D printed artificial rock mass with pre-existing fracture

Discontinuities or structural planes are widely distributed in natural rock masses and significantly influence their geo-mechanical and geometric properties.Herein,a batch of rock samples,each with a single structural plane,is created using a 3D printer equipped with two robotic manipulators.One of the manipulators is connected via a nozzle to a concrete pumping truck,which can extrude brittle rock-like material to form layered intact rock masses;the rock-like material is mainly composed of cement,silica fume,sand and water.The other manipulator features a knife,which can carve discontinuities onto each layer of the printed model.By means of this system,rock masses with discontinuous joints are formed,and the failure strengths of rock masses with different joints are demonstrated via uniaxial compression tests and direct shear tests.The results thereof obtained via digital image correlation technology show that discontinuities lower the strength of the rock mass models significantly.With the increase of the angle between the fracture and horizontal plane,the uniaxial compressive strength first decreases,and then increases.During shear testing,the shear strength of the rock mass models increases with the surface roughness of the preset joint.These test results indicate that the influence of artificial joints on the mechanical properties of the models is consistent with that of natural rock mass joints.Using digital modeling and 3D printing technology,cracks hidden in a rock mass can be reproduced.

New method to identify optimal discontinuity set number of rock tunnel excavation face orientation based on Fisher mixed evaluation

Discontinuity is critical for strength,deformability,and permeability of rock mass.Set information is one of the essential discontinuity characteristics and is usually accessed by orientation grouping.Traditional methods of identifying optimal discontinuity set numbers are usually achieved by clustering validity indexes,which mainly relies on the aggregation and dispersion of clusters and leads to the inaccuracy and instability of evaluation.This paper proposes a new method of Fisher mixed evaluation(FME)to identify optimal group numbers of rock mass discontinuity orientation.In FME,orientation distribution is regarded as the superposition of Fisher mixed distributions.Optimal grouping results are identified by considering the fitting accuracy of Fisher mixed distributions,the probability monopoly and central location significance of independent Fisher centers.A Halley-Expectation-Maximization(EM)algorithm is derived to achieve an automatic fitting of Fisher mixed distribution.Three real rock discontinuity models combined with three orientation clustering algorithms are adopted for discontinuity grouping.Four clustering validity indexes are used to automatically identify optimal group numbers for comparison.The results show that FME is more accurate and robust than the other clustering validity indexes in optimal discontinuity group number identification for different rock models and orientation clustering algorithms.

利用“岩体裂隙率”评价工程岩体的质量

本文提出用建立在岩体结构面网络三维模拟基础上的“岩体裂隙率”来表征岩体的质量。它可以用来衡量结构面的发育程度及岩体的完整性 ,评价岩体质量 。

复杂环境下围岩变形大型三维模拟实验

以宁夏宁东矿区复杂环境(历史性强震区内破碎围岩与富含水)下围岩局部化变形演化规律为目标,综合分析地球物理特征、加载框架及其力学性能、围岩变形指标与定量识别方法、围岩结构与缺陷以及相似模拟材料复合特性等,构建了三维物理模拟装置与"声-光-电"多元指标实时测试系统,完成了恒定与可变围压下的"动-静"耦合加载实验,对围岩局部化损伤的声发射特征规律与开采扰动下实验模型中扰动区内岩体径向和切向应力分布进行辨识。结果表明:复杂岩体破裂与变形经历"振荡-沉寂"后,极有可能会出现持久性破坏,进一步揭示了复合煤岩体变形具有局部化失稳特征。

三维任意裂隙网络渗流模型及其解法

首先,分析三维裂隙网络渗流分析模型需解决的2个关键问题,即如何获得结构面网络相交形成的裂隙渗流通道、如何计算二维任意形态区域的渗流问题。采用全空间块体搜索(三维块体切割)技术,得到封闭块体的边界就是渗流通道,块体边界的连接关系就是渗流有限元计算节点的连接关系;块体边界的裂隙面(或临空面)由不同形态、不同数量的回路构成,将每个回路上的渗流考虑为二维连续介质渗流,在面的局部坐标系下,通过单纯形积分解决任意形态回路上的渗流问题。然后,根据计算节点连接关系,形成总体渗流矩阵和渗流控制方程后就可实现三维任意结构面网络渗流计算。最后,采用算例对理论分析过程和计算程序进行检验,并将三维结构面网络渗流分析结果应用到块体系统渐进失稳分析中。

连拱隧道围岩压力的释放率分析

连拱隧道作为公路隧道新的结构型式,理论上还不成熟。以云南省元磨高速公路的两座连拱隧道作为工程背景,按弹性阶段相似原则进行两组连拱隧道室内模型试验,包括隧道处于常规应力状态下和偏压状态下的模型试验。采用压力盒量测施工过程中隧道围岩压力,并提出了围岩压力释放率的概念,对连拱隧道开挖过程中围岩压力的变化特征进行了分析,同时对两种应力状态下的试验结果进行了对比分析。得出的结论对连拱隧道的设计和施工有积极的指导作用。

基于激光测量和FKM聚类算法的隧洞岩体结构面的模糊群聚分析

岩体隧洞结构面的数量、产状和发育情况是评价隧洞透水性和稳定性的重要指标。采用三维激光测量技术可以快速获取隧洞周围岩体激光点云数据和结构面的几何信息。提出了基于柱面投影和Delaunay生长算法的激光点云的三角网重构技术,利用构建的三角网平面方程的法向向量计算出单个三角网平面的产状,并应用FKM聚类算法进行隧洞岩体结构面产状的模糊群聚分类。该方法可以快速得到不同组的优势产状,且分类结果可用不同颜色进行空间显示。最后运用自主研发的FSS软件对某隧洞的岩体结构面优势产状进行了研究,研究结果表明:1)基于柱面投影和Delaunay生长法的点云构网方法特别适合于隧洞工程,构网速度快、效率高,重构得到的三角网表面与被采样的岩体表面拓扑差别最小;2)FKM模糊群聚方法对隧洞岩体结构面的群聚分类结果可靠、合理,具有较强的通用性和推广性。

大型地下铁矿覆岩移动破坏规律数值模拟

通过对劳服铁矿的工程地质调查、矿岩力学性质试验,选取了表征矿山岩体工程质量的各种指标,获得了岩体工程分类结果的工程岩体质量级别。在系统的劳服铁矿开采现状、水文地质和采矿方法等研究的基础上,采用FLAC3D建立劳服铁矿地下开采的数值模型,通过三维数值模拟,揭示了劳服铁矿采用无底柱分段崩落采矿方法的力学环境,分析了劳服铁矿覆岩的应力、位移量、塑性区,其分析结果对劳服铁矿地下安全高效开采具有重要的指导意义。