三峡库区近水平厚层斜坡滑动稳定性研究——以重庆巫山箭穿洞危岩为例

以重庆巫山箭穿洞近水平巨厚层危岩体为例,通过地质环境条件、基座位移及应力监测数据等分析,总结归纳了危岩体目前的变形和受力状态,发现危岩体的强度仍在持续降低。同时,运用FLAC2D模拟手段,设置了初始天然、初始饱和、临滑、失稳4种模拟工况,研究了危岩基座岩体及泥质条带灰岩层面对危岩体阻滑规律。研究结果表明,基座泥质条带灰岩层强度的持续降低将会使得危岩体处于临滑乃至失稳状态。该稳定性分析也为进一步的防治设计提供了依据。      

3D instability analysis of an underground geological repository—an Indian case study

Conceptual geological repositories are generally used for disposing spent nuclear wastes containing both high and low level of nuclear radiation and heat. Due to its long-lasting effect, it is imperative to analyze its long-term effect on the surrounding rock. Before analyzing radiation and thermal effect, it is important to have structurally stable cavern because designing an opening in rock is a more difficult problem than designing the structure made of steel. Underground rocks are under stress because of the weight of the overlying rock, and in addition, an underground opening will produce a stress concentration and stress relaxation in the surrounding rock. If the induced stress in the surrounding rock exceeds its strength, the opening will fail either by fracturing or by deforming more than the tolerable limit. In this paper, the stability of four different shapes of excavation has been examined for conceptual geological repositories in Indian context. This has been done using equivalent continuum numerical model which has been incorporated in the commercial finite difference code-FLAC-3D. Effects of opening shapes on stress distribution, subsidence of crown and side wall, and their stability have been analyzed and discussed. The validation of FLAC^3D software for its applicability in conceptual underground geological repositories has been done with a published literature.     

Numerical Application of Safe Thickness Between a Tunnel and Surrounding Concealed Caves

This paper first analyzes the factors influencing the safe thickness and the broken mechanism of rock between a tunnel and the surrounding concealed caves on the Cheng-gui railway line. Then, based on the analysis of broken mechanism, a comprehensive numerical analysis method, which is based on the Yujingshan Tunnel project, is put forward. This method of analysis is simulated using FLAC^3D software to perform three-dimensional numerical simulations for different positions, providing the basis for the subsequent safe thickness analysis and construction scheme design. Actual monitoring and computational results shows the safety distance of the range of the tunnel’s diameter, which proved the rationality and effectiveness of the calculation of the safe thickness between the tunnel and the surrounding concealed caves.     

复杂矿区三维地质可视化及数值模型构建

复杂三维地质可视化和数值模型的构建是采矿、岩土及水利水电工程中常常遇到的关键问题。针对数值模拟软件在复杂矿区地质体模型构建及单元网格划分等前处理问题上存在的不直观、工作量大等缺点,结合矿业软件在复杂三维地质体建模的强大优势,在研究线框模型和块体模型差异的基础上,提出了基于线框模型的复杂矿区三维地质可视化及数值模型构建技术。根据线框模型特点不同,以地表和采空区模型为型,分别阐述了基于Surpac的表面模型和实体模型无缝转换成MIDAS/GTS数值模型的有效方法,并将该技术成功应用于冬瓜山铜矿复杂采空区群围岩稳定性研究中。结果表明,该方法是可行、有效的,从而为矿山开采设计、安全分析及复杂地质体结构的岩土工程数值模拟分析提供了一种新的建模方法。     

Gas outburst affected by original rock stress direction

In this paper, it was determined that all of the three-dimensional principal stresses increase with depth and that both the maximum and the minimum stresses tend to be aligned in the horizontal orientation. The numerical simulation model was built using the software FLAC^3D to simulate two times, as in two different states of original rock stress, respectively; this simulation was used to investigate how the original rock stress affects the gas outburst risk. The results suggest that an outburst is most likely to happen when the maximum original rock stress is perpendicular to the roadway, rather than parallel to the roadway. The results were demonstrated to be correct by a field experiment. The results suggest that most of the roadways in gas outburst risk coal mines should be designed to lie parallel to the maximum stress direction to avoid the high stress concentration in front of the heading face, thereby reducing the gas outburst risk.     

Experiments on failure process of new rock-like specimens with two internal cracks under biaxial loading and the 3-D simulation

A new resin material has been developed by massive formula exploration. The resin is thoroughly transparent and rock-like at low temperatures. Its tension–compression strength ratio is up to 1/6.6 in the temperature range of ??10 to ??15 °C. It can simulate quite a few kinds of engineering rocks. Specimens have been made with two internal cracks. The progressive failures under uniaxial and biaxial compressions are systematically studied. The uniaxial failure process is divided into four stages as conventional rock mechanics test. Several forms of secondary cracks, like anti-wing cracks in the biaxial experiment with high lateral pressure, have seldom been described by former scholars. Three-dimensional numerical simulation has been conducted using FLAC^3D. A novel elastic-brittle constitutive model is developed and programed. Superfine mesh generation is demanded as well. Both uniaxial and biaxial results of the new numerical approach show excellent consistency with experimental results in this paper.     

金沙江某高拱坝坝肩变形稳定计算分析

为了论证和评价金沙江拟建某水电站高拱坝坝肩岩体的变形稳定性,应用有限差分程序FLAC3D对坝肩岩体在天然状态和荷载后的应力、变形和破坏的发展特征模拟研究,分析了坝肩岩体在正常工程荷载下的变形特征及超载状态下变形破坏特征,结果表明坝肩岩体在正常工程荷载下处于稳定状态,得到了坝肩岩体在超载条件下的变形破坏机制,并评价了坝肩岩体的整体稳定安全度和超载能力.     

Three-Dimensional Back-Analysis of an Instrumented Shallow Tunnel Excavated by a Conventional Method

The excavation of a shallow tunnel induces deformations of the soil volume in the vicinity and above the tunnel and consequently on the nearby buildings. The range of these deformations depends among other on the geological conditions, the geometry of the tunnel, and the excavation method. In this context, this research focuses on the 3D numerical modeling of a shallow tunnel instrumented during its construction, located on the Toulouse (France) subway line B for which the excavation has been carried out in a conventional manner in an over consolidated molassic geological context. The objective of this analysis is to estimate the tunnel behavior in terms of vertical and horizontal movements of the surrounding soil and the deformations of the existing buildings. The explicit finite differences numerical code FLAC^3D is used to model the various implementation phases of the work where the fluid–soil interaction is taken into account through an undrained coupled analysis. The results of this 3D model are compared to those of the in situ measurements in order to validate the geotechnical characteristics of the molasses. The latter are a useful basis for the back-analysis of the different monitoring sections implemented in areas where the tunnel excavation is made by TBM with pressurized front.     

拱坝联合坝肩岩体三维计算模型构建

坝址区复杂的地质条件与岩体力学环境变化,直接影响坝肩岩体抗滑稳定及拱坝的安全。我国西南乌东德超高拱坝坝址区工程地质条件极为复杂。坝体载荷后,区域内地层岩性、断层构造、岩溶系统、拱座内不连续裂隙等自然地质条件,成为影响坝肩岩体稳定性的主要因素。基于可研阶段地质勘探数据、二维地质剖面和工程设计数据,采用面向对象技术、多种软件协同作业,建立自然地质条件和工程对象的几何模型。构建适用于地应力反演分析,坝体载荷、工程开挖等因素影响下坝肩稳定性分析的三维精细有限元计算模型。该三维模型最大程度地模拟了工程岩体复杂结构,为高拱坝坝肩岩体稳定性综合分析提供良好的基础。计算结果表明:河谷两侧近地表地应力带及河床深部地应力区应力水平与实际量测值接近。坝肩槽开挖完成后,右岸拱肩槽800 m高程附近位移值最大达到12.9 mm。两岸9个可能滑动楔块在不同荷载组合条件下有一定差异,整体上左岸坝肩稳定性强于右岸。组合地震荷载作用下,所有楔块安全系数均大幅下降,但仍具有一定的安全裕度。     

西南某水电站坝肩抗力体长期稳定性分析

水电工程对坝肩抗力体长期稳定性要求极高,因此,对于复杂岩土体坝肩抗力体在水推力作用下的稳定性评价显得尤为重要。西南某水电工程坝肩岩体普遍发育有蚀变岩,因此需对其抗力体长期稳定性进行评价。根据考虑蚀变岩体流变特性的黏-弹-塑性本构模型,对水库蓄水运行期抗力体边坡应力、形变场等特征进行了三维数值模拟研究。研究表明,坝肩抗力体在蓄水6个月后三次应力场基本形成,即此时抗力体处于最危险状态,可能会出现蚀变岩带与断层交叉部位的局部破坏; 通过对蓄水5a后模拟得到的变形值及塑性区变化情况分析,得出坝肩抗力体整体上是长期稳定的。     

复杂条件下高拱坝应力及坝肩稳定分析

众所周知,研究复杂地质条件下的高拱坝应力和坝肩稳定对确保工程安全具有重要的意义。研究的江坪河高拱坝地质构造较复杂,坝基及坝肩岩体存在大量断层、软弱夹层、泥化夹层和卸荷、风化岩体等地质缺陷,引起两岸坝肩岩体变形不对称、压缩变形量增大以及坝肩局部岩体承载能力低,直接影响到拱坝正常运行和稳定性。因而,对各种工况下的坝体及坝肩岩体进行了三维有限元分析,研究了坝体及坝肩的应力和变形发展状态、可能失稳模式、破坏形态和破坏机制。研究成果表明,未加固时坝肩岩体不稳定,因此,通过研究采用合理的加固处理措施,右岸采用6个传力洞进行加固;左岸采用锚洞进行加固。采取加固措施以后对其进行三维有限元分析,其研究成果表明,加固有一定的效果,改善了两岸的受力状况和变形分布,提高了坝肩稳定性,但左岸坝肩仍不能完全满足规范要求,还需要进一步增加锚洞的面积。     

三维无缝工程地质建模系统的研制

在边界表示法的基础上,提出了无缝工程地质模型的概念,实现了基于模型线框架的无缝工程地质建模方法,研制了无缝建模系统（ROCKModel）。该系统包括3个部分：原始数据转换工具、实体建模工具与辅助工具,涉及剖分、插值、曲面求交等8个基本功能模块。在基本功能模块的基础上,提出并实现了形态复杂曲面的创建、构建模型线框架、界面编辑与重构、块体搜索、岩体质量三维分级等关键技术。该系统能够实现复杂地质对象与工程对象的无缝建模与可视化,并为数值模拟软件直接提供几何模型。     

高地应力条件下锦屏一级主厂房围岩松弛深度形成规律和支护时机研究

近年来我国西部已建成发电或正在建设的一批大型、特大型水电工程,其地下洞室群多处于高山峡谷地区,地质条件复杂、地应力较高。受高地应力影响,施工期洞室群围岩易出现不同程度的变形破坏,并常常导致超常规深度的围岩松弛。本文结合锦屏一级水电站主厂房围岩松弛长期物探检测成果,系统分析了围岩松弛深度的形成、发展和演化趋势,再采用数值分析手段,通过围岩位移、塑性区发展趋势来研究最佳支护时机,研究表明:高地应力地区厂房轴线宜尽量与最大主应力σ₁方向平行,能有效减小时效变形导致的不同部位不同程度的围岩松弛;洞室分层开挖时,围岩松弛深度的80%在本层开挖后间隔2～3层时形成;相比开挖后滞后支护,及时支护围岩位移量、塑性区明显较小,因此及时支护为最佳支护时机。研究成果对高地应力条件下大型地下洞室轴线选择、支护设计、支护时机选择具有参考意义。     

西南某水电站坝区岩体绿泥石化蚀变及其工程对策

西南某水电站坝区地质史上构造-热液活动复杂,岩体绿泥石化程度较高。经调查研究表明,坝区岩体绿泥石化蚀变既有热液成因,又有构造动力成因,其分布受岩性、构造、应力集中和浅表风化作用影响,在辉绿岩脉中蚀变强度最高,花岗岩中蚀变最强处往往远离断层分布,整体上由地表及深部,蚀变变弱。受蚀变影响,岩体总体性状变差,表现为变形模量偏低,结构面性状恶化。文章初步讨论了绿泥石化蚀变可能引起的主要工程地质问题及其工程对策。     

考虑地应力分布形式的坝址区初始应力场二次反演方法

在建的乌东德水电站区域构造运动强烈,断层、褶皱及节理较为发育,加之河谷纵横、沟谷深切,导致该区域岩体地应力分布极为复杂,非线性特征显著。为准确获取坝址区初始地应力场的分布特征,通过对地应力分布形式进行优化,提出了考虑地应力张量分布特征的岩体应力场二次反演方法。首先,将地应力张量分解成自重应力、构造应力及非线性应力3个部分,同时依据坝址区地形地貌、地质构造及非均匀性岩层等因素,构建FLAC3D计算模型,利用叠加法原理对坝址区初始地应力场进行一次反演。然后,主要考虑坝址区附近小规模构造及局部开挖条件的影响,构建三维离散元（3DEC）精细模型,同时从一次反演中提取精细模型的初始地应力侧压系数和自重修正系数,并利用均匀设计法进行优化,对精细模型进行二次反演。研究结果表明：一次反演计算获得的初始应力场整体上与实际情况吻合较好,但在局部构造附近与实测值相差较大;二次反演考虑局部地质构造及开挖条件的影响,同时结合一次反演的计算成果,各测点的应力计算值与实测值基本一致;通过将大型商业软件FLAC3D和3DEC相结合来反演复杂条件下工程区初始应力场,在一定程度上实现了岩体应力场在大范围内整体连续、小范围内受局部地质构造等影响导致不连续分布的特点。该研究方法可为类似工程提供借鉴。     

Design of a Displacement Monitoring System Based on Optical Grating and Numerical Verification in Geomechanical Model Test of Water Leakage of Tunnel

The displacement monitoring of surrounding rock is necessary in geomechanical model test. However, traditional monitoring technology is difficult to meet the needs of displacement monitoring in small geological model tests. To solve the problems mentioned above, the authors developed a multi-point displacement monitoring system based on optical grating including multi-point extensometer, grating scale and multi-channel data acquisition system. Firstly, 3D anchor head with six barbs is designed and connected to the grating ruler by the steel wire, which proved to be rather sensitive to the rock deformation. Additionally, the displacement data collected can be transformed into electrical signal, which can be obtained by multi-channel acquisition system. Finally, the system was used in the model test of tunnel water leakage. The designed anchors were pre-embedded in some key monitoring points around the section in order to investigate measurement of displacements in the lining during the loading of geostress and hydraulic pressure. Afterward, FLAC^3D, the finite-difference method, is adopted to simulate the whole process of physical model test and to compare with the experimental results. The results show that the experimental data was in good agreement with the numerical simulation results. In conclusion, the multi-point displacement monitoring system based on optical grating has higher precision and can be widely used in the physical model test of geotechnical engineering.     

Numerical Investigation of the Dynamic Mechanical State of a Coal Pillar During Longwall Mining Panel Extraction

This study presents a numerical investigation on the dynamic mechanical state of a coal pillar and the assessment of the coal bump risk during extraction using the longwall mining method. The present research indicates that there is an intact core, even when the peak pillar strength has been exceeded under uniaxial compression. This central portion of the coal pillar plays a significant role in its loading capacity. In this study, the intact core of the coal pillar is defined as an elastic core. Based on the geological conditions of a typical longwall panel from the Tangshan coal mine in the City of Tangshan, China, a numerical fast Lagrangian analysis of continua in three dimensions (FLAC^3D) model was created to understand the relationship between the volume of the elastic core in a coal pillar and the vertical stress, which is considered to be an important precursor to the development of a coal bump. The numerical results suggest that, the wider the coal pillar, the greater the volume of the elastic core. Therefore, a coal pillar with large width may form a large elastic core as the panel is mined, and the vertical stress is expected to be greater in magnitude. Because of the high stresses and the associated stored elastic energy, the risk of coal bumps in a coal pillar with large width is greater than for a coal pillar with small width. The results of the model also predict that the peak abutment stress occurs near the intersection between the mining face and the roadways at a distance of 7.5 m from the mining face. It is revealed that the bump-prone zones around the longwall panel are within 7–10 m ahead of the mining face and near the edge of the roadway during panel extraction.     

Anchoring Parameters Optimization of Tunnel Surrounding Rock Based on Particle Swarm Optimization

In the highway tunnel project, due to the uncertainty and complexity of geotechnical parameters, it is difficult to design and optimize the anchorage parameters. In order to solve this problem, based on the Zhenfengling tunnel project as the research object, 3D tunnel model was established by ANSYS software, the model was imported into FLAC^3D software for numerical analysis and calculation for the displacement and stress of surrounding rock during construction, using orthogonal experiment methods to analyze factors affecting the stability of surrounding rock. The influence of anchor length, anchor spacing, anchor diameter, the thickness and elastic modulus of spray layer on the displacement of arch waist, arch crown and arch bottom of the tunnel was obtained by using range and variance analysis. The regression model of the relationship between arch surrounding rock displacements and anchorage parameters was determined by fitting regression. The particle swarm optimization algorithm was used to optimize the anchorage parameters in combination with the tunnel section cost formula, and the parameters were compared with those not optimized. Finally, the anchor length is designed as 3 m, the anchor spacing is designed as 1.4 m, the anchor diameter is designed as 21 mm, the thickness of spray layer is designed as 24 cm, and the elastic modulus of spray layer is designed as 24 GPa. The stability requirements can be met, and the economic efficiency is also greatly improved. The cost of support with optimized parameters is 19.4% lower than that of the original design parameters.

     

A three-dimensional equivalent continuum constitutive model for jointed rock masses containing up to three random joint sets

A three dimensional constitutive model is formulated for deformation analysis of jointed rock masses containing up to three joint sets with arbitrary spatial configurations. A representative elementary volume (REV) that represents the deformational response of the rock mass is defined and the constitutive relationships are developed based on superposition of deformations of the REV components. By representing the constitutive relationships in a tensorial form, the model is able to implement deformation anisotropy of jointed rock masses. The Mohr-Coulomb failure criterion with tension cut-off is used for the intact rock and the joint sets. The model is implemented in FLAC^3D and the deformations and strength values calculated by the model are compared with the results from a 3DEC model and analytical solutions. The model results are in good agreement with those obtained from 3DEC.     

起伏地表下的复杂三维地质模型建立与重力异常计算

由于地质体和矿体的形态非常复杂，使用长方体网格离散建立正演模型时可能和真实情况有很大差别，因此计算结果可靠性差。本文提出一种基于约束Delaunay网格剖分的方法对地质体进行离散并进行重力建模，在模型边界等复杂区域使用网格自适应加密技术，将三维地质体离散为有限个四面体；并详细推导出针对四面体网格的重力正演公式，实现了基于约束Delaunay网格剖分技术的三维重力数值模拟；最后，针对一个合成数据模型，将计算解与解析解对比。结果表明，细化网格的模拟结果比粗糙网格更好，满足数值模拟的精度要求。将该方法应用到金川矿区实际地质体建模中，根据局部需要，建立各处网格密度不均匀的三维模型，并计算该模型的地表重力场，而后对比模拟数据与实测数据，结果表明Delaunay网格建模方法具有很强的适用性，能够模拟复杂的地质体重力异常。