WO2023197821A1 - 一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法 - Google Patents

一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法 Download PDF

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WO2023197821A1
WO2023197821A1 PCT/CN2023/082079 CN2023082079W WO2023197821A1 WO 2023197821 A1 WO2023197821 A1 WO 2023197821A1 CN 2023082079 W CN2023082079 W CN 2023082079W WO 2023197821 A1 WO2023197821 A1 WO 2023197821A1
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damage
rock
permeability
relationship
strain
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PCT/CN2023/082079
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French (fr)
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顾清恒
谭云亮
赵光明
陈蕾蕾
孙建
张若飞
刘之喜
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安徽理工大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
    • G01N3/12—Pressure testing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
    • G01N15/082—Investigating permeability by forcing a fluid through a sample
    • G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G06F30/28—Design optimisation, verification or simulation using fluid dynamics, e.g. using Navier-Stokes equations or computational fluid dynamics [CFD]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0019—Compressive
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/003—Generation of the force
    • G01N2203/0042—Pneumatic or hydraulic means
    • G01N2203/0048—Hydraulic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/025—Geometry of the test
    • G01N2203/0256—Triaxial, i.e. the forces being applied along three normal axes of the specimen
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2111/00—Details relating to CAD techniques
    • G06F2111/10—Numerical modelling
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2113/00—Details relating to the application field
    • G06F2113/08—Fluids
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces

Definitions

  • the invention relates to the technical field of overlying rock damage zoning and height prediction in mine stopes, and specifically relates to a method for overlying rock damage zoning and height determination based on the penetration-damage relationship during water-retaining mining.
  • the loss of water above the working surface is directly related to the degree of damage to the water-isolating rock layer.
  • the cracks in the damaged rock layer are connected to each other, the water in the aquifer is likely to be lost through the connected cracks. That is to say, damaged cracks are generated but there is no connection between the cracks.
  • the water-proof rock formation still has water-proof ability.
  • people generally divide the overlying rock that is fractured by movement into caving zones, fissure zones and curved subsidence zones in the vertical direction.
  • the caving zones and fissure zones are generally regarded as water-conducting fissure zones. Obviously, this The division method is not scientific enough for the judgment of water-proof overlying rock layers. In view of this, it is necessary to start from the perspective of damage and establish the relationship between rock layer damage and permeability to regionally divide the mobile damaged rock layers after coal mining to accurately identify good water-proof layers. , can isolate and conduct water within the rock formation range.
  • the methods for determining and predicting the water conductivity range of overlying rocks include empirical methods, geophysical methods, borehole observation methods and numerical simulation methods. Among them, empirical methods lack theoretical foundation, calculation errors often fluctuate greatly, and geophysical methods are not suitable for fractures. The detection accuracy is low, and on-site detection methods can generally obtain more accurate results. However, on-site detection workload is large, and only local areas are detected. Guiding the production of the entire working surface requires a large amount of detection hole layout and detection work. The numerical simulation method can visually display the movement and destruction process of the entire coal seam mining overlying rock, and has been increasingly used in recent years to determine the development range of water-conducting fissures in coal seams.
  • the key to accurately determining the water conductivity range of the overlying rock using numerical simulation methods is based on the constitutive relationship that accurately describes the deformation and damage behavior of the rock mass. Since the theoretical model that comes with the current numerical simulation software has been simplified to a certain extent, although it has certain universality, However, it affects the accuracy of rock formation damage simulation to a certain extent. Therefore, it is necessary to establish a constitutive relationship suitable for describing the mechanical behavior of soft rock in western mining areas and realize its secondary development in simulation software, so as to accurately simulate the development degree of overlying rock damage. and scope.
  • the purpose of the present invention is to provide a method for zoning and height determination of overlying rock damage based on the penetration-damage relationship, which can divide the damage area and determine the height of the roof of the working face after mining, so as to scientifically guide coal seam water conservation mining.
  • a method for overlying rock damage zoning based on the penetration-damage relationship which method includes the following steps:
  • geological and hydrological data of the mine and the design of the mining area of the working face to be mined determine the distribution of overlying rock formations and in-situ stress characteristics of the working face
  • Step 3 Conduct triaxial compression-seepage tests on rocks in different rock layers.
  • a triaxial compression-penetration test was conducted on the standard specimen on a multi-field coupling test system.
  • the axial direction of the testing machine adopts an axial graded loading method. Multiple loading levels are set before and after the peak, and the loading is stepped from low to high throughout the process. , wait until the pore water pressure stabilizes before applying the next level of load until the specimen is damaged; the confining pressure is determined through the previous in-situ stress test, and the water pressure is applied to the standard specimen in a flow control manner; the deformation and deformation of the standard specimen are monitored during the test. The flow of water through the standard specimen is used to obtain the rock stress-strain and seepage-strain relationships during the compression process.
  • the permeability calculation formula is: ;
  • q is the seepage flow rate, mL/min
  • ⁇ is the water injection viscosity
  • mPa ⁇ s is the water injection viscosity
  • L is the length of the standard specimen
  • mm is the length of the standard specimen
  • A is the cross-sectional area of the standard specimen
  • mm 2 is the hydraulic pressure difference, MPa;
  • a and b are parameters related to material properties; is the energy dissipation value corresponding to the initial damage; ;
  • ⁇ is the Poisson's ratio of the rock
  • E is the elastic modulus of the rock
  • GPa is the elastic modulus of the rock
  • ⁇ is the strain
  • ⁇ A is the strain at the compression closure point
  • Step 5 Division of overlying rock damage area based on damage-permeability relationship
  • the stage in which permeability increases slowly with strain is called the slight permeability stage.
  • the rock is slightly cracked and the water barrier properties of the rock are good.
  • the medium permeability stage the stage in which the rock permeability increases.
  • the rapid permeability stage the stage in which the rock permeability increases with strain acceleration.
  • the boundary value between the slight damage area and the medium damage area is D A
  • the medium damage area is D B .
  • a method for determining the height of the overlying rock damage area based on the penetration-damage relationship After the above-mentioned overlying rock damage zoning method based on the penetration-damage relationship, it also includes the following steps:
  • the force acting on the rock is divided into two parts: matrix and fissure.
  • the stress acting on the rock can be expressed by the sum of the stress of the matrix part and the stress of the fissure part, that is ; ;
  • ⁇ e is the partial stress of the matrix
  • ⁇ cr is the residual stress
  • Step 7. Embed the damage constitutive relationship into FLAC3D software
  • the central difference method is used to derive the three-dimensional difference format of the custom constitutive equation:
  • Step 9 Numerical simulation to determine the height of each damage zone
  • the deformation and damage pattern of the overlying rock strata after coal seam mining is simulated. After the calculation is completed, the damage conditions of the plastic failure unit units are retrieved. By comparing with the boundary value of the rock damage area, the range of mild, moderate and severe damage areas is determined.
  • the present invention scientifically and specifically divides the permeability of rock formations damaged by mining. By establishing the relationship between damage and penetration, it divides the rock formation into three stages: slight penetration when the rock formation is slightly damaged, medium penetration when the rock formation is moderately damaged, and rapid penetration when the rock formation is severely damaged. Correspondingly, three areas of slight, moderate and severe damage to the mining overburden are divided, and the damage boundaries at the boundaries of adjacent damage areas are given, which can well and accurately divide the overlying rock damage range.
  • the method for determining the damage height of the mining overburden of the present invention is based on the on-site geological data and the constitutive relationship that truly reflects the rock damage and deformation behavior. It can intuitively obtain the overburden damage degree and regional distribution characteristics without the need for a large number of on-site drilling and detection, and the implementation process fast and convenient.
  • This invention can judge whether the coal seam can achieve water-retaining mining by comparing the development height of the seriously damaged area of the working face and the position of the aquifer, combined with relevant safety mining regulations, and provide a basis for safe and water-retaining mining of coal seams in mines.
  • Figure 1 is a flow chart of an embodiment of the present invention
  • Figure 2 is a schematic diagram of the compression-seepage test according to the embodiment of the present invention.
  • Figure 3 is a schematic diagram of the damage-seepage-strain relationship and stage division according to the embodiment of the present invention.
  • Figure 4 is a schematic diagram of overlying rock damage zoning according to the embodiment of the present invention.
  • Figure 5 is a schematic diagram of the height of the damaged area obtained through numerical simulation according to the embodiment of the present invention.
  • the terms “inside”, “outside”, “upper”, “lower”, “front”, “back”, etc. indicate the orientation or positional relationship based on those shown in the drawings.
  • the orientation or positional relationship is only for the convenience of describing the present invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.
  • the terms “first” and “second” are used for descriptive purposes only and are not to be understood as indicating or implying relative importance.
  • the overlying rock damage zoning and height determination method based on the penetration-damage relationship in this embodiment is applied to a typical submersible coal seam mining mine in an ecologically fragile area in the west. Please refer to Figures 1 to 5.
  • the above method includes the following steps:
  • the distribution of overlying rock strata and in-situ stress characteristics of the working face are determined, which provides a basis for subsequent compression-seepage tests and numerical model construction.
  • the cores are weather-proof packed and transported to the laboratory.
  • the cores from different rock strata are processed into standard specimens. Specifically, the sandy mudstone and fine sandstone cores taken from the site were drilled, cut and cross-section polished to produce a cylindrical standard specimen with a diameter of 50mm and a height of 100mm.
  • Step 3 Conduct triaxial compression-seepage tests on rocks in different rock layers.
  • a triaxial compression-penetration test was conducted on standard specimens (sandy mudstone specimens and fine sandstone specimens) on a multi-field coupling test system.
  • the testing machine adopted an axial graded loading method in the axial direction, with multiple settings before and after the peak. Each loading level is loaded step by step from low to high throughout the process. After the pore water pressure stabilizes, the next level of load is applied until the specimen is damaged.
  • the experimental design is to load 6 to 10 levels before the peak and 8 to 12 levels after the peak.
  • the confining pressure was determined to be 1.5MPa, 3.0MPa, 4.5MPa and 6MPa through preliminary in-situ stress testing, and the water pressure was applied to the standard specimen in a flow control manner;
  • the rock sample is saturated with water. Place the prepared rock standard specimen in a water basin, submerge 1/4 of the height of the specimen, and soak for 2 hours. Then add water to 1/2 of the height of the specimen. After 2 hours, raise the water level to 3 inches of the specimen. /4, soak for 2 hours, then add water to completely submerge the specimen until the mass of the specimen continues to change.
  • test piece Installation of test piece. Install the test piece in the triaxial pressure chamber, as shown in Figure 2. Add permeable plates to the upper and lower surfaces of the test piece and seal them with the upper and lower pressure heads of the testing machine with rubber tubes. Install the axial and circumferential deformation sensors and adjust them to a reasonable range, close the three-axis pressure chamber, and clear the sensor value.
  • Triaxial chamber saturated rock sample After the confining pressure is stabilized, a constant water pressure of 0.1 mL/min is applied to the specimen in a flow control mode, and the rock sample is saturated in a triaxial chamber until the water pressure reaches a predetermined value when water flows out of the water outlet.
  • Axial compression loading adopts graded loading with a loading rate of 0.06 mm/min. After each level of loading, the pore water pressure is stabilized before the next level of loading is carried out until the specimen is damaged.
  • the permeability calculation formula is: ;
  • q is the seepage flow rate, mL/min
  • ⁇ is the water injection viscosity
  • mPa ⁇ s is the water injection viscosity
  • L is the length of the standard specimen
  • mm is the length of the standard specimen
  • A is the cross-sectional area of the standard specimen
  • mm 2 is the hydraulic pressure difference, MPa.
  • a and b are parameters related to material properties; is the energy dissipation value corresponding to the initial damage; ;
  • ⁇ is the Poisson's ratio of the rock
  • E is the elastic modulus of the rock
  • GPa is the elastic modulus of the rock
  • ⁇ is the strain
  • ⁇ A is the strain at the compression closure point
  • Step 5 Division of overlying rock damage area based on damage-permeability relationship
  • the stage in which permeability increases slowly with strain is called the slight permeability stage.
  • the rock is slightly cracked and the water barrier properties of the rock are good.
  • the medium permeability stage the stage in which the rock permeability increases.
  • the rapid permeability stage the stage in which the rock permeability increases with strain acceleration.
  • the areas where water can penetrate slightly, moderately, and quickly after deformation of the rock layer become slight damage areas, moderate damage areas, and severe damage areas respectively, as shown in Figure 4.
  • the boundary values D A and D B between the slightly damaged area and the moderate damage area, and the moderate damage area and the severe damage area of sandy mudstone and fine sandstone are obtained.
  • the force acting on the rock is divided into two parts: matrix and fissure.
  • the stress acting on the rock can be expressed by the sum of the stress of the matrix part and the stress of the fissure part, that is ; ;
  • ⁇ e is the partial stress of the matrix
  • ⁇ cr is the residual stress
  • Step 7. Embed the damage constitutive relationship into FLAC3D software
  • the central difference method is used to derive the three-dimensional difference format of the custom constitutive equation:
  • the three-dimensional difference format of the custom constitutive equation is embedded into the FLAC3D software to obtain a secondary development program for the new constitutive model, which is used to simulate the deformation and damage behavior of rock formations.
  • Step 9 Numerical simulation to determine the height of each damage zone
  • This invention scientifically and specifically divides the permeability of rock formations damaged by mining. By establishing a damage-penetration relationship, it divides the rock formations into three stages: slight penetration when the rock layer is slightly damaged, medium penetration when the rock layer is moderately damaged, and rapid penetration when the rock layer is severely damaged. The corresponding Three areas of slight, moderate and severe damage to the mining overburden are divided, and the damage boundary values at the boundaries of adjacent damage areas are given, which can effectively and accurately divide the overlying rock damage range.
  • the method for determining the damage height of the mining overburden of the present invention is based on the on-site geological data and the constitutive relationship that truly reflects the rock damage and deformation behavior.
  • the damage degree and regional distribution characteristics of the overburden can be intuitively obtained without the need for a large number of on-site drilling detection, and the implementation process is quick and convenient.
  • This invention can judge whether the coal seam can achieve water-retaining mining by comparing the development height of the seriously damaged area of the working face overlying rock and the positional relationship of the aquifer, combined with relevant safety mining specifications, and provide a basis for safe and water-retaining mining of coal seams in mines.

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Abstract

一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法，涉及矿井采场覆岩损伤分区及高度预测技术领域，包括如下步骤：步骤1、岩层分布与地应力环境调查；步骤2、试件制备；步骤3、对不同岩层层位岩石进行三轴压缩-渗流试验；步骤4、建立损伤-渗透关系；步骤5、基于损伤-渗透关系的覆岩损伤区域划分；步骤6、损伤本构关系构建；步骤7、损伤本构关系嵌入至FLAC3D软件；步骤8、建立数值模型；步骤9、数值模拟确定各损伤区高度。该方法可以对工作面开采后工作面顶板进行损伤区域划分及高度确定。

Description

一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法 技术领域
发明涉及矿井采场覆岩损伤分区及高度预测技术领域，具体地说是涉及一种在保水开采时基于渗透-损伤关系的覆岩损伤分区及高度确定方法。
 背景技术
煤层工作面开采后，覆岩运动变形产生破裂损伤，不同层位的岩层损伤也不尽相同，当工作面埋藏较浅或工作面上方有含水层时，覆岩的移动损伤很可能引发地表的沉陷和含水层水的流失。尤其在我国生态环境脆弱的西部矿区，浅部煤层的开采会导致地表宝贵潜水的流失，危害矿区生态环境安全。
 技术问题
工作面上方水的流失与隔水岩层的损伤程度直接相关，当损伤岩层内的裂隙间相互联通时，含水层水才有可能通过联通裂隙流失，也就是说，产生损伤裂隙但裂隙间没有联通的隔水岩层仍具有隔水能力。现阶段，人们一般将运动破裂的覆岩在竖直方向上通常划分为垮落带、裂隙带和弯曲下沉带，其中垮落带和裂隙带一般被视为导水裂隙带，显然这种划分方式对于隔水覆岩层的判断不够科学，鉴于此，有必要从损伤的角度出发，通过建立岩层损伤与渗透能力的关系，对煤层开采后的移动破坏岩层进行区域划分，准确识别良好隔水、可隔水以及导水岩层范围。
覆岩损伤分区后还需对各损伤区范围进行确定，从而指导煤层保水开采。现阶段确定和预判覆岩导水范围的方法包括经验方法、地球物理方法、钻孔观测方法和数值模拟方法等，其中经验方法缺乏理论基础，计算误差往往波动较大，地球物理方法对裂隙的探测精度低，现场探测方法一般可得到较准确的结果，但现场探测工作量大，而且探测出来的只是局部区域的，指导整个工作面的生产需要大量的探测孔布设及探测工作。而数值模拟方法作可直观显示整个煤层开采覆岩运动破坏过程，近年来被越来越多应用于煤层导水裂隙发育范围的判断。
数值模拟方法准确判断覆岩导水范围关键是需要基于准确描述岩体变形损伤行为的本构关系，由于目前数值模拟软件自带的理论模型做了一定的简化，虽然具有一定的普适性，但一定程度上影响了岩层破坏模拟的精准性，因此还需建立适用于描述西部矿区软岩力学行为的本构关系并实现其在模拟软件中的二次开发，进而准确模拟覆岩损伤发育程度和范围。
 技术解决方案
本发明的目的在于提供一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法，可以对工作面开采后工作面顶板进行损伤区域划分及高度确定，以科学指导煤层保水开采。
为了达到上述目的，本发明所采用的技术解决方案如下：
一种基于渗透-损伤关系的覆岩损伤分区方法，所述方法包括如下步骤：
步骤1、岩层分布与地应力环境调查
根据矿井地质水文资料和待开采工作面采区设计，确定工作面覆岩地层分布以及地应力特征；
步骤2、试件制备
在待开采工作面顺槽内向工作面顶板的不同岩层层位打孔取芯，将不同岩层层位的岩芯加工制作成为标准试件；
步骤3、对不同岩层层位岩石进行三轴压缩-渗流试验
在多场耦合试验系统上对标准试件进行三轴压缩-渗透试验，试验机轴向采用轴向分级加载方式，峰前、峰后均设置多个加载等级，全程从低到高逐级加载，待孔隙水压力稳定后再施加下一级载荷，直至试件破坏；围压通过前期的地应力测试确定，水压以流量控制方式对标准试件施加；试验过程中监测标准试件变形和水通过标准试件的流量，获得压缩过程中岩石应力-应变和渗流-应变关系，其中，渗透率的计算公式为： ；
式中， q为渗流流量，mL / min，μ 为注水粘度，mPa·s， L为标准试件长度，mm， A 为标准试件截面积，mm 2， 为水力压差，MPa；
步骤4、建立损伤-渗透关系
根据岩石三轴压缩-渗流试验中的应力-应变关系，得到岩石的损伤演化方程，损伤变量表达式为： ；
式中， a、 b为与材料性质有关的参数； 为初始损伤对应的能量耗散值； ；
式中， υ为岩石的泊松比， E为岩石的弹性模量，GPa， ε为应变， ε A为压密闭合点处的应变；
以应变为横坐标，以损伤变量和渗透率为纵坐标，绘制损伤-应变和渗透率-应变关系于坐标系中，得到损伤和渗透率的对应关系；
步骤5、基于损伤-渗透关系的覆岩损伤区域划分
根据渗透率-应变关系，将渗透率随应变增加缓慢增长的阶段称为轻微渗透阶段，此阶段岩石轻微破裂，岩石隔水性能较好；将轻微渗透阶段后渗透率随应变呈近似线性增长的阶段称为中等渗透阶段，此阶段岩石损伤速度增加，但总体的渗透能力依然不高，仍具备一定的隔水能力；将中等渗透阶段之后岩石渗透率随应变加速增加的阶段称为快速渗透阶段，此阶段岩石损伤急剧增加，裂隙联通导致岩石失去隔水能力；
对应的，岩层变形后水可以轻微渗透、中等渗透和快速渗透的区域分别成为轻微损伤区、中等损伤区和严重损伤区，其中，轻微损伤区与中等损伤区界值为 D A，中等损伤区与严重损伤区界值为 D B。
一种基于渗透-损伤关系的覆岩损伤区高度确定方法，在上述的一种基于渗透-损伤关系的覆岩损伤分区方法之后，还包括以下步骤：
步骤6、损伤本构关系构建
将作用在岩石上的力分为基质和裂隙两部分，作用在岩石上的应力可用基质部分应力和裂隙部分应力之和表示，即 ； ；
其中， σ e为基质部分应力， σ cr为残余应力；
步骤7、损伤本构关系嵌入至FLAC3D软件
采用中心差分法推导得到自定义本构方程的三维差分格式：
球应力： ；
偏应力： ;
其中， ， ；
式中， 、 为一个时间步内新、老球应力； 为时间步 内的球应变； δ ij为kronecker delta符号； 、 分别为一个时间增量步内新、老偏应力； D t为材料在 t时刻的损伤变量； G为材料剪切模量，GPa， K为材料体积模量，GPa， 为时间步 内的偏应变；
将自定义本构方程的三维差分格式嵌入到FLAC3D软件中，得到新建本构模型的二次开发程序，用于对岩层变形损伤行为的模拟；
步骤8、建立数值模型
根据需要研究的煤层开采及覆岩水文地质条件，建立数值模型，设置边界条件并赋予各模拟岩层力学参数，岩层受力-变形演化采用步骤7的二次开发程序进行运算；
步骤9、数值模拟确定各损伤区高度
模拟煤层开采后上覆岩层的变形损伤规律，在运算结束后，对发生塑性破坏单元体的损伤情况进行调取，通过和岩石损伤区域界值对比，确定出轻微、中等及严重损伤区范围。
 有益效果
本发明的有益技术效果是：
1、本发明对采动损伤岩层渗透性能进行了科学具体的划分，通过建立损伤-渗透的关系，划分了岩层轻微损伤时轻微渗透、中等损伤时中等渗透以及严重损伤时快速渗透三个阶段，对应的划分了采动覆岩轻微、中等和严重损伤三个区域，并给出了相邻损伤区分界处的损伤界值，可很好并且准确的对覆岩损伤范围进行分区。
2、本发明采动覆岩的损伤高度确定方法依据现场地质资料以及真实反映岩石损伤变形行为的本构关系，不用现场大量打孔探测便可直观得到覆岩损伤程度和区域分布特征，实现过程快捷方便。
3、本发明可通过对比工作面覆岩严重损伤区发育高度与含水层的位置关系，结合相关安全开采规范，判断煤层能否实现保水开采，为矿井煤层安全、保水开采提供依据。
 附图说明
图1为本发明实施例的流程图；
图2为本发明实施例压缩-渗流试验示意图；
图3为本发明实施例损伤-渗流-应变关系及阶段划分示意图；
图4为本发明实施例覆岩损伤分区示意图；
图5为本发明实施例数值模拟获得损伤区高度示意图。
 本发明的实施方式
为使本发明的目的、技术方案和有益效果更加清楚明白，以下结合具体实施例，并参照附图，对本发明进一步详细说明。本发明某些实施例于后方将参照所附附图做更全面性地描述，其中一些但并非全部的实施例将被示出。实际上，本发明的各种实施例可以许多不同形式实现，而不应被解释为限于此数所阐述的实施例；相对地，提供这些实施例使得本发明满足适用的法律要求。
在本发明的描述中，需要说明的是，术语“内”、“外”、“上”、“下”、“前”、“后”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性。
本实施例的一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法，应用于西部某生态脆弱区典型潜水下煤层开采矿井，请参考图1至图5所示。
上述方法包括如下步骤：
步骤1、岩层分布与地应力环境调查
根据矿井地质水文资料和待开采工作面采区设计，确定工作面覆岩地层分布以及地应力特征，为后续的压缩-渗流试验及数值模型构建提供依据。
步骤2、试件制备
在待开采工作面顺槽内向工作面顶板的不同岩层层位打孔取芯，岩芯进行防风化包装并运送到实验室，将不同岩层层位的岩芯加工制作成为标准试件。具体的，通过对取自现场的砂质泥岩和细砂岩岩芯进行钻取、切割及断面打磨，制作成为直径50mm、高度100mm的圆柱形标准试件。
步骤3、对不同岩层层位岩石进行三轴压缩-渗流试验
在多场耦合试验系统上对标准试件（砂质泥岩试件和细砂岩试件）进行三轴压缩-渗透试验，试验机轴向采用轴向分级加载方式，峰前、峰后均设置多个加载等级，全程从低到高逐级加载，待孔隙水压力稳定后再施加下一级载荷，直至试件破坏。其中，试验设计峰前加载6~10个等级，峰后加载8~12个等级。围压通过前期的地应力测试确定为1.5MPa、3.0MPa、4.5MPa和6MPa，水压以流量控制方式对标准试件施加；
试验过程中保持室内温度在25℃，岩石三轴压缩-渗流试验的具体步骤为：
① 岩样饱水处理。将制取的岩石标准试件放在水盆里，淹没试件高度的1/4，浸泡2 h，然后加水至试件高度的1/2，2 h后，升高水面至试件的3/4处，浸泡2 h，再加水全部淹没试件，直至试件质量连续不再变化。
② 试件安装。将试件安装在三轴压力室内，如图2所示，试件上下表面加透水板并与试验机上下压头用橡胶管连接密封，安装轴向和环向变形传感器并将其调整到合理量程，封闭三轴压力室内，对传感器数值清零。
③ 施加围压。向压力室内充油至出油管内没有气泡产生为止，关闭出油管路，施加至预定围压并进行伺服控制。
④ 三轴室饱和岩样。围压稳定后，以流量控制方式对试件施加0.1mL/min的恒定水压，对岩样进行三轴室内饱和，直到出水口有水流出时加载水压至预定值。
⑤ 轴向加载。轴压加载采用分级加载，加载速率为0.06mm/min，每级加载后待孔隙水压稳定后再进行下一级加载，直到试件破坏。
试验过程中监测标准试件变形和水通过标准试件的流量，获得压缩过程中岩石应力-应变和渗流-应变关系，其中，渗透率的计算公式为： ；
式中， q为渗流流量，mL / min，μ 为注水粘度，mPa·s， L为标准试件长度，mm， A 为标准试件截面积，mm 2， 为水力压差，MPa。
步骤4、建立损伤-渗透关系
根据岩石三轴压缩-渗流试验中的应力-应变关系，得到岩石的损伤演化方程，损伤变量表达式为： ；
式中， a、 b为与材料性质有关的参数； 为初始损伤对应的能量耗散值； ；
式中， υ为岩石的泊松比， E为岩石的弹性模量，GPa， ε为应变， ε A为压密闭合点处的应变；
以应变为横坐标，以损伤变量和渗透率为纵坐标，绘制损伤-应变和渗透率-应变关系于坐标系中，得到损伤和渗透率的对应关系，如图3所示。
步骤5、基于损伤-渗透关系的覆岩损伤区域划分
根据渗透率-应变关系，将渗透率随应变增加缓慢增长的阶段称为轻微渗透阶段，此阶段岩石轻微破裂，岩石隔水性能较好；将轻微渗透阶段后渗透率随应变呈近似线性增长的阶段称为中等渗透阶段，此阶段岩石损伤速度增加，但总体的渗透能力依然不高，仍具备一定的隔水能力；将中等渗透阶段之后岩石渗透率随应变加速增加的阶段称为快速渗透阶段，此阶段岩石损伤急剧增加，裂隙联通导致岩石失去隔水能力；
对应的，岩层变形后水可以轻微渗透、中等渗透和快速渗透的区域分别成为轻微损伤区、中等损伤区和严重损伤区，如图4所示。通过划分损伤-渗透-应变关系曲线得到砂质泥岩和细砂岩轻轻微损伤区与中等损伤区、中等损伤区与严重损伤区界值D A、D B。
步骤6、损伤本构关系构建
将作用在岩石上的力分为基质和裂隙两部分，作用在岩石上的应力可用基质部分应力和裂隙部分应力之和表示，即 ； ；
其中， σ e为基质部分应力， σ cr为残余应力。
步骤7、损伤本构关系嵌入至FLAC3D软件
采用中心差分法推导得到自定义本构方程的三维差分格式：
球应力： ；
偏应力： ；
其中， ， ；
式中， 、 为一个时间步内新、老球应力； 为时间步 内的球应变； δ ij为kronecker delta符号； 、 分别为一个时间增量步内新、老偏应力； D t为材料在 t时刻的损伤变量； G为材料剪切模量，GPa， K为材料体积模量，GPa， 为时间步 内的偏应变；
将自定义本构方程的三维差分格式嵌入到FLAC3D软件中，得到新建本构模型的二次开发程序，用于对岩层变形损伤行为的模拟。
步骤8、建立数值模型
根据需要研究的煤层开采及覆岩水文地质条件，建立数值模型，设置边界条件并赋予各模拟岩层力学参数，岩层受力-变形演化采用步骤7的二次开发程序进行运算，直至运算达到平衡状态为止。
步骤9、数值模拟确定各损伤区高度
模拟煤层开采后上覆岩层的变形损伤规律，在运算结束后，对发生塑性破坏单元体的损伤情况进行调取，通过和岩石损伤区域界值（ D A、 D B）对比，确定出轻微、中等及严重损伤区范围，如图5所示。
至此，已经结合附图对本实施例进行了详细描述。依据以上描述，本领域技术人员应当对本发明一种基于渗透-损伤关系的覆岩损伤分区及高度确定方法有了清楚的认识。本发明对采动损伤岩层渗透性能进行了科学具体的划分，通过建立损伤-渗透的关系，划分了岩层轻微损伤时轻微渗透、中等损伤时中等渗透以及严重损伤时快速渗透三个阶段，对应的划分了采动覆岩轻微、中等和严重损伤三个区域，并给出了相邻损伤区分界处的损伤界值，可很好并且准确的对覆岩损伤范围进行分区。本发明采动覆岩的损伤高度确定方法依据现场地质资料以及真实反映岩石损伤变形行为的本构关系，不用现场大量打孔探测便可直观得到覆岩损伤程度和区域分布特征，实现过程快捷方便。本发明可通过对比工作面覆岩严重损伤区发育高度与含水层的位置关系，结合相关安全开采规范，判断煤层能否实现保水开采，为矿井煤层安全、保水开采提供依据。
以上所述的具体实施例，对本发明的目的、技术方案和有益效果进行了进一步详细说明，所应理解的是，以上所述仅为本发明的具体实施例而已，并不用于限制本发明，凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (2)

  1. 一种基于渗透-损伤关系的覆岩损伤分区方法，其特征在于，所述方法包括如下步骤：
    步骤1、岩层分布与地应力环境调查
    根据矿井地质水文资料和待开采工作面采区设计，确定工作面覆岩地层分布以及地应力特征；
    步骤2、试件制备
    在待开采工作面顺槽内向工作面顶板的不同岩层层位打孔取芯，将不同岩层层位的岩芯加工制作成为标准试件；
    步骤3、对不同岩层层位岩石进行三轴压缩-渗流试验
    在多场耦合试验系统上对标准试件进行三轴压缩-渗透试验，试验机轴向采用轴向分级加载方式，峰前、峰后均设置多个加载等级，全程从低到高逐级加载，待孔隙水压力稳定后再施加下一级载荷，直至试件破坏；围压通过前期的地应力测试确定，水压以流量控制方式对标准试件施加；试验过程中监测标准试件变形和水通过标准试件的流量，获得压缩过程中岩石应力-应变和渗流-应变关系，其中，渗透率的计算公式为： ；
    式中， q为渗流流量，mL / min，μ为注水粘度，mPa·s， L为标准试件长度，mm， A 为标准试件截面积，mm 2， 为水力压差，MPa；
    步骤4、建立损伤-渗透关系
    根据岩石三轴压缩-渗流试验中的应力-应变关系，得到岩石的损伤演化方程，损伤变量表达式为： ；
    式中， a、 b为与材料性质有关的参数；
    为初始损伤对应的能量耗散值；
    ；
    式中， υ为岩石的泊松比， E为岩石的弹性模量，GPa， ε为应变， ε A为压密闭合点处的应变；
    以应变为横坐标，以损伤变量和渗透率为纵坐标，绘制损伤-应变和渗透率-应变关系于坐标系中，得到损伤和渗透率的对应关系；
    步骤5、基于损伤-渗透关系的覆岩损伤区域划分
    根据渗透率-应变关系，将渗透率随应变增加缓慢增长的阶段称为轻微渗透阶段，此阶段岩石轻微破裂，岩石隔水性能较好；将轻微渗透阶段后渗透率随应变呈近似线性增长的阶段称为中等渗透阶段，此阶段岩石损伤速度增加，但总体的渗透能力依然不高，仍具备一定的隔水能力；将中等渗透阶段之后岩石渗透率随应变加速增加的阶段称为快速渗透阶段，此阶段岩石损伤急剧增加，裂隙联通导致岩石失去隔水能力；
    对应的，岩层变形后水可以轻微渗透、中等渗透和快速渗透的区域分别成为轻微损伤区、中等损伤区和严重损伤区，其中，轻微损伤区与中等损伤区界值为 D A，中等损伤区与严重损伤区界值为 D B。
  2. 一种基于渗透-损伤关系的覆岩损伤区高度确定方法，其特征在于，在权利要求1的一种基于渗透-损伤关系的覆岩损伤分区方法之后，还包括以下步骤：
    步骤6、损伤本构关系构建
    将作用在岩石上的力分为基质和裂隙两部分，作用在岩石上的应力可用基质部分应力和裂隙部分应力之和表示，即 ； ；
    其中， σ e为基质部分应力， σ cr为残余应力；
    步骤7、损伤本构关系嵌入至FLAC3D软件
    采用中心差分法推导得到自定义本构方程的三维差分格式：
    球应力： ；
    偏应力： ；
    其中， ， ；
    式中， 、 为一个时间步内新、老球应力； 为时间步 内的球应变； δ ij为kronecker delta符号； 、 分别为一个时间增量步内新、老偏应力； D t为材料在 t时刻的损伤变量； G为材料剪切模量，GPa， K为材料体积模量，GPa， 为时间步 内的偏应变；
    将自定义本构方程的三维差分格式嵌入到FLAC3D软件中，得到新建本构模型的二次开发程序，用于对岩层变形损伤行为的模拟；
    步骤8、建立数值模型
    根据需要研究的煤层开采及覆岩水文地质条件，建立数值模型，设置边界条件并赋予各模拟岩层力学参数，岩层受力-变形演化采用步骤7的二次开发程序进行运算；
    步骤9、数值模拟确定各损伤区高度
    模拟煤层开采后上覆岩层的变形损伤规律，在运算结束后，对发生塑性破坏单元体的损伤情况进行调取，通过和岩石损伤区域界值对比，确定出轻微、中等及严重损伤区范围。
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