CN104655820A - Judging, grading and processing method of rockburst of hard rocks for tunnel - Google Patents

Abstract

The invention discloses a judging, grading and processing method of rockburst of hard rocks for a tunnel. The method comprises the steps of geological survey, designing of schemes, geological generalization and numerical simulation modeling to finally obtain rockburst prevention and control suggestions and measures. The method has the advantages that tunnel construction with high stress can be improved, the security risk caused by rockburst in the tunnel construction is reduced, the security expenses are reduced, the active economic benefit is achieved, the security risk is greatly reduced, the construction period is shortened, the cost is reduced, and the input of security expenses is reduced.

Description

The judgement of tunnel hard rock rock burst, grade classification and disposal route

Technical field

The present invention relates to the differentiation of a kind of tunnel hard rock rock burst and the technology of improvement, the judgement of specifically a kind of tunnel hard rock rock burst, grade classification and disposal route, belong to hard rock rock burst field, tunnel.

Background technology

Rock burst, mainly by testing the intensity of rock, mainly comprises indoor Rock Under Uniaxial Compression strength test and triaxial test of rock, the test of Test in Situ elastic modulus, field geological investigation.After terrestrial stress size is surveyed, generally Prediction for Rock Burst appraisal procedure can adopt Standard for classification of engineering rock masses diagnostic method, Russenes diagnostic method, Turchaninov diagnostic method, the one in Hoek diagnostic method generally adopted in strength theory to differentiate, but above-mentioned traditional method security is lower, security costs drops into larger, long in time limit, add production cost.

Summary of the invention

In order to solve the problem, the present invention devises the judgement of a kind of tunnel hard rock rock burst, grade classification and disposal route, can high-ground stress constructing tunnel, to reducing rock burst causes in constructing tunnel security risk, reduce security costs and have positive economic benefit, greatly reduce security risk, shorten the duration, reduce cost, decrease the input of security costs.

Technical scheme of the present invention is:

The judgement of tunnel hard rock rock burst, grade classification and a disposal route, comprise the following steps:

(1) geologic examination, comprises physical geography situation, bottom lithology, tectonic structure landform, unfavorable geology and Special Rock, hydrogeological condition;

(2) according to geology investigation result, design proposal;

(3) by indoor sillar Experiments of Machanics, detecting earth stress and the test of bullet mould, Project Areas Study on Rock Stress and rock burst assessment, geological generalization and numerical simulation model is obtained;

(4) by coffer mechanics deterioration research and Analyses of Tunnel Wall Rock Stability analysis, rock burst prevention and control suggestion and measure is obtained.

Wherein, indoor sillar Experiments of Machanics are the sillar of tunnel surrounding and rock mass strength test, comprise indoor Rock Under Uniaxial Compression strength test and triaxial test of rock, the test of Test in Situ elastic modulus, field geological investigation.

Experimentation adopts the mode of Bit andits control, adopts one-time continuous Loading Method step by step, continuously record load and strain value, until test specimen destroys.Axle pressure in experiment is measured by the load measurement column demarcated, and longitudinal, the transversely deforming of sample are measured by foil gauge.The stress suffered by sample and vertical and horizontal strain curve is recorded in test.The breakdown strength of sample is the peak stress in stress ~ strain, and elastic modulus E is defined as the ratio of stress and straight-line segment starting point on longitudinal strain relation curve and terminal stress difference and corresponding strain difference; Poisson ratio is defined as stress and straight-line segment starting point on longitudinal strain relation curve and the ratio of terminal transverse strain difference with longitudinal strain difference.

Modulus of Elasticity of Rock Mass test adopts boring elastic modulus method: boring elastic modulus experiment adopts BJ-91A borehole jack to carry out, and this borehole jack forms primarily of two road compression systems, displacement measurement system and pressure measurement system.Utilize four of instrument internal jack pistons to promote during experiment two pieces of rigid bearing plates apply symmetry band load to the wall of a borehole rock mass.Bearing plate is equipped with LVDT linear differential transformer displacement transducer, is used for measuring the radial deformation of borehole wall rock mass when loading, directly measures with the dynamometer be arranged on piston and exerting oneself.

Wherein, detecting earth stress: comprise and survey and draw in detail typical hole section and sample, and carry out field survey, assesses tunnel different buried depth country rock rock burst in conjunction with field data, provides country rock rock burst grade and the Close Tunnel soft rock large deformation buried depth degree of depth.

Rock mass detecting earth stress adopts hydraulic fracturing to survey.Hydraulic fracturing geostress survey utilizes a pair expandable rubber packer, and in predetermined MTD packing one section boring, then pumping liquid is exerted pressure to this section of boring, and the pressure characteristic value according to fracturing process curve calculates terrestrial stress.

When hydraulic pressure increases, boring crag tangential stress drops to tensile stress state gradually, and along with the increase of hydraulic pressure, tension also increases gradually, and when tension is equal to or greater than the tensile strength of country rock, crack appears in boring crag.At this moment the hydraulic pressure of pressure-bearing section is exactly parting pressure.

In hydraulic fracturing geostress survey, according to maximum, minimum horizontal principal stress size of holing can be determined in process of the test, orientation of principal stress can be determined according to the fracture breaks direction of die device record simultaneously.

Wherein, the deterioration of tunnel surrounding mechanical property judges: comprise and carry out on-the-spot sonic test to tunnel surrounding diverse location, and binding tests data separate numerical simulation means analyzes surrounding rock stress distribution law and coffer mechanics property-deterioration rule under specifically stress condition.

Adopt isotropy damage model, according to regulation in " hydraulic structure rock foundation excavation project technical manual ", as η > 10%, namely judge that rock mass is subject to explosion damage and failure.Corresponding Rock Damage threshold value is D=0.19.

Wherein, Analyses of Tunnel Wall Rock Stability is analyzed and rock burst prevention and control: be included on the previous computation model basis set up and carry out the regularity that country rock weakens experimental study surrouding rock stress adjustment under large ground pressure, and carry out predicting for contingent rock burst destruction and divide rock burst grade, measure is targetedly proposed.

The present invention is in conjunction with indoor sillar mechanical test, the terrestrial stress size of hydraulic fracturing test, the result of Project Areas Study on Rock Stress and rock burst assessment and advance geologic prediction, and the region of location and rock burst divided rank occurs in comprehensive descision rock burst; By the treatment measures under the research of coffer mechanics property-deterioration, the different rock burst grade of the analysis integrated formulation of Analyses of Tunnel Wall Rock Stability.

Whether the present invention carries out comprehensive descision rock burst in conjunction with situations such as advance geologic prediction situation, boring announcement situation, rock mass strengths exists; Hydraulic fracturing is adopted the rock mass in tunnel to be carried out to the actual measurement of terrestrial stress size; Adopt Standard for classification of engineering rock masses diagnostic method, Russenes diagnostic method, Turchaninov diagnostic method, these four kinds of diagnostic methods of Hoek diagnostic method to carry out qualitative and quantitative analysis, and combination actual excavation announcement situation carry out comprehensive evaluation, divides rock burst grade.

The invention has the advantages that: occur that the possibility of rock burst hazard is very large at high-ground stress region Deep-buried Long And Big Tunnels, carry out the test of terrestrial stress and the prevention work of rock burst hazard, effectively ensure that the personal safety of site operation personnel, strong technical support is provided for tunnel is through as early as possible, effective means are provided to the prediction of geology engineering project disaster and control in real time, to safety in production, there is directive significance; Can high-ground stress constructing tunnel, to reducing security risk that in constructing tunnel, rock burst causes, reduce security costs and have positive economic benefit, greatly reduce security risk, shorten the duration, reduce cost, decrease the input of security costs.

Below in conjunction with accompanying drawing, the invention will be further described with enforcement.

Accompanying drawing explanation

Fig. 1 is the stress envelope containing a boring in the rock mass of the embodiment of the present invention;

Fig. 2 is the enlarged drawing of Fig. 1;

Fig. 3 is the technical route figure of the embodiment of the present invention.

Embodiment

Below the preferred embodiments of the present invention are described, should be appreciated that preferred embodiment described herein is only for instruction and explanation of the present invention, is not intended to limit the present invention.

Embodiment 1

The judgement of tunnel hard rock rock burst, grade classification and a disposal route, comprise the following steps:

1) sillar of tunnel surrounding and rock mass strength test: comprise indoor Rock Under Uniaxial Compression strength test and triaxial test of rock, the test of Test in Situ elastic modulus, field geological investigation.

Sillar Experimental Study On Mechanical Properties carries out in RMT-150 Rock experiment system, sample is grouan, take from the terrestrial stress drilling core at DK223+100 place, Meihuashan Nature Reserve tunnel, sample is all processed in pilot plant of Wuhan rock-soil mechanics research institute of the Chinese Academy of Sciences, the direct deviation of sample is less than 0.2mm, section nonparallelism is less than 0.02mm, and the deviation of end face and axis verticality is less than 0.001 radian, and all samples are axially axially consistent with core.As requested, carried out the compressive strength of rock test of single shaft and normal triaxial respectively, specimen size is φ 50mm × 100mm.

Experimentation adopts the mode of Bit andits control, adopts one-time continuous Loading Method step by step, continuously record load and strain value, until test specimen destroys.Axle pressure in experiment is measured by the load measurement column demarcated, and longitudinal, the transversely deforming of sample are measured by foil gauge.The stress suffered by sample and vertical and horizontal strain curve is recorded in test.The breakdown strength of sample is the peak stress in stress ~ strain, and elastic modulus E is defined as the ratio of stress and straight-line segment starting point on longitudinal strain relation curve and terminal stress difference and corresponding strain difference; Poisson ratio is defined as stress and straight-line segment starting point on longitudinal strain relation curve and the ratio of terminal transverse strain difference with longitudinal strain difference, such as formula shown:

$\mathrm{\σ}=\frac{P}{A}$

$E=\frac{{\mathrm{\σ}}_b-{\mathrm{\σ}}_a}{{\mathrm{\ϵ}}_{\mathrm{hb}}-{\mathrm{\ϵ}}_{\mathrm{ha}}}$

$v=\frac{{\mathrm{\ϵ}}_{\mathrm{db}}-{\mathrm{\ϵ}}_{\mathrm{da}}}{{\mathrm{\ϵ}}_{\mathrm{hb}}-{\mathrm{\ϵ}}_{\mathrm{ha}}}$

In formula: σ-peak stress or breakdown strength, (MPa);

P-load, N;

A-specimen cross section area, mm2;

E-elastic modulus of rock, MPa;

V-rock elasticity Poisson ratio;

σ _astraight-line segment starting point stress value on-stress and longitudinal strain relation curve, MPa;

σ _bstraight-line segment terminal stress value on-stress and longitudinal strain relation curve, MPa;

ε _ha-stress is σ _atime longitudinal strain value;

ε _hb-stress is σ _btime longitudinal strain value;

ε _da-stress is σ _atime transverse strain value;

ε _db-stress is σ _btime longitudinal strain value;

Modulus of Elasticity of Rock Mass test adopts boring elastic modulus method: boring elastic modulus experiment adopts BJ-91A borehole jack to carry out, and this borehole jack forms primarily of two road compression systems, displacement measurement system and pressure measurement system.Utilize four of instrument internal jack pistons to promote during experiment two pieces of rigid bearing plates apply symmetry band load to the wall of a borehole rock mass.Bearing plate is equipped with LVDT linear differential transformer displacement transducer, is used for measuring the radial deformation of borehole wall rock mass when loading, directly measures with the dynamometer be arranged on piston and exerting oneself.

Distortion by experiment under different pressures, calculates deformation modulus or elastic modulus E (GPa) value of test position rock mass according to formula (1):

$E=A*H*D*T^{*}(v,\mathrm{\β})*\frac{\mathrm{\ΔQ}}{\mathrm{\ΔD}}$

In formula: the influence coefficient of A-three-dimensional problem;

H-pressure correcting coefficient;

D-bore diameter (mm);

Δ Q-pressure increment (MPa);

Δ D-incremental deformation (mm);

T ^*the coefficient of ()-relevant with rock mass Poisson ratio with bearing plate width when hole wall (contact angle of circumference size), T* (0.25,22.50)=2.141, T* (0.25,150)=2.547.

When calculating the elastic modulus of boring rock mass, the Δ Q in formula, Δ D get the linearity range increment size of Diagram of change in pressure high-pressure section; When calculating deformation modulus, the Δ Q in formula, Δ D get the low-pressure section change value in Diagram of change in pressure.

2) tunnel detecting earth stress: comprise and survey and draw in detail typical hole section and sample, and carry out field survey, assesses tunnel different buried depth country rock rock burst in conjunction with field data, provides country rock rock burst grade and the Close Tunnel soft rock large deformation buried depth degree of depth.

Rock mass detecting earth stress adopts hydraulic fracturing to survey

The method of testing council of ISRM has promulgated " measuring the suggesting method of rock stress " for 1987.Comprise the stress recovery mensuration of the boring aperture deformation measurement method of USBM type boring aperture deformation gauge, CSIR (CSIR O) type boring triaxial strain meter borehole wall strain measurement method, hydraulic fracturing and rock mass surface stress.

Compared with other three kinds of measuring methods, hydraulic fracturing has other advantage following:

A. fathom dark;

B. do not need Rock Elastic Parameters to participate in calculating during data compilation, can avoid because Rock Elastic Parameters value is forbidden the error that causes;

C. crag field of load comparatively wide (boring pressure-bearing section degree can reach 1-2 rice), can avoid the limitation of " point " stress state and the impact of geologic condition unevenness;

D. simple to operate, test period is short.

Therefore, hydraulic fracturing is widely used in the every field of the rock engineerings such as water power, traffic, mine and geodynamic study.

Hydraulic fracturing geostress survey utilizes a pair expandable rubber packer, and in predetermined MTD packing one section boring, then pumping liquid is exerted pressure to this section of boring, and the pressure characteristic value according to fracturing process curve calculates terrestrial stress.

Hydraulic fracturing geostress survey principle based on elasticity plane problem, and introduces following three hypothesis:

A. country rock is linear, even, isotropic elastic body;

B., when country rock is porous medium, the fluid of injection flows at rock mass hole by Darcy's law;

C. in rock mass, a principal direction of terrestrial stress is vertical, and consistent to gaging hole with vertical, size equals the pressure of superincumbent stratum.

According to theory of elasticity, when boring a boring in the rock mass with stress field, borehole circumference rock mass will produce secondary state of stress, and the relation between it and terrestrial stress is as follows:

${\mathrm{\σ}}_z^{\′}=-2\mathrm{\μ}[({\mathrm{\σ}}_x-{\mathrm{\σ}}_y)\frac{a^2}{r^2}\cos 2\mathrm{\θ}+2{\mathrm{\τ}}_{\mathrm{xy}}\frac{a^2}{r^2}\sin 2\mathrm{\θ}]+{\mathrm{\σ}}_v$

${\mathrm{\σ}}_r^{\′}=\frac{{\mathrm{\σ}}_x+{\mathrm{\σ}}_y}{2}(1-\frac{a^2}{r^2})+\frac{{\mathrm{\σ}}_x-{\mathrm{\σ}}_y}{2}(1+3\frac{a^4}{r^4}-4\frac{a^2}{r^2})\cos 2\mathrm{\θ}+{\mathrm{\τ}}_{\mathrm{xy}}(1+3\frac{a^4}{r^4}-4\frac{a^2}{r^2})\sin 2\mathrm{\θ}$

${\mathrm{\σ}}_{\mathrm{\θ}}^{\′}=\frac{{\mathrm{\σ}}_x+{\mathrm{\σ}}_y}{2}(1+\frac{a^2}{r^2})-\frac{{\mathrm{\σ}}_x-{\mathrm{\σ}}_y}{2}(1+3\frac{a^4}{r^4})\cos 2\mathrm{\θ}-{\mathrm{\τ}}_{\mathrm{xy}}(1+3\frac{a^4}{r^4})\sin 2\mathrm{\θ}$

${\mathrm{\τ}}_{\mathrm{\θr}}^{\′}=\frac{{\mathrm{\σ}}_x-{\mathrm{\σ}}_y}{2}(1-3\frac{a^4}{r^4}+2\frac{a_2}{r^2})\sin 2\mathrm{\θ}+{\mathrm{\τ}}_{\mathrm{xy}}(1-3\frac{a^2}{r^2}+2\frac{a^2}{r^2})\cos 2\mathrm{\θ}$

${\mathrm{\τ}}_{\mathrm{\θz}}^{\′}=({\mathrm{\τ}}_{\mathrm{xy}}\cos \mathrm{\θ}-{\mathrm{\τ}}_{\mathrm{zx}}\sin \mathrm{\θ})(1+\frac{a^2}{r^2})$

${\mathrm{\τ}}_{\mathrm{rz}}^{\′}=({\mathrm{\τ}}_{\mathrm{yz}}\sin \mathrm{\θ}-{\mathrm{\τ}}_{\mathrm{zx}}\cos \mathrm{\θ})(1-\frac{a^2}{r^2})$

In formula, a is boring radius, and r is radial distance, and θ is the angle of footpath, pole and axle X, and Z is borehole axial, points to aperture.μ is Rock Poisson Ratio Using, σ _vfor original axial direction principle stress (covering rock gravity to determine from above).

In the stress state of borehole wall place (r=a) be:

σ′ _θ＝(σ _x+σ _y)-2(σ _x-σ _y)cos2θ-4τ _xysin2θ

τ′ _θz＝2τ _yzcos2θ-2τ _zxsinθ

Notice that the principle stress in stress field is drilling axis direction, have τ ' _xy=τ ' _yz=τ ' _zx=0, meanwhile, coordinate axis X is taken at the orientation of principal stress in boring cross section, and remove the subscript in formula 5-3 for simplicity, formula 5-4 is:

σ _θ＝(σ _H+σ _h)-2(σ _H-σ _h)cos2θ

σ _z＝-2μ(σ _H-σ _h)cos2θ+σ _v

In formula, σ _hand σ _hbe respectively minimum and maximum horizontal principal stress on boring xsect, θ is polar angle, being just counterclockwise.

As boring pressure-bearing fluid injection pressurized P _wtime, namely country rock produces additional profiled bar.According to unlimited thick cyclinder Solution of Elasticity Theory, the additional profiled bar that country rock produces is:

${\mathrm{\σ}}_{\mathrm{\θ}}^{\′\′}=-P_w\frac{a^2}{r^2}$

${\mathrm{\σ}}_r^{\′\′}=P_w\frac{a^2}{r^2}$

At borehole wall (r=a) place, the surrouding rock stress state that fluid injection pressurized causes is:

${\mathrm{\σ}}_{\mathrm{\θ}}^{\′\′}=-P_w$

${\mathrm{\σ}}_r^{\′\′}=P_w$

Stress state on hydraulic fracturing geostress survey boring crag is superposing of the additional profiled bar that causes with hydraulic pressure of terrestrial stress secondary state of stress, namely

σ _θ＝(σ _H+σ _h)-2(σ _H-σ _h)cos2θ-P _w

σ _z＝-2μ(σ _H-σ _h)cos2θ+σ _v

σ _r＝P _w

The classical theory of hydraulic fracturing geostress survey adopts maximum uniaxial tensile stress failure criteria.Under the restriction of this failure criteria, axial stress σ in formula (7) _zonly relevant with crustal stress states, have nothing to do with hydraulic pressure size, it and radial stress σ _rmerely provide the condition of boring crag three-dimensional stress constraint, produce with country rock situation of breaking and have nothing to do, will not discuss.That broken control action to country rock is tangential stress σ _θ, when after boring pressure-bearing section fluid injection pressurized, tangential pressure σ _θreduce with values such as hydraulic pressure, be finally converted into tensile stress state.

During hydraulic fracturing geostress survey, the seam that breaks produces the position that tension is maximum on boring crag.From formula (7), on the position of holing crag polar angle θ=0 or π, namely orientation of principal stress, the tangential stress minimum (compressive stress is just) of boring crag, its value is:

σ _θ＝3σ _h-σ _H-P _w

From formula, when hydraulic pressure increases, boring crag tangential stress σ _θdrop to tensile stress state gradually, along with hydraulic pressure P _wincrease, tension also increases gradually, when tension is equal to or greater than the tensile strength sigma of country rock _ttime, there is crack in boring crag.At this moment the hydraulic pressure of pressure-bearing section is exactly parting pressure P _b.Therefore, around the pressure-bearing section of holing, crag country rock produces the stress condition of break (not considering pore water pressure) and is:

3σ _h-σ _H-P _b+σ _t＝0

In deep rock mass, also there is pore water pressure P ₀, therefore, the effective stress in rock mass is σ-P ₀.Consider the effects such as the pore water pressure in rock mass, around boring pressure-bearing section, crag country rock produces the stress condition broken and is:

$P_b-P_0=\frac{3({\mathrm{\σ}}_h-P_0)-({\mathrm{\σ}}_H-P_0)+{\mathrm{\σ}}_t}{K}$

In formula, K is hole infiltration elastic parameter, and can determine in testing laboratory, its variation range is 1≤K≤2.To impermeability rock, K value is approximately equal to 1, then above formula can be reduced to

P _b-P ₀＝3σ _h-σ _H-2P ₀+σ _t

After boring perisporium country rock breaks, close fracturing pump immediately, at this moment maintain the instantaneous closing presure P of fracture open _swith the minimum horizontal principal stress σ that crack surface is perpendicular _hbe balanced, have:

σ _h＝P _s

According to formula (11), maximum horizontal principal stress σ _hfor:

σ _H＝3P _s-P _b+σ _t-P ₀

After borehole circumference country rock first time breaks, (parting pressure is P _b), carry out repetition fluid injection to boring and be depressed into the seam that breaks and continue to open, pressure is at this moment pressure P of re-opening _r.Because country rock is broken, its tensile strength is approximately zero, and according to formula (11), reopening pressure is:

P _t＝3σ _h-σ _H-P ₀

Therefore, formula (13) is:

σ _H＝3P _s-P _t-P ₀

Due in measuring process, generally measurement instrument and pressure transducer are put on the ground, measured value is actually each fracturing parameter eigenwert P _b, P _rand P _snominal value P _b', P _r' and P _s', consider hydrostatic force P _himpact, meets following relation between fracturing parameter eigenwert and nominal value:

P _b＝P′ _b+P _H

P _r＝P′ _r+P _H

P _s＝P′ _s+P _H

P _h=γ _waterh

In formula, γ _waterfor the severe of water, H is the test point degree of depth.

Consider that the hydrostatic level of testing bore holes is generally in aperture, the pore water pressure P of test section ₀general value is the hydrostatic force P of test section to ground _h.By the P of (12), (15) formula _rand P _suse P _r' and P _shave after ' substitution:

σ _h＝P _S′+P _H

σ _H＝3(P′ _s+P _H)-(P′ _r+P _H)-P ₀＝3P′ _S-P′ _r+2P _H-P ₀

Formula 5-17

In sum, in hydraulic fracturing geostress survey, according to the P obtained in process of the test _b', P _r', P _s', P ₀namely can determine by formula (17) maximum, minimum horizontal principal stress size of holing, orientation of principal stress can be determined according to the fracture breaks direction of die device record simultaneously.

3) deterioration of tunnel surrounding mechanical property judges: comprise and carry out on-the-spot sonic test to tunnel surrounding diverse location, and binding tests data separate numerical simulation means analyzes surrounding rock stress distribution law and coffer mechanics property-deterioration rule under specifically stress condition.

In constructing tunnel explosion, drilling and blasting method remains a kind of Main Means, and the impact of explosion on stability of surrounding rock is mainly reflected in two aspects: one is the mechanical property deterioration making rock, and the strength and modulus of rock is reduced; Two is in rock mass, crack or make rock mass original crack expansion etc., thus affects the integrality of rock.The coupling of these two kinds effects will have influence on the stability of tunnel surrounding.Therefore, pole is necessary to launch the dynamic analysis to tunnel surrounding damage, adopts FLAC3D finite difference software to carry out numerical evaluation in this research.

FLAC-3D (Three Dimensional Fast Lagrangian Analysis of Continua) is the three-dimensional control network program that American I tasca Consulting Goup lnc develops, the mechanical behavior of the destruction that this program energy simulate geological materials occurs when reaching strength degree or yield limit or Plastic Flow, is specially adapted to analyze Progressive failure and unstability and simulate large deformation.It comprises 10 kinds of elastic-plastic material constitutive models, there are static(al), power, creep, seepage flow, temperature five kinds of computation schemas, can close by lotus root mutually between various pattern, various structures form can be simulated, as rock mass, the soil body or other materials entity, beam, anchor unit, stake, shell and artificial structure, can the Geotechnical Engineering of Simulation of Complex or mechanics problems as supporting, lining cutting, anchor cable, bysmalith, geotextile, friction pile, sheet pile, boundary element etc.Adopt FLAC3D software to simulate the dynamic damage of tunnel surrounding under high-ground stress in this research.

FLAC3D has following advantage:

1 pair simulation plastic failure and Plastic Flow adopt be " mixing discrete method ".This method than usually adopt in finite element method " discrete set established law is " more accurate, reasonable.

Even if the systems of 2 simulations are static, still have employed dynamic motion equation, this makes the erratic process of FLAC3D on analog physical there is not obstacle numerically.

3 have employed " explicit solution " a scheme.Therefore, explicit solution scheme solves the spent time to nonlinear strain-stress relation, several identical with linear constitutive relation mutually, and Implicit Method scheme will spend the longer time to solve nonlinear problem.Face and, it there is no need to store stiffness matrix, and this just means, adopts the internal memory of intermediate size to solve multi-unit structure; Simulation large deformation problem is several mutually unlike the many consumption of small deformation problem more computing time, because will be modified without any stiffness matrix.

In addition, in Flac3D, develop distinctive constitutive model for solving of geotechnical engineering problems, altogether contain 10 kinds of material models:

1. excavate model null

2.3 elastic models (isotropy, transverse isotropy and orthogonal isotropic elasticity model)

3.6 plasticity models (the cam clay model of Drucker-Prager model, Morh-Coulomb model, strain hardening/softening modulus method, Ubiquitous-Joint model, bilinearity strain hardening/softening Ubiquitous-Joint model and correction).

Different material models can be given in each region in Flac3D grid, and allows statistical distribution and the variable gradient of specified material parameter.Further comprises Joint Element, also referred to as boundary element, the discontinuous nature of two or more material interface differing material properties can be simulated.Joint permission occurs to slide or be separated, and therefore can be used for simulating tomography, the joint in rock mass or the border that rubs.

Mesh generator gen in FLAC3D, generates Local grid by mating, connecting by mesh generator, can generate required three-dimensional structure grid easily.Automatically can also produce and hand over trouble structured grid (such as the tunnel of intersecting), 3D grid is by global coordinate system x, and y, z system determined, which provides and produces and define three dimensions parameter more flexibly.

FLAC3D provides 5 kinds of computation schemas to adapt to the computation process under different situations simultaneously:

(1) hydrostatic model: this is FLAC-3D default mode, obtains steady-state solution by dynamic slave method.

(2) dynamic mode: user can direct defeated people's acceleration, speed or stress wave as the boundary condition of system or starting condition, border can fixed boundary and free boundary.Cable Power Computation can be closed with Seepage problems phase lotus root.

(3) creep pattern: have five kinds of creep constitutive models available with the stress-strain-time relation of simulation material: Maxwell model, biexponential model, reference creep model, Visco-plastic Model, crisp salt model.

(4) Seepage mode: can simulate formation current, pore pressure dissipate and being coupled of deforming porous media and viscous fluid therebetween.Seepage flow obeys isotropy Darcy's law, and fluid and pore media are all counted as deformable body.Consider unsteady fluid flow, steady flow is regarded as the special case of unsteady fluid flow.Boundary condition can be fixing pore pressure or steady flow, can simulate water source or deep-well.Seepage calculation can be coupled with static(al), power or temperature computation, also can calculate separately.

(5) temperature model: can transient heat conduction in simulation material and temperature stress.Temperature computation can be closed with static(al), power or seepage calculation lotus root, also can calculate separately.

FLAC3D can also simulate various structures form

(1) for common rock mass, the soil body or other materials entity, with eight node hexahedral element simulations.

(2) FIAC-3D includes four kinds of structural units: beam element, anchor unit, pile element, shell unit.Can be used to simulate artificial structure in Geotechnical Engineering as supporting, lining cutting, anchor cable, bysmalith, geotextile, friction pile, sheet pile etc.

(3) can have interface in the grid of FLAC-3D, computing grid is divided into some parts by this interface, and the grid on both sides, interface can be separated, and also can slide, and therefore, joint, tomography or virtual physical boundary can be simulated in interface.

FLAC-3D has powerful embedded language FISH, makes user can define new variable or function, to adapt to the special requirement of user, such as, utilizes FHSH to do following thing:

(1) user can the space distribution rule of self-defined material, as nonlinear Distribution etc.

(2) user can defining variable, follows the trail of its Changing Pattern and draw to represent or printout.

(3) user can the inner element form do not had of oneself design FLAC-3D.

(4) servocontrol can be carried out in numerical experimentation.

(5) user can specify special boundary condition.

(6) automatically Parameter analysis is carried out.

(7) utilize Fish variable or the function of the definition of FLAC-3D inside, user can obtain computation process interior joint, cell parameters, as coordinate, displacement, speed, material parameter, stress, strain, out-of-balance force etc.

Explosion damage evolution equation

According to the viewpoint of damage mechanics, under Blast Loads, the dynamic failure of rock is a continuous damage evolution accumulation, and its damage mechanisms can be summed up as the dynamic evolution of rock interior micro-crack or microfissure.Rock is as a kind of hard brittle material, there is the defects such as a large amount of microfissures, micro-crack, explosion on the impact of rock mass basic quality and destructive process be due to its inner a large amount of micro-crack expansion, develop and run through and cause the process being deteriorated to ultimate failure or destruction of rock macro-mechanical property.The research of Yang and Liu etc. is thought, the rock crack number activated under can representing dynamic load function by Probability Forms and the expansion process of damage; Equivalent volume accumulation stretching strain in rock mass is the important references index determining whether micro-crack activates and expand, and meanwhile, the rate of strain and the time that reach critical strain and the loading cracked are relevant.

Rock Damage evolution equation is represented with Probability Forms:

$D=1-e^{-C_d^2}$

In formula: Cd is crack density, the crackle number that representation unit volume comprises, can find out, Damage coefficient D value is between 0 ~ 1, and correspond respectively to complete, nondestructive material and the full-blown material of crackle, crack density is defined as follows:

$C_d=\left\{\begin{array}{c}\mathrm{\α}{(\mathrm{\ϵ}-{\mathrm{\ϵ}}_c)}^{\mathrm{\β}}t,(\mathrm{\ϵ}>{\mathrm{\ϵ}}_c)\\ 0,(\mathrm{\ϵ}\≤{\mathrm{\ϵ}}_c)\end{array}\right.$

In formula, α, β are material constant, ε _cfor critical stretching strain; ε is equivalent accumulation stretching strain, and definition is

$\mathrm{\&epsiv;}=\sqrt{\underset{i=1}{\overset{3}{\mathrm{\&Sigma;}}}{(<{\mathrm{\&epsiv;}}_i>)}^2}$

In formula: <> is effective when the variable in square bracket is greater than zero, namely

$<{\mathrm{\&epsiv;}}_i>=\frac{\left|{\mathrm{\&epsiv;}}_i\right|+{\mathrm{\&epsiv;}}_i}{2}$

For material constant α, β and ε _c, need be determined by the Dynamic Crack characteristic of rock mass, usually also can be obtained by rock mass triaxial extension test result.But rock mass triaxial extension test is difficult to realize in reality, because rock mass its major axes orientation under stress wave activity not only tensile strain occurs, also there is compressive strain simultaneously.According to correlative study achievement, the damage of rock mass is often produced by stretching strain, so material constant α, β and ε _cdetermine by the test of rock mass uniaxial tension is approximate.So the critical stretching strain of rock mass can be as follows by uniaxial static stretch experiment calculation:

${\mathrm{\&epsiv;}}_c=\frac{1-2\mathrm{\&mu;}}{E}{\mathrm{\&sigma;}}_{\mathrm{st}}$

In formula: σ _stfor the static tensile strength of rock mass, E is rock mass materials equivalent elastic modulus, and μ is Poisson ratio., for formula 7-8, the stretching strain corresponding to rock mass crack stress in i direction and crack density are designated as fi and Cdfi respectively, then the crack density corresponding to rock mass crack stress can be expressed as:

$C_{\mathrm{dfi}}={\mathrm{\&alpha;}}_i{({\mathrm{\&epsiv;}}_{\mathrm{fi}}-{\mathrm{\&epsiv;}}_{\mathrm{cri}})}^{{\mathrm{\&beta;}}_i}(t_i-t_{\mathrm{ci}}),(i=\mathrm{1,2,3})$

In formula: ti gets to T.T. required for crack stress by original state for rock mass, and tci is the time being reached critical conditions by the strain regime that crack stress is corresponding, is expressed as follows respectively:

$t_i=\frac{{\mathrm{\&epsiv;}}_{\mathrm{fi}}}{{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}_i},(i=\mathrm{1,2,3})$

$t_{\mathrm{ci}}=\frac{{\mathrm{\&epsiv;}}_{\mathrm{cri}}}{{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}_i},(i=\mathrm{1,2,3})$

In formula: for rock mass uniaxial tensile strain rate, thus have

$C_{\mathrm{cff}}={\mathrm{\&alpha;}}_i{(t_i{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}_i-t_{\mathrm{ci}}{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}_i)}^{{\mathrm{\&beta;}}_i}(t_i-t_{\mathrm{ci}}),(i=\mathrm{1,2,3})$

Relation between rock masses fracturing stress and corresponding strain can be write:

${\mathrm{\&sigma;}}_{\mathrm{fi}}=\frac{E_i(1-D_{\mathrm{fi}})}{1-2\mathrm{\&mu;}}{\mathrm{\&epsiv;}}_{\mathrm{fi}},(i=\mathrm{1,2,3})$

In formula: damage variable when Dfi is material damage.

The time of rock mass required for Critical Damage state to state of rupture is

$t=t_i-t_{\mathrm{ci}}={\left(\frac{C_{\mathrm{dfi}}}{{\mathrm{\&alpha;}}_i}\right)}^{\frac{1}{1+{\mathrm{\&beta;}}_i}}{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}^{\frac{{\mathrm{\&beta;}}_i}{1+{\mathrm{\&beta;}}_i}},(i=\mathrm{1,2,3})$

The rate constitutive equation obtaining Rock Damage according to formula 7-9 ~ formula 7-14 is:

${\mathrm{\&sigma;}}_{\mathrm{fi}}=(1-D_{\mathrm{fi}}){\mathrm{\&sigma;}}_{\mathrm{sti}}+\frac{E_i(1-D_{\mathrm{fi}})}{1-2\mathrm{\&mu;}}{\left(\frac{C_{\mathrm{dfi}}}{{\mathrm{\&alpha;}}_i}\right)}^{\frac{1}{1+{\mathrm{\&beta;}}_i}}{\stackrel{\&CenterDot;}{\mathrm{\&epsiv;}}}^{\frac{1}{1+{\mathrm{\&beta;}}_i}},(i=\mathrm{1,2,3})$

With reference to existing damage result of study, isotropy damage model is adopted in this research, impairment correlation parameters gets=3.5e10,=2, regulation in " hydraulic structure rock foundation excavation project technical manual " that China formulates, as η > 10%, namely judge that rock mass is subject to explosion damage and failure.Corresponding Rock Damage threshold value is D=0.19.

4) Analyses of Tunnel Wall Rock Stability analysis and rock burst prevention and control: be included on the previous computation model basis set up and carry out the regularity that country rock weakens experimental study surrouding rock stress adjustment under large ground pressure, and carried out predicting for contingent rock burst destruction and divided rock burst grade, propose measure targetedly.

Analysis on rock is set about from terrestrial stress angle, adopts the four kinds of diagnostic methods such as Standard for classification of engineering rock masses diagnostic method, Russenes diagnostic method, Turchaninov diagnostic method, Hoek diagnostic method generally applied in strength theory to carry out qualitative or quantitative comprehensive evaluation.

(1) Standard for classification of engineering rock masses diagnostic method

" Standard for classification of engineering rock masses " (GB GB50218-94) intactly considers these terrestrial stress factors relatively on the cavitation of underground chamber and impact, and evaluates the principal phenomena occurred in underground cavern excavation process.Table 5.3, table 5.4 are respectively the principal phenomena that the hardness degree of rock corresponding relation of uniaxial saturated compressive strength of rock Rc and qualitative division and high primary stress area rock mass occur in digging process.

The corresponding relation of the hardness degree of rock of table 5-3 Rc and qualitative division

The principal phenomena that table 5-4 high primary stress area rock mass occurs in digging process

(2) Russenes rock burst diagnostic method

Russenes rock burst diagnostic method is the relation of maximum tangential stress σ e according to cavern and rock point load intensity I s, sets up rockburst intensity graph of a relation.Point loading Is is converted into the uniaxial compressive strength Rc of rock, and differentiates whether occur with or without rock burst according to rockburst intensity graph of a relation.It differentiates that relation is as follows:

(3) Turchaninov rock burst diagnostic method

Turchaninov rock burst diagnostic method is the [underground experience according to Xi Bin plot, Ke La island, proposes rock burst activity and is determined by the ratio of cavern tangential stress σ θ and axial stress σ L sum and rock uniaxiality strength Rc:

(4) Hoek rock burst diagnostic method

Hoek etc. summarize the observed result of South Africa mining tunnel surrounding rock failure, propose the discriminant to rock burst classification:

(5) calculating of tunnel section stress

Axial stress: σ L=σ h sin2 α+σ Hcos2 α;

The maximum tangential stress of xsect: σ θ=3 σ max-σ v;

The maximum primary stress of xsect: σ max=σ H sin2 α+σ h cos2 α.

In above formula: the minimum horizontal principal stress of σ H to be maximum horizontal principal stress, the σ h of actual measurement be actual measurement, α are the angle of the trend of maximum horizontal principal stress and tunnel, σ v is gravity stress.

Claims (5)

1. the judgement of tunnel hard rock rock burst, grade classification and a disposal route, is characterized in that, comprise the following steps:

(1) geologic examination, comprises physical geography situation, bottom lithology, tectonic structure landform, unfavorable geology and Special Rock, hydrogeological condition;

(2) according to geology investigation result, design proposal;

(3) by indoor sillar Experiments of Machanics, detecting earth stress and the test of bullet mould, Project Areas Study on Rock Stress and rock burst assessment, geological generalization and numerical simulation model is obtained;

(4) by coffer mechanics deterioration research and Analyses of Tunnel Wall Rock Stability analysis, rock burst prevention and control suggestion and measure is obtained.

2. the judgement of tunnel according to claim 1 hard rock rock burst, grade classification and disposal route, it is characterized in that: indoor sillar Experiments of Machanics are the sillar of tunnel surrounding and rock mass strength test, comprise indoor Rock Under Uniaxial Compression strength test and triaxial test of rock, the test of Test in Situ elastic modulus, field geological investigation.

3. the judgement of tunnel according to claim 1 hard rock rock burst, grade classification and disposal route, it is characterized in that, detecting earth stress: comprise and typical hole section is surveyed and drawn in detail and sampled, and carry out field survey, in conjunction with field data, tunnel different buried depth country rock rock burst is assessed, provide country rock rock burst grade and the Close Tunnel soft rock large deformation buried depth degree of depth.

4. the judgement of tunnel according to claim 1 hard rock rock burst, grade classification and disposal route, it is characterized in that, the deterioration of tunnel surrounding mechanical property judges: comprise and carry out on-the-spot sonic test to tunnel surrounding diverse location, and binding tests data separate numerical simulation means analyzes surrounding rock stress distribution law and coffer mechanics property-deterioration rule under specifically stress condition.

5. the judgement of tunnel according to claim 1 hard rock rock burst, grade classification and disposal route, it is characterized in that, Analyses of Tunnel Wall Rock Stability is analyzed and rock burst prevention and control: be included on the previous computation model basis set up and carry out the regularity that country rock weakens experimental study surrouding rock stress adjustment under large ground pressure, and carry out predicting for contingent rock burst destruction and divide rock burst grade, measure is targetedly proposed.