CN102183411A - Prediction method for fracture mode of brittle rocks under long-term steady load function - Google Patents

Abstract

The present invention relates to a kind of prediction techniques of fracture mode of brittle rocks under long-term steady load function. Technical problem to be solved by the invention is to provide a kind of prediction techniques of fracture mode of brittle rocks under long-term steady load function, reliably predict the fracture mode of rock. Solving the problems, such as this technical solution is, steps are as follows: a, at the construction field (site) boring sample; B, rock sample is mounted in loading apparatus, and axial, circumferential displacement sensor, acoustic emission probe and sonic probe is installed on rock sample; C, it is loaded by displacement control mode, until increasing suddenly for the first time occurs in acoustic emission signal, maintain the stress level constant, and record rock sample under steady load continuous action, axial displacement ε 1 and lateral displacement ε 3 change with time, until the second minor peaks occurs in acoustic emission signal; D, basis

With

Calculate dilatation index

To predict the fracture mode of rock sample. Present invention is mainly used for the optimizations that the estimation of stability of deep cavern and permanent support design.

Description

The Forecasting Methodology of RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under the load action steady in a long-term

Technical field

The present invention relates to the Forecasting Methodology of RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under a kind of load action steady in a long-term, mainly be applicable to the estimation of stability of buried cavern and the optimization of permanent supporting design.

Background technology

The destruction unstability of Geotechnical Engineering is always closely related with time factor.Under very long earth history condition, rock is subjected to various tectonizations, thereby has produced the structural plane that comes in every shape, differs in size.When load is further done the time spent, these mechanical properties of rock are controlled by these structural planes to a certain extent, in other words, rock strength character in time prolongation and weaken, when stress reaches certain critical value, initial fissure can be expanded in the rock, or brings out new rock fracture, thereby has influence on the permanent stability of rock engineering structure.

A large amount of tests has proved that the distress severity of rock depends on the time.Breaking owing to the progressively formation of a large amount of newborn crackles or the expansion of existing crackle of rock, dilatation is to produce like this.Different with metal material, rock can produce significant irreversible volumetric expansion before it destroys under load action, and this phenomenon is referred to as the dilatancy of rock.Dilatation is a very important character of rock, time effect to the further investigation rock strength, the mechanical mechanism that the announcement brittle rock destroys under the high-ground stress effect has great significance, thereby dilatation should be used as a standard judging the RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern.

Brittle rock is under action of long-term load, and the strain that steady load produces trends towards non-resilient and irrecoverable, and wherein the bulk strain of Zeng Jiaing means the expansion of axial crack, and the growth of shear strain means shearing slip, and two kinds of failure modes are handed over knot mutually.In process of the test the rock failure mechanism of rock usually vertically micro-crack extension and along the shearing slip of inclination crackle all show apparent in view, with which kind of pattern destroy at last, lack a Forecasting Methodology that is simple and easy to usefulness always.

Summary of the invention

The technical problem to be solved in the present invention is: the Forecasting Methodology that RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under a kind of load action steady in a long-term is provided at the problem of above-mentioned existence, doping the fracture mode of rock accurately and reliably, for the monolithic stability that improves the cavern and the design optimization of supporting provide further technical support.

The technical solution adopted in the present invention is: the Forecasting Methodology of RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under a kind of load action steady in a long-term is characterized in that step is as follows:

A, boring sample and processing are at the construction field (site) guaranteed the integrality and the homogenieity of rock sample;

B, the rock sample that step a is obtained are installed on the loading instrument, simultaneously shaft position sensor, hoop displacement transducer, acoustic emission probe and sonic probe are installed on this rock sample, and can be guaranteed real-time transmission data;

C, load according to the displacement control model, when increasing suddenly for the first time appears in the acoustic emission signal that monitors, stop to increase stress and keep this stress level constant, and the record rock sample is under the steady load continuous action, the axial displacement ε of generation ₁With lateral shift ε ₃Process peak value for the second time occurs until acoustic emission signal over time, and rock sample destroys fully;

D, basis

With

Calculate the dilatation index Thereby the fracture mode of prediction rock sample, wherein ε ₁And ε ₃Represent the axial displacement and the lateral shift of writing down among the step c respectively, σ ₁And σ ₃Represent the stress and the confined pressure that remain unchanged among the step c respectively, E is an elastic modulus, and v is a Poisson ratio,

Be the increment of the long-pending strain of inelastic body, representing the axial expansion crackle,

Be the increment of non-elastic shear strain, representing the shearing running crack.

Described loading instrument is a triaxial tester.

The invention has the beneficial effects as follows: the dilatation index that the present invention proposes can be judged the last fracture mode of rock accurately and reliably, when DI＞1, breaks based on axial splitting; When DI＜1, break based on shear failure, thereby, adopt different supporting measures at different failure modes for the monolithic stability that improves the cavern and the design optimization of supporting provide further technical support, not only save quantities, and reduced construction costs.

Description of drawings

Fig. 1 is an acoustic emission signal monitoring synoptic diagram among the present invention.

Fig. 2 is non-resilient shear strain and a non-resilient volume strain value under the steady load continuous action among the present invention.

Embodiment

The implementation step of present embodiment is as follows:

A, boring sample and processing are at the construction field (site) guaranteed the integrality and the homogenieity of rock sample, and the failure mode that prevents rock sample is subjected to the influence of other extraneous factor.

B, the rock sample that step a is obtained are installed on the loading instrument, load the instrument selection triaxial tester in this example, simultaneously shaft position sensor, hoop displacement transducer, acoustic emission probe and sonic probe are installed on this rock sample, and can be guaranteed real-time transmission data.

C, load according to the displacement control model, when increasing suddenly for the first time appears in the acoustic emission signal that monitors, as shown in Figure 1, stop to increase stress and keep this stress level constant, this stress comprises axle pressure σ ₁And confined pressure σ ₂And σ ₃, and σ ₂=σ ₃Write down rock sample then under the steady load continuous action, the axial displacement ε of generation ₁With lateral shift ε ₃Process peak value for the second time occurs until acoustic emission signal over time, and this moment, rock sample destroyed fully.

D, according to formula

With

Calculate the dilatation index

Thereby the fracture mode of prediction rock sample promptly when DI＞1, breaks based on axial splitting; When DI＜1, break based on shear failure.ε wherein ₁And ε ₃Represent the axial displacement and the lateral shift of writing down among the step c respectively, σ ₁And σ ₃Represent the axle pressure and the confined pressure that remain unchanged among the step c respectively, E is an elastic modulus, and v is a Poisson ratio,

Be the increment of the long-pending strain of inelastic body, representing the axial expansion crackle,

Be the increment of non-elastic shear strain, representing the shearing running crack.It is to be noted the increment of non-resilient volume strain

Usually be negative value, but not the increment of elastic shear strain

For on the occasion of, therefore for simply, with the absolute value of both ratios as dilatation index DI.

Be to be the function of variable with time, but both values are the certain proportion relation, as shown in Figure 2, and this dilatation index just, in whole gatherer process, remain unchanged substantially as can be seen, the dilatation index is a certain value for specific rock under the load action steady in a long-term of appointment substantially, therefore it can be able to be regarded as a kind of attribute of rock itself, the influence of the long duration load that it is applied.

Can judge the surrounding rock supporting situation of sampling spot according to dilatation index DI at last,, should pay attention to the concrete spray coating quality, then will improve anchor pole density accordingly to be cut into main destruction for destruction based on axial splitting.

The derivation of above-mentioned two formula is as follows: the distortion of brittle rock under action of long-term load is made up of elastic deformation and inelastic deformation, supposes that elastic modulus remains unchanged in entire test, according to Hooke's law:

${\mathrm{\ϵ}}_1^e=\frac{1}{E}[{\mathrm{\σ}}_1-v({\mathrm{\σ}}_2+{\mathrm{\σ}}_3)]---\left(1\right)$

${\mathrm{\ϵ}}_2^e=\frac{1}{E}[{\mathrm{\σ}}_2-v({\mathrm{\σ}}_1+{\mathrm{\σ}}_3)]---\left(2\right)$

${\mathrm{\ϵ}}_3^e=\frac{1}{E}[{\mathrm{\σ}}_3-v({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)]---\left(3\right)$

In the formula,

Represent the principal strain under the elastic stage, σ ₁, σ ₂, σ ₃Represent principle stress, E is an elastic modulus, and v is a Poisson ratio.

For triaxial test, on octahedral plane, strain paths can be by octahedra shear strain γ _OctWith octahedra normal strain ε _OctRepresent.

Octahedra shear strain γ _OctCan be expressed as

${\mathrm{\γ}}_{\mathrm{oct}}=\frac{2}{3}\sqrt{{({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_2)}^2+{({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_3)}^2+{({\mathrm{\ϵ}}_2-{\mathrm{\ϵ}}_3)}^2}---\left(4\right)$

In the triaxial test process, confined pressure σ ₂=σ ₃, so ε ₂=ε ₃, can obtain

${\mathrm{\γ}}_{\mathrm{oct}}=\frac{2}{3}\sqrt{{2({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_3)}^2}=\frac{2\sqrt{2}}{3}({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_3)---\left(5\right)$

Shear strain ε _qBe defined as octahedra shear strain γ _Oct

ε _q＝γ _oct (6)

Octahedra normal strain ε _OctBe

${\mathrm{\ϵ}}_{\mathrm{oct}}=\frac{1}{3}({\mathrm{\ϵ}}_1+{\mathrm{\ϵ}}_2+{\mathrm{\ϵ}}_3)=\frac{1}{3}({\mathrm{\ϵ}}_1+2{\mathrm{\ϵ}}_3)---\left(7\right)$

Bulk strain ε _vBe defined as 3 times of octahedra normal strain ε _Oct

ε _v＝3ε _oct＝(ε ₁+2ε ₃) (8)

Non-resilient shear strain

Be

${\mathrm{\ϵ}}_q^{\mathrm{ie}}={\mathrm{\ϵ}}_q-{\mathrm{\ϵ}}_q^e={\mathrm{\ϵ}}_q-\frac{2\sqrt{2}}{3}({\mathrm{\ϵ}}_1^e-{\mathrm{\ϵ}}_3^e)---\left(9\right)$

With formula (1) and formula (3) substitution (9), can obtain

${\mathrm{\ϵ}}_q^{\mathrm{ie}}={\mathrm{\ϵ}}_q-\frac{2\sqrt{2}}{3}\frac{1+v}{E}({\mathrm{\σ}}_1-{\mathrm{\σ}}_3)=\frac{2\sqrt{2}}{3}({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_3)-\frac{2\sqrt{2}}{3}\frac{1+v}{E}({\mathrm{\σ}}_1-{\mathrm{\σ}}_3)---\left(10\right)$

Non-resilient volume strain can be expressed as

${\mathrm{\ϵ}}_v^{\mathrm{ie}}={\mathrm{\ϵ}}_v-{\mathrm{\ϵ}}_v^e={\mathrm{\ϵ}}_v-({\mathrm{\ϵ}}_1^e+2{\mathrm{\ϵ}}_3^e)---\left(11\right)$

With formula (1) and (3) substitution (11), can obtain

${\mathrm{\ϵ}}_v^{\mathrm{ie}}={\mathrm{\ϵ}}_v-\frac{1-2v}{E}({\mathrm{\σ}}_1+2{\mathrm{\σ}}_3)=({\mathrm{\ϵ}}_1+2{\mathrm{\ϵ}}_3)-\frac{1-2v}{E}({\mathrm{\σ}}_1+{2\mathrm{\σ}}_3)---\left(12\right)$

During test, also can only apply axle pressure, and not apply confined pressure rock sample, so under the single shaft situation, σ ₃=0, get final product,

${\mathrm{\ϵ}}_q^{\mathrm{ie}}={\mathrm{\ϵ}}_q-\frac{2\sqrt{2}}{2}\frac{1+v}{E}{\mathrm{\σ}}_1=\frac{2\sqrt{2}}{3}({\mathrm{\ϵ}}_1-{\mathrm{\ϵ}}_3)-\frac{2\sqrt{2}}{3}\frac{1+v}{E}{\mathrm{\σ}}_1---\left(13\right)$

${\mathrm{\ϵ}}_v^{\mathrm{ie}}={\mathrm{\ϵ}}_v-\frac{1-2v}{E}{\mathrm{\σ}}_1=({\mathrm{\ϵ}}_1+2{\mathrm{\ϵ}}_3)-\frac{1-2v}{E}{\mathrm{\σ}}_1---\left(14\right)$

Claims (2)

1. the Forecasting Methodology of RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under the load action steady in a long-term is characterized in that step is as follows:

A, boring sample and processing are at the construction field (site) guaranteed the integrality and the homogenieity of rock sample;

B, the rock sample that step a is obtained are installed on the loading instrument, simultaneously shaft position sensor, hoop displacement transducer, acoustic emission probe and sonic probe are installed on this rock sample, and can be guaranteed real-time transmission data;

C, load according to the displacement control model, when increasing suddenly for the first time appears in the acoustic emission signal that monitors, stop to increase stress and keep this stress level constant, and the record rock sample is under the steady load continuous action, the axial displacement ε of generation ₁With lateral shift ε ₃Process peak value for the second time occurs until acoustic emission signal over time, and rock sample destroys fully;

D, basis

With

Calculate the dilatation index

Thereby the fracture mode of prediction rock sample, wherein ε ₁And ε ₃Represent the axial displacement and the lateral shift of writing down among the step c respectively, σ ₁And σ ₃Represent the stress and the confined pressure that remain unchanged among the step c respectively, E is an elastic modulus, and v is a Poisson ratio,

Be the increment of the long-pending strain of inelastic body, representing the axial expansion crackle,

Be the increment of non-elastic shear strain, representing the shearing running crack.

2. the Forecasting Methodology of RUPTURE EXPERIMENTS OF BRITTLE ROCKS pattern under the load action steady in a long-term according to claim 1 is characterized in that: described loading instrument is a triaxial tester.

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