CN101957343B - Novel acoustic-emission ground-stress-field measuring technology based on plane stress condition - Google Patents

Abstract

The invention discloses a novel acoustic-emission ground-stress-field measuring technology based on a plane stress condition, which comprises the following concrete steps of: supposing that the vertical direction is a known principal stress direction sigmaZ, and obtaining the magnitude of a principal stress according to a formula sigmaZ=gammad; in the horizontal direction, sampling a rock sample in the two mutually vertical directions and the directions with included angle of 45 degrees with the two directions; and loading and recording data, analyzing to obtain a Kaiser point, computing the magnitudes and the directions of the two principal stresses in the horizontal direction according to a theoretical computing formula, and adding the supposed sigmaZ to realize the three-dimensional stress measurement of a ground stress. The novel acoustic-emission ground-stress-field measuring technology based on the plane stress condition is a novel ground-stress-field testing technology, can make up for the deficiency of a traditional testing method, simultaneously can greatly save the measuring consumption, has the advantages of strong operability, accurate measurement and the like, is combined with means, such as rock mass mechanical testing, numerical simulation analysis and the like, can supply a powerful scientific basis for geotechnical engineering design and is a brand-new and internationally-advanced ground-stress-field testing technology.

Description

A kind of based on the novel acoustic emission stress field measuring method under the plane stress condition

Technical field

The present invention relates to a kind of Geotechnical Engineering terrestrial stress measuring technology, especially a kind of based on the novel acoustic emission stress field measuring method under the plane stress condition.

Background technology

Along with fast development of national economy, the stability problem that runs in the construction projects such as mining, communications and transportation, water conservancy construction also becomes increasingly conspicuous.A large amount of Geotechnical Engineering examples show, the size of major principal stress in the terrestrial stress, direction are very big to the engineering stability influence, and many places flatly stress be higher than and vertically should.In recent years, earth stress measuring method is mainly based on traditional acoustic-emission, hydraulic fracturing and hollow inclusion strain measurement technique.

Rock type materials is when being subjected to external load function, and the strain energy of its internal reservoir can produce elastic wave because the micro rupture effect discharges fast, and the sound takes place, and is called acoustic emission.The tradition acoustic-emission is measured terrestrial stress and just is based on a kind of like this phenomenon, be material through after once or several times loading a unloading repeatedly, when again it being loaded, if do not surpass previous maximum stress, then rare acoustic emission, only meet and exceed former maximum stress, could produce a large amount of acoustic emissions, this phenomenon also is the Kaiser effect.Will obtain to be present in triaxiality state in excavation rock mass and the peripheral region thereof during in-site measurement just must get at rock mass and be intersected in the directed core that six of measuring points are not parallel to each other, in testing laboratory, each the directed standard sample that processes is loaded one by one then, measure the maximum stress that the bioassay standard sample before had been subjected to by acoustic emission, and it is decided to be the stress of adopting certain direction of core place, according to the basis of Elasticity, the batch total of solving an equation is calculated major principal stress size and the direction of this point at last.The shortcoming of the method is very trouble of directed sampling, will be accurately to obtain the rock sample of six different directions at a point very difficult, simultaneously, even obtained the rock sample of 6 directions, as long as but have the rock sample of a direction to fail, must not go out solution of equations so and analyse solution, namely the major principal stress of this point can't draw.Therefore for guaranteeing the success of test, some scholar's suggestion is got 4 samples in each direction, and 6 directions are exactly 24 samples so, and the core that to get so many diameters on so on one point be 50mm is what difficult, is difficult to also guarantee that they are same points even obtained.Therefore, this method also rests on theoretical research stage always, and actual application value is very low.The hollow inclusion strain measurement technique is normally finished by point-to-point measurement, the triaxiality state that will obtain so to be present in excavation rock mass and the peripheral region thereof just must be beaten the trepanning that diameter reaches 150mm in the deep, because difficulty of construction is big, the construction operation conditional request is special, so the place a little less than technical force's relative thin is difficult to guarantee the accuracy measured, thereby also limited applying of these class methods, major part needs to measure the zone of the initial stress simultaneously, there is not tunnel to lay as yet, so it is particularly outstanding to be difficult to possess the condition of hollow inclusion strain measurement, particularly surface mine.And hydraulic fracturing to be the supposition gravity stress be a principle stress and overlap with a principal direction of stress, the result who records according to boring determines the three-dimensional ground stress state, its outstanding advantage is can measure ground, deep to press, yet the initial cracking of rock of thinking of this method machinery is to take place in the direction perpendicular to least principal stress, if rock just had planes of weakness such as bedding, joint to exist originally, so initial crack just might take place along plane of weakness.Therefore, this method can only be used for more complete rock, the more important thing is that this method cost is very expensive, grasps very complicated, so also limited its development to a certain extent.Therefore, how to find a kind of not only cheap but also suitable earth stress measuring method to become the task of top priority that the rock mass engineering project interface is faced.

Summary of the invention

The object of the present invention is to provide a kind of based on the novel acoustic emission stress field measuring method under the plane stress condition, the method also is that the supposition gravity stress is a principle stress, under the plane stress condition, utilize the method for acoustic emission to find the solution major principal stress and direction on the surface level then, so the method has the characteristics of acoustic emission and hydraulic fracturing concurrently, but rational more than hydraulic fracturing on economy and applicability.

Technical scheme of the present invention is: a kind of based on the novel acoustic emission stress field measuring method under the plane stress condition, its concrete steps are: (1) supposes that vertical direction is known principle stress σ _Z, the big I of principle stress is by formula σ _Z=γ d tries to achieve, and γ is rock stratum, top unit weight in the formula, and d is buried depth; (2) on the horizontal direction, in orthogonal both direction and the direction of angle 45 degree therewith, i.e. X, Y gets 4 diameter 30mm, the rock sample of high 60mm on each direction of X45Y; (3) standard specimen that processes is done the single shaft compression test at the electro-hydraulic servo pressing machine, the acoustic emission probe is spread vaseline, and be close to the standard sample side with adhesive tape.During on-test, need to guarantee that Acoustic radiating instrument and stress-strain data acquisition system record test figure simultaneously, the testing requirements loading speed is controlled at 0.006mm/s-0.008mm/s, is loaded on standard sample and residual strength occurs, stops to load and record; (4) the Acoustic radiating instrument record obtains energy accumulation counting-time curve, and stress-strain data acquisition system record obtains stress time curve, and two groups of data are unified coordinate axis with time, draw energy accumulation counting-stress-time curve.Analyze this relation curve, the corresponding stress of catastrophe point of energy accumulation counting-time curve slope is the Kaiser point; (5) utilize above-mentioned test method, obtain the Kaiser point stress of three direction correspondences, be respectively σ _X, σ _Y, σ _X45YBut size and direction according to two principle stresses of following theoretical calculation formula calculated level direction:

$\left\{\begin{array}{c}{\mathrm{\σ}}_1=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})+\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ {\mathrm{\σ}}_2=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})+\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ \tan 2\mathrm{\θ}=\frac{2{\mathrm{\σ}}_{\mathrm{II}}-{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}{{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}\end{array}\right.$

In the formula: σ ₁And σ ₂Be the minimum and maximum principle stress value of asking; θ is σ ₁With σ ₂Angle; σ ₁=σ _X, σ _IIσ _X45Y, σ _III=σ _Y

According to above formula, can try to achieve the size and Orientation of measuring point place maximum, least principal stress, add the σ of hypothesis _Z, can realize the Determination of Three-dimensional Stress of terrestrial stress.

The invention has the advantages that: be a kind of novel stress field method of testing based on the novel acoustic emission stress field measuring method under the plane stress condition, can remedy the deficiency of conventional test methodologies, also can save greatly simultaneously to measure and expend, have advantages such as workable, that measurement is accurate, in conjunction with means such as rock mass mechanics test and numerical simulation analysis, can be the Geotechnical Engineering design strong scientific basis is provided, is a kind of brand-new, international advanced stress field method of testing.

Description of drawings

Fig. 1 is a kind of based on normal stress and shear stress synoptic diagram on arbitrary cross section in the novel acoustic emission stress field measuring method under the plane stress condition for the present invention;

Fig. 2 presses 45 ° of distribution plans for the present invention is a kind of successively based on three known cross sections in the novel acoustic emission stress field measuring method knot under the plane stress condition;

Fig. 3 is a kind of based on sample position synoptic diagram in the novel acoustic emission stress field measuring method under the plane stress condition for the present invention;

Fig. 4 is a kind of based on the novel acoustic emission stress field measuring method standard sample acoustic emission test synoptic diagram under the plane stress condition for the present invention.

Embodiment

The theoretical foundation geostress survey that acoustic emission is measured under the plane stress condition is often based on flat state.Regard geostress survey boring as in the infinitely great thin plate circular hole, and stress direction is parallel with surface level, according to the Elasticity computing formula, known two couples of horizontal principal stress σ ₁And σ ₂, then the normal stress on arbitrary cross section and shear stress are (as shown in Figure 1):

$\left\{\begin{array}{c}{\mathrm{\σ}}_{\mathrm{\θ}}=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos 2\mathrm{\θ}\\ \mathrm{\τ}{\mathrm{\θ}}_{}=\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\sin 2\mathrm{\θ}\end{array}\right.$

If the normal stress on three different cross sections of cicada then can be obtained the major principal stress size and Orientation on the surface level according to above formula so.Convenient for considering the acoustic emission sample preparation here, three known cross sections only are discussed successively by the situation (as shown in Figure 2) of 45 ° of distributions, then have:

$\left\{\begin{array}{c}{\mathrm{\σ}}_I=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos 2\mathrm{\θ}\\ {\mathrm{\σ}}_{\mathrm{II}}=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos (90+2\mathrm{\θ})\\ {\mathrm{\σ}}_{\mathrm{III}}=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos (180+2\mathrm{\θ})\end{array}\right.$

The expansion trigonometric function gets:

$\left\{\begin{array}{c}{\mathrm{\σ}}_I=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos 2\mathrm{\θ}\\ {\mathrm{\σ}}_{\mathrm{II}}=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)+\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\sin 2\mathrm{\θ}\\ {\mathrm{\σ}}_{\mathrm{III}}=\frac{1}{2}({\mathrm{\σ}}_1+{\mathrm{\σ}}_2)-\frac{1}{2}({\mathrm{\σ}}_1-{\mathrm{\σ}}_2)\cos 2\mathrm{\θ}\end{array}\right.$

Solve an equation and organize:

$\left\{\begin{array}{c}{\mathrm{\σ}}_1=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})+\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ {\mathrm{\σ}}_2=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})-\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ \tan 2\mathrm{\θ}=\frac{2{\mathrm{\σ}}_{\mathrm{II}}-{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\text{III}}}{{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}\end{array}\right.$

Can obtain maximum, least principal stress size and Orientation on the surface level according to above derivation formula, add the σ of hypothesis _Z, can realize the Determination of Three-dimensional Stress of terrestrial stress.

The concrete steps that acoustic emission is measured under the plane stress condition:

The concrete steps of the novel acoustic emission stress field measuring technique under the plane stress condition are:

(1) supposes that vertical direction is known principal direction of stress σ _Z, the big I of principle stress is by formula σ _Z=γ d tries to achieve (γ is rock stratum, top unit weight, and d is buried depth);

(2) on the horizontal direction, in orthogonal both direction and the direction of angle 45 degree therewith, i.e. X, Y gets 4 diameter 30mm, the rock sample of high 60mm on each direction of X45Y;

(3) standard specimen that processes is done the single shaft compression test at the electro-hydraulic servo pressing machine, the acoustic emission probe is spread vaseline, and be close to the standard sample side with adhesive tape.During on-test, need to guarantee that Acoustic radiating instrument and stress-strain data acquisition system record test figure simultaneously, the testing requirements loading speed is controlled at 0.006mm/s-0.008mm/s, is loaded on standard sample and residual strength occurs, stops to load and record;

(4) the Acoustic radiating instrument record obtains energy accumulation counting-time curve, and stress-strain data acquisition system record obtains stress time curve, and two groups of data are unified coordinate axis with time, draw energy accumulation counting-stress-time curve.Analyze this relation curve, the corresponding stress of catastrophe point of energy accumulation counting-time curve slope is the Kaiser point;

(5) utilize above-mentioned test method, obtain the Kaiser point stress of three direction correspondences, be respectively σ _X, σ _Y, σ _X45YCan calculate size and the direction of two principle stresses of horizontal direction according to following theoretical calculation formula:

$\left\{\begin{array}{c}{\mathrm{\σ}}_1=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})+\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ {\mathrm{\σ}}_2=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})-\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ \tan 2\mathrm{\θ}=\frac{2{\mathrm{\σ}}_{\mathrm{II}}-{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\text{III}}}{{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}\end{array}\right.$

In the formula:

σ ₁And σ ₂Be the minimum and maximum principle stress value of asking;

θ is σ ₁With σ ₂Angle;

σ _I＝σ _X，σ _II＝σ _X45Y，σ _III＝σ _Y。

According to above formula, can try to achieve the size and Orientation of measuring point place maximum, least principal stress, add the σ of hypothesis _Z, can realize the Determination of Three-dimensional Stress of terrestrial stress.

Claims (1)

1. one kind based on the novel acoustic emission stress field measuring method under the plane stress condition, and its concrete steps are: (1) supposes that vertical direction is known principle stress σ _Z, the big I of principle stress is by formula σ _Z=γ d tries to achieve, and γ is rock stratum, top unit weight in the formula, and d is buried depth; (2) on the horizontal direction, orthogonal both direction and therewith two angular separations become the directions of 45 degree, i.e. X, Y gets 4 diameter 30mm, the rock sample of high 60mm on each direction of X45Y; (3) standard specimen that processes is done the single shaft compression test at the electro-hydraulic servo pressing machine, the acoustic emission probe is spread vaseline, and be close to the standard sample side with adhesive tape; During on-test, need to guarantee that Acoustic radiating instrument and stress-strain data acquisition system record test figure simultaneously, the testing requirements loading speed is controlled at 0.006mm/s-0.008mm/s, is loaded on standard sample and residual strength occurs, stops to load and record; (4) the Acoustic radiating instrument record obtains energy accumulation counting-time curve, stress-strain data acquisition system record obtains stress time curve, two groups of data are unified coordinate axis with time, draw energy accumulation counting-stress-time curve, analyze this relation curve, the corresponding stress of catastrophe point of energy accumulation counting-time curve slope is the Kaiser point; (5) utilize above-mentioned test method, obtain the Kaiser point stress of three direction correspondences, be respectively σ _X, σ _Y, σ _X45YBut size and direction according to two principle stresses of following theoretical calculation formula calculated level direction:

$\left\{\begin{array}{c}{\mathrm{\σ}}_1=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})+\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ {\mathrm{\σ}}_2=\frac{1}{2}({\mathrm{\σ}}_I+{\mathrm{\σ}}_{\mathrm{III}})-\frac{1}{2\cos 2\mathrm{\θ}}({\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}})\\ \tan 2\mathrm{\θ}=\frac{2{\mathrm{\σ}}_{\mathrm{II}}-{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}{{\mathrm{\σ}}_I-{\mathrm{\σ}}_{\mathrm{III}}}\end{array}\right.$

In the formula: σ ₁And σ ₂Be the minimum and maximum principle stress value of asking; θ is σ ₁With σ ₂Angle; σ _I=σ _X, σ _II=σ _X45Y, σ _III=σ _Y

According to above formula, can try to achieve the size and Orientation of measuring point place maximum, least principal stress, add the σ of hypothesis _Z, can realize the Determination of Three-dimensional Stress of terrestrial stress.

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