CN104390844A - Method for testing tensile strength of rock at random schistosity angle through single rock sample - Google Patents

Abstract

A test method for measuring the tensile strength of rock under any schistosity angle through a single rock sample, comprising the following steps: 1. Prepare the rock sample to be tested; According to the schistometry angle of the rock sample, do the first splitting test along the schistometry direction of the rock sample; 3. Cement the rock sample after splitting; The second splitting test; 5. Cement the split rock sample; repeat steps 4 and 5 to obtain the maximum loading force when the rock sample splits and fails at any required angle with the schistosity of the rock sample. The present invention provides a test method for measuring the tensile strength of rocks at any schistosity angle through a single rock sample. The present invention can obtain the desired rock tensile strength at any schistosity angle by performing a splitting test on one rock sample or a small number of rock samples. Tensile strength, greatly reducing the number of rock samples. Reduce the error of test results caused by the discrete type of rock samples.

Description

Test method for determining the tensile strength of rocks at any slicing angle through a single rock sample

technical field

The invention relates to the field of rock tensile strength measurement, in particular to a test method for measuring the rock tensile strength at any slab angle through a single rock sample.

Background technique

In the design and construction of underground engineering, the tensile strength of rock is a very important mechanical index. The surrounding rock mass of underground engineering is often in a complex stress state, such as the surrounding rock mass of railway tunnels, highway tunnels, engineering slopes and underground engineering caverns, some places are in a state of tensile stress, while some parts are in a state of compressive stress , because the tensile strength of the rock is much lower than the compressive strength, the surrounding rock always begins to fail from the tensile stress area. Therefore, the correct regional division of the stress state of the underground surrounding rock, that is, the determination of the failure risk zone is the key to the analysis and evaluation of the stability of the underground engineering surrounding rock, and the rock tensile strength is one of the basic data for determining the failure area of the engineering surrounding rock.

There are often various structural planes in rock mass, such as cracks, schistoses, joints, bedding, faults, fault zones, etc., and various combinations thereof. The complete rock mass is reduced, and the tensile strength of the rock mass will vary greatly under different bedding angles. In actual engineering, the anisotropy of layered rock mass is very obvious. In order to correctly analyze the stability of anisotropic rock mass after excavation, it is necessary to accurately grasp the tensile strength values of rock mass at different schistosity angles.

At present, the indoor determination method of rock tensile strength generally adopts the direct tension method and the split method. In the direct tension test of the rock specimen, it is difficult to clamp and ensure that the axis of the tensile load coincides with the axis of the specimen. The tensile method is relatively less used to test the tensile strength of rocks, but the splitting method, namely the Brazilian test method, is more commonly used to indirectly measure the tensile strength of rocks. Regardless of whether the direct tension method or the traditional Brazilian test method is used, when measuring the tensile strength of rocks with different schistosity angles, the tensile strength is measured by screening rock samples with different natural schistosity angles. As a result, the following two existing problems are caused:

1. The test rock sample is large. In order to obtain rock samples with different natural angles of schistosity, a large number of rock blocks must be drilled and screened, which will inevitably lead to an increase in manpower, material resources and time costs for testing.

2. It is very difficult to obtain rock samples at any schistosity angle. The schistosity structure of natural rock mass is complex, and it is difficult to find several rock samples with the same specified schistosity angle for testing. In most cases, the rock samples with similar schistosity structure can only be grouped together, which makes the test error larger.

Contents of the invention

The technical problem to be solved by the present invention is to provide a test method for measuring the tensile strength of rock under any schistosity angle through a single rock sample, which can reduce the demand for the number of rock sample samples and enhance the accuracy of test results.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is: a test method for measuring the tensile strength of rock under any schistosity angle by a single rock sample, comprising the following steps:

1. Prepare rock samples to be tested;

If the rock sample is a cylindrical specimen, the schistosity direction of the rock sample should be parallel to its axial direction;

2. Select the angle between the schistograph and the schistograph of the rock sample, and do the first splitting test along the direction of the schistograph of the rock sample;

3. Cement the split rock samples;

4. Replace the non-cemented position, re-select the different angles with the rock sample slab, and conduct the second splitting test;

5. Cement the split rock samples;

Repeat steps 4 and 5 to obtain the maximum loading force when the rock sample splits and fails at any required angle with the rock sample schistosity.

The aspect ratio of the rock sample is 0.5-1, the two ends of the rock sample are ground flat, and the side is smooth without protrusions.

Take out the damaged rock sample, apply cementing material evenly on the damaged surface of the rock sample, and then press it to make the contact surface basically free of gaps, ensure that both ends are flat and the sides are smooth, and wait for the glue on the contact surface to solidify;

The tensile strength of the cemented material after consolidation should be as close as possible to the tensile strength of the rock sample to be tested.

Substitute the measured results into the formula for calculating the tensile strength of the rock splitting test:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;Dh</span>}}$

Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, D is the diameter of the cylindrical specimen, and h is the height of the circular specimen;

or

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, and a is the side length of the cube specimen;

The rock tensile strengths R ₁ , R ₂ ···R _n measured many times are obtained.

The present invention provides a test method for measuring the tensile strength of rocks at any slicing angle through a single rock sample. The measuring method of the present invention can obtain any desired slab by only performing a splitting test on one rock sample or a small number of rock samples. The tensile strength of the rational angle rock has the following beneficial effects:

1. Greatly reduce the number of rock samples. If the traditional method wants to obtain the tensile strength values of rocks with different schistosity angles, it is necessary to obtain a large number of rock samples with different schistosity angles, but the present invention adjusts the angle between the splitting plane and the schistosity of the rock sample, and single or a few The tensile strength values of rocks with different schistosity angles can be obtained by repeated tests on rock samples.

2. Reduce the error of test results caused by discrete rock samples. Different rock samples, even if they are drilled from the same rock block, may have great differences in lithology. The traditional method of measuring the tensile strength of rocks with different schistosity angles by testing multiple rock samples will inevitably fail. There are errors caused by different rock properties, but the present invention only conducts repeated tests on one rock sample, which greatly reduces the error of test results caused by the discrete type of rock samples.

3. Accurately obtain the tensile strength value of the rock under any schistosity angle. The schistometry development of natural rock mass is extremely complicated, and it is very difficult to obtain a rock sample with a specific schistosity angle, but the present invention adjusts the angle between the splitting plane and the inside of a specific schistosite sample, so that it can be very Accurately obtain the tensile strength value of rocks with any schistosity angle. In summary, the present invention has obvious technical superiority and wide engineering application prospect for measuring the tensile strength of schist with different schistosity angles compared with the traditional method.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

Fig. 1 is the schematic diagram of rock sample and rock sample schistograph in the present invention.

Fig. 2 is a schematic diagram of selection of splitting planes during multiple loadings in the present invention.

Fig. 3 is a schematic diagram of rock sample fixing in the present invention.

In the figure: rock sample 1, the first splitting surface 2, the second splitting surface 3, the third splitting surface 4, the fourth splitting surface 5, the Nth splitting surface 6, splitting test Device 7, indenter 8, rock sample schistosome 9.

Detailed ways

A test method for measuring the tensile strength of rock under any schistosity angle through a single rock sample, comprising the following steps:

1. Prepare the rock sample 1 to be tested;

If the rock sample is a cylindrical specimen, the schistosity direction of the rock sample should be parallel to its axial direction; as shown in Figure 1.

Preferably, the aspect ratio of the rock sample 1 is 0.5-1, both ends of the rock sample 1 are ground flat, and the sides are smooth without protrusions.

2. Select the schistograph included angle with the schistosome 9 of the rock sample, and do the splitting test for the first time along the direction of the schistograph 9 of the rock sample;

After the test instrument and rock sample are ready, put the rock sample into the RMT-150C rock splitting test device 7 and fix it. The sheeting surface and the upper and lower pads 10 form a required sheeting angle, such as a ₁ in FIG. 1 . Debug and run the test instrument, start the splitting test, and record the maximum loading force P ₁ when the rock sample 1 is damaged.

3. Cementing the split rock sample 1;

Take out the damaged rock sample, apply cement evenly on the damaged surface of the rock sample, and then press it firmly, so that the contact surface is basically free of gaps, the two ends are kept flat, and the sides are smooth, and the rock sample is restored to the state before the damage as much as possible. Then put it on a dry and flat table. The curing time depends on the properties of the cementing material and the ambient temperature, generally 12 hours is appropriate. Wait for the glue to solidify on the contact surface. The inventor's previous experiments found that if the cementing method is not used, the splitting surface of the rock sample will be broken at the previous splitting surface when the splitting is repeated, and the splitting surface cannot penetrate the entire rock sample section. After the cementing method is adopted, It ensures the transmission of internal force and the restoration of its mechanical state when the rock sample is split.

The tensile strength of the cemented material after consolidation should be as close as possible to the tensile strength of the rock sample 1 to be tested.

4. Replace the non-cemented position, reselect a different angle with the rock sample slab 9, such as a ₂ in Figure 1, and conduct the second splitting test;

Since the splitting surface is not repeated each time, and the rock sample failure is only related to the tensile strength of the splitting surface, the actual cemented thickness of the rock sample is about 0.5mm, the diameter of the rock sample is 50mm, and the cemented area occupies the entire splitting surface. 1% or less. We define the influence factor ξ=δ×λ of the test results of the cemented surface, where δ is the proportion of the cemented area to the entire split surface, and λ is the tensile strength ratio of the cemented material to the rock. Since δ<1%, if If the tensile strength ratio of the cemented material to the rock is not much different, its influence on the results is very limited. In addition, considering the inhomogeneity of schist, in order to reduce this effect, it is advisable that the angle between the two splitting planes should be greater than 30°.

5. Cement the split rock samples;

Repeat steps 4 and 5 to obtain the maximum loading force P _n when the rock sample splits and fails at any required angle a _n between the rock sample schistosome 9 .

Substitute the measured results into the formula for calculating the tensile strength of the rock splitting test:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;Dh</span>}}$

Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, D is the diameter of the cylindrical specimen, and h is the height of the circular specimen;

or

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, and a is the side length of the cube specimen;

The rock tensile strengths R ₁ , R ₂ ···R _n measured many times are obtained.

Attached Table 1 is a comparison of the determination results of the rock tensile strength (Mpa) of multiple traditional rock samples and a single rock sample of the present invention with different schistosity angles.

Note: scheme 1 is the traditional method, has selected 5 groups of schistograph angles, and each group is 5 rock samples; scheme 2 is the test technical scheme of the present invention, has selected 5 schistographs and axially parallel rock samples, above The results in the table are the average values of the measurement results of each group.

As can be seen from the above table, the deviations of the test results of the two methods are all below 10% under each schistosity angle, which also proves the accuracy and rationality of this technical solution. 5, scheme 2 saves 80% rock samples compared with scheme 1, shows the economic superiority of the present invention.

Claims (4)

1. a method of testing rock tensile strength under any schistosity angle by single rock sample survey, it is characterized in that comprising the following steps: 1. Prepare the rock sample to be tested (1); If the rock sample is a cylindrical specimen, the schistosity direction of the rock sample should be parallel to its axial direction; Two, select the schistograph included angle with rock sample schistosom (9), do splitting test for the first time along the rock sample schistograph (9) direction; 3. Cementing the rock sample (1) after splitting; 4. Replace the non-cemented position, reselect the different angles with the rock sample slab (9), and carry out the second splitting test; 5. Cement the split rock samples; Repeat steps 4 and 5 to obtain the maximum loading force when the rock sample splits and fails at any required angle with the rock sample schistosity (9). 2. A kind of test method of rock tensile strength under any schistosity angle by single rock sample according to claim 1, it is characterized in that: described rock sample (1) aspect ratio is 0.5～1, rock Sample (1) has both ends ground flat, and the sides are smooth without protrusions. 3. a kind of test method of measuring the rock tensile strength under any schistosity angle by a single rock sample according to claim 1, is characterized in that: the rock sample that destroys is taken out, evenly smears cementing substance on the rock sample failure surface After pressing, the contact surface is basically free of gaps, the two ends are guaranteed to be flat, and the sides are smooth, and the glue on the contact surface is solidified; The tensile strength of the cemented material after consolidation should be as close as possible to the tensile strength of the rock sample (1) to be tested. 4. according to claim 1, a kind of test method of measuring the rock tensile strength under any schistosity angle by a single rock sample, is characterized in that: the measured result is substituted into the rock splitting test tensile strength calculation formula for many times: $\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;Dh</span>}}$ Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, D is the diameter of the cylindrical specimen, and h is the height of the circular specimen; or $\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$ Among them: R is the tensile strength of the rock, P is the maximum loading force when the rock is damaged, and a is the side length of the cube specimen; the tensile strength R ₁ , R ₂ ···R _n of the rock has been measured many times.