CN105021444A - Steady rheology rate cross point-based determination method of rock long-time strength parameters - Google Patents

Abstract

The invention discloses a method for determining long-term rock strength parameters based on the intersection point of steady-state rheological rates. The rock core sample is taken and processed into a standard cylindrical sample, and the standard cylindrical sample is subjected to a triaxial rheological mechanical property test. Two steady-state rheological rate curves are fitted by the axial rheological rate and volumetric rheological rate in the steady-state rheological stage, and the long-term strength parameters of the rock are quantitatively determined by using the intersection of the axial and volumetric rheological rate curves. The present invention compares the axial steady-state rheological rate curve and the volume steady-state rheological rate curve calculated by the test results of rock rheological characteristics, and through the critical value of rock compression deformation and volume expansion, that is, two steady-state rheological rate curves Quantitatively determine the long-term strength parameters of rocks by using the intersection point of the rate curves, which overcomes the problem of fuzzy inflection points in rock samples with inconspicuous rheological properties of the traditional stress-strain isochronous curve cluster method and steady-state rheological rate method. It is of reference value to evaluate the long-term stability of rocks.

Description

A method for determining long-term rock strength parameters based on steady-state rheological rate intersection

technical field

The invention relates to the field of rock mechanics and engineering, in particular to a method for determining long-term rock strength parameters.

Background technique

The determination of long-term strength is an important aspect of long-term stability and safety analysis of rock engineering, and has very important engineering background and significance. According to the actual requirements of different projects, the understanding of the long-term strength of rocks is also quite different. A more accepted definition of long-term rock strength is that the rock undergoes rheological phenomena under long-term constant external loads; when the external load is greater than or equal to a certain value, the rheological deformation of the rock will continue to increase and eventually fail. ; When the external load is less than a certain value, the rheological deformation rate of the rock will gradually decrease with time, and the rheological deformation will gradually converge, and the rock will not crack; the critical value of this stress level can be called the long-term strength of the rock. Theoretically, long-term strength is a specific value, but it is still difficult to conduct theoretical derivation based on existing methods and accurately determine it through experimental results, so an interval or approximate value is often used to measure it.

The rheological properties test of rock is one of the main means to determine the long-term strength of rock. The research on long-term strength mainly focuses on the stress state of rock in rock rheological properties test. In simple stress state, direct method, initial creep method, expansion method, etc. can be used to directly determine; while in complex stress state, it is mainly According to the rheological test results, the stress-strain isochronous curve cluster method and the steady-state rheological rate inflection point method are used to determine the stress-strain isochronous curve cluster method and the steady-state rheological rate inflection point method. The inflection point of the segment is used to determine the long-term strength parameters of the rock. The inflection point of the curve here refers to the sudden change point or turning point of the curve of the stress-strain isochronous curve cluster method and the steady-state rheological rate inflection point method when the rheological properties of the rock are relatively significant. The inflection point method widely used at present is to randomly select any one of the axial, circumferential or volume rheological rate curves for visual inspection of the sudden change point, so it is relatively random and inaccurate. In addition, the inflection point of the initial straight line section of the curve and the later curve section is relatively obvious, but if the rheological properties of the rock are not obvious, the inflection point of the curve is relatively vague, and it is difficult to directly detect it visually, and the effect is not good.

Contents of the invention

Purpose of the invention: The purpose of the present invention is to address the deficiencies in the prior art, to provide a method for determining the long-term strength parameters of rock based on the steady-state rheological rate intersection point, through the rock axial steady-state rheological rate curve and the volumetric steady-state flow rate The intersection point of the rate curve can be used to quantitatively determine the long-term strength parameters of the rock.

Technical solution: The present invention provides a method for determining long-term rock strength parameters based on the intersection point of steady-state rheological rates. The rock core sample is processed into a standard cylindrical sample, and the triaxial rheological mechanical properties of the standard cylindrical sample are analyzed. In the experiment, two steady-state rheological rate curves were fitted by the axial rheological rate and volumetric rheological rate in the steady-state rheological stage, and the long-term strength of the rock was quantitatively determined by the intersection of the axial and volumetric rheological rate curves. parameter.

When the rock is in a low-stress state, the axial steady-state rheological rate is greater than the volumetric steady-state rheological rate, and the rock is in a state of compression deformation; when the rock is in a high-stress state, the volumetric steady-state rheological rate increases sharply, If the axial steady-state rheological rate is exceeded, rock failure will occur in a short period of time, and the rock deformation will mainly transform from compression deformation to volume expansion. Therefore, there is an intersection point between the axial and volumetric steady-state rheological rate change curves. Before the stress is at this intersection point, the rock does not produce obvious ductile failure; when the stress exceeds this intersection point, the rock shows obvious volume expansion, and the expansion failure occurs soon. Therefore, the intersection point is the critical value of rock compression deformation and volume expansion, and the corresponding deviatoric stress value is the long-term strength parameter value of the granite gneiss.

Further, the rock core is required to be intact and undamaged, and the original internal structure of the rock sample should not be damaged during processing.

Further, the confining pressure of the triaxial rheological properties test is taken from the stress value of the rock in the actual engineering, and the method of loading in stages is adopted: before the rock rheological properties test, the same batch of samples is first triaxially Transient mechanical properties test, the instantaneous peak strength is obtained, the initial loading level of the rheological test is 55% to 65% of the instantaneous test peak strength, and then each stage is loaded with 3% to 5% of the instantaneous peak strength, taking an integer value, and each stage is loaded Not less than 50 hours until rheological damage occurs to the rock sample.

The basic characteristics of rock's steady-state rheological stage characteristics can be expressed as steady-state rheological rate. The rock rheological loading stages are divided into initial attenuation rheology and steady-state rheological stage, and the average value calculation of the rheological rate in the steady-state rheological stage of each loading level is carried out to obtain the steady-state rheological rate. Among them, the last In the primary rheological stage, the deformation data in the accelerated rheological stage should also be eliminated to calculate the steady-state rheological rate.

Further, taking the axial steady-state rheological rate and the volumetric steady-state rheological rate as the research objects, taking the deviatoric stress value of each loading level as the abscissa data, and the steady-state rheological rate as the ordinate data, in the plane coordinate system using The exponential function fits the two steady-state rheological rate curves respectively, and the horizontal axis of the plane coordinate system is the deviatoric stress (σ ₁ -σ ₃ )/MPa, where σ ₁ /MPa is the axial pressure of the rheological test, and σ ₃ /MPa is the confining pressure of the rheological test, and the vertical axis is the steady-state rheological rate

Beneficial effects: the present invention compares the axial steady-state rheological rate curve and the volume steady-state rheological rate curve calculated by the test results of rock rheological mechanical properties, and through the critical value of rock compression deformation and volume expansion, that is, two steady-state rheological rate curves Quantitatively determine the long-term strength parameters of rocks by using the intersection point of the state rheological rate curves, which overcomes the problem of fuzzy inflection points of the traditional stress-strain isochronous curve cluster method and steady-state rheological rate method in rock samples with inconspicuous rheological properties , which has reference value for accurately evaluating the long-term stability of rocks.

Description of drawings

Fig. 1 is the rock rheological characteristic test curve figure of present embodiment rock sample;

Fig. 2 is a schematic diagram of determining long-term rock strength parameters by the method of the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below, but the protection scope of the present invention is not limited to the embodiments.

Embodiment: the present invention obtains its rheological characteristic test curve and data through the rheological characteristic test of rock sample; For the calculation of the steady state rheological rate of loading stages at all levels, the axial and volume steady state are obtained by fitting the exponential function. State rheological rate curves; use the intersection of axial and bulk rheological rate curves to quantitatively determine long-term rock strength parameters.

The specific implementation steps of this embodiment are as follows:

① Use the core drilling tool to obtain the granite gneiss core sample of the underground rock cavern, and process it into a standard cylindrical sample with a height of 100 mm and a diameter of 50 mm. The core sample must be intact and undamaged. It is required not to destroy the original internal structure of the rock sample.

②Put the prepared rock sample on the rock triaxial rheological tester, take the confining pressure (σ ₃ /MPa) as the actual in-situ stress value of 4MPa on the rock in the underground cavern, and adopt the method of staged loading for triaxial flow Variable mechanical properties test. Before the rheological properties test of the rock, the triaxial transient mechanical property test was carried out on the same batch of samples, and the peak strength was obtained as 224.50 MPa; the initial loading level of the rheological test was taken as 56% of the instantaneous strength, and after rounding, it was 125.00MPa; then each stage loads 5% of the instantaneous peak strength, which is 10.00MPa after rounding; as shown in Figure 1, ε ₁ is the axial strain of the rock, ε ₃ is the hoop strain of the rock, _v is the volumetric strain of the rock, and t/h is the rheological time parameter of the rock; the rheological time of each stage is 72 hours to ensure that the deformation of the rock sample tends to be stable, and then the next stage of loading is carried out until the fifth stage of loading , the rock sample undergoes accelerated rheological phenomenon after 35 hours of rheology, and finally rheological failure occurs.

③According to the triaxial rheological test data, the average value of the steady-state rheological stage rate of each loading level is calculated to obtain the steady-state rheological rate of each loading level of the rock, and the axial and volumetric rheological rates are taken as the steady-state rheological rate For the research object, the abscissa data is the deviatoric stress value of each loading level, and the steady-state rheological rate is the ordinate data, as shown in Figure 2, and two steady-state flows are fitted by exponential functions in the plane coordinate system The variable rate curve, the horizontal axis (X axis) of the plane coordinate system in the figure is the deviatoric stress ((σ ₁ -σ ₃ )/MPa), where (σ ₁ /MPa) is the axial pressure of the rheological test, (σ ₃ / MPa) is the confining pressure of the rheological test; the vertical axis (Y axis) is the steady-state rheological rate

④As shown in Figure 2, when the rock is in a low stress state, the axial steady-state rheological rate (curve 1) is greater than the volumetric steady-state rheological rate (curve 2), and the rock is in a state of compression deformation; Under high stress state, the volumetric steady-state rheological rate (curve 2) increases sharply, exceeding the axial steady-state rheological rate (curve 1), rock failure occurs in a short period of time, and the rock deformation changes from compression deformation to volumetric deformation. Expansion is the main thing. Therefore, there is an intersection point 3 between the axial and volumetric steady-state rheological rate change curves. This intersection point is the critical value of rock compression deformation and volume expansion, and the corresponding deviatoric stress value of 153.20 MPa is the long-term strength parameter value of the granite gneiss.

Claims (5)

1. A method for determining the long-term strength parameters of rock based on the intersection point of steady-state rheological rates, characterized in that: the rock core sample is processed into a standard cylindrical sample, and the standard cylindrical sample is subjected to a triaxial rheological mechanical property test , two steady-state rheological rate curves are fitted by the axial rheological rate and volumetric rheological rate in the steady-state rheological stage, and the long-term strength parameters of the rock are quantitatively determined by the intersection of the axial and volumetric rheological rate curves . 2. The method for determining long-term strength parameters of rock based on the intersection of steady-state rheological rates according to claim 1, wherein the rock core is required to be intact and undamaged, and the original internal structure of the rock sample is not destroyed during processing. 3. the rock long-term strength parameter determination method based on the intersection point of steady-state rheological rate according to claim 1, is characterized in that: the confining pressure of described triaxial rheological mechanical property test takes the stress suffered by rock in actual engineering value, adopt the method of staged loading: before the rock rheological properties test, the triaxial transient mechanical properties test is carried out on the same batch of samples to obtain the instantaneous peak strength, and the initial loading level of the rheological test is taken as 55% of the instantaneous peak strength. % to 65%, and then each stage is loaded with 3% to 5% of the instantaneous peak strength, taking an integer value, and each stage is loaded for no less than 50 hours until rheological damage occurs to the rock sample. 4. the rock long-term strength parameter determination method based on the intersection of steady-state rheological rates according to claim 3, is characterized in that: carry out the division of initial decay rheology and steady-state rheological stage by rock rheological loading stages at all levels, The average value of the rheological rate in the steady-state rheological stage of each loading level is calculated to obtain the steady-state rheological rate. Among them, the deformation data in the accelerated rheological stage are eliminated in the last stage of rheological stage to calculate the steady-state rheological rate. 5. the rock long-term strength parameter determination method based on the intersection of steady-state rheological rates according to claim 1, is characterized in that: utilize exponential function to fit respectively described two steady-state rheological-rate curves in the plane coordinate system, The horizontal axis of the plane coordinate system is the deviatoric stress (σ ₁ -σ ₃ )/MPa, where σ ₁ /MPa is the axial pressure of the rheological test, σ ₃ /MPa is the confining pressure of the rheological test, and the vertical axis is the steady flow variable speed