CN109856243A - A kind of evaluation method of deep rock mass three-dimensional ground stress - Google Patents

Abstract

The invention provides a method for estimating three-dimensional in-situ stress of deep rock mass. First, a tunnel section is selected for macroscopic in-situ stress direction analysis, and then sound wave tests are carried out in different directions on the surrounding rock of the tunnel excavation section, and the rock blasting excavation is determined according to the current specification. The size of the damage zone in the process is divided into inner damage zone and outer damage zone according to the degree of damage, and is divided into blast load damage zone, in-situ stress transient damage zone, and static unloading damage zone according to different causes; and then based on the distribution state of the damage zone Determine the magnitude relationship between the direction of the in-situ stress and the magnitude of the principal stress, and determine the magnitude of the maximum principal stress according to the damage depth of different causes in the direction of the maximum principal stress; select two non-parallel planes in a certain area, and reflect the magnitude and direction of the principal stress in the vertical direction. And in the horizontal direction, the three-dimensional in-situ stress state of the test area is finally determined. The invention requires low test conditions, is economical and efficient, and can measure the three-dimensional in-situ stress of the deep rock mass in a short time.

Description

A method for estimating three-dimensional in-situ stress of deep rock mass

technical field

The invention belongs to the fields of water conservancy and hydropower and geotechnical engineering, in particular to a method for estimating three-dimensional in-situ stress of deep rock mass, which is suitable for estimating in-situ stress during tunnel excavation in the fields of water conservancy and hydropower engineering, transportation, open-pit mining and the like.

Background technique

With the further development of hydropower development in southwest my country and the increasing depth of mineral resources mining, engineering geological disasters induced by high ground stress during the excavation of deep caverns are becoming more and more common and serious. In order to predict the occurrence of rock mass failure and rock burst and provide a basis for rock mass support and reinforcement, it is necessary to dynamically grasp the stress magnitude and direction of surrounding rock near the tunnel face in real time during the construction of the cavern.

The existing in-situ stress measurement methods can be roughly classified into three categories according to their measurement principles: the first category is based on the measurement of the strain and deformation in the rock mass based on mechanical methods, such as stress relief method, hydraulic fracturing method and stress recovery. The second category is a geophysical method based on the measurement of changes in acoustic emission, sound wave propagation, resistivity or other physical quantities in the rock mass; the third category is to determine the stress based on the information provided by the geological structure or the failure state of the rock mass direction. Among them, the stress relief method and the hydraulic fracturing method are the most widely used. The stress relief method requires operations such as drilling, taking cores, and installing sophisticated electronic instruments. The measurement period is long, and when it is used near the tunnel face, it affects the construction progress and cannot meet the needs of real-time dynamics. High in-situ stress, serious borehole deformation, and core fracture lead to difficulty in core extraction, low measurement success rate, and significant impact on the reliability of measurement results. The hydraulic fracturing method uses huge equipment, large drilling diameter, long drilling time, expensive measuring instruments, and high testing costs, which cannot be applied to the rapid measurement of in-situ stress in the surrounding rock of deep-buried caverns.

SUMMARY OF THE INVENTION

The invention proposes a method for estimating the three-dimensional in-situ stress of deep rock mass in order to solve the problems of expensive measuring instruments, high testing cost and long testing period in in-situ stress measurement in the fields of water conservancy, hydropower and geotechnical engineering. For the excavated tunnel, the acoustic wave test is carried out on a plane parallel to the direction of the tunnel face, and the distribution of the inner and outer damage areas of the surrounding rock of the tunnel is obtained, and then the current plane is obtained through the distribution characteristics of the inner and outer damage areas. The magnitude and direction of the major and minor principal stresses, combined with the stress data of the nearby cross tunnels, can obtain the three-dimensional in-situ stress distribution in the nearby area.

The technical scheme adopted by the present invention for solving the problems existing in the prior art is as follows:

A method for estimating three-dimensional in-situ stress of a deep rock mass, comprising the following steps:

Step 1: According to the high stress situation on site, combined with the tunnel conditions such as auxiliary tunnels in the production process, select two tunnels that cross each other, select an area with complete rock structure on the excavation surface of the tunnel, observe the high stress failure characteristics of the tunnel macroscopically, and determine the main The angular relationship between the stress direction and the tunnel axis, to preliminarily determine the local in-situ stress direction;

Step 2: Select a plane parallel to the excavation face on the axes of the two tunnels near the intersection of the tunnels, and drill a number of sonic detection holes on the surrounding rock around the plane, and drill two sonic detection holes each time. Drill holes separately in multiple directions of the tunnel;

Step 3: Perform sonic detection on sonic detection holes in multiple directions through the sonic detection system, draw the curve of the velocity of sonic longitudinal waves with the depth of the borehole, and determine the degree of rock damage according to the reduction rate of sonic longitudinal wave velocity, and select a reasonable reduction rate. The rate threshold divides the damage into the inner damage zone and the outer damage zone;

Step 4: According to the depth of damage zone in different directions measured in Step 3, draw the distribution map of the inner and outer damage zone of the tunnel surrounding rock on two planes, and determine the section according to the distribution of the total damage zone of the inner and outer damage zone. The direction of the principal stress; the damage area is divided into blasting load damage, in-situ stress transient unloading damage and in-situ stress static unloading damage according to different causes, and the equivalent blasting load on the surrounding rock of the tunnel excavation is calculated from the blasting design, and the blasting is calculated. In the load damage area, the maximum principal stress is determined according to the depth relationship between the blasting load damage, the transient unloading damage of the in-situ stress and the static unloading damage of the in-situ stress in the direction of the maximum principal stress; size ratio, and combined with the previous steps to obtain the minimum principal stress size;

Step 5: According to the magnitude and direction of the maximum principal stress and the minimum principal stress on the current excavation section obtained in step 4, convert the size principal stress into the normal stress in the vertical and horizontal directions and the shear stress on the plane, and synthesize the two openings. The three-dimensional in-situ stress state of the current area is obtained from the stress state on the plane of the excavation section and the direction information of the macro-observed in-situ stress.

Further, in the step 3, the sound wave velocity attenuation rate is used to represent the damage degree of the rock:

In the above _formula , η is the attenuation rate of the acoustic longitudinal wave velocity of the rock mass, v1 is the acoustic longitudinal wave velocity _of the intact rock before excavation, and v2 is the acoustic longitudinal wave velocity of the surrounding rock after excavation, which is determined by the change degree of the acoustic wave velocity according to different site conditions. Reasonable thresholds for the inner damage zone and the outer damage zone. The velocity of the longitudinal acoustic wave in the inner damage zone varies greatly with the depth, and the velocity of the longitudinal acoustic wave in the outer damage zone varies little with the depth. Depth of outer damage zone.

Further, the method for confirming the magnitude and direction of the ground stress on the interrupted surface in the step 4 is as follows:

First, observe the distribution of the total damage area in the inner and outer damage areas of the section to determine the direction of the large and small principal stress _on the plane. Maximum principal stress, σ ₃ is the minimum principal stress;

In the direction of σ ₁ , the inner damage zone depth d ₁ , the outer damage zone depth d ₂ , the blast load damage depth d ₃ , the transient in-situ stress unloading damage depth d ₄ , and the static in-situ stress unloading damage depth d ₅ are determined according to the measured data. According to the blasting design, the maximum equivalent blasting load p on the excavation section is determined. Combined with the damage law of the equivalent blasting load p on the specific rock to blasting under the condition of low in-situ stress, a reasonable damage threshold is selected to determine the explosion during blasting excavation. The damage range of the load, in the direction of σ ₁ , takes the damage depth analysis on one side of the tunnel to determine the size of σ ₁ , and determines the damage depth d _{3 of} the blasting load according to the calculation. d ₂ , where the depth of the transient in-situ stress unloading damage zone is d ₄ =d ₁ -d ₃ , and the depth of the static in-situ stress unloading damage zone is d ₅ =d ₂ ;

Take the ratio α of the transient in-situ stress unloading damage depth to the blasting damage depth in the direction of the maximum principal stress and the ratio of static in-situ stress unloading damage depth to blasting damage depth β In the high in-situ stress area, the values of α and β are large, and in the low in-situ stress area, the values of α and β are small. By comparing the magnitudes of α and β, the maximum principal stress in-situ stress of the test plane is calculated;

The depth of the damage zone on both sides in the principal stress direction on the comprehensive tunnel is determined by the size of σ ₁ , and the average value of the two analyses is taken as the final maximum principal stress size;

The damage depth in the direction of the maximum principal stress and the minimum principal stress is obtained from the measured data, and D ₁ (D ₁ =D ₃ +D ₄ ) is taken as the damage depth in the direction of the maximum principal stress, D ₂ (D ₂ =D ₅ +D ) ₆ ) is the damage depth in the direction of the minimum principal stress, taking The larger the γ, the larger the lateral compression coefficient, the larger the ratio of σ ₁ to σ ₃ , and the more inhomogeneous the in-situ stress field. The relationship between σ ₁ and σ ₃ is determined by γ, and the minimum principal stress σ ₃ is finally obtained.

Further, in the step 5, the magnitude and direction of the maximum principal stress and the minimum principal stress on the current excavation section are obtained based on the step 4, and according to the step 1, on the selected mutually intersecting tunnel A and tunnel B, the Two normal stresses σ _V1 , σ _H1 and one shear stress τ _VH1 in the direction perpendicular to the tunnel A, σ _V1 is the vertical stress of the current excavation face of the tunnel A, σ _H1 is the horizontal direction perpendicular to the axis of the tunnel A In-situ stress, τ _VH1 is the shear stress on the excavation surface of tunnel A, use the same method to determine the normal stress σ _V2 , σ _H2 and shear stress τ _VH2 on tunnel B, take the average value σ _V of σ _V1 and σ _V2 as The measured vertical stress, assuming that the shear stress on the plane with σ _H1 and σ _H2 as the normal stress is τ _H12 , that is, the three-dimensional stress field of the current test area is obtained, and the stress state can be represented by the following matrix:

Combined with this matrix, the three-dimensional in-situ stress field is obtained, and the principal stress direction determined by the macroscopic observation results is brought in, and the size of τ _H12 is finally determined.

The present invention has the following advantages:

1. Compared with the conventional on-site in-situ stress testing method, the present invention obtains the three-dimensional in-situ stress by measuring the damage state of the test plane through the acoustic wave detection system, and the test method is simple. The data information can be fed back in a more timely manner, the test cycle is short, and the test cost is greatly reduced;

2. The present invention has very simple requirements for test conditions. In water conservancy and hydropower projects, it is a common technical measure to excavate a tunnel before excavating a deep rock mass. The present invention can fully combine and utilize the actual production conditions on site. The three-dimensional stress state of the test area can be estimated by testing, and the distribution state of the large and small principal stress can also be determined at any position of a single tunnel through the present invention, and the applicable conditions are very wide.

Description of drawings

Fig. 1 is the flow chart of implementing steps of the present invention;

Figure 2 is a schematic diagram of the selection of cross-tunnel and acoustic wave test sections;

Fig. 3 is the arrangement diagram of acoustic wave test hole of acoustic wave test section;

Fig. 4 is a graph showing the variation of acoustic longitudinal wave velocity with drilling depth;

Figure 5 shows the distribution of damage areas inside and outside the excavation section in high ground stress areas;

Figure 6 shows the distribution of damage areas of different causes of damage in high ground stress areas;

Among them: 1-Tunnel A, 2-Tunnel B, 3-Sound wave inspection hole, 4-Excavation section, 5-Inner damage zone, 6-Outer damage zone, 7-Explosive load damage, 8-Transient in-situ stress unloading damage , 9- Static in-situ stress unloading damage.

Detailed ways

The technical solution of the present invention is further described in detail below through the examples and in conjunction with the accompanying drawings, a method for estimating the three-dimensional in-situ stress of a deep rock mass, and the specific implementation steps are as follows:

Step 1. According to the high in-situ stress situation on site, combined with the tunnel conditions such as auxiliary tunnels in the production process, select two tunnels that cross each other, as shown in Figure 2, select an area with complete rock structure on the excavation surface of the tunnel, and observe the high stress failure of the tunnel macroscopically characteristics, determine the angular relationship between the principal stress direction and the tunnel axis, and preliminarily determine the local in-situ stress direction;

Step 2. Select planes parallel to the excavation face on the two tunnels near the intersection of the tunnels, such as the I-I plane and the II-II plane in Figure 2, and drill on the surrounding rock around these two planes. For the acoustic wave inspection holes 3, two acoustic wave inspection holes 3 are drilled each time, and the holes are respectively drilled in 8 directions evenly distributed in the circumferential direction of the tunnel, as shown in Figure 3.

Step 3. After the hole is drilled, the sound wave detection system is used to perform sound wave detection on the sound wave detection holes in 8 directions, and plot the change curve of the sound wave longitudinal wave velocity with the drilling depth, as shown in Figure 4, because the sound wave velocity when the sound wave propagates in the rock It will attenuate with the rock damage, and the damage degree of the rock is expressed by the attenuation rate of the sound wave velocity:

In the above formula, η is the attenuation rate of the acoustic longitudinal wave velocity of the rock mass, v1 is the acoustic longitudinal wave velocity _of the intact rock before excavation, v2 is the acoustic longitudinal wave velocity of the surrounding rock after excavation, and η= ₁₀ % is taken as the total damage area of the rock mass. According to different site conditions, the reasonable thresholds of the inner damage zone 5 and the outer damage zone 6 are determined according to the change degree of the acoustic wave velocity. , according to the selected threshold control curve to obtain the depth of the inner and outer damage zone of the rock mass in different directions.

Step 4. According to the depth of the damage zone in different directions obtained by the measurement, draw the distribution map of the damage zone of the surrounding rock of the tunnel on two planes respectively. The following takes an auxiliary tunnel of a hydropower station (a circular tunnel with a cross-section diameter of 8m) as an example to describe the method for determining the magnitude and direction of the in-situ stress on the cross-section. An excavation section of the auxiliary hole is selected to detect the internal and external damage areas. The auxiliary hole is located in a high ground stress area. The inspection number is shown in Figure 3.

The inner damage zone is composed of blast load damage7 and damage caused by transient in-situ stress unloading, and the outer damage zone is produced by static in-situ stress unloading. For a circular tunnel, the damage area caused by the blast load 7 is also a circle on the surrounding rock, and the damage area caused is related to the blast load on the excavation surface. According to this depth, the internal damage is divided into blast load damage 7 and instantaneous damage. In-situ stress unloading damage 8, as shown in Figure 6.

The direction and magnitude of the in-situ stress on the section are determined as follows:

First, observe the distribution of the total damage area in the inner damage area and the outer damage area to determine the direction of the large and small principal stress on the plane. , σ ₁ is the maximum principal stress, σ ₃ is the minimum principal stress.

In the direction of σ ₁ , according to the measured data, determine the depth d 1 of the inner damage zone, the depth d ₂ of the outer damage zone, and the damage depth _{d 3 of} the blast load _. The unloading damage depth d ₅ is shown in FIG. 6 .

According to the blasting design, the maximum equivalent blasting load p on the excavation section is determined. Combined with the damage law of the equivalent blasting load p on the specific rock to blasting under the condition of low in-situ stress, a reasonable damage threshold is selected to determine the explosion during blasting excavation. The damage range of the load. In the direction of σ ₁ , the damage depth on one side of the tunnel is taken as an example to determine the size of σ ₁ . The damage depth d ₃ of the blasting load is determined according to the calculation, and the depths d ₁ and d ₂ of the internal and external damage zones in different directions are obtained according to the measured data, as shown in Figures 5 and 6, where the depth of the damage zone of transient in-situ stress unloading is d ₄ = d ₁ -d ₃ , the static in-situ stress unloading damage zone depth is d ₅ =d ₂ .

Take the ratio α of the transient in-situ stress unloading damage depth to the blasting damage depth in the direction of the maximum principal stress and the ratio of static in-situ stress unloading damage depth to blasting damage depth β In the high in-situ stress area, the values of α and β are larger, and in the low in-situ stress area, the α and β values are smaller. By comparing the magnitudes of α and β, the maximum principal stress in-situ stress of the test plane is calculated.

The depth of the damage zone on both sides in the principal stress direction on the comprehensive tunnel is determined by the size of σ ₁ , and the average value of the two analyses is taken as the final maximum principal stress size.

The damage depth in the direction of the maximum principal stress and the minimum principal stress is obtained from the measured data. As shown in Fig. 5, D ₁ (D ₁ =D ₃ +D ₄ ) is the damage depth in the direction of the maximum principal stress, and D ₂ (D ₂ =D ₅ +D ₆ ) is the damage depth in the direction of the minimum principal stress, taking The larger the γ, the larger the lateral compression coefficient, the larger the ratio of σ ₁ to σ ₃ , and the more inhomogeneous the in-situ stress field. The relationship between σ ₁ and σ ₃ is determined by γ, and the minimum principal stress σ ₃ is finally obtained.

Step 5. Through step 4, the magnitude and direction of the maximum principal stress and the minimum principal stress on the current excavation section are obtained. As shown in Figure 2, on the tunnel A1 and the tunnel B2, two positive directions perpendicular to the tunnel A direction can be obtained. Stress σ _V1 , σ _H1 and a shear stress τ _VH1 , σ _V1 is the vertical in-situ stress of the current excavation face of tunnel A, σ _H1 is the horizontal in-situ stress perpendicular to the tunnel A’s axis, τ _VH1 is the excavation of tunnel A Use the same method to determine the normal stress σ _V2 , σ _H2 and shear stress τ _VH2 on the tunnel B, and take the average value σ _V of σ _V1 and σ _V2 as the measured vertical stress, assuming The shear stress on the plane where σ _H1 and σ _H2 are normal stresses is τ _H12 , thus the three-dimensional stress field of the current test area is obtained, and the stress state can be represented by a matrix:

The three-dimensional in-situ stress field obtained by synthesizing this matrix is brought into the principal stress direction determined by the macroscopic observation results, and finally the size of τ _H12 is determined.

The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications belong to the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims (4)

1. an estimation method of three-dimensional in-situ stress of deep rock mass, is characterized in that, comprises the steps: Step 1: According to the high stress situation on site, combined with the tunnel conditions such as auxiliary tunnels in the production process, select two tunnels that cross each other, select an area with a complete rock structure on the excavation surface of the tunnel, observe the high stress failure characteristics of the tunnel macroscopically, and determine the main The angular relationship between the stress direction and the tunnel axis, to preliminarily determine the local in-situ stress direction; Step 2: Select a plane parallel to the excavation face on the axes of the two tunnels near the intersection of the tunnels, and drill a number of sonic detection holes on the surrounding rock around the plane, and drill two sonic detection holes each time. Drill holes separately in multiple directions of the tunnel; Step 3: Perform sonic detection on sonic detection holes in multiple directions through the sonic detection system, draw the curve of the velocity of sonic longitudinal waves with the depth of the borehole, and determine the degree of rock damage according to the reduction rate of sonic longitudinal wave velocity, and select a reasonable reduction rate. The rate threshold divides the damage into the inner damage zone and the outer damage zone; Step 4: According to the depth of damage zone in different directions measured in Step 3, draw the distribution map of the inner and outer damage zone of the tunnel surrounding rock on two planes, and determine the section according to the distribution of the total damage zone of the inner and outer damage zone. The direction of the principal stress; the damage area is divided into blasting load damage, in-situ stress transient unloading damage and in-situ stress static unloading damage according to different causes, and the equivalent blasting load on the surrounding rock of the tunnel excavation is calculated from the blasting design, and the blasting is calculated. In the load damage area, the maximum principal stress is determined according to the depth relationship between the blasting load damage, the transient unloading damage of the in-situ stress and the static unloading damage of the in-situ stress in the direction of the maximum principal stress; size ratio, and combined with the previous steps to obtain the minimum principal stress size; Step 5: According to the magnitude and direction of the maximum principal stress and the minimum principal stress on the current excavation section obtained in step 4, convert the size principal stress into the normal stress in the vertical and horizontal directions and the shear stress on the plane, and synthesize the two openings. The three-dimensional in-situ stress state of the current area is obtained from the stress state on the plane of the excavation section and the direction information of the macro-observed in-situ stress. 2. The method for estimating three-dimensional in-situ stress of a deep rock mass as claimed in claim 1, characterized in that: in the step 3, the damage degree of the rock is represented by the decay rate of sound wave velocity: In the above _formula , η is the attenuation rate of the acoustic longitudinal wave velocity of the rock mass, v1 is the acoustic longitudinal wave velocity _of the intact rock before excavation, and v2 is the acoustic longitudinal wave velocity of the surrounding rock after excavation, which is determined by the change degree of the acoustic wave velocity according to different site conditions. Reasonable thresholds for the inner damage zone and the outer damage zone. The velocity of the longitudinal acoustic wave in the inner damage zone varies greatly with the depth, and the velocity of the longitudinal acoustic wave in the outer damage zone varies little with the depth. Depth of outer damage zone. 3. The method for estimating three-dimensional in-situ stress of a deep rock mass as claimed in claim 1, wherein the method for confirming the magnitude and direction of in-situ stress on the interrupted surface in the step 4 is as follows: First, observe the distribution of the total damage area in the inner and outer damage areas of the section to determine the direction of the large and small principal stress _on the plane. Maximum principal stress, σ ₃ is the minimum principal stress; In the direction of σ ₁ , the inner damage zone depth d ₁ , the outer damage zone depth d ₂ , the blast load damage depth d ₃ , the transient in-situ stress unloading damage depth d ₄ , and the static in-situ stress unloading damage depth d ₅ are determined according to the measured data. According to the blasting design, the maximum equivalent blasting load p on the excavation section is determined. Combined with the damage law of the equivalent blasting load p on the specific rock to blasting under the condition of low in-situ stress, a reasonable damage threshold is selected to determine the explosion during blasting excavation. The damage range of the load, in the direction of σ ₁ , takes the damage depth analysis on one side of the tunnel to determine the size of σ ₁ , and determines the damage depth d _{3 of} the blasting load according to the calculation. d ₂ , where the depth of the transient in-situ stress unloading damage zone is d ₄ =d ₁ -d ₃ , and the depth of the static in-situ stress unloading damage zone is d ₅ =d ₂ ; Take the ratio α of the transient in-situ stress unloading damage depth to the blasting damage depth in the direction of the maximum principal stress and the ratio of static in-situ stress unloading damage depth to blasting damage depth In the high in-situ stress area, the values of α and β are large, and in the low in-situ stress area, the values of α and β are small. By comparing the magnitudes of α and β, the maximum principal stress in-situ stress of the test plane is calculated; The depth of the damage zone on both sides in the principal stress direction on the comprehensive tunnel is determined by the size of σ ₁ , and the average value of the two analyses is taken as the final maximum principal stress size; The damage depth in the direction of the maximum principal stress and the minimum principal stress is obtained from the measured data, and D ₁ (D ₁ =D ₃ +D ₄ ) is taken as the damage depth in the direction of the maximum principal stress, D ₂ (D ₂ =D ₅ +D ) ₆ ) is the damage depth in the direction of the minimum principal stress, taking The larger the γ, the larger the lateral compression coefficient, the larger the ratio of σ ₁ to σ ₃ , and the more inhomogeneous the in-situ stress field. The relationship between σ ₁ and σ ₃ is determined by γ, and the minimum principal stress σ ₃ is finally obtained. 4. The method for estimating three-dimensional in-situ stress of a deep rock mass as claimed in claim 1, wherein further, in the step 5, the maximum principal stress and the minimum principal stress on the current excavation section are obtained based on the step 4. The magnitude and direction of the stress, according to step 1, on the selected intersecting tunnel A and tunnel B, two normal stresses σ _V1 , σ _H1 and a shear stress τ _VH1 , σ _V1 in the direction perpendicular to the tunnel A are obtained is the vertical in-situ stress on the current excavation face of tunnel A, σ _H1 is the horizontal in-situ stress perpendicular to the axis of tunnel A, τ _VH1 is the shear stress on the excavation face of tunnel A, and the same method is used to determine the Normal stress σ _V2 , σ _H2 and shear stress τ _VH2 , take the average value σ _V of σ _V1 and σ _V2 as the measured vertical stress, assuming that the shear stress on the plane with σ _H1 and σ _H2 as normal stress is τ _H12 , that is, the three-dimensional stress field of the current test area is obtained, and the stress state can be represented by the following matrix: Combined with this matrix, the three-dimensional in-situ stress field is obtained, and the principal stress direction determined by the macroscopic observation results is brought in, and the size of τ _H12 is finally determined.