Method for determining peak strength and residual strength of surrounding rock of cavern based on drilling data

Abstract

The invention provides a method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data, which comprises the following steps of: respectively arranging geological drill holes in a side wall on one side, a top arch and a front tunnel face of the underground cavern, testing longitudinal wave velocities of rock masses at different depths in the geological drill holes, and determining the thickness of the excavated loose and fractured rock masses according to the wave velocities; calculating the volumes and joint condition coefficients of the complete rock mass and the loose and fractured rock mass, and calculating the GSI value of the complete rock mass and the residual GSIr value of the loose and fractured rock mass; and a generalized Hoek-Brown failure criterion is adopted to estimate and obtain the peak strength of the complete rock mass and the participation strength parameters of the relaxed and fractured rock mass. The method can accurately and quickly estimate the peak strength of the complete rock mass and the residual strength parameter of the rock mass in the loose fracture area, has the advantages of good economy, convenience in field operation and the like, and can provide reliable basis for stability evaluation and support design of underground engineering surrounding rock, optimize a design scheme and save the construction cost.

Description

Technical Field

[0001] The invention relates to a method for determining peak strength and residual strength of surrounding rock of a cavern, and belongs to the technical field of underground engineering. Background Art

[0002] In projects such as tunnels, underground caverns, and roadways, better understanding of the strength characteristics of rock mass, including peak and residual strength, will help save costs and improve safety. However, it is a difficult task to quickly and accurately obtain rock mass mechanical parameters.

[0003] In-situ tests on rock masses, such as uniaxial compression, triaxial compression and shear tests, are the most direct methods to study rock mass strength. Although in-situ tests can obtain the peak strength and residual strength parameters of jointed rock masses, most tests have long cycles, are expensive and have difficult testing techniques.

[0004] Rock mass classification is an important indicator for evaluating rock mass quality. Establishing a connection between rock mass classification and rock mass mechanical parameters is a relatively convenient and objective method for determining rock mass mechanical parameters. However, among the current rock mass classification systems, only the GSI classification system is directly linked to rock mass parameters. When using GSI classification, the characteristics of rock mass structure and structural surface are mainly described qualitatively. This method relies on the rich experience and reasonable judgment of engineers and has a certain degree of subjectivity.

[0005] Drilling is the main means of engineering investigation. This method can reveal various information such as underground faults, joints, groundwater, etc. It is also economical and practical. How to use drilling data to find an accurate way to quantify the GSI value of rock mass in different parts, especially the residual GSI of rock mass in the excavated loose fracture area? r The values ​​can be used to accurately and quickly obtain the peak strength and residual strength parameters of the rock mass, which is particularly important for engineers to analyze and evaluate the stability of the surrounding rock of underground caverns. It can also reduce the influence of personal subjective factors. Summary of the invention

[0006] The purpose of the present invention is to provide a method for determining the peak strength and residual strength of cavern surrounding rock based on drilling data, which can accurately quantify the GSI values ​​of the rock mass in the intact surrounding rock area and the excavated relaxation and fracture area, and then accurately and quickly determine the peak strength characteristics and residual strength characteristics of the surrounding rock on site based on the Hoek-Brown criterion.

[0007] To this end, the technical solution adopted in the present invention is:

[0008] A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data, characterized by comprising the following steps:

[0009] (1) Arrange a geological borehole on one side wall, top arch and front face of the underground cavern respectively;

[0010] (2) Testing the longitudinal wave velocity of the rock mass at different depths in the geological borehole and determining the thickness of the excavated relaxed and fractured rock mass based on the wave velocity;

[0011] (3) Based on the drilling camera data and core conditions, the volume V of the complete rock mass is calculated. b and the volume V of the relaxed and fractured rock mass br , and the complete rock mass joint condition coefficient J c and the relaxation fracture rock mass joint condition coefficient J cr ;

[0012] (4) Based on The GSI value of the intact rock mass and the residual GSI of the relaxed and fractured rock mass are calculated respectively. r value;

[0013] (5) The generalized Hoek-Brown failure criterion is used to estimate the peak strength of the intact rock mass and the participating strength parameters of the relaxed and fractured rock mass, including the deformation modulus, internal friction angle, cohesion, compressive strength and tensile strength of the rock mass.

[0014] Preferably, for drilling, the drilling depth is 2 to 3 times of the hole diameter, and it is ensured that the three drill holes are in a perpendicular relationship with each other in space.

[0015] Furthermore, the core data is obtained through the drilling, and the core with good integrity is collected to conduct indoor uniaxial compression test to obtain the uniaxial saturated compressive strength σ of the rock block. c ;

[0016] Furthermore, to determine the thickness of the excavated relaxed and fractured rock mass, first determine the average longitudinal wave velocity v0 of the deep intact rock mass, and then determine the thickness of the excavated relaxed and fractured rock mass in each borehole based on the principle that the longitudinal wave velocity of the excavated relaxed and fractured rock mass is lower than that of the intact rock mass.

[0017] Furthermore, a panoramic camera for drilling holes is used to digitally image the borehole wall, and the planar expansion images of the top arch, side wall and front face borehole are obtained respectively; the planar expansion images of the boreholes are analyzed to obtain the spatial occurrence of the dominant structural planes in the images; according to the determined excavation relaxation fracture zone and intact rock mass zone, a group of dominant structural planes with the smallest spacing corresponding to the intact rock mass zone in the three boreholes are statistically obtained respectively, and the corresponding spacings are s1, s2, and s3 respectively; a group of dominant structural planes with the smallest spacing corresponding to the excavation relaxation fracture zone in the three boreholes are statistically obtained respectively, and the corresponding spacings are s 1r 、s 2r 、s 3r ;

[0018] According to V b =s1s2s3 to calculate the initial volume V of the rock mass in the complete rock mass area b , according to V br =s 1r s 2r s 3r The residual rock volume V in the excavated relaxation and fragmentation zone is calculated br .

[0019] Furthermore, the deformation modulus of the intact rock mass E m , Deformation modulus of relaxed fractured rock mass E mr The calculation method is:

[0020] When σ c ≤100MPa:

[0021]

[0022] When σ c >100MPa:

[0023]

[0024] Where D is the excavation disturbance parameter. r The influence of excavation damage has been considered in the value selection process, so D=0 is taken when this method is used for parameter calculation.

[0025] Peak compressive strength of intact rock mass σ cm , Residual compressive strength of relaxed fractured rock mass The calculation method is:

[0026]

[0027] Peak internal friction angle of intact rock mass Residual internal friction angle of relaxed fractured rock mass The calculation method is:

[0028]

[0029] Peak cohesion of intact rock mass c, residual cohesion of relaxed and fractured rock mass c r The calculation method is:

[0030]

[0031] Where: 3n =σ 3max / σ c ,

[0032] For tunnel projects:

[0033]

[0034]

[0035] Peak tensile strength of intact rock mass σ t , Residual tensile strength of relaxed fractured rock mass The calculation method is:

[0036]

[0037] in,

[0038]

[0039]

[0040]

[0041] m i is a constant related to lithology.

[0042] The beneficial effects of the present invention are as follows: the present invention provides a method for quickly determining the peak strength and residual strength of cavern surrounding rock based on drilling data, uses the drilling acoustic wave test results to obtain the thickness of the excavated relaxed and fractured rock mass, combines the core and the drilling camera images, and respectively calculates the GSI values ​​of the intact rock mass and the relaxed and fractured rock mass, and then the generalized Hoek-Brown failure criterion can be used to accurately and quickly estimate the peak strength of the intact rock mass and the residual strength parameters of the rock mass in the relaxed and fractured zone. The method has the advantages of good economy and convenient on-site operation, and can provide a reliable basis for the evaluation of the stability of the surrounding rock and the support design of underground projects, optimize the design scheme, and save the project cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings required for use in the embodiments are briefly introduced below.

[0044] Figure 1 It is a flow chart of the method for determining the peak value and residual strength parameters of the surrounding rock of a cavern according to the present invention;

[0045] Figure 2 A schematic diagram of geological drilling arrangement in an embodiment of the present invention;

[0046] Figure 3 Schematic diagram of drilling sonic test results in an embodiment of the present invention

[0047] Figure 4 Schematic diagram of the distance between the advantageous structural surfaces based on drilling photography in an embodiment of the present invention DETAILED DESCRIPTION

[0048] Referring to the accompanying drawings, the present invention provides a method for determining the peak strength and residual strength of surrounding rock of a cavern based on drilling data, and the specific implementation steps are as follows:

[0049] Step 1: Arrange a geological borehole on the side wall, top arch and front face of the underground cavern, numbered 2, 1, and 3 respectively. The drilling depth is required to be 2 to 3 times the hole diameter. At the same time, ensure that the three boreholes are in a perpendicular relationship in space, drill and coring, and obtain core data; collect cores with good integrity, conduct indoor uniaxial compression tests, and obtain the uniaxial saturated compressive strength σ of the rock block. c ;

[0050] Step 2: Clean the geological borehole and test the rock mass longitudinal wave velocity at different depths in the borehole;

[0051] Step 3: Analyze the longitudinal wave velocity data of the rock mass, and determine the excavation relaxation and fracture zone and the intact rock mass zone according to the longitudinal wave velocity. First, determine the average longitudinal wave velocity v0 of the deep intact rock mass. According to the principle that the longitudinal wave velocity of the excavated relaxation and fractured rock mass is lower than that of the intact rock mass, determine the thickness of the relaxation and fractured rock mass excavated in each borehole. The typical acoustic test results and the method for determining the thickness of the relaxation and fractured rock mass are as follows: Figure 3 As shown;

[0052] Step 4: Use a drilling panoramic camera to digitally image the borehole wall, and obtain the planar expansion images of the top arch, side wall and front face borehole respectively;

[0053] Step 5: Analyze the planar unfolded image of the borehole to obtain the spatial occurrence of the dominant structural surface in the image. According to the excavation relaxation fracture zone and the intact rock mass zone determined in step 3, respectively obtain a group of dominant structural surfaces with the smallest spacing corresponding to the intact rock mass zone in the three boreholes, which are numbered as the first joint (top arch borehole), the second joint (side wall borehole), and the third joint (face borehole), and their corresponding spacings are s1, s2, and s3, respectively; similarly, respectively obtain a group of dominant structural surfaces with the smallest spacing corresponding to the excavation relaxation fracture zone in the three boreholes, which are numbered as the fourth joint (top arch borehole), the fifth joint (side wall borehole), and the sixth joint (face borehole), and their corresponding spacings are s1, s2, and s3, respectively. 1r 、s 2r 、s 3r The minimum spacing of a certain drilling advantage structure surface is defined as follows: Figure 4 As shown;

[0054] Step 6: According to V b =s1s2s3 to calculate the initial volume V of the rock mass in the complete rock mass area b , and according to V br =s 1r s2r s 3r The residual rock volume V in the excavated relaxation and fragmentation zone is calculated br ;

[0055] Step 7: Based on the plane unfolded image of the borehole described in step 4, the macroscopic volatility scores J of the joints in the intact rock mass area and the excavated relaxed and fragmented area are obtained according to Table 1. w , J wr .

[0056] Table 1 Joint macroscopic volatility J w score

[0057] Volatility Fluctuation / % score Tight locking - 3.0 Step-shaped >3.0 2.5 Strong ups and downs 0.3～3.0 2.0 Slight ups and downs <0.3 1.5 Straight - 1.0

[0058] Step 8: According to the state of the dominant structural surface revealed by the drill core in step 1, the joint micro-smoothness scores J of the intact rock mass area and the excavated relaxed and fragmented area are obtained according to Table 2. s , J sr .

[0059] Table 2 Joint microsmoothness J s score

[0060]

[0061] Step 9: According to the filling state of the dominant structural surface revealed by the drill core in step 1, the structural surface alteration influence coefficient score J of the intact rock mass area and the excavated relaxation and fragmentation area is obtained according to Table 3. A , J Ar .

[0062] Table 3 Structural surface alteration influence coefficient J A score

[0063]

[0064]

[0065] Step 10: According to J c =J w J s / J A The joint condition coefficient J of the complete rock mass area is calculated c , according to J cr =J wr J sr / J Ar The residual joint condition coefficient J of the excavated relaxation and fragmentation zone is calculated cr .

[0066] Step 11: According to The initial volume V of the rock block in the complete rock mass area band joint condition coefficient J c Substitute it into the GSI of the intact rock mass and calculate the residual rock volume V in the relaxed and fractured zone. br and residual joint condition coefficient J cr Substituting into the above equation, the residual GSI of the relaxed fractured rock mass is calculated as r ;

[0067] Step 12: Use the intact rock mass GSI and the relaxed fractured rock mass residual GSI obtained in step 11 r The peak strength and residual strength of the surrounding rock are calculated respectively, including the deformation modulus, internal friction angle, cohesion, compressive strength and tensile strength of the rock mass:

[0068] In step 12, the deformation modulus of the intact rock mass E m , Deformation modulus of relaxed fractured rock mass E mr The calculation method is:

[0069] When σ c ≤100MPa:

[0070]

[0071] When σ c >100MPa:

[0072]

[0073] Where D is the excavation disturbance parameter. r The influence of excavation damage has been considered in the value selection process, so D=0 is taken when this method is used for parameter calculation.

[0074] The peak compressive strength of the intact rock mass in step 12 is σ cm , Residual compressive strength of relaxed fractured rock mass The calculation method is:

[0075]

[0076] Peak internal friction angle of the intact rock mass in step 12 Residual internal friction angle of relaxed fractured rock mass The calculation method is:

[0077]

[0078] The peak cohesion c of the intact rock mass and the residual cohesion c of the relaxed and fractured rock mass in step 12 r The calculation method is:

[0079]

[0080] Where:3n =σ 3max / σ c ,

[0081] For tunnel projects:

[0082]

[0083]

[0084] The peak tensile strength σ of the intact rock mass in step 12 t , Residual tensile strength of relaxed fractured rock mass The calculation method is:

[0085]

[0086] in,

[0087]

[0088]

[0089]

[0090] m i is a constant related to lithology.

[0091] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the methods and core ideas of the present invention; this part of the content should not be understood as limiting the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for determining the peak strength and residual strength of surrounding rock of a cavern based on drilling data, characterized in that The following steps are involved: (1) Arrange a geological borehole on one side wall, top arch and front face of the underground cavern respectively; (2) Testing the longitudinal wave velocity of the rock mass at different depths in the geological borehole and determining the thickness of the excavated relaxed and fractured rock mass based on the wave velocity; (3) Based on the drilling camera data and core conditions, the volume V of the complete rock mass is calculated. b and the volume V of the relaxed and fractured rock mass br , and the complete rock mass joint condition coefficient J c and the relaxation fracture rock mass joint condition coefficient J cr ; (4) Based on The GSI value of the intact rock mass and the residual GSI of the relaxed and fractured rock mass are calculated respectively. r value; (5) The generalized Hoek-Brown failure criterion is used to estimate the peak strength of the intact rock mass and the participating strength parameters of the relaxed and fractured rock mass, including the deformation modulus, internal friction angle, cohesion, compressive strength and tensile strength of the rock mass.

2. A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data as claimed in claim 1, characterized in that For drilling, the drilling depth is 2 to 3 times the hole diameter, and at the same time, ensure that the three holes are in a perpendicular relationship to each other in space.

3. A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data as claimed in claim 1, characterized in that The core data is obtained by drilling the core, and the core with good integrity is collected to conduct indoor uniaxial compression test to obtain the uniaxial saturated compressive strength σ of the rock block. c .

4. A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data as claimed in claim 1, characterized in that To determine the thickness of the excavated relaxed and fractured rock mass, first determine the average longitudinal wave velocity v0 of the deep intact rock mass. Based on the principle that the longitudinal wave velocity of the excavated relaxed and fractured rock mass is lower than that of the intact rock mass, determine the thickness of the excavated relaxed and fractured rock mass in each borehole.

5. A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data as claimed in claim 1, characterized in that A panoramic camera for drilling holes is used to digitally image the borehole wall, and the planar expansion images of the top arch, side wall and front face borehole are obtained respectively; the planar expansion images of the boreholes are analyzed to obtain the spatial occurrence of the dominant structural planes in the images; according to the determined excavation relaxation fracture zone and intact rock mass zone, a group of dominant structural planes with the smallest spacing corresponding to the intact rock mass zone in the three boreholes are statistically obtained, and the corresponding spacings are s1, s2, and s3 respectively; a group of dominant structural planes with the smallest spacing corresponding to the excavation relaxation fracture zone in the three boreholes are statistically obtained, and the corresponding spacings are s1, s2, and s3 respectively. 1r 、s 2r 、s 3r ; According to V b =s1s2s3 to calculate the initial volume V of the rock mass in the complete rock mass area b , according to V br =s 1r s 2r s 3r The residual rock volume V in the excavated relaxation and fragmentation zone is calculated br .

6. A method for determining peak strength and residual strength of surrounding rock of a cavern based on drilling data as claimed in claim 1, characterized in that Deformation modulus of intact rock mass E m , Deformation modulus of relaxed fractured rock mass E mr The calculation method is: When σ c ≤100MPa: When σ c >100MPa: Where D is the excavation disturbance parameter. r The influence of excavation damage has been considered in the value selection process, so D=0 is taken when this method is used for parameter calculation. Peak compressive strength of intact rock mass σ cm , Residual compressive strength of relaxed fractured rock mass The calculation method is: Peak internal friction angle of intact rock mass Residual internal friction angle of relaxed fractured rock mass The calculation method is: Peak cohesion of intact rock mass c, residual cohesion of relaxed and fractured rock mass c r The calculation method is: where: σ 3n = σ 3max / σ c , For tunnel projects: Peak tensile strength of intact rock mass σ t , Residual tensile strength of relaxed fractured rock mass The calculation method is: in, m i is a constant related to lithology.

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