A method for experimentally determining the loosening zone and ultimate displacement of tunnel surrounding rock

Abstract

The present invention discloses a method for determining the loosening zone and limit displacement of tunnel surrounding rock by actual measurement, comprising the following steps: when the initial support of tunnel surrounding rock is stable, pre-burying an inclinometer tube in the tunnel; determining multiple measuring points along the length direction of the inclinometer tube, and determining the initial depth value of each measuring point by observing and positioning the inclinometer tube mouth point A; during normal tunnel construction, the displacement of the measuring point is monitored once for each cycle of footage; when the face passes through the end point O of the inclinometer tube, and the displacement of point O is stable, the cumulative displacement curve of the internal displacement of the surrounding rock along the radial direction of the tunnel is determined by the final displacement of each measuring point, the loosening zone of the surrounding rock is determined according to the characteristics of the cumulative displacement curve, and the limit displacement value is determined according to the final displacement value of the inclinometer tube mouth point A. By adopting this scheme, the conventional post-diametric measurement of the internal displacement of the surrounding rock can be changed to the pre-diametric measurement of the radial displacement of the surrounding rock along the longitudinal direction of the tunnel, so that the measurement results of the loosening zone of the surrounding rock and the limit displacement value are more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly relates to a method for actually measuring and determining the loose circle and ultimate displacement of tunnel surrounding rock. Background Technique

[0002] The loose circle of surrounding rock is a relaxation and fragmentation zone generated by stress adjustment after tunnel excavation due to the tangential surface stress difference of the surrounding rock exceeding the strength of the surrounding rock, and its mechanical properties are manifested as stress reduction. The size of the loose circle of surrounding rock is mainly related to the strength of the surrounding rock and the in-situ stress. The formation of the loose circle of surrounding rock has typical time characteristics and stage characteristics. Field measurements show that the formation time of the loose circle takes at least 3 - 7 days and at most 1 - 3 months. The formation process of the loose circle is divided into two stages. The first is the "instant loose circle" formed after excavation, that is, the loose circle formed when the concentrated stress in the surrounding rock exceeds the instantaneous strength of the surrounding rock. The value of the instant loose circle is generally 60% - 90% of the value of the finally stable loose circle. This ratio is higher for hard rocks and lower for soft rocks. The second stage is after the support is completed. Along with the decrease of the long-term strength of the surrounding rock, the loose circle further expands until the value of the stable loose circle under the condition of the final long-term strength is formed.

[0003] Determining the depth of the loose circle of surrounding rock is an important basis for determining the length of the systematic bolt. Tunnel convergence measurement shows that the stable time of the development of the loose circle is consistent with the stable time of the convergence deformation. Therefore, it is feasible to determine the loose circle of surrounding rock by measuring the internal displacement of the surrounding rock, and it is also a commonly used method in the industry. Measuring the internal displacement of the surrounding rock in the tunnel is mainly to set up multi-point displacement or single-point displacement gauges by radially drilling holes, measure the relative displacement value relative to the tunnel wall within the set depth range, and determine the range of the loose circle of surrounding rock through certain rules.

[0004] Patent CN112345647A discloses a method for testing the loose circle of surrounding rock: By using the methods of on-site testing and laboratory tests, analyze the influence of tunnel construction disturbance on the surrounding rock, and quantitatively determine the size and damage degree of the loose circle of surrounding rock. Use a sonic wave instrument to measure the wave velocity of the surrounding rock on site, and characterize the wave velocity evolution law of surrounding rock with different damage degrees through indoor cyclic loading and unloading tests. The on-site wave velocity test plan adopts the single-hole test method to measure the acoustic wave transmission velocity of rock masses at different depths. Use the reduction of rock stiffness to describe rock damage, and then clarify the wave velocity and the evolution law of surrounding rock parameters under different damage degrees. Compare the rock mass wave velocity obtained from on-site testing with the wave velocity evolution curve determined by laboratory tests to provide a reference basis for the support design of the surrounding rock. The present invention has good practicability, and can not only give the range of the excavation loose circle of the surrounding rock, but also quantitatively evaluate the quality of the rock mass in the loose circle. This method belongs to an indirect method, and its accuracy depends on the representativeness of the sampled rock blocks.

[0005] CN111708077A discloses a method for testing the loosening zone of tunnel surrounding rock by acoustic wave method. CN109239779A discloses a method for testing the loosening zone of surrounding rock by determining it based on velocity sensors. CN104792965A discloses a method for testing the loosening zone of surrounding rock based on borehole energy. CN101251498 is a method for testing and evaluating the loosening zone of surrounding rock based on the principle of electromagnetic radiation. CN109357935A is a method for testing the loosening zone of a broken soft rock tunnel based on the micro-strain analysis of glass fiber bolts. Among the above methods, except for the bolt micro-strain analysis method which directly measures the displacement of the surrounding rock, the others are all indirect methods, and there is generally a problem of low accuracy in secondary interpretation. Another biggest problem is that these methods are all arranged radially in the tunnel, that is, equipment, sensors need to be installed or tested after excavation is completed, and by this time the immediate loosening zone has already formed. Therefore, it is very meaningful to adopt a relatively accurate method to directly measure the internal displacement of the surrounding rock, especially to obtain the displacement of the immediate loosening zone.

[0006] The ultimate displacement (or allowable displacement) of tunnel surrounding rock refers to the allowable value of the final cumulative displacement of the surrounding rock under the condition of ensuring that there are no obvious loosening, cracks and other harmful conditions in the surrounding rock. Invention CN109948294A discloses a method for calculating the ultimate displacement by using the finite element numerical method, which belongs to an indirect method. Since it is very difficult to determine the ultimate displacement (Article 18.6.3 of the "Technical Specification for Highway Tunnel Construction" JTGT3660-2020), the existing monitoring and measurement methods can only be carried out after excavation, and the immediate displacement of drill and blast excavation cannot be obtained. In design, the reserved deformation amount is used instead of the ultimate displacement for control. Obviously, using a larger reserved deformation amount (that is, the ultimate displacement estimated according to experience) in design will lead to engineering waste. Therefore, it is very meaningful to adopt a relatively accurate method to directly measure the ultimate displacement of the surrounding rock. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for actually measuring and determining the loosening zone and ultimate displacement of tunnel surrounding rock. By adopting this solution, the conventional post-positioned radial measurement of the internal displacement of the surrounding rock can be changed to pre-positioned longitudinal measurement of the radial displacement of the surrounding rock along the tunnel, so as to make the measurement results of the loosening zone and ultimate displacement value of the surrounding rock more accurate.

[0008] The present invention is realized through the following technical solutions:

[0009] A method for actually measuring and determining the loosening zone and ultimate displacement of tunnel surrounding rock, the method comprising the following steps:

[0010] Step 1: When the initial support of the tunnel surrounding rock is stable, embed an inclinometer tube in the tunnel; there is an external insertion angle between the inclinometer tube and the tunnel longitudinal direction, and the pipe orifice A point of the inclinometer tube extends out of the surface of the initial support;

[0011] Step 2: Determine equally spaced measuring points A, B, C... up to O in the length direction of the inclinometer tube. Determine the initial value of each measuring point by observing and positioning point A at the orifice of the inclinometer tube.

[0012] Step 3: During normal tunnel construction, each time the tunneling footage advances one cycle, use an inclinometer to monitor the displacement of the inclinometer tube once.

[0013] Step 4: After the heading face passes the end point O of the inclinometer tube and the displacement at point O is stable, calculate the final displacement of each measuring point, draw the cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radius direction, determine the loosened zone of the surrounding rock according to the characteristics of the cumulative displacement curve, and determine the ultimate displacement value according to the final displacement value of point A at the orifice of the inclined tube.

[0014] Compared with the prior art, in which they are all arranged in the tunnel radial direction, that is, equipment, sensors need to be installed or tested after the excavation is completed. By this time, even if the loosened zone has been formed, it is impossible to accurately obtain the loosened zone of the surrounding rock, and it is also impossible to obtain the instantaneous displacement during drill and blast excavation, resulting in the problem that the loosened zone of the surrounding rock and the ultimate displacement value cannot be measured more accurately. This solution provides a method for actually measuring and determining the loosened zone and ultimate displacement of tunnel surrounding rock. In the specific steps, when the initial support of the tunnel surrounding rock is stable, an inclinometer tube can be pre-buried in the tunnel. The inclinometer tube is inserted into the tunnel surrounding rock at a certain external insertion angle to facilitate the measurement of the radial displacement of the surrounding rock at different depths. The orifice point A of the inclinometer tube needs to protrude from the surface of the initial support, that is, protrude from the heading face, so as to facilitate the monitoring device to monitor the measuring points of the inclinometer tube at point A at the orifice of the inclinometer tube; equally spaced measuring points A, B, C... up to O are arranged on the inclinometer tube, and the measuring point spacing is generally taken as 0.5 m, that is, the wheelbase of the inclinometer is 0.5 m; each measuring point is used to measure the radial displacement of different surrounding rock depths. In the initial stage, first determine the initial value of each measuring point, and then during normal tunnel construction, during the tunnel construction process, each time the tunneling footage advances one cycle, intensified monitoring is carried out once. Since the inclinometer tube is inclined upward, the inclinometer cannot move by gravity. An aluminum alloy rod with a scale and can be extended is needed to push the inclinometer obliquely upward from the orifice to the bottom of the hole, and a reading is collected every 0.5 m of advancement. Then record the corresponding values. The depth value measured each time minus the depth value measured last time is the displacement value of this time; during each monitoring, it is necessary to organize and form the cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radius direction for this time; after the heading face passes the end point O of the inclinometer tube and the displacement at point O is stable, organize the above results to form the total cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radius direction, and then determine the loosened zone of the surrounding rock according to the characteristics of the cumulative displacement curve, and determine the ultimate displacement value according to the final displacement value of point A at the orifice of the inclined tube.

[0015] The above solution aims to achieve the following: By pre-burying inclinometers before excavation, the displacement of the surrounding rock during tunnel excavation can be monitored. Through multi-cycle footage excavation, the displacement along the tunnel radius of each measuring section over time can be obtained. Through equivalent projection, the radial displacement of the surrounding rock at different depths away from the tunnel wall when the tunnel face passes through can be obtained, thereby determining the depth of the loosened zone of the surrounding rock, including the depth of the immediate loosened zone, and at the same time obtaining the ultimate displacement value of the tunnel wall.

[0016] For further optimization, when determining the ultimate displacement value based on the final displacement value of point A at the inclinometer pipe orifice, the following specific steps are also included: In the cumulative displacement curve, connect the final deformation amounts of the two measuring points C and B in front of the tunnel face and closest to the tunnel face, and extend the line cb to intersect the baseline of the position of point A at a'; this is used to determine the actual ultimate displacement value.

[0017] For further optimization, when determining the loosened zone of the surrounding rock based on the characteristics of the cumulative displacement curve, the following steps are also included: According to the cumulative displacement curve when the displacement is stable, take the position of the steep change of the curve as the boundary position between the strong and weak of the loosened zone of the surrounding rock, and thus determine the loosened zone of the surrounding rock.

[0018] For further optimization, the extrapolation angle is 10° - 15°; Selecting an appropriate extrapolation angle can measure the radial displacement of the surrounding rock at different depths and is also convenient for workers to operate; If the extrapolation angle exceeds 15° or is even larger, it is very difficult for the inclinometer to move on the rail groove of the inclinometer pipe, which is not conducive to construction.

[0019] For further optimization, when the inclinometer pipe is located at the crown of the arch, the extrapolation angle takes a larger value.

[0020] For further optimization, the higher the strength of the tunnel surrounding rock, the smaller the extrapolation angle.

[0021] For further optimization, the orifice of the inclinometer pipe needs to be no less than 1 / 2 of a footage away from the tunnel face; This is used to prevent damage to the orifice during blasting construction.

[0022] For further optimization, one of the rail groove directions of the inclinometer pipe faces the tunnel radius.

[0023] For further optimization, during normal tunnel construction, when constructing the system bolts, it is necessary to avoid the inclinometer pipe by at least 0.3 m or more.

[0024] For further optimization, a total station is used to observe and position the orifice of the inclinometer pipe.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] The present invention provides a method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement. By pre-embedding an inclinometer tube before excavation, the displacement of surrounding rock during tunnel excavation can be monitored. The radial displacement of each measuring section along the tunnel over time can be obtained through multi-cycle excavation. The radial displacement of surrounding rock at different depths away from the tunnel wall when the tunnel face passes through can be obtained through equivalent projection, thereby determining the depth of the loosening zone of surrounding rock, including the immediate loosening zone depth, and obtaining the ultimate displacement value of the tunnel wall. That is, the conventional post-diametric measurement of the internal displacement of surrounding rock is changed to pre-diametric measurement of the radial displacement of surrounding rock along the longitudinal direction of the tunnel, thereby making the measurement results of the loosening zone of surrounding rock and ultimate displacement value more accurate.

[0027] This invention provides a method for determining the loosening zone and ultimate displacement of tunnel surrounding rock through direct displacement measurement. This method, which is more accurate than indirect methods such as acoustic wave testing, solves the problem of determining the ultimate displacement of surrounding rock, providing valuable insights for determining allowable deformation in support design and reducing project investment. It also captures the staged development and time history of surrounding rock radial displacement as tunnel excavation progresses, providing valuable insights for determining the timing of system anchor bolt installation and evaluating its effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0029] Figure 1 A schematic diagram of the arrangement of longitudinal measuring points of the surrounding rock along the tunnel vault according to an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the arrangement of longitudinal measuring points of the surrounding rock along the haunch of a tunnel according to an embodiment of the present invention;

[0031] Figure 3 A cumulative curve diagram of radial displacement of surrounding rock according to an embodiment of the present invention;

[0032] Figure 4 A partial schematic diagram of the cumulative curve of radial displacement of surrounding rock in an embodiment provided by the present invention.

[0033] Markings and corresponding parts names in the accompanying drawings:

[0034] 1- Inclinometer casing. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and shall not be construed as limiting the present invention.

[0036] Embodiment 1

[0037] As Figures 1 to 4 shown, Embodiment 1 of the present invention provides a method for actually measuring and determining the loosening zone and ultimate displacement of tunnel surrounding rock. The method comprises the following steps:

[0038] Step 1: When the initial support of the tunnel surrounding rock is stable, inclinometer tubes 1 are embedded in the tunnel; there is an external insertion angle between the inclinometer tubes 1 and the longitudinal direction of the tunnel, and the pipe orifice A point of the inclinometer tube 1 extends out of the surface of the initial support;

[0039] Step 2: Equally spaced measuring points A, B, C... up to O are sequentially determined in the length direction of the inclinometer tube 1. By observing and positioning the pipe orifice A point of the inclinometer tube 1, the initial value of each measuring point is determined;

[0040] Step 3: During normal tunnel construction, every time the tunneling footage advances one cycle, the displacement of the inclinometer tube is monitored once by using an inclinometer;

[0041] Step 4: After the heading face passes through the end O point of the inclinometer tube 1 and the displacement of the O point is stable, calculate the final displacement of each measuring point, draw the cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radial direction, determine the loosening zone of the surrounding rock according to the characteristics of the cumulative displacement curve, and determine the ultimate displacement value according to the final displacement value of the pipe orifice A point of the inclinometer tube 1.

[0042] Compared with the existing technology, which is all arranged in the radial direction of the tunnel, that is, the equipment and sensors can only be installed or tested after the excavation is completed. At this time, the immediate loosening circle has been formed, and the surrounding rock loosening circle cannot be accurately obtained, and the immediate displacement of the drilling and blasting excavation cannot be obtained, resulting in the problem that the surrounding rock loosening circle and the ultimate displacement value cannot be measured more accurately. This solution provides a method for actually measuring the tunnel surrounding rock loosening circle and the ultimate displacement. In the specific steps, when the initial support of the tunnel surrounding rock is stable, the inclinometer tube 1 can be pre-buried in the tunnel, wherein the inclinometer tube 1 is inserted into the tunnel surrounding rock according to a certain external insertion angle, so as to facilitate the radial measurement of the surrounding rock at different depths. To measure displacement, the mouth of the inclinometer casing 1, point A, must extend beyond the initial support surface, that is, beyond the tunnel face, to facilitate monitoring by the monitoring device at the mouth of the inclinometer casing 1, point A. Measuring points A, B, C, and so on, up to O, are evenly spaced on the inclinometer casing 1, typically spaced 0.5m apart, corresponding to a 0.5m wheelbase for the inclinometer. Each measuring point measures radial displacement at different surrounding rock depths. Initially, the initial value for each measuring point is determined, and then normal tunnel construction proceeds. During tunnel construction, intensified monitoring is conducted with each advance cycle. Due to the upward tilt of the inclinometer casing 1, the inclinometer cannot rely on gravity for movement. An extendable aluminum alloy rod with a scale is used to push the inclinometer diagonally upward from the hole mouth to the bottom of the hole, with a reading collected every 0.5m of advancement. Then record the corresponding values. The displacement value for that time is the depth value measured each time minus the depth value measured last time. During each monitoring, it is necessary to organize and form the cumulative displacement curve of the internal displacement of the surrounding rock along the radial direction of the tunnel. When the tunnel face passes through the end point O of the inclinometer tube and the displacement of point O is stable, organize the above results to form the total cumulative displacement curve of the internal displacement of the surrounding rock along the radial direction of the tunnel. Then, the surrounding rock loosening zone is determined based on the characteristics of the cumulative displacement curve, and the ultimate displacement value is determined based on the final displacement value of point A at the outlet of inclined tube 1.

[0043] The above scheme aims to achieve the following: by pre-embedding the inclinometer tube 1 before excavation, the displacement of the surrounding rock during tunnel excavation can be monitored, and the radial displacement of each measuring section along the tunnel that changes with time can be obtained through multi-cycle excavation. Through equivalent projection, the radial displacement of the surrounding rock at different depths away from the tunnel wall when the tunnel face passes can be obtained, and then the depth of the surrounding rock loosening zone, including the immediate loosening zone depth, can be determined, and the ultimate displacement value of the tunnel wall can be obtained at the same time.

[0044] See also Figure 3 and Figure 4, in the theoretical solution, the displacement value of point A at the orifice of the inclinometer tube 1 is the ultimate displacement value. However, during the actual monitoring process, since point A at the orifice of the inclinometer tube 1 is located outside the heading face, that is, it penetrates the surface of the initial support, therefore, its actual ultimate displacement value is the displacement value at the intersection of the inclinometer tube 1 and the heading face. And the calculated displacement value of point A will have a certain loss relative to the actual ultimate displacement value. To further determine the actual ultimate displacement value, in this embodiment, when determining the ultimate displacement value based on the final displacement value of point A at the orifice of the inclinometer tube 1, the following specific steps are further included: In the cumulative displacement curve, connect the final deformation amounts of the two measurement points C and B that are in front of the heading face and closest to the heading face to form a line cb and extend it to intersect the baseline of the position of measurement point A at a'; in this solution, it is necessary to calculate using the two measurement points that are in the surrounding rock and closest to the heading face. The ultimate displacement value and the displacement amounts of these two points tend to be stable, that is, point b and point c at t3 in the cumulative displacement curve. Connect point b and point c to form a straight line and extend it outward to obtain the first extension line. Then, along the direction of the deformation amount, make the second extension line of the deformation amount of orifice point A. At this time, the intersection of the first extension line and the second extension line is the ultimate displacement value of the tunnel wall. By obtaining the actual ultimate displacement value, the accuracy is further improved.

[0045] Please continue to refer to Figure 3 and Figure 4 , in this embodiment, when determining the loosening zone of the surrounding rock according to the characteristics of the cumulative displacement curve, the following steps are further included: According to the cumulative displacement curve when the displacement amount is stable, take the position of the steep change of the curve as the position of the strong and weak boundary of the loosening zone of the surrounding rock, and thus determine the loosening zone of the surrounding rock; the position with the maximum steep change intensity of the curve is the position of the strong and weak boundary of the loosening zone of the surrounding rock, and thus determine the loosening zone of the surrounding rock, which can be used for the design of the bolt length.

[0046] In this embodiment, the external insertion angle is 10° to 15°; Selecting an appropriate external insertion angle can measure the radial displacement of the surrounding rock at different depths and is also convenient for workers to operate; if the external insertion angle exceeds 15° or even larger, it is very difficult for the inclinometer to move on the track groove of the inclinometer tube 1, which is not conducive to construction.

[0047] In this embodiment, when the inclinometer tube 1 is located at the crown, the external insertion angle takes a larger value.

[0048] In this embodiment, the higher the strength of the tunnel surrounding rock, the smaller the external insertion angle.

[0049] In this embodiment, the orifice of the inclinometer tube 1 needs to be no less than 1 / 2 of a cycle advance away from the heading face; it is used to prevent damage to the orifice during blasting construction.

[0050] In this embodiment, one of the track groove directions of the inclinometer tube 1 faces the tunnel radial direction.

[0051] In this embodiment, during normal tunnel construction, when constructing the systematic bolts, it is necessary to avoid the inclinometer tube 1 by at least 0.3 m or more.

[0052] In this embodiment, a total station is used to observe and position the orifice of the inclinometer tube.

[0053] Embodiment 2

[0054] Based on Embodiment 1, Embodiment 2 further defines a specific implementation method, including the following specific steps:

[0055] Step 1: When the initial support of the surrounding rock is stable, drill holes at a certain external inclination angle, pre-bury and install the inclinometer tube 1. The orifice of the inclinometer tube 1 should be no less than 1 / 2 of the cycle footage away from the heading face to prevent damage to the orifice by blasting, and it should preferably protrude appropriately from the surface of the initial support, subject to being observable and positioned by the total station. The groove direction of the inclinometer tube 1 faces the tunnel radial direction. The external inclination angle of the inclinometer tube 1 should preferably be 10 - 15°. When the surrounding rock is good, a smaller value is taken; when it is larger, a larger value is taken. When the measurement is located at the crown, a larger value is preferably taken.

[0056] Step 2: Use a total station to observe and position the orifice of the inclinometer tube 1, and measure the initial values of each measuring section of the inclinometer.

[0057] Step 3: During normal construction, monitor according to the monitoring and measurement frequency required by the specifications. After each cycle of excavation, it is necessary to conduct additional monitoring once. It should be noted that when constructing the systematic bolts, it is necessary to avoid the inclinometer tube 1 by more than 0.3 m.

[0058] Step 4: Conduct monitoring once after each cycle of excavation, and organize and form a cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radial direction. As Figure 3 the monitoring curves obtained at the corresponding excavation progress times of t1 and t2 in the figure, and the t0 point is the initial monitoring point, and the displacement of all points is zero.

[0059] Step 5: After the heading face passes through point O and the deformation of point O tends to be stable, taking the t3 moment as an example, organize and form a cumulative displacement curve of the internal displacement of the surrounding rock along the tunnel radial direction, and determine the loose circle of the surrounding rock according to the curve characteristics; then conduct a regression analysis on the cumulative displacement curve of the ultimate displacement corresponding to the hole wall at point B, and determine it by extrapolation. That is, in the cumulative displacement curve, connect the final deformation amounts of the two measuring points located inside the surrounding rock and closest to the surface of the initial support and make the first extension line, along the direction of the deformation amount, make the second extension line of the deformation amount at the orifice point A, and find the intersection deformation amount of the first extension line and the second extension line, which is the ultimate displacement value of the hole wall.

[0060] Step 6: According to the stable cumulative displacement curve, take the position where the curve steeply changes as the position of the boundary between the strong and weak parts of the loose circle of the surrounding rock, that is, according to the cumulative displacement curve when the displacement is stable, take the position where the curve steeply changes as the position of the boundary between the strong and weak parts of the loose circle of the surrounding rock, which can be used for the design of the bolt length.

[0061] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement, characterized in that The method comprises the following steps: Step 1: When the initial support of the tunnel surrounding rock is stable, an inclinometer tube (1) is pre-buried in the tunnel; an external insertion angle is formed between the inclinometer tube (1) and the longitudinal direction of the tunnel, and the tube mouth point A of the inclinometer tube (1) extends out of the initial support surface; Step 2: determine the equally spaced measuring points A, B, C, ..., until O in the length direction of the inclinometer tube (1), and determine the initial value of each measuring point by observing and positioning the point A at the tube mouth of the inclinometer tube (1); Step 3: During normal tunnel construction, the displacement of the inclinometer is monitored once per each cycle of advancement. Step 4: After the tunnel face passes through the end point O of the inclinometer tube (1) and the displacement at point O is stable, calculate the final displacement of each measuring point, draw the cumulative displacement curve of the surrounding rock internal displacement along the tunnel radial direction, determine the surrounding rock loosening zone based on the characteristics of the cumulative displacement curve, and determine the ultimate displacement value based on the final displacement value of point A at the tube mouth of the inclinometer tube (1); When determining the surrounding rock loosening zone based on the characteristics of the cumulative displacement curve, the following steps are also included: According to the cumulative displacement curve when the displacement is stable, the position where the curve changes abruptly is taken as the strong and weak boundary position of the surrounding rock loosening zone, so as to determine the surrounding rock loosening zone; When determining the limit displacement value (a') based on the final displacement value of the pipe opening point A of the inclinometer pipe (1), the following specific steps are also included: In the cumulative displacement curve, the final deformation of the two measuring points C and B located in front of the tunnel face and closest to the tunnel face is connected by a line cb, and the extended line intersects the baseline of the measuring point A at a'.

2. The method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement according to claim 1, characterized in that, The external insertion angle is 10° to 15°.

3. A method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement according to claim 2, characterized in that When the inclinometer casing is located at the top of the arch, the external interpolation angle takes a large value.

4. A method for actually measuring and determining the loosening zone and ultimate displacement of tunnel surrounding rock according to claim 2, characterized in that The higher the strength of the tunnel surrounding rock, the smaller the external insertion angle.

5. A method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement according to claim 1, characterized in that, The nozzle of the inclinometer tube (1) needs to be at least 1 / 2 of the cycle footage away from the tunnel face.

6. A method for determining the loosening zone and ultimate displacement of tunnel surrounding rock by actual measurement according to claim 1, characterized in that One of the track grooves of the inclinometer casing (1) is oriented toward the radial direction of the tunnel.

7. A method for determining the loosening zone and ultimate displacement of tunnel surrounding rock through actual measurement according to claim 1, characterized in that, During normal construction of the tunnel, the system anchor rod construction needs to avoid the inclinometer tube (1) by at least 0.3m.

8. A method for actually measuring and determining the loosening zone and ultimate displacement of tunnel surrounding rock according to claim 1, characterized in that Use a total station to observe and locate point A at the mouth of the inclinometer tube (1).

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