Roadway support precision intervention method

Abstract

The application discloses a roadway supporting precise intervention method, which utilizes a roadway surrounding rock fracture zone and stress testing technology to monitor the fracture zone and stress state of the roadway surrounding rock, judges the roadway surrounding rock stress peak position and the fracture zone boundary position according to the monitoring data, determines the surrounding rock fracture zone range index R f , the surrounding rock damage zone range index R d , the surrounding rock stress rising zone range index R u , the surrounding rock stress falling zone range index R l , and thus determines the roadway supporting parameters, and determines the intervention time of the supporting measures according to the roadway surrounding rock fracture zone development speed index t f and the stress field development speed index t s , accurately determines the supporting intervention scheme according to the roadway surrounding rock stability state, fully plays the supporting efficiency of the supporting measures, significantly improves the supporting efficiency, reduces the supporting cost, realizes the coupling effect and collaborative control of the supporting structure and the surrounding rock, and guarantees the long-term stability of the deep roadway.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of well and roadway engineering and mining engineering, and particularly relates to a roadway supporting precise intervention method. BACKGROUND

[0002] Due to the prominent contradiction between high ground stress and low strength of surrounding rock, large deformation instability disasters are prone to occur after deep roadway excavation in coal mines. Most of the existing roadway supporting designs adopt engineering analogy method or rely on field experience, and it is difficult to scientifically design the roadway supporting according to different engineering geological conditions or spatial position characteristics of the roadway, resulting in that the roadway supporting structure cannot guarantee the long-term stability of the roadway. To realize the long-term stability of the deep roadway, it is the key to master the evolution law of the roadway surrounding rock structure and stress field, which is the prerequisite for realizing the collaborative control and accurate implementation of the roadway supporting structure. Therefore, a supporting precise intervention or implementation method for the deep roadway is needed. SUMMARY

[0003] In order to solve the above problems, the embodiment of the present application provides a roadway supporting precise intervention method to fully exert the supporting efficiency of the supporting structure and guarantee the long-term stability of the roadway. The technical scheme is as follows:

[0004] The present application provides a roadway supporting precise intervention method, which comprises the following steps: S1 roadway surrounding rock drilling, arranging a plurality of fracture zone test drillings and a plurality of stress field test drillings in the roadway surrounding rock; S2 roadway surrounding rock fracture zone test and stress field test: adopting surrounding rock structure refinement monitoring technology to carry out test in the fracture zone test drilling, obtaining surrounding rock fracture zone range index R f , surrounding rock damage zone range index R d and surrounding rock fracture zone development speed index t f ; adopting rheological stress recovery method in-situ stress test technology to carry out test in the stress field test drilling, obtaining surrounding rock stress rising zone range index R u , surrounding rock stress falling zone range index R l and stress field development speed index t s ; S3 supporting parameter determination: determining the shallow hole grouting depth according to the surrounding rock fracture zone range index R f , determining the deep hole grouting depth according to the surrounding rock damage zone range index R d , determining the anchor rod length according to the surrounding rock stress rising zone range index R u , and determining the anchor cable length according to the surrounding rock stress falling zone range index R l ; S4 supporting time determination: determining the shallow hole grouting and anchor rod implementation time according to the surrounding rock fracture zone development speed index t f , and determining the deep hole grouting and anchor cable implementation time according to the stress field development speed index t s .

[0005] For example, in the roadway support precise intervention method provided by an embodiment, in S2, a homogenous weak reflection fiber grating strain cable sensor is arranged in the fracture zone test borehole to carry out the roadway surrounding rock fracture zone test, and a plurality of fiber grating six-direction pressure sensors are arranged in the stress field test borehole to carry out the roadway surrounding rock stress field test.

[0006] For example, in the roadway support precise intervention method provided by an embodiment, in S2, the position of the anchoring point in the deepest homogenous weak reflection fiber grating strain cable with a strain value of 10000±2000με is taken as the fracture zone boundary of the roadway surrounding rock, and the length from the deepest fracture zone boundary of each fracture zone test borehole to the roadway surface is taken as R f ; the position of the anchoring point in the deepest homogenous weak reflection fiber grating strain cable with a strain value of 2000±500με is taken as the damage zone boundary of the roadway surrounding rock, and the length from the deepest damage zone boundary of each fracture zone test borehole to the roadway surface is taken as R d ; the time required for the fracture zone boundary to reach 0.5 times the roadway width is taken as t f ; the position of the roadway surface to the stress peak position of the surrounding rock is taken as the stress rising zone of the roadway surrounding rock, and the deepest position of the stress peak point of each test line is taken as R u ; the position of the stress peak position of the surrounding rock to the in-situ stress of the deep surrounding rock is taken as the stress falling zone of the roadway surrounding rock, and the deepest position of the disturbance stress influence boundary of each test line is taken as R l ; the time for the peak stress position to develop to 1 times the roadway width is taken as t s .

[0007] For example, in the roadway support precise intervention method provided by an embodiment, the spacing between the anchoring points of the homogenous weak reflection fiber grating strain cable arranged in the fracture zone test borehole is 1m, and the spacing between the fiber grating six-direction pressure sensors arranged in the stress field test borehole is 1m.

[0008] For example, in the roadway support precise intervention method provided by an embodiment, after the homogenous weak reflection fiber grating strain cable sensor is buried in the fracture zone test borehole and the fiber grating six-direction pressure sensor is buried in the stress field test borehole, the boreholes are grouted respectively, so that the homogenous weak reflection fiber grating strain cable sensor and the fiber grating six-direction pressure sensor are deformed cooperatively with the roadway surrounding rock and sense the stress of the surrounding rock.

[0009] For example, in the roadway support precise intervention method provided by an embodiment, in S3, the shallow hole grouting depth is R f ±0.2m~3m, the deep hole grouting depth is 6m~R d ±0.2m, the length of the anchor rod is R u ±0.2m~2.8m, and the length of the anchor cable is R l ±0.2m.

[0010] For example, in the roadway support precise intervention method provided by one embodiment, the length of the anchor rod is not more than 2.8 m, and the maximum depth of the shallow hole grouting is not more than 2 m.

[0011] For example, in the roadway support precise intervention method provided by one embodiment, in the S4, according to the development speed index t f The implementation time of the shallow hole grouting and the anchor rod is determined as follows: t f ± 2 days after the roadway is excavated; and according to the stress field development speed index t s The implementation time of the deep hole grouting and the anchor cable is determined as follows: t s ± 3 days after the roadway is excavated.

[0012] For example, in the roadway support precise intervention method provided by one embodiment, in the S1, the fracture zone test boreholes and the stress field test boreholes each include five, which are arranged at the left side, the right side, the left arch shoulder, the right arch shoulder and the top of the roadway respectively, and are perpendicular to the surface of the surrounding rock, and the fracture zone test boreholes and the stress field test boreholes are located at the same section and have a distance of 0.5-1.0 m.

[0013] For example, in the roadway support precise intervention method provided by one embodiment, the fracture zone test borehole has a diameter of 60-90 mm and a depth of 3 times of the width of the roadway; and the stress field test borehole has a diameter of 100-130 mm and a depth of 3 times of the width of the roadway.

[0014] The roadway support precise intervention method provided by some embodiments has the beneficial effects that the fracture zone and the stress state of the surrounding rock of the roadway are monitored through the surrounding rock fracture zone and the stress test means, the position of the stress peak value and the position of the boundary of the fracture zone of the surrounding rock of the roadway are determined according to the monitoring data, the surrounding rock fracture zone range index R f , the surrounding rock damage zone range index R d , the surrounding rock stress rising zone range index R u , and the surrounding rock stress falling zone range index R l are determined, the support parameters are determined, the support intervention time of the support measures is determined according to the surrounding rock fracture zone development speed index t f and the stress field development speed index t s , the support intervention scheme is precisely determined according to the state of the surrounding rock of the roadway, the support efficiency of the support measures is fully exerted, the support efficiency is significantly improved, the support cost is reduced, and the long-term stability of the surrounding rock of the roadway is maintained. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present specification or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0016] Figure 1 is a roadway support precise intervention method flowchart of the present application;

[0017] Figure 2 is a roadway surrounding rock drilling layout of the present application;

[0018] Figure 3 is a fracture zone test drilling internal strain sensor layout and surrounding rock strain curve schematic diagram of the present application;

[0019] Figure 4 is a stress field test drilling internal stress sensor layout and surrounding rock stress curve schematic diagram of the present application;

[0020] Figure 5 is a schematic diagram of the present application for determining the length of the anchor rod and the length of the anchor cable;

[0021] Figure 6 is a schematic diagram of the present application for determining the range of deep and shallow hole grouting;

[0022] Figure 7 is a timing diagram of the present application for precise intervention of roadway support. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0024] Unless otherwise defined, technical terms or scientific terms used in the present disclosure shall have the meanings as generally understood by one of ordinary skill in the art to which the present disclosure belongs. The terms "first", "second", and similar terms are used herein to distinguish one element from another, and are not necessarily used in a sequence or to denote importance or quantity. The terms "comprise", "comprising", "include", "including" and the like are used herein to mean including but not limited to. The terms "connected", "coupled", and the like are used herein to mean either a direct connection or an indirect connection through one or more intervening elements, unless otherwise specified. The terms "above", "below", "upper", "lower", and the like are used herein to denote relative positions for the purpose of illustration only, and can be reversed when the positions of the described objects are changed.

[0025] The present application provides a roadway support precise intervention method, as shown in the following steps: Figure 1 The present application provides a roadway support precise intervention method, as shown in the following steps:

[0026] S1, drilling in the roadway surrounding rock, arranging a plurality of fracture zone test drillings and a plurality of stress field test drillings in the roadway surrounding rock;

[0027] S2, carrying out the roadway surrounding rock fracture zone test and stress field test: using the surrounding rock structure refinement monitoring technology to carry out the test in the fracture zone test drilling, obtaining the surrounding rock fracture zone range index R f , the surrounding rock damage zone range index R d , and the surrounding rock fracture zone development speed index t f ; using the rheological stress recovery method of in-situ stress test technology to carry out the test in the stress field test drilling, obtaining the surrounding rock stress rising zone range index R u , the surrounding rock stress falling zone range index R l , and the stress field development speed index t s ;

[0028] S3, support parameter determination: determining the shallow hole grouting depth according to the surrounding rock fracture zone range index R f , determining the deep hole grouting depth according to the surrounding rock damage zone range index R d , determining the anchor rod length according to the surrounding rock stress rising zone range index R u , and determining the anchor cable length according to the surrounding rock stress falling zone range index R l ;

[0029] S4, support timing determination: determining the shallow hole grouting and anchor rod implementation time according to the surrounding rock fracture zone development speed index t f , and determining the deep hole grouting and anchor cable implementation time according to the stress field development speed index t s .

[0030] According to the above embodiment, the rupture zone of the roadway surrounding rock and the stress test technology are used to monitor the rupture zone and stress state of the roadway surrounding rock, the stress peak position and the rupture zone boundary position of the roadway surrounding rock are determined according to the monitoring data, the rupture zone range index R f , the surrounding rock damage zone range index R d , the surrounding rock stress rising zone range index R u , the surrounding rock stress falling zone range index R l , so as to determine the roadway supporting parameters, and the intervention time of the supporting measures is determined according to the roadway surrounding rock rupture zone development speed index t f and the stress field development speed index t s . According to the stability state of the roadway surrounding rock, the supporting intervention scheme is accurately determined, the supporting efficiency of the supporting measures is fully played, the supporting efficiency is significantly improved, the supporting cost is reduced, and the long-term stability of the roadway surrounding rock is maintained.

[0031] The roadway supporting precise intervention method provided by the present application can accurately master the stability evolution law of the deep roadway surrounding rock through the monitoring of the rupture zone and stress field evolution process of the roadway surrounding rock, and scientifically determine the supporting parameters and supporting time based on the same, so as to fully play the supporting effect of the supporting structure, realize the coupling and collaborative control of the supporting structure and the surrounding rock, and ensure the long-term stability of the deep roadway.

[0032] For example, in the roadway supporting precise intervention method provided by one embodiment, as shown in S2 in Figures 3-4 , a homologous weak reflection type fiber grating strain cable sensor is arranged in the rupture zone test drill hole to carry out the roadway surrounding rock rupture zone test, and a plurality of fiber grating six-direction pressure sensors are arranged in the stress field test drill hole to carry out the roadway surrounding rock stress field test.

[0033] For example, in the roadway supporting precise intervention method provided by one embodiment, in S2, the position of the anchoring point in the deepest homologous weak reflection type fiber grating strain cable with a strain value of 10000±2000με is taken as the rupture zone boundary of the roadway surrounding rock, and the length from the deepest rupture zone boundary of each rupture zone test drill hole to the surface of the roadway is taken as R f ; the position of the anchoring point in the deepest homologous weak reflection type fiber grating strain cable with a strain value of 2000±500με is taken as the damage zone boundary of the roadway surrounding rock, and the length from the deepest damage zone boundary of each rupture zone test drill hole to the surface of the roadway is taken as R d ; the time required for the rupture zone boundary to reach 0.5 times the roadway width is taken as t f ; the surface of the roadway to the stress peak position of the surrounding rock is taken as the stress rising zone of the roadway surrounding rock, and the deepest position of the stress peak point of each test line is taken as R uThe stress reduction zone of the roadway surrounding rock is defined as the area from the peak stress location of the surrounding rock to the original stress location of the deep surrounding rock. The deepest point of the boundary of the excavation disturbance stress influence of each survey line is defined as R. l The time it takes for the peak stress location to develop to one lane width is taken as t. s .

[0034] For example, in a precise intervention method for roadway support provided in one embodiment, such as Figures 3-4 As shown, the spacing between each anchor point in the identical weak reflection fiber optic strain cable arranged in the test borehole of the fracture zone is 1m, and the spacing between the six-axis fiber optic pressure sensors arranged in the test borehole of the stress field is 1m.

[0035] For example, in a precise intervention method for roadway support provided in one embodiment, after embedding an identical weak reflection fiber optic strain cable sensor in the test borehole of the fracture zone and an optical fiber optic six-axis pressure sensor in the stress field test borehole, the boreholes are grouted with micro-expansion grouting material, so that the identical weak reflection fiber optic strain cable sensor and the optical fiber optic six-axis pressure sensor deform in tandem with the surrounding rock of the roadway and sense the stress of the surrounding rock.

[0036] For example, in a precise intervention method for roadway support provided in one embodiment, such as Figures 5-6 As shown, in S3, the shallow hole grouting depth is: R f ±0.2m~3m, deep hole grouting depth is: 6m~R d ±0.2m, anchor bolt length: R u ±0.2m~2.8m, anchor cable length: R l ±0.2m.

[0037] For example, in one embodiment of the precise intervention method for roadway support, the length of the anchor bolt does not exceed 2.8m, and the maximum depth of shallow hole grouting does not exceed 2m.

[0038] For example, in a precise intervention method for roadway support provided in one embodiment, such as Figure 7 As shown, Figure 7 In S4, t0 represents the tunnel excavation time, and the time is determined based on the development rate index t of the surrounding rock fracture zone. f The implementation time for shallow hole grouting and anchor bolts is determined to be: t after tunnel excavation. f ±2 days; based on the stress field development rate index t s The implementation time for deep hole grouting and anchor cables is determined to be: t after tunnel excavation. s ±3 days.

[0039] For example, in a precise intervention method for roadway support provided in one embodiment, in step S1, as follows: Figure 2As shown, the rupture zone test boreholes and the stress field test boreholes each include five, arranged at the left and right sides of the roadway, left and right arch shoulders, and the top, and perpendicular to the surrounding rock surface, and the rupture zone test boreholes and the stress field test boreholes are located at the same section and have a distance of 0.5-1.0 m, facilitating field construction, Figure 2 KS-1-KS-5 are roadway surrounding rock strain test boreholes, i.e. rupture zone test boreholes; and KP-1-KP-5 are roadway surrounding rock stress test boreholes, i.e. stress field test boreholes.

[0040] For example, in the roadway support precise intervention method provided in one embodiment, the rupture zone test borehole has a diameter of 60-90 mm and a depth of 3 times the roadway width; and the stress field test borehole has a diameter of 100-130 mm and a depth of 3 times the roadway width.

[0041] Specifically, the rupture zone test borehole has a diameter of 70 mm, the stress field test borehole has a diameter of 110 mm, and the rupture zone test borehole and the stress field test borehole at the same section have a distance of 0.5 m.

[0042] In actual application, the roadway support precise intervention method of the present application is used to measure that the rupture zone range index R f of a certain roadway is 3 m, the damage zone range index R d of the surrounding rock is 7 m, the rupture zone development speed index t f is 5 days, the stress rise zone range index R u of the surrounding rock is 3 m, the stress drop zone range index R l of the surrounding rock is 7 m, and the stress field development speed index t s is 15 days, the length of the anchor rod is determined to be 2 m, the length of the anchor cable is determined to be 7 m, the stress drop zone is reached to ensure that the anchor cable fully plays a supporting and reinforcing role, the depth of the shallow hole grouting is usually not more than 3 m, the high-performance slurry is filled into the surrounding rock cracks to meet the requirement of improving the mechanical properties of the surrounding rock in the rupture zone, the depth of the shallow hole grouting is determined to be 0-3 m according to the rupture zone range index R f of the surrounding rock. The deep hole grouting mainly targets the deep surrounding rock (i.e. the damage zone of the surrounding rock), and the mechanical properties of the deep surrounding rock are strengthened through grouting to realize the transfer of the surrounding rock stress to the deep surrounding rock in cooperation with the anchor cable structure. In order to cooperate with the shallow hole grouting, the depth of the deep hole grouting should be greater than 6 m. The depth of the deep hole grouting is finally determined to be 6-7 m according to the damage zone range index R d of the surrounding rock. Accurate judgment of the rupture zone of the surrounding rock and the stress distribution zone of the roadway can accurately guide the grouting depth, avoid damage to the surrounding rock structure caused by blind drilling on the basis of fully exerting the grouting support efficiency, and the stress field development speed index t sIt is determined to apply deep hole grouting and anchor cable support 15 days after the roadway is excavated. The development speed index t of the surrounding rock fracture zone can be fully mastered by monitoring the stress and strain state of the surrounding rock f and the stress field development speed index t s The intervention time of the support structure is determined by the speed index to fully exert the support efficiency of the support structure. The specific support process is to perform anchor rod support and shallow hole grouting according to the fracture zone development speed index t f (about 5 days) after the roadway surrounding rock is excavated, to ensure short-term stability of the roadway; and to perform anchor cable support and deep hole grouting according to the stress field development speed index t s (about 15 days), to realize stress transfer of the roadway surrounding rock to deep surrounding rock, realize collaborative bearing, and ensure long-term stability of the roadway.

[0043] The precise intervention method of the roadway support of the present application is suitable for precise support of a large deformation roadway. The support scheme is scientifically formulated and the support time is determined by monitoring the state of the roadway surrounding rock. Compared with the traditional support scheme, the support intervention scheme is accurately determined according to the stability state of the roadway surrounding rock in the present application, the support efficiency of the support measures can be fully exerted, the support efficiency is significantly improved, the support cost is reduced, and the long-term stability of the roadway surrounding rock is maintained.

[0044] Although the embodiments of the present application have been disclosed as above, it is not limited to the use listed in the specification and embodiments, and can be fully applied to various fields suitable for the present application. Additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein.

Claims

1. A method for precise intervention in roadway support, characterized in that, Includes the following steps: S1 tunnel surrounding rock drilling: Several fracture zone test boreholes and several stress field test boreholes are arranged in the surrounding rock of the tunnel. Specifically, there are 5 fracture zone test boreholes and 5 stress field test boreholes, respectively arranged on the left side, right side, left shoulder, right shoulder and top of the tunnel, and perpendicular to the surrounding rock surface. The fracture zone test boreholes and the stress field test boreholes are located on the same cross section and the distance between them is 0.5~1.0 m. The diameter of the fracture zone test borehole is 60~90 mm and the depth is 3 times the tunnel width; the diameter of the stress field test borehole is 100~130 mm and the depth is 3 times the tunnel width. S2 conducted tests on the fractured zone and stress field of the surrounding rock in the tunnel: Refined monitoring technology for the surrounding rock structure was used to conduct tests within the fractured zone test borehole to obtain the R value representing the extent of the fractured zone. f , Range index of surrounding rock damage zone R d and the development rate index t of the surrounding rock fracture zone f The rheological stress recovery method was used to conduct in-situ stress testing in a stress field test borehole to obtain the range index R of the stress rise zone in the surrounding rock. u , Range index R of the surrounding rock stress reduction zone l and the stress field development rate index t s Specifically, a uniformly weakly reflective fiber optic strain gauge sensor is deployed in the test borehole for the fracture zone to conduct tests on the surrounding rock fracture zone of the roadway. Several fiber optic six-axis pressure sensors are deployed in the stress field test borehole to conduct stress field tests on the surrounding rock. The anchor point of the uniformly weakly reflective fiber optic strain gauge sensor at the deepest point, where the strain value reaches 10000±2000 με, is taken as the boundary of the fracture zone of the surrounding rock. The length from the boundary of the deepest fracture zone in each test borehole to the roadway surface is taken as R. f The anchor point in the deepest identical weakly reflective fiber optic strain cable with a strain value of 2000±500 με is taken as the boundary of the roadway surrounding rock damage zone, and the length from the boundary of the deepest damage zone in each fracture zone test borehole to the roadway surface is taken as R. d The time required for the boundary of the fracture zone to reach 0.5 times the roadway width is taken as t. f The area from the roadway surface to the peak stress point of the surrounding rock is defined as the stress rise zone of the roadway surrounding rock, and the deepest location of the stress peak point of each measuring line is defined as R. u The stress reduction zone of the roadway surrounding rock is defined as the area from the peak stress location of the surrounding rock to the original stress location of the deep surrounding rock. The deepest point of the boundary of the excavation disturbance stress influence of each survey line is defined as R. l The time it takes for the peak stress location to develop to one lane width is taken as t. s ; S3 support parameters are determined based on the surrounding rock fracture zone range index R. f Determine the shallow hole grouting depth based on the surrounding rock damage zone range index R. d Determine the deep hole grouting depth based on the R value of the surrounding rock stress rise zone. u Determine the anchor bolt length based on the R value, which represents the range of the surrounding rock stress reduction zone. l Determine the anchor cable length; S4 support timing determination: based on the development rate index t of the surrounding rock fracture zone. f Determine the timing of shallow hole grouting and anchor bolt installation; based on the stress field development rate index t s Determine the timing of deep hole grouting and anchor cable implementation; specifically, based on the development rate index t of the surrounding rock fracture zone. f The implementation time for shallow hole grouting and anchor bolts is determined to be: t after tunnel excavation. f ±2 days; based on the stress field development rate index t s The implementation time for deep hole grouting and anchor cables is determined to be: t after tunnel excavation. s ±3 days.

2. The precise intervention method for roadway support according to claim 1, characterized in that, The spacing between each anchor point in the identical weak reflection fiber optic strain cable arranged in the test borehole of the fracture zone is 1m, and the spacing between the six-axis fiber optic pressure sensors arranged in the test borehole of the stress field is 1m.

3. The precise intervention method for roadway support according to claim 2, characterized in that, After embedding the identical weak reflection fiber optic strain cable sensor in the test borehole of the fracture zone and the fiber optic six-axis pressure sensor in the stress field test borehole, grouting was performed on the boreholes respectively, so that the identical weak reflection fiber optic strain cable sensor and the fiber optic six-axis pressure sensor could deform in tandem with the surrounding rock of the roadway and sense the stress of the surrounding rock.

4. The precise intervention method for roadway support according to claim 1, characterized in that, In S3, the shallow hole grouting depth is: R f ±0.2 m ~ 3 m, deep hole grouting depth is: 6 m ~ R d ±0.2 m, anchor bolt length: R u ±0.2 m ~ 2.8 m, anchor cable length: R l ±0.2 m.

5. The precise intervention method for roadway support according to claim 4, characterized in that, The length of the anchor bolt shall not exceed 2.8m, and the maximum depth of shallow hole grouting shall not exceed 2m.

Images