CN116085017A - Layered rock anchoring effect testing method under variable cross-section anchor rod and impact effect - Google Patents
Layered rock anchoring effect testing method under variable cross-section anchor rod and impact effect Download PDFInfo
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- 238000004873 anchoring Methods 0.000 title claims abstract description 133
- 239000011435 rock Substances 0.000 title claims abstract description 125
- 238000012360 testing method Methods 0.000 title claims abstract description 56
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- 239000003795 chemical substances by application Substances 0.000 claims description 4
- 239000004570 mortar (masonry) Substances 0.000 claims description 3
- 238000004080 punching Methods 0.000 claims description 3
- 239000003469 silicate cement Substances 0.000 claims description 3
- 230000005483 Hooke's law Effects 0.000 claims description 2
- 238000009826 distribution Methods 0.000 claims description 2
- 238000010998 test method Methods 0.000 abstract description 5
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0026—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts
- E21D21/0046—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts formed by a plurality of elements arranged longitudinally
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D20/00—Setting anchoring-bolts
- E21D20/003—Machines for drilling anchor holes and setting anchor bolts
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D20/00—Setting anchoring-bolts
- E21D20/02—Setting anchoring-bolts with provisions for grouting
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0026—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/30—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight
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Abstract
The invention relates to a variable cross-section anchor rod and a layered rock anchoring effect testing method under the impact action, belonging to the technical field of rock dynamics test simulation. The method is characterized in that: the main body of the variable-section type anchor rod is composed of three parts, namely a tunnelable drill bit, a hollow seamless steel pipe and screw thread steel, wherein the diameters of the hollow seamless steel pipe and the screw thread steel are in accordance with the distribution function of axial force and shearing stress of the anchor rod obtained by stress analysis of a conventional rock anchor rod during anchoring. The construction and test methods are respectively carried out by applying the characteristics of the variable-section anchor rod, the invention aims to simulate the actual surrounding rock damage condition of the blasting construction site according to an experimental method, systematically study the damage characteristics of layered rock under different anchoring angles and anchor rod quantity, and provide reference value for related engineering.
Description
Technical field:
the invention belongs to the technical field of rock dynamics test simulation, and particularly relates to a test method for simulating impact action of lamellar rock under a variable cross-section anchor rod and an anchoring state of the variable cross-section anchor rod.
The background technology is as follows:
in the actual blasting construction process, due to the heterogeneity of the rock, the rock is often provided with some crack joints, so that the structure of the rock is discontinuous, and a layered rock structure is formed. The layered composite rock structure is one of rock mass structures commonly occurring in underground engineering, is different from a rock mass with a single structure, is formed by compositing multiple layers of rock with different performances, has different rock properties of each component, has defects at rock junctions, and has a damage mechanism and a mode which are obviously different from those of common rock masses, so that the layered composite rock structure is a very necessary engineering procedure for strengthening surrounding rocks in the actual engineering to strengthen the surrounding rocks and reduce engineering accidents.
In the measure of reinforcing surrounding rock, the method of anchoring and supporting the anchor rod is widely applied in engineering because of economy and practicability, the anchor rod is used as an auxiliary tool for stabilizing the surrounding rock, the anchor rod is essentially a tension lever, and the action of the anchor rod is to connect an unstable surrounding rock structure with a bedrock through a rod piece, so that a plurality of rock blocks are combined into a stable composite structure, the integrity of the whole engineering body is ensured, the shearing and tensile resistance of the rock is greatly improved by using the anchor rod, and the bearing capacity and stability of the whole rock body are enhanced, so that the aim of consolidating the surrounding rock is fulfilled. However, the conventional rock bolt needs to be drilled and then anchored in the construction process, and cannot be anchored while drilling, so that the efficiency is low. Secondly, the whole stress of the conventional rock bolt is not the same everywhere during anchoring, the whole material of the conventional rock bolt is the same everywhere, the waste of the material is caused to a certain extent, and the cost is increased, so that a variable-section rock bolt is urgently needed to solve the problems.
Due to the instability of the layered rock, the damage form of the surrounding rock under the blasting impact often shows an uncertainty, but the uncertainty of the damage form of the surrounding rock under the blasting impact is difficult to judge, and no good solution exists at present.
The invention comprises the following steps:
the invention aims to:
the invention provides a method for testing the anchoring effect of layered rock under the actions of variable-section anchor rods and blasting impact, which aims to simulate the damage condition of actual surrounding rock of a blasting construction site according to an experimental method, systematically study the damage characteristics of layered rock under different anchoring angles and anchor rod quantity, and provide reference values for related engineering.
The technical scheme is as follows:
the utility model provides a variable cross section stock, but includes tunnelling type drill bit, its characterized in that: the main body of the variable-section type anchor rod is composed of three parts, wherein the first part is a tunneling type drill bit, the second part is a hollow seamless steel pipe with the diameter larger than that of the tunneling type drill bit, both ends of the hollow seamless steel pipe are provided with internal threads, one end of the hollow seamless steel pipe is connected with the tunneling type drill bit, the other end of the hollow seamless steel pipe is connected with threaded steel with the diameter smaller than that of the hollow seamless steel pipe, the third part is threaded steel, both ends of the third part are provided with external threads, one end of the third part is connected with the hollow seamless steel pipe, and the other end of the third part is used as a free end of the anchor rod; the diameters of the hollow seamless steel tube and the deformed steel bar are in line with the distribution function tau (x) of the axial force P (x) and the shearing force of the anchor rod obtained by the stress analysis of the conventional rock anchor rod during anchoring:
wherein D is the diameter of the anchoring body, E is the composite elastic modulus of the anchoring body and the anchoring agent, K is the shear rigidity of the anchoring body, P is the axial load of the anchoring body, tau (x) is the shear stress when the axial anchoring length is x, and P (x) is the axial force when the axial anchoring length is x.
2. The construction method adopting the variable cross-section anchor rod is characterized by comprising the following steps of: the construction flow comprises the following steps:
(1) Connecting a tunnelable drill bit to one end of a large-diameter hollow seamless steel pipe, and connecting the other end of the large-diameter hollow seamless steel pipe to an anchor rod drilling machine to drill and anchor a rock mass;
(2) When the anchor rod drilling machine drills to the depth required by construction, stopping drilling and taking down the anchor rod drilling machine, grouting the inside of the large-diameter hollow seamless steel pipe, and screwing a connecting pipe sleeve after grouting is finished;
(3) Combining the small-diameter screw-thread steel with the large-diameter hollow seamless steel pipe through a connecting pipe sleeve, and then carrying out integral grouting;
(4) And sleeving a gasket on the free end of the anchor rod, and screwing the bolt.
3. The method for testing the layered rock anchoring effect under the blasting impact effect by adopting the variable-section anchor rod is characterized by comprising the following steps of: the method comprises the following steps:
(1) Processing a rock sample taken out of actual engineering into a standard cylinder test piece with the length of 50mm multiplied by 50 mm;
(2) Cutting with equal thickness, cutting into four mutually independent pieces along the axial direction of a sample, equidistant drilling by using a deep hole bench drill along the radial direction of the sample, equally dividing the hole pitch of a porous sample, respectively processing into single holes, two holes and three holes, punching at angles of 0 degrees, 30 degrees, 60 degrees and 90 degrees along the circumferential position, wherein the hole diameter is 10mm, and then bonding the four independent pieces of the sample together by using silicate cement mortar to form a layered rock structure;
(3) Respectively anchoring the test piece at different anchoring angles and the number of the anchor rods;
(4) The Hopkinson system is utilized to impact the test piece;
the tensile deformation of the anchoring section in the elastic state can be obtained according to the anchoring force distribution and Hooke's law:
wherein: d is the diameter of the anchoring body; p is the axial load of the anchor body; e is the elastic modulus of the anchoring body; omega (x) is shear displacement deformation of the anchoring section; u (x) is the axial displacement of the anchor at coordinate x; wherein the method comprises the steps of
G is the shear modulus of the anchor; e is a special mathematical constant in mathematics, an infinite non-cyclic decimal, also called Euler number;
according to the propagation conditions of elastic waves at interfaces of different media, the resultant forces at two sides of the interface are equal, and the resultant force of the interface and the incident rod end is as follows: p (P) 1 (t)＝A 0 E(ε i +ε r ) The method comprises the steps of carrying out a first treatment on the surface of the The resultant force of the interface and the transmission rod end is: p (P) 2 (t)＝A 0 Eε t . According to the balance principle of the stress of the sample in the test, the average stress of the sample is as follows:
wherein: e is the elastic modulus; wherein A and A 0 The cross-sectional areas of the sample and the rod, respectively; epsilon r (t)、ε t (t) is the reflected strain and transmitted strain on the elastic SHPB bar; epsilon i (t) is a strain pulse incident on the rod for a time t; time is referred to as the argument in the function;
the method simulates blasting impact on surrounding rocks in the engineering site, performs strength analysis on layered rocks in different anchoring states, and provides data for actual engineering construction.
In step (2), an anchoring angle of 60 ° is used as optimum.
In the step (2), two anchor rods are adopted to achieve the best anchoring effect.
The advantages and effects:
compared with the prior art, the structure and the test method are reasonable, and have the following advantages:
1. the rod body of the variable-section type anchor rod consists of two rod bodies with different diameters, has higher tensile capacity and shearing capacity than that provided by a common rock anchor rod, can be anchored on demand for different strata, and can improve the anchoring effect and save the cost.
2. The rock cutting technology is adopted to slice the complete rock, and the silicate cement mortar is utilized to bond the complete rock again, so that the layered rock structure encountered in the actual engineering is simulated, and the layered characteristic of the layered rock in the actual engineering is reduced.
3. In the blasting construction process, the rock is subjected to the repeated impact load actions of blasting impact, mechanical vibration and the like and is in a high strain rate state, so that an impact experiment is carried out by using a Hopkinson system, the state of layered rock under the high strain rate is simulated, the rock performance is explored, and a reference is provided for practical engineering.
4. Because the actual construction process is complex in working condition, the multi-layer rock anchoring direction cannot be controlled directionally, and the anchoring angle and the number of anchor rods are required to be adjusted according to the actual working condition of the site, the experimental method fully simulates the diversity of surrounding rock structures of the site, and rock test pieces with different anchoring angles (comprising 0 DEG, 30 DEG, 60 DEG and 90 DEG) and different numbers of anchor rods (1-3) are prepared respectively, so that the site condition of the engineering is fully simulated.
Description of the drawings:
FIG. 1 is a flow chart of a layered rock bolting effectiveness test method;
FIG. 2 is a diagram of a rock processing form;
FIG. 3 is a diagram of a conventional rock bolt force analysis;
FIG. 4 is a variable cross section anchor bar diagram;
FIG. 5 is a diagram of an experimental use variable cross section anchor;
FIG. 6 is a view of the post-anchoring test piece;
FIG. 7 is a stress-strain graph of a anchored rock at different anchoring angles;
FIG. 8 is a graph of dynamic compressive strength, elastic modulus and anchoring angle of anchored rock at different anchoring angles;
FIG. 9 is a graph of stress-strain curves for anchored rock for different anchor rod numbers;
FIG. 10 is a graph of dynamic compressive strength, modulus of elasticity versus number of anchors for a anchored rock of different numbers of anchors;
FIG. 11 is a schematic view of a partial anchor rod in actual engineering;
the drawing is marked: 1.2 parts of lamellar rock slices, 2 parts of prefabricated holes, 3 parts of tunnelable drill bits, 4 parts of gaskets, 5 parts of seamless steel pipes, 6 parts of screw reinforcing steel bars, 7 parts of nut sleeves.
The specific embodiment is as follows:
in order to better understand the above technical solution, the following will describe the above technical solution in detail with reference to the accompanying drawings and specific embodiments, and a flow chart of a method for testing the anchoring effect of layered rock under the blasting impact action is shown in fig. 1, and the specific flow is as follows:
s1: and (5) selecting and processing the patterns. Selecting a complete rock mass without a crack joint from an engineering site, preparing a test piece according to national standard engineering rock mass test method standard (GB/T50266-2013), processing the rock mass into a cylindrical test sample by adopting a linear cutting mode, carefully polishing both ends and side surfaces of the test sample by using sand paper until the outer surface of the test sample is smooth and has no protrusion, performing equal thickness cutting on the processed rock test sample along the axial direction by using a rock cutter to obtain four mutually independent lamellar rock slices 1, and then performing equidistant drilling (equal hole pitch division of a porous test sample) along the radial direction of the test sample by using a deep hole bench drill, wherein the hole angles are respectively equal to the diameter direction of the test sample slice, and the hole angles are respectively equal to 10mm, and the processing forms are as shown in figure 2.
S2: the sample is anchored. Cement mortar is selected as the anchoring agent, and an independently developed variable-section anchor rod is adopted to penetrate through the drill hole to anchor the cement mortar. The variable cross-section anchor rod is concretely implemented as follows.
As shown in fig. 3, the conventional rock bolt is subjected to a pulling force P, and the bolt body is pulled to generate displacement under the pulling force P, so that resistance is generated to the anchoring agent around the bolt body, the pulling force is transmitted to the anchoring body through the resistance and the adhesion force of the anchoring body to the bolt body, and then the pulling force is transmitted to the stratum through the friction resistance between the anchoring body and the surrounding rock body. As the pulling force P gradually increases, the anchoring effect fails and the anchoring segment enters the residual strength stage. It follows that the ultimate pullout resistance of the anchor is mainly controlled by the frictional resistance between the anchor body and the surrounding rock body.
In order to analyze the stress condition of the anchoring section, the diameter of the anchoring body is set as D, and the elastic modulus is set as E m The tensile elastic modulus of the anchor rod is E s The diameter of the anchor rod is d, and the designed anchoring length is l. To facilitate analysis, the following assumptions are made: (1) the surrounding rock body and the anchoring body are both made of linear elastic materials; (2) the contact surface of the surrounding rock body and the anchoring body is in accordance with the traditional molar-coulomb rule; (3) the stress on the axial section of the anchoring body is evenly distributed. Obtaining the axial force P (x) and the shearing force distribution function tau (x) of the anchor rod:
it is further known that the diameter of the anchor rod plays an important role in the anchoring effect, the larger the diameter is, the larger the scope of the anchor rod is, the better the control effect on the integrity of the rock mass is, but as the rock belongs to natural materials, the discreteness is larger, the rock properties of different rock layers of the rock mass are flexibly anchored, the anchoring effect of the anchor rod is improved, the cost is reduced, and based on the expectation on the anchoring effect, the variable cross-section anchor rod is independently developed. The variable cross-section anchor rod is shown in fig. 4, the variable cross-section anchor rod main body is divided into three parts, the first part is a tunnelable drill bit 3 which is used for drilling a rock mass, a punching process in the anchoring process is omitted, and the anchoring efficiency is improved. The second part is a large-diameter hollow seamless steel tube 5, both ends of the second part are provided with internal threads, one end of the second part is connected with a tunneling drill bit 3, the other end of the second part is connected with a small-diameter deformed steel bar 6, the second part mainly plays a role in tensile pulling in the anchor rod structure, and the diameter of the second part can be adjusted according to the construction process. The third part is small-diameter screw steel 6, two ends of the small-diameter screw steel are provided with external threads, one end of the small-diameter screw steel is connected with a large-diameter seamless steel pipe 5, the other end of the small-diameter screw steel is used as the free end of the anchor rod, the small-diameter screw steel mainly plays a role in shearing resistance in the anchor rod structure, and the diameter of the small-diameter screw steel can be adjusted. Because the diameters of the large-diameter hollow seamless steel pipe 5 and the small-diameter deformed steel pipe 6 are different at the connecting point, the connection condition can not be realized, and therefore, the connecting pipe sleeve 7 with internal and external threads is added at the connecting point of the large-diameter hollow seamless steel pipe 5 to balance the condition that the diameters are not uniform and the connection can not be realized.
The construction process of the variable-section anchor rod is as follows:
(1) The tunnelable drill bit is connected to one end of the large-diameter hollow seamless steel pipe 5, and the other end of the large-diameter hollow seamless steel pipe 5 is connected to the jumbolter to drill and anchor rock.
(2) When the jumbolter drills to the depth required by construction, the drilling is stopped, the jumbolter is taken down, grouting is carried out on the inside of the large-diameter hollow seamless steel pipe 5, and the connecting pipe sleeve 7 is screwed after grouting is finished.
(3) The small-diameter deformed steel bar 6 is combined with the large-diameter hollow seamless steel pipe through the connecting sleeve, and then the whole grouting is performed.
(4) And sleeving a gasket on the free end of the anchor rod, and screwing the bolt.
The variable section type anchor rod is different from a common rock anchor rod, can be used for immediately anchoring while drilling a rock body, achieves the effect of' anchoring while drilling, and timely controls the integrity of the rock body. The rod body of the variable-section type anchor rod consists of two rod bodies with different diameters, has higher tensile capacity and shearing capacity than that provided by a common rock anchor rod, and can be anchored according to different strata, so that the anchoring effect is improved and the cost is saved. Because of the limitation of indoor test conditions, the variable-section type anchor rod can be suitable for indoor test only by slightly modifying the variable-section type anchor rod, and in order to fix the anchor rod position by screwing a nut on an external thread during anchoring, the internal thread at one end of the large-diameter hollow seamless steel tube 5 is changed into the external thread, and other parts are not modified. The modified product is shown in figure 5.
The tunnelling type drill bit 3 is connected to one end of the large-diameter hollow seamless steel pipe 5, the other end of the large-diameter hollow seamless steel pipe 5 is connected to a drilling machine, rock mass drilling is anchored, when the drilling machine drills to the depth required by construction, drilling is stopped, the drilling machine is taken down, grouting is conducted inside the large-diameter hollow seamless steel pipe, after grouting is finished, a gasket 4 is installed, a nut pipe sleeve 7 is screwed on, small-diameter threaded steel bars 6 are combined with the large-diameter hollow seamless steel pipe through the connecting pipe sleeve, then integral grouting is conducted, the free end of the anchor rod is sleeved with the gasket, bolts are screwed, and fig. 6 is a test piece diagram after anchoring.
According to different anchoring angles and anchoring numbers, 3 samples of each type are prepared, the numbers are in the form of 0-1-1, wherein the first number of the numbers represents the anchoring angle of the anchor rod, the second number represents the anchoring number of the anchor rod, the third number represents the sample sequence, the impact air pressure is selected to be 0.15MPa, and a group of data with the smallest data discrete type is selected from each group of three samples for numerical analysis.
S3: the hopkinson system performs an impact test. The split Hopkinson pressure bar test equipment is adopted for simulating impact test, and the equipment mainly comprises three parts: the support part is mainly used for supporting and fixing the compression bar part and ensuring the level of the compression bar, and the support part is made of aluminum alloy profiles for facilitating system installation and disassembly. The plunger body portion includes a barrel, a striking rod (commonly known as a bullet), an incident rod, a projection rod, an energy absorber, a corresponding air pressure device, and the like. The data acquisition system consists of strain gauges stuck on the rod, wheatstone bridge circuits (strain gauge junction bridge boxes), super-dynamic strain gauges and a high-speed acquisition system.
Respectively sticking strain gauges at the middle positions of an incidence rod and a transmission rod, fixing a lead of the strain gauges on a rod piece by using an adhesive tape, connecting the other end of the lead to a data acquisition system, checking whether a bullet pipe, the incidence rod and the transmission rod are completely aligned, adjusting the device to enable the bullet pipe, the incidence rod and the transmission rod to be in a normal working state, closing a combined valve, then opening a nitrogen cylinder switch, adjusting the air pressure value in an air pressure chamber by using an air pressure valve, and adjusting parameters of the acquisition system;
the method comprises the steps of enabling an incident rod to be in aligned contact with a transmission rod, then setting impact air pressure, opening an air pressure valve to conduct air flushing, closing the valve after the air flushing is finished, adjusting a dynamic strain acquisition instrument according to a waveform chart during the air flushing, setting instrument parameters, smearing butter on two ends of a quartz sandstone sample to reduce the influence of friction effect, clamping the sample between the incident rod and the transmission rod, and guaranteeing that the center positions of the incident rod, the transmission rod and the quartz sandstone sample are aligned in a straight line as much as possible.
Setting the impact air pressure to a preset value, opening a switch to enable nitrogen to enter an air pressure chamber, then rapidly closing the switch, clicking an impact button on an operating system, rapidly impacting an incident rod by a bullet, performing data acquisition by a data acquisition system through a strain gauge on the rod, then performing data processing and analysis, closing all equipment after the test is finished, screwing a nitrogen cylinder switch, finally taking out a sample, and exporting data.
S4: impact result analysis. The test results of the samples of the anchored rock with different anchoring angles after the conventional uniaxial impact test are summarized as shown in table 1. Representative samples (numbers 90-1-3, 60-1-3, 30-1-1 and 0-1-2) of each group are selected according to the table 1 for research analysis, wherein the representative samples refer to the dynamic compressive strength values of the representative samples are close to the average value of the dynamic compressive strength values of the samples in the group, and the stress-strain curves of the anchored rock at different anchoring angles in fig. 7 and the relationship diagrams of the dynamic compressive strength and the elastic modulus of the anchored rock at different anchoring angles in fig. 8 are respectively plotted. Table 1 is a statistical table of conventional uniaxial impact test results of anchored rock at different anchoring angles;
TABLE 1
As can be seen from FIG. 7, the 30℃anchoring sample (30-1-1) has a peak stress of 117.02MPa and a peak strain of 0.008, which is 15.9% and 2.2% higher than the 0℃anchoring sample (0-1-2); the peak stress of the 60-degree anchoring sample (60-1-3) is 136.14MPa, the peak strain is 0.00566, and the peak stress is increased by 35.1 percent and reduced by 27.7 percent compared with the peak stress of the 0-degree anchoring sample (0-1-2); the peak stress of the 90 degree anchoring sample (90-1-3) is 122.39MPa, the peak strain is 0.00682, and the peak stress is improved by 22.1 percent and reduced by 8.7 percent respectively compared with the peak stress of the 0 degree anchoring sample (0-1-2). As the anchoring angle increases, the peak stress increases and then decreases, and the peak strain increases and then decreases, and from the analysis of the stress angle of the sample, the included angle between the anchor rod and the vertical direction of the stress is smaller when the anchoring angle is smaller, and larger resistance cannot be provided, so that the lamellar rock slices in the sample bear the stress, and the dynamic compressive strength of the lamellar rock slices is necessarily smaller because the lamellar rock slices are not complete rocks, so that the damage easily occurs; the anchor rod provides larger resistance when the anchoring angle is larger, so that the sample is not easy to damage. From the analysis of sample deformation angle, because the existence of stock has restrained the lateral deformation of sample, the duration that leads to taking place the collaborative deformation between sample and the stock is longer to delay the expansion of the inside crack of rock mass along axial direction, make the axial strain of sample reduce. When the anchoring angle is 60 degrees, the axial strain of the sample is minimum, the lateral constraint of the anchor rod on the sample is most obvious, and the control effect of the angle anchoring mode on the deformation of the anchored rock is more obvious.
From fig. 8, it can be seen that when the anchoring angle is less than 60 °, the dynamic compressive strength of the test specimen increases with an increase in the anchoring angle, and when the anchoring angle is greater than 60 °, the compressive strength of the test specimen decreases with an increase in the anchoring angle. The analytical reasons may be that the larger the anchoring angle of the anchor rod is, the stronger the supporting effect generated in the sample is, namely, the greater the dynamic compressive strength is generated, when the anchoring angle is increased to 60 degrees, the supporting effect of the anchor rod is weakened and the generated resistance is also reduced, so that the dynamic compressive strength of the sample is reduced. It is stated that the larger the anchoring angle, the greater the dynamic compressive strength of the test specimen, so that the anchoring angle of the anchor should be selected with a limit value in the range of 60 DEG to 90 deg. The original properties of the sample are changed due to the anchoring, so that the capability of the sample for bearing the maximum damage load is different and the deformation is different under different anchoring angles, namely the elastic modulus of the sample is different, and the elastic modulus of the sample can be seen from the figure to be increased and then decreased along with the increase of the anchoring angle, wherein the increase amplitude is increased along with the increase of the anchoring angle. When the anchoring angle is 60 degrees, the elastic modulus slope of the sample is increased rapidly, the elastic modulus value is 24GPa, and the elastic modulus value is far greater than other three anchoring angles, so that analysis shows that the anchor rod can play a good anchoring effect when the anchoring angle is 60 degrees, the integrity of the anchored rock can be controlled, and the bearing capacity of the anchored rock is improved.
The test results of the samples of the conventional uniaxial impact test of the anchored rock under different anchor rod numbers are summarized and shown in table 2. Representative samples (numbered 90-1-3, 90-2-2 and 90-3-2) of each group are selected for research, and the stress-strain curve graphs of the anchored rocks with different anchor rod numbers in fig. 9 and the dynamic compressive strength and the elastic modulus-anchor rod number relation graphs of the anchored rocks with different anchor rod numbers in fig. 10 are respectively plotted. Table 2 is a statistical table of conventional uniaxial impact test results for anchored rock at different anchor rod numbers.
TABLE 2
As can be seen from fig. 9, the dynamic mechanical properties of the samples are different, and when the number of the anchors is increased from 1 (90-1-3) to 3 (90-3-2), the peak stress of the samples tends to be increased first and then decreased with the increase of the number of the anchors. Two groups of control tests are respectively carried out in the step 2, one group is a test under different anchoring angles of a single anchor rod, the other group is a comparative test under the same angle when 2 (90-2-2) anchor rods are anchored, and the peak stress of a sample is 130.33MPa, which is 1.2 times of the peak stress when 3 anchor rods are anchored; the peak stress of the sample is 122.39MPa when 1 anchor rod is anchored, which is 1.1 times of the peak stress when 3 anchor rods are anchored; from the analysis, when 2 anchor rods are anchored, the peak stress of the anchor body is improved to the greatest extent, and the number of the anchor rods can influence the bearing capacity of the test sample. The stress-strain curve change trend of the test sample under the quantity of the three anchor rods is observed, when the 2 anchor rods are anchored, the stress of the test sample is the largest, the corresponding peak strain is the smallest, the mechanical properties of high strength and low strain are shown, the anchoring effect of the 2 anchor rods is better, the anchor rods have no group anchoring effect, the anchor rod anchoring interval is reasonable in design, and the more the anchor rods are proved to be from the side face, the better the anchoring effect is.
From fig. 10, a graph of dynamic compressive strength, modulus of elasticity, and number of anchors for different numbers of anchors is known. From the graph, when the number of the anchor rods is increased from 1 anchor rod to 3 anchor rods, the dynamic compressive strength of the test sample tends to be increased firstly and then decreased. The dynamic compressive strength of the test sample is 122.39MPa and 111.68MPa when the number of the anchor rods is 1 and 3, and 93% and 85% of the dynamic compressive strength of the test sample when the number of the anchor rods is 2; in summary, the increase of the number of the anchor rods effectively improves the dynamic compressive strength of the test sample, which indicates that the increase of the number of the anchor rods is truly beneficial to improving the mechanical property of the test sample, but meanwhile, attention should be paid to the arrangement of the spacing of the anchor rods, and in a limited area, if the number of the anchor rods is too much, abnormal conditions (the dynamic compressive strength is reduced, and the group anchor effect occurs) of the test samples of three anchor rods can occur. Therefore, the reasonable interval selection can enable the anchor rod to fully play an anchoring role, better combine with the sample and effectively reduce the influence of dynamic load on the sample.
When the number of the anchor rods is increased from 1 anchor rod to 3 anchor rods, the elastic modulus of the test sample tends to be increased and then decreased, which is consistent with the dynamic compressive strength change trend. The elastic modulus of the samples is 18.2GPa and 13.9GPa when the number of the anchor rods is 1 and 3, respectively, and is 83% and 64% of the elastic modulus when the number of the anchor rods is 3. The test sample has the advantages that the test sample has the largest elastic modulus under the anchoring of 2 anchor rods, the larger the elastic modulus is, the stronger the deformation resistance of the test sample is, the less deformation is easy to generate, the anchor rod can effectively control the integrity of the test sample under the impact load action, and the impact resistance of the test sample is improved.
According to the above, when the anchoring angle is 60 degrees or the number of anchoring points is 2, the anchoring effect of the rock is best, therefore, when the actual layered surrounding rock body is anchored, different layering directions of the surrounding rock body rock are required to be subjected to differential anchoring, so that the anchoring angle between the anchor rod and the surrounding rock body is 60 degrees or the number of anchoring points of the anchor rod in a small range is two, and in actual engineering, the anchoring of the surrounding rock body in a local range is shown in fig. 11, the anchoring direction of the variable-section anchor rod forms an included angle of 60 degrees with the layering directions of the rock, the material performance and the anchoring attribute of the variable-section anchor rod are fully exerted, the stability and the integrity of the surrounding rock body are enhanced to a certain extent, the high stress generated by the rock is shared, and the engineering disasters are reduced.
Claims (5)
1. The utility model provides a variable cross section stock, but includes tunnelling type drill bit, its characterized in that: the main body of the variable-section type anchor rod is composed of three parts, wherein the first part is a tunneling type drill bit, the second part is a hollow seamless steel pipe with the diameter larger than that of the tunneling type drill bit, both ends of the hollow seamless steel pipe are provided with internal threads, one end of the hollow seamless steel pipe is connected with the tunneling type drill bit, the other end of the hollow seamless steel pipe is connected with threaded steel with the diameter smaller than that of the hollow seamless steel pipe, the third part is threaded steel, both ends of the third part are provided with external threads, one end of the third part is connected with the hollow seamless steel pipe, and the other end of the third part is used as a free end of the anchor rod; the diameters of the hollow seamless steel tube and the deformed steel bar are in accordance with the distribution function P (x) of the axial force and the distribution function tau (x) of the shearing force obtained by the stress analysis of the conventional rock bolt during the anchoring:
wherein D is the diameter of the anchoring body, E is the composite elastic modulus of the anchoring body and the anchoring agent, K is the shear rigidity of the anchoring body, P is the axial load of the anchoring body, tau (x) is the shear stress when the axial anchoring length is x, and P (x) is the axial force when the axial anchoring length is x.
2. A construction method using the variable cross-section anchor rod according to claim 1, characterized in that: the construction flow comprises the following steps:
(1) Connecting a tunnelable drill bit to one end of a large-diameter hollow seamless steel pipe, and connecting the other end of the large-diameter hollow seamless steel pipe to an anchor rod drilling machine to drill and anchor a rock mass;
(2) When the anchor rod drilling machine drills to the depth required by construction, stopping drilling and taking down the anchor rod drilling machine, grouting the inside of the large-diameter hollow seamless steel pipe, and screwing a connecting pipe sleeve after grouting is finished;
(3) Combining the small-diameter screw-thread steel with the large-diameter hollow seamless steel pipe through a connecting pipe sleeve, and then carrying out integral grouting;
(4) And sleeving a gasket on the free end of the anchor rod, and screwing the bolt.
3. A method for testing the anchoring effect of layered rock under the blasting impact action by adopting the variable-section anchor rod as claimed in claim 1, which is characterized by comprising the following steps: the method comprises the following steps:
(1) Processing a rock sample taken out of actual engineering into a standard cylinder test piece with the length of 50mm multiplied by 50 mm;
(2) Cutting with equal thickness, cutting into four mutually independent pieces along the axial direction of a sample, equidistant drilling by using a deep hole bench drill along the radial direction of the sample, equally dividing the hole pitch of a porous sample, respectively processing into single holes, two holes and three holes, punching at angles of 0 degrees, 30 degrees, 60 degrees and 90 degrees along the circumferential position, wherein the hole diameter is 10mm, and then bonding the four independent pieces of the sample together by using silicate cement mortar to form a layered rock structure;
(3) Respectively anchoring the test piece at different anchoring angles and the number of the anchor rods;
(4) The Hopkinson system is utilized to impact the test piece;
the tensile deformation of the anchoring section in the elastic state can be obtained according to the anchoring force distribution and Hooke's law:
wherein: d is the diameter of the anchoring body; p is the axial load of the anchor body; e is the elastic modulus of the anchoring body; omega (x) is shear displacement variation of anchoring sectionShape; u (x) is the axial displacement of the anchor at coordinate x; wherein the method comprises the steps of
G is the shear modulus of the anchor; e is a constant in mathematics;
according to the propagation conditions of elastic waves at interfaces of different media, the resultant forces at two sides of the interface are equal, and the resultant force of the interface and the incident rod end is as follows: p (P) 1 (t)＝A 0 E(ε i +ε r ) The method comprises the steps of carrying out a first treatment on the surface of the The resultant force of the interface and the transmission rod end is: p (P) 2 (t)＝A 0 Eε t The method comprises the steps of carrying out a first treatment on the surface of the According to the balance principle of the stress of the sample in the test, the average stress of the sample is as follows:
wherein: e is the elastic modulus; wherein A and A 0 The cross-sectional areas of the sample and the rod, respectively; epsilon r (t)、ε t (t) is the reflected strain and transmitted strain on the elastic SHPB bar; epsilon i (t) is a strain pulse incident on the rod for a time t; t refers to time;
the method simulates blasting impact on surrounding rocks in the engineering site, performs strength analysis on layered rocks in different anchoring states, and provides data for actual engineering construction.
4. A method for testing the anchoring effect of layered rock under the action of blasting impact according to claim 3, wherein: in step (2), an anchoring angle of 60 ° is used as optimum under different anchoring angles.
5. A method for testing the anchoring effect of layered rock under the action of blasting impact according to claim 3, wherein: in the step (2), under different anchoring numbers, two anchor rods are adopted to achieve the best anchoring effect.
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| CN117592169A (en) * | 2024-01-02 | 2024-02-23 | 中国电力工程顾问集团中南电力设计院有限公司 | Horizontal bearing capacity calculation method for variable-section anchor rod foundation of power transmission line |
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| CN117592169A (en) * | 2024-01-02 | 2024-02-23 | 中国电力工程顾问集团中南电力设计院有限公司 | Horizontal bearing capacity calculation method for variable-section anchor rod foundation of power transmission line |
| CN117592169B (en) * | 2024-01-02 | 2024-05-28 | 中国电力工程顾问集团中南电力设计院有限公司 | Horizontal bearing capacity calculation method for variable-section anchor rod foundation of power transmission line |
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