CN107167385B - Indoor test method for stress loss of anchor rod - Google Patents
Indoor test method for stress loss of anchor rod Download PDFInfo
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- CN107167385B CN107167385B CN201710471695.5A CN201710471695A CN107167385B CN 107167385 B CN107167385 B CN 107167385B CN 201710471695 A CN201710471695 A CN 201710471695A CN 107167385 B CN107167385 B CN 107167385B
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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
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/003—Generation of the force
- G01N2203/0042—Pneumatic or hydraulic means
- G01N2203/0048—Hydraulic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
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Abstract
The invention provides an indoor testing device for stress loss of an anchor rod, which comprises a model box with an inner box body and an outer box body, two free steel plates, two jacks for supporting the free steel plates, a hollow jack and a cushion block. The two jacks are fixed at the centers of the free steel plates through bolts, flexible connecting pieces are connected between the two free steel plates, the two free steel plates are in close contact with the side wall of the outer box, and the hollow jacks pay attention to maintain stable stress when the anchor rod model is pulled. The invention also provides a test method using the device. The indoor testing device and method for the stress loss of the anchor rod are simple in structure, convenient to operate, small in measuring error, high in accuracy and easy to control boundary conditions and experimental variables. The device and the method can be applied to theoretical verification and practical operation, and have important significance for guidance of construction sites and improvement of construction designs.
Description
Technical Field
The invention belongs to the technical field of civil engineering, and particularly relates to an indoor testing device and method for stress loss of an anchor rod.
Background
In geotechnical engineering, the anchor rod has long history, and is widely applied to the support of foundation ditch, tunnel etc. because of the complexity of anchor rod-surrounding rock atress, it is important to design and construction to study the stress loss problem in soil body after the anchor rod stretch-draw.
The problem of stress loss after the anchor rod tensioning is studied, and the two aspects of field experiment and indoor simulation experiment are jointly started. Based on field experiments, the approximate stress distribution rule of the tensioned anchor rods in the soil body can be obtained, but because the field conditions are extremely complex, the economic cost and the labor cost are both large, the error in the tensioning process of the anchor rod tensioning machine is also large, and the boundary conditions are difficult to control to study the influence of different factors. Compared with the field experiment, the indoor simulation experiment is simple and easy to implement, and has great significance for verifying the conclusion of theoretical analysis and guiding field construction and improved design. Therefore, it is important to develop a method for testing stress loss of the anchor rod in a laboratory.
Disclosure of Invention
In order to solve the technical problems, the invention provides an indoor testing device and method for stress loss of an anchor rod.
The specific technical scheme of the invention is as follows:
the invention provides an indoor testing device for stress loss of an anchor rod, which comprises a model box, wherein the model box comprises a first box body, and the first box body comprises a bottom plate, and a first side plate, a second side plate, a third side plate and a fourth side plate which are arranged on the bottom plate and are sequentially connected end to end; the inner side of the first side plate is vertically provided with a first free steel plate, the inner side of the second side plate is vertically provided with a second free steel plate, the first free steel plate, the second free steel plate, the first side plate, the second side plate and the bottom plate are enclosed to form a second box body, soil is filled in the second box body, an anchor rod is inserted in the soil body, and a hollow jack is sleeved outside the anchor rod; a first jack is arranged between the first free steel plate and the fourth side plate, and a second jack is arranged between the second free steel plate and the third side plate.
Further, the first free steel plate is connected with the adjacent part of the second free steel plate through a flexible connecting piece, so that the soil body can not flow out of a gap between the two steel plates in the extrusion process of the two steel plates.
Further, a cushion block is arranged between the bottom of the hollow jack and the top of the soil body.
The model box used in the experiment is designed into a square steel box body, cast-in-situ mortar is adopted as an anchor rod anchoring body, a cushion block is used for replacing an anchor rope tray, concrete is adopted for manufacturing the cushion block, gypsum is added into the cushion block to strengthen the strength of the cushion block, the cushion block is square in actual engineering, the upper surface of the box body is square, and the square cushion block is selected for better transmitting the counterforce provided by the anchor rod to a soil body uniformly. When in use, the cylindrical barrel and the round cushion block can be adopted, and the required effect can be achieved.
The joint of the first free steel plate and the first side plate and the joint of the second free steel plate and the second side plate are not provided with gaps, and lubricating materials can be smeared, so that the blocking force of the first free steel plate and the second free steel plate is reduced, and the soil body is prevented from rushing out of the gaps in the pressurizing process of the free steel plate 1 and the free steel plate 2.
Further, two ends of the first jack are respectively fixed on the center of the first free steel plate and the fourth side plate through bolts; the two ends of the second jack are fixed on the center of the second free steel plate and the third side plate through bolts respectively so as to ensure that soil bodies on each side are uniformly stressed. The first jack and the second jack are preferably oil jack, pressure is applied through the oil jack, and the first free steel plate and the second free steel plate generate lateral pressure on soil under the action of the first jack and the second jack, so that the soil confining pressure is changed. The pressure value is displayed through the oil pressure gauge, so that the pressure exerted by the first free steel plate and the second free steel plate on the soil body can be known, and the soil body internal pressure can be obtained.
The indoor testing device for the stress loss of the anchor rod has the advantages of simple structure, convenience in use, low cost, small error, flexible application, high accuracy of experimental results and easiness in control of boundary conditions, and can be applied to practice.
The invention further provides an indoor test method for stress loss of an anchor rod, which comprises the following steps:
s1: after the soil body is remolded, the undisturbed soil is transported to a laboratory, the undisturbed soil is smashed, sieved and air-dried, and the remolded soil body is conveniently configured to meet the experimental requirement;
s2: filling soil into the second box body in multiple layers, and uniformly spraying water with certain mass after each layer of soil is filled; after each layer of soil filling is completed, tamping soil body, covering a plastic film for primary curing, wherein the curing time is 7d, and the pore water pressure is completely dissipated;
s3: burying a PVC pipe in advance in the process of filling soil, and burying the PVC pipe in the center of the model so as to facilitate the manufacture of grouting holes of the subsequent anchor rod anchoring section; slowly pulling out the PVC pipe after the filling height reaches the required anchoring length to form a grouting hole;
s4: the anchor rod is inserted into the grouting hole, and the perpendicularity of the anchor rod is ensured through an upper round plug and a lower round plug of the anchor rod centering device; grouting into the grouting holes, slightly stirring with iron wires, covering a plastic film after grouting is finished, and performing secondary curing for 28 days to prevent soil body water evaporation and ensure that the strength of the anchor rod anchoring body meets the test requirement;
s5: after curing, continuing to fill soil until reaching a set filling height, compacting soil body, sealing by using a plastic film after compacting, curing for the third time, preventing water loss, standing and dissipating pore water pressure;
s6: after curing, loading prestress, uniformly operating the hollow jack, and collecting stress applied by the hollow jack;
s7: and collecting data, and observing the loss condition of stress on the anchor rod along with time.
Further, in the step S2, when the soil is filled, the first jack (11) is used to limit the pushing distance of the first free steel plate (6) after being subjected to pressure, and the second jack (12) is used to limit the pushing distance of the second free steel plate (7) after being subjected to pressure, so as to prevent the pushing distance of the first free steel plate and the second free steel plate from being too large in the process of applying confining pressure to the soil, so that the soil structure is damaged to cause cracks or excessive uplift in the soil.
Further, in the step S2, when filling the soil, the soil infiltration speed is improved by setting a sand well, and the method specifically comprises the following steps:
s2.1: arranging at least one longitudinal sand well in the soil body to serve as a soaking channel;
s2.2: and laying a layer of middle sand at the bottom end of the soil body to enable the soil layer to be soaked in water bidirectionally.
The purpose of setting up the sand well is to simplify the process of changing the moisture content of soil body. When the experiment requires to configure soil bodies with various water contents, only the soil body with the lowest water content is required to be configured, and water is sprayed to the soil body in the model box according to the proportion after one experiment is completed. The sand well can improve the soil body permeation speed, shorten the test time and reduce the test cost.
Further, the specific method of step S2.1 is as follows:
and (3) embedding a plurality of plastic pipes in the model box, slowly pulling out the plastic pipes after the soil filling is finished, filling in medium sand and tightly scraping by using a fine drill rod.
Further, the specific method of step S6 is as follows:
s6.1, applying confining pressure to the soil body through the first jack and the second jack;
and S6.2, the hollow jack applies prestress to the anchor rod, and after the applied stress reaches an experimental design value, the hollow jack stops increasing the prestress and maintains the stability of the prestress.
The application of the prestress of the anchor rod is the most important part of the model test, firstly, the confining pressure value of the experimental design is applied to the soil body through the first jack and the second jack according to the experimental requirement, then the prestress is applied to the anchor rod through the hollow jack, the lower end of the hollow jack is propped against the cushion block, and the force is uniformly transmitted to the soil body through the cushion block; and after the applied stress reaches the experimental design value, the hollow jack stops loading and keeps stable. In the experimental process, the jack is not unloaded so as to ensure the stability of stress in the anchor rod and reduce the stress loss caused by the loading of the hollow jack.
Further, in step S7, the static collector is used to record the experimental data.
The beneficial effects of the invention are as follows: the indoor testing device for the stress loss of the anchor rod and the testing method using the device provided by the invention have the advantages of simple result, convenience in operation, small measurement error, high precision and easiness in control of boundary conditions and experimental variables. The device and the method can be applied to theoretical verification and practical operation, and have important significance for guidance of construction sites and improvement of construction designs.
Drawings
FIG. 1 is a top view of an indoor test apparatus for anchor stress loss according to example 1;
FIG. 2 is a longitudinal cross-sectional view of an indoor test device for anchor stress loss according to example 1;
FIG. 3 is a perspective view of an indoor test device for anchor stress loss according to example 1;
fig. 4 shows the change of the prestress value of the anchor rod under the condition of different water contents in the experimental example.
Wherein: 1. a bottom plate; 2. a first side plate; 3. a second side plate; 4. a third side plate; 5. a fourth side plate; 6. a first free steel plate; 7. a second free steel plate; 8. soil mass; 9. a bolt; 10. a hollow jack; 11. a first jack; 12. a second jack; 13. a flexible connection member; 14. and (5) cushion blocks.
Detailed Description
The invention will be described in further detail with reference to the accompanying drawings and the following examples.
Example 1
As shown in fig. 1 to 3, embodiment 1 of the present invention provides an indoor testing device for anchor rod stress loss, which comprises a model box, wherein the model box comprises a first box body, the first box body comprises a bottom plate 1, and a first side plate 2, a second side plate 3, a third side plate 4 and a fourth side plate 5 which are sequentially connected end to end and are arranged on the bottom plate 1; the inner side of the first side plate 2 is vertically provided with a first free steel plate 6, the inner side of the second side plate 3 is vertically provided with a second free steel plate 7, the first free steel plate 6, the second free steel plate 7, the first side plate 2, the second side plate 3 and the bottom plate 1 are enclosed to form a second box body, the adjacent part of the first free steel plate 6 and the second free steel plate 7 is connected with a flexible connecting piece 13, the flexible connecting piece 13 is preferably canvas, the second box body is internally filled with a soil body 8, an anchor rod 9 is inserted in the soil body 8, and a hollow jack 10 is sleeved outside the anchor rod 9; a first jack 11 is arranged between the first free steel plate 6 and the fourth side plate 5, and a second jack 12 is arranged between the second free steel plate 7 and the third side plate 4. A cushion block 14 is arranged between the bottom of the hollow jack 10 and the top of the soil body 8.
Example 2
The embodiment 2 provides an indoor testing device for stress loss of an anchor rod on the basis of the embodiment 1, and the embodiment 2 further defines that two ends of the first jack 11 are respectively fixed on the center of the first free steel plate 6 and the fourth side plate 5 through bolts; the two ends of the second jack 12 are respectively fixed on the center of the second free steel plate 7 and the third side plate 4 through bolts.
Example 3
This example 3 provides an indoor test method for anchor rod stress loss using the apparatus of example 1 or 2, comprising the steps of:
s1: remolding soil 8;
s2: filling soil bodies 8 into the second box body in multiple layers, and uniformly spraying water with certain mass after each layer of soil is filled; after each layer of soil filling is completed, tamping soil body 8, covering a plastic film for primary curing, wherein the curing time is 7d;
s3: burying a PVC pipe in advance in the process of filling soil, and slowly pulling out the PVC pipe after the filling soil reaches the required anchoring length to form a grouting hole;
s4: inserting the anchor rod 9 into the grouting hole, grouting into the grouting hole, slightly stirring, covering a plastic film for secondary curing after grouting is finished, wherein the curing time is 28d;
s5: after curing, continuing to fill soil until reaching a set filling height, tamping the soil body 8, sealing with a plastic film after tamping, and curing for the third time;
s6: after curing, loading prestress, uniformly operating the hollow jack 10, and collecting stress applied by the hollow jack 10;
s7: data are collected and the stress on the anchor rod 9 is observed for loss over time.
Example 4
In this embodiment 4, an indoor test method for stress loss of an anchor rod is provided on the basis of embodiment 3, and in this embodiment 4, the pushing distance of the first free steel plate 6 after being pressed is limited by the first jack 11 while the pushing distance of the second free steel plate 7 after being pressed is limited by the second jack 12 in the step S2 when the soil body 8 is filled. Meanwhile, the penetration speed of the soil body 8 is improved by arranging a sand well, and the sand well comprises the following steps:
s2.1: embedding a plurality of plastic pipes in the model box, slowly pulling out the plastic pipes after filling soil, filling in medium sand and compacting by using fine drills, thereby arranging at least one longitudinal sand well in the soil body 8;
s2.2: and laying a layer of middle sand at the bottom end of the soil body 8.
Example 5
The embodiment 5 provides an indoor test method for stress loss of the anchor rod based on the embodiment 3, and the embodiment 5 further defines the specific method of the step S6 as follows:
s6.1, applying confining pressure to the soil body 8 through the first jack 11 and the second jack 12;
s6.2, the hollow jack 10 applies prestress to the anchor rod 9, and after the applied stress reaches an experimental design value, the hollow jack 10 stops increasing the prestress and maintains the stability of the prestress.
In the step S7, the static collector is used to record experimental data, and the stress loss condition of the anchor rod 9 along with time is observed.
Experimental example
The sample is taken from urban Longquan post urban area, and the soil body is mainly characterized by grey yellow, brown yellow, slightly wet and plastic, contains a small amount of iron and manganese tuberculosis, has smooth section, slightly luster, higher strength and toughness in dry state, has denser network cracks on the surface, the cracks are filled with a small amount of grey white kaolin, smooth mirror surfaces are visible among the cracks, the cracks shrink after meeting water, the soil body is rapidly softened, and the sample has the characteristic of typical expansive soil. According to the physical and mechanical test of clay and powdery clay in the report of the indoor geotechnical test, the following statistical analysis is carried out on each index:
1. early preparation
When the soil is transported, the soil is seriously dehydrated and agglomerated, and the soil is smashed and sieved by a sieve with 1mm for better configuration of the expansive soil with corresponding water content.
2. Filling model box
The soil in the model box is 600mm in height and is filled in 6 layers. Each layer is filled with about 4kg of expansive soil each time, the height is about 2cm, water with calculated weight is uniformly sprayed by a small spray can, the expansive soil with 16% water content (the water content of the expansive soil is 16% in the natural state) is prepared, the soil is compacted by adopting a manual compaction method after each layer of the expansive soil is filled, the dry density of the soil body is controlled to be 1.6 by using a quality control method (the dry density of the soil is generally 1.4-1.7, but the dry density of the expansive soil is generally 1.6), and after the compaction is finished, a plastic film is covered on the surface of the soil body to prevent the evaporation of water. The soil sample was placed 7d in order to allow the pore water pressure to dissipate completely.
PVC pipes with the diameter of 50mm and the length of 300mm are buried in advance in the process of filling soil, so that grouting holes of the anchoring section of the follow-up anchor rod 9 can be manufactured. When the filling height reaches 300mm, the PVC pipe is slowly pulled out to form holes, and the hole wall is shaved by iron wires, so that the follow-up grouting body and the soil body are better bonded together.
The anchor body is poured by C30 cement, and the proportion of water to cement and sand in the mortar is 0.45:1:1. The perpendicularity of the anchor rod 9 is ensured by the upper round plug and the lower round plug of the anchor rod centering device. And during grouting, iron wires are slightly stirred, so that the integrity of the anchoring body of the pouring anchor rod 9 is ensured, and the details after pouring are shown in fig. 3.15. And after grouting is finished, covering a film for curing 28d, preventing the moisture evaporation of the soil body 8 and ensuring the strength of the anchoring body of the anchor rod 9 to meet the test requirement.
And after the curing stage is finished, continuing to fill the soil until the filling height reaches 600mm of the calibrated height, closing by using a plastic film after the compaction is finished and covering a cover as in the previous stage, so as to prevent the water from being lost and still standing to dissipate pore water pressure.
3. Stress loading and data collection
After curing, firstly connecting the strain gauge to a data acquisition instrument, opening corresponding acquisition software to enter an acquisition interface, setting parameters of the strain gauge, and inputting the elastic modulus of the anchor rod 9 to be 2 multiplied by 10 5 And (3) Mpa. Then, the prestress loading is carried out, and the hollow jack 10 is uniformly operated, so that four bolts 9 are requiredThe number of the variable sheet is evenly increased until the average value is 300KPa (the data acquisition instrument can directly convert the acquired strain into stress through software) and the anchor head is quickly locked.
The strain gauge is stuck on the anchor rod 9, the change of stress is calculated by measuring the strain of the anchor rod 9, the length of the free end of the anchor rod 9 is 300mm, the strain gauge is stuck at the position of every 100mm of the free section, and the total of four strain gauges are stuck at each position. The data acquisition instrument can directly convert the measured strain into stress, and the average value of the four stresses is taken as the stress value of the free section of the anchor rod 9.
The strain gauge adopts a resistance strain gauge with the size of BE120-3AA, the resistance value is 120.2+/-0.1 omega, and the sensitivity coefficient is 2.22+/-1%; the data acquisition instrument adopts a digital display type static strain gauge of model HJ 3816.
Automatic acquisition data are set, and the loss condition of prestress on the anchor rod 9 along with time is observed. After the anchor head is locked, observing for 1 time every 5 min; after 0.5h, observing for 1 time instead of 10 min; observing for 1 time after 1h instead of 0.5 h; thus, observation was performed 1 time every 0.5h, and after 2h, observation was performed 1 h. If the difference value of the two adjacent observation results is below 3KPa, the prestress instantaneous loss of the anchor rod is considered to be ended, and the data acquisition is ended.
The second set of tests was performed with 19% water content, first the anchor head was opened and the jack 10 was unloaded. The water quantity required to be added is calculated and uniformly added into a model box, the plastic film is sealed, kept stand and maintained for 7 days, water can be uniformly permeated into soil body while water evaporation is prevented, the soil body fully reacts, the loading process is repeated, the loaded prestress is 300KPa, and the data acquisition process is repeated.
The third and fourth sets of tests were performed at 22% and 25% water content, respectively, with the prestressing force loading and data acquisition being the same as the first two sets.
4. Test results and analysis
The result of establishing a coordinate system with time as X-axis and prestress of the anchor rod 9 as Y-axis is shown in fig. 4. From the figure the following information can be obtained:
(1) The reduction of the prestressing force can be divided into 3 phases:
a. the first stage is a prestressing force rapid reduction stage, and the time is 0-20min: this is because as the moisture content of the soil body 8 increases, the porosity of the soil body 8 increases, the clay content of the soil body 8 increases, the creep property of the soil body 8 also increases more significantly, and simultaneously, chemical and physical changes occur inside the soil body 8 under the action of water, so that the internal coupling force and the structural strength decrease, which results in rapid deformation of the soil body 8 under the action of external force within the first 20 minutes, so that the stress in the anchors 9 decreases rapidly (the unavoidable retraction of the anchor cable of the jack returns after the end of loading in actual engineering, so that the prestress is lost instantaneously, but more importantly, the influence of water on the expansion effect of the expansion soil on the anchor rod 9 tends to be studied, so the hollow jack 10 is not unloaded while the tapered end is anchored in the experimental process);
b. the second stage is a prestress slow reduction stage, and the time is 20-60min: in the first stage, the continuous external force and the creep of the self lead the porosity ratio of the soil body 8 to be reduced and the compactness to be increased, and the factors such as the reduction of the external force lead the deformation of the soil body 8 to be not so steep, so the prestress of the second stage enters a relatively slow reduction stage;
c. the third stage is a relatively stable pre-stress stage for 1-5h, in which the pre-stress is reduced slowly and the loss per hour is below 10KPa, and the system relatively reaches a relatively stable state.
(2) The water content is 16%,19%,22% and 25%, the prestress loss percentages are 52.67%,65.33%,74.67% and 87.33% respectively, and the loss ratio is increased along with the increase of the water content, which also shows that the increase of the water content makes the expansion effect of the expansive soil body more remarkable. The prestress loss in 60min accounts for 82.27%,82.65%,84.38% and 85.11% of the total loss, but in practice, more than 80% of the loss occurs in the previous hour, so that the drainage work must be quickly performed in the weather of rainwater in the practical engineering, otherwise, the prestress in the anchor rod is quickly reduced due to the action of water in a short time, and hidden danger is caused to the engineering. The prestress loss law can be seen in table 1.
TABLE 1 prestress loss law table
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (9)
1. The indoor testing method for the anchor rod stress loss is characterized by comprising an indoor testing device for the anchor rod stress loss, wherein the device comprises a model box, the model box comprises a first box body, the first box body comprises a bottom plate (1), and a first side plate (2), a second side plate (3), a third side plate (4) and a fourth side plate (5) which are arranged on the bottom plate (1) and are sequentially connected end to end; the novel soil body is characterized in that a first free steel plate (6) is vertically arranged on the inner side of the first side plate (2), a second free steel plate (7) is vertically arranged on the inner side of the second side plate (3), the first free steel plate (6), the second free steel plate (7), the first side plate (2), the second side plate (3) and the bottom plate (1) are enclosed to form a second box body, soil bodies (8) are filled in the second box body, anchor rods (9) are inserted in the soil bodies (8), and hollow jacks (10) are sleeved outside the anchor rods (9); a first jack (11) is arranged between the first free steel plate (6) and the fourth side plate (5), and a second jack (12) is arranged between the second free steel plate (7) and the third side plate (4);
the test method comprises the following steps:
s1: remolding soil (8);
s2: filling soil bodies (8) into the second box body in multiple layers, and uniformly spraying water with certain mass after each layer of soil is filled; after each layer of soil filling is completed, tamping soil body (8), covering a plastic film for primary curing, wherein the curing time is 7d;
s3: burying a PVC pipe in advance in the process of filling soil, and slowly pulling out the PVC pipe after the filling soil reaches the required anchoring length to form a grouting hole;
s4: inserting the anchor rod (9) into the grouting hole, grouting into the grouting hole, slightly stirring, covering a plastic film for secondary curing after grouting is finished, wherein the curing time is 28d;
s5: after the second curing is finished, continuing to fill the soil until the set filling height is reached, tamping the soil body (8), and sealing by using a plastic film after the tamping is finished, and performing third curing;
s6: after the third maintenance is finished, loading prestress, uniformly operating the hollow jack (10), and collecting stress applied by the hollow jack (10);
s7: data are collected, and the loss condition of stress on the anchor rod (9) along with time is observed.
2. A method of indoor testing for bolt stress loss according to claim 1, characterized in that the first free steel plate (6) is connected adjacent to the second free steel plate (7) by a flexible connection (13).
3. The indoor testing method of anchor rod stress loss according to claim 2, characterized in that a cushion block (14) is arranged between the bottom of the hollow jack (10) and the top of the soil body (8).
4. A method for indoor testing of bolt stress loss according to claim 3, characterized in that the two ends of the first jack (11) are fixed on the center of the first free steel plate (6) and the fourth side plate (5) by bolts respectively; the two ends of the second jack (12) are respectively fixed on the center of the second free steel plate (7) and the third side plate (4) through bolts.
5. The method for indoor testing of rock bolt stress loss according to claim 4, wherein in said step S2, when filling the soil body (8), the pushing distance of said first free steel plate (6) after being subjected to pressure is limited by said first jack (11), and the pushing distance of said second free steel plate (7) after being subjected to pressure is limited by said second jack (12).
6. The indoor test method for anchor rod stress loss according to claim 5, wherein in the step S2, when filling the soil body (8), the penetration speed of the soil body (8) is increased by setting a sand well, and the method specifically comprises the following steps:
s2.1: arranging at least one longitudinal sand well in the soil body (8);
s2.2: and paving a layer of middle sand at the bottom end of the soil body (8).
7. The indoor test method for anchor rod stress loss according to claim 6, wherein the specific method of step S2.1 is as follows:
and (3) embedding a plurality of plastic pipes in the model box, slowly pulling out the plastic pipes after the soil filling is finished, filling in medium sand and tightly scraping by using a fine drill rod.
8. The indoor test method for anchor rod stress loss according to claim 7, wherein the specific method of step S6 is as follows:
s6.1, applying confining pressure to the soil body (8) through the first jack (11) and the second jack (12);
s6.2, the hollow jack (10) applies prestress to the anchor rod (9), and after the applied stress reaches an experimental design value, the hollow jack (10) stops increasing the prestress and maintains the stability of the prestress.
9. The indoor test method for anchor rod stress loss according to claim 8, wherein in the step S7, the static acquisition instrument is used to record experimental data.
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| CN201710471695.5A CN107167385B (en) | 2017-06-20 | 2017-06-20 | Indoor test method for stress loss of anchor rod |
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| CN107167385B true CN107167385B (en) | 2023-07-25 |
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| CN109752266A (en) * | 2019-01-04 | 2019-05-14 | 中国地质大学（武汉） | Explosion is on gunite concrete-country rock boundary strength influence experimental rig and method |
| CN109827851A (en) * | 2019-03-22 | 2019-05-31 | 河南理工大学 | A kind of bilateral servo load an-chored body stability experimental provision and experimental method |
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