CN104763001A - Testing device and testing method suitable for creep property of anchor cable anchoring segment - Google Patents

Abstract

The invention discloses a testing device and a testing method suitable for a creep property of an anchor cable anchoring segment. In order to fill up the blank of creep property research of the pre-stressed anchor cable anchoring segment and disclose the deformation time effect between an anchor cable and a section of a grouting body, the testing device and the testing method suitable for the creep property of the anchor cable anchoring segment are provided. On the basis of a space axial symmetric equilibrium differential equation, a physical equation and a geometric equation, similar relations of all parameters are provided, and a similitude ratio of a model test is formulated. The testing device is composed of pre-stressed anchor cables (bars), a loaded jack, an anchoring device, anchoring meters, a counter-force frame, the grouting body, a modal groove and anchoring bolts from top to bottom. A monitoring device is composed of a micrometer gauge and a strain gage. According to the testing device, the creep test of the anchoring segment can be stimulated, and the pull-out test of the anchor cables (rods) can be conducted.

Description

A kind of experimental rig and test method being applicable to anchorage cable anchoring section creep properties

Technical field

The invention belongs to Geotechnical Engineering field, be specifically related to indoor model test device and the test method thereof of anchor cable creep.

Background technology

Prestressed anchorage technology because it is little to Rock And Soil disturbance, fast, the economic dispatch advantage of construction day by day becomes prefered method in side slope consolidation projects, and achieves huge economic benefit and social benefit.This efficient, economic prestressed consolidation technology have also been obtained at present and applies widely in other field of civil engineering, as engineerings such as tunnel, ship lock, dam body, underground power house, deep foundation ditchs, and how to be applied in the higher engineering of some safe classes requirement as permanent supporting measure.But by stress distribution, anchoring, the factor such as mechanical properties of materials and creep affects, loss can be there is and even lost efficacy in prestressd anchor cable, first three plants influence factor and time effect has nothing to do, Chinese scholars have also been made a large amount of experimental studies, but the research for creep properties is only confined to the deformation of creep rule under high pre-stress load action to anchoring section surrounding rock body, the research of interface creep properties between anchoring section anchor cable and injecting cement paste is not also carried out, the present invention is the blank filling up the research of prestressed cable anchorage section creep properties, disclose the deformation time effect between anchor cable and injecting cement paste interface, a kind of test method and the experimental rig that are applicable to anchorage cable anchoring section creep properties are proposed.

Be in the patent of [201310476174.0], disclose a kind of nonmetal anti-float anchor rod creep test charger at application number, although this device can implement effective loading to anchor pole, but this device jack after loading completes can not take out, and generally jack originally can produce oil return under long-time load action, namely jack provides counter-force can be more and more less, trial load is caused to be less than design load, impact test accuracy; Reaction beam adopts i iron simultaneously, although i iron bending rigidity is large, span centre still can occurs under heavily stressed load action and bend; Moreover this experimental rig can only carry out the loading of an anchor cable at every turn, anchor cable creep is a time effect process, and required time is long, thus this device to carry out creep test efficiency low.

Summary of the invention

The present invention is the deficiency overcoming prior art theory and experimental study, proposes a kind of test method and the experimental rig that are applicable to prestressed cable anchorage section creep properties.

The technical solution used in the present invention is as follows:

A kind of experimental rig being applicable to prestressed cable anchorage section creep properties, comprise a model groove, described model groove comprise two parallel arrange and be vertically fixed with the device of anchor cable, the strain meter of its distortion of test is all fixed with two anchor cable ends, one end of two anchor cables is fixed in model groove by injecting cement paste, the other end all through the reaction frame be fixed on above model groove, one of them anchor cable through after reaction frame, installation rope meter and anchor bolt on it; Another anchor cable, through after reaction frame, it is installed rope meter, punching jack, pressure sensor and anchor bolt.

Described rope meter is fixed on the top of reaction frame by anchor bolt.

Described punching jack is fixed on a jack stand, and described jack stand is fixed on the top of reaction frame.

Described pressure sensor is fixed on the top of jack by anchor bolt.

Described model groove comprises two columniform cylinders, by being welded to connect integrally structure between two cylinders, is reserved with the hole for installing anchoring leading screw in the bottom of each cylinder.

Anchoring leading screw is fixed in the hole of cylinder by described bottom of cylinder bolt, then with epoxy resin, encapsulation process is done in hole.

Be provided with two gripper shoes in the both sides of model groove, described gripper shoe is connected with the reaction frame of the side of being located thereon.

The top of described model groove is provided with dial gauge.

Said apparatus content measurement comprises anchor cable (bar) prestressing force Changing Pattern in time, anchoring section anchor cable (bar) creep, injecting cement paste distortion and free section distortion; Described anchor rod prestress is measured by rope meter, and anchoring section and free segment distortion are by measuring at anchor cable (bar) surface mount strain meter, and injecting cement paste distortion is measured by arranging fixing dial gauge on its surface.

The method of testing of said apparatus is as follows:

Step 1, according to the similarity relation of experimental rig and realistic model, determines each component;

Model groove and reaction frame are connected into entirety by step 2, and anchoring leading screw is fixed on cylinder by the bottom of cylinder bolt of model groove, with epoxy resin, encapsulation process are done in the hole of bottom of cylinder afterwards;

The step 2 within the barrel heart places the anchor cable posting strain meter, and anchor cable top is first fixed on reaction frame by anchor bolt;

Step 3 builds injecting cement paste in cylinder, and the time of the setting of maintenance at the standard conditions placed by the model after having built;

After step 4 test piece maintenance is complete, carry out prestressed stretch-draw, reaction frame places firm cushion block successively, rope meter, lower anchor bolt, jack stand, punching jack, pressure sensor and upper anchor bolt, and the dial gauge being used for measuring injecting cement paste displacement is installed at model groove top;

Step 5: first upper anchor bolt is tightened, lower anchor bolt and backing plate keep certain distance, carry out strain testing, carry out prestressed stretch-draw, after reaching design load, tighten lower anchor bolt according to design stress distribution, prestressing force on unloading punching jack;

Step 6: measure the load on rope meter, and compare with design load, if both differ by more than 100N, stretch-draw again, load when now increasing stretch-draw, loss of prestress during to offset anchoring, this process should be carried out repeatedly, until meet design requirement;

Step 7: after completing prestressed stretch-draw, measures strain and the injecting cement paste top displacement of anchoring section anchor cable, then every other day measures a reinforcing bar strain.

In described method of testing, content measurement comprises anchor cable (bar) prestressing force Changing Pattern in time, anchoring section anchor cable (bar) creep, injecting cement paste distortion and free section distortion.

Described anchor rod prestress is measured by rope meter, and anchoring section and free segment distortion are by measuring at anchor cable (bar) surface mount strain meter, and injecting cement paste distortion is measured by arranging fixing dial gauge on its surface.

In step 1, the defining method of similarity relation is as follows:

For the accuracy of guarantee test result, test model according to geometric similarity condition determination physical dimension, and should formulate corresponding test method according to content of the test, and condition of similarity of the present invention is as follows:

The physical quantity relevant to this test mainly contains

In formula: L: physical dimension; ε: strain; δ: distortion; μ: poisson's ratio; γ: material severe; C: cohesion; angle of friction; E: modulus of elasticity; σ: stress; T: time.

Subscript " p " represents prototype, and " m " represents model, then prototype and model performance parameter ratio can be expressed as: all the other basic mechanical performance parameter likelihoods ratio of (meaning of parameters provides) material are 1;

In formula:

C _l: the prototype and model physical dimension likelihood ratio;

C _e: the prototype and model modulus of elasticity likelihood ratio;

C _σ: prototype and model stress similitude ratio;

C _t: prototype and model time similarity ratio;

C _γ: the prototype and model severe likelihood ratio;

L _p, L _m: prototype and model physical dimension;

E _p, E _m: prototype and model modulus of elasticity;

σ _p, σ _m: prototype and model stress;

T _p, t _m: the prototype and model time;

γ _p, γ _m: prototype and model severe.

Prestress anchorage cable creep test model belongs to Space Axisymmetric structure, prototype Space Axisymmetric balance differential equation:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+f_z)}_p=0$

Model space axial symmetry balance differential equation:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+f_z)}_m=0$

By the likelihood ratio bring prototype Space Axisymmetric equation into, abbreviation obtains:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+\frac{C_L{C}_{\mathrm{\γ}}}{C_{\mathrm{\σ}}}{f}_z)}_m=0$

Contrast abbreviation equation and model space axial symmetry balance differential equation can draw:

C _LC _γ＝C _σ，

Can draw with reason Three Dimensional Axisymmetric Elasticity geometric equation and physical equation:

C _LC _ε＝C _δ，C _EC _ε＝C _σ

In formula:

C _ε: the prototype and model strain likelihood ratio;

C _δ: the prototype and model distortion likelihood ratio;

In the present invention, the anchoring depth likelihood ratio of experimental rig and master mould gets 1:10;

The time effect likelihood ratio is

Anchor cable diameter, injecting cement paste diameter geometric similarity is than being 1:1;

Anchor cable stress similitude ratio is 1:10,

The interface deformation likelihood ratio of reinforcing bar and injecting cement paste is 1:10.

Beneficial effect of the present invention:

1. the present invention proposes a kind of test method and test model of anchoring section creep properties, can be used for testing study on creep properties between prestress anchorage cable (bar) and injecting cement paste cross section, based on condition of similarity, formulate the rational test model basic parameter likelihood ratio.

2. formulate deformation time effect test method between anchoring section creep test injecting cement paste and prestress anchorage cable (bar) interface.

3. model groove of the present invention is splicing structure, except can carrying out the test of prestressed cable anchorage section creep properties, also can study prestressing force and Bolted Rock Masses creep and to act synergistically the loss of prestress of time anchor structure and failure mechanism experimental study.The limit resistance to plucking model investigation of prestress anchorage cable (bar) can be carried out simultaneously.

4. this device is the anchorage cable anchoring section creep test under operating mode of the same race, and the anchor cable on left side and right side contrasts parallel test each other, and left side is anchoring schematic diagram after prestress application completes, and right side is loading procedure schematic diagram; During test, the same pretightning force is implemented to two anchor cables, then experimental data is gathered, under equivalent assay conditions, loading result can be contrasted, error of observation value.

Accompanying drawing explanation

Fig. 1 is anchoring section creep test device front view;

Fig. 2 is anchoring section creep test device graphics;

Fig. 3 is anchor cable pullout tests schematic diagram;

In figure: 1. anchor bolt, 2. pressure sensor, 3. punching jack, 4. jack stand, 5. billet, 6. rope meter, 7. reaction frame, 8. anchor cable, 9. dial gauge, 10. cylinder, 11. anchoring leading screws, 12.PVC manages.

Detailed description of the invention

Below in conjunction with accompanying drawing, technical solution of the present invention is remarked additionally further:

Be applicable to test method and the experimental rig of prestressed cable anchorage section creep properties, experimental rig comprises prestress anchorage cable from top to bottom, loads jack, anchor device, rope meter, reaction frame, injecting cement paste, model groove and anchor bolt composition.Monitoring device is by dial gauge, and foil gauge forms.

Model groove comprise two parallel arrange and be vertically fixed with the cylinder 10 of anchor cable, the strain meter of its distortion of test is all fixed with two anchor cable ends, one end of two anchor cables is fixed in model groove by injection slurry, the other end is all through the reaction frame 7 be fixed on above model groove, after one of them anchor cable 8 passes reaction frame 7, installation rope meter 6 on it; Another anchor cable 8, through after reaction frame 7, it installs rope meter 6, punching jack 3 and pressure sensor 2; Rope meter 6 is fixed on the top of reaction frame 7 by anchor bolt 1.

Pressure sensor 2 is fixed on the top of jack by anchor bolt.

By being welded to connect integrally structure between two cylinders 10, be reserved with the hole for installing anchoring leading screw 11 in the bottom of each cylinder.

Anchoring leading screw is fixed in the hole of cylinder by bottom of cylinder bolt, then with epoxy resin, encapsulation process is done in hole.

Be provided with two gripper shoes in the both sides of model groove, described gripper shoe is connected with the reaction frame of the side of being located thereon.

The top of described model groove is provided with dial gauge 9.

Prestress anchorage cable (muscle) diameter is between 5 ~ 30mm, and prestress anchorage cable is 1 ~ 7 bundle, is fixed by anchor head; Prestressing force dowel is bolted, and bottom arranges punching cushion block;

Loading jack is horizontal punching jack 3, and its maximum load counter-force is not less than 300kN, and corresponding rope meter is not less than 300kN; Punching jack 3 is fixed on a jack stand 4, and described jack stand 4 is fixed on the top of reaction frame 7.

Reaction frame 7 material is carbon constructional quality steel, its length is 1m, be highly 30cm ~ 50cm, beam shape is " work " font, width is 20cm, and in the punching of model groove center position, aperture is 10 ~ 30mm, each reaction frame arranges 3 vertical supporting structures, is connected with bottom model groove by bolt.

Model groove is two cylindrical barrel structures, its material is Q235 common iron, wall thickness is 15 ~ 20mm, drum diameter is 30 ~ 50cm, be highly 40 ~ 50cm, by being welded to connect integrally structure between two cylinders, reserved 4 diameters in bottom are 10 ~ 20mm hole, arrange 4 diagonal braces between bottom and cylinder side wall.Be welded to outside cylinder on the steel plate of both sides, be connected with reaction frame by bolt.

Concrete test method is as follows:

1. utilize the device in Fig. 3 first to carry out pullout tests to prestress anchorage cable, specific as follows:

As shown in Figure 3, be applicable to the device of prestress anchorage cable pullout tests test, mainly comprise 10 cylinders and 7 reaction frames, be welded on the steel plate of both sides outside cylinder 10, be connected with reaction frame 7 by bolt.Bottom cylinder 10, reserved 4 diameters are 10 ~ 20mm hole, for settling 11 anchoring leading screws; Experimental technique is as follows:

First cylinder 9 and reaction frame 7 should be connected into entirety by bolt by step 1, be fixed on cylinder 10, with epoxy resin, 4 holes bottom cylinder 10 done encapsulation process afterwards bottom cylinder 10 with bolt by anchoring leading screw 11;

After the installation of step 2 anchoring leading screw 11, place pvc pipe 12 in center, bottom epoxy sealing, and build and simulate rock mass around;

After step 3 treats that simulation rock mass reaches some strength, take out pvc pipe 12, place the anchor cable (bar) 8 posting strain meter at cylinder 10 center, for ensureing that body does not depart from center, anchor cable (bar) 8 top should first be fixed on reaction frame 7 by anchor bolt 1;

Step 4 builds injecting cement paste in cylinder 10, and injecting cement paste height is 40cm, and the model after having built should to be placed under standard conditions (constant temperature, constant humidity) maintenance 28 days.

After step 5 test piece maintenance to 28, carry out anchor cable (bar) 8 pullout tests, punching jack 3, pressure sensor 3 and upper anchor bolt 1, anchor bolt 1 should first be tightened, and installs and be used for for thousand point 9 measuring injecting cement paste displacement and anchor pole displacement.

Before step 5 stretch-draw, first carry out strain testing, and carry out pullout tests according to CYCLIC LOADING method.

2. utilize device described as shown in Figure 1, Figure 2 to carry out the experimental study of prestressed cable anchorage section creep model

As shown in Figure 1 and Figure 2, be applicable to the experimental rig of prestressed cable anchorage section creep properties, mainly comprise 10 cylinders and 7 reaction frames, be welded on the steel plate of both sides outside cylinder 10, be connected with reaction frame 7 by bolt.Bottom cylinder 10, reserved 4 diameters are 10 ~ 20mm hole, and for settling 11 anchoring leading screws, concrete test procedure is as follows:

First cylinder 9 and reaction frame 7 should be connected into entirety by bolt by step 1., be fixed on cylinder 10, with epoxy resin, 4 holes bottom cylinder 10 done encapsulation process afterwards bottom cylinder 10 with bolt by anchoring leading screw 11;

After the installation of step 2. anchoring leading screw 11, place the anchor cable (bar) 8 posting strain meter at cylinder 10 center, for ensureing that body does not depart from center, anchor cable (bar) 8 top should first be fixed on reaction frame 7 by anchor bolt 1;

Step 3. builds injecting cement paste in cylinder 10, and injecting cement paste height is 40cm, and the model after having built should to be placed under standard conditions (constant temperature, constant humidity) maintenance 28 days.

After step 4. test piece maintenance to 28, carry out prestressed stretch-draw, reaction frame 7 successively places firm cushion block 5, rope meter 7, lower anchor bolt 1, jack stand 4, punching jack 3, pressure sensor 3 and upper anchor bolt 1 are also installed dial gauge 9 and are used for measuring injecting cement paste displacement.

Upper anchor bolt 1 is first tightened by step 5., and lower anchor bolt 1 keeps certain distance, before stretch-draw with backing plate 5, first should carry out strain testing, carry out prestressed stretch-draw, after reaching design load according to design stress distribution, tighten lower anchor bolt 1, prestressing force on unloading punching jack 3.

Step 6. measures the load on rope meter 5, and compares with design load, if both differ by more than 100N, again stretch-draw should be carried out, load when now should increase stretch-draw, loss of prestress during to offset anchoring, this process should be carried out repeatedly, until meet design requirement.

After step 7. completes prestressed stretch-draw, measure the strain of anchoring section reinforcing bar and injecting cement paste top displacement, every other day measure a reinforcing bar strain later.

In step 1, the defining method of similarity relation is as follows:

For the accuracy of guarantee test result, test model according to geometric similarity condition determination physical dimension, and should formulate corresponding test method according to content of the test, and condition of similarity of the present invention is as follows:

The physical quantity relevant to this test mainly contains

In formula: L: physical dimension; ε: strain; δ: distortion; μ: poisson's ratio; γ: material severe; C: cohesion; angle of friction; E: modulus of elasticity; σ: stress; T: time.

Subscript " p " represents prototype, and " m " represents model, then prototype and model performance parameter ratio can be expressed as: all the other basic mechanical performance parameter likelihoods ratio of (meaning of parameters provides) material are 1;

In formula:

C _l: the prototype and model physical dimension likelihood ratio;

C _e: the prototype and model modulus of elasticity likelihood ratio;

C _σ: prototype and model stress similitude ratio;

C _t: prototype and model time similarity ratio;

C _γ: the prototype and model severe likelihood ratio;

L _p, L _m: prototype and model physical dimension;

E _p, E _m: prototype and model modulus of elasticity;

σ _p, σ _m: prototype and model stress;

T _p, t _m: the prototype and model time;

γ _p, γ _m: prototype and model severe.

Prestress anchorage cable creep test model belongs to Space Axisymmetric structure, prototype Space Axisymmetric balance differential equation:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+f_z)}_p=0$

Model space axial symmetry balance differential equation:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+f_z)}_m=0$

By the likelihood ratio bring prototype Space Axisymmetric equation into, abbreviation obtains:

${(\frac{\∂{\mathrm{\σ}}_z}{\∂z}+\frac{\∂{\mathrm{\τ}}_{\mathrm{\ρz}}}{\∂\mathrm{\ρ}}+\frac{{\mathrm{\τ}}_{\mathrm{\ρz}}}{\mathrm{\ρ}}+\frac{C_L{C}_{\mathrm{\γ}}}{C_{\mathrm{\σ}}}{f}_z)}_m=0$

Contrast abbreviation equation and model space axial symmetry balance differential equation can draw:

C _LC _γ＝C _σ，

Can draw with reason Three Dimensional Axisymmetric Elasticity geometric equation and physical equation:

C _LC _ε＝C _δ，C _EC _ε＝C _σ

In formula:

C _ε: the prototype and model strain likelihood ratio;

C _δ: the prototype and model distortion likelihood ratio.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (10)

1. one kind is applicable to the experimental rig of anchorage cable anchoring section creep properties, it is characterized in that: comprise a model groove, described model groove comprise two parallel arrange and be vertically fixed with the device of anchor cable, the strain meter of its distortion of test is all fixed with two anchor cable ends, one end of two anchor cables is fixed in model groove by injection slurry, the other end all through the reaction frame be fixed on above model groove, one of them anchor cable through after reaction frame, installation rope meter on it; Another anchor cable, through after reaction frame, it is installed rope meter, punching jack and pressure sensor.

2. experimental rig as claimed in claim 1, is characterized in that: described rope meter is fixed on the top of reaction frame by anchor bolt.

3. experimental rig as claimed in claim 1, is characterized in that: described punching jack is fixed on a jack stand, and described jack stand is fixed on the top of reaction frame.

4. experimental rig as claimed in claim 1, is characterized in that: described pressure sensor is fixed on the top of jack by anchor bolt.

5. experimental rig as claimed in claim 1, is characterized in that: described model groove comprises two columniform cylinders, by being welded to connect integrally structure between two cylinders, being reserved with the hole for installing anchoring leading screw in the bottom of each cylinder.

6. experimental rig as claimed in claim 5, is characterized in that: anchoring leading screw is fixed in the hole of cylinder by described bottom of cylinder bolt, then with epoxy resin, encapsulation process is done in hole.

7. experimental rig as claimed in claim 1, is characterized in that: be provided with two gripper shoes in the both sides of model groove, described gripper shoe is connected with the reaction frame of the side of being located thereon.

8. be applicable to the experimental rig of prestressed cable anchorage section creep properties as claimed in claim 1, it is characterized in that: the top of described model groove is provided with dial gauge.

9. experimental rig as claimed in claim 1, is characterized in that: described experimental rig and the similarity relation of realistic model are: C _lc _γ=C _σ, C _lc _ε=C _δ, C _ec _ε=C _σ;

Wherein: C _l: the prototype and model physical dimension likelihood ratio; C _e: the prototype and model modulus of elasticity likelihood ratio; C _σ: prototype and model stress similitude ratio; C _t: prototype and model time similarity ratio; C _γ: the prototype and model severe likelihood ratio, C _ε: the prototype and model strain likelihood ratio; C _δ: the prototype and model distortion likelihood ratio.

10. the test method of experimental rig as claimed in claim 9, is characterized in that:

The similarity relation of step 1 experimentally device and realistic model, determines each component;

Model groove and reaction frame are connected into entirety by step 2, and anchoring leading screw is fixed on cylinder by the bottom of cylinder bolt of model groove, with epoxy resin, encapsulation process are done in the hole of bottom of cylinder afterwards;

The step 2 within the barrel heart places the anchor cable posting strain meter, and anchor cable top is first fixed on reaction frame by anchor bolt;

Step 3 builds injecting cement paste in cylinder, and the time of the setting of maintenance at the standard conditions placed by the model after having built;

After step 4 test piece maintenance is complete, carry out prestressed stretch-draw, reaction frame places firm cushion block successively, rope meter, lower anchor bolt, jack stand, punching jack, pressure sensor and upper anchor bolt, and the dial gauge being used for measuring injecting cement paste displacement is installed at model groove top;

Step 5: first upper anchor bolt is tightened, lower anchor bolt and backing plate keep certain distance, carry out strain testing, carry out prestressed stretch-draw, after reaching design load, tighten lower anchor bolt according to design stress distribution, prestressing force on unloading punching jack;

Step 6: measure the load on rope meter, and compare with design load, if both differ by more than 100N, stretch-draw again, load when now increasing stretch-draw, loss of prestress during to offset anchoring, this process should be carried out repeatedly, until meet design requirement;

Step 7: after completing prestressed stretch-draw, measures strain and the injecting cement paste top displacement of anchoring section anchor cable, then every other day measures a reinforcing bar strain.