The anchoring technology is extensively applied in reinforcing protection of the earth relics. Now that no specification is available for different new anchor rods in earth relics protection due to diversified destruction modes of earth relics and complexity of engineering technology conditions, it is urgent to guide reinforcing design and construction with a complete detailed anchor rod research document. With the new carbon fiber
The anchor rod is mainly applied in two aspects in earth relics protection. First, it is used to pull and connect the new built adobe and earth relics. For possible unstable erosive area, it is the most effective protection method to build the adobe. To make the adobe and earth relics bear the force together, after repair building, the building body should be connected with the body of the relics by using an anchor rod. The connected wall features better integrity and higher rupture and vibration resistance. Second, the anchor rod is used to reinforce the structural crack in the body of the relics by using an anchor rod based on grouting [
The anchoring technology is extensively applied in reinforcing protection of earth relics. Now that no specification is available for different new anchor rods in earth relics protection due to diversified destruction modes of earth relics and complexity of engineering technology conditions, it is urgent to guide reinforcing design and construction with a complete detailed anchor rod research document [
Now application problems of the anchoring technology in earth relics protection are described as follows [ Some references show that the size of the anchoring force is related to the length of the anchor rod, diameter of bore, diameter of the anchor rod, strength of the grouting body, surface state of the rod body, and inclination angle. Only influences of anchoring length and grouting body on the anchoring force are studied in the past anchor rod research of the earth relics. No systematic research on factors affecting anchor body stress distribution is conducted. Most experiments on the anchor rod of earth relics mainly focus on anchoring force of the anchor rod. Few researchers focus on stress distribution of the anchor rod in the earth relics, which obstructs research on application of anchoring theory in earth relics protection.
For Gaochang Ruins protection engineering, by conducting in situ experiment of the carbon fiber
The
Carbon fiber
A total of six independent experiment lots are designed, including 20 experiment teams and 3 experimental parts for each team. Six independent experimental lots are divided as follows: anchor rod length
Design parameter of each specimen grouping.
Factor | Parameter | ||||||
---|---|---|---|---|---|---|---|
Anchor rod length (mm) | Anchor rod diameter (mm) | Bore diameter (mm) | Grouting number | Fiber winding distance (mm) | Deployment angle of anchor rod | The number or anchor rod | |
|
800 | 33 | 85 | N1 | 75 | 0° | 3 |
1200 | 3 | ||||||
1500 | 3 | ||||||
2000 | 3 | ||||||
3000 | 3 | ||||||
|
1500 | 25 | 85 | N1 | 75 | 0° | 3 |
35 | 3 | ||||||
55 | 3 | ||||||
|
1500 | 33 | 75 | N1 | 75 | 0° | 3 |
85 | 3 | ||||||
110 | 3 | ||||||
|
1500 | 33 | 85 | N1 | 75 | 0° | 3 |
N2 | 3 | ||||||
N3 | 3 | ||||||
|
1500 | 33 | 85 | N1 | 0 | 0° | 3 |
30 | 3 | ||||||
150 | 3 | ||||||
|
1500 | 33 | 85 | N1 | 75 | 0° | 3 |
10° | 3 | ||||||
15° | 3 |
The influences of different lots on anchoring force of the anchor rod should be considered, respectively. The field experimental conditions of each experimental lot are independent of each other. The single-factor test method is used. Influence of single factor on anchoring force is considered under same environmental conditions. Other five influence factors are not changed. Three proportioning is used for grouting body. For the strength of proportioning of the grouting body, refer to the material performance test of the grouting body.
The diameter of the
The 20 mm wide fiber is wound by three layers along the vertical direction of the anchor rod, and the spacing is identified in the test scheme. The end is wound by five layers and then is uniformly coated with epoxy resin. The epoxy resin should be soaked into the carbon fiber cloth in case of coating to closely stick the
The strain foil of the test anchor rod should be deployed at two ends, 1/4 position, 1/2 position, and 3/4 position. The compensator should be deployed around the middle position. After the strain foil is stuck according to the requirements, the lead wire and shielding leads are welded with the tin. The leads are numbered from inside to outside. The installed strain foil should be protected with reliable and practicable measures. The nude part of the strain foil should be coated with the epoxy resin and wound with waterproof tape. Finally one layer of epoxy resin is coated for protection. For the experiment anchor rod diagram, refer to Figure
The experiment anchor rod diagram. (1) Rebar; (2)
The manufacture of the experiment anchor rod.
The
The specimens of bamboo.
Three groups of sample parts are, respectively, prepared. The rate of water content of the bamboo is about 11.5%. The tensile test (Figure
The extension test.
The bending test.
The tensile strength along the grain of the bamboo material.
Specimen number | Moisture content | The tensile strength along the grain (MPa) | The average value (MPa) |
---|---|---|---|
BS1 | 11.2% | 304.9 | 314.1 |
BS2 | 11.8% | 309.7 | |
BS3 | 12.3% | 327.6 |
The tensile elasticity modulus along the grain of the bamboo material.
Specimen number | Moisture content | Tensile elasticity modulus along the grain 104 (MPa) | The average value 104 (MPa) |
---|---|---|---|
BSE1 | 12.1% | 3.80 | 3.83 |
BSE2 | 11.3% | 3.91 | |
BSE3 | 11.6% | 3.78 |
The flexural strength along the grain of the bamboo material.
Specimen number | Moisture content | The flexural strength along the grain (MPa) | The average value (MPa) |
---|---|---|---|
BB1 | 11.5% | 213.9 | 214.6 |
BB2 | 11.4% | 217.6 | |
BB3 | 11.8% | 212.2 |
The flexural modulus along the grain of the bamboo material.
Specimen number | Moisture content | The flexural modulus along the grain 104 (MPa) | The average value 104 (MPa) |
---|---|---|---|
BBW1 | 12.5% | 1.5897 | 1.5814 |
BBW2 | 11.3% | 1.5634 | |
BBW3 | 11.8% | 1.5912 |
The Gaochang Ruins wall body (Figure
Gaochang Ruins wall: a view.
Physical and mechanical parameters of rammed earth.
Test lock | Moisture content, |
Density, |
Angle of internal friction, |
Cohesion strength, |
Elastic modulus, |
---|---|---|---|---|---|
1 | 3.1 | 1.76 | 25.1 | 28.3 | 17.94 |
2 | 2.9 | 1.82 | 24.8 | 29.2 | 18.88 |
3 | 2.4 | 1.85 | 23.5 | 25.5 | 20.03 |
Average | 2.8 | 1.81 | 24.4 | 27.67 | 18.95 |
Proportion three grouting bodies according to the actual engineering experiences. The grouting body proportioning is calculated by the weight proportioning [ No. 1 grouting body proportioning: earth : cement : flyash = 85 : 5 : 10. 5% ludox emulsion is mixed. No. 2 grouting body proportioning: earth : cement : flyash = 80 : 10 : 10. 5% sweller is used. No. 3 grouting body proportioning: earth : cement : flyash = 70 : 20 : 10. 5% sweller emulsion is mixed.
The ratio of water to ash of the three slurries is 31% (weight ratio). The 70.7 × 70.7 mm mortar test die is used to make the grouting test block. After 34-day maintenance, its compressive mechanical performance is shown in Table
The mechanical performance of the grouting.
Test block | Number | Compression strength (MPa) | Compression elastic modulus 105 (MPa) | ||
---|---|---|---|---|---|
Experimental value | Average | Experimental value | Average | ||
No. 1 | 1 | 1.94 | 1.92 | 62.35 | 61.26 |
2 | 1.83 | 55.66 | |||
3 | 1.98 | 65.78 | |||
No. 2 | 1 | 1.81 | 1.84 | 67.95 | 68.38 |
2 | 1.82 | 68.04 | |||
3 | 1.90 | 69.14 | |||
No. 3 | 1 | 6.54 | 6.28 | 178.8 | 178.5 |
2 | 6.02 | 168.3 | |||
3 | 6.27 | 188.4 | |||
2 | 6.02 | 168.3 | |||
3 | 6.27 | 188.4 |
The west section of the rampart in the Gaochang Ruins is selected as the experimental section. The drawing resistance test of the anchor rod is performed on the rammed earth wall relics. The whole process is completed at the construction field. The geological conditions are same as those of the reinforcing objects.
Drilling is performed according to the test scheme. Vibration-free machinery is used for drilling. The vertical and horizontal spacing between holes is more than 1 m to avoid mutual influences. Protective supports should be used to secure relics and persons.
Clean bore diameter and moisture it prior to grouting. Clean the bore diameter by using an electric blower’s peripheral bushing, and moisture it with soft brush and small sprinkler.
Place the grouting pipe and anchor rod into the bore simultaneously, remotely transport grouting with a hose, and avoid vibration influences of grouting machinery. The distance from the grouting pipe end to bore bottom should be 100 mm.
The grouting pressure of the grouter is 0.5 MPa. The grouting should be grouted densely. 100 mm deep grouting materials (modified loess grouting) are used for grouting and anchoring at two ends of the bore. The field anchoring test parts are shown in Figure
The field anchoring test parts.
The structure of the anchor rod. (1) Rebar; (2) epoxy mortar; (3)
The ZY-10 anchor rod tension meter from Chinese Coal Science Research Institute is used as the dynamometer (Figure
Test apparatus. (a) Pullout apparatus and the reaction frame. (b) The TDS-303 data collection instrument.
The experimental device diagram. (1) Anchorage; (2) magnetic stand; (3) displacement sensor; (4) support displacement sensor; (5) reaction frame; (6) wood footplate; (7) load sensor; (8) hollow jack; (9) rebar; (10) grouting; (11)
The experiment was performed in Gaochang Ruins, Turpan, Sinkiang. After the grouting body is fully solidified (about 50 days), the in situ drawing test is performed for the embedded anchor rod due to experimental place and weather factor.
500 N pulling force is first applied prior to loading to eliminate the force gap between devices. The pulling force is slowly and continuously applied. 200 N force is applied per second till the test part is destructed [
Arrange experimental data, observe and record experimental phenomena, and get the drawing destruction mode and ultimate anchoring force in different experimental groups shown in Tables
The test results by different anchor rod length.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
L8-1 | Anchor pullout | 12.3 | 12.45 |
L8-2 | Anchor pullout | 12.6 | |
L8-3 | Anchor-end split, rebar slip | 8.3 |
|
L12-1 | Anchor pullout | 15.5 | 14.85 |
L12-2 | Anchor pullout | 14.2 | |
L12-3 | Anchor-end split, rebar slip | 12.2 |
|
L15-1 | Anchor pullout | 19.6 | 18.47 |
L15-2 | Anchor pullout | 17.2 | |
L15-3 | Anchor pullout | 18.6 | |
L20-1 | Anchor pullout | 29.7 | 31.60 |
L20-2 | Anchor pullout | 33.5 | |
L20-3 | Anchor-end split, rebar slip | 22.4 |
|
L30-1 | Soil-part loosening | 30.6 |
45.90 |
L30-2 | Anchor pullout | 43.5 | |
L30-3 | Anchor-end split, grout-soil interface damage | 48.3 |
The test results by different anchor rod diameter.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
D25-1 | Anchor pullout | 10.5 | 11.53 |
D25-2 | Anchor pullout | 12.8 | |
D25-3 | Anchor pullout | 11.2 | |
D35-1 | Anchor pullout | 18.7 | 17.50 |
D35-2 | Anchor pullout | 17.6 | |
D35-3 | Anchor pullout | 16.2 | |
D55-1 | Anchor-end split, anchor pullout | 18.4 | 21.23 |
D55-2 | Anchor pullout | 23.6 | |
D55-3 | Anchor pullout | 21.7 |
The test results by different bore diameter.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
H75-1 | Anchor pullout | 15.5 | 16.65 |
H75-2 | Anchor-end split, grout-soil interface damage | 14.2 |
|
H75-3 | Anchor pullout | 17.8 | |
H85-1 | Anchor-end split, anchor pullout | 20.3 | 18.70 |
H85-2 | Anchor pullout | 19.7 | |
H85-3 | Anchor pullout | 16.1 | |
H110-1 | Anchor pullout | 26.5 | 24.9 |
H110-2 | Grout-part loosening | 18.8 |
|
H110-3 | Anchor-end split, anchor pullout | 23.3 |
The test results by different grouting strength.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
S1-1 | Anchor-end split | 9.4 |
16.15 |
S1-2 | Anchor pullout | 15.1 | |
S1-3 | Anchor pullout | 17.2 | |
S2-1 | Anchor pullout | 17.6 | 16.40 |
S2-2 | Anchor pullout | 16.2 | |
S2-3 | Anchor pullout | 15.4 | |
S3-1 | Anchor pullout | 15.9 | 17.20 |
S3-2 | Anchor pullout | 17.5 | |
S3-3 | Anchor pullout | 18.2 |
The test results by different surface state.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
R0-1 | Anchor pullout | 11.2 | 9.77 |
R0-2 | Anchor pullout | 9.4 | |
R0-3 | Anchor pullout | 8.7 | |
R75-1 | Anchor pullout | 15.9 | 17.23 |
R75-2 | Anchor pullout | 19.6 | |
R75-3 | Anchor pullout | 16.2 | |
R150-1 | Anchor pullout | 14.3 | 13.43 |
R150-2 | Anchor pullout | 13.2 | |
R150-3 | Anchor pullout | 12.8 |
The test results by different deployment angle of anchor rod.
Number | Destruction mode | Fracture load (kN) | Average (kN) |
---|---|---|---|
A0-1 | Anchor pullout | 19.3 | 17.76 |
A0-2 | Anchor pullout | 17.2 | |
A0-3 | Anchor pullout | 16.8 | |
A10-1 | Soil-part loosening | 10.4 |
16.25 |
A10-2 | Anchor pullout | 15.8 | |
A10-3 | Anchor pullout | 16.7 | |
A15-1 | Anchor-end split, grout-soil interface damage | 9.2 |
14.95 |
A15-2 | Anchor pullout | 14.7 | |
A15-3 | Anchor pullout | 15.2 |
As could be seen from the experimental results, there were four types of anchorage system failure: anchor pullout (Figure
Most cases fell into the category of “anchor pullout.” This was mainly due to the anchor-grout interface sliding owing to the insufficiently high anchoring force against the grout generated by relatively short anchors.
The anchoring force is relatively big, and the shift is small in case of grout-soil interface damage. The force of the anchoring system is fully exerted. Based on analysis on the force, the grout-soil interface damage is an ideal destruction mode of the anchoring system, though it should not occur in relics protection.
The anchor-end split and the epoxy rebar are drawn out. This destruction is caused because the inner wall of
Soil-part loosening is due to visible crackles that appear in the earth around the grouting. This destruction only happens at two places in the experiment and is related to the earth characteristics of the anchoring position. The earth characteristics of the anchoring part should be fully considered in anchoring design of the earth relics, which should be excessively intervened.
The destruction modes are not separate in the experiment. Generally multiple destruction forms happen in the process from initial drawing of the anchoring system to final destruction. The destruction with bigger shift of the anchoring system should be regarded as the final destruction.
By analyzing the
From the macroview, bigger anchoring system will lead to bigger ultimate anchoring force, but too big geometric size will lead to local destruction of the anchoring system, in which case the anchoring system cannot fully realize anchoring and the body of the relics will be destructed.
15 m long From the experimental results of From experimental results of
Increased anchoring deployment angle will reduce the ultimate anchoring force because the pulling force is perpendicular to the wall while the anchor rod is not perpendicular to the wall in the experiment, leading to press rupture of local earth around the anchor rod and early exit of the anchoring system.
It is not preferential to horizontally deploy the anchor in actual application. The deployment angle of the anchor rod is designed according to the force of the anchored body to keep the action line of the anchoring force coincide with the action line of the sliding force as much as possible (Figure
The main destruction mode. (a) Anchor pullout. (b) Grout-soil interface damage. (c) Anchor-end split. (d) Soil-part loosening.
By removing bad values in experiment groups and averaging experimental results, we can get the P-S load shift curve of
The curve of L-P-S.
The curve of D-P-S.
The curve of H-P-S.
The curve of 16 S-P-S.
The curve of R-P-S.
The curve of A-P-S.
Influences of anchoring length
The L-P-S curve (Figure Influences of anchoring diameter
The D-P-S curve (Figure Influences of bore diameter
The H-P-S curve (Figure Influences of grouting body strength
The S-P-S curve (Figure Influences of anchor rod surface state
The R-P-S curve (Figure
It indicates that change of anchor rod surface state can effectively increase the ultimate anchoring force and control the shift. By analyzing the destruction mode in Section Influences of anchoring deployment angle
The A-P-S curve (Figure
The destruction results show that generally the anchoring system is ineffective when the pulling force reaches the ultimate load, the anchoring system has no visible destruction symptom, and the anchor rod is suddenly drawn out. Sufficient security preparations should be made when the anchor rod technology is used in design due to significance of relics protection engineering. The anchoring system should be on the elastic phase. By combining practical applications, 30% of the ultimate load
Six experimental lots (
The permitted application value
|
|
|
|
|
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|---|---|---|
L8 | 3.72 | D25 | 3.46 | H75 | 5.00 | S1 | 4.85 | R0 | 2.93 | A0 | 5.33 |
L12 | 4.46 | D35 | 5.25 | H85 | 5.61 | S2 | 4.92 | R150 | 4.03 | A10 | 4.88 |
L15 | 5.54 | D55 | 6.37 | H110 | 7.47 | S3 | 5.16 | R75 | 5.17 | A15 | 4.49 |
L20 | 9.3 | — | — | — | — | — | — | — | — | — | — |
L30 | 13.77 | — | — | — | — | — | — | — | — | — | — |
We can get strain distribution curve (Figures
The curve of
The curve of
The curve of
The curve of
The curve of
The curve of
Influences of anchor rod length
The
On the whole, longer anchor length indicates more uniform stress distribution and smaller adjacent strain change under action of the permitted application value Influences of anchoring diameter
The
The pulling and shearing action is the main factor to destruct the anchor rod in the pulling force anchor rod. Based on the above test conclusion, the bigger diameter of the anchoring body is preferred, so the shear stress on the anchoring body can be uniform. The diameter of the anchoring body cannot be increased without a limitation due to influences of material properties of the grouting body. When the diameter increases to certain extent, its contribution to the ultimate anchoring force is not significant. Influences of bore diameter
The Influences of grouting body strength
The Influences of the anchor rod surface state
The Influences of anchoring deployment angle
The
The following conclusions can be concluded from in situ drawing experiment of the anchor rod of the rammed earth relics: The destruction does not separately happen in the experiment. When the anchoring system is drawn till final destruction, generally multiple destruction forms will be accompanied. The anchoring system mainly becomes ineffective due to debonding and sliding between the anchor rod and grouting body interface and shift between grouting body and earth body, and rupture of pipe hole grouting body and earth relics body cutting and expansion are accompanied.
The anchoring force is bigger, and the shift is smaller in case of destruction between the grouting body and earth body, so the force of the anchoring system is fully exerted. This destruction is an ideal destruction mode from the view of mechanics, but this destruction form is unfavorable to relics protection. Draw-out destruction of the anchor rod is favorable to protection over the earth relics body.
We recommend that anchorage strength should not be the sole factor for consideration in designing anchoring systems for earthen heritage sites. Characteristics of the earthen fabric around the drive-in point are also to be taken into full accounts. It is essential that a site itself is protected and the minimum intervention principle is observed.
Bigger
For earthen heritage sites with higher strength, shorter and thicker anchor piles are required while for those with lower strength, longer and thinner ones. Piles could thus function more effectively in load bearing. As the analysis of the rammed earth of Gaochang city walls revealed, parameters The
Therefore for the anchoring system, performance enhancing is not advisable to be achieved by an increase of strength in the grout body. For the rammed earth of Gaochang city walls, grout body S2 has been proved suitable for anchoring needs. The
With decrease of the rib spacing on the surface of the anchor rod, the peak strain of the anchor rod will increase and the strain distribution becomes centralized. If the surface of the anchor rod is too coarse, it will lead to destruction between the grouting body and earth body and is unfavorable to relics protection.
The surfaces of anchor piles, fashioned of The
A qualitative stability analysis for a site is advised to precede anchor pile designing. Potential surfaces of failure could thus be located to inform the design and installation processes.
The authors declare that they have no conflicts of interest.
This study was sponsored by the Youth Science and Technology Fund of Xi’an University of Architecture & Technology, Xi’an, China (Grant no. QN1531), and Fund of Shaanxi Province Education Department (Grant no. 16JK1430). In the preparation of the paper, the authors hold gratitude for Mr. Xi Lin for his suggestions in proofreading and English wording.