As a relatively new construction technology, self-drilling hollow anchors have been gradually applied in the retaining wall slope protection in recent years, and solved some technical problems in anchorage construction of loose rock and soil. In the construction of slope protection and support for a project, self-drilling hollow anchors are adopted to overcome the problems of easy collapse of holes and difficulty in forming holes in rock bolts in extremely loosely broken rock and soil. stable. The following is a summary of the method of self-drilling hollow anchors anchored into holes in slope protection construction.
1. Characteristics of self-drilling hollow anchors Self-drilling hollow anchors are hollow anchors. The bolts are threaded through the body and are connected by long sleeves. The front end is fitted with a disposable drill.
1.1 The special structure of self-drilling hollow anchors is used for anchorage construction with the following advantages: (1) high construction efficiency; (2) suitable for difficult formation of pores; (3) strong adaptability; (4) high anchorage force; (5) Good anchorage effect; (6) Simple construction 1.2 Slope protection works Overview Pipeline design of this project is designed to output 5.75 million tons/year, and the initial output is 450,000 tons/year (intermittent delivery). The transportation oils are 93# gasoline, 97# gasoline and diesel. Nanning Station is the incoming oil from the North Sea. The oil pipeline is φ508 × 8.7 and then transferred to Baise, φ456 × 7.9, and merged with Maoming-Guiyang Section 11 million tons/year increase transmission reconstruction project Nanning-Litang Section together. The three stations were merged together to construct and connect with each other, and they were transferred to each other. The design pressure of the long-distance pipeline main line was 9.5 MPa, and the main pipe was L415 (APl5LX60 pipeline steel).
The main contents of this project include site leveling, general plans, technology, electrical, instrumentation, water supply and drainage, and large-scale slope protection. Newly-built mixing tanks and discharge tanks; new ball collection area. The process pipeline extends from the original pure download function to receiving the pressurized transport function from the North Sea to the southwestern pipeline and the Baise branch line.
The site of the station is hillside. The geology of the slope is a eroded residual hillock landform, and the terrain is undulating. The planned elevation of the proposed site is 107.5-108.1 meters, which is mainly an excavation slope. The main working face of the project is located on the west side and the south side of the site. The height of the slope on the west side of the hillside is 24.2m, the height in the southwest corner is 26m, and the height on the south side is 19.4m. According to the requirements of the design drawings, the station must be dug up to one-third of the three links and one flat, and an open space with a length of 130 meters and a width of 100 meters should be used for construction. Therefore, the amount of earthwork in the project is relatively large and the difficulty in construction of the slope bolt hole is high.
The main workload of the slope is: 1120m3 for C30 retaining wall, 1826m for φ130 anchorage, 550m for C20 rubble concrete, 4300m for φ90 anchor and 2400m2 for grid.
1.3 The characteristics of this slope protection construction The construction slope is a permanent slope. According to the design requirements, the four slopes are divided into two levels of protection;
The first-grade slope of No. 1 slope is protected by C20 rubble concrete, with a height of 6m and a slope ratio of 1:0.3. The second-grade slope adopts a concrete grid frame protection surface, and the grid is planted with green grass.
The No. 2 slope side slope is protected by a C30 retaining wall with a height of 8-10m, a retaining wall thickness of 50cm, a basic buried depth of 1m, and two rows of walls with 4×7φ5 pressure-dispersed prestressed anchorage anchorage. The length of the anchor cable is 20-22m, the spacing is 4m, staggered arrangement, the design load is 500KN. The second-grade slope adopts a concrete grid frame protection surface, and the grid is planted with green grass. The slope ratio is 1:1.2.
On the first edge of No. 3 slope, the C30 retaining wall is used for protection, the height is 12m, the thickness of the retaining wall is 50cm, and the basic buried depth is 1m. The wall body is provided with three rows of 4×7φ5 pressure dispersion type prestressed anchorage anchorage. The length of the anchor cable is 20-24m, the spacing is 4m, staggered arrangement, and the design load is 500KN. The second-grade slope adopts a concrete grid frame protection surface, and the grid is planted with green grass. The slope ratio is 1:1.2.
On the first side of No. 4 slope, the C30 retaining wall is used for protection, and the height is 12m. The thickness of the retaining wall is 50cm, and the basic depth is 1m. The three walls of the wall are designed with 4×7φ5 pressure-dispersed prestressed anchorage. The length of the anchor cable is 20-24m, the spacing is 4m, staggered arrangement, and the design load is 500KN. The second-grade slope uses a concrete grid frame protection surface, the slope ratio is 1:0.6, and the frame joints are provided with 5 rows of qb28 full-length bonded anchor rods with a length of 9-12m, and the grass is planted with green grass.
Due to the complex geological conditions of this slope, ordinary anchor support methods are difficult to form into holes and are difficult to work. Therefore, the use of self-drilling hollow bolts effectively solves the difficult problem of anchoring holes in loose rock and soil. It also has the advantages of high construction efficiency and guaranteed construction quality, especially the use of self-drilling with larger diameters and depths. Hollow anchors are effective. Self-drilling bolt construction technology is simple, easy to operate, and has high reliability. It is suitable for loose rock and soil slope support.
1.4 Application of self-drilling hollow anchors in holes anchored in slopes Due to the difficulty in solving the problem of hole formation by conventional methods, we decided to use self-drilling hollow anchors on slopes No. 2, No. 3 and No. 4. Support for poor geological conditions.
To demonstrate the feasibility of using self-drilling hollow anchors for slope support, we conducted a total of two stages of self-drilling hollow anchor anchoring construction process tests. Four holes were drilled in the first phase and the second phase test drills. Two holes, totaling 72 meters of trial bolts.
The test area is located on the lower side of the No. 2 slope. The stratum in this section is mainly weathered argillaceous sandstone, and the geological conditions are slightly better than the actual support construction area.
The main test content: 1, drilling process test; 2, grouting process test.
1. Drilling process test drilling rig adopts QZJ-100D DTH drilling rig and Yuchai-12m3 air compressor for air supply. A three-page drill with an aperture of φ90 mm was used, and the drill was tested for 90 mm.
The drilling rig power head is connected to a self-drilling bolt to perform rotary drilling. The air compressor is used for air drilling. The drilling speed is even and the air is emptied. The impact is installed between the self-drilling bolt and the power head. For top drive impact drilling.
2. Grouting technology test This project uses grouting from the center hole of the self-propelled anchor rod. The ratio of slurry is: water: ash = 1:0.5. After the slurry reaches the bottom of the hole through the center hole of the self-drilling bolt, the slurry returns from the hole bottom to the hole along the anchor rod and the hole wall. The perfusion pressure is 0.3-0.5Mpa.
3. Basic conclusions of the test The borehole test showed the use of 50 self-drilling anchors.
1.5 Actual construction conditions on site The self-drilling bolts are arranged according to the hole and row spacing of 2m×2m. The total project volume is 3808.6m2 for retaining wall, 2588m for anchor cable, 4861m for lattice beams, and 3048m for anchor bolts. The deepest hole is 24m, and the shallowest hole is 9m.
The construction sequence of self-drilling bolts is:
Drilling positioning → drilling with open hole → acceptance of hole depth → installing anchor bolts → grouting → hanging reinforcement mesh → concrete spraying → pouring of anchor piers → construction of drainage holes 1. Installation of self-drilling hollow anchor drilling with anchor rod The preliminary results are guided by the Ministry of Education. The Ministry of Construction further studies countermeasures based on specific issues during construction.
For the stratum with large thickness of overburden and less content of rock and gravel, the method of adopting anchor rod as drill pipe and rotary drilling has good effect.
For the formations dominated by fully weathered rock, holes are drilled using conventional methods for drilling holes with a hole diameter of φ990. After the final hole comes out of the drilling tool, the original hole is generally collapsed, and the drilling machine is drilled again with a self-drilling bolt. Reach the original hole depth. Although one more hole was drilled, it solved the problem that the hole depth of large formations was not large in the case of the rotary drilling method. The self-drilling bolt could be installed smoothly.
Construction according to the above two methods can cope with various complex conditions of the formation and the construction efficiency is also high.
2. The grouting of self-drilling hollow anchor adopts the pure pressure infusion process directly connected with the orifice and the anchor rod. The grouting end criterion is: When the hole in the anchor rod is fully filled, the concentration of the returned slurry is basically the same as when entering the slurry, the grouting can be ended.
Due to the characteristics of the slope itself, the amount of grouting is large and most grouting is over-consumption. More than twenty-three holes have exceeded the consumption of nearly seven tons of cement.
3. Grouting of self-drilling hollow anchor rods The construction of anchor piers is performed after the concrete injection is completed. The qualified steel bars are installed in the self-drilling bolt zone according to the position in the design drawings. With the use of small steel formwork vertical moulds, the external dimensions of the anchor piers should be ensured, and the secondary level concrete of the C30 should be used for pouring. The technical parameters meet the specifications. Casting uses a small vibrator to vibrate and ensure the inside of the concrete is even and dense.
II. Conclusions (1) This slope protection adopts comprehensive measures to rectify and self-drilling hollow anchors play a key role.
(2) Self-drilling anchor rod construction of this side slope protection support has the following characteristics: single anchor rod has large pull-out resistance; the depth of anchor rod is large; the project volume is large; and the geological conditions are complex.
(3) The original design was prestressed anchor rods. After the ground layer was extremely loosely broken, the grouting could not form a reliable anchoring section and tensioning section. The surface rock mass could not provide enough support reaction force, and the prestress could not be applied. Prestressed. The problem of prestressing in this case deserves further study.
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