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Anchor Cage Foundation Construction Process for Wind Mill Project

Most wind generator mainly used in wind farms adopt anchor cage foundation, main function of anchor plate is to connect the bolt and concrete structure
Anchor Cage Foundation Project

In recent years, wind power has been increasing in both the number and scale in China, however, most wind generator mainly used in wind farms adopt anchor cage foundation, main function of anchor plate is to connect the bolt and concrete structure, the upper structure of main parts, so the anchor plate is responsible for the wind machine structure are all load to the anchor cage foundation, ensure its structure with high stability. However, the foundation anchor plate is not deeply buried, the wall of the foundation anchor plate has few pores, the amount of internal reinforcement is small, there is no fixed pin, and the foundation reinforcement is not welded together, resulting in poor durability, load resistance and integrity of the foundation ring. The prestressed anchor bolt foundation is mainly distributed in the whole foundation by anchor bolt. The steel bar and anchor bolt adopt alternate frame, which has a high integrity. In addition, a high-strength tensioning tool is used to apply pretension on the anchor bolt, which enhances its durability and load-resisting ability.

Wind Foundation Anchor Cage
Wind Foundation Anchor Cage

The wind mill foundation used in a wind farm is a plate independent form, with a diameter length of 18 m and a buried depth of 3 m. The wind mill anchor cage foundation mainly applies the pre-stressed anchor and bolt technology and is installed in the construction site. The installation of high strength anchor bolts and anchor plate is strictly required. After secondary grouting, the flatness error of anchor plate should be controlled within 2 mm.

The pre-stressed anchor bolt foundation construction technology is used in many project, and the process is mainly as follows: pre-construction work, selection of embedded parts, setting and adjusting lower anchor plate, matching fixed anchor bolt and upper anchor plate, setting common anchor bolt, reasonably combining and inspecting anchor bolt, and then starting the construction of reinforcement and concrete.

Anchor Bolt Assembly Test and Standard

Test items Type test Factory inspection Standard method
Chemical composition 20MnTiB 、42CrMoA、40CrNiMoA、30CrMnSiA GB/T3077 — 1999
35VB GB/T1231-2006 Appendix A
45、35 GB/T699 — 1999
Tolerance class Bolts, screws, studs GB/T3103.1 — 2002
Nut GB/T3103.1 — 2002
washer GB/T3103.3 — 2000
Mechanical properties Bolts, screws, studs GB/T 3098.1 — 2010
Nut GB/T 3098.2 — 2000
Dacromet coating thickness   GB/T 18684 — 2002
Salt spray test   GB/T18684 — 2002
Ammonia drop test   GB/T18684 — 2002
Adhesion test   GB/T18684 — 2002
Surface defects Bolts, screws, studs GB / T5779.1 – 2000 GB / T5779.3 – 2000
Nut GB / T5779.2 – 2000

Pre-construction of Anchor Cage Foundation

  • Determine the number of anchor bolts, check the appearance of upper and lower anchor plates, anchor bolts and thread, and clean up non-conforming materials.
  • The anchor bolt assembly shall be delivered to the site by loading truck and protected by cork pad to prevent deformation of the upper and lower anchor plate and damage to the original state of screw thread.
  • The embedded parts shall be retained, and the embedded parts of the anchor plate shall be set according to the standard of the foundation design drawing of the prestressed anchor bolt, and the quantity, size and position of the embedded parts shall be adjusted.

Set Down Anchor Plate and Adjust Its Flatness

  1. The lower anchor plate is mainly raised by the crane, and then moved to the position of 300mm above the embedded parts to stop the movement. First, the bolts of the lower anchor plate are inserted into the corresponding screw hole, and the bolts from inside to outside are exactly corresponding to the embedded parts. At this time, the crane lowers the lower anchor plate to the top of the embedded parts.
  2. The center of the lower anchor plate is matched with the foundation center. The bolts of the lower anchor plate and embedded parts are tightly welded together, and the height is controlled at ≥ 6mm.
  3. The plane of the lower anchor plate tends to be flat. By rotating the supporting anchor bolts, the lower anchor plate meets the height requirements of the drawing design, and its levelness is controlled at ≤ 3mm. Figure 1 shows setting the lower anchor plate and adjusting its flatness.
Auto Pouring Concrete to Anchor Cage Foundation

The Positioning Anchor Bolt and Upper Anchor Plate Are Paired Together

The upper anchor plate is hoisted by the crane, and the upper positioning anchor bolts are evenly matched from top to bottom on all bolt holes of the upper anchor plate, and then the anchor bolts are firmly fixed with temporary nuts. The anchor bolts are fixed with black nuts, and the outside of the anchor bolts is wrapped with PVC sleeves Tube, plus a heat-shrinkable tube sleeve. Nylon adjusting nut is used to fix the head of the anchor bolt.

The Upper and Lower Anchor Plates Are Precisely Matched

The upper anchor plate and the positioning anchor bolt are slowly raised and fixed directly above the lower anchor plate. The positioning anchor bolt and the matching bolt hole of the lower anchor plate are connected together. A gasket is placed below the lower anchor plate to fix the black nut, and the fixed torque is controlled at 300 N·m. FIG. 2 shows the exact matching of the upper and lower anchor plates.

Installation Work of Other Anchor Bolt Parts

After positioning anchor is fixed, the fixed anchor bolt is mainly based on the principles of diagonal sequence, ordinary bolt head through the first anchor plate, the other part through the anchor plate, based on the same principle, the other anchor fixed well, the bottom of the anchor bolt nut is fixed, with black coated PVC casing, and then add a layer of heat shrinkable tube, each floor installation gaskets, with black nut is fixed, the fixed torque control at 300 n. m.

Adjust and Check Anchor Bolt Assembly

  1. Adjust the concentricity of the upper and lower anchor plates. The Angle of the four bolts was measured by theodolite as 90°, which was taken as a reference. A pile was installed on the ground outside the wind power foundation at an interval of 90°, and was connected between the upper anchor plate and the pile with drag rope. The center line of the anchor bolt hole of the upper and lower anchor plate was regarded as a reference for adjusting the concentricity, and the standard length was within 3 mm.
  2. Adjust the level of anchor plate. The leveler is used to measure the levelness of the upper anchor plate. When the levelness does not meet the standard, the upper anchor plate shall be raised by jack and the nylon nut shall be further fixed to make the levelness meet the requirements.
  3. The excess length of the upper anchor plate at the anchor bolt head shall be controlled at L Within ± 1.5 mm.
  4. Heat the heat shrinkable tube, place the plug between the anchor bolt and the upper anchor plate anchor bolt hole, and fix the anchor bolt in the center of the anchor bolt hole.
Erecting Formwork and Pouring Concrete
Erecting Formwork and Pouring Concrete

Strapping Steel Rebars, Erecting Formwork and Pouring Concrete

  1. After finishing the adjustment work, the top and upper anchor plate of the steel bar are welded together through 4 steel bar anchor and bolt assemblies, which are strengthened according to the cross shape. The bottom and the embedded parts of the anchor cage foundation are welded together, and the cross spot welding of the 4 steel bars is done to strengthen the firmness of the anchor and bolt assemblies.
  2. Before concrete pouring, the upper anchor plate shall be tested for its levelness for the second time, and the levelness shall be no more than 2mm.
  3. When pouring concrete, the upper anchor plate and anchor bolt are sealed with plastic to prevent contamination.

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