Method for installing overhead transmission line supports on permafrost soils

Abstract

A method for installing pile foundations for power transmission towers or the like in different types of soil prone to frost heaving provides piles with bearing capacity against horizontal loads, reduced labor content and installation cost, and increased reliability against the impact of frost heaving forces of the soil on the pile. A casing pipe is driven in and then the pile is inserted into it, while installing rigid elements on the pile shaft by welding. When driving the pile, when a mark indicating a point of installation for a rigid element reaches the top of the casing pipe, a geometric measurement of gaps is made between the casing pipe and the pile. Based on the measurement, rigid elements are sized and welded in pairs on the opposite side in a vertical plane. The operation of placing and welding is then repeated during the pipe inserting.

Claims

1. A method of installation of a power transmission tower on permafrost soil, comprising: driving a casing pipe into soil to a depth greater than a level of seasonal freezing and thawing of soils for transferring horizontal loads from the power transmission tower to surrounding soil; inserting a pile into the casing pipe, including driving the pile; while inserting and driving the pile, installing rigid elements in pairs on a shaft of the pile by welding at predetermined locations for installation of the rigid elements, wherein said installing includes for each pair of the rigid elements: measuring gaps in between a top of the casing pipe and the pile at a lower end of each predetermined location; manufacturing each pair of rigid elements comprising a pair of generally flat plates fitting in the gaps, based on the measuring; welding each pair of rigid elements on opposite sides of and transverse to the shaft at each predetermined location in a vertical plane, positioned to transfer horizontal force from the pile to the casing pipe; and repeating the installing and manufacturing for each of the pairs of rigid elements during the pile insertion and driving.

2. The method of claim 1, wherein a height of a zone of the shaft in which the rigid elements are installed is at least 3 meters.

3. The method of claim 1, wherein a length of the rigid elements is in a range of 5-15 cm.

4. The method of claim 1, wherein the pile is inserted and driven at intervals in a range of 0.5-0.7 m, and a distance between installed pairs of the rigid elements is in a range of 0.35-0.65 m.

5. The method of claim 1, further comprising mounting a cutoff screen on the shaft from an upper part of the shaft to a level of seasonal freezing and thawing of soils.

6. The method of claim 5, wherein the cutoff screen comprises a plastic film or sheet.

7. The method of claim 5, wherein the cutoff screen comprises a galvanized metal sheet.

8. The method of claim 1, further comprising positioning the pairs of the rigid elements on opposite sides of the shaft in a common plane.

9. The method of claim 1, further comprising filling a space between the casing pipe and the shaft with soil.

10. The method of claim 1, further comprising filling a space between the casing pipe and the shaft with one of concrete or mortar.

11. The method of claim 1, wherein each of the rigid elements comprises a steel material.

12. The method of claim 1, wherein each of the rigid elements is in the range of 1-50 cm long, 1-20 cm wide, and 0.1-5 cm thick.

13. The method of claim 1, wherein the shaft comprises a steel material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.

(2) FIG. 1 is a schematic diagram illustrating a foundation pile with the casing pipe and rigid elements.

DETAILED DESCRIPTION

(3) Various aspects are now described with reference to the drawings.

(4) Referring to FIG. 1, the following components are illustrated: 1pile, 2pile shaft, 3pile toe bulb, 4casing pipe, 5filler, 6cutoff screen (not visible), 7rigid elements. Pile 1 comprises shaft 2 and toe bulb 3. The pile shaft 1 may be made of concrete of grade B10-640, of metal roll with 17G1S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, 9G2S steel grade, K34-K60 strength class, or reinforced concrete. The pile shaft 2 may have a length of L.sub.1, for example, in a range of 6-20 m, and a cylindrical shape with a diameter d.sub.1, for example, in a range of 15-150 cm. In an alternative, the pile shaft 2 may be rectangular in cross section with sides of dimension, for example, in a range of 10-100 cm. The pile shaft 2 serves to accommodate vertical, horizontal and other loads. The bottom of the pile shaft 2 may be attached with a pile toe bulb 3, which may be tapered, rounded or flat in shape and mounted to the shaft 2 by welding or molded as a single monolithic structure, in the case of configuration of concrete and reinforced concrete piles.

(5) The top of the shaft 2, which is 1 m to m long, may be attached with a cutoff screen 6 and rigid elements 7. The cutoff screen 6 may be made of plastic sheet or metal galvanized sheet. The cutoff screen 6 is installed close to the shaft 2 and fixed to it using a clamp before or during driving the pile 1. The cutoff screen 6 is used to separate the pile 1 from the filling material in order to increase the reliability against the impact of frost heaving of the soil on the pile 1.

(6) Rigid elements 7 of the shaft 2 may be made of metal plates with 09G2S, 10G2, 15GS, 16GS, 17GS steel grade, h long having a length, for example, in a range of 1-50 cm long, S wide a width, for example, in a range of 1-20 cm wide, and a thickness, for example in a range of 0.1-5 cm thick. Rigid elements 7 may comprise a generally flat plate having a shape of square, triangular, circular or other non-arbitrary geometric shape. Rigid elements 7 are installed transverse to the anticipated horizontal forces acting on the pile 1, for example, horizontal forces from transmission lines. As shown in FIG. 1, the rigid elements may be attached in pairs on opposite sides of the shaft 2. The rigid elements 7 may be attached to the shaft 2 by welding vertically spaced apart by not less than the length of the metal plates. Rigid elements 7 serve to transfer horizontal forces of the pile on the casing pipe 4.

(7) The pile shaft 2 is mounted into the casing pipe 4. The casing pipe 4 may be made of pipe metal-roll with 17G1S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, 9G2S steel grade, K34-K60 strength class, with L.sub.2 length, for example, in a range of 1-10 m, with a diameter d.sub.2, for example, in a range of 20-200 cm. The casing pipe 4 serves to accommodate horizontal loads from the pile 1 and transfer them to the surrounding soil with a larger work area. The filler 5 of the space between the pile 1 and the casing pipe 4 is cement and sand mortar of M100-M350 grade, or B10-B40 grade concrete, or granular inert non-frost heaving material.

(8) An embodiment is implemented as follows. The casing pipe 4 is driven in and the pile 1 is inserted into it. While inserting the pile 1, rigid elements 7 are installed on the shaft 2 of the pile 1 by welding, for which the pile 1 is marked at the point of installation of rigid elements 7. When driving the pile 1, when the lower mark reaches the top of the casing pipe 4, a geometric measurement of gaps is being made between the casing pipe 4 and the pile 1, based on which rigid elements 7 are manufactured to be welded in pairs on the opposite sides. The operation is similarly repeated during the pile insertion.