A concrete variable cross-section prefabricated square pile comprises pile bodies of large cross-section sections and small cross-section sections alternately arranged along a longitudinal direction. Lateral transition surfaces are formed between side surfaces of the large cross-section sections and adjacent small cross-section sections; at least part of the lateral transition surfaces have a front edge and/or a rear edge that are offset from a vertical direction in a lateral projection, and a vertical projection of an intersection line between the lateral transition surface and a first horizontal plane is located outside a vertical projection of an intersection line between the lateral transition surface and a second horizontal plane; the first horizontal plane is a horizontal plane located above in any two horizontal planes, and the second horizontal plane is a horizontal plane located below in any two horizontal planes.

A combination pier includes: a pile disposed in a bore hole from the bottom of the bore hole to a desired depth; and a pier disposed in the bore hole from the desired depth to the surface. A method for constructing a combination pier includes: forming a pile in a bore hole from the bottom of the bore hole to a desired depth; and forming a pier from the desired depth to the surface.

A combination pier includes: a pile disposed in a bore hole from the bottom of the bore hole to a desired depth; and a pier disposed in the bore hole from the desired depth to the surface. A method for constructing a combination pier includes: forming a pile in a bore hole from the bottom of the bore hole to a desired depth; and forming a pier from the desired depth to the surface.

This invention is detailing a construction method for a cast in-situ pile having an upper section with a larger diameter and at least one subsequent section with a smaller diameter, and a drilling device equipped with continuous flights which allows the construction of one pile having multiple diameters using the innovative construction method in a single continuous drilling phase while each drilling tool is penetrating through the soil in one pass. The drilling tool according to the invention has a central hollow space that allows accommodation through it of at least one another smaller diameter drilling tool that can drill continuously and can be coupled by means of a coupling-decoupling device in a specific manner to the other drilling tool in order to act as a fixed assembly, at any given position in relation to the smaller drilling tool length and rotating position.

This invention is detailing a construction method for a cast in-situ pile having an upper section with a larger diameter and at least one subsequent section with a smaller diameter, and a drilling device equipped with continuous flights which allows the construction of one pile having multiple diameters using the innovative construction method in a single continuous drilling phase while each drilling tool is penetrating through the soil in one pass. The drilling tool according to the invention has a central hollow space that allows accommodation through it of at least one another smaller diameter drilling tool that can drill continuously and can be coupled by means of a coupling-decoupling device in a specific manner to the other drilling tool in order to act as a fixed assembly, at any given position in relation to the smaller drilling tool length and rotating position.

Provided is a method for burying a precast pile in which a borehole and a buried precast pile are strongly integrated, the end bearing capacity and the circumferential frictional force of the precast pile are increased, and the extraction resistance strength thereof is improved. Provided is a method for burying a precast pile in which a foaming agent having an expanding effect is added to the cement milk or mortar in advance, whereby the soil cement formed around the base of the precast pile in the borehole is caused to expand.

Provided is a method for burying a precast pile in which a borehole and a buried precast pile are strongly integrated, the end bearing capacity and the circumferential frictional force of the precast pile are increased, and the extraction resistance strength thereof is improved. Provided is a method for burying a precast pile in which a foaming agent having an expanding effect is added to the cement milk or mortar in advance, whereby the soil cement formed around the base of the precast pile in the borehole is caused to expand.

Apparatus for making foundation pilings includes a lead section with screw threads, at least one extension section, and a bit carried by the first of the extension sections. The bit slides onto the first, lower end of the extension section and is operable to compress the soil laterally to the extension sections and form a lateral groove in the soil. Grout fills the annular region of the hole bored by the apparatus including the grooves for lateral stability. Each extension section is formed to fit into the next one and to be secured to it by lateral bolts. The bolt heads prevent the bit from moving vertically as the lead section advances into the soil. Bits may be added to increase the size of the opening bored.

Apparatus for making foundation pilings includes a lead section with screw threads, at least one extension section, and a bit carried by the first of the extension sections. The bit slides onto the first, lower end of the extension section and is operable to compress the soil laterally to the extension sections and form a lateral groove in the soil. Grout fills the annular region of the hole bored by the apparatus including the grooves for lateral stability. Each extension section is formed to fit into the next one and to be secured to it by lateral bolts. The bolt heads prevent the bit from moving vertically as the lead section advances into the soil. Bits may be added to increase the size of the opening bored.

Contemplated are simplification and cost reduction in arrangement of connecting a pair of steel pipes to each other. A joint mechanism for a pair of steel pipes 1A, 1B include inner joints 10A, 10B and an outer joint 20 disposed circumferentially across and between the inner joints 10A, 10B. The outer joint 20 incudes inward key portions 23 engageable with outward circumferential grooves 13 of the inner joints 10A, 10B. The outer joint 20 is formed of a plurality of unit members 12 disposed side by side around the inner joints 10A, 10B. A standard unit member 21A includes an engaging projecting portion 24 whereas the inner joints 10A, 10B respective include an engaging sunk portion 14 engageable with the engaging projecting portion for preventing detachment of the standard unit member 21A to the outside. A wall face constituting the engaging sunk portion 14 includes a cutout portion 15A, 15B which allows insertion of the standard unit member 21A to a position where the engaging projecting portion 24 is engageable with the engaging sunk portion 14.