JPS6128773B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention reduces the negative frictional force that the sunken foundation pile receives due to ground subsidence, while also being able to sufficiently withstand the lateral bending moment received from the structure. The purpose of the present invention is to provide a foundation pile constructed as described above.

Foundation piles that are buried in the ground that is formed on a hardened support layer, or that are sunk in a soft stratum formed on the ground surface due to the accumulation of volcanic ash, may suffer from subsidence due to the consolidation phenomenon of the soft stratum. A downward negative frictional force is applied to the pile circumferential surface, and when this negative frictional force is added to the vertical load of the structure acting on the pile, the pile itself may be crushed or the hardened support layer may be destroyed. There is also a risk of unexpected settlement of piles and structures.

In order to solve this problem, there is a method in which a ring member provided at the lower part of the pile forms a gap between the outer periphery of the pile and the soft stratum.
In addition, by coating the outer periphery of the pile with a thin film, or fitting a skin layer with low friction on the outer periphery of the pile, or fitting an outer pipe onto the pile, only the thin film or skin layer can be used in the event of ground subsidence. There are some structures in which only the outer tube made of these thin films or steel tubes is made to sink with the ground. However, the first method described above has the disadvantage that the voids remaining after sinking reduce the stiffness against bending moments due to lateral loads acting on the pile. In addition, piles with a thin film or skin layer around the outer periphery have the problem that when the pile is sunk, the soft thin film is easily scratched by the surrounding soil, so a double pipe structure with an outer pipe fitted is a problem. However, there are various problems such as high cost.

In addition, a technique is known in which sand or cement is filled into the gap between the friction reducing layer formed around the outer circumference of the pile and the soft stratum, but when the soft stratum sinks, the friction reducing layer on the inner side also collapses. Although it is possible to reduce the negative friction force by sinking, the load bearing capacity of the pile is insufficient. Therefore, the present invention is proposed in order to solve this problem with conventional foundation piles, and its structure consists of a pile upper part 24, a tip support part 11 thicker than this pile upper part 24, and both parts 2.
This foundation pile has a truncated conical part 13 between 4 and 11, and has a friction reducing layer 15 on the outer periphery of the upper part of the pile, and this foundation pile is sunk with the tip support part 11 at the lowest position. The reinforcing layer 25 is formed in the void 20 formed in the soft stratum 4 around the friction reducing layer 15 when
This is a negative friction force reducing foundation pile characterized by having a deformable layer 21 in a void 20 formed in a soft stratum 4 around a truncated conical portion 13.

Next, one embodiment of the present invention will be described based on the drawings. As shown in Fig. 3A, the thick tip support part 1
1, and the upper part of the thin intermediate portion 12 of the pile as shown in FIG.
A truncated conical part 13 whose lower part has a cross section equivalent to that of the tip support part 11 is formed into one body, and the pile further has a cross section equal to the middle part 12 of the pile as shown in FIG. The outer peripheral surface of the pile upper part 24, which forms the top part 14 and consists of the pile intermediate part 12 and the pile top part 14, is provided with a friction reducing layer 15 thinly coated with bituminous material, etc. If the intermediate part 12 and the pile top part 14 are fixed to each other in this order, the tip support part 1 is located at the bottom, the pile upper part 24 consisting of the pile top part 14 and the pile middle part 12 is located at the top, and both of the above parts are attached. 2
Between 4 and 11, there is constructed a stake 16 in which the truncated conical portion 13 is integrated. An example of the construction method is as shown in each figure in Fig. 2.First, as shown in Fig. 2A, the tip support part 11 is inserted into the soft stratum 4 on the ground surface by the driving method or the digging method. The end plate 18 of the truncated conical part 13 is placed on the end plate 17 of the tip support part 11, and the two end plates 17 and 18 are fixed by welding. Then, the integrated tip support part 11 and the pile intermediate part 12 are sunk successively, and the friction reducing layer 15 and the tip support part 11 of the pile intermediate part 12, which sinks following the thick tip support part 11. Between the holes 19 formed by the friction reducing layer 1 as shown in FIG.
A void 20 is created to prevent scratches on the 5. Therefore, by filling the void 20 with sand to the extent that it almost fills the outer periphery of the truncated conical part 13, a deformable layer 21 is formed on the outer periphery of the truncated conical part 13, which can be deformed by external force. form. Then, the intermediate portion 12 of the pile is sunk almost completely, and the end plate 23 of the pile top portion 14 is aligned with the upper end plate 22 of the intermediate portion 12 of the pile, as shown in Fig. 2D, and the end plates 22 and 23 are welded. If the pile upper part 24 is made up of the pile top part 14 and the pile intermediate part 12, one pile 16 is formed in which the pile upper part 24 is joined to the tip support part 11, so the process of sinking this pile 16 is As the deformable layer 21 progresses, the deformable layer 21 sinks together with the truncated conical portion 13, and a gap 20 that gradually becomes deeper is formed on the outer periphery of the friction reducing layers 15, 15. Therefore, a hardening agent such as cement milk is continuously flowed or press-fitted into this gap 20, and as shown in FIG. In the completed state of submersion in the relatively strong stratum 6 on the layer 5, the hardening agent filled in the void 20 hardens onto the deformable layer 21, so that the cylindrical reinforcing layer 25 becomes a soft layer. 4 and the outer periphery of the friction reducing layer 15. If hard fibers such as steel fibers or glass fibers are mixed into the cement milk flowing into the voids 20, the strength of the reinforcing layer 25 will be further improved. In addition, in deep soft strata, the above-mentioned pile top 14 is placed on top of the pile intermediate portion 12.
By connecting two of them, a longer upper part of the pile than the illustrated example is formed.

Although different from the construction method described above, the piles 16 may be formed in one piece before being sunk.In this case, there is an advantage that the piles 16 can be efficiently produced all within the factory.

The negative friction force reducing foundation pile according to the present invention is constructed as described above, and the thick tip support portion 11 reaching the support layer 5 can sufficiently bear the vertical load, and, The void 20 around the friction reducing layer 15 of the pile upper part 24, which is sunk after the thick tip support part 11 is sunk, is closed by the reinforcing layer 25, so that it bends due to the lateral load acting on the pile 16. This reinforcing layer 25 can sufficiently reinforce the rigidity of the pile upper part 24 against moments. Then, the negative frictional force accompanying the subsidence of the soft stratum 4 after the pile 16 is sunk is no longer transmitted to the pile 16 by the friction reducing layer 15 formed around the outer periphery of the pile 16, and at this time the soft stratum 4 4, the reinforcing layer 25 also sinks, but the deformable layer 21 formed on the outer periphery of the truncated conical portion 13
Since the reinforcing layer 25 can undergo plastic deformation or elastic deformation when sinking, the reinforcing layer 25 can sink relatively freely, and a sufficient reinforcing effect by the reinforcing layer 25 can be expected even after the sinking is completed.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which FIGS. 1A to 1C are partially longitudinal front views showing the constituent members of a foundation pile, and FIGS. 2A to 2E are diagrams of the process of sinking the foundation pile. Explanation of symbols, 4... Soft stratum, 5... Supporting layer, 6... Geological stratum, 11... Tip support part, 12... Pile middle part, 13...
14... Pile top, 15... Friction reduction layer, 16... Pile, 19... Hole, 20... Void, 21... Deformable layer, 24... Pile top, 25... Reinforcement layer.

Claims (1)

[Claims] 1. A foundation pile that has an upper part of the pile, a tip support part that is thicker than the upper part of the pile, and a truncated conical part between the two parts, and has a friction reducing layer on the outer periphery of the upper part of the pile, When this foundation pile is sunk with the tip support part at the lowest position, a reinforcing layer is formed in the void formed in the soft stratum around the friction reducing layer, and is formed in the soft stratum around the truncated conical part. A foundation pile that reduces negative frictional force, characterized by having a deformable layer in the void.