EP4206405A1

EP4206405A1 - Method of forming a widened pile base

Info

Publication number: EP4206405A1
Application number: EP22460079.1A
Authority: EP
Inventors: Mateusz Wyrolsak; Eligiusz Mieloszyk
Original assignee: Politechnika Gdanska
Current assignee: Politechnika Gdanska
Priority date: 2021-12-31
Filing date: 2022-12-28
Publication date: 2023-07-05
Also published as: PL440070A1

Abstract

The application relates to a method of forming a widened pile base, wherein at the bottom of a hole (1) a blasting agent (2) is installed in the calculated amount so as to obtain, after its detonation, a cavern below a pile base widening the hole in the ground, preferably from 1 kg to 2.5 kg, wherein the blasting agent (2) is mining explosives. The blasting agent (2) is connected to a blasting wire (3) brought outside the hole (1), and in the next stage, structural concrete is fed into the hole (1) in the amount calculated for the load power and soil parameters, so that it fills not less than half of the hole (1) and that the blasting agent is covered, after which detonation is carried out by firing the blasting agent (2), during which the impact of the shock wave caused by detonation affects the ground and the post-explosion gases are expanded, forming a cavern constituting the extension of the hole in the ground around the base of the pile . Then, the entire cavern is filled by gravity with structural concrete.

Description

The invention refers to method for obtaining a widened pile base - broadening in the base of pile, extended pile base, having industrial application in building construction, together with the improvement of the soil around the base of the pile, as well as to method of elaborating an explosive charge in the base of the formed pile.
Piles and various piling methods are commonly used in construction. Particularly noteworthy are the pile foundations that enable the foundation of the building especially on weak soil. The use of pile solutions for foundations on weak soils also reduces the costs of the entire investment. The bearing capacity of piles is an important parameter from the engineering and economic point of view. One of the methods of increasing their bearing capacity is to use a widened/enlarged pile base. This is the case, for example, with Franki piles, Soilex piles, Compaction Grounting Omega piles.
The patent description CN 101235639 discloses an explosive expansion device to form bell-shaped bottom of piles, in other words for expanding the pile base, and a method of forming piles using this device. The mechanism of directed impact of the shock wave is described - downwards, which limits the possibility of swelling of the pile shaft in the immediate vicinity of the pile base (approx. 1-1.5 m).
The aim of the invention was to provide a technology for obtaining a widened pile base and improving the soil around the pile base, without the need to use additional mechanical elements. The invention allows for the dynamic shaping of the pile tip depending on the soil flexibility for this process.
The method of forming an extended pile base - extension in the base, according to the invention, comprises following process steps. In the first stage an appropriate hole in the ground is provided - made, that can cover location below the groundwater level, using common known and freely chosen method by the person skilled in the art, preferably by drilling or driving in a temporary casing or a temporary cast pipe with a lost tip. In the next stage, at the bottom of the hole, a blasting agent is placed with a fuse, preferably formed into a compact cuboid package, in the calculated amount, preferably from 1 kg to 2.5 kg, such that after the explosion a cavern is obtained below the base of the pile, widening the hole made in the ground. The blasting agent is mining explosives, preferably ammonite, ergodium or TNT. The blasting agent is connected to a blasting conduit outside the hole. Then, structural concrete is fed into the hole in the amount calculated for the power of the load and soil parameters in such a way that the given concrete covers the blasting medium and fills not less than half of the hole, then the casing pipe is raised by at least 1 meter and the blasting medium is fired. The shock wave and the expanding post-explosion gases, affecting the ground, widen the hole in the base of the pile being formed, creating a cavern, which is gravitationally filled with structural concrete. In the last stage, the pile is formed to the end, by filling the hole with structural concrete to the ground surface and preferably installing a reinforcing cage if required for design reasons. After the entire pile is formed, the temporary casing pipe is removed by vibrating it out.
Preferably, in the hole obtained by vibrating the casing pipe or the casing pipe with a lost tip, structural concrete is fed in the amount calculated for the load power and soil parameters, so that it fills not less than half of the casing pipe, then the casing pipe is raised by at least 1 meter, and after detonation of the blasting agent and installation of the reinforcement cage and filling with structural concrete, the temporary casing pipe is removed.
The proposed method according to the invention is based on the selection of blasting techniques that have not been used so far in the piling process, although in remote geotechnics the so-called blasting method is known and appropriate for soil improvement.
On the other hand the advantages of the proposed invention include: simplicity of implementation, effectiveness, low implementation costs and short implementation times. The method of forming a widened pile base with an explosive charge (in geological and mining terminology, these are blasting agents) can be used in known technologies for making piles, e.g. piles made by drilling or piles made by driving the casing pipe with the so-called lost tip.
The invention provides and is based on the method of widening the base of the pile as such, as well as the methodology of elaborating the load. A package of explosives preferably in the form of a compact cuboid with a detonator detonated with an electric wire is placed at the bottom of the hole in the ground after drilling, for example by lowering it on a steel cable (it is also possible to feed a gel or loose blasting agent through a chute), then the charge is covered with concrete by partially concreting the pile shaft. Fresh, unbound concrete, due to the influence of its mass, directs the spreading and accumulation of the shock wave in the low-bearing ground. Thus, according to the invention, the method of elaborating the blasting agent comprises the step of placing a package of explosives, preferably in the form of a compact cuboid with a detonator detonated by a blasting wire, for example, by lowering it on a steel wire, at the bottom of the hole in the ground after drilling or driving the temporary casing with lost tip, just before partial concreting of the pile. It is also possible to use a gel/loose blasting agent fed to the bottom of the hole with a discharge pipe).
By acting on the ground matter with the impulse of the shock wave, a controlled process of soil compression and reduction of its porosity is carried out. The control comprises in choosing the right amount of explosive for the type of soil. Therefore, according to the invention, it is important that structural concrete is fed into the hole in the amount calculated for the load power and soil parameters, so that it fills not less than half of the hole and covers the blasting agent. Then, detonation is carried out by firing the blasting agent, during which we cause the impact of the shock wave by detonation on the ground and the expansion of the post-explosion gases forms a cavern which is an extension of the hole in the ground around the base of the pile. The entire cavern is then gravitationally filled with structural concrete.
According to the invention the cavern means a widened hole in the base of the pile, made as a result of the action of an explosive charge, into which concrete flows by gravity. The cavern therefore means the widening of this hole in the ground around the base of the pile.
The invention enables to achive improvement (compaction or consolidation) of the soil around the widened base of the pile. The technologies known so far either do not take this phenomenon into account or compact the soil in a small area around the widening of the pile base. In the invention, the passage of the shock wave consolidates the soil more profoundly and at a greater distance from the base of the pile.
The subject of the invention is shown in the embodiment in the drawing, in which Fig. 1 to Fig. 4 show the successive stages of the method of forming an extended pile base using the method of drilling or driving a temporary casing pipe with a lost tip, i.e. Fig. 1 shows a cross-section of a hole with a drilled steel pipe, Fig. 2 shows a mounted blasting agent with a wire and raised temporary casing, Fig. 3 shows the detonation of the blasting agent, Fig. 4 shows a cross-section of a pile with an enlarged base. Fig. 5 to Fig. 8 show the successive steps of the method of forming a widened pile base using the screw rotary head on the central tube method, while Fig. 9 to Fig. 12 show the successive initial steps of the method of forming a widened pile base using the bored piles in temporary casing method.
The method of forming the expanded pile base is illustrated by the following examples.
Example 1 The example is illustrated successively in Fig. 1- Fig. 4. Vibro technology was used in one embodiment, Vibro-Fundex and Vibrex in other embodiments. The pile was 0.4 m in diameter and 5 m long in one example and 9 m in another embodiment. The blasting agent 2 used was an elaborated package: ammonite, TNT, ergodine with a total weight of 0.5 kg. Detonation: blasting agent 2 fired remotely by a primer (igniter) through an electric wire 3. Soil type: hydrated cohesive or non-cohesive. The cavern obtained in this way, i.e.: diameter of the widened pile base 0.8 m, volume of the resulting cavern: 0.3 m³. After driving the steel temporary casing pipe 5 with the lost tip 6, a hole 1 is obtained in the ground. A package of blasting agent 2 connected by a blasting wire 3 with a detonating igniter located on the ground surface is lowered to its bottom. The resulting hole 1 is half filled with structural concrete. After the blasting agent 2 is detonated, the post-explosion gases expand, which in turn causes the concrete plug to be lifted upwards and a post-explosion cavern is created in the base of the pile. At this stage, soil improvement outside the cavern is initiated. The post-explosion gas pressure is lowered and the created cavern is gravitationally filled with structural concrete from the inside of the casing pipe 5. The remains of the post-explosion gas rise through the casing pipe 5. Subsequently, reinforcement is installed, i.e. a reinforcing cage 4 and the casing pipe 5 is filled with structural concrete. Then, the casing pipe is drilled. A pile with a widened base is obtained, increasing its load bearing capacity.
Example 2 The example is illustrated successively in Fig. 5 - Fig. 8. Atlas screw pile technology was used, diameter 560/810 mm and length 10 m in one example and 15 m in another embodiment. The blasting agent 2 used was suspension or emulsion saltpeter, hydroammonite with a weight of 1.5 kg. Detonation: blasting agent 2 fired remotely by a primer (igniter) through an electric wire 3. Soil type: hydrated cohesive or non-cohesive. The cavern obtained in this way, i.e.: diameter of the widened pile base 1,2 m, volume of the resulting cavern: 0.9 m³.
After screwing the rotary guide head 7 onto the central tube 8 to the designed depth, the lost tip 9 remains at the bottom of the hole 1. The blasting cap 10 with the blasting wire 3 brought to the surface is lowered to the bottom of the hole 1. While gradually undrilling the head 7, the blasting agent 2 is fed through the central tube 8 in a loose or emulsion form, then the central tube 8 is partially filled with structural concrete. After detonation of the blasting agent 2, a cavern is created in the ground, which is gravitationally filled with structural concrete, forming a widened base of the pile.
Example 3 The example is illustrated successively in Fig. 9 - Fig. 12 and Fig. 4. The technology of drilling in a temporary casing pipe (large diameter piles) was used. The diameter was 1.2 m and the length was 25 m in one example and 30 m in another embodiment. The blasting agent 2 used was an elaborated package: ammonite, TNT, ergodine weighing 2.5 kg. Detonation: blasting agent 2 fired remotely by a primer through an electric wire 3. Soil type: hydrated cohesive or non-cohesive. The resulting diameter of the widened pile base is 2 m, the volume of the resulting cavern is 3 m³.
With the drilling device 11, a hole 1 in the ground was drilled in the temporary casing pipe 5. After reaching the target length of the pile, the blasting medium 2 connected by the blasting wire 3 brought to the surface was lowered to the bottom of the hole 1. Hole 1 was partially filled with structural concrete using the pouring pipe (the so-called contractor) 12. Then the temporary casing pipe 5 was pulled up_ After the blasting agent 2 was detonated, a cavern was created into which structural concrete flowed by gravity. A widened pile base was created.

Claims

Method of forming widened pile base according to that in the first stage an appropriate hole is made in the ground, including below the groundwater level, by a known method, preferably by drilling or driving a casing pipe or a casing pipe with a lost tip, characterized in that at the bottom of the hole (1), a blasting agent (2) is installing in the calculated amount in order to obtain a cavern below the base of the pile that widen the hole in the ground after its detonation, preferably from 1 kg to 2.5 kg, wherein the blasting agent (2) is mining explosive materials, preferably ammonite, ergodium or trinitrotoluene, and the blasting agent (2) is connecting to the blasting wire (3) brought outside the hole (1), and in the next stage structural concrete is providing into the hole (1) in the amount calculated based on the power of its charge and parameters of the soil, so that it fills not less than half of the hole (1) and covers the blasting agent, after which detonation is carried out by firing the blasting agent (2), during which the impact of the shock wave is providing by detonation in the ground and providing the expansion of post-explosion gases that form a cavern which is an extension of the hole in the ground around the base of the pile, and then the entire cavern is gravitationally filling with structural concrete.
The method of claim 1, wherein after firing the blasting medium (2), a reinforcing cage (4) is installed in the hole (1) by lowering it.
The method of claim 1, wherein in the hole (1) obtained by driving the casing pipe (5) or the casing pipe (5) with a lost tip (6), structural concrete is provided in the amount calculated based on the load power and soil parameters, so that it fills less than half of the casing pipe (5) and the casing pipe (5) is then raised by at least 1 meter, and after the blasting agent (2) is detonated and the reinforcing cage (4) is installed and filled with structural concrete, the casing pipe (5) is driven out.