Description

METHOD OF CONSTRUCTING UNDERGROUND PILE HAVING EXPANDED BULB AND UNDERGROUND PILE

THEREBY

Technical Field

[1] The present invention relates generally to methods of constructing underground piles for reinforcing the ground and, more particularly, to a method of constructing an underground pile having an expanded bulb on a lower end or an intermediate portion thereof. Background Art

[2] As well known to those skilled in the art, when structures, such as buildings, railroad lines, bridges, etc., are constructed on soft ground, pile foundations are widely used to prevent the structures from sinking and to ensure supporting force for the structures.

[3] In methods of constructing a pile foundation, there are a method of driving or embedding a premanufactured concrete pile into the ground, and a method of boring a hole in the ground, and charging grout, such as mortar, concrete, molten glass and asphalt, into the hole, thus forming an underground pile. The present invention relates to the method of boring a hole in the ground at a construction site and charging grout such as mortar into the hole, thus forming an underground pile.

[4] The inventor of the present invention proposed, in Korean Patent Registration No.

10-0213577 and in Korean Patent Laid-open Publication No. 2003-6083, rapidly expanding metal compounds, which comprise metal salt as an oxidizing agent, metal powder that is oxidized by the metal salt and is thus increased in volume by an exothermic reaction due to the oxidation, and a promoter that promotes the oxidation reaction between the metal salt and the metal powder. Here, metal nitrate, metal oxide, metal oxalate, metal carbonate and metal sulfate can be used as the metal salt. Aluminum, manganese, magnesium and metal, which can be used as reducers, are used as the metal powder. Furthermore, the inventor of the present invention proposed, in Korean Patent Laid-open Publication No. 2003-37707, a room temperature an- tioxidized rapidly expanding metal compound, in which oil or inorganic antiseptic is added to a rapidly expanding metal compound including metal salt and metal powder.

[5] In the present invention, a rapidly expanding metal compound means the rapidly expanding metal compound proposed in Korean Patent Laid-open Publication No. 2003-6083 or Korean Patent Laid-open Publication No. 2003-37707.

[6] When the rapidly expanding metal compound is detonated using a high temperature spark or shock heat in a sealed space, a sequence of momentary oxidation-reduction

reactions results, so that superhigh pressure metal and metallic oxide steam is generated, thus rapid expansion occurs. After the rapidly expanding metal compound has been rapidly expanded, when the expansion volume and expansion pressure reach predetermined levels, expansion energy is lost, so that it instantly contracts into a liquid or solid phase of metal or metallic oxide. The reason for this is that, because the coefficient of expansion is relatively small, power thereof is exhibited merely within a relatively small range. Using such characteristics of the rapidly expanding metal compound, a noiseless, vibrationless and spatterless rock fracturing operation can be conducted.

[7] Furthermore, the inventor of the present invention developed a method and device for contact-detonating a rapidly expanding metal compound, which were registered in Korean Patent Registration Nos. 10-283505 and 10-442551. In Korean Patent Registration Nos. 10-283505 and 10-442551, when high voltage is applied to a conducting wire (a resistor wire), which is embedded in the rapidly expanding metal compound, the conducting wire is rapidly heated and a spark is caused. Thus, the rapidly expanding metal compound is ignited by the spark.

[8] The inventor of the present invention has conducted many rock fracturing operations in the world using the rapidly expanding metal compounds and the contact-detonating devices therefor. The present invention represents a new use for the rapidly expanding metal compound.

[9] FIGS. 1 through 3 illustrate a typical method of constructing an underground pile. In the conventional underground pile constructing method, a straight hole 3 having a predetermined depth is formed in the ground by boring using an auger 1. Thereafter, grout, such as mortar, concrete, molten glass, or asphalt, is charged into the straight hole 3 using a hydraulic pump or the like and is cured, thus forming an underground pile. However, because the underground pile formed through the above method only has a straight shape, the force for supporting a structure constructed thereon is insufficient. Therefore, to avoid the above-mentioned problem, in the conventional art, a method of forming the straight hole until it reaches solid rock or forming many holes is used. However, as such, if the depth of the hole or the number of holes is increased, the amount of grout to be charged into the holes is also increased. This is very uneconomical. Furthermore, the operation of boring the straight hole 3 using the auger 1 merely forms a hole in the ground without hardening the soil around the hole. Therefore, there is a disadvantage in that, even after the underground pile is constructed, the ground around the underground pile is still soft.

Disclosure of Invention Technical Problem

[10] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an underground pile constructing method in which an outward expanded bulb can be formed around the pile at a lower end or at an intermediate position, and an underground pile having an expanded bulb constructed by the method.

[11] Another object of the present invention is to provide a method of constructing an underground pile, which has a relatively superior supporting force, at reduced cost and in a short period.

[12] Another object of the present invention is to provide an underground pile having an expanded bulb which can exhibit superior supporting force despite having reduced length and diameter compared to a straight pile, thus providing superior ground reinforcing ability despite the use of a reduced number of piles compared to the conventional art. Technical Solution

[13] In order to accomplish the above object, the present invention provides a method of constructing an underground pile having an expanded bulb, including: charging liquefied grout into a hole bored in the ground; inserting a rapidly expanding metal compound of metal powder and a metal salt into the grout; and exploding the rapidly expanding metal compound in the grout before the grout is cured, so that a portion of the hole is widened and the grout is charged into the widened portion.

[14] Preferably, the rapidly expanding metal compound is contained in an outer casing made of steel, fiber reinforced plastic or polycarbonate, and is inserted into the grout.

Advantageous Effects

[15] According to the present invention, expanded bulbs which protrude outwards can be easily formed on predetermined portions of an underground pile and, simultaneously, the soil around the pile can be hardened. Furthermore, the construction period and construction cost of the underground pile having the expanded bulbs are markedly reduced. As well, the underground pipe having the expanded bulbs according to the present invention can exhibit superior supporting force despite having reduced length and diameter compared to the straight pile. Therefore, the present invention makes it possible to provide superior ground reinforcing ability despite using a reduced number of piles compared to the conventional art. Brief Description of the Drawings

[16] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[17] FIGS. 1 through 7 are views showing steps of a method of constructing an un-

derground pile having expanded bulbs, according to an embodiment of the present invention; and

[18] FIG. 8 is a sectional view of a rapidly expanding metal compound capsule used in the underground pile constructing method according to the present invention. Best Mode for Carrying Out the Invention

[19] Hereinafter, a method of constructing an underground pile having expanded bulbs according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[20] FIGS. 1 through 7 are views showing steps of the method of constructing the underground pile having the expanded bulbs, according to the present invention. FIG. 8 is a sectional view of a rapidly expanding metal compound capsule used in the underground pile constructing method of the present invention.

[21] First, a rapidly expanding metal compound 101 used in the present invention and the capsule 100 containing the rapidly expanding metal compound 101 therein will be explained herein below.

[22] The rapidly expanding metal compound 101 is a compound in which metal powder and a metal salt, which oxidizes the metal powder at a high temperature using its own oxygen atoms, are mixed at a weight ratio of 0.1:99.9 to 99.9:0.1. It is preferable that the metal salt be one selected from among a metal nitrate, a metal perchlorate, a metal peroxide, a metal oxide, a metal oxalate, a metal carbonate and a metal sulfate, or be a compound of at least two of them. Furthermore, it is preferable that the metal powder be one selected from among aluminum (Al) powder, sodium (Na) powder, potassium (K) powder, lithium (Li) powder, magnesium (Mg) powder, manganese (Mn) powder, barium (Ba) powder, chromium (Cr) powder and silicon (Si) powder, or be a compound of at least two of them.

[23] The rapidly expanding metal compound 101 is contained in an inner casing 103, which is made of synthetic resin such as PVC (polyvinyl chloride), and is contained in an outer casing (105, 107a and 107b), which is sealed and is made of steel, fiber reinforced plastic or polycarbonate, thus forming the capsule 100. Carbon fiber reinforced plastic and glass fiber reinforced plastic are representative examples of the fiber reinforced plastic used in the present invention. Furthermore, the carbon fiber reinforced plastic and the glass fiber reinforced plastic, which are high-strength plastic, and polycarbonate have superior plasticity despite having strength similar to steel. Therefore, the outer casing is preferably made of the above high-strength material rather than steel. Furthermore, for oxidation-reduction reaction of the rapidly expanding metal compound 101, a high oxidation detonating temperature and a sealed space ensuring a predetermined pressure are required. Therefore, the above high-

strength material is preferably used as the material of the outer casing. Although the outer casing is illustrated in FIG. 8 as comprising an outer casing body 105 having a pipe shape and a pair of outer casing caps 107a and 107b that closes the opposite ends of the outer casing body 105, the structure of the outer casing is not limited to this. The outer casing can have any structure as long as it has a pressure resisting and sealing structure.

[24] Meanwhile, a resistor wire 109, which generates a spark for creating an oxidation reaction, is embedded in the rapidly expanding metal compound 101. The resistor wire 109 is connected to power supply wires 111, which extend outside the inner casing 103 and the outer casing (107a, 107b) of the capsule 100. The power supply wires 111 are connected to a contact-detonation device 113, which generates high instantaneous voltage. When high voltage is applied to the resistor wire 109 by the contact- detonation device 113, heat is supplied, and the resistor wire 109 fuses, thus inducing a high current discharge. Then, a spark is generated by the high current discharge, thereby the rapidly expanding metal compound 101 explodes.

[25] Hereinafter, the method of constructing the underground pile having expanded bulbs using the rapidly expanding metal compound capsule 100 having the above-mentioned construction and operation will be explained with reference to FIGS. 1 through 7.

[26] FIG. 1 illustrates a process of boring a hole 3 in the ground 5 using an auger 1. FIG.

2 illustrates a process of charging grout 7, such as mortar, concrete, molten glass and asphalt, into the bored hole 3. Although it is schematically shown in FIG. 2, the grout 7 is pumped and charged into the hole 3 through a hose using a pump. This is well known to those skilled in the art.

[27] As shown in FIG. 3, after the grout 7 has been charged into the hole 3 until it is level with the surface of the ground, a desired number of rapidly expanding metal compound capsules 100 are connected to each other through the power supply wire 111 and are inserted into the grout 7 to the depth at which expanded bulbs are to be formed, as shown in FIG. 4. Here, in the case where the outer casing (105, 107a and 107b) of each rapidly expanding metal compound capsule 100 is made of steel, it can be easily inserted into the liquefied grout 7 because it is relatively heavy. However, in the case where the outer casing of the rapidly expanding metal compound capsule 100 is made of fiber reinforced plastic or polycarbonate, it is inserted into the grout 7 using a tool, such as a long pole. When it is desired to form two or more expanded bulbs in the pile at different heights, a corresponding number of the rapidly expanding metal compound capsules 100 is inserted into the grout 7 such that they are disposed at the desired heights.

[28] After the process of inserting the rapidly expanding metal compound capsules 100 into the grout 7 has been completed, the power supply wire 111 is connected to the

contact-detonation device 113 as shown in FIG. 5, and high voltage power (3,000V or more) is applied. Then, the rapidly expanding metal compounds and the capsules 100 containing them explode and expand, so that portions of the ground 5 around the rapidly expanding metal compound capsules 100 are widened and the grout 7 is instantaneously charged into the widened portions, as shown in FIG. 6. In this process, the soil around the widened portions is firmly hardened. In addition, a space corresponding to the volume of grout 7 charged into the widened portions is formed in the upper end of the hole 3. Here, if a detonator such as an explosive is used, the grout 7 is discharged and spattered outside the hole 3 by the explosive pressure. However, in the case where the rapidly expanding metal compound 101 according to the present invention is used, because the rapidly expanding metal compound 101 contracts just after being rapidly expanded to a predetermined volume, the grout 7 is completely prevented from being discharged outside the hole 3 and is reliably charged into the widened portion.

[29] Thereafter, as shown in FIG. 6 and FIG. 7, additional grout is charged into the space formed in the upper end of the hole 3, and the grout is subsequently cured, thus forming an underground pile 9 having the expanded bulbs 11 at predetermined positions, for example, at the lower end or an intermediate position of the pile 9. Industrial Applicability

[30] As described above, according to the present invention, expanded bulbs which protrude outwards can be easily formed on predetermined portions of an underground pile and, simultaneously, the soil around the pile can be hardened. Furthermore, the construction period and construction cost of the underground pile having the expanded bulbs are markedly reduced. As well, the underground pipe having the expanded bulbs according to the present invention can exhibit superior supporting force despite having reduced length and diameter compared to the straight pile. Therefore, the present invention makes it possible to provide superior ground reinforcing ability despite using a reduced number of piles compared to the conventional art.