STEEL-COLUMN PILE RECOVERY PROCESS AND

CONCRETE PILE AND EARTH FLOW WALL USING THE

SAME Technical Field [1] The present invention relates to a steel-column pile recovery method (hereinafter, referred to as "SPR method"), wherein a plurality of vertical bores are formed until reaching a firm ground by excavating a soft ground using an auger, cement mortar is filled into each of the bores, a steel-column pile with a cover formed thereon and a cylindrical, spiral steel-rod structure are then inserted thereinto and cured with the cement mortar, and the steel-column piles are withdrawn and recovered after an earth retaining wall is formed, and a concrete pile and an earth retaining wall using the SPR method. Background Art [2] In engineering and construction works, there have been proposed a variety of methods of retaining earth, which are employed in ground excavation works. Among the methods, an earth retaining wall method, a cast-in-placed pile (CIP) method, and a soil cement wall (SCW) method have been generally used. [3] The earth retaining wall method is a method of constructing a concrete wall by excavating the ground between section shape steel (H-shaped piles) up to a pre¬ determined depth and pouring concrete. The CIP method is a method of constructing an earth retaining wall with cast-in-placed piles by excavating the ground to obtain bores with a predetermined diameter and by pouring mortar, and has the following processes: ground excavation -> casing installation (if soft ground) -> gravel input, and pour -> cement paste injection -> casing dismantlement -> section shape steel or steel column insertion. [4] The SCW earth retaining wall method is a method of constructing an earth retaining wall as an underground wall with a row of piles by excavating the ground up to a planned depth, pouring an injection material to form a wall body, and inserting a steel column or section shape steel into the wall body, and has the following processes: auger excavation -> injection, mixing and stir of stabilizing material -> withdrawing, re-excavation, mixing and stir -> insertion of steel column or section shape steel. [5] The SCW earth retaining wall method refers to a construction method for achieving the objective of a cutoff wall by considering natural earth and sand existing at a con¬ struction site as aggregate and adding, stirring and mixing a cement solution with a water/cement ratio greater than 100% to and in the earth and sand. The SCW earth retaining wall method has the following features: [6] (1) There is little noise and vibration as compared with a pile driving method; [7] (2) Since earth and sand existing at a construction site are used as aggregate, mud is less produced, resulting in good economical efficiency; [8] (3) Since a row of piles with a high degree of vertical accuracy can be constructed, the ability of cutting off water is excellent; [9] (4) Since an earth retaining wall with high strength is constructed, it is possible to ensure structural stability for the surroundings; [10] (5) The method is relatively advantageous to a soft ground area, a wet area, or an area with buildings standing close together; [11] (6) An earth retaining wall constructed by means of the method does not require an additional earth retaining plate and an additional water-cutoff construction work; and [12] (7) It is possible to attempt to shorten a term of works. [13] Due to these features, the SCW earth retaining wall method is the most employed method at present. However, an earth retaining wall should be constructed with an earth retaining plate using additional H-shaped piles at a construction site with a firm ground (rock floor). [14] The aforementioned CIP earth retaining wall method or SCW earth retaining wall method are methods of preventing earth and sand from breaking loose upon excavating the ground when a building is constructed on a soft ground or in an area where adjacent buildings stand close together. These methods employ a plurality of steel- column piles or section shape steel piles. [15] That is, the steel columns form an earth retaining wall to prevent earth and sand from breaking loose upon excavating a soft ground, thereby performing the function of eliminating an obstacle to the construction of an underground building. The earth retaining wall functions to reduce the influence of earth pressure resulting from the soft ground on the building and the like. [16] However, since the constructed earth retaining wall is a structure constructed through curing of poured concrete and thus has sufficient strength, the steel-column piles that have already been inserted into the earth retaining wall can be considered to finish their function. Therefore, it is reasonable to recycle the steel-column piles, thereby contributing to saving of resources. In the conventional CIP earth retaining wall method or SCW earth retaining wall method, the steel-column piles adhere to the constructed earth retaining wall as cement is cured, and thus, cannot be recovered. Disclosure of Invention Technical Problem [17] Accordingly, the present invention is conceived to solve the problem in which it is impossible to recover steel-column piles that have been used for an earth retaining wall constructed by means of a conventional CIP earth retaining wall method or SCW earth retaining wall method. An object of the present invention is to provide a steel-column pile recovery (SPR) method, wherein a cover is provided to wrap a steel column for use in constructing an earth retaining wall by means of a conventional CIP earth retaining wall method or SCW earth retaining wall method so that the steel column can be easily recovered from the constructed earth retaining wall, and contrary to the con¬ ventional method, an additional cylindrical steel-rod frame structure is used for re¬ inforcing the earth retaining wall to maintain the strength of the constructed earth retaining wall from which the steel-column pile will be recovered. [18] Another object of the present invention is to provide an earth retaining wall, wherein a furring can be installed laterally on an inner surface of an earth retaining wall with low strength. Technical Solution [19] The SPR method of the present invention comprises the steps of excavating the ground to form a bore; pouring cement mortar into the bore, and inserting a pile with an outer periphery enclosed by a cover into the bore; if the cement mortar is cured, withdrawing and recovering the pile from the interior of the cover; and filling a bore defined by the cover with the cement mortar, or earth and sand. [20] At this time, a spiral steel-rod structure may be made by spirally winding a steel rod to be in the form of a hollow cylinder, and the pile may be disposed within the spiral steel-rod structure and then inserted into the bore. An upper end of the pile preferably protrudes beyond an upper end of the cover. The cover is preferably made to be longi¬ tudinally split into two halves. [21] A concrete pile of the present invention introduced into a bore formed in the ground to form a fence comprises cement mortar poured into the bore; and a cover that is in the form of a pipe with a closed lower end surface and filled with cement mortar or earth and sand and then inserted into the bore. [22] Moreover, the concrete pile may further comprise a spiral steel-rod structure made by spirally winding a steel rod to be in the form of a hollow cylinder and introduced into the cement mortar. The cover may be inserted inside the spiral steel-rod structure. [23] An earth retaining wall of the present invention comprises a plurality of concrete piles constructed as above and arranged in a row; a plurality of structural piles which are arranged among and coupled to the concrete piles and each of which includes a cover made in the form of a pipe with a closed lower end surface and inserted into a bore formed in the ground, a "U- shaped" section shape steel pile, and a convexoplane bracket for coupling the cover to the "U-shaped" sectional shape steel pile; and a furring attached to outer surfaces of the "U-shaped" section shape steel piles of the respective structural piles. [24] At this time, the structural piles may be coupled such that each of them is interposed every two or more concrete piles. Brief Description of the Drawings [25] Fig. 1 is an exploded perspective view of a steel-column pile, a steel-column cover, and a spiral steel-rod structure employed in an SPR method according to the present invention. [26] Fig. 2 is a perspective view showing an assembled state where the steel-column pile, the steel-column cover, and the spiral steel-rod structure employed in the SPR method according to the present invention. [27] Fig. 3 is a sectional side view of an earth retaining wall constructed by means of the SPR method according to the present invention. [28] Fig. 4 is a plan view showing a state where the steel-column pile has been withdrawn from the earth retaining wall constructed by means of the SPR method according to the present invention. [29] Fig. 5 is a plan view showing a state where a bore formed after withdrawing the steel-column pile from the earth retaining wall constructed by means of the SPR method according to the present invention is filled with mortar. [30] Fig. 6 is a plan view of an earth retaining wall constructed by means of the SPR method according to the present invention so that a furring can be installed on the earth retaining wall. [31] Fig. 7 is a perspective view of a structural pile for constituting the earth retaining wall constructed by means of the SPR method according to the present invention. [32] Best Mode for Carrying Out the Invention [33] Hereinafter, preferred embodiments of an SPR method and an earth retaining wall using the same according to the present invention will be described in detail with reference to the accompanying drawings. [34] Fig. 1 is an exploded perspective view of a steel-column pile 110, a steel-column cover 120, and a spiral steel-rod structure 130 employed in the SPR method according to the present invention, and Fig. 2 is a perspective view showing an assembled state where the steel-column pile 110, the steel-column cover 120, and the spiral steel-rod structure 130. [35] The designation of the present invention as "SPR method" is intended to make dif¬ ferentiation from a conventional CIP method and SCW method. An earth retaining wall constructed by means of the method of the present invention capable of recovering steel columns has strength comparable to that of an earth retaining wall constructed by the conventional CIP method or SCW method even though the steel columns are recovered. [36] According to the SPR method of the present invention, a cylindrical bore H is formed by excavating a soft ground g using an auger or the like until reaching a firm ground at a position in a construction site where an earth retaining wall will be constructed, as shown in Fig. 3. At this time, a plurality of bores are serially formed to establish a fence. [37] The respective bores are filled with cement mortar M, or cement mortar obtained by mixing cement with water and natural earth and sand existing at the construction site. [38] Before the cement mortar is cured, a spiral steel-rod structure 130 that is in the form of a hollow cylinder made by spirally winding a steel rod is inserted into the cement mortar, and the steel-column pile 110 is enclosed by the steel-column cover 120 and then inserted into the hollow of the spiral steel-rod structure 130. [39] Here, there are a case where a steel-column pile 110 is inserted into every bore (CIP method), and a case where a steel-column pile 110 is inserted into every two bores (SCW method). [40] After the steel-rod structures 130 and the steel-column piles 110 are inserted into the bores in such a manner, the cement mortar M is cured and functions as an earth retaining wall. Then, a construction site where a building or the like will be constructed is excavated, and facilities are constructed in the excavated underground space. Sub¬ sequently, the steel-column piles 110 are withdrawn from the earth retaining wall. [41] In the earth retaining wall from which the steel-column piles 110 have been withdrawn, a bore h is formed at a position where the steel-column pile was placed, as shown in Fig. 4. The bore h is filled with earth and sand existing at the construction site or cement mortar m that in turn is cured, thereby completely constructing a concrete pile 100 (see Fig. 5). [42] The steel-column cover 120 is made of a synthetic resin to be in the form of a pipe with an inner diameter equal to or slightly larger than an outer diameter of the steel- column pile 110, or in the form of a pipe with split two halves (see Fig. 1), thereby enclosing an outer periphery of the steel-column pile 110. Further, the length of the steel-column cover 120 is slightly shorter than that of the steel-column pile 110, which is to facilitate the withdrawal of the steel-column pile 110. [43] An earth retaining wall comprising a plurality of concrete piles 100 constructed as above can maintain sufficient strength by means of the remaining steel-column cover 120 and particularly the spiral steel-rod structure 130 together with the refilled earth and sand or cement mortar m. Therefore, when the method of the present invention is performed, it is required to construct few facilities and structures for supporting earth pressure in construction works of desired underground facilities that are intended to be constructed. [44] The steel-column pile 110 used in the present invention can be replaced with a variety of piles including a steel-pipe pile, which does not depart from the scope of the present invention. [45] Moreover, the earth retaining wall constructed according to the present invention may be further provided with a furring. [46] Fig. 6 is a plan view of an earth retaining wall constructed by means of the SPR method according to the present invention so that a furring can be installed on the earth retaining wall. [47] As shown in Fig. 6, the structure of the earth retaining wall constructed by means of the SPR method according to the present invention is a structure in which a wall comprises a plurality of concrete piles 100 arranged in a row and a structural pile 200 is interposed every two or more concrete piles. This embodiment is implemented in such a manner that one structural pile 200 is placed every four bores, i.e. three concrete piles 100 are arranged and one structural pile 200 is then placed. However, the concrete piles 100 and the structural piles 200 may be arranged in a variety of con¬ figurations such as alternate arrangement of them, or interposition of a structural pile 200 every two, four or more concrete piles 100. [48] As shown in Figs. 6 and 7, the structural pile 200 is constructed by integrally coupling a "U-shaped" section shape steel pile 210, a steel-column pile 220 and a con- vexoplane bracket 230 to one another and pouring cement mortar M. The cement mortar M poured at this time may be replaced with concrete. [49] The convexoplane bracket 230 is not limited to the bracket with the configuration shown in Fig. 7, but any brackets with structures capable of connecting the steel- column pile 220 covered with a steel-column cover 220c to the "U-shaped" section shape steel pile 210 to structurally integrate them will fall within the scope of the present invention. [50] The steel-rod pile 220 is accommodated in the steel-column cover 220c and then recovered after the cement mortar is poured and cured, and an empty space of the steel- column cover 220c is filled with cement mortar, or earth and sand existing at a con¬ struction site. [51] The earth retaining wall of this embodiment constructed as above can obtain higher strength since furrings 300 formed of "H-shaped" section shape steel are horizontally attached to an inner surface of the earth retaining wall as shown in Fig. 7. At this time, it is preferred that the furrings 300 be configured to horizontally connect the concrete piles 100 and the structural piles 200 to each other. [52] Although the present invention has been described in connection with the preferred embodiments, the scope of the present invention is not limited to the specific em¬ bodiments but should be construed based on the appended claims. It can be understood by those skilled in the art that various modifications and changes can be made without departing from the scope of the present invention. [53] Industrial Applicability [54] According to the SPR method of the present invention constructed as above, steel- column piles are recovered from an earth retaining wall in underground excavating construction work as described above. Thus, the SPR method is an environment- friendly and economical method in view of reuse of resources. Further, the SPR method is advantageous in that even though the steel-column piles are withdrawn and recovered from the earth retaining wall, the earth retaining wall maintains strength comparable to that of a conventional earth retaining wall from which steel-column piles are not recovered. Moreover, since an earth retaining wall of the present invention on which a furring can be installed allows the furring to be installed thereon, it is possible to provide a firm earth retaining wall under any construction conditions.