JPS6132452B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for pulling out a steel material inserted into a cement-based hardened material, for example, a method for pulling out an H-beam steel mortar inserted into a cast-in-place cement mortar pile without requiring a large force after it has solidified and hardened. The steel material here refers to all rod-shaped and linear materials such as H-beam steel and I-beam steel, but in the following description, H-beam steel will be taken as an example for convenience. Also,
The cement-based cured product will also be explained using cement mortar as an example. Until now, after cement mortar had hardened,
When pulling out the H-shaped steel inserted in this, it is difficult to pull it out because the cement mortar adheres to the surface of the H-shaped steel, and if you try to pull it out with too much force, the H-shaped steel may break. However, there were disadvantages such as damage to the cement mortar or adverse effects on surrounding structures. For this reason, conventionally, a sliding surface has been provided on the surface of the H-shaped steel, and the H-shaped steel that is no longer needed is pulled out and collected after construction is completed. As this sliding surface, a method has been adopted in which grease, paraffin, asphalt, tar, sheet, cement setting inhibitor, etc. are applied or attached to the surface of the H-beam steel to reduce the sliding resistance. However, these methods have problems such as the high fluidity of the materials used and poor workability.
It has disadvantages such as being easy to peel off during insertion, insufficient reduction in slip resistance, and increasing slip resistance as time passes after insertion. According to the present invention, as a method for eliminating the above-mentioned drawbacks and pulling out steel materials with less labor and mechanical force, before inserting the steel material into the cement-based hardened material, cement is added to the portion where the steel material comes into contact with the cement-based hardened material. A method of making steel material easier to pull out by applying in advance a resin coating that deteriorates due to the action of the alkali components in the cured product and allowing the resin coating to deteriorate over time due to the action of the alkali components. is provided. Generally, resin compounds exhibit good resin strength (elongation, tension, compression, etc.) during gel formation, but
Certain resin compounds change their gel properties in a relatively short period of time when affected by water or alkaline components of cement mortar. The method of the present invention utilizes this fact to form a strong film and maintain good workability until the H-beam comes into contact with the cement mortar, and after the H-beam comes into contact with the cement mortar, The film deteriorates after a certain period of time (becomes like grease)
It utilizes the property of reducing the resistance on the sliding surface. In the present invention, any resin can be used as long as it is degraded by alkali. Examples of these include hydrophilic polyurethane-based, polyester-based, acrylamide-based, and urea-based resins. Among these, hydrophilic polyurethane resins are particularly preferred because of the ease of controlling the properties of the resin and the ease of gel formation. Deterioration of these resins due to alkaline components has heretofore been regarded as a disadvantage, but in the present invention, positive benefits are obtained by taking advantage of this disadvantage. These resins are preferably used together with additives such as calcium carbonate, asbestos, rock wool, and bentonite to increase weight and prevent sagging, and water as a solvent. Next, a case in which the method of the present invention is applied to a column-type underground continuous wall construction method, which is an example of its implementation target, will be described with reference to the accompanying drawings. As shown in Figures 1 to 3, a mortar pile 3 consisting of mortar 31 and a core material (H-beam steel) 32 whose surface is coated (not shown for simplicity) is installed in a continuous manner in the ground 1. The ground surrounded by these mortar piles 3 is dug down to a predetermined depth while giving risers 21 and struts 22. The above mortar pile 3 is made by first digging a vertical hole 4 in the ground 1 as shown in FIG. Core material (H-shaped steel) 3
It is created by inserting 2. H-beam 3
As shown in FIG. 8, a resin coating 33 is provided in advance on the surface of No. 2 that is in contact with the mortar.
The coating may be formed by spraying, coating, or dipping in a resin solution bath. The thickness of the coating is approximately 0.4-1.0 mm. After the role of the dug vertical shaft 2 is completed, that is, after the structure inside the vertical shaft is completed, the mortar pile 3
Pull out the H-beam 32 that has finished its role. During this time,
The coating on the surface of the H-section steel 32 has gradually deteriorated, and the slip resistance has significantly decreased. The drawing is carried out by using a drawing device 5 as shown in FIG. 7, for example, by holding the H-beam 32 with chucks 51 from both sides, and repeating the operation of extending and pulling up the jacks 52. In addition to the illustrated pulling device 5, there are vibrating pile pulling machines, multiple pulley type pulling devices, etc.
Equipment readily available at the construction site can also be used. According to the method of the present invention, the pull-out resistance is
Normally, it can be reduced to about 2 tons/ ^m2 or less, so
H-shaped steel with flange size 30cm and length 15m (surface area 27
m ² ), the required pulling force is approximately 54 tons or less per piece. Therefore, it can be easily pulled out using a commercially available vibrohammer or the like. Note that if an impact is applied to the head of the steel material 32 with a weight before the mortar 31 is sufficiently hardened, it will be easier to pull it out after hardening. The results of measuring the pull-out resistance of mortar piles made of H-shaped steel with a flange size of 30 cm and a length of 15 m and coated with various film-forming compositions are shown in the table below.

【table】

[Table] In the present invention, the film-forming composition is not limited to a specific formulation as long as the film-forming composition is based on a resin that is degraded by alkali, and can bring about the desired effects of the present invention. I can do it. As mentioned above, the present invention has produced unexpected effects by taking advantage of the deterioration caused by alkali, which was previously thought to be a drawback of resin compounds, and has overcome the drawbacks of conventional steel drawing methods. It is something that will be resolved. In other words, when applied to steel materials, it has appropriate fluidity, so it does not drip or become sticky, and it is less likely to peel off when inserting mortar, so the coating can be thin.
Furthermore, the resistance force when pulling out the steel material is significantly reduced.

[Brief explanation of the drawing]

Figures 1 to 3 show the concept of the column-type underground continuous wall construction method using cast-in-place mortar piles, which is the subject of the present invention. Figure 1 is a plan view, and Figure 2 is a cross-sectional view. , FIG. 3 is a cross section taken along line AA in FIG. 2. FIGS. 4 to 7 are longitudinal cross-sectional views illustrating an implementation procedure using a cast-in-place mortar pile according to the present invention as an example.
FIG. 8 is a cross section taken along line BB in FIG. 6. In the figure, 1 is the ground, 2 is a vertical shaft, 21 is an elevation, 22 is a strut, 3 is a mortar pile, 31 is mortar, 32 is a steel material, 33 is a resin coating, 4 is a vertical hole,
5 is a pulling device, 51 is a chuck, 52 is a jack, and 53 is a base.

Claims (1)

[Claims] 1. A method of pulling out a steel material inserted into a cement-based hardened material after the cement-based hardened material has solidified and hardened and achieved the intended purpose of the steel material and the cement-based hardened material. Before inserting the steel material into the cured product, a resin film that is degraded by the alkaline component in the cement-based cured product is applied in advance to the part where the steel material comes into contact with the cement-based cured product, and the resin film is deteriorated by the alkali component. A method for pulling steel material from a cement-based hardened material, characterized by making it easier to pull out steel material.