JPH0259355B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cement-concrete propulsion tube with reinforced tube ends. Generally, the propulsion method that uses propulsion pipes is a method in which the end of the propulsion pipe is pushed into the soil with a jack, and the pipes are successively passed on.The longer the propulsion distance, the more economical the sewerage etc. will be installed. Conventionally, the propulsion tube used in this construction method is made of cement concrete (hereinafter referred to as concrete) with a compressive strength of about 500 Kg/cm ² and a maximum allowable propulsion stress of about 130 Kg/cm ² , but the propulsion tube has a limited propulsion distance. As the length of the tube increases, the frictional resistance with the soil increases, which eventually causes the tube to break, making it impossible to extend the propulsion distance. In response, the present inventors came up with the idea of increasing the compressive strength of the concrete itself of the propulsion tube, and have already developed a high-strength propulsion tube made of high-strength concrete. (Patent Application No. 57-166692) However, although this high-strength concrete has high strength, it is considerably more expensive than ordinary concrete made of Portland cement. It has the disadvantage that it becomes a propulsion tube and loses economic efficiency. As a result of research aimed at eliminating such drawbacks of conventional propulsion tubes, the present inventors recognized that the end of the propulsion tube is extremely pressurized in the propulsion method, and The present invention was completed based on the finding that a high-strength concrete propulsion pipe with excellent performance can be provided extremely economically by reinforcing the parts with high-strength or ultra-high-strength concrete. That is, the present invention provides a pipe end section extending at least 200 mm and at most 1000 mm from the pipe end in the pipe axial direction, where the compressive strength of the concrete itself is greater than that of the pipe center part, and where the compressive strength of the concrete itself is 1200 Kg/cm ² or more. This is a cement-concrete propulsion pipe characterized by being made of cement concrete. The present invention will be explained in detail below. Generally, in the propulsion method, pressure is applied by applying a jack to the end of the propulsion pipe, but the largest compressive strain occurs at the jack pressurizing point, and the force is distributed inside the pipe as it moves away from the pipe end. Distortion decreases as it moves toward the center, and this will be explained in detail below based on the drawings. Figure 1 is a partial vertical cross-sectional view of a concrete pipe in the axial direction.Eight jacks with a diameter of 135φ are applied to both ends of a concrete pipe 1 with a diameter of 1200φ and a length of 2430mm, and the pipe end 2 is destroyed. The tube was pressurized until F, and the compressive strain at each point at the end of the tube was measured. As shown in Figure 1, 80mm (points a, a'), 135mm (points b, b'), 200mm from the tube end on the jack pressure line.
Attach stress strain gauges in the tube axis direction at points c, c' (points c, c') and 1100 mm (point d), check the strain on the verge of failure of the tube, and measure the strain (10 ^-6 ) at each position on the vertical axis at the tube end. FIG. 2 is a graph in which the horizontal axis shows the distance from the center. As is clear from Figure 2, the strain reaches 3000×10 ^-6 near the tube end 2, but rapidly decreases to about 1500×10 ^-6 and 800×10 ^-6 at points b and c, respectively. It can be seen that at point d in the center of the tube 3, the value is 750×10 ^-6 , which is almost the same as at point c. It is thought that even though the jacking pressure acts intensively on the tube end, stress is dispersed and strain decreases as the distance from the tube end increases. Also, since strain and stress are proportional, it is natural that a large compressive stress acts on the end of the tube, and it is thought that fracture will occur first in this portion. However, it can be seen from point c in FIG. 2 that there is still sufficient residual force in the center of the tube, even though a large enough strain or stress is acting on the end of the tube to reach the point of failure. Therefore, if the concrete at the end of the pipe is strengthened to increase the compressive strength of this part, there is still some residual strength in the center of the pipe, resulting in an even stronger pipe as a whole.
Examples of concrete with relatively high compressive strength include concrete with a compressive strength of 900 to 1000 Kg/ ^cm2 (hereinafter referred to as "A concrete"), compressive strength
1200-1500Kg/ ^cm2 concrete (hereinafter referred to as "B concrete") and compressive strength 1500-2000
Kg/ ^cm2 concrete (hereinafter referred to as "C concrete")
Although there are high-strength and ultra-high-strength concretes such as (referred to as ``concrete''), concrete with a high compressive strength of 1200 Kg/cm ² or more is used among the above concretes for use in the concrete propulsion pipe of the present invention. By using a material with a compressive strength of 1200 Kg/cm ² or more, if the center part of the tube is made of a material normally used for propulsion tubes, the propulsion distance can be reliably and significantly increased. Examples of A-concrete include high-strength concrete made by adding a high-strength admixture that produces Ettrin guide. Examples of high-strength admixtures include "Denka Sigma 1000" (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd., and Nippon Cement (trade name). Co., Ltd.'s product name "Asano Super Mix", Showa Mining Co., Ltd.'s product name "Daimics", etc. are used. As an example of B concrete, 3 to 50 parts by weight of ultrafine powder and at most 10 parts by weight of high performance water reducer are added to 100 parts by weight of cement, and the water-cement ratio is adjusted.
Ultra-high strength concrete adjusted to 0.25 or less and the above composition further increased in strength by adding 1 to 20 parts by weight of at least one of calcium sulfate dihydrate or anhydrous salt to 100 parts by weight of cement. Examples include ultra-high strength concrete. The ultrafine powder is preferably a powder with an average particle size of 1 μm or less, and although there are no particular restrictions on the composition, those easily soluble in water are not suitable. In the present invention, silica dust (silica fume) and siliceous dust, which are produced as by-products during the production of silicon, silicon-containing alloys, and zirconia, are particularly suitable, such as fly ash, calcium carbonate, silica gel, opalescent silica, titanium oxide, aluminum oxide, etc. can also be used. The amount of ultrafine powder to be used is 3 to 50 parts by weight, preferably 10 to 70 parts by weight, and preferably 4 to 15 parts by weight when used in combination with calcium sulfate. If it exceeds 50 parts by weight, the fluidity of mortar and concrete will be significantly reduced, making it difficult to mold, and the strength will not be sufficiently developed, and if it is less than 3 parts by weight, the strength will not be sufficiently developed. High-performance water reducing agents use surfactants that have a high dispersion ability without causing too much delay in setting or excessive air entrainment even when added to cement in large quantities.A specific example is melamine sulfonic acid formaldehyde condensation. Examples include salts of naphthalene sulfonic acid formaldehyde condensates, high molecular weight lignin sulfonates, polycarboxylate salts, etc. as main components. The amount of superplasticizer used is at most 10 parts by weight, preferably 2 to 5 parts by weight, per 100 parts by weight of cement.
If the amount exceeds 10 parts by weight, the water reduction effect needed to obtain ultra-high strength mortar and concrete with a low water-to-cement ratio will not be achieved as the amount added is increased, and conversely it will adversely affect hardening, which is undesirable. Furthermore, in order to increase the strength of the pipe body, at least one type of anhydrous or dihydrate calcium sulfate, preferably insoluble anhydrite, is used, and the amount of calcium sulfate added is 1 to 20 parts by weight per 100 parts by weight of cement. If it is less than 1 part by weight, there is no effect of increasing the strength, and if it exceeds 20 parts by weight, a higher effect cannot be obtained. The above materials are mixed to prepare ultra-high strength mortar and concrete, and the amount of water at that time is 0.25 or less in terms of water-cement ratio, preferably 0.15 to 0.23.
If the amount of water exceeds 0.25, the ultra-high strength propulsion tube that is aimed at cannot be obtained. An example of C concrete is one in which the aggregate used for B concrete is selected according to the following criteria. The selection criteria is preferably Mohs hardness of 6 or more, preferably 7 or more, or Knoop indenter hardness of 700Kg/mm2 ^{or more} . Specific examples include silica, pyrite, hematite, and magnetite. , yellow jade, lawsonite, corundum, fenasite, spinel, beryl, chlorite, tourmaline, granite, andalusite, cross stone, zircon, calcined pauxite, boron carbide, tungsten carbide, ferrosilicon nitride, silicon nitride,
Examples include fused silica, fused magnesia, and silicon carbide. Among these, nitrides such as ferrosilicon nitride, silicon nitride, and electrofused magnesia react with alkali to increase the adhesive strength at the interface between concrete and aggregate, resulting in high strength and wear resistance. Excellent ultra-high strength mortar and concrete can be obtained. On the other hand, various types of iron ore are preferred in terms of price and availability. The compressive strength of the concrete itself is the compressive strength of a hardened cement body containing arbitrary amounts of the above-mentioned cement, ultrafine powder, high performance water reducing agent, water, admixtures and/or admixtures, fiber reinforcement and/or This is the compressive strength without reinforcing steel. The concrete propulsion pipe of the present invention may be reinforced with a reinforcing material, and the reinforcing material may be reinforcing bars, long fibers, or short fibers conventionally used in propulsion pipes. The reinforcing bars used in conventional propulsion tubes are sufficient, and the amount used can be the same as conventional ones.
The long fibers are rovings, and the material is preferably at least one of inorganic fibers such as iron:carbon and alkali-resistant glass, and organic synthetic fibers such as polyvinyl alcohol, polyester, and polypropylene. The pipe ends and the pipe center part of the concrete propulsion pipe in the present invention are made of concrete with a high compressive strength at the pipe ends, corresponding to the graph showing the compressive strain of the concrete pipe in Fig. 2, and two types of concrete with different compressive strengths are used. It is composed of the above concrete, but the length of each varies depending on the propulsion distance, concrete characteristics, etc., and it is difficult to specify a uniform distance, so it is determined relatively. is within 1000 mm, preferably within 400 mm from the tube ends, and the tube center is preferably in a range other than both tube ends. The end of the pipe is made of concrete that has a higher compressive strength than the center of the pipe in order to withstand large compressive stress during jack pressurization in the propulsion method. The structure may be constructed in stages such that the concrete has a higher compressive strength and becomes strongest near the pipe resistance. Specifically, as the first example of the present invention, in FIG. 1, point e is 400 mm from the pipe end and
The concrete between points e' and C is concrete, for example, B concrete or C concrete, but between points e and e' at the center of the pipe, concrete is made of ordinary Portland cement (in this case, the compressive strength is
Concrete propulsion pipes made of 450 to 500 kg/cm ² (approximately 450 to 500 kg/cm 2 ) exhibit great resistance to jerky pressurization. In this way, when ordinary concrete is used in the center of the pipe and the ends of the pipe are made of concrete with higher strength than ordinary concrete, the end of the pipe is located at the bending point C in the graph showing compressive strain in Figure 2. The range is the length obtained by adding the safety factor to the point, and the length added to the point C can be arbitrarily set depending on the propulsion distance, concrete physical properties, etc. As a second example of the present invention, for example, C concrete is used up to about 100 mm from the pipe end, and the following 100 mm is used.
As shown in Figure 2, a concrete propulsion pipe constructed by using B concrete between mm and 300 mm and A concrete in the center of the pipe has the highest compressive strength at the part of the pipe end where the amount of strain is greatest. The pipe is made of concrete, and is constructed of concrete with a low compressive strength in accordance with the reduction in strain, resulting in a pipe that can resist jacking pressure more rationally as a whole. Normally, concrete with high compressive strength is expensive, and if used for the entire pipe, it would be an expensive pipe, so by rationally synthesizing the strength distribution according to the generated stress, it is possible to create a higher performance propulsion pipe. The aim is to obtain the most economically. As a third example, B concrete or C concrete, which has a higher strength than ordinary concrete, is used for the area from the pipe end to point C, which is about 200 mm away, and A concrete or it is used for the area between points c and c' in the center of the pipe. An example is a concrete propulsion pipe made of concrete with equivalent strength. Each of the above examples shows a large difference in the strength of concrete, making its characteristics even clearer.
On the other hand, for example, even if only Portland cement is used, the ends of the pipe may be mixed with a larger amount of cement, or the concrete at both ends may be mixed with a water reducing agent such as Mighty and mixed with cement. Even if the strength is relatively increased in the center of the tube by decreasing the strength, the effectiveness of the present invention will not be diminished. In addition, there are cases in which stress is distributed by applying another material to the end of the pipe in advance.For example, a circular plate of iron or wood is installed at the end of the pipe in advance, and jacks connect the concrete pipe through this. There is a device that applies pressure, but even in this case, the strain is slightly reduced compared to when the jack is directly applied, but the tendency is almost the same as in Figure 2, and in any case, the largest strain is at the pipe end. Even in this case, the concrete propulsion pipe according to the present invention is still much more rational and advantageous than a concrete pipe that is uniform throughout. As explained above, in the concrete propulsion tube of the present invention, the ends of the tube in the axial direction are made of concrete that has a higher compressive strength than the center of the tube, so the propulsion stress is extremely large compared to conventional propulsion tubes, and the propulsion distance is extremely large. It is possible to lengthen the length and also to obtain it economically. In addition, in conventional propulsion tubes, the entire tube is made of the same concrete, so if the concrete at the end of the tube breaks, it loses its value as a tube, but in the concrete propulsion tube of the present invention, the end of the tube is reinforced with high strength. This has the advantage that there is less damage to the tube ends and the occurrence of pipe breakage accidents can be prevented. In particular, in the present invention, since the pipe ends and the pipe center are made of different concrete, it is easy to obtain the necessary strength at the pipe ends, and the pipe ends can be made in harmony with the concrete and strength of the pipe center. It's easy. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 and 2 and Comparative Example 1 Preparation of Γ Concrete Concrete was prepared according to the formulation shown in Table-1. Material molded with the concrete 14 days old φ10×
The compressive strength of the 20cm specimen is also listed in Table 1. For curing, after pre-curing for 6 hours, the temperature was raised to 70℃ at a rate of 15℃/hr, held at that temperature for 4 hours, then the steam was removed, the temperature was allowed to cool naturally in the curing tank, and the next day the mold was demolded. The plants were cured outdoors until the end of the day.

[Table] Γ Concrete propulsion tube A propulsion tube with an inner diameter of 800 mm, a tube thickness of 80 mm, and a length of 2430 mm is made of alkali-resistant glass fibers at 1% by weight based on the total weight of the tube, and the points e are 400 mm from the tube end and the other tube end. The pipe end concrete shown in Table 2 was used for the period from 400 mm to point e', and
The pipe center concrete shown in Table 2 was used to manufacture the pipe between points e'. The tube is manufactured using centrifugal molding method, and first, 2 to 5G
Continuously spray long fibers, cement milk, and/or cement mortar together in the circumferential direction of the rotating formwork to fix it, then pour in concrete, and then add long fibers and cement milk in the same manner as above. Spray to the specified thickness. The formwork continued to rotate, increasing to about 30G and compacting, then stopped rotating and was then cured in the same way as the concrete adjustment described above. To calculate the maximum propulsive stress, place a jack with a piston diameter of 135φ directly on the pipe at 8 points equidistantly spaced in the circumferential direction of the pipe cross section, pressurize it in the same way as in a compression test, and divide the breaking load by the total cross-sectional area of the pipe. The value was taken as the maximum propulsion stress. The results are also listed in Table 2.

[Table] Examples 3 to 5 Concrete propulsion pipes with concrete shown in Table 3 were obtained using the same pipe manufacturing, curing, and testing methods as in Example 1. The results of measuring the maximum propulsion stress of the concrete propulsion pipe are also listed in Table 3. Further, a vertical cross-sectional explanatory view showing the configuration of the concrete propulsion pipe of Example 4 is shown in FIG.

【table】 [Brief explanation of the drawing]

Figure 1 is a partial vertical sectional view of the concrete pipe, Figure 2
The figure is a graph showing the strain at each position that occurs when a concrete pipe is jacked and pressurized. 1... Concrete pipe, 2... Pipe end. 3...Central part of the tube.

Claims (1)

[Scope of Claims] 1. The pipe end portion at least 200 mm and at most 1000 mm in the pipe axis direction from the pipe end has a compressive strength of concrete itself greater than that of the pipe center portion, and the concrete itself has a compressive strength of 1200 Kg/cm ² A cement-concrete propulsion pipe characterized by being composed of the above cement-concrete. 2. The cement-concrete propulsion pipe according to claim 1, wherein the pipe ends are made of cement concrete whose compressive strength is sequentially larger than the pipe center part toward the pipe ends.