JP2008038379A - Liquefaction prevention construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquefaction prevention construction method for arranging air bubbles simply and uniformly. <P>SOLUTION: In this liquefaction prevention construction method 1, a gas-dissolved solution 3 having lower temperature than temperature of sand bed ground 2 is poured into the sand bed ground 2 and permeates into the sand bed ground 2, and then the dissolved gas is formed into minute air bubbles as temperature of the gas dissolved solution 3 rises. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquefaction prevention method.

It is known that when air is fed into the sand layer ground and the degree of unsaturation in the sand layer ground is increased, the rising process of excess pore water due to earthquake vibration will be delayed compared to full saturation, making it difficult to liquefy. . Fig. 4 shows the relationship between the pore pressure coefficient (B value) in the sand layer ground and the number of repetitions until liquefaction. It is a value represented by a ratio of increments, and is a value that becomes 100% when the degree of saturation inside the ground increases and becomes fully saturated. From this figure, it can be seen that the number of repetitions leading to liquefaction increases 10 times by lowering the pore pressure coefficient by about 0.1. That is, the liquefaction strength of the ground increases by lowering the pore pressure coefficient. Therefore, as a construction method to bring the ground into an unsaturated state, for example, (1) After lowering the groundwater in the ground enclosed in a rectangle with a sheet pile etc. and sending air, the groundwater is raised again and the unsaturated ground (2) Method of sending air into the ground (JP 2000-34736), (3) Water in which air is dissolved at a pressure higher than the groundwater pressure Has been proposed (Japanese Patent Laid-Open No. 2001-193048).
JP-A-8-3975 JP 2000-34736 A JP 2001-193048 A

  However, in the construction method (1) described above, a uniform unsaturated ground is formed stochastically. However, since it is difficult to adjust the degree of unsaturation, auxiliary construction such as surrounding with a sheet pile is necessary and costs are high. There was a problem. In the methods (2) and (3), there is a problem that the amount of bubbles changes depending on the distance from the injection point and it is difficult to arrange the bubbles uniformly.

  This invention is made | formed in view of the above problems, The objective is to provide the liquefaction prevention construction method which can arrange | position a bubble easily and uniformly.

In order to solve the above problems, the liquefaction prevention method involves injecting a gas-dissolved solution having a temperature lower than the temperature of the sand-layer ground into the sand-layer ground and then infiltrating it, and as the temperature of the gas-dissolved solution increases. It is characterized by making dissolved gas into minute bubbles. The gas-dissolved solution is either a gas-dissolved aqueous solution in which gas is dissolved in water, a gas-dissolved silica aqueous solution in which gas is dissolved in a silica aqueous solution, or a gas-dissolved silica aqueous solution in which a silica aqueous solution and a gas-dissolved aqueous solution are mixed. Including things. Here, the silica concentration (SiO ² concentration) in the silica aqueous solution at the time of placing on the sand layer ground is 1 to 10% by weight. Further, when the silica concentration is less than 1%, the effect is not exhibited, and when the silica concentration exceeds 10%, there is a problem that the construction becomes difficult and cannot be evenly dispersed.

  The temperature of the low-temperature gas-dissolved solution injected into the sand layer ground rises to the temperature of the groundwater while penetrating the sand layer ground. Along with this, the amount of gas that can be dissolved in the solution decreases, so that the dissolved gas becomes minute bubbles. For this reason, the water temperature and the amount of gas that can be dissolved can be ascertained in advance, and the change in the temperature of the solution over time can be predicted from the temperature difference between the temperature of the groundwater and the temperature of the solution. It can be arranged in the sand layer ground, and the liquefaction strength of the sand layer ground can be increased. Further, since the gas-dissolved silica aqueous solution is solidified after the generation of minute bubbles, the bubbles are permanently fixed, and the increase in the liquefaction strength of the sand layer ground can be made permanent.

  Hereinafter, embodiments of the liquefaction prevention method of the present invention will be described in detail with reference to the drawings. This liquefaction prevention method is intended for saturated sand layer ground, injecting a gas dissolved solution at a temperature lower than that of this sand layer ground, and making this dissolved gas a fine bubble to lower the saturation, thereby reducing the degree of saturation of the sand layer ground during an earthquake. It prevents liquefaction. In each embodiment of the construction method, the same components are described with the same reference numerals, and different configurations are described with different reference numerals.

FIG. 1 shows a liquefaction prevention method 1 according to the first embodiment. In this liquefaction prevention method 1, water having a temperature lower than that of the sand layer ground 2 to be liquefied is first aerated, and CO ₂ is supplied into the water. A dissolved CO ₂ dissolved aqueous solution 3 is produced. For example, the solubility of CO ₂ in water is 171% (0 ° C., 1 atm) of water volume when the water temperature is 0 ° C., 125% at 10 ° C., 88% at 20 ° C., and 0% When the solution in a completely dissolved state at 20 ° C. is raised to 20 ° C., 83% by volume of dissolved gas is bubbled in the 1 atm state.

Therefore, for example, a CO ₂ dissolved aqueous solution 3 having a lower temperature than this, for example, a CO ₂ dissolved aqueous solution 3 having a temperature of 5 ° C. to 12 ° C. It injects into the sand layer ground 2. The dissolved gas by the CO ₂ dissolved solution 3 rises to the water temperature of 20 ° C. while penetrating the sand ground 2 medium (CO ₂₎ is aerated. Thereby, minute bubbles can be arranged in the gaps in the sand layer ground 2.

For example, in the case of a saturated ground of 1000 cc, assuming that the soil particles are about 50% of the volume and the pore water is 50%, the CO ₂ is completely dissolved and the 500 cc pore water becomes 20 ° C. Since CO ₂ to be bubbled is 185 cc (20 ° C., 1 atm), the pore pressure coefficient (B value) is greatly reduced when CO ₂ is bubbled.

Since the dissolved gas (CO ₂ ) is bubbled for about 2 hours and the injection time is about 2 to 4 hours, the bubbles can be uniformly arranged in the sand layer ground 2 and the sand layer ground. The degree of unsaturation in 2 can be increased and the liquefaction strength can be increased. This does not directly inject bubbles into the sand layer ground 2 as in the prior art, but bubbles the dissolved gas (CO ₂ ) in the aqueous solution that has penetrated into the sand layer ground 2 so that the bubbles are uniformly distributed in the sand layer ground. Can be arranged.

CO also Figure 2 is a liquefaction prevention method 7 of the second embodiment, in which the liquefaction prevention method 7 silica solution 8 was prepared by mixing a CO ₂ dissolved solution 3 obtained by dissolved the CO _{2 2} Dissolved silica aqueous solution 9 is used. This makes it possible to maintain a constant liquefaction preventing effect for a long time without continuing to inject the low temperature CO ₂ dissolved aqueous solution 3 into the sand layer ground 2.

As shown in FIG. 2, first, a silica aqueous solution 8 having a consolidation time of 2 to 10 hours and a CO ₂ dissolved aqueous solution 3 of about 5 ° C. in which substantially the same amount of CO ₂ is dissolved are produced. . Then, this aqueous silica solution (30-70 wt%) 8, CO ₂ dissolved in water (30-70 wt%) 3 and stirring and mixing the low temperature of 10 ° C. of CO ₂ dissolved silica than the water temperature of the sand layer ground 2 An aqueous solution 9 is produced. The silica concentration (SiO ² concentration) in the CO ₂ -dissolved silica aqueous solution 9 is 1 to 10% by weight. When this is injected into the sand ground 2 in the same manner as described above, which dissolved gas (CO ₂₎ by raising to 20 ° C. While penetrating the sand ground 2 medium is aerated. Thereby, minute bubbles can be arranged in the gap between the sand layer ground 2.

Since the dissolved gas (CO ₂ ) is bubbled in about 2 hours, the bubbles are uniformly arranged in the sand layer ground 2 before the CO ₂ dissolved silica aqueous solution 9 having a consolidation time of 2 to 10 hours is consolidated. can do. Therefore, after the bubbles are uniformly arranged, the CO ₂ -dissolved silica aqueous solution 9 is solidified in a gel state and the uniformly arranged bubbles are permanently fixed, so that the degree of unsaturation is increased and the liquefaction strength is increased. It becomes possible to be permanent. For this reason, a constant liquefaction prevention effect can be maintained for a long time without continuing to inject the low temperature CO ₂ dissolved aqueous solution 3 into the sand layer ground 2.

The Figure 3 is a liquefaction prevention method 10 of the third embodiment, the liquefaction prevention method 10 CO ₂ dissolved was prepared by dissolved the CO ₂ in the silica aqueous solution 8 of consolidation time 2 to 10 hours A silica aqueous solution 9 is used.

As shown in FIG. 3, first, an aqueous silica solution 8 having a temperature of 10 ° C. lower than the soil temperature (20 ° C.) of the sand layer ground 2 to be liquefied is aerated, and CO ₂ is contained in the aqueous silica solution 8. A dissolved CO ₂ -dissolved silica aqueous solution 9 is produced. The silica concentration (SiO ² concentration) in the CO ₂ -dissolved silica aqueous solution 9 is 1 to 10% by weight. When this is injected into the sand ground 2 in the same manner as described above, which is bubbled dissolved gas (CO ₂₎ is by raising up soil temperature (20 ° C.) while penetrating the sand ground 2 medium. Thereby, minute bubbles can be arranged in the gap between the sand layer ground 2. Therefore, in the same manner as described above, the CO ₂ -dissolved silica aqueous solution 9 is solidified in a gel state and the uniformly arranged bubbles are permanently fixed, so that the degree of unsaturation is increased and the increase in liquefaction strength is made permanent. It becomes possible.

The gas dissolved solution in liquefaction prevention method 1,7,10 of the first to third embodiments described above has been described as a target of CO ₂ dissolved solution 3, which is not limited to CO ₂ dissolved solution 3 It is also possible to use an air-dissolved aqueous solution in which air having a temperature lower than that of the sand layer ground 2 to be liquefied is aerated and air is dissolved in the water. That is, air can be used in addition to CO ₂ as the dissolved gas.

It is sectional drawing of the liquefaction prevention construction method of 1st Embodiment. It is sectional drawing of the liquefaction prevention construction method of 2nd Embodiment. It is sectional drawing of the liquefaction prevention construction method of 3rd Embodiment. It is a figure showing the liquefaction intensity curve.

Explanation of symbols

1,7,10 liquefaction prevention method 2 sand ground 3 CO ₂ dissolved solution 4 pump 5 injection hole 6 injection outer tube 8 silica solution 9 CO ₂ dissolved silica solution

Claims (2)

  A gas dissolved solution having a temperature lower than the temperature of the sand layer ground is injected into and infiltrated into the sand layer ground, and then the dissolved gas is made into fine bubbles as the temperature of the gas dissolved solution increases. Liquefaction prevention method.   The gas-dissolved solution is either a gas-dissolved aqueous solution in which gas is dissolved in water, a gas-dissolved silica aqueous solution in which gas is dissolved in a silica aqueous solution, or a gas-dissolved silica aqueous solution in which a silica aqueous solution and a gas-dissolved aqueous solution are mixed. The liquefaction prevention method according to claim 1, wherein:

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